Membrane resistance and current distribution measurements under various operating conditions in a polymer electrolyte fuel cell

The ability to make spatially resolved measurements in a fuel cell provides one of the most useful ways in which to monitor and optimise their performance. Localised membrane resistance and current density measurements for a single channel polymer electrolyte fuel cell are presented for a range of operating conditions. The current density distribution results are compared with an analytical model that exhibited generally good agreement across a broad range of operating conditions. However, under conditions of high air flow rate, an increase in current is observed along the channel which is not predicted by the model. Under such circumstances, localised electrochemical impedance measurements show a decrease in membrane resistance along the channel. This phenomenon is attributed to drying of the electrolyte at the start of the channel and is more pronounced with increasing operating temperature. Under conditions of reactant depletion, an increase in electrolyte resistance with decreasing current is observed. This is due to the hydrating effect of product water and electro-osmotic drag through the membrane when ionic current is flowing. Localised conduction is shown to be an effective means of conditioning previously unused membrane electrode assemblies by forcing passage of ionic current through the electrolyte.