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Description
In industrially available systems the organic electrolytes are used in capacitors, which operate in a high potential range of 2.5-2.8 V. However, organic electrolytes are environmentally unfriendly, and the assembly of the capacitors with organic electrolytes is complicated and required inert atmosphere. Because of this drawbacks, recent research has been focused on the identification of new types of electrolytes. Among them aqueous electrolytes have emerged as promising candidates due to their low-cost and safe usage. In addition, the conductivity of aqueous electrolytes is much higher than that of organic electrolytes, which leads to increased power generation. Moreover, a considerable limitation in the implementation of aqueous electrolytes in supercapacitors is their narrow potential range (less than 1 V), which is a consequence of the theoretical potential of water decomposition at approximately 1.2 V. To overcome this limitation, asymmetric or hybrid systems can be developed as an outstanding alternative to symmetric systems. Electrodes with different working potential ranges would allow to increase the cell voltage in an aqueous electrolyte, thereby enhancing the energy density to satisfy the requirements for numerous applications. Moreover, the new type of materials as composites containing transition metal oxide (sulfide, nitride) and nanostructural carbon material which are proposed exhibit hybrid properties combining battery and supercapacitor types of chemistry which is desirable for hybrid supercapacitor as a novel type of energy storage devices.
Proposed combination of electrodes and used aqueous solution as an electrolyte can give an outstanding, needed and expected energy storage device.