In-situ Raman spectra were collected on Renishaw Invia system with a 633 nm laser. The output powder is 5 mW. Before each experiment, Raman frequency calibration was conducted by measuring a Si wafer (520 nm). A laser line focus module was utilized to obtain spectra by spreading out the laser intensity with approximately 20x lower signal intensity per area. The accumulation time per spectrum was set to 1s and the total signal acquisition time is 60s (average of 60 spectra). An immersion objective (numerical aperture of 0.8) was used to decrease the distance between the laser and the surface of the electrode to a obtain better Raman signal. The spectra were collected under different potential, range from open circuit potential to -0.98V vs. RHE, with the step of -0.2V. The reaction cell is similar with electrochemical measurement. The same three-electrode configuration was used for the operando Raman measurement; working electrode, counter and reference electrode are the identical. KOH was used as electrolyte, with or without the addition of sulfite. CO2 or N2 was fed into the reactor, with flow rate of 10 mL min -1 .