Oxygen Electrocatalysis with Mesoporous Co−N−C Catalysts: Towards Understanding the Active Site and Development of Rechargeable Zn‐Air Batteries

Abstract

AbstractWe demonstrate the synthesis of two bifunctional electrocatalysts (Co−N−C‐TET and Co−N−C‐Phen) based on cobalt‐ and nitrogen‐doped mesoporous carbon derived from cobalt complexes and their bifunctional electrocatalytic activity towards oxygen electrocatalysis. Both catalysts are bifunctionally active towards the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in alkaline pH. Co−N−C‐TET has excellent OER activity and delivers the benchmark current density of 10 mA cm−2 at a remarkably low overpotential of 0.28 V. The Co−N−C‐Phen catalyst is superior in terms of overall bifunctional activity and durability. The nitrogen and cobalt content of the catalyst controls the overall oxygen electrocatalytic performance. The nitrogen content, and its chemical nature in the catalyst, decides the ORR activity, whereas the metal content of the catalyst regulates the OER activity. Cobalt‐rich Co−N−C‐TET has significantly high OER activity compared to Co−N−C‐Phen. The enhanced OER activity of the Co−N−C‐TET catalyst is ascribed to the presence of a high cobalt content. The graphitic‐N‐ and pyridinic‐N‐rich Co−N−C‐Phen catalyst has enhanced ORR activity. An aqueous rechargeable Zn‐air battery (ZAB) is fabricated using the Co−N−C‐Phen‐based air‐cathode. The ZAB shows an open‐circuit voltage of 1.40 V and power density of 128.2 mW cm−2 with >48 h of galvanostatic charge‐discharge cycling stability. It outperforms the reference ZAB made of Pt and IrO2 catalysts.