Investigating the redox behavior of activated carbon supercapacitors with hydroquinone and p-phenylenediamine dual redox additives in the electrolyte.

Activated carbon (AC) with large surface area and high electrical conductivity is widely applied on supercapacitors (SC), but the energy storage mechanism for the pure electrical double layer capacitor of carbon leads to a low energy density. Developing stable aqueous electrolytes with abundant redox reactions via incorporating more than one redox additive in the electrolyte is one of the efficient strategies to improve the energy storage capacity of the AC-based SC. In this study, the dual redox additives of hydroquinone (HQ) and p-phenylenediamine (PPD) are incorporated in the aqueous solution as the electrolyte for SC. The effects of the aqueous solution type as well as the total redox additive concentration and the relative amounts of HQ and PPD on the electrochemical performance of SC are carefully studied. Two binders are used for assembling the AC electrodes, and the binder-dependent electrochemical behaviors and energy storage capabilities for SC are obtained. The symmetric SC assembled with the optimized electrolyte and the AC electrode prepared using the LA132 binder shows the potential window of 1.6 V, the specific capacitance of 116.23 F/g at 2 A/g, and the maximum energy density of 1.85 W h/kg at the power density of 0.15 kW/kg.