UBC Theses and Dissertations

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UBC Theses and Dissertations

Development of a polyiodide aqueous/non-aqueous flow battery Jameson, Alexander


Redox flow batteries are considered to be one of the most realistic candidates for stationary energy storage applications in the range of kW/kWh up to tens of MW/MWh. The recently proposed zinc-iodine flow battery (ZIFB) is among the most promising flow batteries for such applications, having achieved the highest reported energy densities of any aqueous flow batteries to date. However, the energy efficiency of the ZIFB during cycling is still very low due to the thick iodine film that forms during charge and activation overpotentials associated with the iodine electrode reactions. In this thesis, I first investigated the effect of organic cosolvent additives and operating conditions on the ZIFB performance. The acetonitrile (5 vol%) cosolvent showed the most significant improvement to charge-discharge performance, increasing the energy efficiency from 59.4% to 70.0%. Cosolvents that were strongly protophilic preferentially interacted with Zn²⁺ over I₂ leading to the formation of insulative iodine deposits on the positive electrode during charge, but constructing a ZIFB with a posolyte absent of Zn²⁺ with 5 vol% DMF was able to increase the energy efficiency from 59% to 65.4% while maintaining the iodine dissolved in solution. I then studied the kinetics of the iodide redox reactions on various carbonaceous materials (carbon blacks and carbon nanotubes) for the purpose of being incorporated as a catalyst layer (CL) into the graphite felt (GF) positive electrode of the ZIFB. The Ketjenblack EC-300J carbon black performed the best out of the electrode materials studied due to a pore network capable of encapsulating iodine and promoting its adsorption on the pore walls. A ZIFB constructed with a Ketjenblack EC-300J CL on the GF surface adjacent to the battery separator increased the energy efficiency (at 40 mA/cm⁻²) from 63% to 76% and the discharge power density from 39.1 mW/cm⁻² to 44.1 mW/cm⁻² compared to the pristine GF without any CL. Addition of 5 vol% cosolvent further increased the operating efficiency of the ZIFB to 80.3% and demonstrates the synergic effect of the improved electrolyte and electrode compositions.

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