Non-aqueous redox flow batteries (NRFBs) are a possible energy storage solution for intermittent renewables (solar, wind). Their long cycle lifetimes and capability to store large quantities of energy make NRFBs attractive for grid level storage, to capture energy during periods of low energy consumption. However, the low energy density and tendency of NRFBs to lose capacity over time result in a high energy cost (approximately $500 per kWh) that hinder them from wider incorporation in grid systems. The problems arise from use of small metal ions as electrolytes in conjunction with expensive ion-exchange membranes (IEMs) that inadequately prevent the crossover of charge-carrying species between compartments. We utilized relatively inexpensive, commercial off-the-shelf (COTS) porous separators in place of IEMs and redox-active polymers (RAPs) in place of metal ions in non-aqueous solvents. In our initial studies, we examined the diffusion rates of varying viologen polymer chain lengths through COTS separators and observed a reduction in polymer crossover with increasing chain lengths (up to 85%), showing size-enhanced rejection of electroactive species. The results demonstrate the feasibility of polymers as charge storage materials but further improvements are required to make NRFBs viable for grid incorporation. Incorporation of organic moieties such as nitrobenzene in RAPs displayed superior electrochemical performance (1.6 V) and solubility (6.0 M) compared to viologen polymers (0.8 V and 2.8 M). Further synthetic modifications on nitrobenzene-based polymers exhibited enhanced electrochemical performance capable of achieving energy cost targets ($180 per kWh), demonstrating the potential of NRFBs to meet grid level storage.<br/>

Investigation of nitrobenzene-based redox-active polymers for non-aqueous redox flow batteries

251st National Meeting (2016)

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