Wiki Physics UW: Graphene Micro-Supercapacitors
::Source: University of Wisconsin Madison::
Co-I GarrettFrankson and AustinJeffries Current Status: Building Project Page
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).
Scalable fabrication of high-power graphene micro-supercapacitors for ﬂexible and on-chip energy storage
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.
Preparation of Graphitic Oxide
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.
Layer-by-Layer Assembly of Ultrathin Composite Films from Micron-Sized Graphite Oxide Sheets and Polycations
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