Doping engineering on carbons as electrocatalysts for oxygen reduction reaction

Oxygen reduction reaction (ORR) is the key reaction for the development of clean and sustainable fuel cells. However, the ORR reaction is sluggish kinetics, thereby it remains a grand challenge to develop high-activity, low-cost, and long-durability electrocatalysts to facilitate the ORR process for practical application. The introduction of dopants into/on the carbon skeleton is known as an efficient route to obtain a novel metal-free electrocatalyst for ORR. Tremendous studies have been performed on the synthesis, structural characterization, catalytic performance and mechanism of the doped carbons as electrocatalysts for ORR in the last decade. In this review, progress in doping engineering on carbons including the types of doping (heteroatom doping, charge-transfer doping, and defective doping) and configurations of heteroatom-doped carbons with corresponding catalytic mechanism will be mainly focused. And the challenges and perspectives on the future development of metal-free doped carbons as electrocatalysts for ORR are given.