Nickel hydroxide growth on renewable activated carbon microfibers for the development of supercapacitors

Abstract

Lignin is one of the most common naturally occurring macromolecules. It is associated with cellulose and hemicelluloses in terrestrial plants, providing mechanical stiffness and contributing to moisture control and defense toward insects and fungi. Lignin is typically a polymer of three different cinnamyl alcohols, para‐coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, which varies with the plant species. Solubilized lignin from the kraft pulping process is mainly concentrated and burned as part of the liquor recovery cycle in the kraft pulping. Given its aromatic nature, other uses of lignin include the development of platform chemicals, polymers, and fuels. This work uses lignin to develop carbon fibers to act as supercapacitors. Lignin microfibers were produced using an electrospinning process, carbonized under an inert atmosphere, and activated to increase surface area and improve capacitance. The activation process is shown to improve the specific capacitance of the material. In addition to activation, nanocrystals were grown on the surface of the carbon microfibers as these nanocrystals have been shown to improve the specific capacitance. When both surface modifications are performed to the lignin‐based carbon fiber, it improves the specific capacitance retention regarding scan rate increase during cyclic voltammetry. The specific capacitance for the carbon fiber, activated carbon fiber, Ni(OH)2 carbon fiber, and Ni(OH)2 activated carbon fiber at 10 mV/s are 189, 206, 10, and 103 F/g.