Degradation Mechanism and Enhancing Strategies of Oxygen Reduction Reaction Catalyzed by Carbon-Based Metal Free Catalysts in Acidic Solution

Carbon-based metal free catalysts (CMFCs) are far away from commercial availability mainly attributed to their poor oxygen reduction reaction (ORR) performance in acidic environment with the causes remaining obscure. By investigating the heteroatoms (N, B, P, S, Se, and Te)-doped reduced graphene oxides, the degradation mechanism of acidic ORR performance of CMFCs is found to be correlated with the oxygen-baring defects in the carbon sp² lattice, which exhibit overpotentials as low as 0.44 V but weak trapping capabilities for oxygen molecules. These findings not only revise the previously reported strategy of modeling the active sites in the basal plane of CMFCs but also highlight the connections between those active sites and the triple-coordinated VIA group elements (XC₃). Further calculations demonstrate that the XC₃ dimer can efficiently enhance the acidic ORR performance and the 2D trigonal carbon-chalcogenides C₆X (X = S, Se, and Te) are accordingly designed toward acidic ORR, which contain homogeneously distributed basal plane active sites and exhibit low overpotentials but strong trapping capabilities for oxygen molecules. This work will help to cease the debates on the active sites in CMFCs for ORR in both acidic and alkaline solutions and to open a new avenue to design CMFCs independent on doping strategy.