Aqueous electrochemical CO₂ reduction (CO₂R) on Cu can generate a variety of valuable fuels, yet challenges remain in the improvement of electrosynthesis pathways for highly selective fuel production. Mechanistically, understanding CO₂R on Cu, particularly identifying the product-specific active sites, is crucial. Herein, we rationally designed and fabricated nine large-area single-crystal Cu foils with various surface orientations as electrocatalysts and identified the voltage- and facet-dependent CO₂R selectivities. Operando grazing incidence X-ray diffraction (GIXRD) and electron back-scattered diffraction (EBSD) were applied to track the top-surface reconstructions of Cu, and we correlate the structural evolution with the change of product selectivities. We extracted three distinct structural descriptors, including crystal facet, atomic coordination number, and step-terrace angle, to reveal the intrinsic structure-function relationships and uniquely identify the specific product-producing sites for CO₂R. Our work guides the rational design of Cu-based CO₂R electrocatalysts and, more importantly, establishes a paradigm to understand the structure-function correlation in catalysis.

Cu上的含水电化学CO ₂还原（CO ₂ R）可以产生各种有价值的燃料，但是在改善高选择性燃料生产的电合成途径方面仍然存在挑战。从机理上讲，了解Cu上的CO ₂ R尤其是确定产品特定的活性位点至关重要。在这里，我们合理地设计和制造了九种具有不同表面取向的大面积单晶Cu箔作为电催化剂，并确定了电压和刻面相关的CO ₂ R选择性。Operando利用掠入射X射线衍射（GIXRD）和电子背散射衍射（EBSD）追踪铜的表面重建，并将结构演化与产物选择性的变化联系起来。我们提取了三个不同的结构描述符，包括晶面，原子配位数和阶跃角，以揭示内在的结构-功能关系，并唯一地标识出CO ₂ R的特定产物产生位点。铜基CO ₂ R电催化剂，更重要的是，建立了一个范式来理解催化中的结构-功能相关性。