N,P-Doped Molybdenum Carbide Nanofibers for Efficient Hydrogen Production

Abstract

Molybdenum (Mo) carbide-based electrocatalysts are considered promising candidates to replace Pt-based materials toward the hydrogen evolution reaction (HER). Among different crystal phases of Mo carbides, although Mo₂C exhibits the highest catalytic performance, the activity is still restricted by the strong Mo–H bonding. To weaken the strong Mo–H bonding, creating abundant Mo₂C/MoC interfaces and/or doping a proper amount of electron-rich (such as N and P) dopants into the Mo₂C crystal lattice are effective because of the electron transfer from Mo to surrounding C in carbides and/or N/P dopants. In addition, Mo carbides with well-defined nanostructures, such as one-dimensional nanostructure, are desirable to achieve abundant catalytic active sites. Herein, well-defined N,P-codoped Mo₂C/MoC nanofibers (N,P-Mo_<i>x</i>C NF) were prepared by pyrolysis of phosphomolybdic ([PMo₁₂O₄₀]^3–, PMo₁₂) acid-doped polyaniline nanofibers at 900 °C under an Ar atmosphere, in which the hybrid polymeric precursor was synthesized via a facile interfacial polymerization method. The experimental results indicate that the judicious choice of pyrolysis temperature is essential for creating abundant Mo₂C/MoC interfaces and regulating the N,P-doping level in both Mo carbides and carbon matrixes, which leads to optimized electronic properties for accelerating HER kinetics. As a result, N,P-Mo_<i>x</i>C NF exhibits excellent HER catalytic activity in both acidic and alkaline media. It requires an overpotential of only 107 and 135 mV to reach a current density of 10 mA cm^–2 in 0.5 M H₂SO₄ and 1 M KOH, respectively, which is comparable and even superior to the best of Mo carbide-based electrocatalysts and other noble metal-free electrocatalysts