Introduction and performance requirements of CCM membrane electrodes for fuel cells
Fuel cells are online generators that convert chemical energy into electrical energy, breaking through the efficiency limitations of traditional internal combustion engines. Therefore, fuel cell engines are considered to be an important development direction for automotive power plants in the future. An important component inside the fuel cell unit is the CCM membrane electrode.
The CCM membrane electrode assembly (MEA), also translated into membrane electrode, is a key component in the development of fuel cells. The membrane electrode and the bipolar plates on both sides constitute a single cell of the fuel cell, which is the basic unit of the fuel cell. In practical applications, according to design requirements, multiple single cells can be combined into a fuel cell reactor to meet power output requirements of different sizes.
The working process of the CCM membrane electrode can be divided into the following stages.
The hydrogen gas reaches the anode through the gas flow field of the anode plate, reaches the anode catalytic layer through the diffusion layer of the electrode, and is adsorbed on the anode catalytic layer. an electron.
High-performance membrane electrodes have the following characteristics:
(1) Both can reduce the transmission barrier of air, so that the chemical reaction air can smoothly travel from the propagation layer to the metal catalyst layer, resulting in electrode reaction. This is to enhance the chemical reaction specificity of metal catalysts per unit range and per unit mass. For this reason, the air-borne electrode material should have reasonable hydrophobicity, so that the chemical reaction air can flow smoothly to the metal catalyst through a short inlet, and at the same time ensure that the converted product water can wet the composite membrane, and too much water can wet the composite membrane. It is possible to flow out the air inlet that prevents clogging.
(2) Generate better ion channels and reduce the obstruction of positive ion transmission. The proton exchange membrane hydrogen fuel cell uses a solid electrolyte solution, and the sulfonic acid group is stabilized on the proton exchange membrane resin and is not locked by the electrode material. For this chemical reaction, an antiproton inlet must be established in the metal catalyst layer of the electrode material. To this end, it is necessary to adopt the three-dimensional technology of the electrode catalytic layer, that is, use the Nafion resin to impregnate or spray the hydrophilic network composed of the catalytic layer to establish an H conductive network composed of Nafion resin.
(3) The CCM membrane electrode forms a good electron channel. The carbon catalyst in the MEA is a good conductor of electrons, but the existence of Nafion and PTFE will have a certain impact on the electrical conductivity. On the basis of satisfying ion and gas conduction, electrons should also be considered Conductivity is considered comprehensively to improve the overall performance of the MEA.
(4) The gas diffusion electrode should ensure good mechanical strength and thermal conductivity
(5) The CCM membrane electrode membrane has high proton conductivity, can block hydrogen and oxygen well, prevent mutual channeling, and has good chemical stability, thermal stability and hydrolysis.
As can be seen from the above analysis, the key is to comprehensively consider the materials for preparing high-performance membrane electrodes and preparing MEAs. The performance of the material itself is combined with the process conditions for preparing the membrane electrode, which can meet the performance requirements of the membrane electrode.