Abstract
Cathode air stoichiometry is one of the crucial factors affecting the electrical performance and local gas starvation of proton exchange membrane fuel cells. A suitable air stoichiometric ratio can not only improve the generated power and working efficiency, but also effectively reduce or eliminate internal reactant gas starvation. At present, the optimal value of cathode air stoichiometry and its changing trends under different operating conditions remains to be further studied, and the optimization indicator in existing researches mainly tends to be maximum power, with rare attention to fuel cell degradation. This paper proposes a quantitative method for calculating the optimal interval of air stoichiometry, which considers synthetically the fuel cell generated power, working efficiency and internal gas starvation reduction, to make these three indicators reach the optimal balance. The local gas starvation inside is evaluated by proportion of gas-starvation area on fuel cell electrode surface. Based on the proposed methodology, a three-dimensional model of a five-channel serpentine flow field fuel cell is established in this paper to simulate and calculate the optimal interval of cathode air stoichiometry under different operational parameters and electrical load conditions. The changing trends of the optimal air stoichiometry with different operating conditions and the impacts of key operational parameters and loads on air stoichiometry optimal interval are also carefully analyzed. Among them, the operating pressure and current density have a significant influence on the optimal interval value. Increasing the working pressure can make the optimal air stoichiometry smaller, and the increase in current density results in a substantial raise of optimal air stoichiometry. The calculation method of cathode air stoichiometry optimal interval proposed in this paper can provide references for fuel cell air supply strategy research, and the conclusions can be beneficial for fuel cell performance optimization and long-lifetime design.
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