Coordination-Engineered\nCu–N_<i>x</i> Single-Site Catalyst for\nEnhancing Oxygen Reduction Reaction

Abstract

Atomic metal–nitrogen–carbon\n(M–N–C)\nmaterials represent a unique class of single-atom catalysts with intriguing\nactivity and selectivity for electrocatalytic applications. For rational\ndesign and synthesis of the M–N–C catalysts, an atomic-scale\ncorrelation of its coordination environment and catalytic properties\nis essential. Here, a unique synthetic strategy via “in situ\nreduction” was proposed to tailor the coordination configurations\nof atomically dispersed Cu–N–C catalyst. By using a\ncombination of synchrotron X-ray spectroscopies, we are able to identify\nthe varied nitrogen coordination numbers of Cu–N_<i>x</i> site. The spectroscopic evidence determines that\nthe Cu atoms with two-coordinated N in the form of unsaturated Cu^I–N₂ configuration are the catalytically\nactive sites, when correlated with their activities in electrochemical\noxygen reduction reaction. The theory calculations support the proposed\nCu^I–N₂ as the active sites for the enhanced\nORR performance via a 4e^– mechanistic pathway.