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Novel Magnetic Flowable Electrode for Redox Flow Batteries: A Polysulfide/Iodide Case Study

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journal contribution
posted on 05.01.2021, 14:03 by Mohammad Rahimi, Asghar Molaei Dehkordi, Hussein Gharibi, Edward P. L. Roberts
A novel approach named a magnetic flowable electrode (MFE) is proposed for the first time to enable enhancement of redox flow batteries (RFBs) performance. This approach enables the formation of a high active surface area electrode from magnetic nanomaterials, without the need to fabricate a self-supporting three-dimensional electrode structure. To form a simple MFE, magnetic modified carbon nanotubes are dispersed in the electrolyte, and permanent magnets are embedded behind the current feeder to apply a magnetic field across the flow cell channels. With circulating electrolyte, magnetic carbon nanotubes are aggregated on the graphite bipolar plate to form a well-structured nanoscale percolating network and chains serving as an electrode. The superior electrochemical activity and stability of the MFE approach is demonstrated successfully relative to a conventional stationary carbon felt electrode using the positive electrode of a polysulfide-iodide RFB. The MFE provides high electrochemical active surface area and porosity, which result in lower cell impedances and pump losses, and higher battery efficiencies. The polysulfide-iodide RFB using an MFE gives stable cycling performance over 200 cycles (with replacement of the electrolyte after 100 cycles) and delivers a high energy efficiency of 79.3% at a current density of 20 mA cm–2, which is larger than all previous reports for this RFB system. The MFE design opens new opportunities to develop the next-generation RFB systems and can be applied in various flow battery chemistries.