Direct Z-Scheme In₂O₃/In₂S₃ Heterojunction for Oxygen-Mediated Photocatalytic Hydrogen Production

Abstract

We demonstrate the viability of the In2O3/In2S3 heterojunction for efficient photocatalytic H2 evolution from a formaldehyde aqueous solution, which is an alternative renewable hydrogen source, in a direct Z-scheme manner under visible light without any electron mediator and cocatalyst. The optimal In2O3/In2S3 heterojunction shows a fast hydrogen evolution rate of 6.16 mmol·g–1·h–1, which is approximately 166 times and 6 times higher than that of pure In2O3 and pure In2S3, respectively. The superior photocatalytic activity of the In2O3/In2S3 heterojunction compared to single-component In2O3 and In2S3 is attributed to its appropriate band gap, enhanced charge separation, and transfer abilities, as attested by various spectroscopic characterization and photoelectrochemistry experiments. Among the different fabrication approaches, the sequential hydrothermal–calcination technique, which produces a hydrangea-like morphology, affords the most active In2O3/In2S3 heterojunction photocatalyst. Molecular O2 is found to play a key role in instigating the photocatalytic H2 evolution from formaldehyde oxidation as a catalytic electron scavenger, which is not consumed throughout the reaction.