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

Two-dimensional transition-metal dichalcogenides (TMDs) are promising as efficient and earth-abundant electrocatalysts for the hydrogen evolution reaction (HER). However, only the edge and defect sites show HER catalytic properties, while the basal plane, which has nonexistent unsaturated sites, is inactive. Herein, we tackle the key challenge of increasing the number of electrocatalytic sites by using a general and facile method for the effective layer-by-layer exfoliation of TMDs in water by using an amino 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 exfoliating agent, the N of His can also serve as a doping agent to modulate the phase of single-layer TMDs nanosheets for greatly improving their electrocatalytic performance. The exfoliated single-layer MoSe₂nanosheets were doped with high surface/bulk ratio Pt nanoparticles (PtNPs) to form MoSe₂/PtNPs composites. Detailed electrochemical characterization shows that the MoSe₂/PtNPs composite (0.45 at % Pt) exhibited an excellent HER performance with an ultralow overpotential of 198 mV (@100 mA cm^-2), a Tafel slope of 24 mV/dec, and long-term electrochemical durability.