The model for fuel cell ignition su

The model for fuel cell ignition suggested that the ignited steady state could be extinguished by raising the fuel cell temperature or increasing the load resistance. Testing this hypothesis produced a surprising result. The STR PEM fuel cell was operated in the autohumidification mode at 95 ◦C with an anode feed of 10 mL/min H2 and a cathode feed rate of 10 mL/min O2. The fuel cell was allowed to come to steady state with a load resistance of ∼ 0.2 for 24 h. The load resistance was then increased stepwise by ∼ 1 and the fuel cell current and voltage were permitted to stabilize for 3–4 h, after which the current and voltage were recorded. The current/voltage data are plotted as the “steady state“polarization curve in Fig. 3A. The water activity at the cathode and anode change along the steady state polarization curve, reflecting the altered balance between water production and water removal as the load resistance is varied. Steady state polarization curves must allow sufficient time for the membrane water content to equilibrate with the water production and removal; equilibration may take many hours depending on the change in load, the reactant flow rates and the temperature. The curvature of the polarization curve is the result of the water activity at the cathode increasing with the decreasing load resistance.