Kinetics of electrochemical reactions are several orders of magnitude slowerin solids than in liquids as a result of the much lower ion diffusivity. Yet,the solid state maximizes the density of redox species, which is at least twoorders of magnitude lower in liquids because of solubility limitations. Withregard to electrochemical energy storage devices, this leads to high-energybatteries with limited power and high-power supercapacitors with a well-knownenergy deficiency. For such devices the ideal system should endow the liquidstate with a density of redox species close to the solid state. Here we reportan approach based on biredox ionic liquids to achieve bulk-like redox densityat liquid like fast kinetics. The cation and anion of these biredox ILs bearmoieties that undergo very fast reversible redox reactions. As a firstdemonstration of their potential for high-capacity / high-rate charge storage,we used them in redox supercapacitors. These ionic liquids are able to decouplecharge storage from ion accessible electrode surface, by storing significantcharge in the pores of the electrodes, to minimize self-discharge and leakagecurrent as a result of retaining the redox species in the pores, and to raiseworking voltage due to their wide electrochemical window.
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