  Water produced in a Polymer Electrolyte Membrane (PEM) fuel cell enhances
membrane proton conductivity; this positive feedback loop can lead to current
ignition. Using a segmented anode fuel cell we study the effect of gas phase
convection and membrane diffusion of water on the spatiotemporal nonlinear
dynamics - localized ignition and front propagation - in the cell. Co-current
gas flow causes ignition at the cell outlet, and membrane diffusion causes the
front to slowly propagate to the inlet; counter-current flow causes ignition in
the interior of the cell, with the fronts subsequently spreading towards both
inlets. These instabilities critically affect fuel cell performance.
