Figure 4. (a) Rechargeable energy density of the redox capacitor (TCHQ-AQ) in 0.5 M H₂SO₄ aqueous solution at 0.28 A/g as a function of cycle time, and (b) the evolution profiles of the potential corresponding to the positive (TCHQ) and negative (AQ) electrodes at the 100^th and 1000^th cycles.