Redox-active ionic liquids in redox-flow-batteries

• Applicants: Professor Dr. Andrea Balducci; Professor Dr. Ulrich S. Schubert
• Subject Area: Polymer Materials
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392851120

• Final Report Year: 2023

Final Report Abstract

Redox flow batteries (RFBs) are interesting candidates for stationary energy storage. Their capacity and power can be scaled independently by adjusting the size of the storage tank and the cell stack, respectively. In contrast to classical batteries, redox flow batteries (RFBs) are based on active materials, which are dissolved (suspended) in a liquid electrolyte. Consequently, the achievable energy densities are limited due to the presence of a non-active solvent (often water). This joined project (Institute for Technical Chemistry and Environmental Chemistry as well as Laboratory of Organic and Macromolecular Chemistry) aimed to develop redox-active ionic liquids (RAIL) as new materials for the electrolytes of RFBs. In these materials, all molecules of the liquid electrolyte would be redox-active. Furthermore, the limited voltage window of aqueous electrolytes will be extended. Within this context, the suitability of ILs for the organic redox couples has been studied by using ILs as electrolytes for organic electrodes. In particular, TEMPO, ferrocene as well as viologen proved to be suitable redox moieties for the design of RAILs. Based on these three redox moieties, three different RAILs have been successfully designed. Whereas the two catholyte materials (TEMPO, ferrocene) resulted in RAILS being liquid at room temperature, the viologen-based IL was melting at lower temperatures. All RAILs showed promising electrochemical properties, but they featured higher viscosities. Their viscosity could be reduced by heating or by diluting with another IL. Up to now, these RAILs are not really suitable for RFBs since their viscosity is too high and the ionic conductivites of the counter ion through the required membranes is too low. Moreover, the IL building blocks could also be utilized for the design of redox-active polymers, which can be utilized in redox flow batteries. For instance, an organosoluble poly(RAIL) based on viologen was prepared.

Publications

• A Comparative Review of Electrolytes for Organic‐Material‐Based Energy‐Storage Devices Employing Solid Electrodes and Redox Fluids. ChemSusChem, 13(9), 2205-2219.
  Chen, Ruiyong; Bresser, Dominic; Saraf, Mohit; Gerlach, Patrick; Balducci, Andrea; Kunz, Simon; Schröder, Daniel; Passerini, Stefano & Chen, Jun
  
• A Critical Analysis about the Underestimated Role of the Electrolyte in Batteries Based on Organic Materials. ChemElectroChem, 7(11), 2364-2375.
  Gerlach, Patrick & Balducci, Andrea
  
• Aprotic and Protic Ionic Liquids as Electrolytes for Organic Radical Polymers. Journal of The Electrochemical Society, 167(12), 120546.
  Gerlach, P.; Burges, R.; Lex-Balducci, A.; Schubert, U. S. & Balducci, A.
  
• Aqueous Redox Flow Battery Suitable for High Temperature Applications Based on a Tailor‐Made Ferrocene Copolymer. Advanced Energy Materials, 10(41).
  Borchers, Philipp S.; Strumpf, Maria; Friebe, Christian; Nischang, Ivo; Hager, Martin D.; Elbert, Johannes & Schubert, Ulrich S.
  
• Emulsion Polymerizations for a Sustainable Preparation of Efficient TEMPO‐based Electrodes. ChemSusChem, 14(1), 449-455.
  Muench, Simon; Gerlach, Patrick; Burges, René; Strumpf, Maria; Hoeppener, Stephanie; Wild, Andreas; Lex‐Balducci, Alexandra; Balducci, Andrea; Brendel, Johannes C. & Schubert, Ulrich S.
  
• A Viologen Polymer and a Compact Ferrocene: Comparison of Solution Viscosities and Their Performance in a Redox Flow Battery with a Size Exclusion Membrane. Macromolecular Chemistry and Physics, 223(2). Portico.
  Borchers, Philipp S.; Elbert, Johannes; Anufriev, Ilya; Strumpf, Maria; Nischang, Ivo; Hager, Martin D. & Schubert, Ulrich S.
  
• Ferrocene containing redox-responsive poly(2-oxazoline)s. Chemical Communications, 57(11), 1308-1311.
  Borchers, Philipp S.; Dirauf, Michael; Strumpf, Maria; Görls, Helmar; Weber, Christine; Hager, Martin D. & Schubert, Ulrich S.
  
• The influence of current density, rest time and electrolyte composition on the self-discharge of organic radical polymers. Electrochimica Acta, 377, 138070.
  Gerlach, P. & Balducci, A.
  
• The Influence of the Nature of Redox-Active Moieties on the Properties of Redox-Active Ionic Liquids and on Their Use as Electrolyte for Supercapacitors. Energies, 14(19), 6344.
  Borchers, Philipp S.; Gerlach, Patrick; Liu, Yihan; Hager, Martin D.; Balducci, Andrea & Schubert, Ulrich S.
  
• Enhancing Capacity and Stability of Anionic MOFs as Electrode Material by Cation Exchange. Frontiers in Chemistry, 10.
  Akintola, Oluseun; Gerlach, Patrick; Plass, Christian T.; Balducci, Andrea & Plass, Winfried