This work presents analysis of water transport phenomena in the 120 Wel high temperature PEM fuel cell stack. Phosphoric acid doped PBI membranes are known for their abilities to work with dry gases; however water in the electrolyte still plays an integral role in the proton conduction mechanism. The presence of water in the membrane increases proton conductivity, however at high operating temperatures in the anhydrous environment phosphoric acid can dehydrate consequently lowering its conductivity. Therefore, understanding of water transport in the PBI- H3PO4 membranes is important as it can explain certain phenomena inside the cell. Tests have shown that water transport from cathode to anode due to water accumulation rises almost linearly with current density while decreases with cathode stoichiometry. Water transport seems to be independent of operating temperature. Also, in some cases, reverse flow water transport (from anode to cathode) appears to take place near the outlet. Ohmic resistance was also found to decrease slightly with an increase in current density and lower stoichiometries.

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