Phosphorus-doped In2S3 with rich sulfur vacancies toward efficient photocatalytic hydrogen production from formaldehyde solution

Abstract

Developing high-efficiency and low-cost hydrogen production catalysts is essential to alleviate environmental problems. Indium sulfide is an effective catalyst for photocatalytic water-splitting reactions to produce hydrogen (H₂). However, the high hole–electron recombination rate of indium-based nanoparticles restricts their practical applications. To overcome this, we fabricated a P-doped In₂S₃ catalyst with S vacancies through a calcination method. When the P-doping magnitude is 0.4 wt%, the resultant catalyst reports the optimal photo-catalytic activity (3853.4 μmol h⁻¹ g⁻¹) in the presence of formaldehyde, molecular oxygen and visible light illumination, which is more than 6.3 times higher than that of pure In₂S₃ (603.3 μmol h⁻¹ g⁻¹). The synergetic effect of sulfur vacancies and the P-doping can lead to a narrower band gap in the In₂S₃ nanoparticles, thereby promoting photogenerated hole–electron pair separation and photo-catalytic hydrogen production ability. We find that molecular O₂ plays a crucial role in promoting the oxidation of formaldehyde to produce photo-catalytic H₂. During the entire reaction process, molecular oxygen will not be consumed (similar to a cocatalyst). Benefiting from the enhanced charge separation and transfer processes, the P-doped In₂S₃ with S vacancies exhibits excellent photo-catalytic hydrogen production performance from formaldehyde solution.