Date of Award

6-1-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Institute for Advanced Studies

Institution

Universiti Malaya

Abstract

Supercapacitors are essential for energy storage due to their high-power density and longevity, particularly in increasing demand for sustainable energy. However, their low energy density and specific capacitance hinder widespread use. Advancements in next-generation electrode materials that are high-performing, cost-effective, and scalable are necessary to address these issues. Herein, this work reports the development of novel electrode materials and explores the fundamental relationship between their structural properties and electrochemical performance in supercapacitors. In this study, biochar was derived from oil palm Empty Fruit Bunch (EFB) via a gasification process. Different samples of metal oxide/biochar composites were subsequently synthesized using a hydrothermal method, followed by heat treatment for developing composite of TiO2/biochar, ZnO/biochar and TiO2/ZnO/biochar. The structural and chemical properties of the synthesized composites materials including crystallinity, phase purity, surface morphology, and functional groups were characterized using X-ray Diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscopy (FESEM). Furthermore, electrochemical performance such as specific capacitance and capacitance retention of the synthesized materials was evaluated through Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) to determine their specific capacitance and long-term cycling stability. Electrochemical analysis of the biochar electrode material revealed a specific capacitance of 125 F/g for device testing. In system 1, TiO2/biochar (1:3) were synthesized and used for supercapacitor application. The fabricated device delivered maximum specific capacitance of 245 F/g, energy density of 34 Wh/kg and power density of 499 W/kg respectively. The stability of the device for TiO2/biochar (1:3) iv was evaluated by analysing the continuous cycles of 5000 charge cycles and achieved capacitance retention of 95%. In system 2, ZnO/biochar (1:2) were synthesized and the fabricated device delivered maximum specific capacitance, energy density and power density values of 226 F/g, 34.5 Wh/kg and 506 W/kg respectively. The stability of the device for ZnO/biochar (1:2) was evaluated by analysing the continuous 5000 charge cycles and achieved excellent cycling stability with 93% capacitance retention. However, both metal oxide/biochar had moderate specific capacitance which motivated the development of system 3 with the incorporation of TiO2 and ZnO with biochar to form ternary composite of TiO2/ZnO/biochar. TiO2/ZnO/biochar (2:3:6) were synthesized and the fabricated device delivered maximum specific capacitance, energy density and power density values of 305 F/g, 36.5 Wh/kg and 564 W/kg respectively. The stability of the device for TiO2/ZnO/biochar (2:3:6) was evaluated by analysing the continuous 5000 charge cycles and achieved excellent cycling stability with 95% capacitance retention. The improved performance of the TiO2/ZnO/biochar electrode is driven by more efficient redox reactions at active sites and the high surface area of biochar, which shortens diffusion paths for faster energy storage. Additionally, the combination of TiO2 and ZnO creates a synergistic electric field that significantly accelerates charge-transfer kinetics.

Initial

khm

Additional Information

Thesis (PhD) – Institute for Advanced Studies, Universiti Malaya, 2026.

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