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

The poisoning of nitrogen oxides (NOx) 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 NOx 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 NOx 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 NOx poisoning as revealed by similar Tafel slopes. Because lower potentials facilitate the reduction of NOx to water soluble NH4+, reducing the working potential can mitigate the poisoning of NOx. However, to completely recover the performance loss due to NOx poisoning through the potential sweeping, it is found that the oxidation removal is more efficient than the reduction removal.