The principle of a fuel cell is an electrochemical device having the same composition as a general battery. The unit cell is composed of two positive and negative electrodes (the negative electrode, that is, the fuel electrode and the positive electrode, that is, the oxidant electrode) and the electrolyte. The difference is that the active material of the general battery is stored inside the battery, thus limiting the battery capacity. The positive and negative electrodes of the fuel cell do not contain active substances, but only a catalytic conversion element. Therefore, fuel cells are truly energy conversion machines that convert chemical energy into electrical energy. When the battery is in operation, the fuel and oxidant are supplied from the outside to react. In principle, as long as the reactants are continuously input and the reaction products are continuously eliminated, the fuel cell can continuously generate electricity. Here, a hydrogen-oxygen fuel cell is taken as an example to illustrate a fuel cell.
(1) Technical principle: water is generated by electrochemical reaction, and electric energy is released
A fuel cell is a generator that uses a reverse reaction of electrolysis of water to generate water by an electrochemical reaction and to release electric energy. The fuel cell uses hydrogen or a hydrogen-rich gas as a fuel, uses oxygen in the air as an oxidant, and electrochemically converts chemical energy into electrical energy isothermally.
The working principle of a fuel cell is similar to that of a conventional electrochemical cell, in which both chemical energy is directly converted into electrical energy by an electrochemical reaction. However, considering the practical application, there is a big difference between the two. A normal battery is just a limited power output and storage device; and a fuel cell is a hydrogen-oxygen generator that can continuously generate electrical energy.
1. Hydrogen fuel cells have the characteristics of high energy conversion efficiency, zero emission, and easy fuel hydrogen.
2. The fuel cell is composed of a positive electrode, a negative electrode, and an electrolyte plate sandwiched between the positive and negative electrodes and an external circuit.
The anode of the fuel cell is a hydrogen electrode, the cathode is an oxygen electrode, and the electrolyte between the two poles can be classified into a basic type, a phosphoric acid type, a solid oxide type, a molten carbonate type, and a proton exchange membrane type. In addition, only the fuel cell body can not work, there must be a corresponding auxiliary system, including the reactant supply system, heat removal system, drainage system, electrical performance control system and safety devices.
(2) Fuel cell types: MCFC, PEMFC, and SOFC are the closest commercial types.
According to the electrolyte, the fuel cell is divided into alkaline fuel cell (AFC); phosphoric acid fuel cell (PAFC); molten carbonate fuel cell (MCFC); solid oxide fuel cell (SOFC); proton exchange membrane fuel cell (PEMFC) Wait for five kinds. According to the working temperature, the fuel cells can be divided into three types: low temperature, medium temperature and high temperature. Low temperature (<100oC); medium temperature (100~500oC) high temperature (>500oC).
From the current commercial application, molten carbonate fuel cells (MCFC), proton exchange membrane fuel cells (PEMFC) and solid oxide fuel cell (SOFC) fuel cells are the main technical routes, of which MCFC and SOFC are mainly There are fixed-fuel cell power stations, domestic cogeneration, PEMFC main applications and fuel cell vehicles.
1. Solid oxide fuel cell (SOFC)
Solid Oxide Fuel Cell (SOFC) is a third-generation fuel cell. It is an all-solid chemical power plant that converts chemical energy stored in fuel and oxidant directly into electric energy at medium and high temperatures. . It is widely recognized as a fuel cell that will be widely used in the future as a proton exchange membrane fuel cell (PEMFC).
Among all fuel cells, the operating temperature of the SOFC** is a high temperature fuel cell. In recent years, distributed power plants have gradually become an important part of the world's energy supply due to their low cost and high maintainability. Due to the high temperature of the exhaust gas generated by SOFC, it has high utilization value, can provide the heat required for natural gas reforming, can also be used to produce steam, and can be combined with gas turbine to form a combined cycle, which is very suitable for distributed generation. The combined power generation system composed of fuel cell, gas turbine and steam turbine not only has high power generation efficiency, but also has low pollution environmental benefits.
Foreign companies and research institutes have successively carried out the design and test of SOFC power stations. The 100kW tubular SOFC power station has been operated in the Netherlands. Westinghouse has not only tested multiple kW-class SOFCs, but is also studying MW-class SOFC and gas turbine power generation systems. Japan's Mitsubishi Heavy Industries and Siemens in Germany have conducted experimental research on SOFC power generation systems.
2. Molten carbonate fuel cell (MCFC)
Molten carbonate fuel cell (MCFC) uses carbonate (lithium carbonate, potassium carbonate) in a molten state at high temperature as electrolyte, operating temperature of 600-700 ° C, power generation efficiency of 45%-55%, and does not require the use of precious metals. The catalyst can also be used without the use of pure hydrogen, and the hot spot has the characteristics of high energy conversion rate. Since the carbonate at 650 ° C is highly corrosive, the MCFC anode usually uses a porous nickel electrode and the cathode uses a sintered nickel battery. After 1991, Japan used this type of battery as a research focus.
3. Proton exchange membrane fuel cell (PEMFC)
Proton Exchange Membrane Fuel Cell (PEMFC), also known as Polymer Electrolyte Fuel Cell (Polymer Electrolyte Membrane Fuel Cells), is a kind of hydrogen and fuel to generate electricity and heat. The fuel cell, the membrane pole set and the collector plate are combined in series to form a fuel cell stack. Proton exchange membrane fuel cells mainly include hydrogen fuel cells, methanol reforming fuel cells and direct methanol fuel cells. At present, hydrogen fuel cells are attracting the attention of power research and development personnel. It has a compact structure, low operating temperature (only 80 ° C), fast start-up, high power density and long working life.
The core of PEMFC is an elastic plastic film coated with a platinum catalyst. The platinum catalyst converts hydrogen into protons and electrons. Only protons can pass through the electrolyte membrane, combine with oxygen on the other side of the membrane to form water, and electrons form a current in the closed external circuit. In fuel cells, the proton exchange membrane fuel cell has relatively low temperature and normal pressure characteristics, and has no chemical danger to the human body and is harmless to the environment. It is suitable for daily use and has been widely used. The world's major automobile groups are competing to invest heavily in research and development of electric vehicles and alternative fuel vehicles. From the current development situation, PEMFC is the most mature power source of electric vehicles. PEMFC electric vehicles are recognized by the industry as the future development direction of electric vehicles.
In the 1960s, the United States first used PEMFC for Gemini aerospace flights. With the application and development of key materials such as perfluorosulfonic acid-type proton exchange membrane carbon-supported platinum catalysts, in the 1980s, PEMFC research made breakthrough progress, and researchers at Los Alamos National Laboratory made a lot of improvements to the catalyst. , reducing the amount of platinum by 90%, while the world's leading fuel cell developer, Canada's Ballard Power Systems by increasing the electrolyte membrane, the energy density of the battery is multiplied, the performance and life of the battery is greatly improved, the battery The group's volumetric power and mass ratio powers reached 1000W/L and 700W/kg, respectively, exceeding the electric vehicle specifications set by DOE and PNGV. Since the 1990s, based on the rapid progress of proton exchange membrane fuel cells, various electric vehicles powered by them have been successively launched. So far, hundreds of PEMFC-powered vehicles, submarines and power stations have been demonstrated at home and abroad.
Due to the outstanding advantages of high-efficiency and environmental protection of proton exchange membrane fuel cells, it has attracted the attention of all developed countries and major companies in the world, and invested heavily in the development of this technology. The US government listed it as one of the 27 key technology areas that are critical to US economic development and national security; the Canadian government has developed the fuel cell industry as one of the pillar industries of the national knowledge economy; the three major US auto companies (GM) , Ford, Chryster), Germany's Dajmier-Benz, Japan's Toytomotor and other car companies have invested heavily in the development of PEMFC cars.
(1) Technical principle: water is generated by electrochemical reaction, and electric energy is released
A fuel cell is a generator that uses a reverse reaction of electrolysis of water to generate water by an electrochemical reaction and to release electric energy. The fuel cell uses hydrogen or a hydrogen-rich gas as a fuel, uses oxygen in the air as an oxidant, and electrochemically converts chemical energy into electrical energy isothermally.
The working principle of a fuel cell is similar to that of a conventional electrochemical cell, in which both chemical energy is directly converted into electrical energy by an electrochemical reaction. However, considering the practical application, there is a big difference between the two. A normal battery is just a limited power output and storage device; and a fuel cell is a hydrogen-oxygen generator that can continuously generate electrical energy.
1. Hydrogen fuel cells have the characteristics of high energy conversion efficiency, zero emission, and easy fuel hydrogen.
2. The fuel cell is composed of a positive electrode, a negative electrode, and an electrolyte plate sandwiched between the positive and negative electrodes and an external circuit.
The anode of the fuel cell is a hydrogen electrode, the cathode is an oxygen electrode, and the electrolyte between the two poles can be classified into a basic type, a phosphoric acid type, a solid oxide type, a molten carbonate type, and a proton exchange membrane type. In addition, only the fuel cell body can not work, there must be a corresponding auxiliary system, including the reactant supply system, heat removal system, drainage system, electrical performance control system and safety devices.
(2) Fuel cell types: MCFC, PEMFC, and SOFC are the closest commercial types.
According to the electrolyte, the fuel cell is divided into alkaline fuel cell (AFC); phosphoric acid fuel cell (PAFC); molten carbonate fuel cell (MCFC); solid oxide fuel cell (SOFC); proton exchange membrane fuel cell (PEMFC) Wait for five kinds. According to the working temperature, the fuel cells can be divided into three types: low temperature, medium temperature and high temperature. Low temperature (<100oC); medium temperature (100~500oC) high temperature (>500oC).
From the current commercial application, molten carbonate fuel cells (MCFC), proton exchange membrane fuel cells (PEMFC) and solid oxide fuel cell (SOFC) fuel cells are the main technical routes, of which MCFC and SOFC are mainly There are fixed-fuel cell power stations, domestic cogeneration, PEMFC main applications and fuel cell vehicles.
1. Solid oxide fuel cell (SOFC)
Solid Oxide Fuel Cell (SOFC) is a third-generation fuel cell. It is an all-solid chemical power plant that converts chemical energy stored in fuel and oxidant directly into electric energy at medium and high temperatures. . It is widely recognized as a fuel cell that will be widely used in the future as a proton exchange membrane fuel cell (PEMFC).
Among all fuel cells, the operating temperature of the SOFC** is a high temperature fuel cell. In recent years, distributed power plants have gradually become an important part of the world's energy supply due to their low cost and high maintainability. Due to the high temperature of the exhaust gas generated by SOFC, it has high utilization value, can provide the heat required for natural gas reforming, can also be used to produce steam, and can be combined with gas turbine to form a combined cycle, which is very suitable for distributed generation. The combined power generation system composed of fuel cell, gas turbine and steam turbine not only has high power generation efficiency, but also has low pollution environmental benefits.
Foreign companies and research institutes have successively carried out the design and test of SOFC power stations. The 100kW tubular SOFC power station has been operated in the Netherlands. Westinghouse has not only tested multiple kW-class SOFCs, but is also studying MW-class SOFC and gas turbine power generation systems. Japan's Mitsubishi Heavy Industries and Siemens in Germany have conducted experimental research on SOFC power generation systems.
2. Molten carbonate fuel cell (MCFC)
Molten carbonate fuel cell (MCFC) uses carbonate (lithium carbonate, potassium carbonate) in a molten state at high temperature as electrolyte, operating temperature of 600-700 ° C, power generation efficiency of 45%-55%, and does not require the use of precious metals. The catalyst can also be used without the use of pure hydrogen, and the hot spot has the characteristics of high energy conversion rate. Since the carbonate at 650 ° C is highly corrosive, the MCFC anode usually uses a porous nickel electrode and the cathode uses a sintered nickel battery. After 1991, Japan used this type of battery as a research focus.
3. Proton exchange membrane fuel cell (PEMFC)
Proton Exchange Membrane Fuel Cell (PEMFC), also known as Polymer Electrolyte Fuel Cell (Polymer Electrolyte Membrane Fuel Cells), is a kind of hydrogen and fuel to generate electricity and heat. The fuel cell, the membrane pole set and the collector plate are combined in series to form a fuel cell stack. Proton exchange membrane fuel cells mainly include hydrogen fuel cells, methanol reforming fuel cells and direct methanol fuel cells. At present, hydrogen fuel cells are attracting the attention of power research and development personnel. It has a compact structure, low operating temperature (only 80 ° C), fast start-up, high power density and long working life.
The core of PEMFC is an elastic plastic film coated with a platinum catalyst. The platinum catalyst converts hydrogen into protons and electrons. Only protons can pass through the electrolyte membrane, combine with oxygen on the other side of the membrane to form water, and electrons form a current in the closed external circuit. In fuel cells, the proton exchange membrane fuel cell has relatively low temperature and normal pressure characteristics, and has no chemical danger to the human body and is harmless to the environment. It is suitable for daily use and has been widely used. The world's major automobile groups are competing to invest heavily in research and development of electric vehicles and alternative fuel vehicles. From the current development situation, PEMFC is the most mature power source of electric vehicles. PEMFC electric vehicles are recognized by the industry as the future development direction of electric vehicles.
In the 1960s, the United States first used PEMFC for Gemini aerospace flights. With the application and development of key materials such as perfluorosulfonic acid-type proton exchange membrane carbon-supported platinum catalysts, in the 1980s, PEMFC research made breakthrough progress, and researchers at Los Alamos National Laboratory made a lot of improvements to the catalyst. , reducing the amount of platinum by 90%, while the world's leading fuel cell developer, Canada's Ballard Power Systems by increasing the electrolyte membrane, the energy density of the battery is multiplied, the performance and life of the battery is greatly improved, the battery The group's volumetric power and mass ratio powers reached 1000W/L and 700W/kg, respectively, exceeding the electric vehicle specifications set by DOE and PNGV. Since the 1990s, based on the rapid progress of proton exchange membrane fuel cells, various electric vehicles powered by them have been successively launched. So far, hundreds of PEMFC-powered vehicles, submarines and power stations have been demonstrated at home and abroad.
Due to the outstanding advantages of high-efficiency and environmental protection of proton exchange membrane fuel cells, it has attracted the attention of all developed countries and major companies in the world, and invested heavily in the development of this technology. The US government listed it as one of the 27 key technology areas that are critical to US economic development and national security; the Canadian government has developed the fuel cell industry as one of the pillar industries of the national knowledge economy; the three major US auto companies (GM) , Ford, Chryster), Germany's Dajmier-Benz, Japan's Toytomotor and other car companies have invested heavily in the development of PEMFC cars.
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