Fuel Cell

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In simple terms, a fuel cell is a power generation device that converts the chemical energy contained in fuel and an oxidizer directly into electrical energy. Fuel and air are fed into the fuel cell respectively, and electricity is produced in a remarkable way. It appears on the outside to have positive and negative electrodes as well as an electrolyte, resembling a battery, but in reality it cannot ‘store electricity’ – it is rather a ‘power plant’. The concept of fuel cells was proposed by G.R. Grove in 1839, and it has a history of about 160 years to date. 　　Fuel cells are highly complex, involving theories from disciplines such as chemical thermodynamics, electrochemistry, electrocatalysis, materials science, power systems, and automatic control. They offer advantages such as high power generation efficiency and low environmental pollution. In general, fuel cells have the following characteristics: (1) High energy conversion efficiency. They convert the chemical energy of the fuel directly into electrical energy, without going through a combustion process; as a result, they are not subject to the limitations of the Carnot cycle. Currently, the fuel-to-electricity conversion efficiency of fuel cell systems ranges from 45% to 60%, whereas the efficiency of thermal power generation and nuclear power is around 30% to 40%. 　　(2) Emissions of harmful gases such as SOx and NOx, as well as noise, are very low. CO2 emissions are significantly reduced due to the high efficiency of energy conversion, and there is no mechanical vibration. 　　(3) Wide range of applicable fuels. (4) High modularity: The scale and installation location can be adjusted flexibly; fuel cell power plants require little land area and have a short construction period. The power output of the plant can be adjusted as needed by assembling different battery stacks, which is very convenient. Fuel cells are highly suitable as centralized power plants, as well as for distributed power generation; they can also serve as independent power sources for residential areas, factories, and large buildings. (5) They offer fast load response and high operational quality – fuel cells can switch from their lowest power level to their rated power level within a few seconds, and the power plant can be located very close to the load sites. This helps to reduce regional frequency variations and voltage fluctuations, lowers the requirements for existing power conversion equipment and current-carrying capacity, and reduces investment in transmission lines as well as line losses. 　　To understand its value, let’s examine the terms “fuel” and “battery” separately. To generate electricity using fuels such as coal or oil, it is first necessary to burn coal or oil. The energy generated when they burn can be used to heat water and turn it into steam, which in turn can be used to rotate turbine generators within a magnetic field. This generates an electric current. In other words, we convert the chemical energy of the fuel into thermal energy, and then convert that thermal energy into electrical energy. During this dual conversion process, much of the original chemical energy is wasted. However, fuel is very cheap, and despite such waste, it does not prevent us from producing large amounts of electricity at no high cost. It is also possible to convert chemical energy directly into electrical energy, without first converting it into thermal energy. For this, we must use batteries. This type of battery consists of one or more chemical solutions, with two metal rods called electrodes inserted into it. A special chemical reaction takes place at each electrode, with electrons either being released or absorbed. The potential at one electrode is higher than that at the other electrode; therefore, if these two electrodes are connected by a wire, electrons will flow from one electrode to the other through the wire. Such an electron flow is what constitutes electric current, and as long as a chemical reaction takes place in the battery, this current will continue to flow. The battery in a flashlight is an example of this type of battery. In some cases, when a battery is depleted, current is forced to flow back into it, causing chemical reactions to occur within the battery; as a result, the battery can store chemical energy and use it to generate electricity once again. The battery in a car is an example of such a reversible battery. In a battery, much less chemical energy is wasted, as chemical energy is converted into electrical energy in just one step. However, the chemicals in batteries are very expensive. Zinc is used to make batteries for flashlights. If you tried to use enough zinc or similar metals to supply electricity to an entire city, it would cost billions of dollars per day. A fuel cell is a device that combines the concepts of fuel and battery. It is a type of battery that does not require expensive metals, but rather uses inexpensive fuels for chemical reactions. The chemical energy of these fuels is also converted into electrical energy in just one step, resulting in much less energy loss compared to the usual two-step process. As a result, the amount of electricity that can be provided to humans **increased significantly**. 　　To date, six types of fuel cells have been developed based on their electrolytes, namely Alkaline Fuel Cells (AFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), Solid Oxide Fuel Cells (SOFC), Solid Polymer Fuel Cells (SPFC, also known as Proton Exchange Membrane Fuel Cells, PEMFC), and Biofuel Cells (BEFC). Based on operating temperature, they are further divided into high-temperature, medium-temperature, and low-temperature fuel cells. Fuel cells whose operating temperature ranges from room temperature to 373 K (100°C) are known as room-temperature fuel cells, such as SPFC ； Fuel cells with an operating temperature ranging from 373 K (100°C) to 573 K (300°C) are medium-temperature fuel cells, such as PAFC ； Fuel cells with an operating temperature of 873 K (600°C) or higher are high-temperature fuel cells, such as MCFCs and SOFCs. 　　Fuel cells are essentially designed based on the concept of controlling hydrogen bomb explosions; those on spacecraft are used to harness the energy generated by hydrogen during interstellar travel. The electromagnetic energy and solar energy collected by the spacecraft’s solar panels are converted into electrical energy, which is then used to gradually replace the hydrogen stored in the fuel cells with fuel. Fuel cells also contain a small amount of controlled fissile material, which is used in sequence to undergo nuclear reactions with hydrogen nuclei. Nuclear reactions take place within fuel cells, providing high energy during space missions and accelerating ion engines to propel the spacecraft. In the final stage of the journey, fuel cells provided the hydrogen required for rocket propulsion. The entire process is controlled by a strong electromagnetic field, which provides energy while preventing excessive energy leakage that could cause the reactor core to melt down. Thermal energy, a byproduct of nuclear reactions, is absorbed by the outer wall of the fuel cell and converted into electrical energy to power computers, life support systems, and other essential functions. 　　After years of research, proton exchange membrane fuel cells are the most promising for use in vehicles. Its working principle is as follows: Hydrogen is sent to the negative electrode, and under the action of a catalyst (platinum), the two electrons in the hydrogen atoms are separated. Drawn toward the positive electrode, these electrons generate an electric current through the external circuit. The hydrogen ions (protons) that have lost their electrons can pass through the proton exchange membrane (i.e., the solid electrolyte), where they recombine with oxygen atoms and electrons at the positive electrode to form water. Since oxygen can be obtained from the air, as long as hydrogen is continuously supplied to the negative electrode and water (vapor) is removed in a timely manner, the fuel cell can continuously generate electrical power.