the major issues limiting the introduction of polymer electrolyte membrane fuel cells (PEMFC) is the low temperature of operation which makes platinum-based anode catalysts susceptible to poisoning by trace amounts of CO, typically present in reformed fuel. In order to alleviate the problem of CO poisoning and improve the power density of the cell, operating at temperature above 100°C is preferred. Nafion® type perfluorosulphonated polymers have been typically used for PEMFC but cannot function at temperatures above 100°C. In addition, higher temperatures will enable more effective cooling of the cell stacks and provide a means for combined electrical and heat energy generation. The solution to improved PEMFCs technology is to develop a new polymer electrolyte membrane which exhibits stability and high conductivity in the absence of liquid water. A HighTemperature PEMFC based on a Phosphoric acid (H3P04) doped Polybenzimidazole poly[2,2- (m-phenylene)-5,5 bibenzimidazole] (PBI) membrane has been developed and demonstrated as an alternative to Nafion® for operation at temperatures up to 200°C. PBI membranes, when doped with phosphoric acid, do not rely on hydration for conductivity; a significantly lower water content of the membrane, compared to Nafion, is required for proton transport. The resulting system improvements include; high CO tolerance, simple thermal and water management, excellent oxidative and thermal stability, and good proton conductivity at elevated temperatures. Two issues associated with phosphoric acid in the PBI based fuel cell are the lower activity of the electrocatalysts and the potential loss of the acid into the fuel cell gas/vapour exhaust streams. The limited oxygen permeability and slow oxygen reduction kinetics in phosphoric acid is a major limitation for the performance ofPBI based PEMFCs. The kinetics of oxygen reduction in PBVH3P04 has been studied in electrochemical single electrode cells. Several Membrane Electrode Assemblies (MEAs) have been manufactured to allow optimisation of the electrode performance. Various electrochemical techniques such as chronoamperometry, polarisation curves and Frequency Response Analysis (FRA) were used to study and separate the effects of the various phenomena taking place at the electrode surface: IR losses, mass transport and kinetics. A new Electrode structure utilizing PTFE has been developed allowing higher oxygen permeability and therefore enhanced performance of 0.55 W cm-2 with oxygen and 0.27 W cm-2 with air (atm) at temperature as low as 120 ·C. The Platinum loading was reduced to 0.4 mgpt cm-2 at the cathode and 0.2 mgpt cm-2 at the anode. Further reduction of cathode platinum loading to 0.2 mgPI cm-2 was achieved without dramatic drop in the performance by utilising Pt based binary alloy catalyst (Pt-Co/C). A simplified thin film steady-state, isothermal, one dimensional model of a proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBD membrane, was developed. The electrode kinetics were represented by the Butler-Volmer equation, mass transport was described by the multi-component Stefan Maxwell equations and Fick's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density and diffusion coefficients, together with the effect of water on the acid concentration and ionic conductivity. The polarisation curves predicted by the model were validated against experimental data for a PEMFC which included the effect of temperature and oxygen/air pressure on cell performance. An additional problem which faces the introduction ofPEMFC technology is that of supplying or storing hydrogen for cell operation, especially for vehicular applications. Consequently the use of alternative fuels such as methanol and ethanol is of interest, especially if this can be used directly in the fuel cell, without reformation to hydrogen. A limitation of the direct use of alcohol is the lower activity of oxidation in comparison to hydrogen, and hence to improve activity and power output higher temperatures of operation are preferable. The performance of a high temperature direct methanol fuel cell (DMFC) using PBI based electrode assemblies was investigated. The performance of the system was limited by poor methanol oxidation kinetics in a phosphoric acid environment and consequently power performance was inferior to that achieved with low temperature DMFCs based on Nafion membranes.

Fuel cell technology is one of the emerging energy technologies, both for stationary applications (block power stations) and mobile applications (portable electrical devices). In a standard fuel cell the chemical energy of fuels such as CH3OH or H2 is transformed to electrical energy. High energy efficiency and low emissions make the fuel cell technology attractive compared to traditional combustion engines. The main obstacles to large scale commercialisation of Polymer Exchange Membrane Fuel Cells (PEMFC) are rooted in the proton conducting membrane, which is the most important component of this device. The primary requisites of the hydrated membranes are: (a) high proton conductivity at relatively low humidity levels; (b) low fuel permeability; (c) high chemical, thermal and mechanical stability. Among the different polymeric membranes studied for fuel cell applications only the perfluorosulphonic acid ionomers membranes, such as Nafion®, are actually used commercially.

A number of techniques have been used to study the anodic behaviour of tin and aluminium in some aqueous electrolytic solutions. In acidic solution the dissolution of tin is relatively fast. The reaction mechanism in perchlorate electrolyte corresponds to two consecutive one-electron steps of comparable rate. In chloride electrolyte the most appropriate mechanism involves simultaneous two-electron transfer. The order of reaction with respect to chloride ion is unity. The measured currents are also dependent upon the concentration of hydrogen ion. The active dissolution of tin in sodium hydroxide solution is relatively fast with an order of reaction with respect to hydroxyl ion of two. The mechanism involves a following chemical reaction to form stannite ions.

No description available.

The electrical conductances of aqueous solutions of magnesium and manganese (II) sulphates and benzenedisulphonates have been measured at several frequencies from 1 KHz to 50 MHz, using two radio-frequency transformer ratio-arm bridges and an audio-frequency Wheatstone bridge. The radio-frequency conductances were determined using a relative method with potassium chloride as a reference electrolyte. The conductance data were analysed by extrapolation and minimisation techniques using the theoretical conductance equations of Fuoss-Hsia[(13,15)], Pitts[(7,14)], Falkenhagen-Leist-Kelbg[(4)], and Murphy-Cohen[(17)]. It was found that the Murphy-Cohen equation was not able to yield a satisfactory interpretation of the audio-frequency data of the bi-bivalent electrolytes examined in this work. The findings of Atkinson et al.[(43, 44)] that magnesium and manganese benzenedisulphonates could be treated as essentially unassociated were not confirmed by the measurements and analyses of the present work. The increases in conductance brought about by the high-frequency field could be explained in terms of ion atmosphere relaxation plus the effect of the relaxation of the ion-pair equilibrium as calculated by Gilkerson[(30)]. All four electrolytes studied showed variations in the values of their association constants with frequency which were attributed to relaxation of the ion-pair equilibrium. This effect, however, was not significant below about 10 MHz. Rate constants for the ion pair dissociation rate have been estimated from the Gilkerson theory. The conductance dispersion maximum at 2 - 3 MHz for manganese sulphate found by Rance[(41)] has not been detected in the present work. It is suggested that the result of Rance was due to inconsistencies in the measurement apparatus then used.

No description available.

The reduction of. electrodeposited P-lead dioxide to lead sulphate in 5M sulphuric acid has been studied at the stationary and RDE. Potential step and sweep experiments have been made and a model for the discharge process of lead dioxide has been proposed based on charge transfer and limited high field conduction. T'he potentiostatic oxidations of lead sulphate overlying lead and lead dioxide have been investigated. The reduction behaviour of porous one-dimensional lead dioxide electrodes have been examined and shown to be independant of rotation speed in a large excess of 5M sulphuric acid. The reduction peak was broadened by the porosity. This broadening was interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more resistive. The effect of different potential sweep rates on the current response and effects of progressive redox cycles can be fully explained on this model. The potentiostatic oxidation of porous electrodes of lead dioxide containing lead sulphate has also been investigated. The form of the current transient was found to depend on the balance of lead sulphate and lead dioxide. Investigations have been carried out on the above electrodes using the techniques of scanning electron microscopy and alternating current. Possible interpretations of the results are discussed. The influence of the solid/porous material interphase on the electrode behaviour has been investigated for a variety of alloy supports with special reference to the charge output on reduction, ease of reoxidation and electrode support/porous phase adhesion. The progress made in the understanding of some of the problems associated with the lead acid cell has been discussed.

No description available.

The work discussed in this thesis is in three parts. The initial work carried out was to develop a differential pulse polarographic (DPP) method for the determination of disodium cromoglycate (INTAL) in human urine samples. The method eventually recommended involves an ion-pair extraction of the cromoglycate with tri-n-butylbenzylphosphonium chloride into chloroform. After evaporating the chloroform and dissolving the residue in a buffer solution, down to 0.5 μg INTAL per ml urine can be determined. The method has the distinct advantages of simplicity and speed over the colorimetric method currently in use.

This thesis reports the effect of applying static and ramped electric fields to quasi-bound Rydberg states of NO, with principal quantum number n = 25 - 32. The Rydberg states are excited by double resonance via the v'= 0,/V' = 0, and v' = 0,N' = 2 rovibrational states of the intermediate A2!' state of NO. Spectroscopic data is obtained by application of a static electric field ranging from 0 to 129 V cm"1, and ramped electric fields. In the presence of DC electric fields, the experimental Stark spectra presented in this thesis reveal a number of new interesting features, simulated using a matrix-diagonalisation approach. In this calculation, the adjustable parameters are the dipole transition moments from the various angular momentum components of the / -state, A, (/), for which just one set is used to obtain the qualitative agreement with the experimental spectra via two different rotational states of the / -state. The first detailed investigations of the selective field ionisation (SFI) of Rydberg states in a molecule are presented. The competition between electron-nuclear coupling and electron-field coupling is investigated and it is shown that the slew rate of the applied electric field can be exploited to control the rotational quantum state composition of field-ionised molecules.