Philosophiae Doctor - PhD / The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. The core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. Research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to form binary, ternary and quarternary catalysts. / South Africa

The work in this thesis addresses the improvement of electrocatalyst performance in hydrogen PEM fuel cells. An agglomerate model for a catalyst layer was coupled with a one dimensional macroscale model in order to investigate the fuel cell performance. The model focuses on the agglomerate scale and the characteristic length in this study was 0.4 µm. The model was validated successfully with the experimental data. Based on the analysis of variance method at a 99% confidence level, the variation in the average fuel cell voltage was significantly sensitive to that in the volume fraction of electrolyte in an agglomerate. The effect of changing electrolyte film thickness was observed to have a significant impact only in the mass transport limited region, whereas the effect of changing agglomerate radius was found over the entire range of current density. An analysis comparing the effect of agglomerate shape at a constant platinum loading, a constant characteristic length and assuming the semi-finite structure was suitable for this study. Sphere, cylinder and slab agglomerate geometries were considered. The behaviour of the utilisation effectiveness was discovered to be strongly affected by the agglomerate shape. The improvement in the utilisation effectiveness was non-linear with current density. The advantage of the slab geometry in distributing reactant through the agglomerate volume was reduced and consequently the increase in utilisation effectiveness for slab-like agglomerates diminishes in the high current density region. At 0.85 Acm−2, the maximum improvement of the catalyst utilisation effectiveness in slab was 27.8% based on the performance in sphere. The improvement in fuel cell maximum power density achieved using slab-like agglomerate was limited to around 3%. The improvement in the overall fuel cell performance by changing the agglomerate shape was not significant. To achieve significant improvements in fuel cell performance will require changes to other features of the catalyst layer.

The continual increase in electricity dependence for the advancement of society has led to increased demand in electricity globally. This increased demand, among other things such as global warming interventions and energy security have encouraged the need to diversify electricity generation sources. Civilian use of nuclear power dates back to the 1950s. The United States of America and France are currently leading with the highest nuclear power generation in the world, generating 101 GWe and 63 GWe, respectively. Several countries such as China and the United Arab Emirates have committed to new nuclear build in order to increase their nuclear power generation capacities. Standing against the prospects of growth of the nuclear power industry are technical and nontechnical challenges. These include proliferation risk, safety, high capital costs and high-level waste management. Most spent nuclear fuel from power reactors is currently stored in the spent fuel pools on reactor sites, and some have been reprocessed. It is estimated that about 32% (370 000 tons of Heavy Metal) of the total spent fuel generated from power reactors have been reprocessed up to date. With most of the spent fuel pools filling up, alternative interim and long term disposal of spent nuclear fuel solutions have been under investigation from as early as the 1970s. South Africa has planned an interim dry storage facility for the spent nuclear fuel to be established at the existing Koeberg power station. The interim dry storage facility will make use of HI-STAR 100 multi-purpose casks to store spent nuclear fuel until the country decides on final disposal solution. There are many aspects that are critical to safe, efficient and cost-effective long term storage of spent nuclear fuel. Some of the physics and engineering aspects concerning dry storage facilities are briefly discussed. The aspects presented here are: radiation containment, spent fuel, sub-criticality, decay heat removal, site location aspects, response to seismic events, cask corrosion, transportation infrastructure, operability and monitoring. The study of the three existing dry cask storages from the USA, Hungary and Belgium gives an overview of the dry cask technology in use today. These presentations are based on publicly available reliable information. The proposed dry storage facility at Koeberg will be in the existing power station footprint using the HI-STAR 100 casks. The decision to have the proposed dry storage facility at Koeberg will minimise related licence applications and part of security installations as the site already has some security. The location of the facility in the power station’s footprint also allows for cost-effective and safe transportation of casks from the reactor building to the proposed facility. The modularity aspect of the dry cask storage facility at MV Paks in Hungary should also be employed at Koeberg to allow for more storage. This will cater for additional casks that may need to be stored if more nuclear power plants are procured in the future. South Africa’s air traffic around the Western Cape is not as congested as Belgium’s. There is, therefore, no need for the casks to be housed in concrete buildings like Doel’s. Most of Koeberg’s high-level waste would have had a longer cooling time in the pools compared to the minimum cooling time required for the chosen cask technology. This will provide a conservative, safe approach for Koeberg’s facility. Dry cask storage technology has provided a reliable interim dry storage solution for several countries. Despite uncertainties for long term disposal options, the proposed dry cask storage facility at Koeberg is a suitable interim storage alternative for South Africa to allow continuous operation of the plant. This conclusion is based on the physics and engineering aspects that have been presented in this minor dissertation.

Numerous investigations have been conducted to determine the effect of fuel composition and molecular structure on particulate emissions using exhaust gas analysis, but relatively few measurements have been obtained in-cylinder or under conditions where fuel effects can be isolated from other variables. In this work, dimethoxymethane was used as the base fuel to produce a non-sooting flame in a constant volume combustion vessel at 1000 K, and a density of 16.6 kg/m3. A second fuel was then added incrementally to determine an incipient soot limit. Line-of-sight extinction measurements were used as the primary diagnostic tool to determine if a correlation exists between soot and fuel properties. These data indicate that fuels with carbon double bonds are more prone to soot than the single bonded fuels. Each of the four pure additives tested began to soot at a structure-weighted available oxygen-to-carbon ratio near one. The commonly used two-color method for measuring temperature and soot concentration (KL) was used as a secondary method. A method for calibrating and analyzing the uncertainty of the temperature and KL measurements with a single color RGB digital camera was demonstrated. Images of reacting jets of different soot concentrations are shown along with an uncertainty analysis. The resulting temperature and KL maps show uneven distributions for flames of various fuels. Analysis shows that the temperature and KL values of heavily sooting fuels are primarily a result of conditions (temperature and soot concentration) within a 1—2 mm region on the surface of the jet, where a turbulent diffusion flame is present. As soot concentration decreases, the region of influence affecting the result thickens, allowing more influence from within the jet, lowering the measured temperature. Therefore, a low-sooting jet appears to have a lower temperature than a high-sooting jet. Extinction and two-color soot measurement results were compared. The two-color KL values were seen to level off at around 0.5, but continue to increase monotonically as soot increased. The broad band method is therefore not good for absolute soot measurements. Natural luminosity measurements were sensitive to the first appearance of soot, but were non-linear.

Fuel cells have long been seen as an alternative to combustion powered and diesel powered engines and turbines. Production of energy via a fuel cell conversion method can generate up to 60% efficiency in comparison to 30% using a combustion powered engine, with low co-production of harmful side-products. The polymer electrolyte membrane (PEM) adapted for the fuel cell application is one of the main components that determines the overall efficiency. This research project was focused towards novel PEMs, such as sulfonated poly(etheretherketone) or SPEEK, which are cost-efficient and robust with high proton conductivities under hydrated conditions. The degree of sulfonation (DS) of a particular SPEEK polymer determines the proton conducting ability, as well as the long term durability. For SPEEK with high DS, the proton conduction is facile, but the mechanical stability of the polymer decreases almost proportionally. While low DS SPEEK does not have sufficient sulfonic acid density for fast proton conduction in the membrane, the membrane keeps its mechanical integrity under fully saturated conditions. The main purpose of this work was to address both issues encountered with SPEEK sulfonated to low and high DS. The addition of both solid acids and synthetic cross-links were studied to address the main downfalls of the respective SPEEK polymers. Optimization of these techniques led to increased understanding of PEMs and notably better electrochemical performance of these fuel cell materials. Oxo-acids such as tungsten (VI) oxide (WO3) and phosphotungstic acid (PTA) have been identified as candidate materials for creating SPEEK composite membranes. The chemistry of these oxo-acids is well known, with their use as highly acidic catalyst iv centers adopted for countless homogeneous and heterogeneous, organic and inorganic reactions. Uniform dispersion of WO3 hydrate in SPEEK solution was done by a sol-gel process in which the filler particles were grown in an ionomer solution, cast and allowed to dry. PTA composites were made by adding the solid acid directly to a solution of the ionomer and casting. The latter casting was allowed to dry and Cs+ - exchanged to stabilize the PTA from dissolution and leaching from the membrane. The chemical and physical properties of these membranes were characterized and evaluated using mainly conductometric and X-ray photoelectron spectroscopic methods. Composite SPEEK/ PTA membranes showed a 50% decrease in PEM resistance under hydrogen fuel cell testing conditions, while SPEEK/ WO3 composites demonstrated a ten-fold increase in the membrane's in-plane proton conductivity. The chemical and physical properties of these composites changed with respect to their synthesis and fabrication procedures. This study will expound upon their relations.

Finding new energy sources has been a major quest in the 21st century. The challenge is not simply to find alternatives for traditional energy sources like crude oil and coal to generate power on a large scale but also to produce power to energize micro and nano scale devices. For electricity production in the nano and the micro scale, research has been done on technologies including fuel cells and batteries.This study is focused on two themes, i.e., the use of a microbial fuel cell and an enzymatic fuel cell for potential bioMEMS/NEMS applications. In the first , a fully functional fuel cell with yeast as the microbe using glucose as the fuel was tested to characterize its performance. In the second phase, a lactate dehydrogenase based enzymatic fuel cell using lactate as the fuel was tested to understand the performance characteristics.

No description available.

No description available.

No description available.

As the world begins to focus more and more on new and more effective means of energy production, fuel cells become increasingly more popular. While different fuel cells are already found in industry today, the direct methanol fuel cell (DMFC) is becoming an increasingly more probable means for portable power production. In such applications a passive air breathing direct methanol fuel cell would be ideal. However, successful use of the passive DMFC in such applications requires that the fuel cell be capable of operating at various temperatures and relative humidities. A passive air breathing direct methanol fuel cell was developed and manufactured for this study. This work studied the effects of varying relative humidity and temperature over a probable range of operating conditions for small scale portable power applications on the performance of the fuel cell, both in relation to power production and fuel consumption. Potentiostatic, electrochemical impedance spectroscopy, and polarization tests were performed in order to characterize the performance of the fuel cell. Additionally, a one dimensional steady state isothermal mass transport model was developed to provide insight to the behavior of the fuel cell. The experimental data and model results show that increasing the fuel cell temperature and decreasing the ambient relative humidity increases the current production capabilities of the fuel cell. Further, the experimental data suggests that the major problem hindering current production in passive air breathing direct methanol fuel cells is flooding of the cathode diffusion layer. / Master of Science