Plastic bottles can be recycled into energy-storing supercapacitors
by Karmela Padavic-Callaghan  /  23 August 2023

“Plastic bottles can be upcycled into parts for supercapacitors, which store energy like batteries but release it much faster. Plastic pollution is prevalent in our environment, from litter in parks to garbage patches in the oceansDisposable drink bottles are a significant part of the problem. According to some sources, 38 billion of the bottles are sent to landfill each year in the US alone. Shengnian Wang at Louisiana Tech University and his colleagues wanted to turn some of them into energy storage devices called supercapacitors instead.

A supercapacitor can be charged like a battery but it releases energy – or discharges – more quickly. In addition, it often functions well for many more charging and discharging cycles than batteries do. The researchers developed a chemical procedure that rearranges the carbon atoms in the clear polyethylene plastic used in bottles into a supercapacitor component.

First, they cut plastic bottles into pieces and reacted them with water, nitric acid and ethanol at a high temperature and pressure for 8 hours. They then placed the resulting mixture into a centrifuge device that spins the solution at high speed, before finally drying it in an oven. This left them with thin sheets of carbon speckled with many carbon nanoparticles, each of which had a diameter of less than 2 nanometres. Their small size gives the carbon nanoparticles unusual electrical properties and makes them what physicists call carbon “quantum dots”.

When it comes to making energy storage devices with carbon components, each shape – sheets and dots – has drawbacks. But using the two in combination makes storage devices more effective, said Wang in a presentation at the American Chemical Society fall meeting in San Francisco, California, last week. He and his colleagues tested whether this “ball-sheet carbon structure” makes for a working supercapacitor electrode. They found that the supercapacitor charged and discharged as expected and, after charging, it could power a small red LED light. Additionally, charging and discharging it 12,000 times decreased its capacity to store energy by only 2 per cent.

In further experiments, the researchers built ball-sheet carbon structures using a more pure and less processed plastic, but when used in supercapacitors, these components had a similar performance level to those made from the old drink bottles. As such, Wang said that their method may offer a way to upcycle plastic waste directly, with no intermediate processing steps. However, Xiaojun Ren at the University of New South Wales in Australia, who was not involved in the research, points out that supercapacitors built using the upcycled plastic did not always release all of the energy they had gained during charging. He says this means  there is still room to further improve the performance of the supercapacitors.”

Upcycling plastic waste toward sustainable energy storage
by Holly Ober  /  August 11, 2020

“What if you could solve two of Earth’s biggest problems in one stroke? UC Riverside engineers have developed a way to recycle plastic waste, such as soda or water bottles, into a nanomaterial useful for energy storage. Mihri and Cengiz Ozkan and their students have been working for years on creating improved energy storage materials from sustainable sources, such as glass bottlesbeach sandSilly Putty, and portabella mushrooms. Their latest success could reduce plastic pollution and hasten the transition to 100% clean energy. “Thirty percent of the global car fleet is expected to be electric by 2040, and high cost of raw battery materials is a challenge,” said Mihri Ozkan, a professor of electrical engineering in UCR’s Marlan and Rosemary Bourns College of Engineering. “Using waste from landfill and upcycling plastic bottles could lower the total cost of batteries while making the battery production sustainable on top of eliminating plastic pollution worldwide.”

“Scanning electron microscope image of a material for energy storage made from upcycled plastic bottles. (Mihri Ozkan & Cengiz Ozkan/UCR)”

In an open-access article published in Energy Storage, the researchers describe a sustainable, straightforward process for upcycling polyethylene terephthalate plastic waste, or PET, found in soda bottles and many other consumer products, into a porous carbon nanostructure. They first dissolved pieces of PET plastic bottles in a solvent. Then, using a process called electrospinning, they fabricated microscopic fibers from the polymer and carbonized the plastic threads in a furnace.

After mixing with a binder and a conductive agent, the material was then dried and assembled into an electric double-layer supercapacitor within a coin-cell type format. When tested in the supercapacitor, the material contained the characteristics of both a double-layer capacitor formed by the arrangement of separated ionic and electronic charges, as well as redox reaction pseudo-capacitance that occurs when the ions are electrochemically absorbed onto surfaces of materials. Though they don’t store as much energy as lithium-ion batteries, these supercapacitors can charge much faster, making batteries based on plastic waste a good option for many applications.

By “doping” the electrospun fibers prior to carbonization with various chemicals and minerals such as boron, nitrogen, and phosphorous, the team plans to tune the final material to have improved electrical properties. “At UCR, we have taken the first steps toward recycling plastic waste into a rechargeable energy storage device,” said doctoral student and first author Arash Mirjalili. “We believe that this work has environmental and economic advantages and our approach can present opportunities for future research and development.”

The authors believe the process is scalable and marketable, and that it represents major progress toward keeping waste PET out of landfills and the oceans. “The upcycling of PET plastic waste for energy storage applications could be considered the holy grail for green manufacturing of electrode materials from sustainable waste sources,” said mechanical engineering professor Cengiz Ozkan. “This demonstration of a new class of electrodes in the making of supercapacitors will be followed by a new generation of Li-ion batteries in the future, so stay tuned.”

The paper, “Upcycling of polyethylene terephthalate plastic waste to microporous carbon structure for energy storage,” is available here. Other authors include Bo Dong and Pedro Pena, also at UC Riverside.”



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