Photocorrosion of cadmium sulfide: Analysis by photoelectron spectroscopy

Photocorrosion of cadmium sulfide electrodes in aqueous electrolytes leads to sulfate formation in the presence and to sulfur formation in the absence of oxygen. All three sulfur species involved (S2−, S0 and SO2−4) can be detected on CdS electrodes after treatment in photoelectrochemical cells using AES or XPS. Both, the S2p/3p XPS and the S Auger peaks are broadened on photoelectrochemical oxidized CdS due to deposition of elemental sulfur. The XPS binding energy of the S electrons is shifted by about 1 eV per sulfur oxidation step from around 161.5 eV for S2− to around 163.5 eV for S0 and around 168 eV for SO2−4. The results obtained by photoelectron spectroscopy of electrodes transferred from the electrolyte directly into the UHV system without any cleaning and special precautions are in excellent agreement with the predictions based on photoelectrochemical experiments. For example, it could be proved by XPS that sulfur was transformed into sulfate in a reductive oxidation step in the presence of oxygen, leading to the CdS surface being cleaned of S0.