In situ and operando observation of surface oxides during oxygen evolution reaction on copper

[Display omitted] •Spectroscopic ellipsometry and Raman spectroscopy used to study surfaces during OER•Layer thickness decreases after start of oxygen evolution•Photoluminescence shows defect formation during running oxygen evolution•Oxide becomes unstable towards defect formation Formation and dissolution of oxide on copper under transpassive conditions, i.e. during OER and transpassive dissolution, in alkaline electrolyte was investigated by a combination of electrochemical techniques and in situ and operando Raman and photoluminescence (PL) spectroscopy, as well as spectropscopic ellipsometry. Experiments were conducted under potentiodynamic and potentiostatic polarisation in 0.1M NaOH. In chronoamperometry experiments with steps between potentials, oxide thickness continued increasing beyond the onset of OER. The thickness dropped significantly from >10 nm to