A General Method for Transition Metal Single Atoms Anchored on Honeycomb-Like Nitrogen-Doped Carbon Nanosheets

Excavating and developing highly efficient and cost-effective nonnoble metal single-atom catalysts for electrocatalytic reactions is of paramount significance but still in its infancy. Herein, reported is a general NaCl template-assisted strategy for rationally designing and preparing a series of isolated transition metal single atoms (Fe/Co/Ni) anchored on honeycomb-like nitrogen-doped carbon matrix (M₁-HNC-T₁-T₂, M = Fe/Co/Ni, T₁ = 500 °C, T₂ = 850 °C). The resulting M₁-HNC-500-850 with M-N₄ active sites exhibits superior capability for oxygen reduction reaction (ORR) with the half-wave potential order of Fe₁-HNC-500-850 > Co₁-HNC-500-850 > Ni₁-HNC-500-850, in which Fe₁-HNC-500-850 shows better performance than commercial Pt/C. Density functional theory calculations reveal a choice strategy that the strong p–d-coupled spatial charge separation results the Fe-N₄ effectively merges active electrons for elevating d-band activity in a van-Hove singularity like character. This essentially generalizes an optimal electronic exchange-and-transfer (ExT) capability for boosting sluggish alkaline ORR activity. This work not only presents a universal strategy for preparing single-atom electrocatalyst to accelerate the kinetics of cathodic ORR but also provides an insight into the relationship between the electronic structure and the electrocatalytical activity.