Effect, mechanism and recovery of nitrogen oxides poisoning on oxygen reduction reaction at Pt/C catalysts

The poisoning of nitrogen oxides (NO_x) on the oxygen reduction reaction (ORR) at the Pt/C catalyst has been studied for proton exchange membrane fuel cells by a three-electrode method in liquid electrolyte solution. The cyclic voltammetry (CV) results reveal that the absorption of NO_x on metallic Pt is more significant than on Pt oxides, and this absorption is probably a chemical rather than an electrochemical process. Linear sweeping voltammetry (LSV) curves for the ORR show that it is the absorption of NO _x on the Pt surface that results in significant performance degradation of Pt/C catalysts. This degradation is mainly due to the reduction of electrochemically active surface area, since the ORR mechanism remains almost the same after the NO_x poisoning as revealed by similar Tafel slopes. Because lower potentials facilitate the reduction of NO_x to water soluble NH4+, reducing the working potential can mitigate the poisoning of NO_x. However, to completely recover the performance loss due to NO_x poisoning through the potential sweeping, it is found that the oxidation removal is more efficient than the reduction removal.