Scientists at the University of Sydney's School of Chemical & Biomolecular Engineering have come up with a way to use durian fruit waste to create energy stores for rapid electric charging.
Turns out the extremely stinky durian fruit—which primarily grows in southeast Asian countries like Malaysia, Indonesia, and Thailand—can synthesize supercapacitors with its biowaste.
Their results were published this month in the Journal of Energy Storage.
The durian, a husked tree fruit from Southeast Asia, may smell unspeakably terrible, but it still tastes sweet and delicious like its closely related cousin, the jackfruit. And the two fleshy fruits could be key ingredients in a cutting-edge approach to lightning-fast electric charging, from your iPhone to your Tesla.
When we say the fruit stinks, we're not exaggerating. The late chef, author, and travel documentarian Anthony Bourdain once said the stench was "indescribable, something you will either love or despise … Your breath will smell as if you’d been French-kissing your dead grandmother."
But that didn't discourage Vincent G. Gomes, an associate professor at the University of Sydney and coauthor of a new scientific paper that describes a novel method for extracting durian and jackfruit biowaste for more efficient, ultra-quick electric chargers. His work was published earlier this month in the Journal of Energy Storage.
Don't expect manufacturers to shove tiny pieces of the spiky fruit into your car battery. Instead, Gomes and his team have uncovered a process wherein they can turn the guts of the fruit into supercapacitors that can store vast amounts of energy. Once again, the researchers note in their paper, nature has already come up with an extraordinary solution. They just needed to mimic it.
"The structural precision of natural biomass with their hierarchical pores, developed over millions of years of biological evolution, affords an outstanding resource as a template for the synthesis of carbon-based materials," they wrote. "Their integrated properties of high surface area, in-plane conductivity and interfacial active sites can facilitate electrochemical reactions, ionic diffusion and high charge carrier density."
What Are Supercapacitors?
Gomes and his fellow scientists wrote in their paper that due to climate change and the aligning rapid depletion of fossil fuels, manufacturers are developing energy storage devices called supercapacitors with high energy density to "promote rapid energy capture and delivery."
We're specifically talking about electrochemical supercapacitors, or "electrical double layer capacitors." These are "ideal energy storage candidates," for applications from portable medical devices to batteries used in transportation, according to the authors.
These kinds of supercapacitors—like the ones being created from durian fruit—are great because they have a superior ability to maintain consistent cycling abilities. In energy talk, a cycle is the process of fully charging and draining a battery.
Adoption of supercapacitors is still pricey, though, which is why Gomes and company have turned to relatively inexpensive organic waste from the jackfruit and the durian. Typically, supercapacitors are constructed with two metal foils that are each coated with an electrode material, like activated carbon.
Better Than Batteries
Due to environmental concerns and high costs, energy research such as Gomes's work is shifting focus from your typical lithium-ion batteries to supercapacitors. So what's the difference?
Batteries have two electrodes, separated by an electrolyte, which is just a chemical substance that serves as a catalyst for a chemical reaction inside the battery. Those reactions convert chemicals inside a battery into new substances that release electrical energy along the way. Once all chemicals inside have been depleted, the processes stop and the battery is dead. Every time you've replaced your smoke alarm batteries (or your Walkman batteries back in the day), you've experienced this energy death.
Rechargeable batteries, by contrast, allow the internal chemical reactions to run in both directions, becoming cyclical in nature. That's why the lithium-ion battery inside your iPhone can be charged and drained over and over and over.
Capacitors use static electricity rather than chemical energy to store energy. To charge a capacitor, it's a little bit like rubbing a latex balloon against your hair to create sticky static. An electrical charge builds up inside as the negative and positive charges build up on the metal plates inside the capacitor. While capacitors are leaps and bounds ahead of batteries in some ways—they don't contain toxic metals and they can be recharged pretty much infinitely–they don't store nearly the same amount of electrical energy as your typical battery does, weight for weight.
Enter supercapacitors, which have larger metal plates inside than your average capacitor. Each is coated with a porous substance like activated charcoal, which creates a larger surface area for storing more charges. If you pretend that electrical energy is water, a regular old capacitor is like a cloth, holding just a bit of the spilled water, and a supercapacitor is like a sponge.
Just Like a Sponge
Maybe creating supercapacitors from fruit sounds crazy. But because the absorbent power of powdery charcoal helps supercapacitors store more energy, it only makes sense that carbon-containing biomatter like the flesh of highly porous fruits such as the durian could make a great addition.
From the smelly fruits, Gomes and the rest of the team synthesized a carbon aerogel, which are just like the silica packets that help keep moisture out of food products or packaged electronics in that they're both highly porous. In the past, scientists have done much the same with watermelons, pomelo peels, and even paper pulp.
"The fibrous, fleshy portions of organic wastes with good mechanical stability were considered as candidate precursors compared to hard, dense ones. The waste fruit cores of durian (Durio zibethinus) and jackfruit (Artocarpus heterophyllus) were selected as candidates based on their structures and their prospect of intrinsic nitrogen doping," the researchers wrote in the paper.
The best part? If widely adopted, this new approach to electrical storage will be a godsend for the environment, according to Gomes and his coauthors.
"Converting food wastes into value-added products will not only improve the overall economy, but also reduce environmental pollution," they write.
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