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°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.