Carbon doped with nitrogen dramatically improves storage capacity of supercapacitors

December 28, 2015 by Bob Yirka report
Carbon doped with nitrogen dramatically improves storage capacity of supercapacitors
Fabrication schematic of ordered mesoporous fewlayer carbon (OMFLC). Credit: Science (2015). DOI: 10.1126/science.aab3798

(Phys.org)—A team of researchers working in China has found a way to dramatically improve the energy storage capacity of supercapacitors—by doping carbon tubes with nitrogen. In their paper published in the journal Science, the team describes their process and how well the newly developed supercapacitors worked, and their goal of one day helping supercapacitors compete with batteries.

Like a , a capacitor is able to hold a charge, unlike a battery, however, it is able to be charged and discharged very quickly—the down side to capacitors is that they cannot hold nearly as much charge per kilogram as batteries. The work by the team in China is a step towards increasing the amount of charge that can be held by supercapacitors (capacitors that have much higher capacitance than standard capacitors—they generally employ carbon-based electrodes)—in this case, they report a threefold increase using their new method—noting also that that their supercapacitor was capable of storing 41 watt-hours per kilogram and could deliver 26 kilowatts per kilogram to a device.

The new supercapacitor was made by first forming a template made of tubes of silica. The team then covered the inside of the tubes with carbon using and then etched away the silica, leaving just the carbon tubes, each approximately 4 to 6 nanometers in length. Then, the carbon tubes were doped with nitrogen atoms. Electrodes were made from the resulting material by pressing it in powder form into a graphene foam. The researchers report that the doping aided in chemical reactions within the supercapacitor without causing any changes to its electrical conductivity, which meant that it was still able to charge and discharge as quickly as conventional supercapcitors. The only difference was the dramatically increased storage capacity.

Because of the huge increase in , the team believes they are on the path to building a supercapacitor able to compete directly with batteries, perhaps even . They note that would mean being able to charge a phone in mere seconds. But before that can happen, the team is looking to industrialize their current new , to allow for its use in actual devices.

Explore further: Researchers find ordinary pen ink useful for building a supercapacitor

More information: T. Lin et al. Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage, Science (2015). DOI: 10.1126/science.aab3798

ABSTRACT
Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).

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9 comments

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Nicku
3.8 / 5 (4) Dec 28, 2015
E-cars vs Hydrogren cars will be the future.
mmclean
5 / 5 (2) Dec 29, 2015
What role does nickel (Ni) play?

Or did your editors really let Ni slip by as the symbol for nitrogen?
mmclean
5 / 5 (2) Dec 29, 2015
oops - my error - sorry, please remove my comment from 18 minutes ago - thx.
Whydening Gyre
5 / 5 (1) Dec 29, 2015
oops - my error - sorry, please remove my comment from 18 minutes ago - thx.


Oops - my error - sorry. Dang - can't take back that 5 star...:-)
Sonhouse
5 / 5 (1) Dec 30, 2015
Faster charging also takes large increase in the capability of power supplies doing the charging so it has to be a multi pronged effort.

If a capacitor or battery took in one amp and takes one hour to fully charge, if you want to do that in one second, you better be able to supply 3600 amps, a huge difference in power supply capacity.
antialias_physorg
5 / 5 (2) Dec 30, 2015
Envision charging stations with a cheap, but slow-to-charge mass power storage (e.g. sodium ion batteries) and an intermediary supercap bank for fast charging of vehicles. Since there is a lull between vehicles at charging stations that time can be sude to fill up the fast charging bank. Fo r home use it would be a supercap 'powerwall' that slowly recharges over the course of a day and dumps it into your car when you get home.

Effectively you'd be charging your vehicle supercap-to-supercap.

(However these supercaps aren't there yet in terms of power density. Also there's the issue that capacitors don't have a constant voltage when discharging as opposed to batteries. So the amount of parallel banks and switching logic is quite a bit more complex with supercaps)
Eikka
not rated yet Dec 30, 2015
Effectively you'd be charging your vehicle supercap-to-supercap.


There's a bit of a problem there due to the charge-voltage behaviour of capacitors.

If you connect a full capacitor to an empty capacitor, the full capacitor's voltage starts to fall immediately until the two voltages equalize and you can never charge the empty capacitor to more than 50% full unless the other capacitor is vastly larger, or there's some sort of charge pump in between to raise the voltage.

It's like connecting two buckets with a hose at the bottom - as soon as the water level equalizes the flow stops.

Meanwhile, batteries typically maintain a voltage plateau due to the chemical potential at work rather than the accumulation of electric charge, so a battery can fill a capacitor without extra electronics.

Capacitor self-discharge is also several orders of magnitude greater than with batteries, so it's questionable whether vehicles or "power walls" will ever make much use of them.
24volts
5 / 5 (1) Dec 30, 2015
I can see one good use for these once they get them commercialized. They would work well
with fuel cell systems in cars. They can provide the extra boost of amps needed in a hurry for passing on the highway or first moving the vehicle when starting at a light etc... Motors pull a lot of extra current then compared to when they are running at speed. It might actually extend the ranges slightly on battery operated vehicles too when in the city and having to stop at a lot of lights.
baudrunner
1 / 5 (2) Dec 31, 2015
You can just keep making foam and pressing it, or you can stop what you're doing, assess why things happen the way they do, and develop the theory that ultimately gets proved and gives us the next great little super battery that we can put in our four-wheelers and not recharge for three months at a go, no matter that I might be the busiest door-to-door salesman in the world (remember them?). I'd buy one, and still take the chance that it has the potential to blow up half the neighborhood (you know, I get spell-checked on 'neighbourhood', and all it does is get me to change the 'ou' to an 'o' but it does absolutely nothing about the 'eigh', which should be corrected to 'ay', if we're to follow the program - I mean, we're not buying into the "queen's" English anymore, are we? I mean, isn't that why we write "neighborhood", because it's the (almost) American English (and I'm all for it) ), but anyway, wouldn't you buy one of those batteries? ..and why is it "neigh", again..?

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