Electrochemical Synthesis and Electrocatalytic Activity of Nano-Powders of Tungsten Carbide

Abstract

Tungsten carbide (WC) is commercially one of the oldest and well-investigated powder metallurgy product, which has a simple hexagonal crystal structure. This compound has been well known for its exceptional hardness and wear/erosion resistance, which make him practically irreplaceable in the production of cemented carbide. Tungsten carbide (WC) has an important advantage – a unique to resist very strong catalytic poisons, such as carbon monoxide, hydrocarbons, and hydrogen sulfide, but its catalytic activity is much less than that of platinum metal. How to improve its catalytic activity is the key problem for realization in practical usage and replacement of platinum catalyst in catalysis [1, 2]. Nanocrystalline powders of tungsten carbides play an important role in improving processes of chemical technology, where they can be used for PEM fuel cell application, methanol electrooxidation [3, 4] and so on. Therefore the preparation of nano-sized powders of tungsten carbide acquires great significance. Today, there are many modern methods of producing nano-scale tungsten carbides. High-temperature electrochemical synthesis (HTES) in molten salts occupies a prominent place in solving this problem because of its advantages: mild synthesis conditions; the simplicity of hardware implementation; the possibility of synthesis control by the electrolysis modes; the low power costs for electrolysis; the use of cheap precursors; easy introduction of dopant during the synthesis; product monodispersity. HTES has great possibilities to produce doped and undoped tungsten carbides in one step in the form of films and ultra-fine powders. The compositions of electrolyte bathes for tungsten carbides synthesis were determined based on literature analysis and own experimental data [5]. Electrochemical study of partial and joint electroreduction of synthesis components (tungsten and carbon) from chloride-oxide, chloride-fluoride-oxide melts under CO2 pressure at 750 °C was studied by cyclic voltammetry. Electrolysis conditions for producing of nano-scale composites based on tungsten carbides with carbon nanomaterials (CNM) and metals were determined. Characterization of produced deposits was made by XRD, ED, SEM, TEM, BET, Raman spectroscopy methods. Present investigations have shown that it is possible to produce the mixtures of nano-sized powders of composites (WC and W2C) with CNM (carbon nanotubes, nanofibers), metals (Co, Fe, Ni, Pt) of different composition, single crystals of hexagonal α-WC with the specific surface up to 40 m2/g. Produced materials were tested as electrode material in the reaction of hydrogen electroreduction in the solution of H2SO4and have shown high electrocatalytic characteristics. References R.B. Levy and M. Boudart, Science, 181, 547-549 (1973).G. Li et al., Microporous and Mesoporous Material, 85, 234–240 (2005).V. M. Nikolic et al., Journal of hydrogen energy, 39, 11175-11185 (2014).Y. Wang et al., Journal of Power Source, 200, 8–13 (2012).I. A. Novoselova et al., Metallofizika i noveiishie tekhnologii, 36, 491-508(2014).