Two Electron Utilization Liquid Anolyte Molecule for High Energy Density

For the purpose of the high energy density of redox flow battery (RFB), the solubility of redox active molecule, which is in competition with concentration of high molarity supporting electrolyte, should be as high as possible. If redox active molecule itself is liquid so that utilized as solo solvent or dissolve the salt, the highest energy density can be achieved. Herein, we report liquid redox molecule 1-butyl-1'-hexyl'-4,4'-bipyridinium bis(trifluoromethanesulfonyl)imide, [C4C6bpy][TFSI]2 as promising anolyte for high energy density RFB. [C4C6bpy][TFSI]2 has the remarkably low melting point of 18.1 °C, which not only enable keep in liquid state for a relatively long range of temperature, but also indicate the high usability as liquid anolyte. In non-aqueous system, [C4C6bpy][TFSI]2 can take advantage of either one electron or two electron storage of viologen moiety and provide - 1.06 V (vs Ag/Ag+) potential at second redox reaction. Using a highly conductive LiTFSI/ACN supporting electrolyte, [C4C6bpy][TFSI]2 showed almost overlapped cycles for continuously recorded 200 cyclic voltammetry cycles, meaning that excellent electrochemical stability. Liquid molecule [C4C6bpy][TFSI]2 that featured with liquid nature that enable high concentration of the redox active molecule and two reversible redox reaction in nonaqueous system give a great potential to achieve high energy density RFB as promising anolyte candidate.