NANOSTRUCTURED Mn-OXIDE AND COMPOSITES FOR SUPERCAPACITOR APPLICATIONS: SYNTHESIS AND CHARACTERIZATION

Author

• Alisha Dhakal

Date

2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Physics

Committee Chair

Sanjay R Mishra

Committee Member

Muhammad S Jahan

Committee Member

Shawn David Pollard

Committee Member

Xiaohua Huang

Abstract

The global transition toward sustainable energy systems has intensified the need for high-performance, low-cost, and environmentally benign electrochemical energy storage materials. Among transition metal oxides, manganese-based compounds offer rich redox chemistry, natural abundance, and structural tunability, making them promising candidates for next-generation supercapacitors. This dissertation presents a comprehensive investigation into the structure–property–performance relationships of Mn oxide–based electrodes, emphasizing morphology engineering, precursor chemistry, electrolyte optimization, and composite formation. Three classes of materials were extensively studied: (i) MnO2, Mn2O3, and Mn3O4; (ii) morphology-controlled Mn2O3 synthesized via urea and piperazine-assisted hydrothermal routes; and (iii) advanced heterostructures including Mn2O3–Co3O4 and LaMnO3-based composites. MnO2 exhibited superior baseline performance compared to Mn3O4, with higher surface area (30.7 m2/g), lower charge transfer resistance (8.32 Ω), and higher specific capacitance (321 F/g at 1 mV/s). Systematic tuning of Mn2O3 morphology demonstrated that precursor chemistry governs crystallite size, lattice expansion, Mn³⁺ concentration, porosity, and electrochemical activity. Optimal urea-derived Mn2O3 (9 mM) exhibited outstanding specific capacitances of 881 F/g (1 M KOH) and 1043 F/g (3 M KOH) at 1 mV/s, attributed to an increased Mn3+/Mn4+ redox density and an oxygen-vacancy–rich architecture. Piperazine-engineered cuboidal Mn2O3 further enhanced performance, with the MNO 6 formulation delivering 952 F/g in 6 M KOH and excellent cycling stability (>99% retention). Electrolyte studies revealed strong dependence on ionic mobility and hydration radius, with KOH consistently outperforming NaOH, NaNO3, and Na2SO4 due to favorable K+ transport and high OH- conductivity. Beyond pristine oxides, composite engineering significantly amplified charge storage. A Mn2O3–Co3O4 heterostructure (40 min deposition) achieved 1290 F/g at 1 mV/s and 706 F/g at 1 A/g, benefiting from synergistic redox activity and enhanced conductivity. Rare–earth–based perovskite composites further elevated performance: LaMnO3–Co3O4 (70:30) delivered an exceptional 1614 F/g (1 mV/s) with 99 % specific capacitance retention. While LaMnO3–Mn3O4 (70:30) achieved 479 F/g at 6 M KOH and remarkable long-term durability (91% retention after 2000 cycles). Across all systems, cyclic voltammetry, charge/discharge analysis, and impedance spectroscopy consistently revealed diffusion-dominated pseudocapacitive behavior, facilitated by mixed Mn oxidation states and abundant oxygen vacancies. The results collectively establish clear design principles linking synthesis, structure, and electrochemical function. Overall, this work provides a unified understanding of manganese oxide-based electrode optimization and introduces several high-performance materials that surpass many reported pseudocapacitive oxides in terms of capacitance, energy density, power density, and cycling stability. The insights gained here offer a strong foundation for developing scalable, cost-effective supercapacitors and hybrid energy storage systems.

Comments

Data is provided by the student.”

Library Comment

Dissertation or thesis originally submitted to ProQuest/Clarivate.

Notes

Embargoed until 09-30-2026

Recommended Citation

Dhakal, Alisha, "NANOSTRUCTURED Mn-OXIDE AND COMPOSITES FOR SUPERCAPACITOR APPLICATIONS: SYNTHESIS AND CHARACTERIZATION" (2026). Electronic Theses and Dissertations Archive. 3957.
https://digitalcommons.memphis.edu/etd/3957