context: A few investigations are recently reported based on dual redox-additive electrolytes, responsible for improving the capacitive performance via anodic and cathodic redox-active electrolytes at negative and positive electrode interfaces, respectively. For example, Zhong et al. constructed an AC-based supercapacitor with two separate redox-additive gel polymer electrolytes: PVA/H2SO4/HQ (in the anodic region) and PVA/H2SO4/MB (in the cathodic region). This approach enhanced the specific capacitance from ∼139 F g−1 to 563.7 F g−1 and specific energy from 4.67 W h kg−1 to 18.7 W h kg−1. Frackowiak et al. reported a significantly improved supercapacitor performance based on dual redox additives KI and VOSO4 in an aqueous H2SO4 electrolyte, respectively, in anodic and cathodic regions. Similarly, Chun et al. showed the effect of dual redox additives methyl viologen chloride and KBr added into a supporting electrolyte on the supercapacitor performance. In another report, Fan et al. examined the effect of redox additives KI and VOSO4, added together in a PVA/H2SO4 polymer electrolyte. The capacitor based on this electrolyte and AC electrodes offered a significantly higher capacitance of 1232.4 F g−1 as compared to that of the PVA/H2SO4 based device (156.4 F g−1). The selection of dual redox additives for redox-active electrolytes is based on various factors. Apart from the factors, namely high solubility, reversible electron-transfer kinetics and chemical/electrochemical stability, their different redox potentials are important criteria to choose the dual redox additives. While one additive with a higher potential is used for the positive electrode, the other one functions at the negative electrode. Simultaneous redox processes at two interfaces, during charge and discharge, are responsible for a high value of the overall pseudocapacitance. Based on the same criteria discussed above, the two redox additives DPA and KI are selected in the present study, which have different redox potentials ∼0.76 V and 0.53 V versus the SHE corresponding to their possible redox reaction(s), respectively.
answer: H2SO4