N,P-Doped Molybdenum
Carbide Nanofibers for Efficient Hydrogen Production
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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 Mo<sub>2</sub>C 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 Mo<sub>2</sub>C/MoC interfaces and/or doping a proper
amount of electron-rich (such as N and P) dopants into the Mo<sub>2</sub>C 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 Mo<sub>2</sub>C/MoC nanofibers
(N,P-Mo<sub><i>x</i></sub>C NF) were prepared by pyrolysis
of phosphomolybdic ([PMo<sub>12</sub>O<sub>40</sub>]<sup>3–</sup>, PMo<sub>12</sub>) 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 Mo<sub>2</sub>C/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<sub><i>x</i></sub>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<sup>–2</sup> in 0.5 M H<sub>2</sub>SO<sub>4</sub> 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