No abstract

Electrochemical capacitors are electrochemical devices with fast and highly reversible charge-storage and discharge capabilities. The devices are attractive for energy storage particularly in applications involving high-power requirements. Electrochemical capacitors employ two electrodes and an aqueous or a non-aqueous electrolyte, either in liquid or solid form; the latter provides the advantages of compactness, reliability, freedom from leakage of any liquid component and a large operating potential-window. One of the classes of solid electrolytes used in capacitors is polymer-based and they generally consist of dry solid-polymer electrolytes or gel-polymer electrolyte or composite-polymer electrolytes. Dry solid-polymer electrolytes suffer from poor ionic-conductivity values, between 10 À8 and 10 À7 S cm À1 under ambient conditions, but are safer than gel-polymer electrolytes that exhibit high conductivity of ca. 10 À3 S cm À1 under ambient conditions. The aforesaid polymer-based electrolytes have the advantages of a wide potential window of ca. 4 V and hence can provide high energy-density. Gel-polymer electrolytes are generally prepared using organic solvents that are environmentally malignant. Hence, replacement of organic solvents with water in gel-polymer electrolytes is desirable which also minimizes the device cost substantially. The water containing gel-polymer electrolytes, called hydrogel-polymer electrolytes, are, however, limited by a low operating potential-window of only about 1.23 V. This article reviews salient features of electrochemical capacitors employing hydrogel-polymer electrolytes.

No abstract

No abstract

Acidic polyvinyl alcohol/polyacrylic acid blend hydrogel electrolytes ͑BHEs͒ were prepared by cross-linking with glutaraldehyde and perchloric acid. These acidic BHEs were treated suitably to realize alkaline and neutral BHEs. Amorphicity of BHEs was followed by differential scanning calorimetry. Ionic conduction in acidic BHEs was found to take place by a Grötthus-type mechanism whereas in alkaline and neutral BHEs it was due to a segmental motion mechanism. Ionic conductivity of BHEs was found to range between 10 −3 and 10 −2 S cm −1 . Electrochemical capacitors assembled with acidic polyvinyl alcohol hydrogel electrolyte yielded a maximum capacitance of ϳ60 and 1000 F g −1 with BP carbon and RuO x ·xH 2 O/C electrodes, respectively.