| Proton exchange membrane (PEM) fuel cell is a highly efficient, environmentally friendly power generation device, and a new generation of green energy power system. And it can help to solve the problem of energy crisis and environmental pollution, etc. Traditional PEM fuel cell working temperature is 80℃, it requires a relative higher water and heat management. By comparison, the operating temperature of high temperature PEM fuel cell (HTPEMFC) is above 120℃, which is an important development direction for PEM fuel cell, for its simplified water and heat management, and a relative low requirement of the purity of fuel. In this paper, the effects of membrane electrode assembly (MEA) compression rates on the performance of HTPEMFC, and the reaction path of oxygen reduction reaction in the cathode are studied by the experiment and molecular simulations. It has a far-reaching implication on a better understanding of the working principle of HTPEMFC as well as its designing and development.Based on a great number of corresponding references, this paper introduces the history, application and working principle of PEM fuel cell, and its structure, function and characters of materials and key parts in HTPEMFC are introduced. The test system for fuel cell was set up. And the operating principle, structure and elements, and experimental procedure were described.The volt-ampere characteristics and alternating-current impedance were measured for HTPEM fuel cell, by the test system set up. We analyzed the influence of the reactant gas flow and battery temperature on the characteristics and alternating-current impedance of the HTPEMFC. The cell performance, under different compression ratios of membrane electrode, was also examined. The experiment result shows that when the reactant gas flow increased, the reactant gas concentration on the catalysis layer will be enlarged and the concentration polarization lowered, and hence the performance of the fuel cell is improved. And when battery temperature elevated, the electrochemical reaction will be accelerated on the catalysis layer, and the Faradaic impedance activity polarization will be lowered, and the ohmic resistance will also be lowered in the PEM, and the performance of the fuel cell is also improved. The optimal performance of the fuel cell is setup under the compression ratio of membrane electrode being 20.8%. For higher compression ratio, the effective porosity will reduce in the diffusion layer, and the concentration polarization aggravated. And for lower compression ratio, the contact resistance between different parts of the cell will be enlarged.The molecular model of the oxygen reduction reaction under the Pt catalysis was constructed for the cathode reaction of fuel cell, under molecular dynamics and quantum mechanics principles. The reaction procedure and energy variation were simulated for the oxygen gas and proton on the catalysis surface. And the optimal path for the oxygen reduction was analyzed. The effect of battery temperature on the reaction of oxygen molecule and protons was also examined by the simulation. The simulation shows that when the oxygen molecule is adsorbed on the Pt catalysis surface by the μ/π (fcc) parallel mode, the energy of the system is lowest, and the corresponding structure most stable, which is the best adsorption mode for oxygen molecule on Pt surface. There are four different paths for the reaction between the oxygen molecule adsorbed on the Pt (111) surface and four hydrogen atoms successively. The same products of the four different paths have similar energy. One reaction path is faster than the others. When the temperature elevated, the oxygen reduction reaction become faster, but the optimal reaction path not changed. |
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