New nitrogen-doped graphitic carbon nanosheets with rich structural defects and hierarchical nanopores as efficient metal-free electrocatalysts for oxygen reduction reaction in Zn-Air batteries

Carbon materials are highly promising alternative metal-free catalysts for oxygen reduction reaction (ORR), an important element reaction involved in various energy storage/conversion processes, while controllable and fine structural and morphological tunning is key for maximizing the catalytic performance. Here, we report the rational design of hierarchical porous graphitic carbon nanosheets with rich defects (d-pGCS) based on a facile two-step thermal treatment route, delivering superior catalytic ORR performance in alkaline electrolytes. The second thermal treatment is critical in creating such structural defects and nanopores. Through optimizing synthesis parameters, d-pGCS-1000 exhibits outstanding electrocatalytic ORR performance in terms of positive onset potential (0.95 V), half-wave potential (0.82 V), and limiting current density (6.02 mA cm⁻²). As a proof-of-concept, the obtained Zn-air battery delivers a large open-circuit voltage (1.42 V), high peak power density (182.8 mW cm⁻²), high specific capacity (773 mAhgZn⁻¹), and good rate performance. Such results are comparable to or even better than the Pt/C-based Zn-air battery.