Synchrotron-based XPS and NEXAFS study of surface chemical species during electrochemical oxidation of chalcopyrite

The surface chemical information of massive chalcopyrite electrode during electrochemical oxidation was studied by SXPS, NEXAFS and Raman spectroscopy. The electrochemical studies show that there was an activated region for chalcopyrite anodic dissolution between 550 and 630 mV (vs. Ag/AgCl), accompanied by two passive regions nearby. The spectroscopic studies suggest a thin film of non-stoichiometric sulfur-rich layer formed in the first passive region, likely to be responsible for the passivation. In the active region, S22 − species and covellite were also found, which could be the cause of the potential surge. When the potential was increased to 650 mV, another passive region appeared. At the same time, S22 − and covellite started to dissolve, leaving a highly metal deficient polysulfide and elemental sulfur layer on the chalcopyrite surface.