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New graphene-derived 3D porous carbon material enables energy-dense supercapacitors

(A) Schematic showing the microwave exfoliation/reduction of GO and the chemical activation of MEGO (a-MEGO) that creates pores while retaining high electrical conductivity. (B–E) Images of a-MEGO. E shows presence of a dense network of nanometer-scale pores surrounded by highly curved, predominantly single layer carbon. Credit: Zhu et al. Click to enlarge.

Researchers at The University of Texas at Austin’s Cockrell School of Engineering have synthesized a new carbon with a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6–5 nm width pores. Two-electrode supercapacitor cells constructed with this material yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes.

Supercapacitors made from the material have an energy density that is approaching the energy density of lead-acid batteries, while retaining the high power density that is characteristic of supercapacitors. The processes used to make this carbon are readily scalable to industrial levels, the group, led by materials science and mechanical engineering Professor Rodney S. Ruoff, reports in a paper published in Science.

Supercapacitors are similar to batteries in that both store electric charge. Batteries do so through chemical reactions between metallic electrodes and a liquid electrolyte. Because these chemicals take time to react, energy is stored and released relatively slowly. But batteries can store a lot of energy and release it over a fairly long time.

Supercapacitors, on the other hand, store charge in the form of ions on the surface of the electrodes, similar to static electricity, rather than relying on chemical reactions. Charging the electrodes causes ions in the electrolyte to separate, or polarize, as well—so charge gets stored at the interface between the electrodes and the electrolyte. Pores in the electrode increase the surface area over which the electrolyte can flow and interact, thereby increasing the amount of energy that can be stored.

Because most supercapacitors can’t hold nearly as much charge as batteries, their use has been limited to applications where smaller amounts of energy are needed quickly, or where long life cycle is essential, such as in mobile electronic devices.

The new material, synthesized by using chemical activation of microwave exfoliated graphite oxide (MEGO), has a BET surface area of up to 3100 m2 per gram, a high electrical conductivity, and a low O and H content.

Ruoff’s research team of about 40 people collaborated with faculty and students from The University of Texas at Dallas, scientific staff at Brookhaven National Laboratory in New York and staff members at QuantaChrome Instruments in Florida.

Ruoff had formed a hypothesis that the activated MEGO (a-MEGO) material consisted of a continuous three-dimensional porous network with single-atom-thick walls, with a significant fraction being “negative curvature carbon,” similar to inside-out buckyballs. He turned to Erich Stach at Brookhaven for help with further structural characterization to verify or refute this hypothesis.

Stach and Brookhaven colleague Dong Su conducted a wide range of studies at the Lab’s Center for Functional Nanomaterials (CFN), the National Synchrotron Light Source (NSLS), and at the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory, all three facilities supported by the DOE Office of Science. Their observations confirmed Ruoff’s hypothesis.

The University of Texas at Austin’s Office of Technology Commercialization has filed a patent with the US Patent Office on behalf of the inventors.


  • Yanwu Zhu, Shanthi Murali, Meryl D. Stoller, K. J. Ganesh, Weiwei Cai, Paulo J. Ferreira, Adam Pirkle, Robert M. Wallace, Katie A. Cychosz, Matthias Thommes, Dong Su, Eric A. Stach, and Rodney S. Ruoff (2011) Carbon-Based Supercapacitors Produced by Activation of Graphene. Science doi: 10.1126/science.1200770



The video here:

also specifies that this is low cost as well as readily industrially scalable.
Anyone know what the cold weather performance is likely to be like?


One day one of these cool approaches will work (silicon nanowires anyone?) in the real world and we'll have storage that puts the last nails in the ICE coffin. I imagine cold weather would be fine since there is no chemical reaction taking place?


I found this on low temperature performance:

It looks as though this is electrolyte dependent, and present capacitors typically function down to -40C and freeze at -45C, with degradation of performance as the temperature drops.
This is in the same ball-park as very good batteries, so there does not seem to be ground from much concern about this.
Anyone got any idea whether capacitors are electrolyte agnostic, so that the super low temperature ones mentioned in the article I have linked could be used in these graphene-based capacitors?


I like this as a replacement for toxic lead acid as a regular 12 volt battery, with stop/start capability thrown in.
The fact that it would put the nail in the coffin of lead carbon and Axion, with their repeated sledging of lithium whilst providing no proper performance testing of their battery and having zero sales is a bonus,


Apparently the ionic liquid electrolytes are good from -90C to 400C - that should do! ;-)

Ionic electrolytes also look good for lithium batteries, and can give an energy density of up to 390Wh/kg:

I particularly like the idea of replacing lead-acid batteries - this alternative is very light weight, around 1.5kgs instead of the massive present batteries.


It could certainly make an excellent lead/acid battery replacement, specially for stop/start equipped vehicles and supply the high energy required to accelerate an HEV/PHEV equipped with very high energy density batteries.

The almost unlimited number of very quick charge/discharge cycles of super caps could recover more deceleration/braking energy and extend on-board batteries duration.

Electrified taxis, city buses and many other electrified vehicles could benefit from super caps/batteries combo.


While I doubt we'll ever find a "golden bullet" innovations like this serve as "silver bbs". Enough of them will eventually kill the ICE.

As HarveyD mentioned, the unlimited cyclic nature of capacitors opens up a lot of interesting applications once energy density passes a certain threshold. The electrification of inner-city busses is a particularly interesting application. Busses could be outfitted with enough capacitors to go 1-2miles. At certain stops there would be a quick charge station that would top off the busses capacitors. For an inner-city bus you might be talking about 2-4kw/hr. That's only about 80kg of capacitors at lead-acid energy densities.

Nick Lyons

If cheap enough, I wonder if these would make a good replacement for lead acid batteries in off-grid solar applications. Sounds like they might last essentially forever, so they might make sense even at a higher price than lead acid.


Supercapacitors tend to have high self-discharge rates, which may limit them both for grid storage and the application I was suggesting to replace lead-acid:


I see caps taking the transient load off of batteries in high demand applications like stop and go trucks and buses. They can be valuable if they extend the life of expensive batteries.


Yes if the cost is low enough and the energy density high enough a set of caps in conjunction with a battery pack can smooth the peaks of demand and greatly extend pack cycle life. I'm not sure exactly where the crossover point is but with batteries improving and getting less expensive it's a moving target which may never be hit. Once you get to an affordable 1000+ cycle 200 mile pack that's 200,000 miles of use, do we really need much more, and is it worth the added expense of caps?


The fact that it would put the nail in the coffin of lead carbon and Axion, with their repeated sledging of lithium whilst providing no proper performance testing of their battery and having zero sales is a bonus
It's always good to have more ammo to throw at Mr. Peterson :)


Capacitors are worth adding to almost any EV or hybrid battery if the price is right, as they do a far better job of capturing the energy from braking and so extend distances travelled.
The exception may be lithium titanate batteries, which have very high C values anyway.


Actually if the batteries are already capable of capturing the available regen there is no improvement from caps. Most lithium chemistries can already bring a vehicle to an uncomfortably fast stop from regen alone, unless you regularly do panic stops in your daily driving caps won't improve range at all, and they will take up space, weight, and cost that would be better used for more batteries.


The current Prius II recovers less than 20% of braking energy in order to protect the batteries.


With 1 kWh of batteries in an HEV at 70% state of charge, I do not see how regenerative braking can be a major contributor to mileage increases. As the battery packs become higher capacity for PHEV, we should see improvements.


It is not the capacity of the battery which matters too much, as the energy recovered from any one braking event is limited.
However, in stop/start traffic it builds up, and what counts is how much of it you can trap, ie power density, which capacitors are superb at.


The discussion was whether you need caps if you have a lot of battery capacity. For large trucks and buses, perhaps. A motor/alternator may be able to produce 30 kW when performing regenerative braking, but if you have no where to put that energy, it does not matter much. 1 kWh of batteries at 70% state of charge can only take a certain amount of energy in a short period of time.


If the amount of storage capacity is limiting how much regen you can recapture then caps are a poor choice compared to adding more cells. Yes caps can transfer energy quickly, but they have even worse capacity to hold energy than batteries. You'd still be better off adding more batteries to a HEV if you want to store more regen energy.


That is what I have been saying.


The question is how long the energy flow happens. At your figure of '30kw' you are only going to be raking for 2 seconds or so in city traffic.
That comes out to 16Wh or so, which can easily be stored in any hybrid battery.
In fact I believe they normally specify capacitors with perhaps 30Wh of storage, sot the bulk isn't too bad even with current low energy density capacitors, and would be a lot less with these.
That way you could store the energy from ~2 braking events, but the second one would be passed on to the battery, so that you don't overload the capacitor but still have energy for accelerations.
Personally, I hardly touch my brakes in city traffic, but that's me! ;-)


It is how fast does the chemistry change in almost fully charged batteries. What is the charge rate? When you look at charge curves for batteries, the last 10% takes longer. Can you charge a battery at 100C for 10 seconds? I don't think so.



I've coasted down a mountain in a 2008 Prius starting with a mostly dissipated battery and ending with a battery at maximum charge per the instruments.

What I noticed is that 8 minutes down the level highway beyond, I was back to half charge and using the ICE to increase the battery state of charge again. Ticked me off.

Separately, I wonder if a capacitor would be able to rapidly capture braking energy and then trickle charge a big battery to free its capacity back up?

HarveyD you down shift at each stop? is certainly possible to do with the proper electronic controls.

In city driving deceleration can produce a lot of energy, specially for heavy vehicles driven hard. Recovery will depend a lot on the capacity of the e-motors/generators and the capacity of the e-storage unit to accept very quick charges. That's where super caps excel.


If you are driving hard, then you are accelerating hard, and using more energy. Regen is always a loss system, you can't get back more than you used. Heavy vehicles use more energy to get moving, all regen can do is replace part of that.

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