To monitor the copper oxidation state, we tracked the crystallinity of the catalysts by means of time-dependent XRD conducted simultaneously with CV measurements. We first apply a constant potential at -1.8 V for 30 minutes under CO2-saturated 1 M KOH with 1.5 M NH3 electrolyte to completely remove any surface oxide species. During the CV, the potential applied to the sample was changed from -0. 6 V and + 0.6 V, and then from +0.6 V to sweeping back to -1.3 V vs. Ag/AgCl, with a rate of 0.5 mV/s. The XRD detection system used a GaliPIX3D detector in 1D mode configuration with BBHD optics with a range of 30° ≤ 2θ ≤ 45°, leading to each spectrum for 160s in total.