Hyper capacitor with electrodes based on cobalt oxide nanowires : 81 Wh/kg

hypercapa nanowires

Hypercapacitor nanowires with brush-like

The electrodes of high density supercapacitor are usually made from conductive carbon mixed with a transition metal oxide. This mixture is then coated on a collector with a high power electric current conductor such as carbon cloth, copper or nickel. This approach often limits access of the electrolyte to the entire volume of the electrode and the surface boundary where redox reactions can take place.

A team of researchers at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia led by Husam N. Alshareef therefore used a different approach to improve device performance.

"We designed the electrode with macroporosity to help electrolyte flow and with mesoporosity to increase oxide surface area and increase the redox reaction rate", said Alshareef.

The team used fibrous carbon-based collectors in place of planar carbon collectors. The cobalt oxide (Co3O4) nanowires grown on fibrous paper collectors enables a self-organization in a brush-like morphology, while the nanowires grown on the carbon surface self-organize into a flower morphology.

Electrodes based on metallic oxide nanowires brush-like morphology and flower-like morphology

The electrodes thus produced provide the desired properties of macroporosity to allow easy flow of the electrolyte, thus reducing peripheral resistance while the nanoporosity allows a faster reaction kinetics over a large area.

Every single cobalt oxide nanowire made contact with the current collector. The fibrous carbon collector resulted in the oxide nanowire nucleating in a three-dimensional fashion, completely surrounding the fibers, unlike what is the case with planar carbon collectors.

With these electrodes based on metal oxide nanowires taking the morphology of a brush, KAUST researchers have succeeded in creating a hypercapacitor reaching an energy density of 81 Wh / kg against 55 Wh / kg with flower-like morphology.

In both cases, the hyper-capacitor offers excellent cyclic durability with 91 to 94% residual capacity after 5000 cycles of charging and discharging.

Given the price of Cobalt, the scientists are currently trying with other metallic oxides to obtain hyper capacitors at low prices but offering as storage capacity of electric power as a good battery.

Source : http://www.nanowerk.com/spotlight/spotid=25066.php

Tags : metallic oxide, nanowires, redox
Published on 2012/07/01
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