What do water bottles, eggs, hemp, and cement have in common? They can be engineered into strange, but functional, energy-storage devices called supercapacitors.
As their name suggests, supercapacitors are like capacitors with greater capacity. Similar to batteries, they can store a lot of energy, but they can also charge or discharge quickly, similar to a capacitor. They’re usually found where a lot of power is needed quickly and for a limited time, like as a nearly instantaneous backup electricity for a factory or data center.
Typically, supercapacitors are made up of two activated carbon or graphene electrodes, electrolytes to introduce ions to the system, and a porous sheet of polymer or glass fiber to physically separate the electrodes. When a supercapacitor is fully charged, all of the positive ions gather on one side of the separating sheet, while all of the negative ions are on the other. When it’s discharged, the ions are randomly distributed, and it can switch between these states much faster than batteries can.
Some scientists believe that supercapacitors could become more super. They think there’s potential to make these devices more sustainably, at lower-cost, and maybe even better performing if they’re built from better materials.
And maybe they’re right. Last month, a group from Michigan Technological University reported making supercapacitors from plastic water bottles that had a higher capacitance than commercial ones.
Does this finding mean recycled plastic supercapacitors will soon be everywhere? The history of similar supercapacitor sustainability experiments suggests not.
About 15 years ago, it seemed like supercapacitors were going to be in high demand. Then, because of huge investments in lithium-ion technology, batteries became tough competition, explains Yury Gogotsi, who studies materials for energy-storage devices at Drexel University, in Philadelphia. “They became so much cheaper and so much faster in delivering energy that for supercapacitors, the range of application became more limited,” he says. “Basically, the trend went from making them cheaper and available to making them perform where lithium-ion batteries cannot.”
Still, some researchers remain hopeful that environmentally friendly devices have a place in the market. Yun Hang Hu, a materials scientist on the Michigan Technological University team, sees “a promising path to commercialization [for the water-bottle-derived supercapacitor] once collection and processing challenges are addressed,” he says.
Here’s how scientists make supercapacitors with strange, unexpected materials:
Water Bottles
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