Principle and application of new energy fuel cell

Fuel cell is a power generation device that directly converts chemical energy existing in fuel and oxidant into electrical energy. Fuel and air are sent into fuel cells respectively, and electricity is produced wonderfully. It looks like a battery with positive and negative electrodes and electrolytes, but in essence it is not a "storage" but a "power plant". The concept of fuel cell was put forward by G.R. Grove in 1839 and has a history of about 160 years.

The fuel cell is very complex, involving the relevant theories of chemical thermodynamics, electrochemistry, electrocatalysis, material science, power system and automatic control, and has the advantages of high power generation efficiency and low environmental pollution. In general, fuel cells have the following characteristics:

(1) The efficiency of energy conversion is good. It directly converts the chemical energy of fuel into electrical energy without combustion, so it is not limited by Carnot cycle. At present, the fuel-electric energy conversion efficiency of fuel cell system is 45%~60%, while the efficiency of thermal power generation and nuclear power is about 30%~40%.

(2) The emissions of harmful gases such as SOx, NOx and noise are very low. The CO2 emissions are greatly reduced due to the high energy conversion efficiency.

(3) Wide range of fuel application

(4) The scale and installation location are flexible, the fuel cell power station covers a small area, the construction period is short, and the power of the power station can be assembled by the battery stack as required, which is very convenient. Fuel cells are very suitable as centralized power stations, distributed power stations, or independent power stations for residential areas, factories, and large buildings

(5) Fast load response and operation quality. The fuel cell can be converted from low power to rated power in a few seconds, and the power plant can be close to the load, thus improving the regional frequency offset and voltage fluctuation, reducing the existing substation equipment and current carrier capacity, and reducing the investment and line loss of transmission and transformation lines.

To understand its value, let's study the words "fuel" and "battery" respectively.

In order to use fuel such as coal or oil to generate electricity, coal or oil must be burned first. The energy generated by their combustion can heat water and turn it into steam, which can be used to make the turbine generator rotate in the magnetic field. This produces an electric current. In other words, we convert the chemical energy of fuel into thermal energy, and then convert thermal energy into electrical energy. In this process of double conversion, many of the original chemical energy is wasted. However, fuel is very cheap. Although there is such waste, it will not prevent us from producing a large amount of electricity without expensive costs. It is also possible to convert chemical energy directly into electrical energy without first converting it into heat energy. To do this, we must use batteries. The battery consists of one or more chemical solutions, in which two metal rods called electrodes are inserted. Each electrode undergoes a special chemical reaction. The electrons are either released or absorbed. The potential on one electrode is larger than that on the other. Therefore, if the two electrodes are connected by a wire, the electrons will flow from one electrode to the other through the wire. Such electron flow is current. As long as there is chemical reaction in the battery, this current will continue. The flashlight battery is an example of this kind of battery. In some cases, when a battery runs out, people force the current back into the battery, and chemical reactions will occur in the battery in turn. Therefore, the battery can store chemical energy and be used to generate the current again. The battery in the car is an example of this reversible battery. In a battery, the waste of chemical energy is much less, because chemical energy is converted into electrical energy in only one step. However, the chemicals in the battery are very expensive. Zinc is used to make batteries for flashlights. If you try to use enough zinc or similar metals to prepare electricity for the whole city, it will cost billions of dollars a day.

Fuel cell is a device that combines the two concepts of fuel and cell. It is a kind of battery, but it does not need to use expensive metals and only uses cheap fuel for chemical reaction. The chemical energy of these fuels can also be converted into electrical energy in one step, which is much less than the energy loss in two steps. As a result, the amount of electricity that can be provided for human beings has greatly increased.

At present, six types of fuel cells have been developed according to electrolyte, namely alkaline fuel cell (AFC), phosphate acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC) Solid Polymer Fuel Cell (SPFC), also known as Proton Exchange Membrane Fuel Cell (PEMFC), and Biofuel Cell (BEFC). According to the working temperature, they are divided into high, medium and low temperature fuel cells. Normal temperature fuel cells with operating temperature from room temperature to 373K (100 ℃), such as SPFC; Medium temperature fuel cells with operating temperature between 373K (100 ℃) and 573K (300 ℃), such as PAFC; High-temperature fuel cells, such as MCFC and SOFC, operate at temperatures above 873K (600 ℃).

The fuel cell is essentially designed with the concept of controlling the hydrogen bomb explosion. The fuel cell on the spacecraft is used to gather the energy generated by hydrogen during interstellar travel. The electromagnetic and solar energy gathered by the solar panel of the spacecraft will be converted into electrical energy, which will be used to slowly replace the hydrogen stored in the fuel cell into fuel. The fuel cell also contains a small amount of controlled substances that can undergo nuclear fission. These substances are used for nuclear reaction with hydrogen nuclei in order. The nuclear reaction is carried out in the fuel cell, which provides high energy and accelerates the ion engine to propel the spacecraft during the space journey. In the final stage of the journey, fuel cells provide the hydrogen needed for fuel rocket power. The whole process is controlled by powerful electromagnetism, which can provide energy and avoid excessive energy leakage leading to melting of reactor core. Thermal energy, a by-product of nuclear reaction, is absorbed by the outer wall of the fuel cell and converted into electrical energy for computers, livelihood systems and other necessary functions.

After years of exploration, the proton exchange membrane fuel cell is the most promising vehicle. Its working principle is that hydrogen is sent to the negative electrode. Through the action of catalyst (platinum), two electrons in the hydrogen atom are separated. The two electrons are attracted by the positive electrode and generate current through the external circuit. The hydrogen ion (proton) that has lost electrons can pass through the proton exchange membrane (i.e. solid electrolyte), and 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 (steam) is taken away in time, the fuel cell can continuously provide electric energy.