Synthesis and Characterization of Nanostructured Niobium and Molybdenum Nitrides by a Two-Step Transition Metal Halide Approach

Abstract

Nanosized NbN x (1.644x41.33) and MoN x (1.324x40.77) crystallites were synthesized at a relatively low temperature (! 6001C) through ammonolysis and nitridation of the corresponding metal chlorides. The ammonolysis reaction in anhydrous chloroform at room temperature and the nitridation mechanism during subsequent heat treatment was investigated using Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric (TG), and mass spectroscopy analysis. The effects of the synthesis parameters on the stoichiometry, structure, specific surface area, density, and electronic conductivity of the final nitrides were studied using TGA, XRD, N 2 adsorption, high-resolution transmission microscopy, helium pycnometry, and four-point probe technique. Preliminary electrochemical responses of the obtained nitrides were studied using cyclic voltammetry to explore their possible use as electrochemical capacitors.

Redox supercapacitor performance of nanocrystalline molybdenum nitrides obtained by ammonolysis of chloride- and amide-derived precursors

“…In samples made at 600 °C and above our capacitances are slightly lower than those previously reported by Choi and Kumta for similar samples cycled in aqueous KOH (111 F g -1 at 2 mV s -1 from a γ-Mo 2 N sample synthesised at 600 °C [23]), although they did report a 40% drop in capacity during cycling. At slow scan rates our highest surface area samples of δ 1 -MoN produced at 500 °C approach 200 F g -1 , comparable with the highest values reported for molybdenum nitrides in the literature [18][19][20][21][22][23][24]. These capacitances fall by around 50% at the fastest scan rates measured, 100 mV s -1 .…”

“…3. Choi and Kumta found γ-Mo 2 N from a similar polymer between 600 and 800 °C [23]. Removal of the NH 4 Cl by-product by sublimation onto aluminium foil was found to be effective, no ammonium chloride reflections were observed.…”

“…Later the same group used temperature programmed reduction of MoO 3 to produce 16 nm γ-MoN crystallites and found both a high specific capacitance (172 F g -1 ) and an increased potential window (1.1 V) [22]. Choi et al reacted MoCl 5 in chloroform with ammonia then heated the precipitate in ammonia to make γ-MoN with ~110 F g -1 capacity at 2 mV s -1 but poorer performance at faster rates and ~40% loss of capacity over 500 cycles [23]. Recently Lee et al used ammonolysis of single crystal MoO 3 nanowires to make mesoporous Mo 3 N 2 wires which exhibited higher capacities than the same material made from commercial MoO 3 and maintained a capacity over 200 F g -1 even at a charge/discharge rate of 200 mV s -1 [24].…”

Molybdenum Nitride Films: Crystal Structures, Synthesis, Mechanical, Electrical and Some Other Properties

“…The good electronic conductivity as well as the moderately high surface area makes the molybdenum nitrides potential candidates for supercapacitors electrodes [61]. Nanostructured materials are especially interesting for such applications.…”

“…Nanostructured materials are especially interesting for such applications. MoNx powders (0.77 < x < 1.32) with a crystallite size of 9 nm, a specific surface area of 49 m display a specific capacitance value equal to 111 Fg −1 [61]. Among all catalyzed reactions, the hydrogen evolution reaction (HER) will have an increasing importance in the future because it is a carbon free alternative for hydrogen generation.…”