Current distribution in PEM fuel cells. Part 2: Air operation and temperature effect

The effect of air flow rate, fuel and oxidant gas stream humidity, and cell operating temperature on the spatial and temporal current density distribution was investigated in a single gas channel PEM fuel cell using a segmented electrode/current collector assembly,. Related studies on oxygen operation and fuel starvation effects are presented in part one of this paper. The current density distribution was found to be a strong function of the available oxygen concentration down the channel that was determined by the air supply rate. Higher flow rates reduced the drop in the current density, profile along the channel. At lower air flow rates, a simultaneous increase in cell temperature and anode humidification level resulted in increasing segment performance near the inlet accompanied by a related decrease in the current densities downstream. Further increasing the air flow rate ultimately led to enhanced reaction rates over the entire length of the channel. If cell temperature elevation were not accompanied by a corresponding increase in the anode humidification level, the dehydration pattern on the anode side tended to dominate the local current density distribution. Beyond a certain point the current density distribution along the channel was exclusively dependent on oxidant availability, and gas diffusion rates and thus neither higher anode humidification nor cell temperature elevation had a significant influence at the chosen operating segment potential. (c) 2005 American Institute of Chemical Engineers.