Water distribution in high temperature polymer electrolyte fuel cells

In this work a high temperature polymer electrolyte fuel cell based on a phosphoric acid doped polybenzimidazole membrane is operated at 160 °C on dry air and dry hydrogen. The anodic stoichiometry was varied to resemble typical operation with pure hydrogen or reformate gas. At the outlet of the fuel cell liquid water was collected by condensers. The resulting amounts of liquid water from cathode and anode were computationally analyzed. The results yielded an effective diffusion coefficient of water vapor of D≈2.7⋅10−7 m2 s−1, which is the average value for the cell based on the water partial pressures at the outlets. From the calculated water partial pressures at the anode and cathode it can be concluded that the concentration of phosphoric acid differs significantly within catalyst layer of the anode and cathode. Finally, the crossover of hydrogen and oxygen was shown to depend on the swelling of the membrane.