Epitaxial Growth of Atomic-Layer Cu on Pd Nanocatalysts for Electrochemical CO2 Reduction

CO₂ reduction reaction (CO₂RR) facilitates the sustainable synthesis of fuels and chemicals. Although copper (Cu) enables CO₂-to-multicarbon product (C₂₊) conversion, Cu-based electrocatalysts, particularly nanocatalysts, face challenges in poor selectivity and stability owing to the highly dynamic nature of Cu atoms under reaction conditions. Core–shell structures present a promising approach to address these issues by modulating the Cu overlayer–substrate interactions with atomic-level precision. Here, we report on Pd@Cu core–shell structures with atomically thin and nanometer-thick Cu overlayers on single-crystal Pd nanocubes with {100} facets promoting the CO₂-to-C₂₊ conversion. The microstructures and surface compositions at the atomically sharp Pd/Cu interface were investigated by atomic-scale scanning transmission electron microscopy (STEM) imaging and electron energy-loss spectroscopy (EELS). Our results reveal that atomic-layer Cu epitaxially grows on Pd and adapts to the lattice of the Pd substrate. The reaction-driven migration of atomic-layer Cu is effectively suppressed on Pd due to the strong Cu–Pd interaction. While Pd only reduces CO₂ to C₁ products, atomic-layer Cu on Pd can initiate the C₂₊ production during the CO₂RR. Thick Cu overlayers (∼15 nm) on Pd further enhance the C₂₊ faradaic efficiency while undergoing significant structural reconstruction, with only the 2–3 nm Cu layers near the Pd surface remaining stable and resistant to Cu migration after the CO₂RR. We anticipate that Pd@Cu core–shell structures with intermediate Cu shell thickness hold significant potential for enhancing C₂₊ selectivity while maintaining high stability of nanocatalysts for CO₂ reduction to liquid fuels.