Density Functional Theory calculations are employed in the investigation of the ethanol oxidation reaction (EOR) at the anode of Direct Ethanol Fuel Cells (DEFC), with a view to mechanistic understanding of the reaction pathways, determination of the factors governing the onset potential of activity and selectivity towards C02, and ultimately the design of an optimal electrocatalyst in these regards. The lowest energy pathway of ethanol decomposition on platinum is identified and it is found that the reaction kinetics do not significantly vary with catalyst morphology. The aqueous medium is found to somewhat facilitate all reaction pathways. Surface hydroxyl is found to oxidise ethanol to acetaldehyde. Surface atomic oxygen is found to selectively oxidise adsorbed carbon monoxide to carbon dioxide. The onset potentials of surface hydroxyl and atomic oxygen on platinum are calculated to be in good agreement with experimental data. It is determined that onset potentials of < 0.1 V vs. SHE will result in inactive hydroxyls, while an onset potential of < 0.2 V results in inactive surface atomic oxygen, providing a target for catalyst optimisation. Onset of EOR is found to occur at potentials between 0.4 V and 0.5 V earlier on a range of platinum tin catalysts than on platinum, and Pt3Sn is found to be kinetically the best example of such a catalyst These findings are in good agreement with experimental observations. The addition of rhodium to platinum is found to result in a hydroxyl onset potential below the 0.1 V threshold for activity, and the near-optimal onset potential of surface atomic oxygen, resulting in excellent selectivity towards C02. However, the stability of the hydroxyl species delays the formation of atomic oxygen and so delays the onset of ethanol oxidation activity to an unacceptably high degree. This effect is believed to be general to metallic systems.

The performance of a Wave Energy Converter (WEC) may be estimated using both physical and numerical modelling techniques. Since numerical models are often informed by, and validated against data obtained from physical models, it is important to assess the accuracy with which a prototype's behaviour is predicted by its physical model. This thesis makes such an assessment for the case of a pitching flap type WEC, by comparing the performance of Aquamarine Power's Oyster1 prototype device to that of a representative physical model. This comparison was informed by considering the device in terms of three sub-systems, namely: the flap; the incident waves; and the power take-off (PTO) system. Understanding the effects of characteristics associated with each of these sub-systems on the device's behaviour was pursued using both physical and numerical modelling techniques. As well as informing the comparison between the device's performance at each scale, the conclusions drawn from this work, particularly in relation to the modelling of sea conditions and PTO systems, are relevant to WEC modelling in general. Agreement between the device's behaviour at each scale was assessed by comparing measurements of the flap's angular position and velocity, and the power captured by the PTO. The velocity measured at prototype scale was 12% greater than that measured at model scale. The disagreement between velocity measurements directly affected agreement between power capture measurements, which were also 12% greater at prototype scale compared to model scale. Damage to the PTO cylinders meant that the device's performance was sub-optimal. Extrapolation of the comparison between the device's performance at each scale suggested that the power captured was 7% greater at prototype scale relative to model scale at magnitudes of power capture more representative of optimal performance.

No description available.

The aim of this thesis is an in depth study of electro-oxidation of ethanol, but also that of alternate fuels to allow a direct comparison under a range of conditions. Polycrystalline metal electrodes are used in a half cell set up as model environment for the electrochemical studies of several catalytic surfaces. Due to the limited research that has been carried out, for the first time chapters 3 and 4 of the thesis provide electrochemical studies into the electro oxidation of ethanol, ethylene glycol, acetaldehyde and acetic acid on polycrystalline rhodium while simultaneously studying temperature, concentration and electrolyte. Chapter 5 investigates the effect of changing platinum coverage on the surface of polycrystalline rhodium on of ethanol electro-oxidation while also changing temperature and concentration. To the best of my knowledge this is an experiment never before carried out and clearly shows the effect of the varying platinum coverage under a range of conditions. Chapters 6&7 investigate electro-oxidation of C2 molecules on polycrystalline platinum again with varying concentration, temperature and electrolyte. Although Chapter 1 shows similar experiments have been carried out before, using the same electrode for all experiments as well as investigating the effect of varying tin coverage on the platinum surface allows for direct comparisons, as well as providing results to compare with the results of the rhodium experiments. Overall, this thesis provides a systematic and comprehensive study into the electrochemical oxidation of ethanol and other C2 molecules using cyclic voltammetry and chrono amperometry techniques to provide activity and stability information to a degree not reported anywhere else.

This thesis focuses on the advanced control methods for multi-terminal High Voltage Direct Current (HVDC) systems integrating offshore wind farms. Several key issues are investigated in this thesis, including controller design to improve the system dynamic performance, power loss reduction with controller optimization, system stability and dynamics assessment. A DC voltage backstepping control method is designed considering the cable dynamics and controller delay effects. DC cable and converter current loop dynamics are included in the voltage controller design. This control method is applied to a point-to-point and a 4-terminal HVDC system with a conjunction point. Simulation results show that the controller performance can be improved in terms of the disturbance rejection., The relation between Voltage Source Converter (VSC) control action and power losses in the multi-terminal HVDC systems is investigated. For a 4-terminal system, it is shown that the transmission loss can be reduced by properly setting the droop gain ratio between different terminals. For each converter, it is demonstrated by simulation that through a proper controller design, the power loss can be significantly reduced while controller performance can be maintained. A new droop setting design method is proposed. It is shown that due to the existence of droop control, DC voltage deviation will affect the power flow accuracy when the steady state is changed. The impact of DC voltage deviation on the power flow accuracy is studied to tackle this problem, and the DC voltage deviation can be kept unchanged, without affecting the steady state power flow. A droop gain selection procedure is proposed to satisfy the system stability requirement. A state feedback enhanced droop controller is proposed to improve the dynamic performance and stability requirement. With the proposed method, it is shown that the system stability can be guaranteed under both small and large droop gains.

With the advent of large scale offshore wind generation the world has taken a significant step closer to reducing its reliance on fossil fuels as the main source of electricity. To this end, plans in Europe have been proposed to interconnect a variety of renewable generation sources, predominantly wind sourced, via the construction of High Voltage DC lines into a Single Multi-Terminal DC (MTDC) grid, dubbed the European Supergrid, In order to meet a large portion of the total European demand. The object of this thesis is to address some of the issues involved with the Implementation of such a complex system. This work presents possible grid management strategies for the safe and efficient operation of MTDC systems to ensure adequate security of supply under varying grid conditions. It proposes power sharing strategies within MTDC systems incorporating several sending and receiving end terminals based on "power priority" at the receiving end to meet demand and ensure stable system operation is maintained. Further, it proposes the utilisation of DC grid management strategies for the provision of frequency support within MTDC systems through the redistribution of active power during periods of load imbalance within the AC system, Additionally, it proposes a potential method of detection of frequency events In onshore AC systems for interconnected decoupled offshore wind systems via utilisation of DC grid voltage manipulation, Finally. it provides a detailed analysis of the behaviour of a two-level AC/DC converter under DC fault conditions (both line-to-line and line-to-earth) from circuit analysis based on the converters behaviour post-fault. For line-to-earth faults, it analyses the effect of different earthing configurations with an,aim to provide additional insight into the differing behaviour of the converter post-fault and thus assist in the development of optimised fault detection and isolation protocols, as well as reconnection procedures post-fault.

Recent development of energy conversion devices namely photovoltaic (PV) cells or solar cells and thermophotovoltaic (TPV) cells require the use of bulk germanium as substrate material for efficient devices performance. Germanium is preferred to be employed in solidstate structure of terrestrial or space energy conversion devices due to its excellent electrical properties. With bandgap of 0.66 e V energy from infrared region of solar or thermal spectrum can be absorbed and converted into electrical energy. At present, multi-junction solar cells show the highest performance with bulk germanium as substrate material.' but have complicated and expensive manufacture processes. The major contributor to the high cells cost is the substrate material, germanium, which is an expensive and scarce material. One of the possibilities to resolve these issues is by using thin film instead of thick bulk germanium. To date, development of thin film germanium for energy conversion devices has not been established. By providing germanium on insulator structures a good quality thin film germanium can be attained and thus, offer a low cost route. The rapid melt growth (RMG) technique has been proposed, where it could potentially produces thin film germanium with quality similar to that of bulk germanium. In the existing technology via the RMG process germanium thickness was limited to 100 run. For photovoltaic applications thicker germanium films are required to have more energy absorption, thus leads to efficient performance.

This thesis investigates the effects of hydrodynamic interactions within arrays of wave energy converters, provides a significant amount of much needed physical model data to the industry for validation purposes and assesses the relative suitability of various numerical models for use in isolated device and array studies. Experience gained from two large sets of physical experiments undertaken early in the project resulted in the planning, preparation, design and execution of a third set of experiments, the results of which have been reported in this thesis. The physical data obtained allowed for the estimation of the effect of array interaction on device response and performance under a wide range of incident, control and array setup conditions. To undertake these experiments novel testing protocols and procedures were developed to allow for the production of useful data where the quantity of interest was much smaller than any particular measured value, It was found that even small errors and uncertainties may have significant implications for data obtained and that the error and uncertainty inherent within a physical system is capable of misrepresenting array interactions. In outline, it has been found that investigating the effects of array interaction experimentally is difficult and requires significant attention to detail. Two different Frequency Domain Models and a Time Domain Model have been produced for modelling the effects of array interactions in regular sea states. A Spectral Domain Model and Time Domain Model were produced to estimate array interactions in irregular sea states. Results obtained from these models have been compared to those obtained from physical testing and by estimating the error in physical results the validity of a variety of industry standard numerical models has been assessed for the first time. The importance of distinguishing between model accuracy, adequacy and suitability is highlighted. It is also argued that in many cases, Time Domain Models will not provide the most accurate results achievable and that Spectral Domain Models provide a suitable alternative in these cases.

No description available.

ZnO nanorods, sensitised to visible light using dyes, quantum dots, or thin films of low-bandgap semiconductors are commonly used as photoanodes in novel solar cells . They have a number of exciting properties for such an application. These include a direct conducting path for electrons, with few grain boundaries, and an increased surface area offering enhanced optical absorption. They are also able to sustain a depletion layer, the electric field this creates can effectively separate charge carriers at the nanorod/sensitiser interface, reducing recombination. However, despite these potential benefits, devices made using 1-D ZnO nanostructures are so far unable to match the performance of devices constructed using mesoporous Ti02 films. One of the reasons given for this is the presence of mid-bandgap states at the surface, which are investigated in this work. ZnO nanorods were grown using a hydrothermal growth technique. Using cyclic voltammetry and photocurrent measurements, mid-band gap trap states were identified and their position found to be centred around 0.8V below the conduction band. Visible luminescence from defect states identified by photoluminescence may be associated with these states. The effects of annealing in air at 180°C, 350°C and 450°C were investigated, all three experimental techniques showed that annealing at temperatures equal to or greater than 350°C was effective in reducing the density of these states. Annealing was also found to have a critical effect on doping density of the nanorods, with implications for both conductivity and the characteristics of the depletion layer that forms at the interface of the nanorods. The doping density was measured using a modified form of MottSchottky analysis and found to be high (> 1020cm-3) for as-grown rods, and only slightly reduced by annealing at temperatures up to 350°C. Annealing at 450°C however reduced the doping density by over two orders of magnitude. These results are consistent with previously reported evidence that incorporated hydrogen acts as a donor for ZnO. A study of the structure of alloyed CdSel-xTex quantum dots was also carried out using a combination of high resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction. This showed that both wurtzite and zinc blende QDs were present at all compositions, with no clear phase transition between different compositions. CdSe QDs were then successfully used to sensitise annealed nanorods to visible light. Electron transport within the rods was shown to be efficient. The results in this work should prove useful in understanding how best to utilise 1D ZnO nanostructures in solar cells, and provide insights into the nature of defect states which have so far limited the efficiency of such devices.