Coordination-Engineered Cu–N_x Single-Site Catalyst for Enhancing Oxygen Reduction Reaction

Atomic metal–nitrogen–carbon (M–N–C) materials represent a unique class of single-atom catalysts with intriguing activity and selectivity for electrocatalytic applications. For rational design and synthesis of the M–N–C catalysts, an atomic-scale correlation of its coordination environment and catalytic properties is essential. Here, a unique synthetic strategy via “in situ reduction” was proposed to tailor the coordination configurations of atomically dispersed Cu–N–C catalyst. By using a combination of synchrotron X-ray spectroscopies, we are able to identify the varied nitrogen coordination numbers of Cu–Nx site. The spectroscopic evidence determines that the Cu atoms with two-coordinated N in the form of unsaturated CuI–N2 configuration are the catalytically active sites, when correlated with their activities in electrochemical oxygen reduction reaction. The theory calculations support the proposed CuI–N2 as the active sites for the enhanced ORR performance via a 4e– mechanistic pathway.