The United States has taken several initiatives to develop hydrogen fuel cells, the infrastructure and technologies to make fuel cell vehicles practical and economical by 2020. More than one billion dollars has been allocated for these purposes.

Fuel cells generate electricity quietly and efficiently without polluting the environment. Unlike fossil fuel energy sources, the by-products of fuel cells are heat and water. How it works?

In this article, we will briefly review each of the existing fuel technologies today, as well as talk about the design and operation of fuel cells, and compare them with other forms of energy production. We will also discuss some of the hurdles researchers face in making fuel cells practical and affordable for consumers.

Fuel cells are electrochemical energy conversion devices. The fuel cell converts chemicals, hydrogen and oxygen, into water, in the process generating electricity.

Another electrochemical device that we are all very familiar with is the battery. The battery has all the necessary chemical elements inside it and turns these substances into electricity. This means that the battery eventually "dies" and you either throw it away or recharge it.

In a fuel cell, chemicals are constantly fed into it so that it never "dies". Electricity will be generated for as long as the chemicals enter the cell. Most fuel cells in use today use hydrogen and oxygen.

Hydrogen is the most abundant element in our galaxy. However, hydrogen practically does not exist on Earth in its elemental form. Engineers and scientists must extract pure hydrogen from hydrogen compounds, including fossil fuels or water. To extract hydrogen from these compounds, you need to expend energy in the form of heat or electricity.

Invention of fuel cells

Sir William Grove invented the first fuel cell in 1839. Grove knew that water could be separated into hydrogen and oxygen by passing electric current through it (a process called electrolysis). He suggested that in the reverse order, electricity and water could be obtained. He created a primitive fuel cell and called it gas galvanic battery. After experimenting with his new invention, Grove proved his hypothesis. Fifty years later, scientists Ludwig Mond and Charles Langer coined the term fuel cells when trying to build a practical model for power generation.

The fuel cell will compete with many other energy conversion devices, including gas turbines in urban power plants, engines internal combustion in cars, as well as all kinds of batteries. Internal combustion engines, like gas turbines, burn various types of fuel and use the pressure created by the expansion of gases to perform mechanical work. Batteries convert chemical energy into electrical energy when needed. Fuel cells need to perform these tasks more efficiently.

The fuel cell provides DC (direct current) voltage that can be used to power electric motors, lighting and other electrical appliances.

There are several different types of fuel cells, each using different chemical processes. Fuel cells are usually classified according to their operating temperature And typeelectrolyte, which they use. Some types of fuel cells are well suited for use in stationary power plants. Others may be useful for small portable devices or to power cars. The main types of fuel cells include:

Polymer exchange membrane fuel cell (PEMFC)

PEMFC is considered as the most likely candidate for transport applications. PEMFC has both high power and relatively low operating temperature (in the range of 60 to 80 degrees Celsius). The low operating temperature means the fuel cells can quickly warm up to start generating electricity.

Solid oxide fuel cell (SOFC)

These fuel cells are most suitable for large stationary power generators that could provide electricity to factories or cities. This type of fuel cell operates at very high temperatures (700 to 1000 degrees Celsius). The high temperature is a reliability problem because some of the fuel cells can fail after several cycles of switching on and off. However, solid oxide fuel cells are very stable in continuous operation. Indeed, SOFCs have demonstrated the longest operating life of any fuel cell under certain conditions. The high temperature also has the advantage that the steam generated by the fuel cells can be directed to turbines and generate more electricity. This process is called cogeneration of heat and electricity and improves overall system efficiency.

Alkaline fuel cell (AFC)

It is one of the oldest fuel cell designs, used since the 1960s. AFCs are very susceptible to pollution as they require pure hydrogen and oxygen. In addition, they are very expensive, so this type of fuel cell is unlikely to be put into mass production.

Molten-carbonate fuel cell (MCFC)

Like SOFCs, these fuel cells are also best suited for large stationary power plants and generators. They operate at 600 degrees Celsius so they can generate steam, which in turn can be used to generate even more power. They have a lower operating temperature than solid oxide fuel cells, which means they do not need such heat-resistant materials. This makes them a little cheaper.

Phosphoric-acid fuel cell (PAFC)

Phosphoric acid fuel cell has the potential for use in small stationary power systems. He works for more high temperature than a polymer exchange membrane fuel cell, so it takes longer to warm up, making it unsuitable for automotive use.

Methanol fuel cells Direct methanol fuel cell (DMFC)

Methanol fuel cells are comparable to PEMFC in terms of operating temperature, but are not as efficient. In addition, DMFCs require quite a lot of platinum as a catalyst, which makes these fuel cells expensive.

Fuel cell with polymer exchange membrane

The polymer exchange membrane fuel cell (PEMFC) is one of the most promising fuel cell technologies. PEMFC uses one of the simplest reactions of any fuel cell. Consider what it consists of.

1. A node – Negative terminal of the fuel cell. It conducts electrons that are released from hydrogen molecules, after which they can be used in an external circuit. It is engraved with channels through which hydrogen gas is distributed evenly over the surface of the catalyst.

2.TO atom - the positive terminal of the fuel cell also has channels for distributing oxygen over the surface of the catalyst. It also conducts electrons back from the outer chain of the catalyst, where they can combine with hydrogen and oxygen ions to form water.

3.Electrolyte-proton exchange membrane. It is a specially treated material that conducts only positively charged ions and blocks electrons. In PEMFC, the membrane must be hydrated to function properly and remain stable.

4. Catalyst is a special material that promotes the reaction of oxygen and hydrogen. It is usually made from platinum nanoparticles deposited very thinly on carbon paper or fabric. The catalyst has a surface structure such that the maximum surface area of ​​the platinum can be exposed to hydrogen or oxygen.

The figure shows hydrogen gas (H2) entering under pressure into the fuel cell from the anode side. When an H2 molecule comes into contact with platinum on the catalyst, it splits into two H+ ions and two electrons. The electrons pass through the anode where they are used in external circuitry (doing useful work such as turning a motor) and are returned to the cathode side of the fuel cell.

Meanwhile, on the cathode side of the fuel cell, oxygen (O2) from the air passes through the catalyst where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts two H+ ions across the membrane where they combine with an oxygen atom and two electrons from the external circuitry to form a water molecule (H2O).

This reaction in a single fuel cell produces only approximately 0.7 volts. In order to raise the voltage to a reasonable level, many individual fuel cells must be combined to form a fuel cell stack. Bipolar plates are used to connect one fuel cell to another and undergo oxidation with decreasing potential. The big problem with bipolar plates is their stability. Metal bipolar plates can be corroded and by-products (iron and chromium ions) reduce the efficiency of fuel cell membranes and electrodes. Therefore, low-temperature fuel cells use light metals, graphite, and composite compounds of carbon and thermosetting material (thermosetting material is a kind of plastic that remains solid even when subjected to high temperatures) in the form of a bipolar sheet material.

Fuel Cell Efficiency

Reducing pollution is one of the main goals of a fuel cell. By comparing a car powered by a fuel cell with a car powered by a gasoline engine and a car powered by a battery, you can see how fuel cells could improve the efficiency of cars.

Since all three types of cars have many of the same components, we will ignore this part of the car and compare efficiencies up to the point where mechanical power is produced. Let's start with the fuel cell car.

If a fuel cell is powered by pure hydrogen, its efficiency can be up to 80 percent. Thus, it converts 80 percent of the energy content of hydrogen into electricity. However, we still have to convert electrical energy into mechanical work. This is achieved by an electric motor and an inverter. The efficiency of the motor + inverter is also approximately 80 percent. This gives an overall efficiency of approximately 80*80/100=64 percent. Honda's FCX concept vehicle reportedly has a 60 percent energy efficiency.

If the fuel source is not in the form of pure hydrogen, then the vehicle will also need a reformer. Reformers convert hydrocarbon or alcohol fuels into hydrogen. They generate heat and produce CO and CO2 in addition to hydrogen. To purify the resulting hydrogen, they use various devices, but this cleaning is insufficient and reduces the efficiency of the fuel cell. Therefore, the researchers decided to focus on fuel cells for vehicles running on pure hydrogen, despite the problems associated with the production and storage of hydrogen.

Efficiency of a gasoline engine and a car on electric batteries

The efficiency of a car powered by gasoline is surprisingly low. All the heat that goes out in the form of exhaust or is absorbed by the radiator is wasted energy. The engine also uses a lot of energy to turn the various pumps, fans, and generators that keep it running. Thus, the overall efficiency of an automobile gasoline engine is approximately 20 percent. Thus, only approximately 20 percent of the thermal energy content of gasoline is converted into mechanical work.

A battery-powered electric vehicle has a fairly high efficiency. The battery is approximately 90 percent efficient (most batteries generate some heat or require heating), and the motor + inverter is approximately 80 percent efficient. This gives an overall efficiency of approximately 72 percent.

But that's not all. In order for an electric car to move, electricity must first be generated somewhere. If it was a power plant that used a fossil fuel combustion process (rather than nuclear, hydroelectric, solar or wind power), then only about 40 percent of the fuel consumed by the power plant was converted into electricity. Plus, the process of charging a car requires converting alternating current (AC) power to direct current (DC) power. This process has an efficiency of approximately 90 percent.

Now, if we look at the whole cycle, the efficiency of an electric vehicle is 72 percent for the car itself, 40 percent for the power plant, and 90 percent for charging the car. This gives an overall efficiency of 26 percent. The overall efficiency varies considerably depending on which power station is used to charge the battery. If the electricity for a car is generated, for example, by a hydroelectric plant, then the efficiency of an electric car will be about 65 percent.

Scientists are researching and refining designs to continue improving fuel cell efficiency. One of the new approaches is to combine fuel cell and battery powered vehicles. A concept vehicle is being developed to be powered by a fuel cell powered hybrid powertrain. It uses a lithium battery to power the car while a fuel cell recharges the battery.

Fuel cell vehicles are potentially as efficient as a battery-powered car that is charged from a fossil fuel-free power plant. But achieving such potential in a practical and accessible way can be difficult.

Why use fuel cells?

The main reason is everything related to oil. America must import nearly 60 percent of its oil. By 2025, imports are expected to rise to 68%. Americans use two-thirds of the oil daily for transportation. Even if every car on the street were a hybrid car, by 2025 the US would still have to use the same amount of oil that Americans consumed in 2000. Indeed, America consumes a quarter of all the oil produced in the world, although only 4.6% of the world's population lives here.

Experts expect oil prices to continue rising over the next few decades as cheaper sources run dry. Oil companies must develop oil fields in an increasingly difficult conditions causing the price of oil to rise.

The fears extend far beyond economic security. A lot of the proceeds from the sale of oil are spent on supporting international terrorism, radical political parties, and the unstable situation in the oil-producing regions.

The use of oil and other fossil fuels for energy produces pollution. It is best for everyone to find an alternative - burning fossil fuels for energy.

Fuel cells are an attractive alternative to oil dependency. Fuel cells produce clean water as a by-product instead of pollution. Although engineers have temporarily focused on producing hydrogen from various fossil sources such as gasoline or natural gas, renewable, environmentally friendly ways to produce hydrogen in the future are being explored. The most promising, of course, will be the process of obtaining hydrogen from water.

Oil dependency and global warming is an international problem. Several countries are jointly involved in the development of research and development for fuel cell technology.

Clearly, scientists and manufacturers have a lot of work to do before fuel cells become an alternative to current energy production methods. And yet, with the support of the whole world and global cooperation, a viable energy system based on fuel cells can become a reality in a couple of decades.

Recently, the topic of fuel cells has been on everyone's lips. And this is not surprising, with the advent of this technology in the world of electronics, it has found a new birth. World leaders in the field of microelectronics race to present prototypes of their future products, which will integrate their own mini power plants. This should, on the one hand, weaken the binding of mobile devices to the "socket", and on the other hand, extend their battery life.

In addition, some of them work on the basis of ethanol, so the development of these technologies is of direct benefit to the producers of alcoholic beverages - in a dozen years, queues of "IT people" standing behind the next "dose" for their laptop will line up at the wine distillery.

We cannot stay away from the "fever" of fuel cells that has gripped the Hi-Tech industry, and we will try to figure out what kind of animal this technology is, what it is eaten with and when we should expect it to come to "catering". In this article, we will look at the path traveled by fuel cells from the discovery of this technology to today. We will also try to assess the prospects for their implementation and development in the future.

How it was

The principle of a fuel cell was first described in 1838 by Christian Friedrich Schonbein, and a year later the Philosophical Journal published his article on this topic. However, these were only theoretical studies. The first working fuel cell saw the light in 1843 in the laboratory of a scientist of Welsh origin, Sir William Robert Grove. When creating it, the inventor used materials similar to those used in modern batteries on phosphoric acid. Subsequently, Sir Grove's fuel cell was improved by W. Thomas Grub. In 1955, this chemist, who worked for the legendary company General Electric, used a sulfonated polystyrene ion-exchange membrane as the electrolyte in the fuel cell. Only three years later, his colleague Leonard Niedrach proposed the technology of laying platinum on the membrane, which acted as a catalyst in the process of hydrogen oxidation and oxygen uptake.

"Father" of fuel cells Christian Schönbein

These principles formed the basis of a new generation of fuel cells, called "Grubb-Nidrach" elements after their creators. General Electric continued to develop in this direction, in which, with the assistance of NASA and the aviation giant McDonnell Aircraft, the first commercial fuel cell was created. The new technology was noticed overseas. And already in 1959, the Briton Francis Bacon (Francis Thomas Bacon) introduced a stationary fuel cell with a power of 5 kW. His patented developments were subsequently licensed by the Americans and used in NASA spacecraft in power systems and drinking water supply. In the same year, the American Harry Ihrig built the first fuel cell tractor (total power 15 kW). Potassium hydroxide was used as an electrolyte in the batteries, and compressed hydrogen and oxygen were used as reagents.

For the first time, the production of stationary fuel cells for commercial purposes was put on stream by UTC Power, which offered backup power systems for hospitals, universities and business centers. This company, which is a world leader in this field, still produces similar solutions with power up to 200 kW. It is also the main supplier of fuel cells for NASA. Its products were widely used during the Apollo space program and are still in demand as part of the Space Shuttle program. UTC Power also offers "consumer consumption" fuel cells for a wide range of vehicle applications. She was the first to create a fuel cell that allows to receive current at negative temperatures through the use of a proton-exchange membrane.

How it works

The researchers experimented with various substances as reagents. However, the basic principles of operation of fuel cells, despite significantly different performance characteristics, remain unchanged. Any fuel cell is an electrochemical energy conversion device. It generates electricity from a certain amount of fuel (on the anode side) and an oxidizer (on the cathode side). The reaction proceeds in the presence of an electrolyte (a substance containing free ions and behaving as an electrically conductive medium). In principle, in any such device, there are certain reagents entering it and their reaction products, which are removed after the electrochemical reaction has been carried out. The electrolyte in this case serves only as a medium for the interaction of the reactants and does not change in the fuel cell. Based on such a scheme, an ideal fuel cell should work as long as there is a supply of substances necessary for the reaction.

Fuel cells should not be confused with conventional batteries here. In the first case, some "fuel" is consumed to produce electricity, which later needs to be refilled. In the case of galvanic cells, electricity is stored in a closed chemical system. In the case of batteries, applying current allows the reverse electrochemical reaction to occur and return the reagents to their original state (i.e., charge it). Various combinations of fuel and oxidizer are possible. For example, a hydrogen fuel cell uses hydrogen and oxygen (an oxidizing agent) as reactants. Often, bicarbonates and alcohols are used as fuel, and air, chlorine and chlorine dioxide act as oxidants.

The catalysis reaction taking place in the fuel cell knocks out electrons and protons from the fuel, and the moving electrons form an electric current. Fuel cells typically use platinum or its alloys as a catalyst to speed up the reaction. Another catalytic process returns electrons by combining them with protons and an oxidizing agent, resulting in the formation of reaction products (emissions). As a rule, these emissions are simple substances: water and carbon dioxide.

In a conventional proton exchange membrane fuel cell (PEMFC), a polymeric proton conductive membrane separates the anode and cathode sides. From the cathode side, hydrogen diffuses onto the anode catalyst, where electrons and protons are subsequently released from it. The protons then pass through the membrane to the cathode, and the electrons, unable to follow the protons (the membrane is electrically insulated), are directed through the external load circuit (the power supply system). On the cathodic catalyst side, oxygen reacts with protons that have passed through the membrane and electrons that enter through the external load circuit. As a result of this reaction, water is obtained (in the form of a vapor or liquid). For example, the products of reactions in fuel cells using hydrocarbon fuels (methanol, diesel fuel) are water and carbon dioxide.

Fuel cells of almost all types suffer from electrical losses, caused both by the natural resistance of the contacts and elements of the fuel cell, and by electrical overvoltage (the extra energy required to carry out the initial reaction). In some cases, it is not possible to completely avoid these losses, and sometimes "the game is not worth the candle", but most often they can be reduced to an acceptable minimum. A solution to this problem is the use of sets of these devices, in which fuel cells, depending on the requirements for the power supply system, can be connected in parallel ( more current) or in series (higher voltage).

Types of fuel cells

There are a great many types of fuel cells, but we will try to briefly dwell on the most common of them.

Alkaline fuel cells (AFC)

Alkaline or alkaline fuel cells, also called Bacon cells after their British "father", are one of the most well developed fuel cell technologies. It was these devices that helped man set foot on the moon. In general, NASA has been using fuel cells of this type since the mid-1960s. AFCs consume hydrogen and pure oxygen to produce drinking water, heat and electricity. Largely due to the fact that this technology is perfectly developed, it has one of the highest scores effectiveness among similar systems(potential about 70%).

However, this technology also has its drawbacks. Due to the specifics of using a liquid alkaline substance as an electrolyte that does not block carbon dioxide, potassium hydroxide (one of the options for the electrolyte used) can react with this component of ordinary air. The result can be a poisonous compound of potassium carbonate. To avoid this, it is necessary to use either pure oxygen, or to clean the air from carbon dioxide. Naturally, this affects the cost of such devices. However, despite this, AFCs are the cheapest fuel cells to manufacture available today.

Direct Borohydride Fuel Cells (DBFC)

This subtype of alkaline fuel cells uses sodium borohydride as fuel. However, unlike conventional hydrogen AFCs, this technology has one significant advantage - no risk of producing toxic compounds after contact with carbon dioxide. However, the product of its reaction is the substance borax, which is widely used in detergents and soap. Borax is relatively non-toxic.

DBFCs can be made even cheaper than traditional fuel cells because they don't require expensive platinum catalysts. In addition, they have a higher energy density. It is estimated that the production of a kilogram of sodium borohydride costs $50, but if mass production is organized and borax is processed, this bar can be reduced by 50 times.

Metal Hydride Fuel Cells (MHFC)

This subclass of alkaline fuel cells is currently being actively studied. A feature of these devices is the ability to chemically store hydrogen inside the fuel cell. The direct borohydride fuel cell has the same ability, but unlike it, the MHFC is filled with pure hydrogen.

Among distinctive characteristics These fuel cells are:

• the ability to recharge from electrical energy;
• work at low temperatures- up to -20°C;
• long shelf life;
• fast "cold" start;
• the ability to work for some time without an external source of hydrogen (for the period of fuel replacement).

Despite the fact that many companies are working on the creation of mass-produced MHFCs, the efficiency of prototypes is not high enough in comparison with competing technologies. One of best performance The current density for these fuel cells is 250 milliamperes per square centimeter, while conventional PEMFC fuel cells provide a current density of 1 ampere per square centimeter.

Electro-galvanic fuel cells (EGFC)

The chemical reaction in EGFC takes place with the participation of potassium hydroxide and oxygen. This creates an electric current between the lead anode and the gold plated cathode. The voltage output from an electro-galvanic fuel cell is directly proportional to the amount of oxygen. This feature has allowed the EGFC to be widely used as an oxygen test device in scuba gear and medical equipment. But precisely because of this dependence, fuel cells based on potassium hydroxide have a very limited period of time. effective work(as long as the oxygen concentration is high).

The first certified EGFC oxygen testers became widely available in 2005, but did not gain much popularity back then. Released two years later, a significantly modified model was much more successful and even received an award for "innovation" at a specialized diver's show in Florida. Currently, organizations such as NOAA (National Oceanic and Atmospheric Administration) and DDRC (Diving Diseases Research Center) use them.

Formic acid direct fuel cells (DFAFC)

These fuel cells are a subtype of PEMFC direct formic acid devices. Due to their specific features, these fuel cells have a great chance of becoming the main source of power for such portable electronics as laptops, cell phones, etc. in the future.

Like methanol, formic acid is directly fed into the fuel cell without a special purification step. It is also much safer to store this substance than, for example, hydrogen, and besides, it is not necessary to provide any specific storage conditions: formic acid is a liquid at normal temperature. Moreover, this technology has two undeniable advantages over direct methanol fuel cells. First, unlike methanol, formic acid does not percolate through the membrane. Therefore, the efficiency of DFAFC, by definition, should be higher. Secondly, in the event of a depressurization, formic acid is not so dangerous (methanol can cause blindness, and with a strong dosage, death).

Interestingly, until recently, many scientists did not see this technology as having a practical future. The reason that prompted researchers to put an end to formic acid for many years was a high electrochemical overvoltage, which led to significant electrical losses. But the results of recent experiments have shown that the reason for this inefficiency was the use of platinum as a catalyst, which has traditionally been widely used for this purpose in fuel cells. After scientists from the University of Illinois conducted a number of experiments with other materials, it turned out that when using palladium as a catalyst, the productivity of DFAFC is higher than that of equivalent direct methanol fuel cells. Currently, the rights to this technology are owned by the American company Tekion, which offers its Formira Power Pack product line for microelectronic devices. This system is a "duplex" consisting of a storage battery and the actual fuel cell. After the supply of reagents in the cartridge that charges the battery runs out, the user simply replaces it with a new one. Thus, it becomes completely independent of the "socket". According to the promises of the manufacturer, the time between charges will double, despite the fact that the technology will cost only 10-15% more than conventional batteries. The only serious obstacle on the way of this technology may be that it is supported by a medium-sized company and it can simply be “filled up” by larger-scale competitors presenting their technologies, which may even be inferior to DFAFC in a number of parameters.

Direct methanol fuel cells (DMFC)

These fuel cells are a subset of proton exchange membrane devices. They use methanol charged into the fuel cell without further purification. However, methyl alcohol is much easier to store and is not explosive (although it is flammable and can cause blindness). At the same time, the energy capacity of methanol is significantly higher than that of compressed hydrogen.

However, due to the fact that methanol is able to percolate through the membrane, the efficiency of DMFC with large volumes of fuel is low. And although for this reason they are not suitable for transport and large installations, these devices are great as battery replacements for mobile devices.

Processed methanol fuel cells (RMFC)

Processed methanol fuel cells differ from DMFCs only in that they convert methanol into hydrogen and carbon dioxide prior to generating electricity. It happens in special device called the fuel processor. After this preliminary stage (the reaction is carried out at a temperature above 250°C), the hydrogen undergoes an oxidation reaction, which results in the formation of water and electricity.

The use of methanol in RMFC is due to the fact that it is a natural carrier of hydrogen, and at a sufficiently low temperature (compared to other substances) it can be decomposed into hydrogen and carbon dioxide. Therefore, this technology is more advanced than DMFC. Processed methanol fuel cells are more efficient, more compact and operate at sub-zero temperatures.

Direct ethanol fuel cells (DEFC)

Another representative of the class of fuel cells with a proton exchange lattice. As the name implies, ethanol enters the fuel cell bypassing the stages of additional purification or decomposition into simpler substances. The first plus of these devices is the use of ethyl alcohol instead of toxic methanol. This means that you do not need to invest a lot of money in the development of this fuel.

The energy density of alcohol is approximately 30% higher than that of methanol. In addition, it can be obtained in large quantities from biomass. In order to reduce the cost of ethanol fuel cells, an active search is underway for an alternative catalyst material. Platinum, traditionally used in fuel cells for these purposes, is too expensive and is a significant obstacle to the mass adoption of these technologies. The solution to this problem can be catalysts made from a mixture of iron, copper and nickel, which demonstrate impressive results in experimental systems.

Zinc Air Fuel Cells (ZAFC)

ZAFC uses the oxidation of zinc with oxygen from the air to generate electricity. These fuel cells are inexpensive to manufacture and provide a fairly high energy density. Currently, they are used in hearing aids and experimental electric cars.

On the anode side there is a mixture of zinc particles with an electrolyte, and on the cathode side, water and oxygen from the air, which react with each other and form hydroxyl (its molecule is an oxygen atom and a hydrogen atom, between which there is a covalent bond). As a result of the reaction of the hydroxyl with the zinc mixture, electrons are released, going to the cathode. The maximum voltage that is given out by such fuel cells is 1.65 V, but, as a rule, it is artificially reduced to 1.4–1.35 V, limiting air access to the system. The end products of this electrochemical reaction are zinc oxide and water.

It is possible to use this technology both in batteries (without recharging) and in fuel cells. In the latter case, the chamber on the anode side is cleaned and refilled with zinc paste. In general, ZAFC technology has proven to be simple and reliable batteries. Their indisputable advantage is the ability to control the reaction only by adjusting the air supply to the fuel cell. Many researchers are considering zinc-air fuel cells as the future main source of power for electric vehicles.

Microbial fuel cells (MFC)

The idea of ​​using bacteria for the benefit of mankind is not new, although it has only recently come to the realization of these ideas. Currently, the issue of commercial use of biotechnologies for the production of various products(e.g. hydrogen production from biomass), neutralization harmful substances and electricity generation. Microbial fuel cells, also referred to as biological fuel cells, are a biological electrochemical system that generates electricity through the use of bacteria. This technology is based on the catabolism (decomposition of a complex molecule into a simpler one with the release of energy) of substances such as glucose, acetate (salt of acetic acid), butyrate (salt of butyric acid) or waste water. Due to their oxidation, electrons are released, which are transferred to the anode, after which the generated electric current flows through the conductor to the cathode.

In such fuel cells, mediators are usually used to improve the permeability of electrons. The problem is that substances that play the role of mediators are expensive and toxic. However, in the case of using electrochemically active bacteria, there is no need for mediators. Such "transmitter-free" microbial fuel cells began to be created quite recently, and therefore, far from all their properties are well studied.

Despite the obstacles that MFC has yet to overcome, this technology has huge potential. Firstly, "fuel" is not difficult to find. Moreover, today the issue of wastewater treatment and disposal of many wastes is very acute. The application of this technology could solve both of these problems. Secondly, theoretically its efficiency can be very high. The main problem for engineers of microbial fuel cells are, and actually the most important element of this device, microbes. And while microbiologists, who receive numerous research grants, rejoice, science fiction writers also rub their hands in anticipation of the success of books on the consequences of the “publication” of the wrong microorganisms. Naturally, there is a risk of bringing out something that would "digest" not only unnecessary waste, but also something valuable. So in principle, as with any new biotechnologies, people are wary of the idea of ​​carrying a bacteria-infested box in their pocket.

Application

Stationary domestic and industrial power plants

Fuel cells are widely used as energy sources in various autonomous systems such as space ships, remote weather stations, military installations, etc. The main advantage of such a power supply system is its extremely high reliability compared to other technologies. Due to the absence of moving parts and any mechanisms in fuel cells, the reliability of power supply systems can reach 99.99%. In addition, in the case of using hydrogen as a reagent, a very small weight can be achieved, which is one of the most important criteria in the case of space equipment.

Recently, combined heat and power installations, widely used in residential buildings and offices, are becoming more widespread. The peculiarity of these systems is that they constantly generate electricity, which, if not consumed immediately, is used to heat water and air. Despite the fact that the electrical efficiency of such installations is only 15-20%, this disadvantage is compensated by the fact that unused electricity is used for heat production. In general, the energy efficiency of such combined systems is about 80%. One of best reagents phosphoric acid is used for such fuel cells. These units provide an energy efficiency of 90% (35-50% electricity and the rest thermal energy).

Transport

Energy systems based on fuel cells are also widely used in transport. By the way, the Germans were among the first to install fuel cells on vehicles. So the world's first commercial boat equipped with such a setup debuted eight years ago. This small vessel, dubbed "Hydra" and designed to carry up to 22 passengers, was launched near the former capital of Germany in June 2000. Hydrogen (alkaline fuel cell) acts as an energy-carrying reagent. Thanks to the use of alkaline (alkaline) fuel cells, the installation is able to generate current at temperatures down to -10°C and is not "afraid" of salt water. Boat "Hydra" powered electric motor with a power of 5 kW, is capable of speeds up to 6 knots (about 12 km / h).

Boat "Hydra"

Fuel cells (particularly hydrogen-powered) have become much more widespread in land transport. In general, hydrogen has long been used as a fuel for automotive engines, and in principle conventional engine internal combustion is quite easy to convert to use this alternative fuel. However, conventional combustion of hydrogen is less efficient than generating electricity by chemical reaction between hydrogen and oxygen. And ideally, hydrogen, if it is used in fuel cells, will be absolutely safe for nature or, as they say, "friendly to the environment", since no carbon dioxide or other substances are released during the chemical reaction that touch the "greenhouse effect".

True, here, as one would expect, there are several big "buts". The fact is that many technologies for producing hydrogen from non-renewable resources (natural gas, coal, oil products) are not so environmentally friendly, since a large amount of carbon dioxide is released in their process. Theoretically, if renewable resources are used to obtain it, then there will be no harmful emissions at all. However, in this case, the cost increases significantly. According to many experts, for these reasons, the potential of hydrogen as a substitute for gasoline or natural gas is very limited. There are already less expensive alternatives, and most likely, fuel cells on the first element of the periodic table will not be able to become a mass phenomenon in vehicles.

Automobile manufacturers are quite actively experimenting with hydrogen as an energy source. And the main reason for this is the rather tough position of the EU in relation to harmful emissions into the atmosphere. Spurred on by increasingly stringent restrictions in Europe, Daimler AG, Fiat and Ford Motor Company have unveiled their vision for the future of fuel cells in the automotive industry, equipping their base models with similar powertrains. Another European auto giant, Volkswagen, is currently preparing its fuel cell vehicle. Japanese and South Korean firms do not lag behind them. However, not everyone is betting on this technology. Many people prefer to modify internal combustion engines or combine them with battery-powered electric motors. Toyota, Mazda and BMW followed this path. As for American companies, in addition to Ford with its Focus model, General Motors also presented several fuel cell cars. All these undertakings are actively encouraged by many states. For example, in the United States there is a law according to which a new hybrid car entering the market is exempt from taxes, which can be quite a decent amount, because as a rule such cars are more expensive than their counterparts with traditional internal combustion engines. Thus, hybrids as a purchase become even more attractive. However, for now, this law only applies to models entering the market until reaching a sales level of 60,000 cars, after which the benefit is automatically canceled.

Electronics

More recently, fuel cells have been increasingly used in laptops, mobile phones and other mobile devices. electronic devices Oh. The reason for this was the rapidly increasing gluttony of devices designed for long battery life. As a result of the use of large touch screens, powerful audio tools and the introduction of support for Wi-Fi, Bluetooth and other high-frequency wireless communication protocols, the requirements for battery capacity have also changed. And, although batteries have come a long way since the days of the first cell phones, in terms of capacity and compactness (otherwise, today fans would not be allowed into stadiums with these weapons with a communication function), they still do not keep up with miniaturization. electronic circuits, nor the desire of manufacturers to build more and more functions into their products. Another significant disadvantage of current batteries is their long charging time. Everything leads to the fact that the more features in a phone or pocket multimedia player designed to increase the autonomy of its owner (wireless Internet, navigation systems, etc.), the more dependent on the "socket" this device becomes.

There is nothing to say about laptops that are much smaller than those limited in maximum sizes. A niche of super-efficient laptops has been formed for a long time, which are not intended for autonomous operation at all, except for such a transfer from one office to another. And even the most cost-effective members of the laptop world struggle to deliver a full day of battery life. Therefore, the question of finding an alternative to traditional batteries, which would not be more expensive, but also much more efficient, is very acute. And the leading representatives of the industry have recently been solving this problem. Not so long ago, commercial methanol fuel cells were introduced, the mass deliveries of which can be started as early as next year.

The researchers chose methanol over hydrogen for some reason. It is much easier to store methanol because it does not require high pressure or special temperature regime. Methyl alcohol is a liquid at -97.0°C to 64.7°C. In this case, the specific energy contained in the Nth volume of methanol is an order of magnitude greater than in the same volume of hydrogen under high pressure. The direct methanol fuel cell technology, widely used in mobile electronic devices, involves the use of methanol after simply filling the fuel cell tank, bypassing the catalytic conversion procedure (hence the name "direct methanol"). This is also a major advantage of this technology.

However, as one would expect, all these pluses had their minuses, which significantly limited the scope of its application. In view of the fact that, nevertheless, this technology has not yet been fully developed, the problem of the low efficiency of such fuel cells caused by methanol "leakage" through the membrane material remains unresolved. In addition, they do not have impressive dynamic characteristics. It is not easy to decide what to do with the carbon dioxide produced at the anode. Modern DMFC devices are not capable of generating high energy, but they have a high energy capacity for a small volume of matter. This means that although much energy is not available yet, direct methanol fuel cells can generate it for a long time. This does not allow them, due to their low power, to be directly used in vehicles, but makes them almost ideal solution for mobile devices where battery life is critical.

Latest trends

Although fuel cells for vehicles have been produced for a long time, so far these solutions have not become widespread. There are many reasons for this. And the main ones are the economic inexpediency and unwillingness of manufacturers to put the production of affordable fuel on stream. Attempts to force the natural process of transition to renewable energy sources, as one might expect, did not lead to anything good. Of course, the reason for the sharp rise in prices for agricultural products is rather hidden not in the fact that they have begun to be massively converted into biofuels, but in the fact that many countries in Africa and Asia are not able to produce enough products even to meet domestic demand for products.

Obviously, the rejection of the use of biofuels will not lead to a significant improvement in the situation on the world food market, but, on the contrary, it may strike at European and American farmers, who for the first time in many years have received the opportunity to earn good money. But one cannot write off the ethical aspect of this issue, it is ugly to fill "bread" in tanks when millions of people are starving. Therefore, in particular, European politicians will now be more cool about biotechnology, which is already confirmed by the revision of the strategy for the transition to renewable energy sources.

In this situation, microelectronics should become the most promising field of application for fuel cells. This is where fuel cells have the greatest chance of gaining a foothold. First, people who buy cell phones are more willing to experiment than, say, car buyers. And secondly, they are ready to spend money and, as a rule, are not averse to "saving the world." The overwhelming success of the red "Bono" version of the iPod Nano can serve as confirmation of this, part of the money from the sale of which went to the Red Cross.

"Bono" version of the Apple iPod Nano

Among those who turned their attention to fuel cells for portable electronics are companies that previously specialized in the creation of fuel cells and now simply opened a new area for their application, as well as leading manufacturers of microelectronics. For example, recently MTI Micro, which has repurposed its business to produce methanol fuel cells for mobile electronic devices, announced that it would begin mass production in 2009. She also introduced the world's first methanol fuel cell GPS device. According to representatives of this company, in the near future its products will completely replace traditional lithium-ion batteries. True, at first they will not be cheap, but this problem accompanies any new technology.

For a company like Sony, which recently showed off its DMFC variant of a media-powered device, these technologies are new, but they are serious about not getting lost in a promising new market. In turn, Sharp went even further and, with its fuel cell prototype, recently set a world record for the specific energy capacity of 0.3 watts per cubic centimeter of methanol. Even the governments of many countries met the companies producing these fuel cells. So airports in the USA, Canada, Great Britain, Japan and China, despite the toxicity and flammability of methanol, canceled the previously existing restrictions on its transportation in the cabin. Of course, this is only allowed for certified fuel cells with a maximum capacity of 200 ml. Nevertheless, this once again confirms the interest in these developments on the part of not only enthusiasts, but also states.

True, manufacturers are still trying to play it safe and offer fuel cells mainly as a backup power system. One such solution is a combination of a fuel cell and a battery: while there is fuel, it constantly charges the battery, and after it runs out, the user simply replaces the empty cartridge with a new container of methanol. Another popular trend is the creation of fuel cell chargers. They can be used on the go. At the same time, they can charge batteries very quickly. In other words, in the future, perhaps everyone will carry such a "socket" in their pocket. This approach may be especially relevant in the case of mobile phones. In turn, laptops may well in the foreseeable future acquire built-in fuel cells, which, if not completely replace charging from the "socket", then at least become a serious alternative to it.

Thus, according to the forecast of Germany's largest chemical company BASF, which recently announced the start of construction of its fuel cell development center in Japan, by 2010 the market for these devices will be $1 billion. At the same time, its analysts predict the growth of the fuel cell market to $20 billion by 2020. By the way, in this center BASF plans to develop fuel cells for portable electronics (in particular laptops) and stationary energy systems. The place for this enterprise was not chosen by chance - the German company sees local firms as the main buyers of these technologies.

Instead of a conclusion

Of course, one should not expect from fuel cells that they will become a replacement for the existing power supply system. At least for the foreseeable future. This is a double-edged sword: portable power plants are certainly more efficient, due to the absence of losses associated with the delivery of electricity to the consumer, but it is also worth considering that they can become a serious competitor to a centralized power supply system only if a centralized fuel supply system for these installations is created. That is, the "socket" should eventually be replaced by a certain pipe that supplies the necessary reagents to every house and every nook and cranny. And this is not quite the freedom and independence from external current sources that fuel cell manufacturers talk about.

These devices have an undeniable advantage in the form of charging speed - I simply changed the methanol cartridge (in extreme cases, uncorked Jack Daniel's trophy) in the camera, and again skipping up the stairs of the Louvre. On the other hand, if, say, a regular phone is charging two hours and will require recharging every 2-3 days, then it is unlikely that an alternative in the form of changing a cartridge sold only in specialized stores, even once every two weeks, will be in such demand by a mass user. If a hermetic container of a couple of hundred milliliters of fuel will reach the end consumer, its price will have time to grow substantially. Only the scale of production will be able to fight this rise in price, but will this scale be in demand on the market? And until the optimal type of fuel is chosen, it will be very difficult to solve this problem. problematic.

On the other hand, a combination of traditional plug-in charging, fuel cells and other alternative energy supply systems (eg solar panels) can be the solution to the problem of diversifying power sources and switching to environmental types. However, for a certain group of electronic products, fuel cells can be widely used. This is confirmed by the fact that Canon recently patented its own fuel cells for digital cameras and announced a strategy for incorporating these technologies into its solutions. As for laptops, if fuel cells reach them in the near future, then most likely only as a backup power system. Now, for example, we are talking mainly about external charging modules that are additionally connected to a laptop.

But these technologies have huge prospects for development in the long term. Particularly in light of the threat of oil starvation, which may occur in the next few decades. Under these conditions, it is more important not even how cheap the production of fuel cells will be, but how much the production of fuel for them will be regardless of the petrochemical industry and whether it will be able to cover the need for it.

Benefits of fuel cells/cells

A fuel cell/cell is a device that efficiently generates direct current and heat from a hydrogen-rich fuel through an electrochemical reaction.

A fuel cell is similar to a battery in that it generates direct current through a chemical reaction. The fuel cell includes an anode, a cathode and an electrolyte. However, unlike batteries, fuel cells/cells cannot store electrical energy, do not discharge, and do not require electricity to be recharged. Fuel cells/cells can continuously generate electricity as long as they have a supply of fuel and air.

Unlike other power generators such as internal combustion engines or turbines powered by gas, coal, oil, etc., fuel cells/cells do not burn fuel. This means no noisy high pressure rotors, no loud exhaust noise, no vibration. Fuel cells/cells generate electricity through a silent electrochemical reaction. Another feature of fuel cells/cells is that they convert the chemical energy of the fuel directly into electricity, heat and water.

Fuel cells are highly efficient and do not produce large amounts of greenhouse gases such as carbon dioxide, methane and nitrous oxide. The only products emitted during operation are water in the form of steam and a small amount of carbon dioxide, which is not emitted at all if pure hydrogen is used as fuel. Fuel cells/cells are assembled into assemblies and then into individual functional modules.

History of fuel cell/cell development

In the 1950s and 1960s, one of the biggest challenges for fuel cells was born out of the US National Aeronautics and Space Administration's (NASA) need for energy sources for long-duration space missions. NASA's Alkaline Fuel Cell/Cell uses hydrogen and oxygen as fuel, combining the two in an electrochemical reaction. The output is three by-products of the reaction useful in spaceflight - electricity to power the spacecraft, water for drinking and cooling systems, and heat to keep the astronauts warm.

The discovery of fuel cells dates back to the beginning of the 19th century. The first evidence of the effect of fuel cells was obtained in 1838.

In the late 1930s, work began on alkaline fuel cells, and by 1939 a cell using high pressure nickel-plated electrodes had been built. During the Second World War, fuel cells/cells for British Navy submarines were developed and in 1958 a fuel assembly consisting of alkaline fuel cells/cells just over 25 cm in diameter was introduced.

Interest increased in the 1950s and 1960s, and also in the 1980s, when the industrial world experienced a shortage petroleum fuel. In the same period, world countries also became concerned about the problem of air pollution and considered ways to generate environmentally friendly electricity. At present, fuel cell/cell technology is undergoing rapid development.

How fuel cells/cells work

Fuel cells/cells generate electricity and heat through an ongoing electrochemical reaction using an electrolyte, a cathode and an anode.

The anode and cathode are separated by an electrolyte that conducts protons. After hydrogen enters the anode and oxygen enters the cathode, a chemical reaction begins, as a result of which electric current, heat and water are generated.

On the anode catalyst, molecular hydrogen dissociates and loses electrons. Hydrogen ions (protons) are conducted through the electrolyte to the cathode, while electrons are passed through the electrolyte and through an external electrical circuit, creating a direct current that can be used to power equipment. On the cathode catalyst, an oxygen molecule combines with an electron (which is supplied from external communications) and an incoming proton, and forms water, which is the only reaction product (in the form of vapor and / or liquid).

Below is the corresponding reaction:

Anode reaction: 2H 2 => 4H+ + 4e -
Reaction at the cathode: O 2 + 4H+ + 4e - => 2H 2 O
General element reaction: 2H 2 + O 2 => 2H 2 O

Types and variety of fuel cells/cells

Similar to the existence of different types of internal combustion engines, there are different types of fuel cells - the choice of the appropriate type of fuel cell depends on its application.

Fuel cells are divided into high temperature and low temperature. Low temperature fuel cells require relatively pure hydrogen as fuel. This often means that fuel processing is required to convert the primary fuel (such as natural gas) to pure hydrogen. This process consumes additional energy and requires special equipment. High temperature fuel cells do not need this additional procedure, as they can "internally convert" the fuel at elevated temperatures, which means there is no need to invest in hydrogen infrastructure.

Fuel cells/cells on molten carbonate (MCFC)

Molten carbonate electrolyte fuel cells are high temperature fuel cells. The high operating temperature allows direct use of natural gas without a fuel processor and low calorific value fuel gas from process fuels and other sources.

The operation of RCFC is different from other fuel cells. These cells use an electrolyte from a mixture of molten carbonate salts. Currently, two types of mixtures are used: lithium carbonate and potassium carbonate or lithium carbonate and sodium carbonate. To melt carbonate salts and achieve high degree mobility of ions in the electrolyte, fuel cells with molten carbonate electrolyte operate at high temperatures (650°C). The efficiency varies between 60-80%.

When heated to a temperature of 650°C, salts become a conductor for carbonate ions (CO 3 2-). These ions pass from the cathode to the anode where they combine with hydrogen to form water, carbon dioxide and free electrons. These electrons are sent through an external electrical circuit back to the cathode, generating electrical current and heat as a by-product.

Anode reaction: CO 3 2- + H 2 => H 2 O + CO 2 + 2e -
Reaction at the cathode: CO 2 + 1 / 2O 2 + 2e - \u003d\u003e CO 3 2-
General element reaction: H 2 (g) + 1/2O 2 (g) + CO 2 (cathode) => H 2 O (g) + CO 2 (anode)

The high operating temperatures of molten carbonate electrolyte fuel cells have certain advantages. At high temperatures, the natural gas is internally reformed, eliminating the need for a fuel processor. In addition, the advantages include the ability to use standard materials of construction, such as stainless steel sheet and nickel catalyst on the electrodes. The waste heat can be used to generate high pressure steam for various industrial and commercial applications.

High reaction temperatures in the electrolyte also have their advantages. The use of high temperatures takes a long time to reach optimal operating conditions, and the system reacts more slowly to changes in energy consumption. These characteristics allow the use of fuel cell systems with molten carbonate electrolyte in constant power conditions. High temperatures prevent damage to the fuel cell by carbon monoxide.

Molten carbonate fuel cells are suitable for use in large stationary installations. Thermal power plants with an output electric power of 3.0 MW are industrially produced. Plants with an output power of up to 110 MW are being developed.

Fuel cells/cells based on phosphoric acid (PFC)

Fuel cells based on phosphoric (orthophosphoric) acid were the first fuel cells for commercial use.

Fuel cells based on phosphoric (orthophosphoric) acid use an electrolyte based on orthophosphoric acid (H 3 PO 4) with a concentration of up to 100%. The ionic conductivity of phosphoric acid is low at low temperatures, for this reason these fuel cells are used at temperatures up to 150–220°C.

The charge carrier in fuel cells of this type is hydrogen (H+, proton). A similar process occurs in proton exchange membrane fuel cells, in which hydrogen supplied to the anode is split into protons and electrons. The protons pass through the electrolyte and combine with oxygen from the air at the cathode to form water. The electrons are directed along an external electrical circuit, and an electric current is generated. Below are the reactions that generate electricity and heat.

Reaction at the anode: 2H 2 => 4H + + 4e -
Reaction at the cathode: O 2 (g) + 4H + + 4e - \u003d\u003e 2 H 2 O
General element reaction: 2H 2 + O 2 => 2H 2 O

The efficiency of fuel cells based on phosphoric (orthophosphoric) acid is more than 40% when generating electrical energy. In the combined production of heat and electricity, the overall efficiency is about 85%. In addition, given operating temperatures, waste heat can be used to heat water and generate steam at atmospheric pressure.

The high performance of thermal power plants on fuel cells based on phosphoric (orthophosphoric) acid in the combined production of heat and electricity is one of the advantages of this type of fuel cells. The plants use carbon monoxide at a concentration of about 1.5%, which greatly expands the choice of fuel. In addition, CO 2 does not affect the electrolyte and the operation of the fuel cell, this type of cell works with reformed natural fuel. Simple construction, low electrolyte volatility and increased stability are also advantages of this type of fuel cell.

Thermal power plants with an output electric power of up to 500 kW are industrially produced. Installations for 11 MW have passed the relevant tests. Plants with an output power of up to 100 MW are being developed.

Solid oxide fuel cells/cells (SOFC)

Solid oxide fuel cells are the fuel cells with the highest operating temperature. The operating temperature can vary from 600°C to 1000°C, which allows the use of various types of fuel without special pre-treatment. To handle these high temperatures, the electrolyte used is a thin ceramic-based solid metal oxide, often an alloy of yttrium and zirconium, which is a conductor of oxygen (O 2-) ions.

A solid electrolyte provides a hermetic gas transition from one electrode to another, while liquid electrolytes are located in a porous substrate. The charge carrier in fuel cells of this type is the oxygen ion (O 2-). At the cathode, oxygen molecules are separated from the air into an oxygen ion and four electrons. Oxygen ions pass through the electrolyte and combine with hydrogen to form four free electrons. Electrons are directed through an external electrical circuit, generating electrical current and waste heat.

Reaction at the anode: 2H 2 + 2O 2- => 2H 2 O + 4e -
Reaction at the cathode: O 2 + 4e - \u003d\u003e 2O 2-
General element reaction: 2H 2 + O 2 => 2H 2 O

The efficiency of the generated electrical energy is the highest of all fuel cells - about 60-70%. High operating temperatures allow for combined heat and power generation to generate high pressure steam. Combining a high temperature fuel cell with a turbine creates a hybrid fuel cell to increase the efficiency of power generation up to 75%.

Solid oxide fuel cells operate at very high temperatures (600°C-1000°C), resulting in a long time to reach optimal operating conditions, and the system is slower to respond to changes in power consumption. At such high operating temperatures, no converter is required to recover hydrogen from the fuel, allowing the thermal power plant to operate with relatively impure fuels from coal gasification or waste gases, and the like. Also, this fuel cell is excellent for high power applications, including industrial and large central power plants. Industrially produced modules with an output electrical power of 100 kW.

Fuel cells/cells with direct methanol oxidation (DOMTE)

The technology of using fuel cells with direct oxidation of methanol is undergoing a period of active development. It has successfully established itself in the field of powering mobile phones, laptops, as well as for creating portable power sources. what the future application of these elements is aimed at.

The structure of fuel cells with direct oxidation of methanol is similar to fuel cells with a proton exchange membrane (MOFEC), i.e. a polymer is used as an electrolyte, and a hydrogen ion (proton) is used as a charge carrier. However, liquid methanol (CH 3 OH) is oxidized in the presence of water at the anode, releasing CO 2 , hydrogen ions and electrons, which are guided through an external electrical circuit, and an electric current is generated. Hydrogen ions pass through the electrolyte and react with oxygen from the air and electrons from the external circuit to form water at the anode.

Reaction at the anode: CH 3 OH + H 2 O => CO 2 + 6H + + 6e -
Reaction at the cathode: 3/2O 2 + 6 H + + 6e - => 3H 2 O
General element reaction: CH 3 OH + 3/2O 2 => CO 2 + 2H 2 O

The advantage of this type of fuel cells is their small size, due to the use of liquid fuel, and the absence of the need to use a converter.

Alkaline fuel cells/cells (AFC)

Alkaline fuel cells are one of the most efficient elements used to generate electricity, with power generation efficiency reaching up to 70%.

Alkaline fuel cells use an electrolyte, i.e. an aqueous solution of potassium hydroxide, contained in a porous, stabilized matrix. The concentration of potassium hydroxide may vary depending on the operating temperature of the fuel cell, which ranges from 65°C to 220°C. The charge carrier in an SFC is a hydroxide ion (OH-) moving from the cathode to the anode where it reacts with hydrogen to produce water and electrons. The water produced at the anode moves back to the cathode, again generating hydroxide ions there. As a result of this series of reactions taking place in the fuel cell, electricity is produced and, as by-product, warm:

Reaction at the anode: 2H 2 + 4OH - => 4H 2 O + 4e -
Reaction at the cathode: O 2 + 2H 2 O + 4e - => 4 OH -
General reaction of the system: 2H 2 + O 2 => 2H 2 O

The advantage of SFCs is that these fuel cells are the cheapest to produce, since the catalyst needed on the electrodes can be any of the substances that are cheaper than those used as catalysts for other fuel cells. SCFCs operate at relatively low temperatures and are among the most efficient fuel cells - such characteristics can respectively contribute to faster power generation and high fuel efficiency.

One of characteristic features SHTE - high sensitivity to CO 2 that may be contained in fuel or air. CO 2 reacts with the electrolyte, quickly poisons it, and greatly reduces the efficiency of the fuel cell. Therefore, the use of SFCs is limited to closed spaces such as space and underwater vehicles, they must operate on pure hydrogen and oxygen. Moreover, molecules such as CO, H 2 O and CH4, which are safe for other fuel cells and even fuel for some of them, are detrimental to SFCs.

Polymer electrolyte fuel cells/cells (PETE)

In the case of polymer electrolyte fuel cells, the polymer membrane consists of polymer fibers with water regions in which there is a conduction of water ions (H 2 O + (proton, red) attached to the water molecule). Water molecules present a problem due to slow ion exchange. Therefore, a high concentration of water is required both in the fuel and on the exhaust electrodes, which limits the operating temperature to 100°C.

Solid acid fuel cells/cells (SCFC)

In solid acid fuel cells, the electrolyte (CsHSO 4 ) does not contain water. The operating temperature is therefore 100-300°C. The rotation of the SO 4 2- oxy anions allows the protons (red) to move as shown in the figure. Typically, a solid acid fuel cell is a sandwich in which a very thin layer of solid acid compound is sandwiched between two tightly compressed electrodes to ensure good contact. When heated, the organic component evaporates, leaving through the pores in the electrodes, retaining the ability of numerous contacts between the fuel (or oxygen at the other end of the cell), electrolyte and electrodes.

Various fuel cell modules. fuel cell battery

1. Fuel Cell Battery
2. Other high temperature equipment (integrated steam generator, combustion chamber, heat balance changer)
3. Heat resistant insulation

fuel cell module

Comparative analysis of types and varieties of fuel cells

Innovative energy-saving municipal heat and power plants are typically built on solid oxide fuel cells (SOFCs), polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PCFCs), proton exchange membrane fuel cells (MPFCs) and alkaline fuel cells (APFCs) . They usually have the following characteristics:

Solid oxide fuel cells (SOFC) should be recognized as the most suitable, which:

• operate at a higher temperature, which reduces the need for expensive precious metals (such as platinum)
• can operate on various types of hydrocarbon fuels, mainly on natural gas
• have a longer start-up time and therefore are better suited for long-term operation
• demonstrate high efficiency of power generation (up to 70%)
• due to high operating temperatures, the units can be combined with heat recovery systems, bringing the overall system efficiency up to 85%
• have near-zero emissions, operate quietly and have low operating requirements compared to existing technologies power generation

Fuel cell type	Working temperature	Power Generation Efficiency	Fuel type	Application area
RKTE	550–700°C	50-70%		Medium and large installations
FKTE	100–220°C	35-40%	pure hydrogen	Large installations
MOPTE	30-100°C	35-50%	pure hydrogen	Small installations
SOFC	450–1000°C	45-70%	Most hydrocarbon fuels	Small, medium and large installations
POMTE	20-90°C	20-30%	methanol	portable
SHTE	50–200°C	40-70%	pure hydrogen	space research
PETE	30-100°C	35-50%	pure hydrogen	Small installations

Since small thermal power plants can be connected to a conventional gas supply network, fuel cells do not require a separate hydrogen supply system. When using small thermal power plants based on solid oxide fuel cells, the generated heat can be integrated into heat exchangers for heating water and ventilation air, increasing the overall efficiency of the system. This innovative technology is best suited for efficient power generation without the need for expensive infrastructure and complex instrument integration.

Fuel cell/cell applications

Application of fuel cells/cells in telecommunication systems

With the rapid spread of wireless communication systems around the world, as well as the growing social and economic benefits of mobile phone technology, the need for reliable and cost-effective backup power has become critical. Power grid losses throughout the year due to bad weather conditions, natural Disasters or limited network capacity present a persistent challenge for network operators.

Traditional telecom power backup solutions include batteries (valve-regulated lead-acid battery cell) for short-term backup power and diesel and propane generators for longer backup power. Batteries are a relatively cheap source of backup power for 1 to 2 hours. However, batteries are not suitable for longer backup periods because they are expensive to maintain, become unreliable after long use, are sensitive to temperatures, and are hazardous to the environment after disposal. Diesel and propane generators can provide continuous backup power. However, generators can be unreliable, require extensive maintenance, and release high levels of pollutants and greenhouse gases into the atmosphere.

In order to eliminate the limitations of traditional backup power solutions, an innovative green fuel cell technology has been developed. Fuel cells are reliable, quiet, contain fewer moving parts than a generator, have a wider operating temperature range than a battery from -40°C to +50°C and, as a result, provide extremely high levels of energy savings. In addition, the lifetime cost of such a plant is lower than that of a generator. Lower fuel cell costs are the result of only one maintenance visit per year and significantly higher plant productivity. After all, the fuel cell is an environmentally friendly technology solution with minimal environmental impact.

Installations on fuel cells provide backup power for critical communications network infrastructures for wireless, permanent and broadband communications in a telecommunications system, ranging from 250W to 15kW, they offer many unrivaled innovative features:

• RELIABILITY– Few moving parts and no standby discharge
• ENERGY SAVING
• SILENCE– low noise level
• STABILITY– operating range from -40°C to +50°C
• ADAPTABILITY– outdoor and indoor installation (container/protective container)
• HIGH POWER– up to 15 kW
• LOW MAINTENANCE NEED– minimum annual maintenance
• ECONOMY- attractive total cost of ownership
• CLEAN ENERGY– low emissions with minimal environmental impact

The system senses the DC bus voltage all the time and smoothly accepts critical loads if the DC bus voltage drops below a user-defined setpoint. The system runs on hydrogen, which enters the fuel cell stack in one of two ways - either from a commercial source of hydrogen, or from a liquid fuel of methanol and water, using an on-board reformer system.

Electricity is produced by the fuel cell stack in the form of direct current. The DC power is sent to a converter that converts the unregulated DC power from the fuel cell stack into high quality, regulated DC power for the required loads. A fuel cell installation can provide backup power for many days, as the duration is limited only by the amount of hydrogen or methanol/water fuel available in stock.

Fuel cells offer a high level of energy savings, improved system reliability, more predictable performance over a wide range of climatic conditions and reliable service life compared to industry standard valve regulated lead-acid battery packs. Lifecycle costs are also lower due to significantly less maintenance and replacement requirements. Fuel cells offer the end user environmental benefits as disposal costs and liability risks associated with lead acid cells are a growing concern.

The performance of electric batteries can be adversely affected by a wide range of factors such as charge level, temperature, cycles, life and other variables. The energy provided will vary depending on these factors and is not easy to predict. The performance of a proton exchange membrane fuel cell (PEMFC) is relatively unaffected by these factors and can provide critical power as long as fuel is available. Increased predictability is an important benefit when moving to fuel cells for mission-critical backup power applications.

Fuel cells generate energy only when fuel is supplied, like a gas turbine generator, but do not have moving parts in the generation zone. Therefore, unlike a generator, they are not subject to rapid wear and do not require constant maintenance and lubrication.

The fuel used to drive the Extended Duration Fuel Converter is fuel mixture from methanol and water. Methanol is a widely available, commercially produced fuel that currently has many applications, including windshield washer, plastic bottles, engine additives, emulsion paints. Methanol is easy to transport, miscible with water, has good biodegradability and is sulfur free. It has a low freezing point (-71°C) and does not decompose during long storage.

Application of fuel cells/cells in communication networks

Security networks require reliable backup power solutions that can last hours or days at a time. emergency situations if the power grid is no longer available.

With few moving parts and no standby power reduction, the innovative fuel cell technology offers an attractive solution compared to currently available backup power systems.

The most compelling reason for using fuel cell technology in communications networks is the increased overall reliability and security. During events such as power outages, earthquakes, storms and hurricanes, it is important that systems continue to operate and have a reliable backup power supply throughout long period time, regardless of temperature or age of the backup power system.

The range of fuel cell power supplies is ideal for supporting secure communications networks. Thanks to their energy saving design principles, they provide an environmentally friendly, reliable backup power with extended duration (up to several days) for use in the power range from 250 W to 15 kW.

Application of fuel cells/cells in data networks

Reliable power supply for data networks, such as high-speed data networks and fiber optic backbones, is of key importance throughout the world. Information transmitted over such networks contains critical data for institutions such as banks, airlines or medical centers. A power outage in such networks not only poses a danger to the transmitted information, but also, as a rule, leads to significant financial losses. Reliable innovative installations on fuel cells, providing backup power, provide the reliability needed to provide uninterrupted power.

Fuel cell units operating on a liquid fuel mixture of methanol and water provide a reliable backup power supply with extended duration, up to several days. In addition, these units feature significantly reduced maintenance requirements compared to generators and batteries, requiring only one maintenance visit per year.

Typical application characteristics for the use of fuel cell installations in data networks:

• Applications with power inputs from 100 W to 15 kW
• Applications with battery life requirements > 4 hours
• Repeaters in fiber optic systems (hierarchy of synchronous digital systems, high speed internet, voice over IP…)
• Network nodes of high-speed data transmission
• WiMAX Transmission Nodes

Fuel cell backup power installations offer numerous advantages for mission-critical data network infrastructures compared to traditional stand-alone batteries or diesel generators, allowing you to increase the possibility of using on site:

1. Liquid fuel technology solves the problem of hydrogen storage and provides virtually unlimited backup power.
2. Due to their quiet operation, low weight, resistance to temperature extremes and virtually vibration-free operation, fuel cells can be installed outdoors, in industrial premises/containers or on rooftops.
3. On-site preparations for using the system are quick and economical, and the cost of operation is low.
4. The fuel is biodegradable and represents an environmentally friendly solution for the urban environment.

Application of fuel cells/cells in security systems

The most carefully designed building security and communication systems are only as reliable as the power that powers them. While most systems include some type of back-up uninterruptible power system for short-term power losses, they do not provide for the longer power outages that can occur after natural disasters or terrorist attacks. This could be a critical issue for many corporate and government agencies.

Vital systems such as CCTV monitoring and access control systems (ID card readers, door closing devices, biometric identification technology, etc.), automatic fire alarm and fire fighting, elevator control systems and telecommunications networks are at risk in the absence of a reliable alternative source of continuous power supply.

Diesel generators are noisy, hard to locate, and are well aware of their reliability and maintenance issues. In contrast, a fuel cell back-up installation is quiet, reliable, has zero or very low emissions, and is easy to install on a rooftop or outside a building. It does not discharge or lose power in standby mode. It ensures the continued operation of critical systems, even after the institution ceases operations and the building is abandoned by people.

Innovative fuel cell installations protect expensive investments in critical applications. They provide environmentally friendly, reliable backup power with extended duration (up to many days) for use in the power range from 250 W to 15 kW, combined with numerous unsurpassed features and, especially, a high level of energy saving.

Fuel cell power backup units offer numerous advantages for mission critical applications such as security and building management systems over traditional battery or diesel generators. Liquid fuel technology solves the problem of hydrogen storage and provides virtually unlimited backup power.

Application of fuel cells/cells in domestic heating and power generation

Solid oxide fuel cells (SOFCs) are used to build reliable, energy-efficient and emission-free thermal power plants to generate electricity and heat from widely available natural gas and renewable fuel sources. These innovative units are used in a wide variety of markets, from domestic power generation to power supply to remote areas, as well as auxiliary power sources.

Application of fuel cells/cells in distribution networks

Small thermal power plants are designed to operate in a distributed power generation network consisting of a large number of small generator sets instead of one centralized power plant.

The figure below shows the loss in power generation efficiency when it is generated in a CHP plant and transmitted to homes through traditional transmission networks used in this moment. Efficiency losses in district generation include losses from the power plant, low and high voltage transmission, and distribution losses.

The figure shows the results of the integration of small thermal power plants: electricity is generated with a generation efficiency of up to 60% at the point of use. In addition, the household can use the heat generated by the fuel cells for water and space heating, which increases the overall efficiency of fuel energy processing and improves energy savings.

Using Fuel Cells to Protect the Environment - Utilization of Associated Petroleum Gas

One of the most important tasks in the oil industry is the utilization of associated petroleum gas. The existing methods of utilization of associated petroleum gas have a lot of disadvantages, the main one being that they are not economically viable. Associated petroleum gas is flared, which causes great harm to the environment and human health.

Innovative fuel cell heat and power plants using associated petroleum gas as a fuel open the way to a radical and cost-effective solution to the problems of associated petroleum gas utilization.

1. One of the main advantages of fuel cell installations is that they can operate reliably and sustainably on variable composition associated petroleum gas. Due to the flameless chemical reaction underlying the operation of a fuel cell, a reduction in the percentage of, for example, methane only causes a corresponding reduction in power output.
2. Flexibility in relation to the electrical load of consumers, differential, load surge.
3. For the installation and connection of thermal power plants on fuel cells, their implementation does not require capital expenditures, because The units are easily mounted on unprepared sites near fields, are easy to operate, reliable and efficient.
4. High automation and modern remote control do not require the constant presence of personnel at the plant.
5. Simplicity and technical excellence design: no moving parts, no friction, no lubrication systems gives significant economic benefits from the operation of fuel cell installations.
6. Water consumption: none at ambient temperatures up to +30 °C and negligible at higher temperatures.
7. Water outlet: none.
8. In addition, fuel cell thermal power plants do not make noise, do not vibrate, do not emit harmful emissions into the atmosphere

FUEL CELL
electrochemical generator, a device that provides direct conversion of chemical energy into electrical energy. Although the same thing happens in electric batteries, fuel cells have two important differences: 1) they function as long as the fuel and oxidizer are supplied from an external source; 2) chemical composition electrolyte does not change during operation, i.e. the fuel cell does not need to be recharged.
see also POWER SUPPLY BATTERY .
Operating principle. The fuel cell (Fig. 1) consists of two electrodes separated by an electrolyte, and systems for supplying fuel to one electrode and an oxidizer to the other, as well as a system for removing reaction products. In most cases, catalysts are used to speed up a chemical reaction. The fuel cell is connected by an external electrical circuit to a load that consumes electricity.

In the one shown in Fig. In an acid fuel cell, hydrogen is fed through a hollow anode and enters the electrolyte through very fine pores in the electrode material. In this case, hydrogen molecules are decomposed into atoms, which, as a result of chemisorption, each donating one electron, turn into positively charged ions. This process can be described by the following equations:

Hydrogen ions diffuse through the electrolyte to positive side element. The oxygen supplied to the cathode passes into the electrolyte and also reacts on the electrode surface with the participation of the catalyst. When combined with hydrogen ions and electrons that come from the external circuit, water is formed:

Fuel cells with alkaline electrolytes (usually concentrated sodium or potassium hydroxides) undergo similar chemical reactions. Hydrogen passes through the anode and reacts in the presence of a catalyst with hydroxyl ions (OH-) present in the electrolyte to form water and an electron:

At the cathode, oxygen reacts with water contained in the electrolyte and electrons from the external circuit. In successive reaction steps, hydroxyl ions (as well as perhydroxyl O2H-) are formed. The resulting reaction at the cathode can be written as:

The flow of electrons and ions maintains the balance of charge and matter in the electrolyte. The water formed as a result of the reaction partially dilutes the electrolyte. In any fuel cell, part of the energy of a chemical reaction is converted into heat. The flow of electrons in an external circuit is a direct current that is used to do work. Most reactions in fuel cells provide an EMF of about 1 V. Opening the circuit or stopping the movement of ions stops the fuel cell from working. The process that occurs in a hydrogen-oxygen fuel cell is, by its nature, the reverse of the well-known electrolysis process, in which water dissociates when an electric current passes through the electrolyte. Indeed, in some types of fuel cells, the process can be reversed - by applying a voltage to the electrodes, water can be decomposed into hydrogen and oxygen, which can be collected at the electrodes. If you stop charging the cell and connect a load to it, such a regenerative fuel cell will immediately begin to operate in its normal mode. Theoretically, the dimensions of the fuel cell can be arbitrarily large. However, in practice, several cells are combined into small modules or batteries, which are connected either in series or in parallel.
Fuel cell types. There are different types of fuel cells. They can be classified, for example, according to the fuel used, the operating pressure and temperature, and the nature of the application.
Elements on hydrogen fuel. In this typical cell described above, hydrogen and oxygen are transferred to the electrolyte through microporous carbon or metal electrodes. High current density is achieved in cells operating at elevated temperatures (about 250°C) and high pressures. Cells using hydrogen fuel obtained from the processing of hydrocarbon fuels, such as natural gas or petroleum products, apparently will find the widest commercial application. Combining a large number of elements, you can create powerful power plants. In these installations, the direct current generated by the cells is converted into alternating current with standard parameters. A new type of elements capable of operating on hydrogen and oxygen at normal temperature and pressure are elements with ion-exchange membranes (Fig. 2). In these cells, instead of a liquid electrolyte, a polymer membrane is located between the electrodes, through which ions freely pass. In such cells, air can be used along with oxygen. The water formed during the operation of the cell does not dissolve the solid electrolyte and can be easily removed.

Elements on hydrocarbon and coal fuels. Fuel cells that can convert the chemical energy of widely available and relatively inexpensive fuels such as propane, natural gas, methanol, kerosene, or gasoline directly into electricity are the subject of intense research. However, notable progress has not yet been achieved in the development of fuel cells operating on gases obtained from hydrocarbon fuels at normal temperatures. To increase the reaction rate of hydrocarbon and coal fuels, it is necessary to increase the operating temperature of the fuel cell. Electrolytes are melts of carbonates or other salts, which are enclosed in a porous ceramic matrix. The fuel "splits" within the cell to form hydrogen and carbon monoxide, which keep the current generating reaction going in the cell. Elements operating on other types of fuel. In principle, reactions in fuel cells need not be oxidation reactions of conventional fuels. In the future, other chemical reactions can be found that will allow efficient direct generation of electricity. In some devices, electricity is obtained by oxidizing, for example, zinc, sodium or magnesium, from which consumable electrodes are made.
Efficiency. Converting the energy of conventional fuels (coal, oil, natural gas) into electricity has so far been a multi-stage process. Burning a fuel to produce the steam or gas needed to run a turbine or internal combustion engine, which in turn drives an electrical generator, is not a very efficient process. Indeed, the energy utilization factor of such a transformation is limited by the second law of thermodynamics, and it can hardly be raised significantly above the existing level (see also HEAT; THERMODYNAMICS). The fuel energy utilization factor of the most modern steam turbine power plants does not exceed 40%. For fuel cells, there is no thermodynamic limitation on the energy utilization factor. In existing fuel cells, 60 to 70% of fuel energy is directly converted into electricity, and fuel cell power plants using hydrogen from hydrocarbon fuels are designed for 40-45% efficiency.
Applications. Fuel cells may in the near future become a widely used source of energy in transport, industry and household. The high cost of fuel cells has limited their use in military and space applications. Intended applications of fuel cells include their use as portable power sources for military needs and compact alternative power sources for near-Earth satellites with solar panels when they pass through extended shadow sections of the orbit. The small size and mass of fuel cells made it possible to use them in manned flights to the Moon. Fuel cells aboard the three-seat Apollo spacecraft were used to power on-board computers and radio communication systems. Fuel cells can be used to power equipment in remote areas, for off-road vehicles, such as in construction. Combined with a DC electric motor, the fuel cell will be an efficient source of vehicle propulsion. For the widespread use of fuel cells, significant technological progress, cost reduction and the possibility of efficient use of cheap fuel are required. When these conditions are met, fuel cells will make electrical and mechanical energy widely available throughout the world.
see also ENERGETIC RESOURCES .
LITERATURE
Bagotsky V.S., Skundin A.M. Chemical Sources current. M., 1981 Crompton T. Current sources. M., 1985, 1986

Collier Encyclopedia. - Open Society. 2000 .

See what "FUEL CELL" is in other dictionaries:

FUEL ELEMENT, ELECTROCHEMICAL ELEMENT for direct conversion of fuel oxidation energy into electrical energy. Accordingly designed electrodes are immersed in an ELECTROLYTE, and fuel (for example, hydrogen) is supplied to one ... Scientific and technical encyclopedic dictionary

A galvanic cell in which the redox reaction is maintained by a continuous supply of reagents (fuel, eg hydrogen, and oxidizer, eg oxygen) from special reservoirs. The most important part... ... Big Encyclopedic Dictionary

fuel cell- A primary element in which electrical energy is generated by electrochemical reactions between active substances continuously supplied to the electrodes from the outside. [GOST 15596 82] EN fuel cell cell that can change chemical energy from… … Technical Translator's Handbook

Direct methanol fuel cell A fuel cell is an electrochemical device similar to, but different from, a galvanic cell ... Wikipedia

Over the next two years, a large number of mass-produced models equipped with chemical fuel cell power sources are expected to appear on the market for mobile computers and portable electronic devices.

Excursion into history

The first experiments on the creation of fuel cells were carried out in the 19th century. In 1839, the English physicist Grove, while carrying out the electrolysis of water, discovered that after turning off the external current source, a direct current arises between the electrodes. However, the discoveries in this area, made by a number of prominent scientists of the 19th century, did not find practical application, becoming the property of only academic science.

Scientists returned to the creation of fuel cells for applied use only in the early 1950s. During this period, research teams in the USA, Japan, the USSR and a number of Western European countries began to actively study the possibilities of practical application of chemical reactors for generating electricity.

The first area of ​​practical application of fuel cells was astronautics. Fuel cells of various designs were used on the American spacecraft Gemini, Apollo and Shuttle, as well as on the reusable space shuttle Buran created in the USSR.

The next wave of interest in chemical fuel cells was caused by the energy crisis of the 70s. During that period, many companies were engaged in research into the use of alternative energy sources for transport, as well as for domestic and industrial applications. By the way, it was in this field that the now well-known ARS company began its activities.

Currently, there are four main areas of application for fuel cell power plants: power plants for various vehicles (from scooters to buses), stationary solutions of large and small scale, and power supplies for mobile devices. In this article, we will focus mainly on solutions for portable devices.

What are fuel cells

First of all, it is necessary to clarify what will be discussed. Fuel cells are specialized chemical reactors designed to directly convert the energy released during the fuel oxidation reaction into electrical energy.

It should be noted that fuel cells have at least two fundamental differences from galvanic batteries, also related to devices that convert the energy of chemical reactions occurring in them into electricity. Firstly, fuel cells use electrodes that are not consumed during operation, and secondly, the substances necessary for the reaction are supplied from the outside, and are not initially laid inside the cell (as is the case with conventional batteries).

The use of non-consumable electrodes can significantly increase the service life of fuel cells compared to galvanic batteries. In addition, due to the use of an external fuel supply system, the procedure for restoring the efficiency of fuel cells is greatly simplified and cheaper.

	Types of chemical fuel cells Fuel cells with ion exchange membrane (Proton Exchange Membrane, PEM) The technology for manufacturing elements of this type was developed in the 50s of the 20th century by engineers from General Electric. Similar fuel cells were used to generate electricity on the US Gemini spacecraft. Distinctive feature PEM-elements is the use of graphite electrodes and a solid polymer electrolyte (or, as it is also called, an ion-exchange membrane Proton Exchange Membrane). PEM cells use pure hydrogen as fuel, while oxygen in the air acts as an oxidizing agent. Hydrogen is supplied from the anode side, where an electrochemical reaction takes place: 2H2 -> 4H++4e. Hydrogen ions move from the anode to the cathode through the electrolyte (ionic conductor), while the electrons through the external circuit. At the cathode, from the side of which an oxidizing agent (oxygen or air) is supplied, hydrogen is oxidized to form pure water: O 2 + 4H + + 4e -> 2H 2 O. The operating temperature of PEM cells is around 80°C. Under these conditions, electrochemical reactions proceed too slowly, so the design of this type of cell uses a catalyst usually a thin layer of platinum on each of the electrodes. One cell of such an element, consisting of a pair of electrodes and an ion-exchange membrane, is capable of generating a voltage of the order of 0.7 V. To increase the output voltage, an array of individual cells is connected to a battery. PEM cells are able to operate at a relatively low ambient temperature and have a fairly high efficiency (40 to 50% efficiency). At present, on the basis of PEM elements, operating prototypes of power plants with a capacity of up to 50 kW have been created; under development are devices with a power of up to 250 kW. There are several limitations preventing wider adoption of this technology. This is a relatively high cost of materials for the manufacture of membranes and catalyst. In addition, only pure hydrogen can be used as fuel. Alkaline Fuel Cells (AFC) The design of the first alkaline fuel cell was developed by the Russian scientist P. Yablochkov in 1887. As an electrolyte in alkaline cells, concentrated potassium hydroxide (KOH) or its aqueous solution is used, and nickel is the main material for the manufacture of electrodes. Pure hydrogen is used as fuel, and pure oxygen is used as oxidizer. The hydrogen oxidation reaction proceeds through the electrooxidation of hydrogen at the anode: 2H 2 + 4OH - 4e -> 4H 2 O and electroreduction of oxygen at the cathode: O 2 + 2H 2 O + 4e -> 4OH -. Hydroxide ions move in the electrolyte from the cathode to the anode, and electrons move along the external circuit from the anode to the cathode. Alkaline cells operate at a temperature of about 80 °C, but they are significantly (by about an order of magnitude) inferior to PEM cells in terms of power density, as a result of which their dimensions (with comparable characteristics) are much larger. However, the production cost of alkaline cells is much lower than PEM. The main disadvantage of alkaline elements is the need to use pure oxygen and hydrogen, since the presence of carbon dioxide (CO2) impurities in the fuel or oxidizer leads to carbonization of the alkali. Phosphoric acid fuel cells (PAFC) The electrolyte used in phosphate cells is liquid phosphoric acid, usually contained in the pores of a silicon carbide matrix. Graphite is used to make electrodes. The hydrogen electrooxidation reactions occurring in phosphate cells are similar to those occurring in PEM cells. The operating temperature of phosphate cells is somewhat higher compared to PEM and alkaline cells and ranges from 150 to 200 °C. Nevertheless, to ensure the required rate of electrochemical reactions, it is necessary to use catalysts (platinum or alloys based on it). Due to the higher operating temperature, phosphate cells are less sensitive to the chemical purity of the fuel (hydrogen) than PEM and alkaline cells. This allows the use of a fuel mixture containing 1-2% carbon monoxide. Ordinary air can be used as an oxidizing agent, since the substances contained in it do not react with the electrolyte. Phosphoric acid elements have a relatively low efficiency (about 40%) and require some time to reach the operating mode during a cold start. However, PAFCs also have a number of advantages, including a simpler design, as well as high stability and low volatility of the electrolyte. At present, on the basis of phosphoric acid elements, a large number of power plants with a capacity of 200 kW to 20 MW have been created and put into commercial operation. Fuel cells with direct oxidation of methanol (Direct Methanol Fuel Cells, DMFC) Elements with direct oxidation of methanol are one of the options for the implementation of elements with an ion exchange membrane. The fuel for DMFC-elements is an aqueous solution of methyl alcohol (methanol). The hydrogen required for the reaction (and a by-product in the form of carbon dioxide) is obtained by direct electrooxidation of the methanol solution at the anode: CH 3 OH + H 2 O -> CO 2 + 6H + + 6e. At the cathode, the reaction of hydrogen oxidation occurs with the formation of water: 3/2O 2 + 6H + + 6e -> 3H 2 O. The operating temperature of DMFC cells is approximately 120°C, which is slightly higher than that of hydrogen PEM cells. The disadvantage of low temperature conversion is the higher requirement for catalysts. This inevitably leads to an increase in the cost of such fuel cells, but this drawback is compensated by the convenience of using liquid fuel and the absence of the need to use an external converter to produce pure hydrogen. Fuel cells with an electrolyte from a melt of lithium carbonate and sodium (Molten Carbonate Fuel Cells, MCFC) This type of fuel cells belongs to high-temperature devices. They use an electrolyte consisting of lithium carbonate (Li 2 CO 3) or sodium carbonate (Na 2 CO 3) located in the pores of the ceramic matrix. Chromium-doped nickel is used as an anode material, and lithiated nickel oxide (NiO + LiO 2) is used for the cathode. When heated to a temperature of about 650 ° C, the electrolyte components melt, resulting in the formation of carbon dioxide salt ions moving from the cathode to the anode, where they react with hydrogen: CO 3 2– + H 2 -> H 2 O + CO 2 + 2e. The released electrons move along the external circuit back to the cathode, where the reaction occurs: CO 2 + 1/2 O 2 + 2e -> CO 3 2–. The high operating temperature of these elements makes it possible to use natural gas (methane) as a fuel, which is converted into hydrogen and carbon monoxide by the built-in converter: CH 4 + H 2 O<->CO + 3H 2 . MCFC elements have a high efficiency (up to 60%) and allow the use of cheaper and more accessible nickel instead of platinum as a catalyst. Due to the large amount of heat released during operation, this type of fuel cell is well suited for creating stationary sources of electrical and thermal energy, but is of little use for operation in mobile conditions. At present, stationary power plants with a capacity of up to 2 MW have already been created on the basis of MCFC elements. Fuel cells with solid electrolyte (Solid Oxide Fuel Cells, SOFC) This type of element has an even higher operating temperature (from 800 to 1000 °C) than the above-described MCFC. SOFC uses a ceramic electrolyte based on zirconium oxide (ZrO 2 ) stabilized with yttria (Y 2 O 3 ). An electrochemical reaction occurs at the cathode with the formation of negatively charged oxygen ions: O 2 + 4e -> 2O 2–. Negatively charged oxygen ions move in the electrolyte in the direction from the cathode to the anode, where the fuel is oxidized (usually a mixture of hydrogen and carbon monoxide to form water and carbon dioxide: H 2 + 2O 2– -> H 2 O + 2e; CO + 2O 2– -> CO 2 + 2e. SOFC cells offer the same benefits as MCFCs, including the ability to use natural gas as fuel. SOFC components have higher chemical stability, but their production cost is slightly higher compared to MCFC.

The operation of chemical fuel cells is supported by the supply of two components used to support the reaction - fuel and oxidizer. Depending on the type of fuel cell, hydrogen gas, natural gas (methane) as well as liquid hydrocarbon fuel (eg methanol) can be used as fuel. The oxidizing agent is usually the oxygen in the air, and some types of fuel cells can only work with pure oxygen.

The design of any chemical fuel cell consists of two electrodes (cathode and anode) and an electrolyte layer located between them, a medium that ensures the movement of ions from one electrode to another and blocks the movement of electrons. In order for the reaction to proceed at a faster rate, catalysts are often used in the electrodes. Depending on the chemical and physical characteristics of the electrolyte used, fuel cells are divided into several different types (for more details, see the sidebar "Types of chemical fuel cells").

Advantages of fuel cells

Compared to currently widely used autonomous power supplies used in mobile PCs and portable devices, chemical fuel cells have a number of important advantages.

First of all, it is worth noting the high efficiency of fuel cells, which, depending on the type, is from 40 to 60%. High efficiency makes it possible to manufacture power supplies with a higher specific energy intensity, due to which a reduction in their weight and size indicators is achieved while maintaining power and battery life. In addition, more energy-hungry power supplies can significantly extend the battery life of existing devices without increasing their size and weight.

Another important advantage of chemical fuel cells is the possibility of almost instant renewal of their energy resource even in the absence of external power sources for this, it is enough to install a new container (cartridge) with the fuel used. The use of electrodes that are not consumed in the reaction process allows you to create fuel cells with a very long service life and a low total cost of ownership.

It should also be noted that chemical fuel cells are much more environmentally friendly than galvanic batteries. Consumables for fuel cells are only containers with fuel, and the main product of the reaction is ordinary water. Replacing current batteries and accumulators with fuel cells will significantly reduce the volume of waste containing toxic and environmentally harmful substances to be recycled.

Platinum problem

Despite the obvious advantages of chemical fuel cells over many of the current power sources for portable PCs and electronic devices, there are certain obstacles to the mass adoption of the new technology.

Most suitable for relatively small portable applications are low operating temperature fuel cells such as PEM and DMCF. However, to ensure an acceptable rate of chemical reactions in such elements, it is necessary to use catalysts. Currently, PEM and DMCF cells use catalysts made of platinum and its alloys. Taking into account the relatively small natural reserves of this substance, as well as its high cost, one of the main tasks for the developers of power sources based on fuel cells is the search and creation of new catalysts. Another possible solution to the problem is the use of high-temperature fuel cells, however, for a number of reasons, such power sources are currently practically unsuitable for use in portable devices.

Moving Forward: Prototyping

Despite the presence of a number of problems, over the past two years, the activity of development teams involved in the creation of fuel cells for portable PCs and electronic devices has increased markedly. In addition, the number of companies conducting such work has also increased.

If we talk about the technologies used, then the most popular solutions in this segment are PEM and DMFC fuel cells. Of the companies developing fuel cells for mobile devices, about 45% relied on PEM technology, about 40% on DMFC and less than 10% on SOFC. The convenience and ease of use of liquid fuels is a significant advantage of DMFC over PEM, and in the past year it has become clear that most projects on the verge of commercialization are based on DMFC technology.

A prototype PDA with an integrated fuel cell created by Hitachi developers

Early last year, Hitachi demonstrated a prototype PDA with an integrated fuel cell and announced its intention to start selling a trial batch of such devices in 2005. The fuel cell is refilled using a cylindrical cartridge (1 cm in diameter and 5 cm high) containing a 20% aqueous methanol solution. According to the developers, the fuel contained in the cartridge is enough to provide active work with a PDA within 6-8 hours.

Last June, Toshiba unveiled a prototype compact DMFC cell designed to power digital media players and mobile phones. The dimensions of this block are 22X56X4.5 mm, weight 8.5 g. It uses concentrated methanol (99.5%) as fuel. One charge of fuel (2 cm3) is sufficient to power a 100 mW load (eg a portable MP3 player) for 20 hours. During the development of this prototype, several new solutions were applied, in particular, the structure of the electrodes and the polymer membrane was optimized, which makes it possible to use concentrated methanol as a fuel.

It is known that one of the manufacturers of mobile phones KDDI is closely eyeing the developments of Toshiba and Hitachi in the field of small-sized fuel cells. KDDI plans to bring fuel cell powered mobile phones to market within the next two years.

Several companies have already demonstrated prototype laptop solutions. In particular, Casio presented a laptop prototype equipped with a power supply that contains a PEM element and a methanol converter. At the beginning of last year, Samsung introduced a prototype laptop based on the Centrino mobile platform, equipped with a fuel cell that ensures the operation of the device for 10 hours.

In November 2004, the staff of the Tokyo Institute for Research in Materials and Energy (Materials and Energy Research Institute Tokyo, MERIT) published information about work on creating a fuel cell of its own design, which will be cheaper and more compact than DMFC. It will use sodium borohydride as fuel. According to the developers, thanks to this, the operating time of the fuel cell will increase four times compared to a DMFC cell filled with the same volume of methanol.

The fuel cell prototype presented by the MERIT employees is made in a package measuring 80X84.6X3 mm and is capable of operating with a load of up to 20 W. To power more powerful devices, you can use batteries consisting of several cells. According to existing plans, deployment serial production such elements are scheduled for early 2006.

The ice has broken...

In mid-December, Intermec Technologies launched the Handheld RFID Reader, the first mass-produced device equipped with a small-sized DMFC element. The Mobion fuel cell used in the device was developed by MTI MicroFuel Cells, which plans to launch production of such power supplies for PDAs, smartphones and other portable devices. According to the developers of MTI MicroFuel Cells, the Mobion element allows several times to increase the operating time of devices without recharging compared to lithium-ion batteries the same size.

According to many experts, a number of mass-produced portable devices equipped with fuel cells should be expected in the coming year. And the future of the portable power supply market will largely depend on how successful their debut will be.