Molecular engineering of nanostructures and activities on bifunctional oxygen electrocatalysts for Zinc-air batteries

Modulating the physicochemical structures of carbon-based electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zinc-air batteries is extremely important. However, it still remains a challenge to control these geometric and chemical nanostructures in a single reaction process under the same conditions. Herein, an approach based on an O₂-mediated solvothermal radical reaction (OSRR) to control the physicochemical conformations of Co/N-doped carbon electrocatalysts in a single reaction is reported. Atomic Co/N-doped carbon (CoCN), nanoparticulate Co/N-doped carbon (AP-CoCN), atomic Co/N-doped hollow carbon (PCA-CoCN-1), and nanoparticulate Co/N-doped porous carbon (PCA-CoCN-2) nanostructures are effectively designed by adjusting the molecular interactions between the organic precursors and metal ions in the OSRR. The activities of the electrocatalysts depend strongly on their structures where PCA-CoCNs exhibit the most outstanding activity and stability for ORR while AP-CoCN displays the most excellent activity and stability for OER. The simulations suggest that the back side carbon of Co-pyridinic N doped nanostructures is an active site for ORR and OER. The Zn-air battery employing PCA-CoCN-1 and AP-CoCN exhibits a lower charge-discharge overpotential and greater durability than the Pt/C and RuO₂ assembly. The OSRR can provide a new avenue for designing diverse carbon-based catalysts with desired structures and activities.