Abstract
Durability and applicability of various types of tungsten bronzes, NaxWO3, (Na-K)xWO3, and (Na-Cs)xWO3, for the inert electrode or catalytic electrode were examined in chloride-containing acidic media by means of polarization measurement, electronmicroscopic observation, activation by noble metal and chemical analysis. Tungsten bronzes of the composition with x ranging from 0.5 to 0.9 were synthetized by fused salt electrolysis of mixtures of Na2WO4+WO3 with or without addition of KOH and CsOH. Cyclic linear sweep voltammgrams of tungsten bronzes in saturated Na2SO4 solution (pH=0) show that the anodic current begins to flow at the potential of ca. 1.5V SCE for sodium tungsten bronze (x=0.91), while practically no current flows up to 4.0V (SCE) for Na-K or Na-Cs tungsten bronzes. These mixed tungsten bronzes are thus very resistant against anodic polarization. Addition of NaCl to the media increased anodic polarization and shifted the curve to more noble direction. Tungsten bronzes activated by RuCl3 treatment show anodic polarization behavior completely different from that mentioned above. Anodic current flows at almost their reversible potentials of Cl2/Cl- or O2/H2O redox systems. Electronmicroscopic observation of the surface of tungsten bronzes after prolonged electrolysis in chloride-containing media reveals a trace of corrosion, which is also confirmed by colorimetric analysis of dissolved tungsten in the electrolyte used for extended time.
