Atomic-Scale Intercalation of Graphene Layers into MoSe₂ Nanoflower Sheets as a Highly Efficient Catalyst for Hydrogen Evolution Reaction

MoSe₂ is an efficient catalyst for the hydrogen evolution reaction (HER) and can potentially replace conventional catalysts composed of noble metals such as Pt. The HER activity of MoSe₂ originates mainly from the edge sites of Se atoms, but the low concentration of Se exposed to the electrolyte hampers the performance. Hence, activating a larger portion of the basal plane of Se atoms is an effective way to improve the HER properties. Herein, a 3D hierarchic nanoflower structure comprising MoSe₂ with atomic-scale interlayered graphene layers in the nanosheets is designed and prepared to improve the electron conductivity and decrease the proportions of inactive basal planes. Raman scattering, transmission electron microscopy, and energy-dispersive X-ray spectroscopy verify effective insertion of graphene layers in MoSe₂, and the HER characteristics are improved as exemplified by a small overpotential of 175 mV at 10 mA cm^-2, small Tafel slope of 58 mV dec^-1, and excellent durability with only small deterioration of 10 mV after 10,000 cycles. First-principles density functional theory and finite element method calculations corroborate the experimental results, revealing better conductivity and hydrogen adsorption/desorption ability rendered by the graphene layers. Our results reveal a new and effective strategy to optimize the structure and composition and reduce the hydrogen adsorption energy barrier in the pursuit of high-efficiency non-noble metal catalysts.