S, N co-doped carbon nanotube encased Co NPs as efficient bifunctional oxygen electrocatalysts for zinc-air batteries

Abstract For the practical application of metal-air batteries, developing high-active and low-cost bifunctional oxygen reduction reaction (ORR) and oxygen evolution reduction (OER) catalysts is crucial and challenging. This study designed a unique ordered three-dimensional (3D) core–shell nanostructure bifunctional ORR and OER electrocatalysts consisting of Co nanoparticles (NPs) embedded in S, N co-doped carbon nanotubes (S,N-Co@CNT). The prepared S,N-Co@CNT exhibited excellent bifunctional electrocatalytic performance, with a high half-wave potential of 0.874 V versus reversible hydrogen electrode (RHE) toward ORR, and a low overpotential of 276 mV at 10 mA·cm−2 for the OER. The unique core–shell nanostructure has delivered considerable durability and stability in the S,N-Co@CNT, demonstrating almost no change in the potential gap between the ORR and OER after more than 5000 cycles of the accelerated durability test. Moreover, the S,N-Co@CNT serves as a high-active and low-price air–cathode catalyst for a rechargeable zinc-air battery, with a high peak power density of 171 mW·cm−2, and a long continuous charging-discharging ability. Based on mechanistic studies, the high activity of the S,N-Co@CNT was derived from the suitable oxygen adsorption energy due to the effects from S, N co-doping. The outcomes from this study offer a novel strategy to prepare non-noble metal bifunctional oxygen catalysts for metal-air batteries.