Monitoring transformations of catalytic active states in photocathodes based on MoS${}_x$ layers on CuInS${}_2$ using in operando Raman spectroscopy

The electrochemical activation of CuInS${}_2$/MoS${}_x$ for photoelectrochemical (PEC) H${}_2$ production was revealed for the first time through in operando Raman spectroscopy. During the activation process, the initial metallic MoS${}_x$ phase was transformed to semiconducting MoS${}_x$, which facilitates charge carrier transfer between CuInS${}_2$ and MoS${}_x$. Ex situ X-ray photoelectron spectroscopy and Raman spectroscopy suggest the existence of MoO${}_3$ after the activation process. However, apart from contradicting these results, in operando Raman spectroscopy revealed some of the intermediate steps of the activation process. (© 2022 Wiley‐VCH GmbH)