Edited by Ryan Jien
We Malaysians sure love our seafood! The perpetual long queues at seafood restaurants especially on weekends are a testament to the popularity of these tempting, cholesterol laden crustaceans; and what seafood meal would be complete without the pièce de résistance – the crab platter! Once we are done cracking the crab legs and sucking every last morsel of meat, a mountainous pile of crab shells sits in front of us, waiting to be thrown out en masse by the restaurant. While the sheer amount of waste discarded may seem inconsequential to us, scientists have discovered that the empty crab shells are worth much more than they appear.
Image 1: Photo of a pile of empty crab shells after consumption. Source: https://modernfarmer.com/2022/04/chitosan-in-agriculture/
Electric vehicles are now rapidly increasing in popularity among consumers as they play an important role in reducing greenhouse gas emissions and mitigating the effects of harmful human activity on the environment. Unfortunately, the batteries which power them aren’t as sustainable as we would like them to be. The conventional batteries which power said electric vehicles, our everyday electronic gadgets, and even toothbrushes, are mainly lithium-ion batteries. These take more than a hundred years to decompose due to the polypropylene and polycarbonate separators¹ inside them, while lithium is gradually becoming a more limited resource in our Earth’s crust. Besides, lithium extraction is proven to have detrimental effects on our environment including loss of biodiversity, soil degradation, air contamination and water shortages². And while more renewable zinc batteries have been in the works, the unwanted zinc dendrite formation, corrosion, and hydrogen production during the stripping and plating process³ make them unlikely to substitute lithium batteries in the long run. Thankfully, research scientists have uncovered a potential solution to this dilemma.
Crabs have exoskeletons made of chitin, a type of polysaccharide which makes their shells hard and resistant.⁴ Chitin is first hydrolysed with concentrated sodium hydroxide solution to form chitosan, whose molecules contain rich hydroxyl and amine groups that can form hydrogen bonds with water to reduce the content of free water in the chitosan-zinc gel electrolyte to be made. Chitosan is then dissolved in acetic acid aqueous solution. Following a filtration process to remove unwanted impurities and evaporation to make a concentrated chitosan solution, the wet film produced is immersed in Zn-NaOH solution, resulting in a porous chitosan-zinc membrane. This is then soaked in ZnSO₄ solution and densified at high pressure to form the chitosan electrolyte. Finally, zinc anodes, poly(benzoquinonyl sulfide) (PBQS) organic cathodes and the chitosan electrolyte make up the chitin-zinc batteries.
Figure 2: Photo of the porous chitosan-zinc membrane. Source: https://www.cell.com/matter/fulltext/S2590-2385(22)00414-3
These chitin-zinc batteries are 99.7% efficient and have a high cycling stability₁ of more than 1000 battery cycles (about 400 hours). This makes them a viable option to store energy generated by wind and solar for power grids.⁶ The water bonding capability of the chitosan-zinc membrane helps reduce side reactions of the aqueous chitosan-zinc electrolyte with the zinc metal anode, improving the battery’s performance. The electrolyte demonstrates high mechanical strength and zinc ion conductivity, which allows a desirable zinc deposition. Furthermore, the electrolyte is non-flammable and biodegradable – it breaks down completely within five months and leaves behind the zinc component of the battery which can then be recycled and reused.⁵ Its low manufacturing costs are comparable to commercial separators used in batteries, and along with the environmental advantages mentioned above, highlight the potential of natural biopolymers for more sustainable and green processes in the industry.
Figure 3: A schematic diagram of the sustainable zinc metal battery based on the chitosan biomaterial, which comes from crab shells and degrades in soil after use. Source: https://www.cell.com/matter/fulltext/S2590-2385(22)00414-3
Figure 4: Process showing the biodegradability of the chitosan-zinc membrane within 5 months. Source: https://www.cell.com/matter/fulltext/S2590-2385(22)00414-3
The manufacturing of chitin-zinc batteries is only one of the many innovations scientists and researchers have designed to improve the sustainability of materials in the industry. This example highlights one of the key concepts of green chemistry₂ — the synthesis of safer, more biodegradable chemicals. Green chemistry aims to design chemicals and processes that reduce the negative impacts on the environment, and its main goals are summarised into twelve key principles. These include the prevention of hazardous waste, the production of safer chemicals, and the designing of more energy efficient processes.⁷ It starts right from the design stage of products by ensuring toxic waste is disposed of properly and by maximising all materials used in the manufacturing process to make the final product.
The potential applications of green chemistry are boundless and among us in our everyday lives, and we only need to open our minds to the abundant sources nature has provided in order to achieve a more sustainable, cleaner and safer future. So the next time you indulge in a hearty crab feast, remember the humble shell could well hold the answer to a greener future for the next generation.
Glossary (subscript):
Cycling stability of a battery – the number of charging or discharging cycles until the capacity of the battery is reduced to a certain amount of its nominal capacity.
Green chemistry – the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.
References (superscript):
Novel zinc battery powered by crabs. (n.d.). Materials Today. https://www.materialstoday.com/biomaterials/news/novel-zinc-battery-powered-by crabs/#:~:text=%E2%80%9CGenerally%20speaking%2C%20well%2Ddeveloped,for%20transfer%20to%20power%20grids
Campbell, M. (2022, November 21). In pictures: South America’s “lithium fields” reveal the dark side of our electric future. Euronews. https://www.euronews.com/green/2022/02/01/south-america-s-lithium-fields-reveal-the-dark-side-of-our-electric-future
Wu, M., Zhang, Y., Xu, L., Yang, C., Hong, M., Cui, M., Clifford, B. C., He, S., Jing, S., Yao, Y., & Hu, L. (2022). A sustainable chitosan-zinc electrolyte for high-rate zinc-metal batteries. Matter, 5(10), 3402–3416. https://doi.org/10.1016/j.matt.2022.07.015
Quaglia, S. (2022, September 1). Crab and lobster shells could be used to make renewable batteries. The Guardian. https://www.theguardian.com/science/2022/sep/01/crab-lobster-shells-could-used-make-renewable-batteries
Stern, B. (2024, January 18). The lithium replacement to revolutionize EV batteries may just be shellfish — and it’s 99.7% efficient after over 400 hours of use. The Cool Down. https://www.thecooldown.com/green-tech/shellfish-batteries-crab-lobster-science-biodegradable/
Patel, P., & Patel, P. (2022, September 8). New biodegradable, recyclable battery is made of crab shells. Anthropocene | Innovation in the Human Age. https://www.anthropocenemagazine.org/2022/09/battery-made-with-crab-shells-is-biodegradable-and-recyclable/
12 Principles of Green Chemistry - American Chemical Society. (n.d.). American Chemical Society. https://www.acs.org/greenchemistry/principles/12-principles-of-green-chemistry.html
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