Hypercapacitor based on Graphene Composites : 77.8 Wh/kg

hyper capacitor graphene composite

Graphene composite used for the creation of a hyper capacitor

Basically, a supercapacitor is composed of two electrodes, a porous membrane and an electrolyte. The energy and the power of supercapacitors depends particularly on the tension between the two electrodes in the electrolyte. However, the supercapacitors voltage reached 2.7 volts for acetonitrile based electrolytes which is unfortunately a toxic solvent and only 0.8 to 1 volt for aqueous electrolytes that are more environmentally friendly.

To improve performance and especially the density of energy stored by a supercapa, some researchers are therefore working on asymmetric super capacitors which two electrodes are made of different materials, which increases the tension.

A team of researchers led by Fan Zhuangjun Harbin Engineering University, Linjie Zhi at the National Center for Nanoscience and Fei Wei at Tsinghua University in China have created an asymmetric hypercapacitor based on a nickel hydroxide - graphene composite positive electrode and a porous graphene negative electrode.

The composite was made by assembling nickel hydroxide Ni(OH)2 flower-shaped structures on graphene sheets using a method of heating by microwaves.

The hybrid material has created a very high specific capacitance of 1735 Farads per gram and a high flow capacity compared to pure nickel hydroxide. The lens is then to obtain a hypercapacitor possessing a high energy density while having a great energy power.

mesoporous graphene

mesoporous graphene

To construct the negative electrode, the scientists have synthesized graphene by using porous magnesium oxide sheets as the template in a chemical vapor deposition (CVD) approach. The result is a mesoporous graphene (3-8 nanometers) with a Brunauer-Emmett-Teller surface of 1654 square meters per gram. The researchers expect that the graphene porosity made by this unique structure would exhibit excellent electrochemical performance compared with chemically reduced graphene.

The asymmetric hypercapacitor based on graphene materials reached a capacity of 218.4 Farads per gram and a maximum density of 77.8 Wh / kg for a voltage of 1.6 Volts. This hyper capacitor battery also has a long life with a capacity of 94.3% after 3000 cycles of charge / discharge.

With such performances, the production of graphene composites should be fostered to allow the creation of hypercapacitors for energy storage, particularly in the field of renewable energy. The solar power is increasing very fast and hyper capacitor should rapidly appear as the ideal storage solution for photovoltaic electricity.

Source : materialsviews.com

Tags : graphene, super fast battery, asymmetric hypercapacitor
Published on 2012/07/01
 
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