Photoelectrochemical salt water splitting using ternary silver-tin-selenide photoelectrodes

Ternary AgSnSe₂ and Ag₈SnSe₆ semiconductor photoelectrodes are prepared on various substrates via the selenization of thermally evaporation of silver-tin metal precursors. The structural, optical and electrical properties of ternary AgSnSe₂ and Ag₈SnSe₆ samples are investigated as a function of the [Ag]/[Ag + Sn] molar ratio in the metal precursors. X-ray diffraction patterns of samples show that the phases of samples change from cubic AgSnSe₂ to cubic Ag₈SnSe₆ phase at a selenization temperature of 410 °C when the molar ratio of [Ag]/[Ag + Sn] in silver-tin metal precursors increase from 0.51 to 0.68. The images obtained from a field-emission scanning electron microscopy show that the surface microstructures of samples change from plate-like microstructures with some pinholes to polygonal microstructures with increasing [Ag]/[Ag + Sn] molar ratios in samples. The energy bang gaps, carrier concentrations and mobilities of the samples are in the ranges of 0.86-1.19 eV, 1.27 × 10¹¹-2.39 × 10¹² cm^-3 and 238-655 cm² V^-1 s^-1, respectively. The highest photo-enhanced current densities of the samples in aqueous Na₂S + K₂SO₃ and NaCl solutions are 3.34 and 0.61 mA cm^-2 at an applied voltage of 0 and + 0.4 V vs. an Ag/AgCl electrode under 100 mW cm^-2 light illumination from a Xe lamp source, respectively.