Synergistically tuning the graphitic degree, porosity, and the configuration of active sites for highly active bifunctional catalysts and Zn-air batteries

Rational design and tailoring of the structural features of Co-N-C catalysts are urgently required to construct highly efficient bifunctional non-noble metal electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we report a series of carbon-based catalysts with varied structural features, specifically the graphitic degree of carbon, porosity, and the configuration of active sites, and their effects on bifunctional oxygen electrocatalytic reactions. Through the synergistic tuning of these structural factors, the well-tailored Co-N-C catalyst exhibits a high bifunctional electrocatalytic activity, as revealed by a half-wave potential of 0.84 V for ORR and a low overpotential of 420 mV at 10 mA.cm(-2) for OER. More impressively, the Zn-air battery using the optimum catalyst delivers excellent performance including a peak power density of 125.2 mW center dot cm(-2) and a specific capacity of 790.8 mAh.g(Zn)(-1), as well as stable cycling durability, outperforming the noble metals-based catalysts. The first-principles calculations reveal that the interlayer interaction between the pyridinic N-doped graphene and the confined Co nanoparticles increases the electronic states of the active C atoms near the Fermi level, thus enhancing the adsorption of the HOO* intermediate and generating superior catalytic activity for bifunctional oxygen electrocatalysis. By comprehensively studying the structural factors of catalysts, the bifunctional catalytic behaviors, the use in a practical Zn-air device, and theoretical simulations, this work may also give inspirations to the design, use, and understanding of other kinds of catalysts.