Fig. 2. In situ X-ray spectroscopy analysis of N–Cu SAC during CO₂RR.

a Wavelet-transform diagram of in situ Cu K-edge EXAFS spectra of N–Cu SAC at various applied potentials in CO₂-saturated 0.1 M KHCO₃ solution during CO₂ reduction. b Extracted oxidation state from in situ Cu K-edge XANES spectra of N–Cu SAC through linear combination of Cu foil, Cu₂O, and Cu(bipy)₄Cl as spectroscopic references in CO₂-saturated 0.1 M KHCO₃ solution. c Quantitative analysis of coordination environment extracted from EXAFS fitting at various potentials in CO₂-saturated 0.1 M KHCO₃ solution. Error bars represent the standard deviation of three independent measurements. d Schematic representation of in situ X-ray emission spectroscopy (XES) apparatus applied to a liquid electrochemical cell and energy diagram for the detection of Kα₁ and Kα₂ emission in transition-metal ion. e In situ XES spectra of Kα₁ and Kα₂ emission for N–Cu SAC and references collected at various potentials during CO₂ reduction in CO₂-saturated 0.1 M KHCO₃ solution. All measurements were performed in 0.1 M KHCO₃ by a typical three-electrode setup using glassy carbon as the working electrode, Hg/HgCl₂ electrode and platinum plate acted as reference and counter electrodes, respectively. The applied potential was calibrated to a reversible hydrogen electrode (RHE).