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.