Effects of current density and water content on electrode ice formation and membrane water uptake at -20°C

A procedure involving isothermal, galvanostatic operation was developed to measure the charge (or ice) accumulation in frozen PEM fuel cells. Charge storage capacity in the membrane and in the electrode was estimated, then compared to measured charge accumulation. Cryo-SEM imaging of electrodes following voltage failure was used to assess pore volume filling in the electrode. At very low currents, in which adequate time allowed for water diffusion, the maximum storage capacity was found in the membrane and electrode. At higher currents, less charge was passed before failure occurred, and significantly less ice had accumulated in the electrode. Lower initial water content corresponded to more available charge storage capacity within the membrane. Operation at high initial water content prevented water uptake by the membrane and allowed isolation of electrode storage capacity, and subsequent estimation of the partition between charge storage in the electrode and membrane at intermediate initial water contents.