Acidic and Alkaline pH Controlled Oxygen Reduction Reaction Pathway over Co‐N₄C Catalyst

Enhanced oxygen reduction reaction (ORR) kinetics and selectivity are crucial to advance energy technologies like fuel cells and metal–air batteries. Single‐atom catalysts (SACs) with M‐N 4 /C structure have been recognized to be highly effective for ORR. However, the lack of a comprehensive understanding of the mechanistic differences in the activity under acidic and alkaline environments is limiting the full potential of the energy devices. Here, a porous SAC is synthesized where a cobalt atom is coordinated with doped nitrogen in a graphene framework (pCo‐N 4 C). The resulting pCo‐N 4 C catalyst demonstrates a direct 4e − ORR process and exhibits kinetics comparable to the state‐of‐the‐art (Pt/C) catalyst. Its higher activity in an acidic electrolyte is attributed to the tuned porosity‐induced hydrophobicity. However, the pCo‐N 4 C catalyst displays a difference in ORR activity in 0.1 m HClO 4 and 0.1 m KOH, with onset potentials of 0.82 V and 0.91 V versus RHE, respectively. This notable activity difference in acidic and alkaline media is due to the protonation of coordinated nitrogen, restricted proton coupled electron transfer (PCET) at the electrode/electrolyte interface. The effect of pH over the catalytic activity is further verified by Ab‐initio molecular dynamics (AIMD) simulations using density functional theory (DFT) calculations.