Dynamic Restructuring of Strongly Interacting Copper Single-Atom and Atomic Cluster Sites for Selective Electrosynthesis of Hydroxylamine

The ambient electrosynthesis of high-value hydroxylamine (NH₂OH) using nitrogenous precursors has garnered significant research attention. However, uncovering the real electrocatalytic sites for the selective synthesis of NH₂OH under operando electrocatalysis remains challenging. Herein, we report an oxygen-coordinated copper (Cu) single atoms and atomic clusters coanchored on a carbonized bacterial cellulose catalyst (Cu-SAs/ACs-CBC) via Cu-O₄/Cu₂ coordination for the selective electrocatalytic synthesis of NH₂OH using nitrate (NO₃^-) as nitrogen source. The Cu-SAs/ACs-CBC exhibits significantly enhanced electrocatalytic activity toward NH₂OH synthesis, achieving a yield rate of 273.6 ± 20.6 μmol h^-1 cm^-2 and a corresponding faradaic efficiency (FE) of 57.8 ± 4.4% at -0.8 V (vs RHE), whereas Cu single atoms alone are inclined to generate ammonia. Furthermore, we propose a one-step electrochemical strategy for synthesizing cyclohexanone oxime (CO) from NO₃^- and cyclohexanone using Cu-SAs/ACs-CBC, achieving a CO yield rate of 525.0 ± 45.3 μmol h^-1 cm^-2 with an FE of 80.5 ± 6.9% at -1.0 V (vs RHE) in a flow cell. The in situ X-ray absorption spectra reveal that Cu-O₄/Cu₂ in Cu-SAs/ACs-CBC is electrochemically reconstituted to form Cu-C₂O/Cu₈ as the real active site for selective NH₂OH synthesis. Theoretical calculations further unveil that the electrochemically reconstituted Cu-C₂O/Cu₈ site, with its synergistic effect, efficiently regulates the adsorption configuration of NO₃^-, therefore greatly improving the selectivity of NH₂OH during electrocatalysis.