(Keynote) Redox Active Polymers: A Size Selective Solution for Nonaqueous Redox Flow Batteries
We will present our advances towards implementing such strategy using RAPs with different chemical functionalities, for both catholytes and anolytes with the aim of creating an “ALL RAP” non-aqueous redox flow battery. Our first studied system, based on viologen RAPs with molecular weight between 21 and 318 kDa exhibited size dependent transport across the porous separator. This was achieved with RAPs that displayed a high solubility of up to 2.7 M, reversible electron transfer, and 94-99% charge/discharge efficiency. In the study of RAPs we have introduced new measurement techniques, including micro- and nano-electrodes for the steady state characterization of this species. Microelectrode voltammetry allowed to prove facile electron transfer even in highly concentrated solutions (+1.0 M). Preliminary testing using a stirred cell showed the possibility of integrating RAPs and porous separators into a working device that achieved stable charge/discharge and only 2% crossover over several hours.
We are working towards the development of guidelines that aid our understanding of RAP electrochemistry.The application of new electrochemical and ionic imaging methods based on scanning electrochemical microscopy using micro- and nano- electrodes developed in our group  has allowed us to better understand the careful balance between RAP size and ion and electron mobility. We will discuss how these guidelines have significantly aided our molecular design and how they impact the performance of this new type of flow batteries.
Acknowledgement. Work supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.
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