The crabmeat is delicious – it’s unassailable, garlic-buttery truth. But here’s something you might not know about your predilection for boiled shellfish: Each year, approximately six to eight million tons of crab, shrimp, and lobster shell waste are produced worldwide, most being dumped directly into the ocean or landfills, depending on the country.
The problem is not so much the colossal waste thrown at the table as the missed opportunity. The sturdy exoskeletons of crabs and their marine counterparts are rich in useful and versatile chemicals like calcium carbonate, which has medicinal and industrial uses, and chitin, the second most abundant natural polymer found on Earth.
All You Need Is Electrons (And Some Conductive Metals)
The spark that ignites your phone is due to chemistry that occurs deep within a battery.
Chemical reactions called redox reactions produce a steady drumbeat of electric current in the form of moving electrons. These travel through a circuit consisting of the battery’s electrodes (made of two different conductive metals), its chemical electrolyte (a gel or liquid-like material containing charged particles called ions), and any device or device to which the battery is connected.
There are various metals and electrolytes used in a battery. For example, in your common household alkaline battery, the positive electrode (the cathode) is made of manganese oxide and the negative electrode (or anode) is made of the trace mineral zinc. The intermediate electrolyte is potassium hydroxide. In lithium-ion batteries, lithium is usually combined with another metal such as cobalt at the cathode and carbon at the anode, and also constitutes the electrolyte.
Lithium-ion batteries are the rising star of the power world for being lightweight yet delivering plenty of power (and they’re rechargeable, to boot). Unsurprisingly, these batteries have found their way into nearly every electronic device and electric vehicle over the past few decades, but lithium mining has a heavy and devastating impact on the environment. Additionally, lithium-ion batteries are not easily degradable or recyclable, making them not entirely compatible with sustainability, at least in their current form.
“Rechargeable batteries as green energy sources are essential to reduce our dependence on fossil fuels and reduce greenhouse gas emissions. However, with the growing demand for electric vehicles in recent years, large amounts of batteries are produced and consumed, which raises the possibility of environmental issues,” said Meiling Wu, first author of the new study and postdoctoral fellow at the University of Maryland. in an email to Popular Mechanics. “For example, polypropylene and polycarbonate separators, which are widely used in Li-ion batteries, take hundreds or thousands of years to degrade and burden the environment.”
Crabs to the Rescue
Scientists have been toying with chitin for the past few years, looking for ways to incorporate the organic substance – which is structurally similar to plant cellulose – into batteries. In 2016, MacLachlan and his lab at the University of British Columbia found that when you cook chitin with nitrogen at temperatures as high as 1,652 degrees Fahrenheit, it turns old crab shells into a carbon-nitrogen material suitable for the electrodes.
But Wu and his colleagues at the University of Maryland took a different approach. They focused on zinc-based batteries, which are common disposable batteries, but not rechargeable. Because the mineral is more readily available than lithium (read: cheaper to produce and supply) and less toxic (zinc batteries use water as an electrolyte), zinc has attracted a lot of interest as a our silver-white energy knight.
Replacing lithium with zinc is not easy, however. In batteries as an electrode, zinc has a tendency to form irregularities on its surface. These irregularities form when electrons move around and form small, snowballing bumps into larger and larger ones called dendrites, which disrupt the battery’s electrical current.
Since chitosan, a chemically processed derivative of chitin, interacts well with water and is able to keep it from floating willy-nilly, Wu and his colleagues thought they could use it to make a battery separator, a semi-permeable membrane that keeps the opposite charged electrodes apart, it’s also biodegradable.
So how did they do it? The researchers took a coin-sized film of chitosan and bathed it in a zinc-filled solution to make the mineral adhere to the film. Then they wrung out the chitosan-zinc film and pressed it tightly to pack it densely. Unlike previous attempts to densify chitosan films, this technique allowed for relatively large pores (up to five micrometers in size), allowing free flow of ions, Jodie Lutkenhaus, professor of chemical engineering at Texas A&M University, who was not involved in this study, says Popular Mechanics.
“It’s critical because when you think of a crustacean shell, you think it’s really hard and dense, and that’s not good for ion conduction,” says Lutkenhaus, who has researched batteries of organic origin.
To complete the construction, a zinc anode was placed above the chitosan-zinc separator with a cathode made of an organic compound called poly(benzoquinonyl sulfide) or PBQS. When Wu and his colleagues ran their Krabby battery in the lab, they saw nothing of this dendrite formation on the zinc anode. Impressively, it generated an electric current of 50 milliamps per square centimeter for 400 hours (or 1,000 charge cycles), which is close to what small lithium batteries are capable of.
Then they buried the chitosan-based electrolyte, not the entire battery itself, to see how long it would take to degrade. Wu says they found that it takes about five months for microorganisms living in dirt to eat away at the electrolyte, which is much faster than conventional electrolytes found in landfills and definitely good for the body. ‘environment.
“That doesn’t mean the battery itself will degrade within five months,” she says. “In fact, the electrolyte is packed in a closed cell, which is separated from air and organisms. This type of device can work much longer.
The Future of Chitosan-Based Batteries
While you’re not going to see crab shell batteries anytime soon, the researchers hope their batteries will become commonplace, used in electronic devices like your cell phone to dedicated renewable energy storages that release into a commercial grid. .
Considering chitosan only costs about $1.70 per gram and you don’t need it to make their prototype (only about 20 micrograms for a 20 millimeter coin-sized stack), this may give the chitosan-zinc battery a price advantage over lithium-ion batteries, which suffer from rising demand and accompanying costs.
However, with soaring temperatures from climate change hitting marine life the hardest, the question arises as to what will happen to costs if chitosan-based batteries take off. It’s also worth thinking about how environmentally friendly its use would really be in the future – we need to consider the carbon footprint of the activities associated with recovering chitin and transforming it into chitosan.
“I think the next important step would be to do a techno-economic analysis to look at what the global production of chitosan is and if we’re going to, say, apply it to grid-scale energy storage, do we have enough access to this?” says Lutkenhaus. “If we start using it, will it change the price because of the demand…[Also] life cycle analysis…the carbon footprint of catching shellfish, shipping it and transformation.”
Luckily, says Wu, we have other sources of chitin, such as in insects and fungal cell walls, so it’s not entirely a misfire if a marine source falls by the wayside. And although no one so far has attempted to synthesize chitin in the lab, who knows what the future holds. Right now, it looks like our brackish seafood waste could be a solution to our current energy problems.
Miriam Fauzia is a contributing writer for Popular Mechanics obsessed with all things energy.
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