Domain-Confined Etching Strategy to Regulate Defective Sites in Carbon for High-Efficiency Electrocatalytic Oxygen Reduction

Coupling sites of nitrogen dopants and intrinsic carbon defects (N/DC) in metal-free carbon are highly active toward electrocatalytic oxygen reduction reaction (ORR), and yet they are hard to be effectively constructed. Here, a novel synthesis strategy for fabrication of N/DC-enriched metal-free carbon from precursors containing metal-nitrogen moieties (M-N-x) is reported. During pyrolysis of the precursors, the M-N-x is in situ converted to endogenous metal oxides (MOx) via a halide-mediated bait and switch mechanism to realize a domain-confined etching of the carbon matrix around the nitrogen dopants, forming abundant N/DC coupling sites in the final carbon products. The optimized N/DC-enriched carbon exhibits an outstanding ORR activity and stability with a half-wave potential of 0.903 V (versus RHE) in 0.1 m KOH solution, outperforming most of the reported metal-free carbon catalysts. Experimental investigations and theoretical calculations demonstrate an improved electron-donating ability and optimized binding energies of the N/DC coupling sites toward the ORR intermediates, which are primarily responsible for such an excellent ORR activity. This domain-confined endogenous MOx etching strategy is also widely applicable to different M-N-x-containing precursors as well as different halide mediators, which opens up new possibilities to fabricate metal/nonmetal doped carbon materials enriched with various coupling sites of desired synergistic properties.

Automated summary

A novel synthesis strategy for fabricating metal-free carbon with nitrogen dopants and carbon defects is reported, which exhibits outstanding activity and stability in the oxygen reduction reaction. The strategy involves the conversion of metal-nitrogen moieties to endogenous metal oxides during pyrolysis, resulting in the formation of abundant coupling sites between nitrogen dopants and carbon defects.