Cl⁻ ions accelerating interface charge transfer in a Si/In₂S₃ Faradaic junction photocathode for solar seawater splitting

Photoelectrocatalytic seawater splitting is a promising low-cost method to produce green hydrogen in a large scale. The effects of Cl⁻ ions in seawater on the performance of a photoanode have been reported in previous studies. However, few researches have been done on the roles of Cl⁻ ions in a photocathode. Herein, for the first time, we find that Cl⁻ ions in the electrolyte improve the photocurrent of a Si/In₂S₃ photocathode by 50% at −0.6 V_RHE. An in-situ X-ray photoelectron spectroscopy (XPS) characterization combined with the time-of-flight secondary-ion mass spectrometry by simulating photoelectrochemical conditions was used to investigate the interface charge transfer mechanism. The results suggest that there is an In₂⁺³S_3−x(OH)_2x layer on the surface of In₂S₃ in the phosphate buffer solution (PBS) electrolyte, which plays a role as an interface charge transfer mediator in the Si/In₂S₃ photocathode. The In₂⁺³S_3−x(OH)_2x surface layer becomes In₂⁺³S_3−x(Cl)_2x in the PBS electrolyte with NaCl and accelerates the charge transfer rate at the In₂S₃/electrolyte interface. These results offer a new concept of regulating interface charge transfer mediator to enhance the performance of photoelectrocatalytic seawater splitting for hydrogen production.