Uniformly Decorated Molybdenum Carbide/Nitride Nanostructures on Biomass Templates for Hydrogen Evolution Reaction Applications

Abstract

Natural fibrils derived from biomass were used as a template to synthesize uniformly decorated nanoparticles (10-12 nm) of molybdenum carbide (Mo₂C) and molybdenum nitride (Mo₂N) supported on carbon. The nanoparticles have been synthesized through the carburization and nitridation of molybdenum on cotton fibrils, using a high-temperature solid-state reaction. The catalyst exhibits an onset potential of 110 mV and an overpotential of 167 mV to derive a cathodic current density of 10 mA cm^-2. The electrocatalyst also demonstrates excellent long-term durability of more than 2500 cycles in acidic media with a Tafel slope value of 62 mV dec^-1.

Scheme 1. Illustrating the Synthesis of the Carbon-Supported Mo₂C/Mo₂N Nanohybrid Electrocatalyst from the Biomass Template and Its Application in Hydrogen Evolution Reaction

Figure 1

Structural characterization (a) PXRD typically shows formation of both Mo₂C–Mo₂N phases and (b) compositional measurements: Rietveld analysis of the catalyst shows a composition 59.12 and 40.88% of Mo₂C and Mo₂N, respectively.

Figure 2

Morphology characterization: scanning electron microscopy (a) of the as-obtained MoCot catalyst and corresponding elemental mapping of the nanostructure showing the (b) carbon, (c) molybdenum, and (d) nitrogen elements that illustrate the uniform distribution of these on the fibril template. (e) SEM image shows the collective distribution of different elements (Mo, C, and N) on the fibril structure.

Figure 3

Microscopic characterization of the MoCot catalyst: a transmission electron microscopic image of MoCot at (a) medium (b) low and inset-(c) high magnification: showing the fringe width 0.26 and 0.24 nm consistent with the (100) and (111) planes of Mo₂C and Mo₂N nanocrystals.

Figure 4

XPS of the MoCot catalyst: wide-scan survey spectra (a) and HR spectra of Mo 3d (b), C 1s (c), and N 1s (d) electron: experimental data (dotted curve) and fitting results (solid curve). The peaks are assigned by oxidation states of different elements with their corresponding binding energy.

Figure 5

Electrochemical measurements of specific electrocatalysts for hydrogen evolution in 0.5 M H₂SO₄ acidic medium. (a) Polarization curves (iR-corrected) of MoCot compared with the other electrode (b) the corresponding Tafel plots derived from the curve (c) EIS Nyquist plot (with corresponding equivalent circuit) of the electrode@50 mV, @150 mV, and @250 mV (inset shows zoomed Nyquist plot of the electrode @50 mV) (d) figure shows the LSV stability curve at 1st, 2500th, and 3000th cycle (inset shows the potential testing at constant current density 10, 20, and 30 mA cm^–2).