Computationally Guided Design to Accelerate Discovery of Doped β-Mo<inf>2</inf>C Catalysts toward Hydrogen Evolution Reaction

Low-cost molybdenum carbides have shown a rapid increase in their efficiency toward catalyzing the hydrogen evolution reaction (HER) owing to their structural flexibility for metal doping and nanostructure engineering. Herein, we employ first-principles quantum mechanical calculations in conjunction with thermodynamic analysis to shortlist ideal single-metal dopants that improve HER catalytic activity of β-Mo2C. We show that Ir or Ti substitutional doping at the Mo sites of β-Mo2C introduces thermoneutral hydrogen adsorption sites for HER, while the other elements in the first-row transition metals and Pt and Ag are not effective dopants for HER. To validate the computational results, we employ a microwave-assisted solvothermal method to synthesize metal-doped β-Mo2C nanoparticles (NPs) and assess their HER performance and structure using a suite of electrochemical and ex situ structural characterizations. From cyclic voltammetry, we find that the HER onset voltage of pristine β-Mo2C NPs decreases by more than 20% through impurity doping with Ti or Ir and is accompanied by a discernable increase in exchange current density. Transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM), and energy-dispersive X-ray spectroscopy (EDS) confirm that such an increase in HER activities originates from impurity doping and is not due to morphological or phase changes of the catalyst. The present study demonstrates that a combined and synergistic experimental and computational approach is indispensable to uncover the atomistic origins of catalytic activity and provide a rational design of the catalyst.