Hydrogen is a promising alternative to fossil fuels and is a versatile energy carrier for energy storage, transportation and distribution. With the wide availability and the decreasing cost of renewable energy, electrochemical water electrolysis powered by renewable energy is a feasible route to generating clean hydrogen. Pt is the most efficient catalyst for water electrolysis, but it is a rare and expensive metal. Pt single-atom catalysts (SACs) supported on two-dimensional layered materials have potential as electrodes for water electrolysis by distributing atomistic catalysts on high-surface-area support. This study investigated Pt SACs supported on MoSe₂ transition metal dichalcogenide (TMD) for hydrogen evolution reaction (HER) in both alkaline and acidic conditions. The effects of electronic metal support interaction (EMSI) between SACs and TMD support on electronic properties of SACs and their HER activity were investigated. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was employed to study the binding of CO probe molecules onto active sites present in Pt SACs. A top-down synthesis approach produced highly exfoliated MoSe₂ nanosheets using a greener liquid-phase exfoliation. The atomistic dispersion of Pt SAC was accomplished by exposing the mixture of the exfoliated MoSe₂ and a Pt precursor to the short pulse of Xe flash lamp. This study demonstrates an outstanding catalytic activity of Pt SAC for HER in both acidic and alkaline conditions. Pt SAC on MoSe₂ exhibits a low overpotential of 84 mV (vs. RHE) at the current of 10 mAcm^-2in alkaline condition and 138 mV (vs. RHE) at 10 mAcm^-2in acidic condition. Compared to commercial Pt/C, Pt-SAC/MoSe₂ exhibits a 14-fold and 20-fold increase in mass activity in alkaline and acidic electrolytes, respectively. In DRIFTS spectra, there are two dominant peaks in 2060 cm^-1 and 2104 cm^-1, which are assigned to Pt nanoclusters and Pt single atoms respectively. There is no peak for bridge-bound CO molecules in the 1800 – 1900 cm^-1 range, reflecting a very different nature of Pt-SAC from Pt nanoparticles. DRIFTS spectra of Pt SACs on WS₂show the blue-shift of the two peaks to 2065 cm^-1 and 2115 cm^-1, indicating the adsorption energy of CO are changed due to the EMSI modulation. This study provides insights on developing novel catalysts by controlling electronic interfaces between SACs and support material, applicable for clean hydrogen production and other electrochemical processes.

Md Tawabur Rahman

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