Experimental and DFT studies of flower-like Ni-doped Mo₂C on carbon fiber paper: A highly efficient and robust HER electrocatalyst modulated by Ni(NO₃)₂ concentration

Developing highly efficient and stable non-precious metal catalysts for water splitting is urgently required. In this work, we report a facile one-step molten salt method for the preparation of self-supporting Ni-doped Mo₂C on carbon fiber paper (Ni-Mo₂C_CB/CFP) for hydrogen evolution reaction (HER). The effects of nickel nitrate concentration on the phase composition, morphology, and electrocatalytic HER performance of Ni-doped Mo₂C@CFP electrocatalysts was investigated. With the continuous increase of Ni(NO₃)₂ concentration, the morphology of Mo₂C gradually changes from granular to flower-like, providing larger specific surface area and more active sites. Doping nickel (Ni) into the crystal lattice of Mo₂C largely reduces the impedance of the electrocatalysts and enhances their electrocatalytic activity. The as-developed Mo₂C-3 M Ni(NO₃)₂/CFP electrocatalyst exhibits high catalytic activity with a small overpotential of 56 mV at a current density of 10 mA·cm^-2. This catalyst has a fast HER kinetics, as demonstrated by a very small Tafel slope of 27.4 mV·dec^-1, and persistent long-term stability. A further higher Ni concentration had an adverse effect on the electrocatalytic performance. Density functional theory (DFT) calculations further verified the experimental results. Ni doping could reduce the binding energy of Mo-H, facilitating the desorption of the adsorbed hydrogen (H_ads) on the surface, thereby improving the intrinsic catalytic activity of Ni-doped Mo₂C-based catalysts. Nevertheless, excessive Ni doping would inhibit the catalytic activity of the electrocatalysts. This work not only provides a simple strategy for the facile preparation of non-precious metal electrocatalysts with high catalytic activity, but also unveils the influence mechanism of the Ni doping concentration on the HER performance of the electrocatalysts from the theoretical perspective.