Tracking Mo speciation in MoS2 under electrochemical conditions via operando grazing incidence XAS

Molybdenum disulfide (MoS2) is recognized as a promising alternative catalyst to platinum for the hydrogen evolution reaction (HER). Despite extensive research, the actual surface chemistry of MoS2 under real electrochemical conditions remains unclear and undermine its stability. Pourbaix diagrams predict diverse chemical states and surface transformations for MoS2 electrodes providing a background for the interpretation of stability data. However, Pourbaix diagram predictions have not been experimentally confirmed under operating conditions. Accordingly, we propose an in situ and operando X-ray absorption spectroscopy (XAS) to directly observe the molybdenum transformations, providing critical insights into the relationship between MoS2 chemical speciation and catalytic performance.