Introduction to the basic characteristics of fuel cells

Fuel cell involves the theories of chemical thermodynamics, electrochemistry, electrocatalysis, materials science, electric power system and automatic control, etc. It has the advantages of high power generation efficiency and low environmental pollution. In general, fuel cells have the following characteristics: high energy conversion efficiency; it directly converts the chemical energy of the fuel into electrical energy without going through the combustion process, so it is not subject to the limitations of the Carnot cycle. The fuel-electricity conversion efficiency of fuel cell system is 45% to 60%, while the efficiency of thermal and nuclear power generation is about 30% to 40%. Flexible installation location; fuel cell power station covers a small area, short construction period, power station power can be conveniently assembled by the battery stack as needed. Fuel cell is very suitable no matter as centralized power station or distributed power station, or as independent power station in community, factory or large building. Fast load response and high quality of operation; fuel cells can be converted from the lowest power to the rated power in a few seconds. Since the fuel cell can directly convert the chemical energy of fuel into electric energy, it does not have the change of energy form through boiler, turbine and generator like the usual thermal generator, so it can avoid the loss of the intermediate conversion and achieve high power generation efficiency. The following features are also available: high power generation efficiency regardless of full load or partial load; high power generation efficiency regardless of the size of the plant; high overload capability; wide range of fuels that can be applied by combining with fuel supply equipment; power generation is determined by the power of the battery stack and the number of groups, and there is a large degree of freedom in the capacity of the unit; good load responsiveness of the battery body, which is superior to other methods of power generation; high power generation efficiency by using natural gas; high power generation efficiency by using natural gas; high power generation efficiency by using natural gas; high power generation efficiency by using natural gas; high power generation efficiency by using natural gas. When natural gas or gas is used as fuel, the amount of NOX and SOX discharged is low, and the environmental compatibility is excellent. The power generation system composed of fuel cells is very attractive to the electric power industry. Advantages of Fuel Cells: There is no energy generation technology that combines as many advantages as fuel cells. Energy security. Since the oil crisis of the 1970s, the dependence of major industrialized nations on oil has continued unabated and is largely dependent on supplies from oil-exporting countries. Passenger vehicles in the U.S. consume about 6 million barrels of oil per day, accounting for 85% of oil imports. If 20% of vehicles were powered by fuel cells, 1.2 million barrels of oil could be saved daily. Defense Security. Fuel cell power generation equipment has the quality of dispersion, which allows regions to get rid of the centralized power station-style power transmission and distribution structure. Long-distance, high-voltage transmission networks are easy targets for military operations. Fuel cell equipment can be harvested or decentralized, reducing the risk of an enemy trying to paralyze a nation's power system. Highly reliable power supply. Fuel cells can be built on top of the transmission and distribution network as backup power, or they can be independent of the network. In special cases, a modular setup (several identical battery systems installed in series to achieve the required power) can provide high stability. Fuel diversity. Although hydrogen is still the main fuel in a wide variety of modern batteries, battery systems equipped with a "fuel reformer" can extract hydrogen from hydrocarbon or alcohol fuels for utilization. In addition, biogas produced by anaerobic microbial decomposition in landfills and wastewater treatment plants is also a major source of fuel. By utilizing electricity from renewable energy sources such as natural solar energy and wind power, water can be electrolyzed to produce hydrogen, which can then be supplied to the fuel cell. In this way, "water" can be regarded as an unconverted fuel, and a completely zero-emission energy system can be realized. As long as the fuel is supplied to the battery, it can generate electricity continuously. High efficiency. As the principle of fuel cell is to convert chemical energy into electricity directly, instead of generating a large amount of exhaust gas and waste heat combustion, the conversion efficiency of electricity of today's power generation system using hydrocarbon fuel can reach 40~50%; the efficiency of the system using hydrogen directly can be more than 50%; the overall efficiency of the power generation facility can be more than 60% if it is used in conjunction with a gas turbine; and the utilization rate of fuel energy can be higher than 60% if the waste heat discharged from the battery is recovered and utilized. If the waste heat emitted from the battery is recycled, the utilization rate of fuel energy can be more than 85%. The energy conversion rate of fuel cells used in vehicles is about three times higher than that of traditional internal combustion engines, and the thermal efficiency of internal combustion engines is about 10~20%. Environmental friendliness. Scientists have identified air pollution as one of the leading causes of cardiovascular disease, asthma and cancer. Recent health studies have shown that polluted air in urban areas is as dangerous to health as second-hand smoke. Fuel cells utilize energy in a way that is vastly superior to fuel-powered engines, which emit large amounts of hazardous emissions, mostly water. Some fuel cells also emit carbon dioxide, but the amount is much lower than that of gasoline (about 1/6). A fuel cell generator produces 1,000 kilowatt-hours of electricity and emits less than 1 ounce of pollutant gas, compared to 25 pounds of pollutants from a conventional oil-fired generator. Therefore, fuel cells can not only improve the air pollution situation, but also promise a clean sky for mankind in the future. Flexible settings / Wide range of uses. The fascinating thing about fuel cells is their variety. In addition to the aforementioned characteristics of centralization and decentralization, it also has the ability to be scaled. Miniaturized fuel cells can be produced using yellow light micrograph technology, and the power supply can be scaled up to the desired output power using a modular stack configuration. A single power generator produces a voltage of about 0.7 volts, just enough to light a lamp. Connecting power generators in series constitutes a fuel cell stack, and the voltage increases to 0.7 volts multiplied by the number of power generators connected in series. The disadvantages of fuel cells are mainly the price and technical bottlenecks, which are summarized as follows: Fuel cell cost is high: the cost of automotive PEMFC proton exchange diaphragm (USD300/m2) accounted for about 35% of the cost; platinum catalyst accounted for about 40%, both of which are expensive materials. Reaction/starting performance: The starting speed of fuel cell is not as fast as that of internal combustion engine. Reactivity can be achieved by increasing the electrode activity, improving the operating temperature and reaction control parameters, but to improve stability, it is necessary to avoid the occurrence of side reactions. Reactivity and stability are not always the same. Hydrocarbon fuels cannot be utilized directly: except for methanol, all other hydrocarbon fuels need to be processed by converters and carbon monoxide oxidizers to produce pure hydrogen before they can be utilized by today's fuel cells. These equipments also increase the investment of fuel cell system. Hydrogen storage technology: The hydrogen fuel of FCV is mainly compressed hydrogen, which limits the carrying capacity of the vehicle, with only 2.5~3.5 kg per filling, which is not enough to satisfy the range of 480~650 kilometers for a single trip of today's vehicles. The liquid hydrogen system, which maintains hydrogen at -253°C, has been successfully tested, but has a major drawback: about 1/3 of the electrical energy must be used to maintain the low temperature of the tank to keep the hydrogen in the liquid state, and about 5% of the total stock is lost through evaporation from the gaps. Insufficient hydrogen fuel infrastructure: Although hydrogen has been used in industry for many years and is economically viable, there are only about 70 hydrogen refueling stations in the world, which is still at the demonstration stage. In addition, the refueling time is quite long, about 5 minutes, which is still not enough to keep up with the pace of the industrial and commercial era.