Carbon nanosheets-based supercapacitors: Design of dual redox additives of 1, 4-dihydroxyanthraquinone and hydroquinone for improved performance

Using thiocarbanilide and Mg(OH)2 powders as carbon precursor and template, respectively, novel 2D carbon nanosheets with large area have been produced. Next, based on the cooperative effect, 1, 4-dihydroxyanthraquinone (DQ) and hydroquinone (HQ) regarded as efficient dual redox additives have been incorporated into the electrode carbon material and H2SO4 electrolyte, respectively, to largely elevate the capacitive performance of supercapacitors. More importantly, the cooperative effect results from the redox processes of DQ and HQ consecutively occurring in the electrode carbon material and aqueous H2SO4 electrolyte, respectively. Besides, the molar ratio of DQ and HQ exerts a crucial role in the determination of the electrochemical behaviors and eventually the optimum condition is the mass ratio of 1:1 concerning the DQ and porous carbon within solid electrode while retaining the HQ concentration as 20 mmol L−1 in 1 mol L−1 H2SO4 electrolyte. As a result, the maximum specific capacitance is achieved of 239 F g−1 at 3 A g−1, and furthermore the maximum energy density up to 21.1 Wh kg−1 is almost 3.5 times larger than that of the one without introducing any redox additive.