EFFECT OF ELECTROCHEMICAL SYNTHESIS CONDITIONS ON THE COMPOSITION, STRUCTURE, AND MORPHOLOGY OF TUNGSTEN CARBIDE POWDERS

Abstract

High-temperature electrochemical synthesis (HTES) in molten salts is highly promising among the up-to-date methods for the production of carbide powders. Ultrafine composite powders based on tungsten carbides (WC|C, WC|C|Pt, W₂C|WC, and W₂C|W) were synthesized using the HTES method in electrolytic baths of different chemical composition under various synthesis conditions (cathode current density, CO₂ pressure in the electrolyzer, temperature, cathode material). Composite powders WC|C (up to 3 wt.% free carbon) with a WC particle size of 20-30 nm were produced from electrolytic baths of the following compositions: Na, K|Cl (1 : 1)-Na₂W₂O₇ (6.4 wt.%)-CO₂ (1.25 MPa) and Na, K|Cl (1 : 1)-Na₂WO₄ (12.0 wt.%)-NaPO₃ (0.7 wt. %)-CO₂ (1.25 MPa) at a temperature of 750 °С. When the CO₂ pressure is reduced to 0.75 MPa, composite powders of W₂C|WC tungsten carbides are produced at the cathode. The ratio of carbide phases in the composite depends on the initial concentration of tungsten salt in the electrolyte and the CO₂ gas pressure in the electrolyzer. The addition of Li₂CO₃ (4.5 wt.%) to the electrolytic salt mixture decreases the size of tungsten carbide particles to 10 nm, changes their morphology, and increases the free carbon content in the composite up to 5 wt.%. The specific surface area of the powder increases by 4-7 times (from 20-35 to 140 m²/g). The use of platinum cathodes makes it possible to modify the composition of the resulting product with fine platinum particles. The HTES method is shown to be a promising one for producing tungsten carbide powders with the properties that allow them to be used as electrocatalysts in the hydrogen evolution reaction. For the WCl|C composite powders produced from the Na, K|Cl-Na₂W₂O₇-Li₂CO₃-CO₂ system, the potential of hydrogen evolution was -0.02 V relative to the normal hydrogen electrode, the overpotential η at a current density of 10 mA/cm² is -110 mV, the exchange current is 7.0• 10^–4 A/cm², and the Tafel slope is -85 mV/dec.