Nanocarbon for Oxygen Reduction Electrocatalysis: Dopants, Edges, and Defects

The oxygen reduction reaction (ORR) is the cornerstone of various sustainable energy-conversion technologies. Metal-free nanocarbon electrocatalysts with competitive activity, enhanced durability, and satisfactory cost, have been proposed as the most promising substitute for precious-metal catalysts. However, their further development is still primarily based on trial-and-error approaches due to the controversial knowledge of critical active sites and mechanisms. Herein, the activity origins of nanocarbon-based ORR electrocatalysts are comprehensively reviewed and correlated, considering the dopants, edges, and defects. Analogously, they can effectively modify the charge/ spin distribution on the sp2-conjugated carbon matrix, leading to optimized intermediate chemisorption and facilitated electron transfer. Specific doping at defective edges is expected to render practical applications for metal-free nanocarbon electrocatalysts.