A long-life aqueous redox flow battery based on a metal-organic framework perovskite [CH3NH3][Cu(HCOO)3] as negative active substance

In this work, one water-soluble metal-organic framework [CH3NH3][Cu(HCOO)3] with a perovskite structure is synthesized as negative active substance, which is used to construct a redox flow battery by combining with the positive active substance 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-OH-TEMPO). The battery voltage of 0.696 V is achieved by utilizing citric acid - disodium hydrogen phosphate (C6H8O7-Na2HPO4) buffer and NaClO4 as supporting electrolyte. Cyclic voltammetry is determined to investigate the electrode reaction kinetics of positive and negative active substance. Moreover, the battery is repeatedly charged and discharged under room temperature at varied current densities, and runs stably for 40 cycles, and the voltage efficiency and energy efficiency at the current density of 7.5 mA cm-2 are up to 74.96 % and 66.52 %, respectively. The highest coulombic efficiency up to 96.87 % is reached at 40 mA cm-2. The infinite ordered structure of [CH3NH3][Cu (HCOO)3] reduces the crossover contamination of electrolyte and the deposition of copper ions, improving the cycle life and stability of the battery.