Strategies for boosting carbon electrocatalysts for the oxygen reduction reaction in non-aqueous metal-air battery systems

Carbon-based materials stand out from all possible non-precious metal-based oxygen reduction reaction (ORR) catalysts, owing to their low cost, high conductivity, and variety of allotropes with different bonding and structures. There have been many reviews on the ORR performance of carbon-based materials in aqueous electrolyte, but until now, there has been no specific review on the ORR activity of carbon-based materials in non-aqueous electrolyte. In this review, a comprehensive insight into carbon-based catalysts for the ORR in non-aqueous electrolyte in terms of the ORR mechanism and strategies for performance modulation (including morphology/nanostructure engineering, strategies for doping with foreign atoms, defect engineering, and functionalization engineering) is provided. Also, the challenges for carbon electrocatalysts in non-aqueous electrolyte and the corresponding solutions are also discussed.