Increasing H2 production on ZnxInySz under visible light via composition modulation and CoS catalysis

Abstract

Zinc indium sulfide materials (Zn_xIn₂S_x+3, x = 1–5) are known to initiate H₂ production under visible light, among which ZnIn₂S₄ is the most active with triethanolamine (TEOA) as the sacrificial agent. Herein a new series of ZIS (ZnIn₆S₁₀, ZnIn₂S₄, Zn₄In₂S₇, Zn₆In₂S₉, and Zn₁₁In₂S₁₄) have been synthesized via a hydrothermal method. For H₂ production in the presence of TEOA under a 420 nm LED lamp, Zn₆In₂S₉ was not only the most active among the ZIS materials, but also much more active than ZnS, In₂S₃, and CdS. With the increase of the Zn content, ZIS had an increased band gap, but a negatively shifted flat band potential in aqueous solution. Because of that, Zn₆In₂S₉ was more active than others. Furthermore, after 20 wt% CoS loading, ZIS had a 2.9–6.8 fold increased activity, in terms of the amount of H₂ evolved in 2 h. Through a measurement of proton reduction, open circuit potential, and charge transfer resistance, a possible mechanism is proposed, involving hole transfer from ZIS to CoS, followed by increased TEOA oxidation and proton reduction. This work provides a simple way to modulate the performance of metal chalcogenides for water splitting under visible light.