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“Fan the Flame with Water”. Current Ignition and Front Propagation in Pem Fuel Cells

Yannick De Decker, Jay B. Benziger, and Yannis G. Kevrekidis. Princeton University, A215 Engineering Quadrangle, Princeton University, Princeton, NJ 08544

Polymer Electrolyte Membrane (PEM) fuel cells exhibit complex non-linear dynamics resulting from an exponential dependence of proton conductivity with water content. Multiple steady states have been identified resulting from the balance between water produced and water removed. When the membrane water content was greater than a critical value the fuel cell current increased to a high value corresponding to an ignited state. The fuel cell current can be ignited by injection of water into the fuel cell; this hydrates the membrane which increases the current and autohumidifies the fuel cell. Spatio-temporal dynamics have been followed in the flow channels of a PEM fuel cell reactor. Co-current flow of the hydrogen and oxygen resulted in current ignition at the outlet of the flow channel, followed by a wave of high current density propagating toward the inlet. Counter-current flow of the hydrogen and the oxygen resulted in ignition at the center of the flow channels. Over time the ignition front fanned out from the center. A beautiful analogy can be drawn between water production and removal in a PEM fuel cell and heat production and removal in exothermic chemical reactors.