UBC Theses and Dissertations
The effect compressed carbon nanofibres made from lignin as electrodes have on the performance of a supercapacitor Rey, Delphine
Anthropogenic climate change entices civilisation to adopt renewable energy that requires electric storage due to its intermittent nature. Batteries are traditionally responsible for storing electricity because of their large density of energy but they are expensive because they degrade significantly faster than supercapacitors. However, supercapacitors store a lower density of energy. Like renewable energy, these devices must minimise their ecological footprint and enforce the concept of circular economy but the current production of both batteries and supercapacitors has much room for improvement. Increasing the area of supercapacitors' electrodes is key to producing more energy. These are made of nanofibres of carbon because they are conductive and hold a large surface. They are made from polymers traditionally produced from fossil fuels. However, recent research successfully replaced these expensive ingredients with a polymer wasted by the industry of pulp and paper. Instead of burning the waste to supply the industry with energy, and releasing greenhouse gases to the atmosphere, it is possible to simply convert the polymer to carbonic nanofibres at scales thanks to electrospinning and thermal treatment. However, their performance remains inferior to those reported in literature. Chemically doping the carbonic nanofibres is a popular option with extensive presence in literature but increasing the surface is a simple mean to also increase the capacity of storing energy. Electrodes made from nanofibres are so porous that much of their volume is void. Compressing the nanofibres to roughly half their volume prior to thermally treating the carbonic nanofibres translated in an increase of 2.21 fold in density after the thermal treatment. The surface of the samples per unit volume increased by 2.34 times yet the volumetric capacitance decreased by 78% even though the resistivity decreased by 56%. First material characterisation on the samples identifies the presence of carbonic nanofibres through measurements of conductivity, Raman spectroscopy, X-ray diffraction and Scanning Electron Microscopy. Then, electrochemical characterisation evaluates the performance of the samples in a device, including Cyclic Voltammetry for 10,000 charging and discharging cycles, Galvanostatic Charge and Discharge, and Electrical Impedance Spectroscopy to evaluate their performance in a supercapacitor.
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