Fig. 2

Decomposition of copper–cuprous oxide electrodes. a Reduction current density in 0.1 M KCl solution saturated with CO₂ and N₂ at applied potential of −0.4 V vs RHE, and the inserts show the current density at initial stage; b SEM images of the electrode with different electroreduction times (0 min, 2 min, 5 min, 10 min, 5 h); c, d Quasi in situ XPS spectra of the catalyst with different electroreduction times (0 min, 2 min, 5 min, 10 min, 5 h). Cu 2p photoelectron peak distribution: (i) Cu^II of Complex-1 structure; (ii) Cu^I/Cu⁰ of Cu–Cu₂O-1 structure; O 1s photoelectron peak distribution: (i) Oxygen of Cu_xO on Complex-1 structure; (ii) Oxygen of Cu_xO on Cu–Cu₂O-1 structure; and (iii) oxygen defect species; e TEM and f, g HR-TEM images of the Cu–Cu₂O-1 with electrorduction time of 5 h