Optimizing the electronic structure of cobalt via synergized oxygen vacancy and Co-N-C to boost reversible oxygen electrocatalysis for rechargeable Zn-air batteries

Rational design of active reversible oxygen electrocatalysts with low overpotentials for both oxygen reduction (ORR) and evolution reactions (OER) requires appropriate adsorption energies of oxygen-containing intermediates close to the equilibrium potential (U-RHE(0) = 1.23 V), which is desirable for efficient rechargeable metalair batteries but highly challenging. Herein, we report on a novel strategy to boost reversible oxygen electrocatalytic performance by a synergistic effect between electronically correlated Co-N-C and oxygen vacancy at the interface of a non-stoichiometry Co3O4-x/N-doped graphene composite catalyst. Both experiments and density functional theory calculations reveal that Co-N-C cooperates with its neighboring oxygen vacancy to effectively modulate the charge density of oxygen-vacant Co active site, thus optimizing its adsorption energies and in turn remarkably enhancing intrinsic ORR/OER activities. The optimized catalyst exhibits remarkably reduced overpotential for ORR/OER, and exhibits an ultra-high specific capacity and energy density for a rechargeable zinc-air battery, as well as a long-term cycling stability.