In situ photodeposition of cobalt nanoparticles onto ZnIn2S4 enhancing H2 production under visible light

• Flower-like ZnIn 2 S 4 photodeposited in situ with metallic Co. • Eleven-fold increased activity obtained for H 2 production under visible light. • The composite was more active than the Co or Pt ex situ deposited ZnIn 2 S 4 . • Metallic Co acted as an electron sink and cocatalyst for proton reduction. Hydrogen production via semiconductor photocatalysis has been the subject of extensive research over the past four decades. Recently, much work has focused on ZnIn 2 S 4 (ZIS), due to its ability to initiate water splitting under visible light. In this work, we report a 11-fold increase of H 2 production via Co 2+ addition (equivalent to 4 wt% Co on ZIS). Reaction was conducted under a 420 nm LED lamp in presence of triethanolamine. During the photocatalytic reaction, Co 2+ ions were quickly reduced into metallic Co. A five-repeat test showed that the in situ Co 0 nanoparticles was relatively stable. By contrast, 4 wt% Co 0 ex situ deposited ZIS via a (photo)chemical or physical route had a low activity, due to partial oxidation of Co 0 into less active CoO x in air. Impressively, all Co - deposited ZIS samples were at least 5 times more active than 0.5 wt% Pt-loaded g-C 3 N 4 , CdS, ZnS, and In 2 S 3 , respectively. Through photoluminescence and (photo)electrochemical measurement, a plausible mechanism is proposed, involving electron transfer from ZIS to Co species, followed by proton reduction. This work shows that cobalt nanoparticles are excellent cocatalysts for H 2 production on ZIS under visible light, but they are better produced in situ without involvement of O 2 . In situ photodeposition of cobalt nanoparticles onto ZnIn 2 S 4 enhancing H 2 production under visible light.