| An efficient design of high energy and power density supercapacitor is a great task. Carbon materials have been used widely for the energy storage, especially porous carbon materials have attracted the attention for energy storage because of their high surface area and high conductivity to store the charge in electrochemical double layer of the supercapacitors. But, these supercapacitors suffers from low energy density and bad cycle life. Furthermore, oxygen functional groups at the surface of these materials are found very attractive to store more amount of energy by mean of charge storage due to their redox reactions with the electrolyte ions. But, these reactions are not stable with cycling of the device which results in limited life time of these kind of supercapacitor devices. Another cheap and attractive way to increase the amount of stored charge by mean of redox activity of this kind of carbon materials is the use of redox active electrolytes instead of conventional electrolyte. These electrolytes introduce extra redox reactions originated from electrolyte ions instead of the material of the electrode itself and hence as a result stores more amount of charges. But, limited redox reactions and cycling instability at the surface of these materials in redox electrolytes are major drawbacks.Here we develop a new efficient strategy that utilizes synergistic interaction between surface oxygen of binder-free porous carbon material and copper ions Cu2+ inside the acidic aqueous electrolyte solution for the generation of redox reactions which tremendously increased the charge storage capability of the supercapacitor. Moreover, chloride along with copper inside the electrolyte solution made possible copper adsorption state and enhanced the reaction stability as well which increased the cycling stability and hence enhanced life time of the supercapacitor. Our strategies provide a versatile methods for designing new energy storage devices and are promising for the development of high-performance supercapacitors. We report following results.(1) We report a 10 time increase in voltammetric capacitance(4700F g-1) compared with the capacitance in conventional acidic aqueous electrolyte, stable 5000 chargedischarge cycles at 60 A g-1 current density and 99.4 % retention of the initial galvanostatic-capacitance(1335 F g-1) after cycling of the binder-free electrode in three electrodes configuration and very high two-electrode cell capacitance of 1010 F g-1 by the same electrode in the same redox-active electrolyte. This high performance is attributed to the low charge-transfer resistance(0.04 ?) of the binder-free porous carbon electrode and synergistic interaction of its surface-oxygen group with redox electrolyte ions.(2) We report high capacitance of 294 F g-1, 73 W h kg-1 energy density and 7 kW kg-1 power density of symmetric two electrodes in this newly discovered redox acidic aqueous electrolyte of CuCl2.(3) Hybrid supercapacitors exhibit efficient electrochemical properties in the field of charge storage. But, binder free symmetric design of micro-scale porous carbon electrodes with high voltage and capacitance is a tremendous challenge. We furthermore report a new preparation method of a micro-scale binder-free symmetricsupercapacitor of porous carbon material. We noticed very high working voltage of 2.5 V of micro-scale interdigitated porous carbon electrodes in neutral aqueous electrolyte, 3 time increased galvanostatic areal capacitance of 3 mF cm-2 in another redox active acidic electrolyte of water. We prepared the redox electrolyte by simultaneous introduction of hydroquinone and indigo carmine in certain concentration and ratio inside the acidic aqueous electrolyte solution. We attribute the improved performance in the redox-electrolyte to the enhanced redox reaction and charge transfer process by the existence of hydroquinone inside the aqueous acidic electrolyte solution. |
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