Active Sites of Metal-Free Carbon Materials in Energy Electrocatalysis

Electrocatalysis offers a viable avenue for building a clean energy future by rationally controlling energy conversion and storage. As an important class of electrocatalysts, metal-free carbon materials are widely used in various electrocatalytic reactions because of their low price, wide range of sources, and adjustable structure. However, owing to the diverse structures and coexisting functional groups, identifying the electrocatalytically active sites of carbon materials is still a challenge. In this review, we first summarize the strategies for activating sp²-hybridized carbon materials, including heteroatom doping and fabricating defects. These strategies endow inert sp² carbon with initial active sites in various reactions. After that, we separately discuss the active sites of carbon materials in specific electrocatalytic reactions, with a special emphasis on determining the static active sites among various functional groups and identifying the active sites during dynamic reconstruction in electrocatalysis. The general methods used to determine whether a specific site is an active site are then summarized. Finally, outlooks on the further development of investigating active sites of carbon materials are presented.