(312h) Teamwork Makes the Dream Work: Performance of Ti3C2 Mxene/Polypyrrole Composites Applied to Wool Yarn and Its Long-Term Performance As a Textile-Based Supercapacitor (TSC)

Humans continue to work towards creating a long-term human presence in space; in order to achieve this goal, it will be necessary to develop robust, sustainable, and recyclable items to eliminate the need for expensive re-supply missions to space stations, the Moon, or other planets/moons in the solar system. This includes ways to collect, store, and deliver clean energy to charge personal electronics or spacesuits. Developing smart energy storing garments that can collect and store power generated by waste body heat and movement will provide a reliable energy source to power small electronics within the spacesuit, allowing for longer space- or moonwalks.

One such energy-storing technology is TSCs which can be made by applying conductive material onto a yarn substrate and then knitting up a supercapacitor. Two popular conductive materials in this area of research are conductive polymers, such as polypyrrole (PPy) and MXenes. MXenes are a two-dimensional conductive material with base chemical formula M_n+1X_nT, where M is a transition metal, X is carbon and/or nitrogen, and T represents the surface terminations created by the method of synthesizing this material. In this case, Ti₃C₂ was selected for its excellent cycling stability, high conductivity, non-toxicity, and hydrophilicity. The main limitation of using MXenes in TSCs is their poor chemical stability which creates problems in their long-term use. The conductive polymer used in tandem with Ti₃C₂ MXenes was polypyrrole (PPy), an organic heterocyclic aromatic compound with chemical formula H(C₄H₂NH)_nH selected for its positive surface terminations. While conductive polymers, including PPy, are chemically stable, they have poor cycling stability and low conductivity, limiting their applications in electronics. In this study, we utilize the unique properties of MXene and apply a thin film of PPy to create composites that address the challenges of each individual material.

The wool yarn was used as a substrate due to its excellent adsorption properties, negatively charged fiber surface, insulating properties, and sustainability. As a protein-based fiber made of keratin, wool fibers contain nitrogen and sulfur, which give wool its adsorptive properties and negatively charged surface. This charged surface makes it easier to coat with conductive material, and its adsorptive properties will allow more uptake of electrolyte, decreasing the distance between the conductive material on the fiber surface and the ions in the adsorbed electrolyte, allowing for faster charge and discharge of the TSCs created with this material.

Here we report on a composite conductive material constructed from Ti₃C₂ MXene flakes intercalated with polypyrrole (PPy) and applied to wool yarn before knitting up TSCs with it. The PPy will compensate for the poor chemical stability of the Ti₃C₂ MXene by acting as an anti-corrosion coating, and in turn the MXene will compensate for the poor cycling stability and conductivity of the PPy. The charged surface of the wool fibers will more readily interact with the conductive material during the coating process, and its adsorptive properties will provide a platform that more readily provides ions to the conductive material during the charge and discharge process.