Kraft lignin-derived carbon nanofibres as electrodes in aqueous alkaline supercapacitors
File(s)
Author(s)
Schlee, Philipp
Type
Thesis
Abstract
Kraft lignin emerges as a by-product of the pulp and paper industry on a megaton scale every year. Besides its use as energy source through combustion, alternative uses are sought after as the amount of lignin rises continuously exceeding the energy demand of pulp and paper mills and their capacity to incinerate lignin. Instead of using Kraft lignin as a fuel, it has been shown in this PhD project that hard- and softwood Kraft lignins extracted by the LignoBoost process and refined via fractionation can be used as precursors for the manufacture of electro-spun carbon nanofibre (CNF) supercapacitor electrodes. Various routes towards highly na-noporous electrode materials with a unique micro- and macro-morphology were developed. At first, the development of nanoporosity in the lignin fibres was investigated with increasing stabilization temperature in the absence of any additive. Hardwood Kraft lignin inherently develops more nanoporosity than softwood Kraft lignin, which was shown to be caused main-ly by the difference in side-chain linkages and functional groups. To further enhance the in-herent development of nanoporosity in hardwood Kraft lignin-derived CNFs, activation with CO2 after carbonization and the addition of NaNO3 in the electrospinning solution were inves-tigated. Softwood Kraft lignin-derived carbon nanofibres were used as electrically conductive scaffolds on which Ni(OH)2 and ZnO were deposited. These composite electrodes were test-ed in nickel-zinc hybrid capacitors. Finally, CNF electrodes with high mass loadings based on free-standing, lignin-derived CNF electrode stacks were demonstrated. The high-mass loading electrode stacks showed no deterioration in energy and power density compared to the elec-trodes with ultra-low loadings. This reveals the potential applicability of these novel lignin-derived CNF electrode stacks in commercial supercapacitor cells.
Version
Open Access
Date Issued
2020-07
Date Awarded
2020-09
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Titirici, Maria-Magdalena
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)