Probing Active Sites on Metal-Free, Nitrogen-Doped Carbons for Oxygen Electroreduction: A Review

The Metal-free nitrogen-doped carbons represent an emerging low-cost nonprecious electrocatalyst for oxygen reduction reaction (ORR) that is a sluggish process at the cathode of polymer electrolyte membrane fuel cells (PEMFCs) and a verity of metal-air batteries. During the past few years, the ORR catalytic activity of nitrogen-doped carbons has been significantly increased, making them highly competitive alternatives to conventional precious metals based electrocatalysts for ORR. However, controversies remain in the unambiguous identification of the ORR active sites on nitrogen-doped carbons. This review summarizes the recent progress in probing the potential active sites on metal-free nitrogen-doped carbons for ORR, aiming to gain in-depth understanding of the ORR catalytic mechanism on nitrogen-doped carbons for further enhancing ORR activity