Reaction dynamics in a parallel flow channel PEM fuel cell

The spatiotemporal dynamic response of a segmented anode parallel channel polymer electrolyte membrane (PEM) fuel cell was monitored following changes in flow rate, temperature and load resistance. Autohumidified operation with dry feeds at 1 bar pressure was achieved at temperatures below 70 degrees C, where the convective transport of water vapor was less than the water production by the fuel cell current. The current could be "ignited" by a single injection of water into the anode feed, or by reducing the temperature and external load resistance. Co-current flow of the hydrogen and oxygen resulted in current ignition at the outlets of the flow channels, followed by a wave of high current density propagating toward the inlets. Counter-current flow of the hydrogen and the oxygen resulted in ignition near the center of the flow channels; over time the ignition front fanned out. The spatio-temporal dynamics of the current ignition along the flow channels can be effectively predicted from a model of a set of coupled differential fuel cells in series. Liquid water condensing in the flow channels gives rise to complex spatio-temporal variations in the current density; these variations are strongly dependent on orientation of the fuel cell with respect to gravity. (c) 2007 The Electrochemical Society.