Date of Award

5-5-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Institute for Advanced Studies

Institution

Universiti Malaya

Abstract

The increasing demand for safe, flexible, and high-performance energy storage devices has intensified research into aqueous zinc-ion hybrid supercapacitors (ZHSCs) as viable alternatives to conventional lithium-based energy storage systems. Although ZHSCs offer advantages such as low cost, high theoretical capacity, and environmental sustainability, their practical implementation is limited by challenges including electrolyte instability, zinc dendrite formation, and inefficient electrode–electrolyte interfacial interactions. In this thesis, a holistic design strategy is adopted in which hydrogel polymer electrolytes and vanadium oxide/MXene composite electrodes are jointly developed as an integrated electrochemical system to address these limitations and enhance overall device performance. Poly(vinyl alcohol) (PVA)-based hydrogel electrolytes were engineered as quasi-solid-state media to replace conventional liquid electrolytes, providing improved safety, mechanical integrity, and interfacial conformity with electrode materials. Corn starch was incorporated as a biodegradable polymeric modifier to regulate the hydrogel network structure, thereby improving ionic conductivity, electrolyte retention, and mechanical robustness. The influence of starch content on the physicochemical and electrochemical properties of the hydrogels was systematically investigated. In parallel, varying concentrations of zinc salt were introduced into the hydrogel matrix to optimize ionic transport behaviour, electrochemical stability, and zinc plating/stripping reversibility, while also examining their effects on morphology, chemical bonding, and thermal stability. Linear sweep voltammetry (LSV) was employed to determine the operational electrochemical potential window of the hydrogels, ensuring compatibility with zinc-based electrochemical reactions and stable operation within the assembled devices. Within this optimized hydrogel electrolyte environment, vanadium oxide/MXene (VOₓ/MXene) composite electrodes were developed as cathode materials that function synergistically with the hydrogel matrix. The VOₓ/MXene composite was designed as a unified charge-storage framework in which pseudocapacitive vanadium oxide is intimately integrated within a highly conductive MXene network, facilitating efficient electron transport and rapid zinc-ion diffusion. The close interfacial contact between the composite electrode and the hydrogel electrolyte promotes uniform ion flux and mitigates localized current density, thereby contributing to stabilized zinc deposition behaviour and suppression of dendrite formation. Structural, morphological, and electrochemical characterizations were conducted to elucidate the cooperative interactions between the hydrogel electrolyte and the VOₓ/MXene composite electrode. The fully assembled ZHSCs were evaluated using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy to assess capacitive behaviour, energy and power densities, rate capability, and long-term cycling stability. The results demonstrate that the co-engineered hydrogel electrolyte and VOₓ/MXene composite electrode system significantly enhances electrochemical stability, improves specific capacitance and cycling durability, and effectively suppresses zinc dendrite growth. Overall, this work presents a system-level approach to the development of safe, high-performance zinc-ion hybrid supercapacitors through the collective optimization of electrolyte structure, electrode architecture, and interfacial compatibility, providing valuable insights for future solid-state zinc-based energy storage technologies.

Initial

khm

Additional Information

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

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