Ultramicroelectrode Based Approaches to Diagnose Utility of Redox Electrolytes in Flow Batteries

The proposed redox electrolyte system, concentrated solutions of Keggin type silicotungstic acid (H4SiW12O40), have been tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid (H4SiW12O40) acts as proton conductors, and undergoes fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing ultramicrodisk electrodes have been adapted to characterization of redox electrolytes. Combination of two parallel ultramicroelectrode-based experiments performed under radial (long-term experiment; e.g., slow scan rate) and linear (short-term experiment; e.g., fast scan rate) diffusion conditions permits determination of both effective concentration of redox centers and transport (diffusion) coefficient parameters, which are crucial to evaluation of the utility of a redox electrolyte for charge storage.