Correlation Between Electronic Properties and Surface Reactions of Doped and Undoped MoS2 Films for Hydrogen Production

MoS₂ is gaining more and more importance in the field of energy applications. In particular, it is well known that MoS₂ has interesting hydrogen evolution reaction (HER) properties for electrochemical water splitting. H 1s - S 3p orbital overlap can be modified by doping MoS₂ with transition metal ions in order to tune H adsorption and thus HER activity. Among these, Co and Mn have shown great potential. To address these issues, we used a multipurpose pulsed-laser deposition (PLD) facility directly connected to the distribution chamber of the synchrotron beamline to produce and characterize MoS₂ films grown on different substrates, with different thickness and doped with Co and Mn. The in-situ transfer technology allowed measurements by surface sensitive X-ray photoemission (XPS) and X-ray absorption (XAS) techniques avoiding any surface contamination that may affect the sample properties. We observed that the MoS₂ interacts with the substrate at the interface which affects the electronic properties. In-operando XAS characterizations were performed with different gas environment on undoped and doped MoS₂ films in a reaction cell. The results demonstrate that the electronic structure is modified by reduction or oxidation atmospheres and are correlated with the electrocatalytic performance for HER, investigated by polarization curves. The measurements show a very high stability after many cycles and a decrease of the overpotential for hydrogen evolution in doped samples. Our study allows to understand the chemical environment, atomic response and changes in the electronic state during the absorption and desorption processes.