XPS was performed using Kratos Axis-165 to analyze the surface composition and the oxidation states of the Ag catalyst before and after electrolysis. The instrument produced monochromatized Al Kα radiation at 12 kV and 10 mA. A survey scan was conducted between binding energies 0 and 900 eV with a resolution of 1 eV. Followed by the survey scan, high resolution scans were conducted between 560 and 620 eV to identify the Ag 3p peaks, between 360 and 380 eV to identify the Ag 3d peaks, and between 520 and 540 eV to identify the O 1s peak with a resolution of 0.1 eV. To minimize the noise, 5 sweeps were performed for the high resolution scans.