| As energy-storage devices,supercapacitors have drawn widespread concern of researchers due to their high power densities,long cycling life and high rate.However,supercapacitors have the disadvantage of lower energy density and this severely handicaps their application domain.Therefore,in order to further improve the energy density of supercapacitors,a great deal of research work has focused on the design of electrode materials and electrolyte systems.In this paper,we first present a direct and efficient template carbonization method to prepare high-performance carbon-based electrode materials.And,secondly,we introduced small amounts of a redox additive into electrolyte to further improve the capacitance of the supercapacitor.The main content of the paper are as follows:1.2D nanoporous carbon material with large specific surface area(2208 m2 g-1)has been synthesized by the template carbonization method,using glucose serves as carbon precursor and zinc nitrate as template.Moreover,adding a novel redox-mediated ferrous ammonium sulphate(FAS)to H2SO4 electrolyte and regulating the potential windows in a two-electrode system can largely improve the capacitance as well as the energy density.What is more,to the best of our knowledge,there is no study of FAS redox additive ever being used in the traditional H2SO4 electrolyte.Incorporating 0.39 mol L-1 FAS into 1 mol L-1 H2SO4 can result in ultrahigh specific capacitance of 1499 F g-1 at 10 A g-1 when designating the potential window as-0.5 to 0.5 V,and it is almost 28 times than that of the pristine one(53 F g-1)without any FAS,which is higher than those of the previous literature.And surprisingly,the maximum energy density can reach up to 58.70 Wh kg-1.These remarkable improvements are attributed to the additional Faradaic pseudocapacitances by the quick reversible Faradaic reactions of the ferrous ions in FAS as well as the edge active carbons showing excellent electrosorption toward Fe2+/3+,NH4+,H+.Furthermore,regulating the potential windows also exerts crucial roles in the capacitive performances,and it is revealed that the potential of-0.5-0.5 V window can lead to optimum capacitance and energy efficiency.2.How to massively produce 2D carbon materials remains an interesting issue.In this work,simply by a template carbonization approach,2D nano-carbon materials possessing large surface area of 1229 m2 g-1 and high pore volume of 1.66 cm3 g-1 have been synthesized,using sodium stearate as the carbon source and magnesium powder as a hard template.More importantly,we demonstate dual redox additives composed of KI and anthraquinone-2-sulfonic acid sodium(AQS)for improving the capacitances of supercapacitor.To date,the intrinsic redox mechanism synchronously occurring both at the negative and positive electrodes especially towards the dual redox additives is still unclear.And therefore,further exploring and understanding this kind of redox mechanism is interesting for the practical application of supercapacitors.Besides,the neutral KNO3 electrolyte can extend the operating voltage window of carbon-based supercapacitors synchronously.It is revealed that KI and AQS undergo redox reactions at the positive and the negative electrode,respectively;and the present operating voltage window has been prolonged up to 1.8V,largely larger than the limitation of water(1.23 V).When dual redox additives of KI and AQS into KNO3 electrolyte results in a high energy density of 33.81 Wh kg-1 at a power density of 1000 W kg-1,which is much higher than that of the pristine one without any redox additive(9.40 Wh kg-1 at the same power density).Moreover,it also exhibits low self-discharge rate and long cyclic durability. |
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