Chloride ions from seawater could power green batteries

While sodium, potassium and zinc have all been promising contenders to replace lithium in rechargeable batteries, researchers at Worcester Polytechnic Institute (WPI) have found that chloride, among the richest negatively charged ions in seawater, could be a viable alternative. Xiaowei Teng, the James H. Manning professor of chemical engineering at WPI, discovered a new redox chemistry empowered by chloride ions for the development of seawater green batteries.

Modern lithium-ion batteries can be problematic for grid storage, due to their high cost and reliance on critical materials, such as cobalt, nickel and lithium, as well as their limited geographical availability. The researchers leveraged chloride ions to empower redox chemistry of iron oxide battery materials, with their research findings published in the journal Chemistry of Materials.

The study revealed that chloride ion insertion into Fe(OH)₂ layered double hydroxide formed a Green Rust intermediate crystalline material, which assisted a one-time transfer Fe(OH)₂/FeOOH conversion reaction and improved cycling stability. This iron redox chemistry was discovered and examined in the WPI lab. Teng also conducted further studies at the Brookhaven National Laboratory to validate the results using operando synchrotron X-ray diffraction and high-resolution elementary mapping.

The researchers made an aqueous battery, a small lab-scale prototype that operated in the water-based electrolyte, using electrodes made from abundant elements such as iron oxides and hydroxides. While the researchers haven’t calculated the cost, the use of earth-abundant materials could be advantageous for the use of chloride in rechargeable batteries. According to the researchers, the US reportedly produces over 15 million tonnes of scrap iron wastes that are not recycled each year, many of which exist in the form of rust. Therefore, the reported rechargeable alkaline iron battery chemistry helps repurpose the iron rust waste into materials for modern energy storage.

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