Stable photoelectrochemical salt-water splitting using the n-ZnSein-Ag8SnS6 photoanodes with the nanoscale surface state capacitances

Interest in the photoelectrochemical water splitting using the metal sulphide photoelectrodes increases due to their good photoelectrochemical performances in aqueous solutions under illumination. However, the accumulation of photo-excited holes at the surfaces of samples results in their poor stabilities for photoelectrochemical water splitting during light illumination. We report the systemic investigations of the physical properties, photoelectrochemical performances and the influence of surface states for the silver-tin-sulphides (Ag8SnS6) photoelectrode in order to find out the reason about its poor stability for photoelectrochemical salt-water splitting. From the electrical impedance spectra of samples in the saltwater solution with various applied voltages, the Fermi-level pinning effect occurs in the Ag8SnS6 photoelectrode due to its high density of surface states. The accumulation of holes in the surface states results in the photocorrosion of the photoanode rather than the photoelectrochemical salt-water splitting. With the ZnSe/Ag8SnS6 heterogeneous junction as the photoelectrode, these surface states at the Ag8SnS6 sample act as the capacitances that can extract photo-excited electrons from the ZnSe layer and holes from the Ag8SnS6 sample. They make the increase in the charge separation rate for photo-excited carriers in the samples, which enhances its photoelectrochemical performance and stability in the salt-water solution. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.