ELECTROREDUCTION OF DITUNGSTATE AND CARBONATE ANIONS IN CHLORIDE MELT

Abstract

Electrocatalysis is one of the actively developing fields of application of tungsten carbides. For the synthesis of catalytically active carbides (materials with a large specific surface area, small particle size and structural defects) a large number of different technologies are being developed in the world. The method of high-temperature electrochemical synthesis is promising one. For its successful realization, it is necessary to study in detail the electrochemical behavior of each carbide component (tungsten and carbon) and the features of their partial and joint discharge. The aim of this paper is a voltammetric study of the partial and joint electroreduction of Na2W2O7 and Li2CO3 in molten NaCl–KCl electrolyte under CO2 pressure at a temperature of 750 °C. As a result of research, it was found that in the system Na,K|Cl–Na2W2O7–Li2CO3–CO2 joint reduction of tungsten carbide synthesis components occurs from lithium complexes of tungstate (LixWO4)2-x and carbonate- (LixCO3)2-x anions at potentials -1.65 – -1.8 V. Introduction of СО2 into the system (creation of its excess pressure in the cell) is necessary for the binding of oxide anions O2-, released during the discharge of anionic complexes, into a carbonate complex. The released oxide anion in the near-electrode layer inhibits the cathodic process. Also, a necessary condition for the sustainability production of tungsten monocarbide WC is the presence of free carbon, which is formed during the decomposition of CO2. Nanosized composites of tungsten carbides with free carbon WC/C (5 wt%) were obtained by potentiostatic electrolysis at a potential of -1.8 V as a cathode product. The properties of the obtained compounds were analyzed by XRD, SEM, BET, and Raman spectroscopy. Tungsten carbide has a particle size of ~ 10 nm and consists of hollow spherical structures. The synthesized composite is mesoporous material with a specific surface area of ~ 140 m2/g. The properties of the synthesized compo­site, namely: structural defects, the presence of free carbon, spherical morphology, nanometer size and high specific surface area, make it possible to use it as an effective electrocatalyst, for example, in the reaction of hydrogen evolution in acidic aqueous solutions.