Evaluation of negolyte properties of supramolecular binary complexes based on viologen-cucurbit[7]urils

Abstract

Viologen-based redox materials have become popular as electrolytes for aqueous organic redox flow batteries (AORFBs) in recent years because of their reversible nature. The main obstacles to their use, however, have been dimerization and solubility of the monocation radicals. Several measures have been deployed to address these shortcomings. The use of supramolecular host–guest interactions has recently been offered as a possible technique for increasing the stability and solubility of AORFB materials. Using cyclic voltammetry, UV-vis, and EPR spectroscopy, we examined the supramolecular complexation with CB[7], electrochemical behavior, and radical stability of substituted propyl viologens bearing various positive charges. The results showed viologen-CB[7] forming a 1 : 1 binary complex displaying high electrochemical reversibility and radical stability due to the monocation radical being stabilized by the less polar environment given by CB[7]. Furthermore, this research has shed light on how the cationic charge on viologen varies with the electrochemical performance of the AORFB.