Non-precious Metal Catalysts for Two-Electron Oxygen Reduction Reaction

Hydrogen peroxide has been used in many industrial sectors including applications such as water purification, bleaching, oxidizing agents, and rocket fuels. As the conventional anthraquinone route of hydrogen peroxide production consumes significant energy and generates a substantial amount of chemical waste, an alternative method, the electrochemical production through the two-electron oxygen reduction reaction (ORR), has garnered attention on the basis of eco-friendly in situ synthesis with low energy input. For practical viability, the use of non-precious metal-based catalysts is necessary, such as a transition metal (Fe, Co, Ni)-heteroatom (N, B, O, P, S) moiety or mesoporous structures with efficient mass transfer of the reactants and products from metal-organic frameworks (MOFs). The ORR reaction pathway and the adsorption energy of the reaction intermediate of *OOH are affected by the combination of transition metals and heteroatoms. For the MOF, the interaction between metal and ligands, types of transition metals, and the synergistic effect between the two metal species of metal alloys can alter the ORR activity. This review discusses recently reported non-precious metal catalysts for the two-electron ORR focusing on modification of the atomic configuration for increasing the electrocatalytic activity towards the two-electron ORR.