Unconventional Inverse Size-Effects Enable Efficient C-N Coupling on Copper Electrocatalysts

Exposed coordinatively unsaturated sites (CUS) with the reducing geometrical sizes of catalysts commonly offers significant advantages in heterogeneous electrocatalytic processes. However, this empirical rule might be unsuitable for the innovative electrocatalytic C-N coupling reaction, as one of the parallel reactions. In this study, we observe an inverse size-effect in the electrocatalytic synthesis of benzaldehyde oximes (BAO) from nitrates and benzaldehyde. Cu nanocatalysts with more exposed CUS thermodynamically favor the over-reduction of coupling intermediates, i.e., adsrobed hydroxylamine (*NH₂OH) and benzaldehyde (*Ph-CHO), leading to a low BAO yield. Notably, Cu foil with few CUS enables the enrichment of *NH₂OH and *Ph-CHO, achieving a BAO yield of 91%. Moreover, this electrosynthesis strategy on Cu foil demonstrates versatility and broad applicability for producing various oximes. This work highlights the significant potential of inverse size effects in guiding the design of catalysts for electrocatalytic C-N coupling reactions.