Measurements of the Electric Conductivity of MWCNT Suspension Electrodes with Varying Potassium Bromide Electrolyte Ionic Strength

Abstract

Suspension electrodes are under intense investigation due to their use in electrochemical systems such as redox flow batteries, capacitive deionization cells and flow supercapacitors. They provide novel functionalities not available with static electrodes, such as spatial power-energy decoupling for flow hybrid batteries, and continuous water desalination by capacitive deionization cells. Yet their electric conductivity is low relative to static electrodes made of the same material. It was previously found that suspension electrodes employing multi-walled carbon nanotubes (MWCNTs) demonstrate among the highest electric conductivities in deionized water, yet the effect of electrolyte ionic strength on their electric conductivity of was not elucidated. We here measure the electric conductivity of MWCNTs suspensions in a KBr electrolyte under flow using two- and four-electrode setups with alternative and direct current (DC) techniques. Only the two-electrode DC technique measured solely electronic conductivity, while all the other techniques measured the combined ionic and electronic conductivity. The electronic conductivity increased with MWCNT concentration in accordance with percolation theory power law. It increased also with electrolyte concentration by one to two orders of magnitude, with the critical exponent value transitioning from ∼2 to ∼1 with the increasing KBr concentration, which was explained in terms of the Derjaguin-Landau-Verwey-Overbeek theory.