Fig. 4. Stability of the Cu sites.

a XRD pattern of Sr₂CuWO₆ after thermochemical reduction. b Schematic illustration of phase transition of Sr₂CuWO₆ after reduction. Sr, Cu, W, and O are represented by green, blue, gray, and red dots, respectively. The red-dotted circle, blue, and gray octahedra represent oxygen vacancy, CuO₆, and WO₆, respectively. c Schematic illustration of the distances between the nearest Cu cations in Fm-3m phase of Sr₂CuWO₆. d XRD patterns of Sr₂CuWO₆ after CO₂RR at different current densities (GDE: gas diffusion layer). e Cu LMM XPS spectra of Sr₂CuWO₆ after CO₂RR at different current densities. f W XPS spectra of Sr₂CuWO₆ after different current densities. g CO₂RR stability test of Sr₂CuWO₆ and CuO/WO₃ in a flow cell at 400 mA cm⁻². In-situ Raman spectra of h Sr₂CuWO₆ and i CuO/WO₃ as a function of CO₂RR time at −1.2 V vs. RHE (RHE: reversible hydrogen electrode).