Recent progress in heteroatom-doped carbon electrocatalysts for the two-electron oxygen reduction reaction

The electrochemical synthesis of hydrogen peroxide has received much attention due to its on-site production, absence of organic impurities during the synthesis, environmentally-friendly and low energy input with no need for further purification. This review focused on the metal-free heteroatom-doped carbon catalyst for the generation of hydrogen peroxide by the two-electron oxygen reduction reaction (2e- ORR). Depending on the type of heteroatoms, the electronic properties of the carbon can be changed, and they significantly affect the ORR catalytic activity. Even with the same heteroatoms, their specific chemical composition in a carbon frame has a large effect on the electrocatalytic activity. The location of the active catalytic sites within the carbon network is also investigated with a theoretical study, which is important for effective electrocatalysis of the 2e- ORR to occur. The physical and chemical properties of base carbon materials and the reaction environment for ORR such as the pH and additives of the electrolyte are discussed. This review provides fundamental insights into how the moiety of heteroatoms enhances the electrocatalytic activity of metal-free carbon materials for the 2e- ORR.