Poisoning the oxygen reduction reaction on carbon-supported Fe and Cu electrocatalysts: Evidence for metal-centered activity

Whether or not the active sites for the oxygen reduction reaction (ORR) in electrocatalysts based on carbon-supported transition-metal complexes are metal-centered has become controversial, especially for heat-treated materials. Some have proposed that the transition metal only serves to form highly active sites based on nitrogen and carbon. Here, we examine the oxygen reduction activity of carbon-supported iron(II) phthalocyanine (FePc) before and after pyrolysis at 800 °C and a carbon-supported copper(II) complex with 3,5-diamino-1,2,4-triazole (CuDAT) in the presence of several anions and small-molecule poisons, including fluoride, azide, thiocyanate, ethanethiol, and cyanide. CuDAT is poisoned in a manner consistent with a Cu-based active site. Although FePc and pyrolyzed FePc are remarkably resilient to most poisons, they are poisoned by cyanide, indicative of Fe-based active sites.