To perform chemical and oxidation state analysis, at the end of the CO2 ER experiments the cell was flushed with nitrogen and transferred to the instrument with EELS capabilities. The dry chip with patterned electrode and copper catalyst was then analyzed through Electron Energy Loss Spectroscopy (EELS) using a Gatan Ultrascan detector on a JEOL NEOARM microscope operating at 200 kV. The spectra were collected with a Gatan imaging filter (GIF) aperture of 2.5 mm and a collection semi-angle of β of 41.7 mrad using a 6C probe size with 0.025 eV of energy dispersion at a 20 mm camera length. Zero-loss and core-loss spectra were obtained using an exposure of 2 × 10 -5 s and 5 s, respectively. Processing of EELS signal was performed using Origin Pro.