RF Sensors for Monitoring the Electrical Properties of Electrolyte Solutions

A radio frequency electrical sensor for the qualitative analysis and monitoring of the electrical properties of electrolyte solutions is designed, simulated and experimentally tested in this research. This work is based on the use of planar inductors for the detection of a change in the concentration of ionic species in a liquid sample. At first a literature review on the physical chemistry of electrolyte solutions is provided. This will include topics on the conductivity and relaxation properties of electrolytes. This will be followed by a look at dielectric spectroscopy sensors, electrochemical sensors and inductive sensing devices. The principles of electrodynamics and constitutive equations are discussed. Based on these, the principles of operation of the RF electrical sensors are analysed. Two methods of theoretical analysis of such structures are investigated. These methods are; analytical solution and finite element computation method. The former offers greater insight into the system’s parameters whilst the latter offers more information regarding the whole system. Given the qualitative nature of the sensors under investigation and finite element approach was selected and used in latter chapters to obtain grater insight into the behaviour of the system. Planar inductor coils are designed on an FR4 substrate and packaged using PDMS to be used as sensors in the monitoring of electrical properties of electrolytes. Experimental results on these sensors are provided and discussed. The effects of solvent, acidity of the solutions, and environmental factors on the behaviour of the sensors shall be discussed. This is followed by finite element simulations of the sensor and the effect of various parameters on the overall behaviour of the sensing device. A transformer apparatus is also constructed and experimental data are provided for it. An electrolyte is placed on one of the coils of the transformer and scattering parameters are looked upon for data analysis. The results obtained using the FE method, is then used to obtain further information about the principle of operation of the device

Preparation and performance of nanostructured iron oxide thin films for solar hydrogen generation

Nowadays, energy and its resources are of prime importance at the global level. During the last few decades there have been several driving forces for the investigation of new sources of energy. Hydrogen has long been identified as one of the most promising carriers of energy. Photoelectrochemical (PEC) water splitting is one of the most promising means of producing hydrogen through a renewable source. Hematite (α-Fe2O3) is a strong candidate material as photoelectrode for PEC water splitting as it fulfils most of the selection criteria of a suitable photocatalyst material for hydrogen generation such as bandgap, chemical and photelectrochemical stability, and importantly ease of fabrication. This work has explored different preparation techniques for undoped and Si-doped iron oxide thin films using microwave-assisted and conventional preparation methods. Two distinct strategies towards improving PEC performance of hematite photoelectrodes were examined: retaining a finer nanostructure and enhancing the photocatalytic behaviour through doping. By depositing thin films using atmospheric pressure chemical vapour deposition (APCVD) and aerosol-assisted CVD (AACVD) at high temperature, it was shown that a combination of different factors (such as silicon incorporation into the hematite structure and formation of lattice defects, along with a nanostructure of small agglomerate/cluster enhancing hole transportation to the surface) were the contributing factors in improving the PEC performance in hematite films. The role of the Si-containing precursors and their consecutive effect on nanostructure of the hematite films were investigated. Further work is needed to study the decomposition pattern of precursors and consequent effects of Si additives as well as co-dopants on fundamental physical and electrical properties of hematite electrodes. In addition, the feasibility of using microwave annealing for the fabrication of iron oxide thin films prepared by electrodeposition at low temperature was also investigated. Hematite films showed improved PEC performance when microwave assisted annealing was used. Microwave heating decreased the annealing temperature by ~40% while the PEC performance was increased by two-fold. The improved performance is attributed to the lower processing temperatures and rapidity of the microwave method that help to retain the nanostructure of the thin films whilst restricting the grain coalescence to a minimum. Around 60% of the energy can be saved using this low carbon foot-print approach compared to conventional annealing procedures for the lab-scale preparation of hematite films – a trait that will have significant implications for scale-up production. The lower processing temperature requirements of the microwave process can also open up the possibility of fabricating hematite thin films on conducting, flexible, plastic electronic substrates

Facile preparation of β-/γ-MgH2 nanocomposites under mild conditions and pathways to rapid dehydrogenation

A magnesium hydride composite with enhanced hydrogen desorption kinetics can be synthesized via a simple wet chemical route by ball milling MgH2 with LiCl as an additive at room temperature followed by tetrahydrofuran (THF) treatment under an Ar atmosphere. The as-synthesized composite comprises ca. 18 mass% orthorhombic γ-MgH2 and 80 mass% tetragonal β-MgH2 as submicron-sized particles. The β-/γ-MgH2 nanocomposite exhibits a dehydrogenation capacity of 6.6 wt.% and starts to release hydrogen at ~260 °C; ca. 140 °C lower than that of commercial MgH2. The apparent activation energy for dehydrogenation is 115±3 kJ mol-1, which is ca. 46 % lower than that of commercial MgH2. Analysis suggests that the meta-stable γ-MgH2 component either directly dehydrogenates exothermically or first transforms into stable β-MgH2 very close to the dehydrogenation onset. The improved hydrogen release performance can be attributed both to the existence of the MgH2 nanostructure and to the presence of γ-MgH2

Erosion and mechanical properties of hydrothermally-resistant nanostructured zirconia components

Large scale 50 × 50 mm sintered nanostructured zirconia ceramics were fabricated via industrially viable dry pressing routes. The green bodies were sintered by a two-stage process and the optimised sintering conditions are reported. The suitability of nanostructured zirconia for demanding applications in petrochemical valve components was investigated by slurry impingement erosion experiments. Zirconia showed a 60-fold improvement compared to commonly used stellite-coated commercial stainless steel specimens under test conditions while no tetragonal to monoclinic phase transformation was observed after erosion. The enhanced performance was also valid when compared with reported erosion resistant properties of alumina and zirconia components by a factor of 36 and 3, respectively. This suggests nanostructured zirconia as a potential robust alternative material for construction of internal trim components of petrochemical valves

Electromagnetic simulation studies of microwave assisted heating for the processing of nanostructured iron oxide for solar driven water splitting

Microwave assisted preparation has been shown to improve the performance of hematite photoelectrodes for solar driven water splitting. To understand the microwave heating process further, the distribution of the electromagnetic (EM) fields within the material is analysed using finite-difference time-domain (FDTD) EM software. The rate of the increase in temperature is calculated from the simulated EM field distributions. In order to validate the simulation results, the calculated temperatures were compared with the experimental temperatures obtained using a thermal imaging camera

Multiscale numerical and experimental analysis of tribological performance of GO coating on steel substrates

Herein, nano-tribological behaviour of graphene oxide (GO) coatings is evaluated by a combination of nanoscale frictional performance and adhesion, as well as macroscale numerical modelling. A suite of characterisation techniques including atomic force microscopy (AFM) and optical interferometry are used to characterise the coatings at the asperity level. Numerical modelling is employed to consider the effectiveness of the coatings at the conjunction level. The macroscale numerical model reveals suitable deposition conditions for superior GO coatings, as confirmed by the lowest measured friction values. The proposed macroscale numerical model is developed considering both the surface shear strength of asperities of coatings obtained from AFM and the resultant morphology of the depositions obtained from surface measurements. Such a multi-scale approach, comprising numerical and experimental methods to investigate the tribological behaviour of GO tribological films has not been reported hitherto and can be applied to real-world macroscale applications such as the piston ring/cylinder liner conjunction within the modern internal combustion engine

Kinetics of oxygen evolution at alpha-Fe2O3 photoanodes: a study by photoelectrochemical impedance spectroscopy

Closed access. This article was published in the journal, Physical Chemistry Chemical Physics [© Royal Society of Chemistry] and the definitive version is available at: http://dx.doi.org/10.1039/C0CP02408BPhotoelectrochemical Impedance Spectroscopy (PEIS) has been used to characterize the kinetics of electron transfer and recombination taking place during oxygen evolution at illuminated polycrystalline α-Fe2O3 electrodes prepared by aerosol-assisted chemical vapour deposition from a ferrocene precursor. The PEIS results were analysed using a phenomenological approach since the mechanism of the oxygen evolution reaction is not known a priori. The results indicate that the photocurrent onset potential is strongly affected by Fermi level pinning since the rate constant for surface recombination is almost constant in this potential region. The phenomenological rate constant for electron transfer was found to increase with potential, suggesting that the potential drop in the Helmholtz layer influences the activation energy for the oxygen evolution process. The PEIS analysis also shows that the limiting factor determining the performance of the α-Fe2O3 photoanode is electron–hole recombination in the bulk of the oxide

A new route to control texture of materials: Nanostructured ZnFe2O4 photoelectrodes

Studies were conducted to investigate the influence of deposition solution composition (methanol ≤ the deposition solvent ≤ ethanol) on their physical and chemical properties that matters in the aerosol formation and subsequent decomposition during the aerosol assisted chemical vapour deposition (AACVD) of ZnFe2O4 electrodes. The FEGSEM studies found that the change of composition of deposition solution produced a dramatic change in the ZnFe2O4 electrode texture. The ZnFe2O4 electrodes deposited from methanol as well as predominately methanolic solvents had a relatively compact morphology. In contrast, the electrodes deposited from ethanol as well as predominately ethanolic solvents showed highly textured rod-like structure at nanoscale. The change in electrode texture is explained in terms of changes occurred in precursor decomposition pathways from heterogeneous and homogeneous when the composition of deposition solution is systematically varied. The photoelectrochemical (PEC) properties of all ZnFe2O4 electrodes were studied by recording JeV characteristics under AM1.5 illumination and the photocurrent spectra. The textured electrodes exhibited a significantly higher photocurrent compared to their compact counterparts. This is attributed to the improved photogenerated minority carrier collection at the ZnFe2O4/electrolyte interface as the average feature size gradually decreased. The photocurrent density (at 0.25 V vs. Ag/AgCl/3M KCl) increases rapidly when the electrode is deposited from the solvent containing 60% ethanol and above, which is in close agreement with the textural changes taken place in ZnFe2O4 electrodes.Web of Scienc

Rapid microwave-assisted bulk production of high-quality reduced graphene oxide for lithium ion batteries

Graphene-based advanced electrodes with improved electrochemical properties have received increasing attention for use in lithium ion batteries (LIBs). The conventional synthesis of graphene via liquid phase exfoliation or chemical reduction of graphene oxide (GO) approaches, however, either involves prolonged processing or leads to the retainment of high-concentration oxygen functional groups (OFGs). Herein, bulk synthesis of high-quality reduced graphene oxide using microwave irradiation (MWrGO) within few seconds is reported. The electromagnetic interaction of GO with microwaves is elucidated at molecular level using reactive molecular dynamic simulations. The simulation suggests that higher power microwave irradiation results in significantly less retainment of OFGs and the formation of structural voids. The synthesized MWrGO samples are thoroughly characterized in terms of structural evolution and physicochemical properties. Specifically, a modified ID/IG-in ratio metric for Raman spectrum, wherein the intensity contribution of D’ peak is deducted from the apparent G peak, is proposed to investigate the structural evolution of synthesized MWrGO, which yields a more reliable evaluation of structural disorder over traditional ID/IG ratio. Li-ion half-cell studies demonstrate that the MWrGO is an excellent candidate for usage as high capacity anode (750.0 mAh g-1 with near-zero capacity loss) and high-performance cathode (high capacity retention of ~70% for LiCoO2 at 10 C) for LIBs