Advanced Transition Metal Oxide Nanomaterials for Energy Technologies
[eng] Transition metal oxides (TMOs) are compounds formed from transition metals and oxygen, known for their complex and versatile structures, including diverse crystal forms and multiple oxidation states. This versatility gives TMOs unique electronic, magnetic, optical, and thermal properties, maki...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/221132 |
| Acceso en línea: | https://hdl.handle.net/2445/221132 http://hdl.handle.net/10803/694472 |
| Access Level: | acceso abierto |
| Palabra clave: | Catalitzadors Electrocatàlisi Materials nanoestructurats Piles de combustible Energies renovables Catalysts Electrocatalysis Nanostructured materials Fuel cells Renewable energy sources |
| Sumario: | [eng] Transition metal oxides (TMOs) are compounds formed from transition metals and oxygen, known for their complex and versatile structures, including diverse crystal forms and multiple oxidation states. This versatility gives TMOs unique electronic, magnetic, optical, and thermal properties, making them valuable in advanced technological applications. The ability of TMOs to engage in redox reactions, coupled with their stability abundant availability, and cost-effectiveness, makes them ideal for applications such as electrochromic devices, catalysis, and batteries. Electrochromic smart windows (ESWs) offer an attractive option for regulating indoor lighting conditions. Electrochromic materials based on ion insertion/desertion mechanisms also present the possibility for energy storage, thereby increasing overall energy efficiency and adding value to the system. However, current electrochromic electrodes suffer from performance degradation, long response time, and low coloration efficiency (CE). In Chapter 2, I detail the synthesis mechanism of defect-engineered brookite titanium dioxide (TiO2) nanorods (NRs) with different lengths and investigate their electrochromic performance as potential energy storage materials. The controllable synthesis of TiO2 NRs with inherent defects, along with smaller impedance and higher carrier concentrations, significantly enhanced their electrochromic performance, including improved resistance to degradation, shorter response times, and enhanced CE. The electrochromic performance of TiO2 NRs, particularly longer ones, is characterized by fast switching speeds (20 s for coloration and 12 s for bleaching), high CE (84.96 cm2 C−1 at a 600 nm wavelength), and good stability, highlighting their potential for advanced electrochromic smart window applications based on Li+ ion intercalation. This work was published in Small in 2023. Direct urea fuel cells (DUFCs), generating electric power from the electrooxidation of urea have great potential as a cost-effective technology to simultaneously treat urea-containing wastewater and produce electricity. DUFCs release only gaseous products, not generating new waste, and they are characterized by a relatively high theoretically open circuit voltage (OCV) of 1.147 V, similar to that of hydrogen fuel cells. However, the relatively low OCVs and peak power densities realized so far have hindered their commercialization. Therefore, improving the OCVs and peak power densities of DUFCs using low-cost and abundant transition oxide nanoparticles as catalysts is required to ensure practical significance. In Chapter 3, I detail the production of self-supported electrodes consisting of NiO nanosheets vertically grown on CuO nanowires and use them to realize the urea oxidation reaction (UOR). Such electrodes show excellent UOR performance requiring 1.39 V vs. reversible hydrogen electrode (RHE) to achieve 100 mA cm-2. Besides, DUFCs provide OCV and power densities up to 0.88 V and 11.35 mW cm-2. Electrochemical characterization and Raman spectroscopy prove the formation of NiOOH to enable the UOR. Mott-Schottky analysis and ultraviolet photoelectron spectroscopy show the NiO/CuO p-p heterostructure to facilitate the charge transfer from CuO nanowires to NiO nanosheets. Besides, at a local level, density functional theory calculations show that the presence of CuO modulates the electronic states of Ni at the very NiOOH/CuO interface, which results in stretched Ni-O bonds and a uniquely elongated N-H bond of urea that favor its oxidation. This work was published in Nano Energy in 2023. Rechargeable aqueous zinc-air batteries (ZABs) have emerged as a promising candidate technology for energy storage applications owing to their high energy density, safety, and environmental friendliness. However, ZABs are limited by the sluggish kinetics of the multiple electron-proton coupling processes involved in the oxygen evolution reaction (OER) that takes place at the air cathode during ZAB charging. Therefore, the development of transition oxide nanoparticles as highly efficient, low- cost, and durable OER catalysts is crucial for the realization of high-performance ZABs, among other electrochemical technologies. Beyond optimizing electronic energy levels, the modulation of the electronic spin configuration is an effective strategy, often overlooked, to boost activity and selectivity in a range of catalytic reactions, including the OER. This electronic spin modulation is frequently accomplished using external magnetic fields, which makes it impractical for real applications. In Chapter 4, I detail the synthesis of Ni/MnFe2O4 heterojunctions and apply them in OER. I investigate the spin modulations of the reconstrued NiOOH/MnFeOOH during the OER by the heterojunctions without an external magnetic field. NiOOH/MnFeOOH shows a high spin state of Ni, which regulates the OH− and O2 adsorption energy and enables spin alignment of oxygen intermediates. As a result, NiOOH/MnFeOOH electrocatalysts provide excellent OER performance with an overpotential of 261 mV at 10 mA cm−2. Besides, rechargeable ZABs based on Ni/MnFe2O4 show a high OCV of 1.56 V and excellent stability for more than 1000 cycles. This outstanding performance is rationalized using density functional theory calculations, which show that the optimal spin state of both Ni active sites and oxygen intermediates facilitates spin-selected charge transport, optimizes the reaction kinetics, and decreases the energy barrier to the evolution of oxygen. This work was published in Adv. Mater. in 2024. The main conclusions of this thesis and some perspectives for future work are presented in the last |
|---|