An aqueous organic redox flow battery employing a trifunctional electroactive compound as anolyte, catholyte and supporting electrolyte

Aqueous organic redox flow batteries (AORFBs) have drawn substantial attention due to their potential to simultaneously achieve high energy density, high power density and low cost, but its development has been hindered by cross-contamination between the negative and positive electrolytes. To address this issue, we demonstrate the first example of symmetric AORFBs using a single ionic compound, the aqueous organic bipolar mono-N-alkylated bipyridinium iodide salt [(bpy-(CH₂)₃NMe₃)]I₂, to serve the three functions of anolyte, catholyte and supporting electrolyte. This strategy has the potential to achieve high energy density with lower cost and in the meantime migitate the problem of cross-contamination. The trifunctional behaviour have been verified in the symmetric battery tests under neutral pH, which achieves an energy efficiency of 72% at the current density of 10 mA/cm² within 100 cycles with a capacity retention rate of 99.5% per cycle. This chemical has superior electrochemical stability with no observable chemical degradation after 290 cycles.