Structure and electrochemical property of amorphous molybdenum selenide H₂-evolving catalysts prepared by a solvothermal synthesis

Amorphous molybdenum selenide nanoparticles were synthesized by the solvothermal treatment of Mo(CO)₆ and Se in dimethylformamide. By varying the Mo(CO)₆ over Se molar ratio, we obtained a family of MoSe nanoparticles having comparable morphology but different chemical composition. Using a combination of experimental analyses (e.g. XRD, ICP-MS, Raman, XPS)and DFT theoretical calculation, we found that the structure of MoSe was close to that of the amorphous molybdenum sulfide analogous but not that of MoSe₂ layers. The MoSe was found to consist of [Mo₃Se₁₃]^2- cluster within its structure together with some structural defects. Thanks to its less ordered structure, the MoSe can be activated by several chemical and electrochemical treatment resulting in a catalytic enhancement. A treatment with fuming HCl resulted in generation of a novel catalyst displaying 1.4 time higher catalytic current. Remarkably, a treatment with reflux NaOH solution resulted in generation of a component being soluble in water and displaying catalytic H₂-evolving activity at a moderate onset overpotential of ca. 200 mV, being one of the most attractives homogeneous catalysts in water.