In order to improve the performance and fundamental understanding of conducting polymers, development of new nanotechnologies for engineering aggregated states and morphologies is one of the central focuses for conducting polymers. In this work, we demonstrated an interfacial engineering method for the rational synthesis of a two-dimensional (2D) polyaniline (PANI) nano-array and its corresponding nitrogen-doped porous carbon nanosheets. Not only was it easy to produce a sandwich-like 2D morphology, but also the thickness, anchored ions and produced various metal phosphides were easily and rationally engineered by controlling the composition of the aqueous layer. The novel structural features of these hybrids enabled outstanding electrochemical capacitor performance. The specific capacitance of the as-produced diiron phosphide embedded nitrogen-doped porous carbon nanosheets was calculated to be as high as 1098 F g−1 at 1 A g−1 and an extremely high specific capacitance of 611 F g−1 at 10 A g−1, outperforming state-of-the-art performance among porous carbon and metal-phosphide-based supercapacitors. We believe that this interfacial approach can be extended to the controllable synthesis of various 2D material coupled sandwich-like hybrid materials with potential applications in a wide range of areas.

This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol–water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode–electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg−1 and a high power density of 6.2 kW kg−1 were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window.

The demand for today's material resources for energy storage is rapidly increasing and can result in both environmental and political conflicts that can affect the development of electronic devices due to high prices and limitations of raw materials for batteries. In this study, potential future composite electrodes were synthesised with an ex-situ approach by compositing redox-active 2,6-Diaminoanthraquinone and 1,3,5-Triformylphloroglucinol covalent organic framework (DAAQ-TFP COF) with conductive delaminated Ti3C2Tx MXene to maximise the number of redox-active moieties during cycling. In addition, solvothermal synthesis with the implementation of mechanical grinding as an exfoliation method was used to try to obtain DAAQ-TFP nanosheets to increase both the contact area between the two materials and the number of charge carriers. The sample was analysed with PXRD and BET surface analysis to characterise the crystallinity meanwhile SEM was utilised to study the morphology of the COF and the composite material. The specific capacitance of each electrode was estimated by cyclic voltammetry. The study showed a decrease in reduced specific capacitance with lower MXene content. Hence, this concludes pure Ti3C2Tx sheets have the highest capacitance contribution with a value of 48.79 Fg-1 meanwhile the composite electrode with a ratio of 1:1 was estimated to 32.26 Fg-1 with 0.0928 % of its moieties undergoing a redox reaction. A reduced capacitance with an increased COF-MXene ratio indicates that MXene contributes with more capacity relative to the COF, in combination with a non-successful exfoliation of DAAQ-TFP to single-layered nanosheets, reducing the interactions between the two materials.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2022 / The gas sensing performance of two-dimensional (2D) hexagonal boron nitride nanosheets (h-BNNSs) has being studied by means of computational and experimental methods. The structural, stability and vacancies properties of both defect free and defected 2D h-BNNSs were studied using the classical molecular dynamics (MD) approach. The calculations were performed in the NVT Evans and NPT hoover ensembles using the Tersoff potentials with the Verlet leapfrog algorithm to obtain reliable structural properties and energies for defect free, boron (B) and nitrogen (N) vacancies. B and N defect energies were calculated relative to the bulk defect free total energies, and the results suggest that N vacancy is the most stable vacancy as compared to the B vacancy. The radial distribution functions and structure factors were used to predict the most probable structural form. Mean square displacements suggests the mobility of B and N atoms in the system is increasing with an increase in the surface area of the nanosheets. Results obtained are compared with the bulk defect free h-BNNSs. Experimentally, 2D h-BNNSs were synthesised using the wet chemical reaction method through chemical vapour deposition (CVD) catalyst free approach. The X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RM), UV-visible Spectroscopy (UV-VIS), dynamic light scattering (DLS), Energy Dispersion Spectroscopy (EDS) and Brunauer-Emmett Teller (BET) were adopted to attain the structural properties of the nanosheets. Each spectroscopic technique affirmed unique features about the surface morphology of h BNNSs. The crystallinity of the nanosheets with the stacking of the B and N vii honeycomb lattice was validated by the XRD, while the TEM disclosed the specimen orientations and chemical compositions of phases with the number of layers of a planar honeycomb BN sheet, the EDS express the atoms present in the samples and BET validated the surface area of the materials. The FTIR, RM, DLS and the UV-vis expressed the formation of the in-plane, out-of-plane h-BN vibrations and, the nature of the surface with the thickness, particles stability together with the optical properties of the nanosheets. From TEM, FTIR, RS and BET the material fabricated at 800°C showed different morphologies, large number of disordering together with high surface area, which enhances the sensing properties of the nanosheets. However, with an increase in temperature the sensitivity of the nanosheets was found to decrease. Additionally, the UV-vis results, confirmed a lower energy band gap of 4.79, 4.55 and 4.70 eV for materials fabricated at 800, 900 and 1000 °C, that improved the semiconducting properties of the materials, which in return enhanced the sensing properties of the nanosheets. The gas sensing properties of the 2D h BNNSs were also investigated on hydrogen sulphide (H2S) and carbon monoxide (CO). The fabricated sensor based on 800 – 900 °C h-BNNSs showed good sensitivity towards ppm of H2S at 250 °C. The excellent gas sensing properties could be attributed to high surface area, small crystallite size, defect/disordering of h BNNSs. Overall, the h-BNNSs were found to be more sensitive to H2S over CO. / University of Limpopo (UL) Mintek Council for Scientific and Industrial Research (CSIR) Center for High Performance Computing (CHPC)

Li-ion thin film battery technology has attracted much attention in recent years due to its highest need in portable electronic devices. Development of new materials for lithium ion battery (LIB) is very crucial for enhancement of the performance. LIB can supply higher energy density because Lithium is the most electropositive (-3.04V vs. standard hydrogen electrode) and lightest metal (M=6.94 g/mole). LIBs show many advantages over other kind of batteries such as, high energy density, high power density, long cycle life, no memory effect etc. The major work presented in this thesis is on the development of nanostructured materials for anode of Li-ion battery. It involves the synthesis and analysis of grapheme nanosheet (GNS) and its performance as anode material in Li ion battery. We studied the synthesis of GNS over different substrates and performed the anode studies. The morphology of GNS has great impact on Li storage capacity. Tin and Tin oxide nanostructures have been embedded in the GNS matrix and their electrochemical performance has been studied. Chapter 1 gives the brief introduction about the Li ion batteries (LIBs), working and background. Also the relative advantages and characterization of different electrode materials used in LIBs are discussed. Chapter 2 discusses various experimental techniques that are used to synthesize the electrode materials and characterize them. Chapter3 presents the detailed synthesis of graphene nanosheet (GNS) through electron cyclotron resonance (ECR) microwave plasma enhanced chemical vapor deposition (ECR PECVD) method. Various substrates such as metallic (copper, Ni and Pt coated copper) and insulating (Si, amorphous SiC and Quartz) were used for deposition of GNS. Morphology, structure and chemical bonding were analyzed using SEM, TEM, Raman, XRD and XPS techniques. GNS is a unique allotrope of carbon, which forms highly porous and vertically aligned graphene sheets, which consist of many layers of graphene. The morphology of GNS varies with substrate. Chapter 4 deals with the electrochemical studies of GNS films. The anode studies of GNS over various substrates for Li thin film batteries provides better discharge capacity. Conventional Li-ion batteries that rely on a graphite anode have a limitation in the capacity (372 mAh/g). We could show that the morphology of GNS has great effect in the electrochemical performance and exceeds the capacity limitation of graphite. Among the electrodes PtGNS shown as high discharge capacity of ~730 mAh/g compare to CuGNS (590 mAh/g) and NiGNS (508 mAh/g) for the first cycle at a current density of 23 µA/cm2. Electrochemical impedance spectroscopy provides the various cell parameters of the electrodes. Chapter 5 gives the anodic studies of Tin (Sn) nanoparticles decorated over GNS matrix. Sn nanoparticles of 20 to 100nm in size uniformly distributed over the GNS matrix provides a discharge capacity of ~1500 mAh/g mAh/g for as deposited and ~950 mAh/g for annealed Sn@GNS composites, respectively. The cyclic voltammogram (CV) also shows the lithiation and delithiation process on GNS and Sn particles. Chapter 6 discusses the synthesis of Tinoxide@GNS composite and the details of characterization of the electrode. SnO and SnO2 phases of Tin oxide nanostructures differing in morphologies were embedded in the GNS matrix. The anode studies of the electrode shows a discharge capacity of ~1400 mAh/g for SnO phase (platelet morphology) and ~950 mAh/g for SnO2 phase (nanoparticle morphology). The SnO phase also exhibits a good coulumbic efficiency of ~95%. Chapter 7 describes the use of SnO2 nanowire attached to the side walls of the GNS matrix. A discharge capacity of ~1340 mAh/g was obtained. The one dimensional wire attached to the side walls of GNS film and increases the surface area of active material for Li diffusion. Discharge capacity obtained was about 1335 mAhg-1 and the columbic efficiency of ~86% after the 50th cycle. The research work carried out as part of this thesis, and the results have summarized in chapter 8.