Chemical synthesis of orthorhombic Ag₈SnS₆/zinc oxide nanorods photoanodes for photoelectrochemical salt-water splitting

Orthorhombic Ag₈SnS₆/ZnO nanorods grown onto indium-tin-oxide conductive glass substrates were prepared using a simple chemical synthesis method for the application in photoelectrochemical salt-water splitting. For the deposition of ZnO nanorods on substrates, the concentrations of ammonium hydroxide in the solution bath were changed to obtain the pristine ZnO nanorods with good morphology for the growth of silver-tin-sulfide layer. Pristine ZnO nanorods prepared with concentration of 5.5 M for ammonium hydroxide in the reaction solution has the highest intensity of (0 0 2) crystal plane, which indicates that pristine ZnO nanorods sample has good morphology for the preparation of the Ag₈SnS₆ core/shell photoanode. From the results of X-ray diffraction patterns and energy-dispersive X-ray spectroscopy analysis for samples, with decreasing [Ag]/[Ag + Sn] molar ratio in the reaction solution, crystal phases of samples changed from Ag₂S/SnS/ZnO, orthorhombic Ag₈SnS₆/ZnO to Ag₈SnS₆/SnS/ZnO mixing phases. The values of sample’s energy band gap were located in the range of 1.36 ~ 1.79 eV. At the [Ag]/[Ag + Sn] molar ratio of 0.4 in the reaction solution, the maximum photoelectrochemical activity of 0.79 mA cm⁻² for samples was obtained with the external bias set at + 1.5 V vs. an Ag/AgCl electrode in 0.5 M NaCl aqueous solution. The photoelectrochemical activity of sample could remain at least 2000 s without any decay in the salt-water solution.