A fuel cell is an energy conversion device that directly converts chemical energy of a supplied fuel into electric energy, and is a power generation device that can continuously obtain electric power by continuously supplying fuel. Due to its high power generation efficiency, adaptability to various fuels and environmental characteristics, it has been actively developed in recent years.
Depending on the electrolyte, fuel cells are classified into alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and proton exchange membrane fuel cells ( PEMFC) and so on.
The fuel cell is not limited by the Carnot cycle, and has high energy conversion efficiency, clean, no pollution, low noise, strong module structure, strong building block and high specific power, and can be concentrated power supply and distributed power supply.
Basic structure and working principle:
(1) Fuel cell
A fuel cell is essentially an electrochemical device whose basic composition is the same as that of a general battery.
To achieve greater power output, fuel cells typically consist of several "cells". Similar to a conventional battery, a single fuel cell is composed of two positive and negative electrodes (a negative electrode, that is, a fuel electrode, a positive electrode, an oxidant electrode), and an 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 discharged, the fuel cell can continuously generate electricity.
The basic working principle of the fuel cell will be described below by taking a hydrogen-oxygen fuel cell as an example.
The reverse process of electrolyzing water. The electrode should be:
Negative electrode: H2 + 2OH- → 2H2O + 2e-
Positive electrode: 1/2O2 + H2O + 2e- → 2OH-
Battery reaction: H2 + 1/2O2 == H2O
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.
The fuel cell is generally composed of an electrolyte plate forming an ion conductor and a fuel electrode (anode) and an air electrode (cathode) disposed on both sides thereof, and a gas flow path on both sides, and the gas flow path functions to make the fuel gas and the air (oxidant) Gas) can pass through the flow path.
In a practical fuel cell, the type of ions associated with the reaction is different depending on the electrolyte to be operated. The reaction between PAFC and PEMFC is related to hydrogen ion (H+), and the reaction occurs as follows:
Fuel electrode: H2 = 2H + + 2e- (1)
Air pole: 2H+ + 1/2O2 +2e-= H2O (2)
All: H2+1/2O2 = H2O (3)
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 electrode side to participate in the reaction on the air electrode side. A series of reactions have contributed to the e-continuous passage through the external loop, thus constituting power generation. Further, it can be seen from the reaction formula (3) in the above formula that H2O formed by H2 and O2 has no other reaction, and the chemical energy of H2 is converted into electric energy. However, in fact, the electrode participating in the electrochemical reaction has a certain resistance, and when the current passes, some heat energy is generated, thereby reducing the ratio of conversion into electrical energy.
(2) System composition of fuel cell electric vehicle
The power system that makes up a fuel cell electric vehicle has three key components, namely
1 reformer (reformer): liquid fuel such as methanol, gasoline, etc. is recombined into a hydrogen-rich gas fuel to provide fuel cell reaction.
2 fuel cell stack (fuel cell stack): The fuel cell is the power source of the fuel cell electric vehicle, which provides hydrogen to react with oxygen in the air and generate current and voltage, while generating by-products such as waste heat (water).
3 power converter (inverter/converter): converts the power generated by the fuel cell into direct current or alternating current, or has a step-up or step-down to adjust the power output.
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