(585d) Impact of Surfactant on Conductivity of Carbon Black Slurry Used in Flow Battery Applications

Formulations of carbon black slurry are critical in the efficient functioning of the flow battery as it impacts the conductivity of the slurry and sedimentation under storage. Sedimentation and adsorption studies have shown that at high nonionic surfactant concentrations (Triton X-100) where α (c_surf./c_CB) > 0.7, surfactants adsorb to the carbon black and saturate the surface. This leads to weakening of carbon black’s interparticle attraction and to a ‘catastrophic collapse’. To test how this attributes to the battery performance, conductivity of the slurry while flowing through the battery cell were measured via cyclic voltammetry. Matching the typical flow battery slurry formulation, we suspended carbon black in 1M H₂SO₄ and 0.55M ZnSO₄ with carbon black loading ranging from 1-8 vol% and α (ratio of nonionic surfactant concentration) ranging from 0-0.7. Our study reveals that while conductivity of the slurry increases at higher carbon black loadings, the loss of conductivity at the end of the cycle (10 hours) also increases. We attribute this to decrease in effective carbon black loadings over time as carbon black particles deposit to the tube walls and aggregate in the reservoir. At constant carbon black loading, the conductivity of the slurry decreases with increasing α until at α 0.7 in which the conductivity of the slurry is completely lost. We attribute this to carbon black particles losing its conductivity as surfactants that are adsorbed to the surface interrupt conductive pathways, and smaller particle stabilization which disrupt the electrical percolated network. Finally, we pre-process the particles in dry form with ball mill to measure how changes in particle size and surface area before suspending in aqueous medium has an impact on the slurry performance.