Manganese Doping of MoSe₂ Promotes Active Defect Sites for Hydrogen Evolution

Transition-metal dichalcogenides (TMDs) are being widely pursued as inexpensive, earth-abundant substitutes for precious-metal catalysts in technologically important reactions such as electrochemical hydrogen evolution reaction (HER). However, the relatively high onset potentials of TMDs relative to Pt remain a persistent challenge in widespread adoption of these materials. Here, we demonstrate a one-pot synthesis approach for substitutional Mn-doping of MoSe₂ nanoflowers to achieve appreciable reduction in the overpotential for HER along with a substantial improvement in the charge-transfer kinetics. Electron microscopy and elemental characterization of our samples show that the MoSe₂ nanoflowers retain their structural integrity without any evidence for dopant clustering, thus confirming true substitutional doping of the catalyst. Complementary density functional theory calculations reveal that the substitutional Mn-dopants act as promoters, rather than enhanced active sites, for the formation of Se-vacancies in MoSe₂ that are known to be catalytically active for HER. Our work advances possible strategies for activating MoSe₂ and similar TMDs by the use of substitutional dopants, not for their inherent activity, but as promoters of active chalcogen vacancies.