Integrated Graphitic Nanoshell/Mesoporous Carbon Nanohybrids as Highly Active and Stable Bifunctional Oxygen Electrocatalysts for Rechargeable Aqueous Na-Air Batteries

Abstract

We present the design of highly integrated, high-performance, bifunctional oxygen electrocatalysts composed of highly graphitic nanoshells embedded in mesoporous carbon (GNS/MC). The GNS/MC exhibited very high oxygen electrode activity, which is one of the best performances among non-precious metal bifunctional oxygen electrocatalysts, and substantially outperformed Ir- and Pt-based catalysts. Moreover, the GNS/MC showed excellent durability for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In situ X-ray absorption spectroscopy and square wave voltammetry revealed the roles of residual Ni and Fe entities in enhancing OER and ORR activities. Raman spectra indicated highly graphitic, defect-rich nature of the GNS/MC, which could contribute to the enhanced OER activity and to high stability for the OER and ORR. In aqueous Na-air battery tests, the GNS/MC air cathode-based cell exhibited superior performance to Ir/C- and Pt/C-based batteries. Significantly, the GNS/MC-based cell demonstrated the first example of rechargeable aqueous Na-air battery.