Plasma electrochemistry: voltammetry in a flame plasma electrolyte

In this paper we present detailed dynamic electrochemical measurements in a flame plasma electrolyte in the presence of tungsten oxide salts. Defined reproducible redox processes are measured using conventional cyclic voltammetry in an operational potential window between 1 and −9 V. This wide potential window is possible due to the absence of solvent and its associated limits due to solvent electrolysis at high over potentials. The measurements were enabled through the development of a new reference electrode, composed of yttria stabilised zirconia (YSZ) which maintains a stable potential at 1100 K. In this paper we focus on developing a phenomenological understanding of electron transfer at the solid–gas interface, using cyclic voltammetry. The effect of working electrode surface area and material, as well as potential scan rate on the voltammetric redox features is presented. We discuss the physical origin of the observed Faradaic current peaks measured in a flame plasma electrolyte, and propose a simple model to describe the redox processes occurring. We conclude that redox processes at the solid–gas interface are actually similar to the analogous processes at the solid–liquid interface described by conventional electrochemical theory; the departures are mainly due to the mass transport processes that dominate in the gas phase. We associate migration effects with the total absence of any oxidation processes.