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

• Synchrotron XPS revealed surface chemistry of chalcopyrite under anodic oxidation.
• S, Cu, Fe chemical species and their evolution under potentials were identified.
• XPS results indicate that S22 − species and CuS form at 600 mV and dissolve at 650 mV
• Chalcopyrite surface became more metal deficient with increasing potential.
• Metal-deficient Sn2 −/S0 layer on the surface may cause the passivation.

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.

S 2p XPS spectra of chalcopyrite oxidized at 530, 600, 650 mV vs. Ag/AgCl for 2 h.Figure optionsDownload as PowerPoint slide