Sustainable carbon nanofibres for electrochemical energy storage devices

Feng, Yifan (2024) Sustainable carbon nanofibres for electrochemical energy storage devices. Doctoral thesis, University of East Anglia.

Preview

PDF Download (7MB) | Preview

Abstract

The rapid development of societal economies and technology has escalated the demand for energy, leading to the overconsumption of fossil fuels. Consequently, there is an urgent need for sustainable energy sources and suitable electrochemical energy storage devices. Among these, carbon nanofibres (CNFs) are promising candidates for electrodes in supercapacitors due to their suitable mechanical strength, flexibility, large specific surface area, and the ease of surface chemistry modification. However, majority CNFs are derived from polyacrylonitrile (PAN), a petroleum-based polymer with various drawbacks, such as high cost and environmental concerns.

To address these issues, this study explores the potential of biopolymers as precursors for obtaining CNFs suitable as electrodes in electrochemical energy storage devices, particularly supercapacitors. Biopolymers as cellulose (CELL), polylactic acid (PLA), and chitosan (CTS) were investigated with this purpose, highlighting the studies performed with CTS as its use in previous literature has been very limited.

Therefore, to explore the potential of these biopolymers in the preparation of CNFs, the research methodology involved three main steps. First, biopolymer nanofibres were fabricated using electrospinning, carrying out a systematic investigation of the impact of several experimental parameters including solution rheological properties, concentration, flow rate, and needle size on the fibres morphology and diameter. Then, these nanofibres underwent a stabilisation process to increase their thermal stability, ensuring the maintenance of their fibrous morphology during carbonisation. Finally, the stabilised nanofibres were carbonised to obtain CNFs. Once the CNFs were produced, chemical activation using H3PO4 or ZnCl2 as activating agents was performed to improve the physicochemical properties of the nanofibres, making them appropriate for use as electrodes in supercapacitors.

The research’s results indicate that CELL, PLA, and CTS nanofibres were successfully fabricated through electrospinning. However, while stabilisation experiments revealed that due to the low melting point of PLA it could not be successfully stabilised, CELL- and CTS-based CNFs were effectively produced. After the activation step, it was observed that cellulose-based CNFs lacked the mechanical strength required to be set up as self-standing electrodes. Consequently, only activated CTS-based CNFs were utilised as electrodes in supercapacitors. The activation experiments and subsequent electrochemical characterisation showed that despite the decrease in specific surface area after activation, the increased mesopore volume and improved surface chemistry enhanced the electrochemical performance of the activated CNFs. When using H3PO4 as activating agent, an impregnation ratio of 1:3 provided the most favourable electrochemical performance, reaching a specific capacitance of 133.67 F/g at 1A/g, retaining 98.5% of its capacitance after 2000 cycles. However, when using ZnCl2, the most effective impregnation ratio was 1:4, resulting in a capacitance of 111.86 F/g, with 97.1% capacitance retention after 2000 cycles. These capacitance values doubled those calculated with non-activated CNFs as electrodes, highlighting the significant enhancement in electrochemical after the activation.

This research contributes to the development of sustainable and cost-effective carbon materials to be used as electrodes in energy storage applications. The results highlight the potential of biopolymer-based CNFs, particularly those derived from chitosan, in meeting the demands for flexible and efficient supercapacitors. The findings underscore the importance of exploring renewable resources and appropriate fabrication technologies for developing electrochemical energy devices, paving the way for further advancements in the field of energy storage.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Engineering (former - to 2024)
Depositing User:	Chris White
Date Deposited:	02 Apr 2025 14:15
Last Modified:	02 Apr 2025 14:15
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98924
DOI:

Downloads

Actions (login required)

View Item