Development of Zeolitic Imidazolate Framework-Derived Carbon Hosts for Advanced Lithium Metal Anodes

Lithium (Li) metal batteries have recently gained tremendous attention owing to their high energy capacity compared to other rechargeable batteries. Nevertheless, Li dendritic growth causes low Coulombic efficiency, thermal runaway, and safety issues, all of which hinder the practical application of Li metal as a promising anodic material. From the material development aspect, new and creative solutions are required to resolve the current technical issues on advanced Li batteries and improve their safety during operation. The research encompassed in this work spans a broad investigation of utilizing Zeolitic imidazolate framework derived carbon (ZIF-C) as a 3D host material in Li metal batteries. The reason behind choosing ZIF-C in this thesis not only relies on its flexibility with which constituents’ geometry, size, and functionality can be modified to match application needs, but also because it exhibits several outstanding properties, such as robust mechanical strength, large surface area and pore volume, and adequate electrical conductivity, making it a potential candidate for cost-effective practical usage. These host materials, however, could suffer from poor Li wettability, which results in significant nucleation barriers and upper surface electrodeposition of Li metal, leading to dendritic growth and safety concerns. This thesis covers multiple aspects related to ZIF-C material. Firstly, the physical properties of porous ZIF-C, which can be controlled by the inorganic components, were thoroughly studied. This provided the basis of enhancing the properties of ZIF-C by varying the ratios of zinc/cobalt ion metallic precursors. A key finding from this study is that the initiation of carbon nanotubes growth and the pore size on the surface of ZIF-C is highly dependent on the Co/Zn ratio. Secondly, we theoretically demonstrated and experimentally correlated the growth mechanism of Li clusters on the surface of Co/Zn ZIF-C by employing different heteroatoms (pyridinic N, pyrrolic N, quaternary N, and Co-N4). As a key feature, the Co-N4 affects the Li deposition behavior with axial Li growth on the surfaces of the carbon frameworks, while the other heteroatoms (i.e., nitrogen defects) induce unfavorable vertical Li growth. Thirdly, we functionalized the Co/Zn ZIF-C with oxidized nitrogen groups by utilizing nitric acid. We found that the functionalized porous carbon demonstrated an enhanced wettability compared to its non-functionalized counterpart. Moreover, by functionalizing the carbon surface with oxidized nitrogen during Li plating and stripping, catalyzed Li nitride (Li3N) formed in the solid electrolyte interphase which effectively enhanced the surface morphology of Li deposition. The electrochemical measurements showed a massive improvement in the capacitive behavior of the functionalized porous carbon and an enhanced electrochemistry performance in terms of cyclability and reversibility. Some additional theoretical and experimental work, involving advanced computational simulations and in situ characterization techniques, opens the door to further work in developing high-performance battery materials for the advance of a new generation of Li-based batteries

Soft-templated synthesis of mesoporous nickel oxide using poly(styrene-block-acrylic acid-block-ethylene glycol) block copolymers

In this work, we report the soft-templated preparation of mesoporous nickel oxide using an asymmetric poly(styrene-block-acrylic acid-block-ethylene glycol) (PS-b-PAA-b-PEG) triblock copolymer. This block copolymer forms a micelle consisting of a PS core, a PAA shell and a PEG corona in aqueous solutions, which can serve as a soft template. Specifically, the PS block forms the core of the micelles on the basis of its lower solubility in water. The anionic PAA block interacts with the cationic Ni ions present in the solution to generate the shell. The PEG block forms the corona of the micelles and stabilizes the micelles by preventing secondary aggregation through steric repulsion between the PEG chains. In terms of textural characteristics, the as-synthesized mesoporous NiO exhibits a large average pore size of 35 nm with large specific surface area and pore volume of 97.0 m g and 0.411 cm g, respectively. It is expected that the proposed soft-templated strategy can be expanded to other metal oxides/sulfides in the future for potential applications in gas sensors, catalysis, energy storage and conversion, optoelectronics, and biomedical applications

Synthesis and Characterisation of Mesoporous Transition Metal Oxides Based on Soft-Templating Method

Mesoporous materials have attracted extensive interest in the past few decades because of their diverse applications in different fields, including chemical, environmental, energy, optics, electronics, medical and biotechnological applications. They display unique properties presumably because of their pores, which are sufficiently large to host large and/or multiple molecules, but not large enough for bulk properties to influence surface interaction. The mesoporous transition metal oxides group is among the mesoporous materials with several properties, including d-shell electrons confined to nanosized walls, redox active internal surfaces and connected pore networks. Among various transition metal oxides, nickel oxide (NiO), a wide bandgap (3.6–4.0 eV) p-type semiconductor, has gained significant attention owing to its exciting intrinsic properties, such as electrochromic, antiferromagnetic and high capacitive properties. In addition, NiO can be utilised in a wide range of applications, such as electrochromic display devices, smart windows, active optical fibres, gas sensors, solar thermal absorbers, catalysis, fuel cell electrodes, supercapacitors and energy storage devices. The soft-templating method is used to synthesise mesoporous materials because it offers many benefits, including achieving cost-effectiveness, creating various porous networks with a wide range of pore sizes and providing access to well-defined morphologies and customisation for various applications. However, this method is extremely sensitive to hydrothermal conditions, such as concentration, temperature and pH. In addition, the synthesis process for some transition metal oxides has extra difficulties, including high tendency to build a stable structure with high lattice and possibility of structure collapsing on template removal. In the present study, an asymmetric poly (styrene-block-acrylic acid-block-ethylene glycol) (PS-b-PAA-b-PEG) triblock copolymer is used as a soft template to synthesise the mesoporous NiO. In aqueous solutions, the block copolymer forms a micelle containing a PS core, a PAA shell and a PEG corona. The PS block serves as the core of the micelles because of its hydrophobicity, while the anionic PAA block interacts with the cationic Ni2+ ions in the solution to form the shell and the PEG block forms the corona of the micelles. The goal of the corona is to stabilise the micelles by avoiding secondary aggregation through steric repulsion between the PEG chains. The synthesised mesoporous NiO was characterised with different techniques, including x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and the Brunauer–Emmett– Teller method. The NiO shows a large average pore size of 35 nm with a large specific surface area (97.0 m2 g-1) and pore volume (0.411 cm3 g-1). It is expected that the proposed soft-templating strategy could be generalised to other metal oxides/sulphides in the future for potential applications in gas sensors, environmental applications, catalysis, energy storage and conversion, optoelectronics and biomedical applications

Enhanced UV-light detection based on ZnO nanowires/graphene oxide hybrid using cost-effective low temperature hydrothermal process

A new low-cost optimized hydrothermal process of direct synthesis of ZnO nanowires (NWs)/graphene oxide (GO) hybrid on silicon substrates at a low growth temperature (∼60°C) is reported. The careful optimization of the growth conditions and ZnO/GO relative ratios have resulted in high-density ZnO NWs formation with homogenous density and size distributions directly on GO sheets. The fabricated nanocomposites were intensively investigated by employing different structural, optical and electrical characterization techniques such as SEM, EDX, XRD, FTIR, UV-VIS and I-V. SEM analysis showed a formation of highly dense ZnO NWs on GO sheets with homogenous size di stributions with average approximate diameter and length of 70 nm and 310 nm, respectively. The EDX combined with FTIR and XRD measurements confirmed the exact chemical composition of the intended structure. The room-temperature UV-VIS spectra revealed an enhance optical absorption of UV-light at an absorption band centered at 370 nm. Under UV-excitation a significant photocurrent increase has been observed. This is can be attributed to the large surface to volume ratio in ZnO-NWs structure, which is associated with oxygen desorption at the large ZnO-NWs surfaces that reduces the recombination rate of photogenerated free charge carriers. The optimum electrical and optical properties of the device have been observed at ZnO-NWs/Go relative ratio of 1:5. These findings could be promising for potential enhanced UV-detectors and flexible optoelectronics devices

Arresting High-Temperature Microstructural Evolution inside Sintered Silver

The surface oxidation of internal pore surfaces of nano-scale sintered silver has increased stability for high temperature applications. Operating temperatures of up to 400 °C have resulted in no or minimal changes in microstructure. By contrast, it is known that the microstructure of untreated pressure-less sintered silver continuously evolves at temperatures above 200 °C, grain and pore growth resulting in microstructure coarsening and increased susceptibility to fatigue. Oxidation of the internal pore surfaces has been shown to freeze the microstructure when the contact metallization is also silver or chemically inert. Samples exhibited no change in microstructure either through continuous observation through glass, or after cross sectioning. The tested specimens under high temperature storage resisted grain growth for more than 1000 h at 300 °C. The oxidising treatment can be performed via many different routes. For example, exposure to steam, or even by dipping in water for 10 min followed by immediate high temperature exposure and the effectiveness of these varying treatments is assessed. In this work we explore the mechanism that causes stabilization and explore the hypothesis that oxidation prevents grain boundary movements by arresting the fast migration of atoms along the internal pore surfaces. Analysis of the surface structure of the sintered silver by X-ray photoelectron spectroscopy shows presence of silver oxide (Ag2O) and computer simulation of grain boundary movements confirm the presence of a barrier to atomic movement on the internal silver surfaces. These findings are very promising for potential applications of sintered silver as a die attach material for High Temperature electronics packaging

Arresting high-temperature microstructural evolution inside sintered silver

The surface oxidation of internal pore surfaces of nano-scale sintered silver has increased stability for high temperature applications. Operating temperatures of up to 400 °C have resulted in no or minimal changes in microstructure. By contrast, it is known that the microstructure of untreated pressure-less sintered silver continuously evolves at temperatures above 200 °C, grain and pore growth resulting in microstructure coarsening and increased susceptibility to fatigue. Oxidation of the internal pore surfaces has been shown to freeze the microstructure when the contact metallization is also silver or chemically inert. Samples exhibited no change in microstructure either through continuous observation through glass, or after cross sectioning. The tested specimens under high temperature storage resisted grain growth for more than 1000 h at 300 °C. The oxidising treatment can be performed via many different routes. For example, exposure to steam, or even by dipping in water for 10 min followed by immediate high temperature exposure and the effectiveness of these varying treatments is assessed. In this work we explore the mechanism that causes stabilization and explore the hypothesis that oxidation prevents grain boundary movements by arresting the fast migration of atoms along the internal pore surfaces. Analysis of the surface structure of the sintered silver by X-ray photoelectron spectroscopy shows presence of silver oxide (Ag2O) and computer simulation of grain boundary movements confirm the presence of a barrier to atomic movement on the internal silver surfaces. These findings are very promising for potential applications of sintered silver as a die attach material for High Temperature electronics packaging

NiO-nanofillers embedded in graphite/PVA-polymer matrix for efficient electromagnetic radiation shielding

In this study, we report on the preparation of NiO/graphite sheets nanofillers in PVA-polymer matrix using a simple cost-effective hydrothermal process for EM shielding effectiveness applications. The careful optimization of the growth conditions and NiO/G/PVA relative ratios have resulted in NiO nanoparticles formation with homogeneous density. In this nanocomposite, the NiO nanoparticles and graphite sheets were incorporated into a polymer to enhance the electromagnetic shielding effectiveness. The morphological, structural, and chemical analysis have been conducted by SEM, EDX and XRD techniques. EDX and XRD analysis confirmed the exact chemical composition with high purity. SEM images showed the best morphology with homogenous NiO-nanoparticles distribution on graphite sheets for 15 wt% NiO relative ratio NiO/G/PVA nanocomposite. The nanocomposite was tested in different environments and shielding chambers that contained relatively high-level exposure to electromagnetic radiation. The shielding effectiveness (SE) measurements of NiO/G/PVA showed a significant increase of shielding effectiveness of about 17 dB compared to the commercial shielding paint. This can be ascribed to the homogenous distribution of NiO-NPs over the entire graphite sheets and the strong interaction of the incident electromagnetic radiation with the magnetic and electric dipoles in the nanocomposite. These finding is promising for enhanced flexible and cost-effective EMI shielding applications