Liquid Metal‐Enabled Tunable Synthesis of Nanoporous Polycrystalline Copper for Selective CO ₂ ‐to‐Formate Electrochemical Conversion

Abstract Copper‐based catalysts exhibit high activity in electrochemical CO ₂ conversion to value‐added chemicals. However, achieving precise control over catalysts design to generate narrowly distributed products remains challenging. Herein, a gallium (Ga) liquid metal‐based approach is employed to synthesize hierarchical nanoporous copper (HNP Cu) catalysts with tailored ligament/pore and crystallite sizes. The nanoporosity and polycrystallinity are generated by dealloying intermetallic CuGa ₂ formed after immersing pristine Cu foil in liquid Ga in a basic or acidic solution. The liquid metal‐based approach allows for the transformation of monocrystalline Cu to the polycrystalline HNP Cu with enhanced CO ₂ reduction reaction (CO ₂ RR) performance. The dealloyed HNP Cu catalyst with suitable crystallite size (22.8 nm) and nanoporous structure (ligament/pore size of 45 nm) exhibits a high Faradaic efficiency of 91% toward formate production under an applied potential as low as −0.3 V _RHE . The superior CO ₂ RR performance can be ascribed to the enlarged electrochemical catalytic surface area, the generation of preferred Cu facets, and the rich grain boundaries by polycrystallinity. This work demonstrates the potential of liquid metal‐based synthesis for improving catalysts performance based on structural design, without increasing compositional complexity.