A positively charged, diffusion resistant, bispyridinylidene derivative as an anolyte for organic redox flow batteries

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University of New Brunswick


Redox flow batteries represent a leading technology for large scale energy storage, which is necessary as the use of renewable energy becomes more important. Organic redox flow batteries are a new class of redox flow batteries that have the potential to provide higher cell voltages and improved energy densities. Organic materials with high redox potentials are suitable for applications as cathode materials and are readily available. Research in our group has focused on developing anode materials, which are much less common. Previously, the Dyker group has evaluated non-flowing cells with bispyridinylidene as an anolyte material and TEMPO as a catholyte material separated by an anion exchange membrane (AEM). Cyclic voltammetry (CV) studies showed that the battery degrades due to diffusion of the neutral active materials across the AEM. This thesis describes the preparation and evaluation of a new anolyte couple which lessened the problem of diffusion through the anion exchange membrane owing to the permanent positive charge in both charged and discharged states. Cells exhibited high coulombic, voltage, and energy efficiencies, though also exhibited a drop in capacity after the first charge, thought to perhaps be associated with the impurity present in the electrolyte or crossover of catholyte materials. In order to determine the relative diffusion rates, cells were assembled with active material on one side of the cell and blank electrolyte on the other side. These cells were left to allow for possible diffusion after which CV was carried out on the disassembled cell to determine the extent of active material diffusion. These results led to the belief that the amount of positive charge affects the extent to which the species cross the AEM. Therefore, as a tetracation / dication redox couple, the new anolyte was successful in reducing the amount of active material diffusion across the AEM.