Polymer electrolyte fuel cell transport mechanisms: simulation study of hydrogen crossover and water content

Hydrogen crossover and membrane hydration are significant issues for polymer electrolyte fuel cells (PEFC). Hydrogen crossover amounts to a quantity of unspent fuel, thereby reducing the fuel efficiency of the cell, but more significantly it also gives rise to the formation of hydrogen peroxide in the cathode catalyst layer which acts to irreversibly degenerate the polymer electrolyte. Membrane hydration not only strongly governs the performance of the cell, most noticeable through its effect on the ionic conductivity of the membrane, it also influences the onset and propagation of internal degradation and failure mechanisms that curtail the reliability and safety of PEFCs. This paper focuses on how hydrogen crossover and membrane hydration are affected by; (a) characteristic cell geometries, and (b) operating conditions relevant to automotive fuel cells. The numerical study is based on the application of a general transport equation developed previously to model multi-species transport through discontinuous materials. The results quantify (1) the effectiveness of different practical mechanisms which can be applied to curtail the effects of hydrogen crossover in automotive fuel cells and (2) the implications on water content within the membrane.