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Title: Morphology and interface design of nickel-based heterostructures for water splitting electrocatalysis
Authors: Li, Yong
Degree: Ph.D.
Issue Date: 2021
Abstract: Due to rapid growth of population and spreading industrialization over the world, total global energy demand is expected to keep increasing in the future. Up to date, the fossil fuels are still the main source of the total energy supply that accounts for ca. 80 %. The foreseeable depletion of fossil fuel and aggravation of global environment have stimulated intensive research on renewable and eco-friendly energy sources. Over the years, hydrogen has been considered as a potential substitute for fossil fuels because of its unique advantages of net-zero carbon emission and recyclable products. So far, noble metal-based electrocatalysts have demonstrated the best performances in catalyzing the oxygen/hydrogen evolution reactions (OER/HER), for examples, Pt for HER and RuO2 for OER, while their wide application is limited by scarcity, poor stability, and high cost. Therefore, cost-effective electrocatalysts are the key to the success in this global challenge. Recently, some earth-abundant transition metals (e.g., Ni, Fe, and Co) have been identified as active electrocatalysts for OER and HER but their poor intrinsic catalytic activities still hamper the large-scale applications and demands further improvements. In this Thesis, some Ni-based electrocatalysts are developed and optimized by morphology tuning and interface engineering to improve the HER and OER activities. In Chapter 1, the mechanisms of OER and HER are summarized with a brief review on the recent progress of Ni-based electrocatalysts. The concise descriptions of characterization techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and some electrochemical methods, are summarized in Chapter 2.
In Chapters 3, 4, and 5, three highly active Ni-based HER electrocatalysts were synthesized by constructing catalytically active interfaces and demonstrated to show highly improved hydrogen generation efficiencies and stabilities. The Ni nanoparticles (NPs) deposited on the (001)-facet-exposed TiO2 nanopyramid arrays (NPAs) show a strong coupling effect that leads to the optimized HER activity. The modification of the Ni/TiO2 NPAs with nitrogen-doped carbon quantum dot layer form an active interface of Ni-N-C bonds, which activates relatively inactive Ni NPs on {110} facets as well as enhances the stabilities of the composite. Owing to the large surface area, high conductivity, and active Ni/Ni3S2 interface, the hybrid Ni/Ni3S2 nanoparticles embedded in S-doped carbon nanosheet arrays (Ni/Ni3S2/SC NSAs) deliver a good HER activity. The reaction barrier of OER, the complementary half reaction of HER in water splitting, is much higher than that of HER because of the multiple electron transfer steps and sluggish kinetics. In Chapter 6, a cost-effective OER catalyst, NiCoO2/CoO/Ni3N nanosheet array (NiCoON NSAs/NF) is demonstrated with excellent catalytic properties toward OER in an alkaline solution, owing to the Ni3+-rich surface and the formation of rock salt-type NiCoO2. The control of active species, defect engineering, and interface formation are combined to lead to high OER activity and stability of NiCoON NSAs/NF. Finally, in Chapter 7, the conclusions of all research works presented in this Thesis are presented with the perspectives for future research direction.
Subjects: Electrocatalysis
Hong Kong Polytechnic University -- Dissertations
Pages: xix, 200 pages : color illustrations
Appears in Collections:Thesis

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