[Mo₂ S₁₂ ]^2- Complex as a Precursor for In-situ Generation of Molybdenum Sulfide Catalyst During the H₂ Evolution

For decades, the sulfido molybdenum complexes like [MoS₄ ]^2- , [Mo₂ S₁₂ ]^2- , [Mo₃ S₁₃ ]^2- have gained great attention because of their chemical versatility as well as their structural similarity to the edge-plan of the molybdenum disulfide (MoS₂ ) which shows promising catalytic ability for the H₂ generation. In this work, we report on the investigation of the dinuclear complex [Mo₂ S₁₂ ]^2- in both organic and aqueous solution. We demonstrate that [Mo₂ S₁₂ ]^2- is not intact during the H₂ evolution catalysis when it is assayed as a homogeneous catalyst in an electrolyte solution (e. g. in DMF or water solvent) nor when it is immobilized on an electrode surface (e. g. mesoporous carbon black). It transforms into the polymeric amorphous molybdenum sulfide [MoS] which subsequently acts as an actual catalyst. We discuss on the possible [Mo₂ S₁₂ ]^2- to [MoS] transformation mechanism by employing an arsenal of electrochemical analysis, spectroscopic analyses and microscopic analyses. Effects of the electrochemical operating conditions to the [Mo₂ S₁₂ ]^2- to [MoS] transformation as well as to the chemical nature and the catalytic performance of the [MoS] product are also emphasized.