In situ constructed metal–semiconductor junctions for enhanced formate electrosynthesis via paired photo-assisted CO2 reduction and methanol oxidation

Photo-assisted electrosynthesis offers a mild and energy-efficient route for carbon upgrading, yet its performance is commonly constrained by inefficient catalytic interfaces that must coordinate light harvesting with rapid electrochemical charge transfer. In situ construction of metal–semiconductor (MS) junction enables precise regulation of interfacial electronic structure and the integration of photocarrier and photothermal effects within a unified electrode architecture. Here, we engineered a barrier-free Ag 2 O/Ag Ohmic interface for selective methanol oxidation and a Bi/Bi 2 O 3 Schottky interface that directs electrons toward CO 2 reduction. Both systems generate formate with Faradaic efficiencies above 95% across wide current ranges and maintain stable operation for over 100 hours. In situ Raman spectroscopy, complemented by X-ray absorption and electron microscopy, directly tracks MS-junction formation and active-site evolution under operating conditions. Under AM 1.5G illumination, a membrane-free flow electrolyzer achieves a total formate Faradaic efficiency of 194.8% at 2.5 V, establishing MS-junction engineering as an effective strategy for multi-field-coupled electrosynthesis.