Energy storage inspired by nature – ionic liquid iron–sulfur clusters as electrolytes for redox flow batteries

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Abstract
The redox flow battery (RFB) is a promising technology for the storage of electric energy. Many commercial RFBs are often based on acidic vanadium electrolyte solutions that have limitations regarding stability and energy density. Here, a new approach is presented that is inspired by nature's electron storage, i.e. iron–sulfur clusters [Fe4S4(SR)4]2−. In combination with imidazolium cations, new ionic liquid electrolyte materials were obtained and characterized with regard to their physico- and electrochemical properties. For flow battery tests, the bromide/bromine redox-couple was used in the second half cell in an ionic liquid solution. In these measurements, liquid iron–sulfur clusters show high coulombic (>95%) and energy (69%) efficiencies combined with a high theoretical energy density (88 W h L−1).
Funding Information
  • Bundesministerium für Forschung, Technologie und Raumfahrt (FKZ 03SF0436C)

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