A green europium-cerium redox flow battery with ultrahigh voltage and high performance

Due to the superiority of decoupled energy and power, high safety, and design flexibility, redox flow batteries (RFBs) have gained much attention as candidates for large-scale electrochemical energy storage. However, the main redox flow batteries like iron-chromium or all-vanadium flow batteries have the dilemma of low voltage and toxic active elements. In this study, a green Eu-Ce acidic aqueous liquid flow battery with high voltage and non-toxic characteristics is reported. The Eu-Ce RFB has an ultrahigh single cell voltage of 1.96 V. The high concentration of electrolyte enables the full-cell energy density to reach 43 Wh/L. Even at the current density of 100 mA cm −2 over 100 cycles, the average coulombic efficiency, voltage efficiency and energy efficiency can reach 98 %, 84 %, and 82.4 %, respectively. In comparison with other reported representative redox flow batteries in recent years, the practical power density calculated at 80 % energy efficiency is at a leading level. These demonstrate the Eu-Ce RFB is a promising solution for green large-scale renewable energy storage.