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.