Static theoretical investigations of organic redox active materials for redox flow batteries

Abstract

New efficient redox flow batteries (RFBs) are currently of great interest for large-scale renewable energy storage. Further development requires improvement of the redox active materials. Quantum chemical methods allow to screen large numbers of redox active molecules for required molecular properties. Especially the redox potentials are calculated in high-throughput studies. In addition, calculations of other properties such as solubility or stability and in-depth analysis of the electronic structure are performed on smaller number of molecules. This review provides an overview of various known classes of active material molecules and their results in quantum chemical calculations. We will focus on electronic structure methods such as density functional theory and wave function-based methods. Significant theoretical results are presented and discussed for each considered class of redox-active molecules. In addition, the various quantum chemical approaches are also examined, specifically with regard to their advantages and limitations. Another focus of this review is on comparing theoretically predicted results with experimental studies, which are discussed using various examples. Finally, further challenges and trends in the theoretical development of active materials are highlighted.

Beyond conventional batteries: a review on semi-solid and redox targeting flow batteries-LiFePO4 as a case study

“…This prediction aids in the screening of suitable redox mediators for RTFBs, offering an advantageous alternative to the timeconsuming and expensive process of laboratory synthesis. [197][198][199] Density Functional Theory (DFT) emerges as a favored method for these computational studies, enabling the rapid and dependable prediction of properties like redox potential and solubility. DFT has demonstrated its efficacy in high-throughput screening of organic molecules for RFBs, achieving accuracies around 70 mV for calculated redox potentials.…”

Development of a multi‐step screening procedure for redox active molecules in organic radical polymer anodes and as redox flow anolytes

“…with the electrode potential E Ag=AgNO3 , the Faraday constant F, the number of electrons n in the half reaction, and the Gibbs energies of oxidation ΔG Ox and reduction ΔG Red . The latter are defined as: The electrode potential E Ag=AgNO3 of the Ag/AgNO 3 reference electrode is calculated using Equation (7). 109…”

“…Many different organic molecules are currently being investigated for use as anode material. 1,4,6,7 Viologens have demonstrated desirable redox potentials and stability for use in organic RFBs and PBBs. [8][9][10][11][12][13] However, it is difficult to chemically modify viologens to optimize their properties, such as their redox potential.…”

“…A compatible redox‐active anode material must have a significantly lower potential for its redox reaction. Many different organic molecules are currently being investigated for use as anode material 1,4,6,7 . Viologens have demonstrated desirable redox potentials and stability for use in organic RFBs and PBBs 8–13 .…”