Tuning Amorphous Surface Microenvironments for Accelerated *OH Adsorption toward Efficient CO₂ Electrocatalysis

The catalyst surface microenvironment, particularly *OH adsorption, plays a decisive role in CO₂ electroreduction. Precise engineering of amorphous surface microenvironments enables efficient *OH adsorption. While Cu-based catalysts show promise for the CO₂ reduction reaction (CO₂RR), controlling atomic-scale surface configurations remains challenging. Herein, we construct amorphous CuSnO_x (a-CuSnO_x) with tailored surface microenvironments through strategic Cu-Sn integration, achieving >90% formate Faradaic efficiency across broad current densities. Unlike its crystalline counterparts, the amorphous structure provides a high density of undercoordinated Cu and Sn sites, which collectively promote the adsorption of *OH, verified by the ¹⁷O NMR experiments. Operando ¹H and ¹⁷O NMR analysis reveals that *OH directly involves formate production via a water-assisted mechanism. This *OH adsorption-dominated microenvironment directly facilitates formate generation, establishing a new design strategy for high-performance CO₂RR catalysts and deepening the fundamental understanding of structure-activity relationships.