Activated Graphite Oxide Supercapacitors

I think that this unusualmaterial just joined the energy storage sweepstakes. It even sounds like theycan make it work.

The target remains a batterycapable of providing a five hundred mile range to a reasonably sized electricvehicle.  These sounds like it may do itand it will soon join a widening field of competitors.

We are still waiting for EEStorto overcome its manufacturing issues while others play coy.

What is clear is that the problemis on the verge of been solved, which is why the auto industry is visibly toolingup for an electric future.  The momentthe battery can be shipped, the automobiles will be on the lot.

On top of that, we have the RossiFocardi Reactors coming on the market in months and that will solve the powerproblem.

I predict that by 2015, theswitch to electrical vehicles will be in full swing.

'Activated' graphite oxide boosts supercapacitors

May 13, 2011 

http://physicsworld.com/cws/article/news/45976

Researchers in the UShave discovered a new form of carbon produced by "activating"expanded graphite oxide. The material is full of tiny nanometre-sized poresand contains highly curved atom-thick walls throughout its 3D structure.The team has also found that the material performs exceptionally well as anelectrode material for supercapacitors, allowing such energy-storage devices tobe used in a wider range of applications.

Capacitors are devices that store electric charge on two conductingsurfaces separated by an insulating gap – the larger the surface area of thecapacitor, the greater its capacity to hold charge. Charging a capacitorrequires electrical energy, which is recovered when the device is discharged.Supercapacitors, also known as electric double-layer capacitors orelectrochemical capacitors, store more charge thanks to the double layer formedat an electrolyte–electrode interface when a voltage is applied. Althoughalready used in applications such as mobile phones, these devices are currentlylimited by their relatively low energy storage density compared with batteries.

Now, Rodney Ruoff and colleagues at the Universityof Texas at Austinand scientists at the Brookhaven National Laboratory, the Universityof Texas at Dallas and QuantaChrome Instruments havesynthesized a new form of porous carbon with a very high surface area. Thecarbon consists of a continuous 3D porous network with single-atom-thick walls,with a significant fraction being "negative curvature carbon" similarto inside-out buckyballs. The researchers used the material to make atwo-electrode supercapacitor with high gravimetric densities of capacitance,energy capacity and power per unit mass. What is more, the team claims that theprocess used to make this form of carbon can be scaled up to produce industrialquantities of the material.

Expanded with microwaves

Ruoff and co-workers begin by converting samples of graphite intographite oxide, which they expand using microwaves to generate what they havedubbed "microwave-expanded graphite oxide" (MEGO). The MEGO is thentreated with potassium hydroxide so that its surface is covered (or decorated)with the chemical. After heating at 800 °C for about an hour in an inertgas, "activated MEGO" or aMEGO is obtained.

"What is quite surprising is that the [potassium hydroxide]remarkably restructures the carbon so that a 3D porous structure is generatedwith essentially no edge atoms," Ruoff toldphysicsworld.com. "Everywall in the structure is one atom thick and all the carbon atoms there are sp2-bonded."

The researchers used aMEGO as the carbon for electrodes in asupercapacitor – mixing it with different electrolytes. They obtained"exceptional" gravimetric energy densities that are about four timeshigher than that of state-of-the-art conventional supercapacitors, forexample those based on porous activated carbon, on the market today.

Best BET

The porous carbon produced also has a "BET"(Brunauer–Emmett&nadash;Teller) surface area of up to 3100 m2/g. Forcomparison, typical activated-carbon materials have BET surface areas in therange of 1000 to 2000 m2

And that is not all: the material is also very stable and continues towork at 97% capacitance even after 10,000 constant current charge/dischargecycles.

"The Texaswork shows an important increase in energy capacity on a gravimetric basis, butunfortunately the graphene material has relatively low density. It will beinteresting to see if further work yields higher-density materials withcorresponding improvements in volumetric energy density," says John Millerof the capacitor maker JME and Case Western Reserve University,who was not involved in the research.

Ruoff and colleagues are optimistic and now plan to further improve thenew carbon and hope to obtain further funding so that they can carry onconducting more fundamental research on generating still better materials basedon similar types of structures. "We also hope to optimize performance in otherelectrical energy-storage systems in parallel," reveals Ruoff.

The work is reported in Science.