Electrocatalysis and electrochemical promotion of CO oxidation in PEM fuel cells: the role of oxygen crossover

The electrochemical promotion of catalysis (or NEMCA effect) was studied for the CO oxidation and water gas shift reaction on a Pt anode in a polymer electrolyte membrane (PEM) fuel cell. It was found that this phenomenon plays a significant role in a normal fuel cell operation (fuel mixture – air) but not in a hydrogen pumping operation (fuel mixture – H2). This implies that the role of oxygen crossover in the electropromotion (EP) of CO oxidation is vital. During fuel cell operation, the increase in the rate of CO consumption is 2.5 times larger than the electrochemical rate, I/2F of CO oxidation, while for oxygen bleeding conditions (fuel mixture + O2−air) the increase is five times larger than I/2F. This shows that the catalytic properties of the Pt anode are significantly modified by varying the catalyst potential. In order to confirm the role of oxygen crossover, Nafion membranes (117, 1135) with different thickness, were studied. The results show that upon decreasing the membrane thickness the crossover is increased and thus the electrochemical promotion effect becomes more pronounced.