Fig. 1.

Feeding gas-dependent structural evolution of Cu₂O nanocubes in the pre-electrolysis at a potential of −1.1 V versus RHE in an H-cell. TEM and HRTEM images and corresponding SAED patterns of a pristine Cu₂O, and those after pre-electrolysis in CO₂ atmosphere for b 1000 s and c 2000 s, and d after pre-electrolysis in Ar atmosphere for 2000 s; The a2 and a3 show the edge of nanocube in a1. The a4 is the SAED pattern of the nanocube in a1. The b2 shows the edge of the nanocube in b1. The d2 is the enlarged rectangle region in d1. The d3 is the enlarged square region in d2. The inset in d3 is the SAED pattern. The c3 and c4 are the enlarged square regions marked with numbers ① and ② in c2, respectively. e XRD patterns and f, g Cu LMM Auger spectra of Cu₂O-CO₂ and Cu₂O-Ar after pre-electrolysis for different periods