Asymmetric Dual Sites Enable Spatially Resolved Biradical-Mediated C-N Coupling for N,N-Dimethylformamide Photoelectrosynthesis.

N,N-dimethylformamide (DMF) is a quintessential industrial solvent and precursor, and its energy-intensive, high-temperature conventional synthesis necessitates the development of mild, sustainable biomass-derived alternatives. Photoelectrocatalysis (PEC) offers a promising green route; however, its performance is limited by competitive adsorption and inadequate control over reaction selectivity. Herein, we engineered an asymmetric dual-site earth-abundant semiconductor to achieve biradical-mediated C-N coupling, attaining a Faradaic efficiency of 86.6%, a selectivity of 90.1%, and a DMF yield of 145.5 mmol m-2 h-1. For practical implementation, the parallel-connect stacked PEC device, with an area of 175 cm2, was recorded as the state-of-the-art PEC system for DMF photoelectrosynthesis. Mechanistic investigations revealed that bismuth vacancies, possessing a high p-band center, preferentially activated methanol to generate *CHO radicals, whereas BiOx sites, characterized by a moderate electronic environment, selectively catalyzed dimethylamine to form *N(CH3)2 radicals. This dual-site architecture effectively decouples the competitive adsorption of alcohol and amine substrates, enabling spatial segregation and achieving biradical-mediated C-N coupling. Importantly, the system demonstrated broad substrate adaptability, including cyclic secondary amines, highlighting its potential for constructing valuable amide derivatives. Our work provides a practical strategy for the mild valorization of biomass feedstocks and establishes an electronic structure-guided paradigm for selectivity control and kinetic optimization in biradical-mediated C-N coupling.