Wiki Physics UW: Graphene Micro-Supercapacitors
The electronic devices we use in our everyday life utilize two different types of electrical sources in order to operate: batteries and capacitors. A battery stores a fair amount of energy but is slow to charge and discharge (low power density). A capacitor can charge and discharge very rapidly (high power density) but stores a very small amount of energy. A supercapacitor combines the best of both by storing a large amount of energy while also being able to charge and discharge very rapidly.
A capacitor is often constructed with two layers of conducting foil separated by a paper-thin layer of insulator. The capacity of such a device is proportional to the area of the foil A and inversely proportional to the insulator thickness t, C∝A/t. A supercapacitor has an atomic scale insulator thickness given by the solvation layer surrounding an ion in an electrolyte, and a large surface area. Supercapacitors on the order of 100 - 103 Farads are now commercially available and approach the energy density of batteries while still offering fast charge and discharge rates.
The authors of the Nature paper below, El-Kady and Kaner, have provided a video introduction to graphene based supercapacitors.
Short Term Goals
Create graphene micro-supercapacitor material using the methods outlined by El-Kady and Kaner.Conduct a series of tests on how to maximize the amount of charge stored within each graphene micro-supercapacitor.
Long Term Goals
Design an apparatus that can hold many graphene micro-supercapcitors in an efficient and usable way for use in application.Experiment with powering small mobile devices (ie. a flash light, a watch, a cellphone).
Maher F. El-Kady & Richard B. Kaner
El-Kady and Kaner demonstrate a scalable fabrication of graphene micro-supercapacitors over large areas by direct laser writing on graphite oxide ﬁlms. More than 100 micro-supercapacitors can be produced on a single disc in 30 min or less. The devices are built on ﬂexible substrates for ﬂexible electronics and on-chip uses. Remarkably, miniaturizing the devices to the microscale results in enhanced charge-storage capacity and rate capability. These microsupercapacitors demonstrate a power density of ~200 W cm-3, which is among the highest values achieved for any supercapacitor.
William S. Hummers & Richard E. Offema
The conventional method for the preparation of graphitic oxide is time consuming and hazardous. Hummers and Offema have developed a rapid, relatively safe method for preparing graphitic oxide from graphite in what is essentially an anhydrous mixture of sulfuric acid, sodium nitrate and potassium permanganate.
Nina I. Kovtyukhova et al.For the synthesis of graphitic oxide, El-Kady and Kaner used a modified Hummers' method developed by Nina I. Kovtyukhova et al.Science 2 August 2013:Vol. 341 no. 6145 pp. 534-537,DOI: 10.1126/science.1239089, Liquid-Mediated Dense Integration of Graphene Materials for Compact Capacitive Energy Storage
"High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance," http://dx.doi.org/10.1038/nmat3601, http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat3601.html
got me wondering about an old amazing thing. Palladium is a sponge for hydrogen, a phenomenon once touted as a means to achieve "cold fusion."
"Hydrogen in thin Pd-based layers deposited on reticulated vitreous carbon—A new system for electrochemical capacitors,"M. Łukaszewskia, A. Żurowskia,cA. Czerwińskia, Journal of Power Sources Volume 185, Issue 2, 1 December 2008, Pages 1598–1604, http://dx.doi.org.ezproxy.library.wisc.edu/10.1016/j.jpowsour.2008.08.002