Stable photoelectrochemical salt-water splitting using the n-ZnSe/n-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 salt-water 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.