A high-performance aqueous Eu/Ce redox flow battery for large-scale energy storage application

We report the performance of an all-rare earth redox flow battery with Eu 2+ /Eu 3+ as anolyte and Ce 3+ /Ce 4+ as catholyte for the first time, which can be used for large-scale energy storage application. The cell reaction of Eu/Ce flow battery gives a standard voltage of 1.90 V, which is about 1.5 times that of the all-vanadium flow battery (1.26 V). Large standard voltage is conducive to the improvement of battery energy density and power density. The Eu 2+ /Eu 3+ electrode reaction in a NaCl solution on platinum electrode was investigated detailedly using cyclic voltammetry, linear sweep voltammetry, tafel plot and chronoamperometry. Unlike zinc-cerium flow battery, the active species of Eu/Ce flow battery are always present in the electrolyte, and no liquid-solid phase transition occurs. Thus, Eu/Ce flow battery is free of the problems associated with dendrite growth and theoretically have a longer cycle lifetime. The negative electrolyte is very sensitive to oxygen and can directly cause battery failure if exposed to air. The average energy efficiency of Eu/Ce flow battery exposed to air is only 22.0 %. However, the average energy efficiency of Eu/Ce flow battery stripped of oxygen reaches 82.7 % at 25 mA/cm 2 . Preliminary experimental studies have shown that Eu/Ce flow batteries are a promising method for large-scale energy storage.