Reciprocal Synergistic Evolution of Cu‐Co Sites Boosts Electrocatalytic Nitrate Reduction to Ammonia

ABSTRACT The electrocatalytic nitrate reduction reaction (NO ₃ RR) offers a promising route for sustainable ammonia synthesis. Due to the interfacial synergistic effects, Cu–Co catalysts exhibit outstanding activity. However, the underlying evolution of active sites remains poorly understood, which induces the reported advantageous phase‐segregating in situ restructuring. By monitoring Co(OH) ₂ /Cu catalysts, our observations revealed that Cu‐ and Co‐related sites undergo dynamic, “seesaw‐like” reciprocal reactivation instead of mutual stabilization. In situ SERS, DMPO‐EPR and DFT calculations show that this process is driven by the competing oxidative/reductive forces under NO ₃ RR conditions, which cause site deactivation, and mediated via the transfer of ∙O/∙OH and H* radicals across interfaces. Critically, these radicals trigger the conversion of deactivated CuO _x and Co(OH) ₂ sites into highly active oxide‐derived Cu ⁰ and CoOOH, respectively. As the interfacial transfer of radicals constitutes an irreversible process, the observed in situ restructuring is inherently rationalized. This conjugated, seesaw‐like mechanism accelerates a dynamic, self‐regulating redox balance at Cu–Co heterointerface, continuously enhancing the synergy between Cu‐ and Co‐related sites and the overall NO ₃ RR performance. Beyond catalyst development, this work offers a mechanistic framework for understanding how competing oxidative and reductive forces are redistributed at heterointerfaces, providing guiding principles for the rational design of next‐generation electrocatalysts.