A number of lab-engineered nanomaterials have thus far just fallen short of providing a suitable alternative material for supercapacitor electrodes. But the answer may be found in the nearest ashtray. That's right: the much-despised cigarette butt may, in fact, offer the solution.
A group of researchers in South Korea has discovered that the material that makes up used cigarette butts outperforms carbon, graphene and carbon nanotubes in energy storage.
The researchers, who published their findings in the journal Nanotechnology, took used cigarette filters and found that under a nitrogen-containing atmosphere, they could be transformed into a porous carbon material that by itself has a pore structure that is perfect for energy storage in the electrodes of supercapacitors.
Supercapacitors, also known as ultracapacitors or electrochemical double-layer capacitors (EDLCs), have held out the promise that they could store as much energy as electrochemical batteries such as lithium-ion batteries, but charge up in a matter of seconds and offer high power density for quick bursts of a large amount of energy. Supercapacitors are currently used for this purpose in applications such as powering cranes or buses.
What’s perhaps most attractive about cigarette butts for supercapacitors is that there is a seemingly endless supply of the discarded filters. According to the press release accompanying the research, there are an estimated 5.6 trillion used cigarettes, or 766,571 metric tons, being deposited into the environment every year. And if, on the off chance that it were possible to completely deplete the resource by using the butts to create these supercapacitor electrodes, doing so would still raise cheers at the fact that a way to eliminate the blight of cigarette butts had been found.
"Our study has shown that used-cigarette filters can be transformed into a high-performing carbon-based material using a simple one step process, which simultaneously offers a green solution to meeting the energy demands of society,” said Jongheop Yi, a professor at Seoul National University, and a coauthor of the study, in the press release. "Numerous countries are developing strict regulations to avoid the trillions of toxic and non-biodegradable used-cigarette filters that are disposed of into the environment each year—our method is just one way of achieving this."
The new material possesses the key features that an electrode storage material for supercapacitors would ideally have. It has a large surface area, but perhaps more critically, it has the proper distribution of pore sizes that makes it capable of utilizing a large amount of electrolyte ions and it has quick transfer mobility. It compares favorably to graphene, which has looked very attractive for the electrodes of supercapacitors because of its transfer mobility, but doesn’t really stack up to activated carbon in terms of surface area.
"A high-performing supercapacitor material should have a large surface area, which can be achieved by incorporating a large number of small pores into the material," said Yi in the release. "A combination of different pore sizes ensures that the material has high power densities, which is an essential property in a supercapacitor for the fast charging and discharging."
The bottom line is that in tests, the used-cigarette filters were capable of storing more electrical energy than commercially available carbon. They also beat previously published results for graphene and carbon nanotubes.
Just conjecture, but it would seem that cigarette manufacturers might be wise to invest in this technology since it offers a way to make an extra buck on each cigarette sold.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.