Regulating Surface Electron Dynamics Enables Selective C─N Coupling in Photoelectrochemical Oxime Synthesis

ABSTRACT

A central challenge in photoelectrochemical multi‐electron transformations is simultaneously achieving efficient charge separation and precise control over reaction selectivity. Herein, we construct a p–n junction photocathode composed of an atomic‐layer‐deposited ZnO _x layer and black silicon (b‐Si) to regulate interfacial electron dynamics and reaction selectivity. Upon illumination, oxygen vacancies in the ZnO _x surface serve as electron‐buffering sites that facilitate reversible charge storage and release, as confirmed by in situ Kelvin probe force microscopy. This modulation of electron chemical potential suppresses competing hydrogen evolution and over‐reduction pathways, while directing nitrogen‐centered intermediates toward selective hydroxylamine formation and subsequent C─N coupling. The optimized photocathode delivers a photocurrent density of 38.6 mA cm ⁻² with a Faradaic efficiency of 94.6% for cyclohexanone oxime production and a cyclohexanone‐to‐oxime selectivity of 99.9%. Mechanistic studies combining operando spectroscopy, density functional theory, and microkinetic analysis reveal that coverage‐dependent site competition governs surface site availability, thereby inhibiting the further reduction of hydroxylamine and promoting its desorption for solution‐phase coupling. Integration of the microkinetic model with the photovoltaic response establishes a quantitative design principle based on the matching between semiconductor photoresponse and interfacial catalytic kinetics, providing a general framework for selectivity control in photoelectrochemical systems.