Like the existence of different types of engines internal combustion, there are different types of fuel cells – the choice suitable type fuel cell depends on its application.
fuel cells 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 that there is no need to invest in hydrogen infrastructure.
Fuel cells on molten carbonate (MCFC)
Molten carbonate electrolyte fuel cells are high temperature fuel cells. High operating temperature allows direct use of natural gas without a fuel processor and low calorific value fuel gas production processes and from other sources. This process was developed in the mid-1960s. Since that time, manufacturing technology, performance and reliability have been improved.
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 / 2 O 2 + 2e - => CO 3 2-
General element reaction: H 2 (g) + 1/2 O 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 fuel cell damage by carbon monoxide, "poisoning", etc.
Molten carbonate fuel cells are suitable for use in large stationary installations. Thermal power plants with an output electric power of 2.8 MW are industrially produced. Plants with an output power of up to 100 MW are being developed.
Phosphoric Acid Fuel Cells (PFC)
Fuel cells based on phosphoric (orthophosphoric) acid were the first fuel cells for commercial use. This process was developed in the mid-1960s and has been tested since the 1970s. Since then, stability, performance and cost have been increased.
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 (MEFCs), 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 2H 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 design, 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 400 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.
Fuel Cells with Proton Exchange Membrane (PME)
Proton exchange membrane fuel cells are considered the best type of fuel cells for vehicle power generation, which can replace gasoline and diesel internal combustion engines. These fuel cells were first used by NASA for the Gemini program. Today, installations on MOPFC with a power of 1 W to 2 kW are being developed and demonstrated.
These fuel cells use a solid polymer membrane (thin plastic film) as the electrolyte. When impregnated with water, this polymer passes protons, but does not conduct electrons.
The fuel is hydrogen, and the charge carrier is a hydrogen ion (proton). At the anode, the hydrogen molecule is separated into a hydrogen ion (proton) and electrons. The hydrogen ions pass through the electrolyte to the cathode, and the electrons travel around the outer circle and produce electrical energy. Oxygen, which is taken from the air, is fed to the cathode and combines with electrons and hydrogen ions to form water. The following reactions take place on the electrodes:
Reaction at the anode: 2H 2 + 4OH - => 4H 2 O + 4e -
Reaction at the cathode: O 2 + 2H 2 O + 4e - \u003d\u003e 4OH -
General element reaction: 2H 2 + O 2 => 2H 2 O
Compared to other types of fuel cells, proton exchange membrane fuel cells produce more power for a given fuel cell volume or weight. This feature allows them to be compact and lightweight. In addition, the operating temperature is less than 100°C, which allows you to quickly start operation. These characteristics, as well as the ability to quickly change energy output, are just some of the features that make these fuel cells a prime candidate for use in vehicles.
Another advantage is that the electrolyte is a solid rather than a liquid substance. Keeping the gases at the cathode and anode is easier with a solid electrolyte and therefore such fuel cells are cheaper to manufacture. Compared to other electrolytes, the use of a solid electrolyte does not cause problems such as orientation, there are fewer problems due to the occurrence of corrosion, which leads to a longer durability of the cell and its components.
Solid oxide fuel 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. The technology of using solid oxide fuel cells has been developing since the late 1950s. and has two configurations: planar and tubular.
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 - => 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%. In addition, 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 electrical power generation by up to 70%.
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 with direct methanol oxidation (DOMTE)
The technology of using fuel cells with direct oxidation of methanol is undergoing a period of active development. She has successfully established herself in the field of nutrition mobile phones, laptops, as well as to create portable sources of electricity. 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 / 2 O 2 + 6H + + 6e - => 3H 2 O
General element reaction: CH 3 OH + 3/2 O 2 => CO 2 + 2H 2 O
The development of these fuel cells began in the early 1990s. After the development of improved catalysts, and thanks to other recent innovations, power density and efficiency have been increased up to 40%.
These elements were tested in the temperature range of 50-120°C. With low operating temperatures and no need for a converter, direct methanol fuel cells are the best candidate for applications ranging from mobile phones and other consumer products to automotive engines. 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 (AFC)
Alkaline fuel cells (ALFCs) are one of the most studied technologies and have been used since the mid-1960s. by NASA in the Apollo and Space Shuttle programs. On board these spacecraft, fuel cells produce electrical energy and drinking water. 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 a by-product, heat:
Reaction at the anode: 2H 2 + 4OH - => 4H 2 O + 4e -
Reaction at the cathode: O 2 + 2H 2 O + 4e - \u003d\u003e 4OH -
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. In addition, SCFCs operate at a relatively low temperature and are among the most efficient fuel cells - such characteristics can respectively contribute to faster power generation and high fuel efficiency.
One of the characteristic features of SHTE is its high sensitivity to CO 2 , which can 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 CH 4 , which are safe for other fuel cells and even fuel for some of them, are detrimental to SFC.
Polymer electrolyte fuel 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 (SCFC)
In solid acid fuel cells, the electrolyte (C s HSO 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.
| 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 units |
| SHTE | 50–200°C | 40-65% | pure hydrogen | space research |
| PETE | 30-100°C | 35-50% | pure hydrogen | Small installations |
Part 1
This article discusses in more detail the principle of operation of fuel cells, their design, classification, advantages and disadvantages, scope, efficiency, history of creation and modern prospects for use. In the second part of the article, which will be published in the next issue of the ABOK magazine, provides examples of facilities where various types of fuel cells were used as sources of heat and electricity (or only electricity).
Introduction
Fuel cells are a very efficient, reliable, durable and environmentally friendly way to generate energy.
Initially used only in the space industry, fuel cells are now increasingly used in a variety of areas - as stationary power plants, autonomous sources of heat and power for buildings, vehicle engines, power supplies for laptops and mobile phones. Some of these devices are laboratory prototypes, some are undergoing pre-series testing or are used for demonstration purposes, but many models are mass-produced and used in commercial projects.
A fuel cell (electrochemical generator) is a device that converts the chemical energy of fuel (hydrogen) into electrical energy in the process of an electrochemical reaction directly, unlike traditional technologies that use the combustion of solid, liquid and gaseous fuels. Direct electrochemical conversion of fuel is very efficient and attractive from an environmental point of view, since the minimum amount of pollutants is released during operation, and there are no strong noises and vibrations.
From a practical point of view, a fuel cell resembles a conventional galvanic battery. The difference lies in the fact that initially the battery is charged, i.e. filled with “fuel”. During operation, "fuel" is consumed and the battery is discharged. Unlike a battery, a fuel cell uses fuel supplied from an external source to generate electrical energy (Fig. 1).
For the production of electrical energy, not only pure hydrogen can be used, but also other hydrogen-containing raw materials, such as natural gas, ammonia, methanol or gasoline. Ordinary air is used as a source of oxygen, which is also necessary for the reaction.
When pure hydrogen is used as a fuel, the reaction products, in addition to electrical energy, are heat and water (or water vapor), i.e. no gases are emitted into the atmosphere that cause air pollution or cause a greenhouse effect. If a hydrogen-containing feedstock, such as natural gas, is used as a fuel, other gases, such as oxides of carbon and nitrogen, will be a by-product of the reaction, but its amount is much lower than when burning the same amount of natural gas.
The process of chemical conversion of fuel in order to produce hydrogen is called reforming, and the corresponding device is called a reformer.
Advantages and disadvantages of fuel cells
Fuel cells are more energy efficient than internal combustion engines because there is no thermodynamic limitation on energy efficiency for fuel cells. The efficiency of fuel cells is 50%, while the efficiency of internal combustion engines is 12-15%, and the efficiency of steam turbine power plants does not exceed 40%. By using heat and water, the efficiency of fuel cells is further increased.
In contrast to, for example, internal combustion engines, the efficiency of fuel cells remains very high even when they are not operating at full power. In addition, the power of fuel cells can be increased by simply adding separate blocks, while the efficiency does not change, i.e. large installations are as efficient as small ones. These circumstances allow a very flexible selection of the composition of equipment in accordance with the wishes of the customer and ultimately lead to a reduction in equipment costs.
An important advantage of fuel cells is their environmental friendliness. Air emissions of pollutants from fuel cell operation are so low that in some areas of the United States they do not require a special permit from government agencies controlling the quality of the air environment.
Fuel cells can be placed directly in the building, thus reducing energy transmission losses, and the heat generated as a result of the reaction can be used to supply heat or hot water to the building. Autonomous sources of heat and power supply can be very beneficial in remote areas and in regions that are characterized by a shortage of electricity and its high cost, but at the same time there are reserves of hydrogen-containing raw materials (oil, natural gas).
The advantages of fuel cells are also the availability of fuel, reliability (there are no moving parts in the fuel cell), durability and ease of operation.
One of the main disadvantages of fuel cells today is their relatively high cost, but this disadvantage may soon be overcome as more companies produce commercial samples fuel cells, they are constantly being improved, and their cost is decreasing.
The most efficient use of pure hydrogen as a fuel, however, this will require the creation of a special infrastructure for its production and transportation. Currently, all commercial designs use natural gas and similar fuels. Motor vehicles can use ordinary gasoline, which will allow maintaining the existing developed network of gas stations. However, the use of such fuel leads to harmful emissions into the atmosphere (albeit very low) and complicates (and therefore increases the cost of) the fuel cell. In the future, the possibility of using environmentally friendly renewable energy sources (for example, solar energy or wind power) to decompose water into hydrogen and oxygen by electrolysis, and then convert the resulting fuel in a fuel cell. Such combined plants operating in a closed cycle can be a completely environmentally friendly, reliable, durable and efficient source of energy.
Another feature of fuel cells is that they are most efficient when using both electrical and thermal energy at the same time. However, the possibility of using thermal energy is not available at every facility. In the case of using fuel cells only for generating electrical energy, their efficiency decreases, although it exceeds the efficiency of “traditional” installations.
History and modern uses of fuel cells
The principle of operation of fuel cells was discovered in 1839. The English scientist William Grove (1811-1896) discovered that the process of electrolysis - the decomposition of water into hydrogen and oxygen by means of an electric current - is reversible, i.e. hydrogen and oxygen can be combined into water molecules without combustion, but with the release of heat and electric current. Grove called the device in which such a reaction was carried out a "gas battery", which was the first fuel cell.
The active development of fuel cell technologies began after the Second World War, and it is associated with the aerospace industry. At that time, searches were conducted for an efficient and reliable, but at the same time quite compact source of energy. In the 1960s, NASA specialists (National Aeronautics and Space Administration, NASA) chose fuel cells as a power source for spacecraft of the Apollo (manned flights to the Moon), Apollo-Soyuz, Gemini and Skylab programs. . The Apollo used three 1.5 kW units (2.2 kW peak power) using cryogenic hydrogen and oxygen to produce electricity, heat and water. The mass of each installation was 113 kg. These three cells worked in parallel, but the energy generated by one unit was enough for a safe return. During 18 flights, the fuel cells have accumulated a total of 10,000 hours without any failures. Currently, fuel cells are used in the space shuttle "Space Shuttle", which uses three units with a power of 12 W, which generate all the electrical energy on board the spacecraft (Fig. 2). Water obtained as a result of an electrochemical reaction is used as drinking water, as well as for cooling equipment.
In our country, work was also underway to create fuel cells for use in astronautics. For example, fuel cells have been used to power Soviet ship reusable "Buran".
Development of methods for the commercial use of fuel cells began in the mid-1960s. These developments were partially funded by government organizations.
Currently, the development of technologies for the use of fuel cells goes in several directions. This is the creation of stationary power plants on fuel cells (for both centralized and decentralized energy supply), power plants of vehicles (samples of cars and buses on fuel cells have been created, including in our country) (Fig. 3), and also power supplies for various mobile devices (laptops, mobile phones, etc.) (Fig. 4).
Examples of the use of fuel cells in various fields are given in Table. one.
One of the first commercial models of fuel cells designed for autonomous heat and power supply of buildings was the PC25 Model A manufactured by ONSI Corporation (now United Technologies, Inc.). This fuel cell with a nominal power of 200 kW belongs to the type of cells with an electrolyte based on phosphoric acid (Phosphoric Acid Fuel Cells, PAFC). The number "25" in the name of the model means the serial number of the design. Most of the previous models were experimental or test pieces, such as the 12.5 kW "PC11" model that appeared in the 1970s. The new models increased the power taken from a single fuel cell, and also reduced the cost per kilowatt of energy produced. Currently, one of the most efficient commercial models is the PC25 Model C fuel cell. Like model "A", this is a fully automatic fuel cell of the PAFC type with a power of 200 kW, designed to be installed directly on the serviced object as an independent source of heat and electricity. Such a fuel cell can be installed outside the building. Outwardly, it is a parallelepiped 5.5 m long, 3 m wide and 3 m high, weighing 18,140 kg. The difference from previous models is an improved reformer and a higher current density.
| Table 1 Scope of fuel cells |
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In some types of fuel cells, the chemical process can be reversed: by applying a potential difference to the electrodes, water can be decomposed into hydrogen and oxygen, which are collected on porous electrodes. When a load is connected, such a regenerative fuel cell will begin to generate electrical energy.
A promising direction for the use of fuel cells is their use in conjunction with renewable energy sources, such as photovoltaic panels or wind turbines. This technology allows you to completely avoid air pollution. A similar system is planned to be created, for example, at the Adam Joseph Lewis Training Center in Oberlin (see ABOK, 2002, No. 5, p. 10). Currently, as one of the energy sources in this building, solar panels. Together with NASA specialists, a project was developed to use photovoltaic panels to produce hydrogen and oxygen from water by electrolysis. The hydrogen is then used in fuel cells to generate electricity and hot water. This will allow the building to maintain the performance of all systems during cloudy days and at night.
The principle of operation of fuel cells
Let us consider the principle of operation of a fuel cell using the simplest element with a proton exchange membrane (Proton Exchange Membrane, PEM) as an example. Such an element consists of a polymer membrane placed between the anode (positive electrode) and the cathode (negative electrode) together with the anode and cathode catalysts. A polymer membrane is used as the electrolyte. The diagram of the PEM element is shown in fig. 5.
A proton exchange membrane (PEM) is a thin (approximately 2-7 sheets of plain paper thick) solid organic compound. This membrane functions as an electrolyte: it separates matter into positively and negatively charged ions in the presence of water.
An oxidative process occurs at the anode, and a reduction process occurs at the cathode. The anode and cathode in the PEM cell are made of a porous material, which is a mixture of particles of carbon and platinum. Platinum acts as a catalyst that promotes the dissociation reaction. The anode and cathode are made porous for free passage of hydrogen and oxygen through them, respectively.
The anode and cathode are placed between two metal plates, which supply hydrogen and oxygen to the anode and cathode, and remove heat and water, as well as electrical energy.
Hydrogen molecules pass through the channels in the plate to the anode, where the molecules decompose into individual atoms (Fig. 6).
Figure 5 () Schematic diagram of a proton exchange membrane (PEM) fuel cell |
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Figure 6 () Hydrogen molecules through the channels in the plate enter the anode, where the molecules are decomposed into individual atoms |
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Figure 7 () As a result of chemisorption in the presence of a catalyst, hydrogen atoms are converted into protons |
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Figure 8 () Positively charged hydrogen ions diffuse through the membrane to the cathode, and the electron flow is directed to the cathode through an external electrical circuit to which the load is connected. |
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Figure 9 () Oxygen supplied to the cathode, in the presence of a catalyst, enters into a chemical reaction with hydrogen ions from the proton-exchange membrane and electrons from the external electrical circuit. Water is formed as a result of a chemical reaction |
Then, as a result of chemisorption in the presence of a catalyst, hydrogen atoms, each donating one electron e - , are converted into positively charged hydrogen ions H +, i.e. protons (Fig. 7).
Positively charged hydrogen ions (protons) diffuse through the membrane to the cathode, and the electron flow is directed to the cathode through an external electrical circuit to which the load (consumer of electrical energy) is connected (Fig. 8).
Oxygen supplied to the cathode, in the presence of a catalyst, enters into a chemical reaction with hydrogen ions (protons) from the proton exchange membrane and electrons from the external electrical circuit (Fig. 9). As a result of a chemical reaction, water is formed.
The chemical reaction in a fuel cell of other types (for example, with an acidic electrolyte, which is a solution of phosphoric acid H 3 PO 4) is absolutely identical to the chemical reaction in a fuel cell with a proton exchange membrane.
In any fuel cell, part of the energy of a chemical reaction is released as heat.
The flow of electrons in an external circuit is a direct current that is used to do work. Opening the external circuit or stopping the movement of hydrogen ions stops the chemical reaction.
The amount of electrical energy produced by a fuel cell depends on the type of fuel cell, geometric dimensions, temperature, gas pressure. A single fuel cell provides an EMF of less than 1.16 V. It is possible to increase the size of the fuel cells, but in practice several cells are used, connected in batteries (Fig. 10).
Fuel cell device
Let's consider the fuel cell device on the example of the PC25 Model C model. The scheme of the fuel cell is shown in fig. eleven.
The fuel cell "PC25 Model C" consists of three main parts: the fuel processor, the actual power generation section and the voltage converter.
The main part of the fuel cell - the power generation section - is a stack composed of 256 individual fuel cells. The composition of the fuel cell electrodes includes a platinum catalyst. Through these cells, a direct electric current of 1,400 amperes is generated at a voltage of 155 volts. The dimensions of the battery are approximately 2.9 m in length and 0.9 m in width and height.
Since the electrochemical process takes place at a temperature of 177 ° C, it is necessary to heat the battery at the time of start-up and remove heat from it during operation. To do this, the fuel cell includes a separate water circuit, and the battery is equipped with special cooling plates.
The fuel processor allows you to convert natural gas into hydrogen, which is necessary for an electrochemical reaction. This process is called reforming. The main element of the fuel processor is the reformer. In the reformer, natural gas (or other hydrogen-containing fuel) reacts with steam at high temperature (900 °C) and high pressure in the presence of a nickel catalyst. The following chemical reactions take place:
CH 4 (methane) + H 2 O 3H 2 + CO
(reaction endothermic, with heat absorption);
CO + H 2 O H 2 + CO 2
(the reaction is exothermic, with the release of heat).
The overall reaction is expressed by the equation:
CH 4 (methane) + 2H 2 O 4H 2 + CO 2
(reaction endothermic, with heat absorption).
To provide the high temperature required for natural gas conversion, a portion of the spent fuel from the fuel cell stack is directed to a burner that maintains the reformer at the required temperature.
The steam required for reforming is generated from the condensate formed during the operation of the fuel cell. In this case, the heat removed from the fuel cell stack is used (Fig. 12).
The fuel cell stack generates an intermittent direct current, which is characterized by low voltage and high current. A voltage converter is used to convert it to industrial standard AC. In addition, the voltage converter unit includes various control devices and safety interlock circuits that allow the fuel cell to be turned off in the event of various failures.
In such a fuel cell, approximately 40% of the energy in the fuel can be converted into electrical energy. Approximately the same amount, about 40% of the energy of the fuel, can be converted into thermal energy, which is then used as a heat source for heating, hot water supply and similar purposes. Thus, the total efficiency of such a plant can reach 80%.
An important advantage of such a source of heat and electricity is the possibility of its automatic operation. For maintenance, the owners of the facility on which the fuel cell is installed do not need to maintain specially trained personnel - periodic maintenance can be carried out by employees of the operating organization.
Fuel cell types
Currently, several types of fuel cells are known, which differ in the composition of the electrolyte used. The following four types are most widespread (Table 2):
1. Fuel cells with proton exchange membrane (Proton Exchange Membrane Fuel Cells, PEMFC).
2. Fuel cells based on orthophosphoric (phosphoric) acid (Phosphoric Acid Fuel Cells, PAFC).
3. Fuel cells based on molten carbonate (Molten Carbonate Fuel Cells, MCFC).
4. Solid oxide fuel cells (Solid Oxide Fuel Cells, SOFC). Currently, the largest fleet of fuel cells is built on the basis of PAFC technology.
One of the key features different types fuel cell is operating temperature. In many ways, it is the temperature that determines the scope of fuel cells. For example, high temperatures are critical for laptops, so proton exchange membrane fuel cells with low operating temperatures are being developed for this market segment.
For autonomous power supply of buildings, fuel cells of high installed capacity are required, and at the same time, it is possible to use thermal energy, therefore, other types of fuel cells can be used for these purposes.
Proton Exchange Membrane Fuel Cells (PEMFC)
These fuel cells operate at relatively low operating temperatures (60-160°C). They are characterized by high power density, allow you to quickly adjust the output power, and can be quickly turned on. The disadvantage of this type of elements is the high requirements for fuel quality, since contaminated fuel can damage the membrane. The nominal power of fuel cells of this type is 1-100 kW.
Proton exchange membrane fuel cells were originally developed by the General Electric Corporation in the 1960s for NASA. This type of fuel cell uses a solid state polymer electrolyte called a Proton Exchange Membrane (PEM). Protons can move through the proton exchange membrane, but electrons cannot pass through it, resulting in a potential difference between the cathode and anode. Due to their simplicity and reliability, such fuel cells were used as a power source on a manned spaceship Gemini.
This type of fuel cell is used as a power source for a wide range of different devices, including prototypes and prototypes, from mobile phones to buses and stationary power systems. The low operating temperature allows such cells to be used to power various types of complex electronic devices. Less efficient is their use as a source of heat and power supply for public and industrial buildings, where large amounts of thermal energy are required. At the same time, such elements are promising as an autonomous source of power supply for small residential buildings such as cottages built in regions with a hot climate.
| table 2 Fuel cell types |
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Phosphoric Acid Fuel Cells (PAFC)
Tests of fuel cells of this type were already carried out in the early 1970s. Operating temperature range - 150-200 °C. The main area of application is autonomous sources of heat and power supply of medium power (about 200 kW).
The electrolyte used in these fuel cells is a solution of phosphoric acid. The electrodes are made of paper coated with carbon, in which a platinum catalyst is dispersed.
The electrical efficiency of PAFC fuel cells is 37-42%. However, since these fuel cells operate at a sufficiently high temperature, it is possible to use the steam generated as a result of operation. In this case, the overall efficiency can reach 80%.
To generate energy, the hydrogen-containing feedstock must be converted to pure hydrogen through a reforming process. For example, if gasoline is used as a fuel, then sulfur compounds must be removed, since sulfur can damage the platinum catalyst.
PAFC fuel cells were the first commercial fuel cells to be economically justified. The most common model was the 200 kW PC25 fuel cell manufactured by ONSI Corporation (now United Technologies, Inc.) (Fig. 13). For example, these elements are used as a source of heat and electricity in a police station in New York's Central Park or as an additional source of energy for the Conde Nast Building & Four Times Square. The largest plant of this type is being tested as an 11 MW power plant located in Japan.
Fuel cells based on phosphoric acid are also used as an energy source in vehicles. For example, in 1994, H-Power Corp., Georgetown University, and the US Department of Energy equipped a bus with a 50 kW power plant.
Molten Carbonate Fuel Cells (MCFC)
Fuel cells of this type operate at very high temperatures - 600-700 °C. These operating temperatures allow the fuel to be used directly in the cell itself, without the need for a separate reformer. This process is called "internal reforming". It allows to significantly simplify the design of the fuel cell.
Fuel cells based on molten carbonate require a significant start-up time and do not allow to quickly adjust the output power, so their main area of application is large stationary sources of heat and electricity. However, they are distinguished by high fuel conversion efficiency - 60% electrical efficiency and up to 85% overall efficiency.
In this type of fuel cell, the electrolyte consists of potassium carbonate and lithium carbonate salts heated to about 650 °C. Under these conditions, the salts are in a molten state, forming an electrolyte. At the anode, hydrogen interacts with CO 3 ions, forming water, carbon dioxide and releasing electrons that are sent to the external circuit, and at the cathode, oxygen interacts with carbon dioxide and electrons from the external circuit, again forming CO 3 ions.
Laboratory samples of fuel cells of this type were created in the late 1950s by the Dutch scientists G. H. J. Broers and J. A. A. Ketelaar. In the 1960s, engineer Francis T. Bacon, a descendant of a famous 17th-century English writer and scientist, worked with these elements, which is why MCFC fuel cells are sometimes referred to as Bacon elements. NASA's Apollo, Apollo-Soyuz, and Scylab programs used just such fuel cells as a power source (Fig. 14). In the same years, the US military department tested several samples of MCFC fuel cells manufactured by Texas Instruments, in which army grades of gasoline were used as fuel. In the mid-1970s, the US Department of Energy began research to develop a stationary molten carbonate fuel cell suitable for practical applications. In the 1990s, a number of commercial units rated up to 250 kW were put into operation, such as at the US Naval Air Station Miramar in California. In 1996, FuelCell Energy, Inc. launched in trial operation 2 MW pre-series plant in Santa Clara, California.
Solid state oxide fuel cells (SOFC)
Solid-state oxide fuel cells are simple in design and operate at very high temperatures - 700-1000 °C. Such high temperatures allow the use of relatively "dirty", unrefined fuel. The same features as in fuel cells based on molten carbonate determine a similar area of application - large stationary sources of heat and electricity.
Solid oxide fuel cells are structurally different from fuel cells based on PAFC and MCFC technologies. The anode, cathode and electrolyte are made of special grades of ceramics. Most often, a mixture of zirconium oxide and calcium oxide is used as the electrolyte, but other oxides can be used. The electrolyte forms a crystal lattice coated on both sides with a porous electrode material. Structurally, such elements are made in the form of tubes or flat boards, which makes it possible to use technologies widely used in the electronics industry in their manufacture. As a result, solid-state oxide fuel cells can operate at very high temperatures, so they can be used to produce both electrical and thermal energy.
At high operating temperatures, oxygen ions are formed at the cathode, which migrate through the crystal lattice to the anode, where they interact with hydrogen ions, forming water and releasing free electrons. In this case, hydrogen is released from natural gas directly in the cell, i.e. there is no need for a separate reformer.
The theoretical foundations for the creation of solid-state oxide fuel cells were laid back in the late 1930s, when Swiss scientists Bauer (Emil Bauer) and Preis (H. Preis) experimented with zirconium, yttrium, cerium, lanthanum and tungsten, using them as electrolytes.
The first prototypes of such fuel cells were created in the late 1950s by a number of American and Dutch companies. Most of these companies soon abandoned further research due to technological difficulties, but one of them, Westinghouse Electric Corp. (now "Siemens Westinghouse Power Corporation"), continued work. The company is currently accepting pre-orders for a commercial model of tubular topology solid oxide fuel cell expected this year (Figure 15). The market segment of such elements is stationary installations for the production of heat and electric energy with a capacity of 250 kW to 5 MW.
SOFC type fuel cells have shown very high reliability. For example, a Siemens Westinghouse fuel cell prototype has logged 16,600 hours and continues to operate, making it the longest continuous fuel cell life in the world.
The high temperature, high pressure operating mode of SOFC fuel cells allows the creation of hybrid plants, in which fuel cell emissions drive gas turbines used to generate electricity. The first such hybrid plant is in operation in Irvine, California. The rated power of this plant is 220 kW, of which 200 kW from the fuel cell and 20 kW from the microturbine generator.
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 pollution 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, 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. Fuel cell converts chemical substances, hydrogen and oxygen into water, in the process of which it generates 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 common 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 split into hydrogen and oxygen by running an 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, internal combustion engines in cars, and batteries of all kinds. Internal combustion engines, like gas turbines, burn different kinds 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. It operates at a higher 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. BUT 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 an external circuit (performing useful work, such as motor rotation) and return 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 beneficial actions to the point where mechanical energy 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 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 the achievement of such a potential by practical and accessible way may prove 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 should develop oil fields in increasingly difficult conditions, causing oil prices to rise.
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. While 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. modern methods energy production. 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.
fuel cell ( fuel cell) is a device that converts chemical energy into electrical energy. It is similar in principle to a conventional battery, but differs in that its operation requires a constant supply of substances from the outside for an electrochemical reaction to occur. Hydrogen and oxygen are supplied to the fuel cells, and the output is electricity, water and heat. Their advantages include environmental friendliness, reliability, durability and ease of operation. Unlike conventional batteries, electrochemical converters can operate virtually indefinitely as long as fuel is available. They do not need to be charged for hours until fully charged. Moreover, the cells themselves can charge the battery while the car is parked with the engine off.
Proton membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC) are the most widely used in hydrogen vehicles.
A fuel cell with a proton exchange membrane operates as follows. Between the anode and cathode are a special membrane and a platinum-coated catalyst. Hydrogen enters the anode, and oxygen enters the cathode (for example, from air). At the anode, hydrogen is decomposed into protons and electrons with the help of a catalyst. Hydrogen protons pass through the membrane and enter the cathode, while electrons are given off to the external circuit (the membrane does not let them through). The potential difference thus obtained leads to the appearance of an electric current. On the cathode side, hydrogen protons are oxidized by oxygen. As a result, water vapor is produced, which is the main element of car exhaust gases. Possessing a high efficiency, PEM cells have one significant drawback - their operation requires pure hydrogen, the storage of which is a rather serious problem.
If such a catalyst is found that will replace expensive platinum in these cells, then a cheap fuel cell will immediately be created to generate electricity, which means that the world will get rid of oil dependence.
Solid oxide cells
Solid oxide SOFC cells are much less demanding on fuel purity. In addition, thanks to the use of a POX reformer (Partial Oxidation - partial oxidation), such cells can consume ordinary gasoline as fuel. The process of converting gasoline directly into electricity is as follows. In a special device - a reformer, at a temperature of about 800 ° C, gasoline evaporates and decomposes into its constituent elements.
This releases hydrogen and carbon dioxide. Further, also under the influence of temperature and with the help of SOFC directly (consisting of a porous ceramic material based on zirconium oxide), hydrogen is oxidized by oxygen in the air. After obtaining hydrogen from gasoline, the process proceeds further according to the scenario described above, with only one difference: the SOFC fuel cell, in contrast to devices operating on hydrogen, is less sensitive to foreign impurities in the original fuel. So the quality of gasoline should not affect the performance of the fuel cell.
The high operating temperature of SOFC (650-800 degrees) is a significant drawback, the warm-up process takes about 20 minutes. However, excess heat is not a problem, since it is completely removed by the remaining air and exhaust gases produced by the reformer and the fuel cell itself. This allows the SOFC system to be integrated into the vehicle as a stand-alone device in a thermally insulated housing.
The modular structure allows you to achieve the required voltage by serial connection set of standard cells. And, perhaps most importantly, from the point of view of the introduction of such devices, there are no very expensive platinum-based electrodes in SOFC. It is the high cost of these elements that is one of the obstacles in the development and dissemination of PEMFC technology.
Types of fuel cells
Currently, there are such types of fuel cells:
- A.F.C.– Alkaline Fuel Cell (alkaline fuel cell);
- PAFC– Phosphoric Acid Fuel Cell (phosphoric acid fuel cell);
- PEMFC– Proton Exchange Membrane Fuel Cell (fuel cell with a proton exchange membrane);
- DMFC– Direct Methanol Fuel Cell (fuel cell with direct methanol decomposition);
- MCFC– Molten Carbonate Fuel Cell (fuel cell of molten carbonate);
- SOFC– Solid Oxide Fuel Cell (solid oxide fuel cell).
Sir William Grove knew a lot about electrolysis, so he hypothesized that by the process (which splits water into its constituent hydrogen and oxygen by conducting electricity through it) he could produce if it was reversed. After calculating on paper, he went to the experimental stage and managed to prove his ideas. The proven hypothesis was developed by scientists Ludwig Mond and his assistant Charles Langre, improved the technology and in 1889 gave it a name that included two words - "fuel cell".
Now this phrase has become firmly established in the everyday life of motorists. You have certainly heard the term "fuel cell" more than once. In the news on the Internet, on TV, newfangled words are increasingly flashing. They usually refer to stories about the latest hybrid vehicles or development programs for these hybrid vehicles.
For example, 11 years ago the program "The Hydrogen Fuel Initiative" was launched in the USA. The program focused on developing the hydrogen fuel cell and infrastructure technologies needed to make fuel cell vehicles practical and economically viable by 2020. By the way, during this time more than $ 1 billion was allocated to the program, which indicates a serious bet that the US authorities made on.
On the other side of the ocean, car manufacturers were also on the alert, starting or continuing their research on fuel cell cars. , and even continued to work on building robust fuel cell technology.
The greatest success in this field among all global automakers has been achieved by two Japanese automakers, and. Their fuel cell models are already in full production, while their competitors are right behind them.
Therefore, fuel cells in the automotive industry are here to stay. Consider the principles of the technology and its application in modern cars.
The principle of operation of the fuel cell
In fact, . From a technical point of view, a fuel cell can be defined as an electrochemical device for energy conversion. It converts particles of hydrogen and oxygen into water, producing electricity, direct current, in the process.
There are many types of fuel cells, some are already in use in cars, others are being tested in research. Most of them use hydrogen and oxygen as the main chemical elements needed for conversion.
A similar procedure occurs in a conventional battery, the only difference is that it already has all the necessary chemicals required for conversion "on board", while the fuel cell can be "charged" from an external source, due to which the process of "production" of electricity may be continued. In addition to water vapor and electricity, another by-product of the procedure is the heat generated.
A proton-exchange membrane hydrogen-oxygen fuel cell contains a proton-conducting polymer membrane that separates two electrodes, an anode and a cathode. Each electrode is usually a carbon plate (matrix) with a deposited catalyst—platinum or an alloy of platinoids, and other compositions.
On the anode catalyst, molecular hydrogen dissociates and loses electrons. Hydrogen cations are conducted through the membrane to the cathode, but electrons are given off to the external circuit, since the membrane does not allow electrons to pass through.
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).
wikipedia.org
Application in cars
Of all types of fuel cells, fuel cells based on proton exchange membranes or, as they are called in the West, Polymer Exchange Membrane Fuel Cell (PEMFC), have become the best candidate for use in vehicles. The main reasons for this are its high power density and relatively low operating temperature, which in turn means that it does not take much time to bring the fuel cells into operation. They will quickly warm up and begin to produce the required amount of electricity. It also uses one of the simplest reactions of all types of fuel cells.
The first vehicle with this technology was made back in 1994 when Mercedes-Benz introduced the MB100 based on the NECAR1 (new electric car 1). Apart from the low power output (only 50 kilowatts), the biggest drawback of this concept was that the fuel cell occupied the entire volume of the van's cargo hold.
Also, from a passive safety point of view, it was a terrible idea for mass production, given the need to install a massive tank filled with flammable pressurized hydrogen on board.
Over the next decade, technology evolved and one of the latest fuel cell concepts from Mercedes had a power output of 115 hp. (85 kW) and a range of about 400 kilometers before refueling. Of course, the Germans were not the only pioneers in developing the fuel cells of the future. Don't forget the two Japanese, Toyota and . One of the biggest automotive players was Honda, which introduced a production car with power plant on hydrogen fuel cells. Leasing sales of the FCX Clarity in the United States began in the summer of 2008; a little later, the sale of the car moved to Japan. 
Toyota has gone even further with the Mirai, whose advanced hydrogen fuel cell system is apparently capable of giving the futuristic car a range of 520 km on a single tank that can be refueled in less than five minutes, just like a conventional one. The fuel consumption figures will amaze any skeptic, they are incredible even for a car with a classic power plant, it consumes 3.5 liters, regardless of whether the car is used in the city, on the highway or in the combined cycle.
Eight years have passed. Honda put that time to good use. The second generation Honda FCX Clarity is now on sale. Its fuel cell stacks are 33% more compact than the first model, with a 60% increase in power density. Honda claims that the fuel cell and integrated powertrain in the Clarity Fuel Cell is comparable in size to a V6 engine, leaving enough interior space for five passengers and their luggage.
The estimated range is 500 km, and the starting price of new items should be fixed at $60,000. Expensive? On the contrary, it is very cheap. In early 2000, cars with these technologies cost $100,000.
