Structure-Tailored Surface Oxide on Cu-Ga Intermetallics Enhances CO2 Reduction Selectivity to Methanol at Ultra-Low Potential

In this work, electrochemical CO2 reduction reaction (eCO2 RR) has been performed on two intermetallic compounds formed by copper and gallium metals (CuGa2 and Cu9 Ga4 ) for the first time. Among them, CuGa2 selectively converts CO2 to methanol with remarkable Faradaic efficiency (FE) of 77.26% at an extremely low potential of -0.3 V versus RHE. The, high performance of CuGa2 compared to Cu9 Ga4 has been driven by its unique two-dimensional structure that retains surface and sub-surface oxide species (Ga2 O3 ) even in the reduction atmosphere. The Ga2O3, species have been mapped by XPS and XAFS techniques and electrochemical measurements. The eCO2 RR activity and selectivity to methanol have been decreased at higher potential due to the lattice expansion caused by the reduction of the Ga2 O3 , which has been probed by in-situ XAFS, quasi in-situ powder XRD and ex-situ XPS measurements. The mechanism of the formation of methanol from CO2 at various potentials has been visualized by in-situ IR spectroscopy and source of carbon of methanol at the molecular level confirmed from the isotope labelling experiments in the presence of 13 CO2 . Finally, to minimize the mass transport limitations and improve the overall eCO2 RR performance, PTFE-based gas diffusion electrode (GDE) has been employed in the flow cell configuration.