Structure‐Tailored Surface Oxide on Cu–Ga Intermetallics Enhances CO₂ Reduction Selectivity to Methanol at Ultralow Potential

Electrochemical CO₂ reduction reaction (eCO₂ RR) is performed on two intermetallic compounds formed by copper and gallium metals (CuGa₂ and Cu₉ Ga₄ ). Among them, CuGa₂ selectively converts CO₂ to methanol with remarkable Faradaic efficiency of 77.26% at an extremely low potential of -0.3 V vs RHE. The high performance of CuGa₂ compared to Cu₉ Ga₄ is driven by its unique 2D structure, which retains surface and subsurface oxide species (Ga₂ O₃ ) even in the reduction atmosphere. The Ga₂ O₃ species is mapped by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) techniques and electrochemical measurements. The eCO₂ RR selectivity to methanol are decreased at higher potential due to the lattice expansion caused by the reduction of the Ga₂ O₃ , which is probed by in situ XAFS, quasi in situ powder X-ray diffraction, and ex situ XPS measurements. The mechanism of the formation of methanol is visualized by in situ infrared (IR) spectroscopy and the source of the carbon of methanol at the molecular level is confirmed from the isotope-labeling experiments in presence of ¹³ CO₂ . Finally, to minimize the mass transport limitations and improve the overall eCO₂ RR performance, a poly(tetrafluoroethylene)-based gas diffusion electrode is used in the flow cell configuration.