Reconstruction of Highly Dense Cu−N4 Active Sites in Electrocatalytic Oxygen Reduction Characterized by Operando Synchrotron Radiation.

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt‐substituted electrocatalyst for oxygen reduction reaction (ORR) in anion‐exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu−N4 SAS with a metal loading of 5.61 wt% supported on 3D N‐doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H2/O2 AEMFC, it could reach an open‐circuit voltage of 0.90 V and a peak power density of 324 mW cm−2. Operando synchrotron radiation analyses identify the reconstruction from initial Cu−N4 to Cu−N4/Cu‐nanoclusters (NC) and the subsequent Cu−N3/Cu−NC under working conditions, which gradually regulate the d‐band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity. [ABSTRACT FROM AUTHOR]