The study aim was to understand the effect of inoculum on bioelectricity production and the interactions that occur between organic load, external resistance and fuel type during the operation of a Microbial Fuel Cell (MFC). The first experiment explored the effect of four different environmental inocula (freshwater sediment, two types of return activated sludge (RAS) and anaerobic sludge) on microbial fuel cell performance. The number of bacteria in each of the inocula were standardised prior to experiments to achieve an inoculum density of 1.29 x 107cells ml-1 so that the comparison between treatments could be carried out fairly. For almost every metric (voltage, current and coulombic efficiency) the RAS inoculum outperformed freshwater sediment and anaerobic sludge inoculum. The treatment efficiency was high in all instances (>79%) with the exception of anaerobic sludge (33%). Microbial community analysis showed that anodes from MFCs exhibited a more complex microbial community profile than anodes from MFCs inoculated with anaerobic sludge. Two experiments were performed to investigate the relationship between fuel type, organic load and external resistance and their effects on MFC performance using an iterative Design of Experiments (DoE) approach. In the first experiment, a half factorial design was used as a screening study to investigate the main effects of fuel type (glucose vs acetate), organic load and external resistance. The study found that acetate performed poorly compared with glucose and that the experimental settings for external resistance should be modified for future experiments. The second experiment used a full factorial design and showed that only organic load exerted a statistically significant effect on cell potential, current and coulombic efficiency and that a statistically significant interaction effect between organic load and external resistance is exerted on cell potential and coulombic efficiency. The dominant effect of organic load was also apparent in DGGE community fingerprint profiles, which clustered according to organic load, of the anode community samples taken from MFCS in this study. In conclusion, the experiments yielded useful insights into inoculum effects and the interactions between basic operational parameters in an MFC that will be useful for selecting the operational parameters of MFCs depending on the field conditions and process requirements. The novelty of the techniques deployed in this study – standardisation the inoculum and exploring MFCs within a Design of Experiments framework – are noted along with the advances to our understanding of MFCs and the fact they have provided new tools with which to study MFCs systems. The wider implications of the performance characteristics of the MFCs used in this study and the findings presented within are discussed.

Proton exchange membrane fuel cells (PEMFCs) are currently based on high cost materials such as Nafion® membrane and Pt based catalysts. The high cost and limited abundance of noble metal hinder the commercialization of such fuel cells. For the future hydrogen economy, alkaline anion exchange membrane fuel cells (AAEMFCs) offer advantages of the potential use of non-Pt group metal catalysts, low-cost membranes (e.g. polysulfone based membranes) and cheaper bipolar plate (e.g. stainless steel). The research described in this thesis focused on the research and development of alternative anion conducting membranes and catalyst materials for fuel cells. Quaternary 1,4-diazabicyclo-[2.2.2]-octane (DABCO) polysulfone (QDPSU) was synthesized with different degree of substitution (DS) and characterized. The higher DS showed the better ionic conductivity; 0.015 S cm-1 for DS 58, 0.027 S cm-1 for DS 80 and 0.039 S cm-1 for DS 106 at 50 oC and 100 % relative humidity (RH). Based on the QDPSU, a thin PTFE-QDPSU composite membrane was prepared. Compared to the pristine QDPSU membrane, the composite membrane exhibited a better mechanical strength (32 MPa, maximum strength), less swelling and lower water uptake. The ionic conductivity of the composite membrane was 0.051 S cm-1 at 55 oC and 100 % RH. In fuel cell tests, power densities of 146 mW cm-2 and 103 mW cm-2 were achieved using oxygen and air, respectively. Severe degradation was found during preliminary experimental investigation on the KOH loaded polybenzimidazole (PBI) membrane including an ammonia smell came out the bottle and anode methanol solution turns yellow brown color in fuel cell tests. The QDPSU membrane was absorbed with phosphoric acid and tested in an intermediate temperature fuel cell. It was found that the higher DS, the higher membrane conductivity. When the DS reached 180 %, the QDPSU polymer cannot form ii a film with a suitable mechanical strength for the fuel cell application. A high power density of 400 mW cm-2 was achieved using DS106 of PA/QDPSU membrane at 150 oC and atmospheric pressure. Pd supported on carbons pre-treated in 5 % nitric acid, 0.07 M phosphoric acid, 0.2 M potassium hydroxide or 10 % hydrogen peroxide and evaluated in a half-cell. All Pd/C catalysts gave Tafel slopes close to 60 mV dec-1. Mass activities, measured at 0.025 V, for the 0.07 M H3PO4 and 0.2 M KOH treated carbon deposited with Pd were 6 mA mg-1Pd. Pre-treatments using 5 % HNO3 and 10 % H2O2 lead to an unfavorable effect on the morphology of Pd/C (metal particle agglomeration). Metal macrocycle based catalysts were examined for the ORR in alkaline media. FePc/KJB was found more active catalyst than the other metal macrocycles (CoPc, CoTMPP). The stability study in half-cell tests suggests that the FePc/KJB catalyst showed no degradation. The FePc/KJB was heat-treated under N2 atmosphere and 800 oC. The electrochemical behavior for ORR was characterized in half cell and single cell tests. The electron transfer number (n) of FePc/KJB-H8 was calculated to be 3.9 for ORR at -0.4 V. In AAEMFC, the peak power densities were 13.5 and 9.2 mW cm-2 for Pt/C and FePc/KJB-H8 under the same operating conditions, respectively. A direct methanol carbonate fuel cell using anion exchange materials and non-noble catalyst was demonstrated. The MEA performance using non-noble catalyst Acta 4020 was superior to the Pt/C based MEA. A maximum power density of 4.5 mW cm-2 was achieved at 50 oC using 6.0 M methanol and 2.0 M K2CO3. For the fuel cell stability study, the MEA exhibited a degradation rate of 2.52 μA cm-2 min-1.

No description available.

Modern technological advancements in our lifestyle have caused a significant increase in the consumption of energy. With this growing demand, people are more concerned about the rational use of existing limited energy and searching for alternative forms of environmentally friendly energy sources to reduce polluting emissions. Proton Exchange Membrane (PEM) fuel cell has shown and demonstrated that potential to be a suitable alternative power source because of its simplicity of design, load following capabilities, efficiency, feasibility and quick start-up. Although having these splendid advantages, cost and durability of PEM fuel cells are one of the major challenges that needed to be overcome. Three-dimensional single-phase and multi-phase isothermal PEM fuel cell models have been developed to investigate the transport limitations of fresh reactants and its effect on cell performance. The governing equations (continuity, momentum and species transport) with appropriate source terms were solved using computational fluid dynamics (CFD) technique. A user defined function (UDF) code was developed considering source terms for porous zones, effective diffusivity models for species transport inside cells and electrochemical reactions at catalyst layers to predict cell voltage at an average current density. The average current density and net water transfer coefficient, used to calculate the source terms, were calculated using auxiliary equations and linked to the solver through UDFs. Parametric studies were performed to determine the optimal operating conditions and geometrical design of PEM fuel cell. The simulation results show that gas diffusion layer permeability has no effect on cell performance for a value lower than 10-11 m2. GDL porosity is one of the major design parameters which have significant influence on limiting current density, hence on cell performance. Land area width of PEM fuel cell shows influence on cell performance. Low membrane thickness provides higher cell performance and approximately 50% reduction in membrane thickness results approximately 100% improvement in cell performance at high current density of 1.0 Acm-2. Bruggeman correlation was used in most of previous modelling work for explaining the diffusion of species though porous GDL and CL, but this thesis considered other types of effective diffusion models and investigated the effect of diffusion models on cell performance at high current densities. Tomadakis and Sotirchos (1993) anisotropic model produces cell voltage much closer to the experimental values. Therefore, anisotropic diffusion model should be utilized in PEM fuel cell modelling to minimize modelling uncertainties. A two-phase flow, steady-state, three-dimensional PEM fuel cell model considering the phase change effect of water has been developed in the final phase of the thesis. Flooding inside the cell was captured at high current density using the model for a condensation value of 10.0 s-1. Finally, parametric studies were performed based on isotropic and anisotropic GDL permeability cases. Modelling results suggest that isotropic permeability cases have strong influence on cell performance compared to anisotropic cases at high current density.

The "Zero Emission Carbon Technology" (ZECA) process aims to produce hydrogen without combustion and to generate electric power via a solid-oxide fuel cell. One of the process stages involves high-pressure steam/hydrogen gasification of coal at temperatures between 850 - 950 degrees C. The present study made use of a high-pressure wire-mesh reactor to gain detailed information and improve our understanding of reactions that will occur in the gasifier stage of this process.

The research described in this thesis focuses on the technological and operational aspects of low temperature polymer electrolyte membrane fuel cell (PEMFC) Stacks. The PEMFC is regarded as an ideal replacement to the internal combustion engine, but is still not an economically attractive prime-mover due to a number of key challenges that have yet to be fully resolved. These challenges include; degradation of cell components resulting in inadequate lifetimes, specialised and costly manufacturing processes and poor gravimetric/volumetric energy densities. The design of a novel modular fuel cell stack is presented which attempts to resolve some of the issues relating to material selection and the manufacturing processes required to produce components of the stack. The bi-polar plate (BPP) is a multifunctional component and is responsible for a considerable proportion of stack weight, size and cost in traditional planar PEMFC stacks. The manufacturing processes associated with BPP are costly and often require specialised machining. The design concept removes the conventional BPP from the stack architecture which improves the volumetric and gravimetric energy density of the stack while considerably reducing the cost of the stack. The new architecture comprises of active and passive zones which have focused on specific functionality originally fulfilled by a planar BPP. Active zones are regions that are in direct contact with the membrane electrode assembly and comprise of components that must have both chemical stability and electrical conductivity. Passive regions are designed for gas distribution and structural rigidity of the stack. The architecture involves a series of integrated chambers that supply a single gaseous stock to two cells simultaneously, which are coupled with external manifolds. Electrical continuity is achieved by utilising mono-polar plates that are connected external to the fuel cell stack. A six cell short stack was designed and assembled and the performance of the stack was experimentally tested. Experimental characterisation of the novel stack produced encouraging results. The stack recorded a maximum electrical output of 232.4W and operated over a wide range of operating conditions, including both steady state and dynamic load sequences. Another design feature is the incorporation of a Fault Tolerant System (FTS) as a result of the electrical connections being made external to the fuel cell stack, thus in the event of a cell failure the cell can be made redundant and the stack continues to operate. The FTS was found to operate as envisaged and continued to produce a steady stack output of 3.6V thereafter under this setting. Inspection of the current collecting plates demonstrated degradation on the TiN coating used, with loss of TiN and surface oxidation seen on the coating surface. The severity of the degradation indicated that the TiN coating technique was not suitable for the application. The estimated cost of the stack based on 10,000,000 item quantities was approximately $10.83, while the total weight of the stack was measured to be 2.26kg, resulting in a gravimetric power density of 101W/kg. Significant further weight and cost savings are planned as part of a continual design process.

Fuel cells as green and sustainable energy sources are at the heart of future Hydrogen Economy. Current research is focused on creating highly active, stable and low content Pt catalysts to improve fuel cell performance up to standards suitable for commercialization. The development of bimetallic Pt structures is the most promising route for achieving this goal. Besides the lower-noble metal content, combination of Pt with other metal at the nano-scale .can result in enhancement of catalytic activity due to the combination of geometric and electronic effects. The main aim of this work is the development of a surface limited redox replacement (SLRR) protocol for the design of epitaxial Pt-films with atomic scale control of the structure. SLRR exploits underpotentially deposited (UPD) layer as sacrificial layer that is replaced by more-noble Pt through a surface-controlled limited red-ox (galvanic) reaction. Different from previously developed SLRR protocols this work explores the one-cell configuration setup as an alternative to improve the efficiency and quality of the growth. The conditions for growth have been optimized and monitored with automated control of the SLRR cycles. The successful growth of Pt films on Au has been demonstrated for SLRR growth via Pb UPD. The electrochemical characterisation showed that using Pb UPD as sacrificial layer produces epitaxial Pt films of high quality with no significant roughness evolution up to 10 layers. Scanning tunnelling microscopy (STM) examination of the morphology has shown that Pt was deposited in clusters of 5-10 nm size, homogeneously and uniformly distributed over the surface. Electrochemical quartz crystal microbalance (EQCM) showed high deposition , yield and the Pt(II):Pb replacement stoichiomentric ratio higher than expected 1 : 1, suggesting an extra reduction power present in the system. The compositional analysis of Pt layers grown by SLRR suggests incorporation of minimum 4 at% of Pb. The SLRR protocol for the homoepitaxial growth of Pt thin films using adsorbed H i.e. under potentially deposited H (H-UPD) has been developed. This work presents first application of the SLRR protocol using a nonmetal UPD system. EQCM experiments demonstrated steady displacement kinetics and a yield equal to the expected stoichiometric Pt(II):H exchange ratio (1 :2). Electrochemical and STM characterization of Pt films showed that the growth via SLRR of H-UPD results in increase of the surface roughness with the number of replacement steps. The roughness of SLRR deposited Pt films has been compared with films grown in the same solution at two constant overpotentials: with and without adsorbed H floating on the surface. The results showed clear advantages of using . the SLRR of H-UPD approach which generated films with two times lower roughness and better quality then the ones grown potentiostatically. The generality of the SLRR approach using H-UPD is validated by growth of Pt films on Pd ultrathin films on Au. The Pt films of well-defined thickness and structure grown by SLRR of Pb UPD have been used in a fundamental study of Pt dissolution during formic acid oxidation (FAO). A quantitative analysis of long term durability tests of Pt films has been conducted by potential cycling over an extended potential range. Direct proportionality between overall life and thickness of the catalyst has been observed. The characteristic stages of the activity decay were correlated with the characteristic electrochemical behaviour during FAO and the surface morphology examined by the atomic force microscopy. An average Pt dissolution rate of 1.90±O.33 ng.cm-2.cycle-1 has been determined during FAO which . was almost four times faster than the rate under the same conditions in the background solution. This study suggests that Pt dissolution mechanism during FAO is influenced in by reaction intermediates and processes on the surface.

The aim of this project was to develop a new preparative route leading to the synthesis of bimetallic precious metal catalysts to be used in, the anode of fuel cells. These catalysts required high metal dispersion and good interaction between the metals used. Control over high metal loading onto the support was also desirable. / Current preparative methods in industry involve the eo-precipitation of mixed metal oxides onto supports together with subsequent high temperatures treatments to achieve the desired bimetallic structure. The final catalysts generally present agglomeration and segregation of the metals when high loadings are required and high temperature applied. As a result, they show poor surface area and low activity. The method studied in this project consisted of two steps: the preparation of mixed metal oxides nanoparticles stabilised by surfactants and the solution reduction of these species under H2. Both the oxide and reduced particles can be isolated in a powder form and easily re-dispersed into an appropriate solvent to give stable dispersions. The oxide and reduced nanoparticles were absorbed onto carbon supports. Using this method, PtRu catalysts for fuel cell applications were prepared. Cyclic voltammetry was used to determine the surface area of the metal particles onto supports and also gave an indication of surface compositions. Preparative variables were investigated in order to manipulate the characteristics of the particles obtained. Firstly, the nature of the stabiliser was examined, showing that the use of a non-ionic stabiliser yielded high dispersions and narrow size distribution. However, the presence of stabiliser in the final products proved to be an issue for their use as catalysts and a firing stage was then introduced. The resulting catalysts showed higher surface areas than their equivalent standard catalysts but surprisingly performance was not increased. Additionally, it was found that no particle growth was observed at high loading; for instance, good dispersion and high surface areas were still obtained at 60wt% metal onto carbon.

Supervised and unsupervised classification algorithms separate a data set into classes or clusters respectively by making use of prior knowledge or some measure of similarity. Vectors in the same class represent objects that have some characteristic in common. In this thesis the application of classification algorithms to inverse problem data is investigated. Frequently, the ill-posedness of the inverse problem Ax = y is due to the compactness of the linear operator A, which maps the state space X onto the measurement space Y. Theory from the field of inverse problems allows the reconstruction of state space data from measurement data via regularization techniques. Often, in applications, discrimination algorithms are applied to measurement data without taking care of the ill-posed nature inherent in the data. The comparison of classification in measurement space with classification of reconstructed data in the state space is the primary focus of this thesis. Two classes are linearly separable if a hyperplane exists that separates the classes. In this thesis, two classes are referred to as being stably separable if there exist two separating hyperplanes with a positive distance between them. For linear classifications it is shown that the instability of the inverse problem is inherited by the classification problem when it is applied to the data in the measurement space. For elliptic classes the stability of the separation is preserved, providing the range of the adjoint of the compact linear operator A is dense in the state space. The illposedness of the classification problem is reflected by a corresponding ill-posedness of standard classification methods, which - as the inverse problem - need regularization. We investigate Fisher's Linear Discriminant, Principal Component Analysis and the K-Means Algorithm. We apply the theory to magnetic tomography for fuel cells, demonstrating the validity of the results in a practically relevant application.

This thesis describes the search for new mixed conductors as potential anodes and cathodes for applications in Solid Oxide Fuel Cells. Several compounds have been synthesised and characterised by means of different diffraction techniques (X-Rays, neutrons and electrons), high resolution electron microscopy and electrical measurements (AC Impedance Spectroscopy and DC resistivity measurements).