N-doped graphene carbon aerogel uniformly embedded RuO2-Co3O4 heterostructures with boosted bifunctional oxygen electrocatalytic performances for efficient rechargeable zinc-air batteries

Heterostructure catalysts with multiple components and interfaces currently attracts widespread attention as a promising candidate for high-efficiency bifunctional (OER/ORR) electrocatalysts in ZABs, but their catalytic activity still needs to be improved for promoting the practical application of ZABs. Here, N-doped porous graphene carbon aerogel (NC) uniformly embedded RuO2-Co3O4 heterostructure (RuO2-Co3O4/NC) catalysts were fabricated through a two-step process including hydrothermal and air oxidation. Owing to the unique 3D interconnected porous network structure and fine conductive feature of the N-doped graphene carbon aerogels, the resultant RuO2-Co3O4/NC catalysts revealed a larger specific surface area, more uniformly-distributed heterostructure interfaces and improved electron transfer capability compared with the RuO2-Co3O4 heterostructure catalyst without NC. Moreover, the electron transfer and oxygen vacancies were further optimized by the electron coupling effect of the RuO2-Co3O4 heterogeneous interfaces, which effectively boosted the intrinsic activity and expedited the reaction kinetics. Thus, RuO2-Co3O4/NC exhibited significantly boosted bifunctional catalytic activity with a much narrower overpotential different value (Delta E = 0.616 V) compared with RuO2-Co3O4 and the commercial Pt/C + RuO2 catalyst, and the ORR and OER mass-specific activity of RuO2-Co3O4/NC is 5.5 and 9.0 times larger than that of RuO2-Co3O4, respectively. When using RuO2-Co3O4/NC as the cathodic catalyst, an assembled reversible Zinc-air battery not only achieved high power density of 100.2 mW cm- 2 at 157 mA cm- 2 and energy density of 815 W h KgZn-1, but also demonstrated an outstanding long-life rechargeable stability over 140 h charging-discharging test at 5 mA cm- 2. This research provides a straightforward approach to boost bifunctional oxygen catalytic performance based on uniformly-embedded heterojunction catalyst in N-doped porous carbon matrixs for Zinc-air battery applications.