Graphene-based Hybrid Electrodes for High-Performance Supercapacitors

This Ph.D. project is to study the materials used in supercapacitors (SC). A supercapacitor is an energy storage device with a much higher capacitance value than other capacitors. The interface between the electrodes and electrolytes is crucial in advancing supercapacitor performance, as this solid electrolyte interface (SEI) is where charge storage occurs, and the electrochemical reactions occur. Hence, controlling the chemistry and structure of the electrodes to enable a high surface area and fast charge transfer with the electrolyte is vital for designing better SC systems. Typically, SC electrodes are composed of carbonaceous materials which are intrinsically lightweight, mechanically robust, and can be easily designed to have a high electrochemically active surface area. However, carbon-based electrodes rely predominantly on non-faradic charge storage (via the electrochemical double layer, EDL), and thus have a low energy density. To overcome this limitation, designing hybrid electrodes, combining faradic and non-faradic charge storage materials has attracted much interest as this couples the high conductivity of carbon-based electrodes and faradic charge storage mechanisms from the secondary material. Fundamentally, hybrid electrodes are designed by combining a typical SC electrode material (e.g., activated carbon (AC), or graphene) and a battery-pseudocapacitive (PC) material (e.g., transition metal oxides/metal disulfides such as TMOs and TMDs). The SC component undergoes the electrostatic mode of charge storage by the formation of an EDL interface. Whereas the PC component provides the faradic mode of charge storage (in addition to the EDL layer). Furthermore, compared with pure PC/battery materials hybrid electrodes maintain their structure and do not undergo a significant structural change which leads to enhanced cyclic stability. Metal disulfides (MDs) are being utilized as an effective electrode for various energy storage applications. Governed by their analogous behavior to graphite, they have a 2D layered structure with an alternative number of layers. Recent research focuses on the utilization of the highly crystalline MDs due to their high conductivity, but rare studies have illustrated the structure and performance of the amorphous/mixed phase MDs. With increasing interest in amorphous materials and their unique applications in sensing and energy storage applications, there is a large scope to design MDs with homogeneously disordered structures in terms of anisotropy and defects. These defects act as additional active charge storage channels thereby increasing the capacitance of SCs. Graphene-based electrodes have been in the spotlight as they fully satisfy most of the requirements for SC electrodes. However, they have low specific energy density compared with TMO- or TMD-based systems. MDs composited with graphene are a promising route to design an electrode capable of giving high energy/power density. However, one of the major challenges is to ensure the uniform deposition of MDs on the surface of graphene. Also, it is vital to control the crystallinity of the MDs/graphene composite to obtain the desired performance. Therefore, hybridizing MDs with graphene can improve electrochemical performance. This thesis details the hydrothermal synthesis and electrochemical performance of graphene-mixed phase MDs nanocomposites for supercapacitor applications. The designed nanocomposites performed exceptionally well in aqueous electrolyte systems in an extended voltage window. The output is a high capacitance and energy-power density, long-life cycle, superior capacitance retention, and a high columbic efficiency, which suggests the potential of the designed nanocomposites for supercapacitors.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemical and Materials Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2022

Author dc:creator

• Bokhari, Syeda Wishal

Advisor dc:contributor.advisor

• Gao, Wei

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/62821

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/62821