Session: General Catalysis:

Electrocatalytic reactions offer alternative routes for the conversion and storage of energy. For instance, the electrocatalytic reduction of carbon dioxide could lead to energy-rich syngas, methanol, or even hydrocarbons. Layered transition metal dichalcogenide nanomaterials, such as MoS₂, have emerged as electrocatalysts towards CO₂ reduction with high efficiency and low overpotentials. However, the underlying chemical and electronic states defining the catalytic activity have not yet been completely defined. These key states can be probed for both metals and ligands in selected MX₂ (M=W, Mo; X=S, Se) using synchrotron-based X-ray absorption spectroscopy (XAS). In the recent work we performed in-situ XAS measurements at Mo K-edge and S K-edge for MoS₂ nanosheets. Measurements at sulfur K-edge showed drastic changes at the pre-edge and edge indicating changes in number of available occupied states and Z_eff respectively, on the other hand Mo K-edge showed only a slight shift. Metal d-states are found to be the active site for the catalysis, ligand K-edge presents a better method to examine catalytic processes as the pre-edge reflects a transition to metal-ligand hybridized states, hence pre-edge intensity and position gives insight into the active metal d states. Given the vast compositional space of metal and ligand for MX₂, the knowledge of how d-state activity will serve to pave the way to a better study of metal and chalcogenide combinations to improve the electrocatalytic performance.