Supercapacitors in Motion: Autonomous Microswimmers for Natural-Resource Recovery

An electroadsorption technique similar to the ultrafast charging mechanism in supercapacitors is utilized to remove metals with different sizes and hydrophilicities from contaminated water using self-propelled microswimmers. The swimmers carry graphite fibre or bismuth with a layered crystal structure providing high electrostatic double-layer capacitances. Unlike previous methods, this electrochemical technique does not only utilize the surface of the swimmers, but due to the interlayer spacing of the graphite and bismuth, it is able to store metals in approximate to 400 layers, allowing removal and recovery of >50 ppm lithium in only 5 min. A larger interlayer distance between bismuth sheets allows the removal of bigger cations (sodium and calcium), expanding the application of this method to a large variety of natural elements. Finally, magnetic navigation of charged swimmers to an oxygen-saturated media causes oxidation and thus immediate release of the metal ions from the swimmers.