Fig. 3: Physical characterizations of the functionalized electrodes using XPS and operando Raman and XAS spectroscopy.

a High-resolution spectra of the Cu 2p regions and Cu L₃M₄₅M₄₅ Auger transition modes measured by ex situ X-ray photoelectron spectroscopy (XPS) of pristine Ag–Cu sample (P), H₂O₂-treated Ag–Cu (H₂O₂-P), C₃-, C₂N-, N₃N- and N₂SN- functionalized Ag–Cu electrodes. The different colored shading areas represent the peaks of Cu 2p_1/2(blue), Cu 2p_3/2(light purple), ¹G (pink) and ³F (light green), respectively. b Ex situ and operando Copper K-edge X-ray absorption near-edge structure (XANES) spectra of pristine and functionalized Ag–Cu electrodes. Inset: Average oxidation state of copper for the corresponding electrodes. c Operando Cu K-edge XANES spectra of N₂SN- functionalized Ag–Cu electrode during CO₂RR. The measurements were performed after holding the applied potential for 30 min. d Evolution of the Faradaic efficiency for C₂₊ and H₂ measured at −1.2 V vs. RHE with the oxidation state of Cu. e Operando Raman spectra for pristine, C₃-, C₂N-, N₃N- and N₂SN-, functionalized Ag–Cu during CO₂RR at a fixed potential of −1.2 V vs. RHE. The different colored shading areas represent the peaks of 280 cm⁻¹ (light green), ~365 cm⁻¹ (pink), and ~2000 cm⁻¹ (blue), respectively. The spectra for all the other potentials are presented in Supplementary Fig. 26. f Relationship between the FE for C₂₊ products and the Raman peak areas of the frustrated rotational mode of CO at 280 cm⁻¹, the Cu–CO stretch at 365 cm^−1, and the C≡O stretch at 1900–2120 cm⁻¹, respectively. g Relationship between the FE for C₂₊ molecules and the ratio of CO_atop and CO_bridge on different Ag–Cu electrodes. The ratio was obtained from the integrated areas of the deconvoluted peaks of the Raman spectra (Supplementary Fig. 27). The error bars in b, d, f, and g correspond to the standard deviation of three independent measurements.