As demand for ever more portable personal electronic devices continues to grow, so does the demand for equally portable and long-lasting energy storage and charging devices. [1] The next logical step is to incorporate energy generating and storing devices, such as supercapacitors, into our clothing to take advantage of the energy produced by body heat and movement as two new and renewable sources of energy. [2] Recently, exciting advancements have been made in textile-based supercapacitors (TSCs). Coating individual yarns with titanium carbide MXene flakes, a two-dimensional conductive material, is proved as a viable approach to create conductive yarns. These yarns can be further knitted into a capacitor structure to create a TSC and decrease the resistance by allowing electrons to take the path of least resistance as opposed to only one path available to them in wires. [3] Typically, synthetic- or cellulose-based yarns have been used to create these TSCs with reported specific areal capacitances of 220 mF/cm² for cotton. Nonetheless, protein-based yarns such as wool have not been used to make TSCs until now.

Here we report on the preparation of TSCs based on wool. Wool yarn was dip-coated in titanium carbide MXene colloidal solution and dried under continuous vacuum four times to achieve a high mass loading of conductive material on the fiber. This increased mass loading in a small area increases the capacitive performance of wool-based TSCs, as well as increasing the pseudocapacitive charge storage behavior. Using wool as a basis for the electrodes in TSCs takes advantage of the desirable properties of wool fibers; their hydrophilicity, hollow structure with high surface area and insulative nature, in addition to its exothermic behavior when wet. [4] The hollow structure of wool will allow for more MXene flakes to adhere to the fibers to boost capacitive behavior by creating more surface area to form an electric double-layer and to perform pseudocapacitive redox reactions with the electrolyte. [5] Wool’s hydrophilicity will increase interactions with the electrolyte to achieve the same result. [4] Wool-based TSCs can achieve specific areal capacitances of 315 mF/cm².

References

[1] S. Yong, J. Owen and S. Beeby, "Solid-State Supercapacitor Fabricated in a Single WovenTextile Layer for E-Textiles Applications," Advanced Engineering Materials, vol. 20, no. 5, 4 january 2018.

[2] S. Zopf and M. Manser, "Screen-printed Military Textiles for Wearable Energy Storage," Journal of Engineered Fibers and Fabrics , vol. 11, no. 3, 2016 .

[3] A. Levitt, D. Hegh, P. Phillips, S. Uzun, M. Anayee, J. Razal, Y. Gogotsi and G. Dion, "3D knitted energy storage textiles using MXene-coated yarns," Materials Today, vol. 34, pp. 17-29, April 2020.

[4] J. G. Cook, Handbook of Textile Fibers: Natural Fibres, 5 ed., vol. 1, Merrow Publishing, 1984.

[5] S. Aderyani, S. Shah, A. Masoudi, M. Green, J. Lutkenhaus and H. Ardebili, "Comparison of Nanoarchitecture to Porous Media Diffusion Models in Reduced Graphene Oxide/Aramid Nanofiber Electrodes for Supercapacitors," ACS Nano, vol. 14, 2020.