Electrochemical Characterization of TEMPO Radical in Ionic Liquids

Abstract

Both p- and n-type redox reactions for 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) successfully proceeded in ionic liquids, although only p-type redox proceeds reversibly in conventional organic electrolytes. The heterogeneous electron-transfer constants estimated from the cyclic voltammograms were in the range of the quasi-reversible system for both p- and n-type TEMPO reactions in ionic liquids. The rate constant for a p-type reaction in ionic liquids were lower by three orders of magnitude than that in the acetonitrile-based electrolyte due to the high viscosity of the ionic liquids. Quasi-reversible p- and n-type redox TEMPO reactions in the ionic liquid-based electrolyte systems suggest the potential realization totally-organic, flexible, safe, and symmetric organic radical batteries (ORBs) which are composed of TEMPO-based polymers for both positive and negative electrodes. The difference between p- and n-type redox electrode potential was 1.7 V in the tested ionic liquids, a value that suggests the electromotive force of symmetric ORB.