Progress of metal-free carbon alloy electrocatalysts for hydrogen peroxide by two-electron oxygen reduction reaction

Hydrogen peroxide (H2O2), an important chemical raw material, has received great attention in civil and industrial applications. Electrocatalysis of two -electron oxygen reduction reaction (2e(-)ORR) is a feasible alternative to the traditional multi-step anthraquinone process to produce H2O2. Metal-free carbon alloy materials (carbon atoms bonding with other metal-free elements) have been developed as effective electrocatalysts due to their low cost, abundance and excellent performance. In this paper, the recent progress on synthesis of H2O2 by metal -free carbon alloy electrocatalysts for 2e(-)ORR is systematically reviewed. First, the mechanism of 2e(-)ORR is outlined. Then, depending on the different electronegativity of heteroatoms, binary carbon alloy (including nitrogen carbon, oxygen carbon, fluorine carbon, boron carbon, sulfur carbon, phosphorus carbon) and ternary carbon alloy are presented in detail for the 2e(-)ORR, especially focusing on their unique structures, catalytic activity, selectivity, stability, H2O2 production rate, and so on. Moreover, the active sites of carbon alloy electrocatalysts for H2O2 are mainly summarized as defect, heteroatoms and synergistic effect. Finally, the key challenges and future opportunities of carbon alloy electrocatalysts for 2e(-)ORR are proposed. It is suggested that reasonable design of structure, functional groups and synergistic effect of components is effective for increasing the H2O2 generation by 2e(-)ORR.