Porous Structure Controlling the Selectivity of Oxygen Reduction Reaction on N‐Doped Carbon in Alkaline Solution

Abstract

AbstractN‐doped carbon materials have been regarded as potential replacements for Pt‐based electrocatalysts for oxygen reduction reaction (ORR). However, the exact catalytic mechanisms are still not completely understood and there is a controversy about which type of N determines the selectivity of the reaction. This study reports a simple pyrolysis method to prepare hierarchical porous‐structured N‐doped graphene using 4‐nitroimidazole as both C and N sources without the presence of two‐dimensional template. The as‐prepared N‐doped graphene exhibits efficient four‐electron transfer pathway for ORR with an onset potential of 0.943 V, a half‐wave potential of 0.823 V, and a limiting current density of 5.58 mA cm−2 in 0.1 M KOH solution. In contrast, N‐doped platelet‐like carbon consisted mainly of micropores prefers the two‐electron pathway with a high selectivity toward peroxide generation over 90 % at potential range of 0.20–0.62 V. We demonstrate that the ORR selectivity is dependent on the H2O transfer dynamics which are controlled by the porous structure. Sluggish H2O transfer rate induces HO2− formation, whereas fast H2O transfer rate ensures the desired four‐electron pathway. This study gives further insight into the ORR selectivity and provides feasible strategies for fabricating N‐doped carbon materials as promising catalysts for either four‐electron oxygen reduction or H2O2 production in alkaline solution.