Layer-by-Layer Exfoliation of Transition-Metal Dichalcogenides byAmino Acid in Water for Promoting Hydrogen Evolution Reaction br

Two-dimensional transition-metal dichalcogenides(TMDs) are promising as efficient and earth-abundant electro-catalysts for the hydrogen evolution reaction (HER). However,only the edge and defect sites show HER catalytic properties, whilethe basal plane, which has nonexistent unsaturated sites, is inactive.Herein, we tackle the key challenge of increasing the number ofelectrocatalytic sites by using a general and facile method for theeffective layer-by-layer exfoliation of TMDs in water by using anamino acid, histidine (His), for the scalable production of single-layer TMDs nanosheets, which cannot be achieved using other common amino acids. Besides serving as an effective exfoliatingagent, the N ofHiscan also serve as a doping agent to modulate the phase of single-layer TMDs nanosheets for greatly improvingtheir electrocatalytic performance. The exfoliated single-layer MoSe2nanosheets were doped with high surface/bulk ratio Ptnanoparticles (PtNPs) to form MoSe2/PtNPs composites. Detailed electrochemical characterization shows that the MoSe2/PtNPscomposite (0.45 at % Pt) exhibited an excellent HER performance with an ultralow overpotential of 198 mV (@100 mA cm-2), aTafel slope of 24 mV/dec, and long-term electrochemical durability