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.