Experimental studies on Nafion ® 112 single PEM-FCs exposed to freezing conditions

Abstract

For automobile applications, the performance of polymer electrolyte membrane fuel cells (PEM-FCs) should be also maintained when exposed to sub-zero temperatures in winter time. To simulate this situation, single cell PEM-FCs assembled with Nafion ® 112 membranes, were kept in operation at 80 °C for several hours, afterwards stopped, kept at −20 °C for 10 h, and finally re-activated for subsequent operation. To prevent the performance degradation due to freezing of the water inside the MEA, which was formed during the FC functioning, water was removed from the PEM-FCs by supplying different dry gases (N 2, air or H 2) to the anode and the cathode compartments prior to the cell freezing. Several freezing/thawing cycles were operated to study the PEM-FCs performance degradation. The adopted purging procedure with N 2 was found to restrain the freezing degradation effects: only a minimal loss in terms of power output (less than 10% of the maximum power output) was recorded after 20 freezing/thawing cycles. On the contrary, the purging procedure with air proved to be ineffective to limit the damages: after 20 freezing/thawing cycles the MEA lost more than 21% in terms of power output at its maximum power output. The best results were obtained by purging the cell with dry air at cathode side and dry H 2 at anode side: on MEA the power density loss was 7.6% after 20 F/T cycles, and 19.3% after 30 F/T cycles. FESEM analysis showed a very limited number of cracks, broken fibers or delamination area, but allowed pointing out a strong migration of Pt particles from the catalytic layer into the membrane.