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Under the action of the electric field, the ions migrate to the anode through the electrolyte, react with the fuel gas, form a circuit, and generate current.

At the same time, due to its own electrochemical reaction and the internal resistance of the battery, the fuel cell will also generate a certain amount of heat.

In addition to conducting electrons, the cathode and anode of the battery also serve as catalysts for redox reactions.

When the fuel is hydrocarbons, the anode requires higher catalytic activity.

The cathode and anode are usually porous structures to facilitate the passage of reaction gases and the discharge of products.

The electrolyte plays the role of transferring ions and separating fuel gas and oxidation gas.

In order to prevent the mixing of the two gases from causing a short circuit in the battery, the electrolyte usually has a dense structure.

The principle of a fuel cell is an electrochemical device, and its composition is the same as that of a general battery.

Its single cell is composed of positive and negative electrodes and an electrolyte.

The difference is that the active materials of general batteries are stored inside the battery, therefore, the battery capacity is limited.

The positive and negative electrodes of the fuel cell do not themselves contain active substances, but are just catalytic conversion elements.

Therefore, the fuel cell is truly an energy conversion machine that converts chemical energy into electrical energy.

When the battery is working, fuel and oxidant are supplied from the outside and 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.

Take the hydrogen-oxygen fuel cell as an example to illustrate the fuel cell.

Hydrogen-oxygen fuel cell reaction principle This reaction is the reverse process of electrolyzing water.

电极应为：负极：H2+2OH-→2H2O+2e-

正极：12O2+H2O+2e-→2OH-

Battery reaction: H2+12O2==H2O

In addition, only the fuel cell itself cannot work, and there must be a set of corresponding auxiliary systems, including reagent supply systems, heat removal systems, drainage systems, electrical performance control systems, and safety devices.

A fuel cell usually consists of an electrolyte plate forming an ion conductor, fuel electrodes and air electrodes arranged on both sides, and gas flow paths on both sides. The function of the gas flow path is to allow fuel gas and air to pass through the flow path.

In practical fuel cells, depending on the working electrolyte, the types of ions that pass through the electrolyte and are related to the reaction are also different. The reactions of PAFC and PEMFC are related to hydrogen ions, and the reactions that occur are:

Fuel electrode: H2==2H++2e-

空气极：2H++12O2+2e-==H2O

Overall: H2+12O2==H2O

In the fuel electrode, H2 in the supplied fuel gas is decomposed into H+ and e-, and H+ moves into the electrolyte to react with O2 supplied from the air electrode side.

e-passes through the external load circuit and then returns to the air pole side to participate in the reaction on the air pole side.

A series of reactions contribute to the uninterrupted flow of e- through the external circuit, thus constituting electricity generation.

And it can be seen from the reaction formula in the above formula that H2O generated from H2 and O2 has no other reactions except that the chemical energy of H2 is converted into electrical energy.

But in fact, there is a certain resistance accompanying the reaction of the electrode, which will cause some heat energy to be generated, thus reducing the proportion of conversion into electrical energy.

The group of cells that causes these reactions is called a module, and the voltage produced is usually less than one volt.

Therefore, in order to obtain large output, it is necessary to use multi-layer stacking of components to obtain a high-voltage stack.

The electrical connection between components and the separation between fuel gas and air are made of components called separators, which have gas flow paths on the upper and lower sides. The separators of PAFC and PEMFC are both made of carbon materials.

The output of the stack is determined by the product of the total voltage and the current, which is proportional to the reaction area in the cell.

The electrolyte of PAFC is a concentrated phosphoric acid aqueous solution, while the electrolyte of PEMFC is a proton conductive polymer-based membrane.

The electrodes are all made of carbon porous bodies. In order to promote the reaction, Pt is used as a catalyst. The CO in the fuel gas will cause poisoning and reduce the electrode performance.

For this reason, the amount of CO contained in the fuel gas must be limited in PAFC and PEMFC applications, especially for PEMFCs operating at low temperatures.

The basic composition and reaction principle of the phosphoric acid fuel cell is: water vapor is added to the fuel gas or city gas and then sent to the reformer to convert the fuel into a mixture of H2, CO and water vapor. The CO and water are further processed in the shift reactor. The catalyst is converted into H2 and CO2.

The fuel gas thus treated enters the negative electrode of the fuel pile, and at the same time, oxygen is transported to the positive electrode of the fuel pile for chemical reaction, and electrical energy and heat energy are quickly generated with the help of the catalyst.

Compared with PAFC and PEMFC, high-temperature fuel cells MCFC and SOFC do not require catalysts. Coal gasification gas with CO as the main component can be directly used as fuel, and it also has the characteristics of being easy to use its high-quality exhaust gas to form combined cycle power generation.

It contains the electrolyte related to the electrode reaction and the two electrode plates connected up and down, as well as the gas chamber through which the fuel gas and the oxidant gas flow outside each of the two electrodes, the electrode clamp, etc. The electrolyte is in a molten state at the operating temperature of MCFC of about 2~600c. liquid, forming an ionic conductor.

The electrode is a nickel-based porous body, and the gas chamber is formed of a corrosion-resistant metal.

MCFC working principle. O2 and CO2 in the air electrode combine with electricity to generate CO32-. The electrolyte moves CO32- to the fuel electrode side, combines with H+ supplied as fuel, releases e-, and generates H2O and CO2 at the same time. The chemical reaction formula is as follows:

燃料极：H2+CO32-==H2O+CO2+2e-

空气极：CO2+12O2+2e-==CO32-

Overall: H2+12O2==H2O

In this reaction, e- is the same as in PAFC. It is released from the fuel electrode and returns to the air electrode through the external circuit. The uninterrupted flow of e- in the external circuit realizes the fuel cell power generation.

In addition, the biggest characteristic of MCFC is that there must be CO32- ions that contribute to the reaction, so the supplied oxidant gas must contain carbonic acid gas.

In addition, a method has been developed in which a catalyst is filled inside the battery to modify CH4, which is the main component of natural gas, inside the battery and H2 is directly generated inside the battery.

When the fuel is coal gas, its main component CO reacts with H2O to generate H2. Therefore, CO can be equivalently utilized as fuel.

In order to obtain greater output, the partitions are usually made of Ni and stainless steel.

SOFC is mainly composed of ceramic materials. The electrolyte usually uses ZrO2, which constitutes the conductor Y2O2 of O3- and is used as stabilized YSZ.

In the electrode, the fuel electrode is made of Ni and YSZ composite porous body to form a cermet, and the air electrode is made of LaMnO3.

The separator is made of LaCrO3.

In order to avoid cracks caused by different shapes of batteries and differences in thermal expansion between electrolytes, SOFCs that operate at lower temperatures have been developed.

Chapter 0239 Preview of technical problems that cannot be solved