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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.

Acid and basic dyes and food colours have been determined by electroanalytical techniques, i.e., amperometric titration, potentiometry using ion selective electrodes developed here, and differential pulse polarography. Several procedures for the determination of the food colours Sunset Yellow FCF and Tartrazine in sparkling orangeade, Green S and Tartrazine in sparkling limeade, Amaranth and Green S in blackcurrant health drink, and Chocolate Brown HT, Green S and Tartrazine in sparkling dandelion & burdock have been developed by differential pulse polarography in Britton-Robinson buffer. Tetraphenylphosphonium chloride removes the large polarographic maximum obtained with Tartrazine at pH values greater than 4 and causes the peak potential of the colour to be shifted towards more negative potentials. The addition of tetramethylammonium chloride improves the polarographic baseline for the peaks of colours by suppressing polarographic maxima. The food colours in each drink could be simultaneously determined by the control of pH in addition to the use of tetraphenylphosphonium chloride. PVC and liquid state ion-selective electrodes have been developed for the determination of acid and basic dyes. The electrodes are based on basic dye 12-tungstosilicate, basic dye tetraphenylborate, tetraphenylphosphonium 12-tungstosilicate, quinoline phosphomolybdate and CI Basic Orange 30:1-Reineckate. PVC electrodes based on Crystal Violet tetraphenylborate and tetraphenylphosphonium 12-tungstosilicate have produced satisfactory results for the potentiometric titration of several acid dyes with Crystal Violet and basic dyes with sodium tetraphenylborate. The response of the electrodes was sufficiently fast that the electrodes could be used in connection with an automatic titrator. In general, the slope factor of these PVC electrodes was Nernstian, but it gradually decreased with time. Liquid state electrodes using a natural rubber membrane containing Crystal Violet 12-tungstosilicate or Crystal Violet tetraphenylborate as active material dissolved in o-dichlorobenzene have also been applied successfully to the potentiometric titration of dyes. The life of these electrodes is relatively long because of their easy regeneration. Amperometric titration employing differential pulse polarography showed a promising applicability for the determination of dyes. The end points for the titration curves of acid dyes with a standard Crystal Violet solution and basic dyes with a sodium tetraphenylborate solution were easily determined by a simple graphical method. The high solubility of the precipitate formed causes the curves to be rounded and also the end point to be reached late.

The electrochemistry of lead and porous lead electrodes has been examined using the techniques of linear sweep voltammetry, potential step and alternating current impedance at static and rotating disG electrodes. Investigations were made using sulphuric acid solutions at ambient and low temperatures. The behaviour of porous electrodes containing additives conventionally used to improve lead-acid battery redox processes were studied. Complementary data has been obtained by Scanning Electron Microscopy and galvanostatic cycling experiments. The solution reaction at the porous electrode of typical commercial thickness, controlled by factors affecting the diffusion layer in a direction away from the porous fsce, was found to be insignificant in comparison with resctions occurring within the porous matrix. The thickness of PbS04 films developed on the electrode is potentialdependent, with thicker films st lower potentials. The development of PbS04 on the solid lesd electrode is controlled by nucleation and growth processes. At low overpotentials the process is three-dimensional but becomes two-dimensional at higher overpotentials. The behaviour of the porous electrode can be interpreted in terms of well-established porous electrode theory, assuming the same crystallisation processes are observed in the qaae of solid electrodes. On reduction at both solid and· porous lead sulphate electrodes, the electrode process has a finite depth of penetration into the electrode. The kinetics of the formation of metallic lead from lead sulphate on both types of electrodes appear to be by instantaneous nucleation and two-dimensional growth, with subsequent current limitations owing to overlap of growing lead and PbS04 depletion. The current limitation processes are complex; the subsequent current decay rate varies with the porosity of the electrode. Ambient temperature investigations of the additives used in the commercial lead electrode demonstrated that lignosulphonate facilitated the nucleation of lead on recharge, and effected a progressive increase in surface area/porosity of the electrode. These effects promoted an increased utilisation of-,tbe electrode active material on discharge. BaS04 was found to provide nucleation centres for PbS04 formation. The low-temperature electrochemistry of solid and porous lead has been investigated and the effects of additives are discussed.

Diabetes is one of the leading causes of death and disability in the world. Even though insulin was discovered in 1920, an intense research on diabetes has been conducted during the last five decades and this is because of the market size. The huge demand is creating the need for the development of new approaches. This project involved the research aimed at better understanding and improvements in performance of glucose biosensors. In general, high surface area electrodes are desired as the high surface area provides more active sites for electrochemical reactions, and hence higher kinetic rate capability. Therefore, the determination of the active electrochemical surface area of the electrode is very important. A study has been conducted to determine the real electrochemical surface area of the Pelikan screen printed electrodes (SPEs) and a method has been optimised and established by Pelikan for the evaluation of their SPEs. Another very important issue that most of the current blood glucose monitoring tests are facing is the haematocrit effect, since the haematocrit differences observed in the blood samples can significantly affect glucose measurements. Therefore a study has been conducted in order to observe the absorption of the blood samples into the working electrode paste according to the haematocrit level. The second part of the study included the characterisation of the novel conjugated polymer made of N-(N, N’ diethyldicarbamoyl ethyl amido ethyl) aniline (NDDEAEA), the optimization of the conditions for the electrochemical polymerization, their application in grafting and finally the development of NDDEAEA based glucose biosensor. The new conducting polymer, acted as a matrix for the biosensor fabrication in this study, possesses macroiniferter properties and is capable of initiation free radical initiated addition polymerisation after formation of the polyaniline (PANI) material while preserving or even enhancing some of the PANI’s electrochemical properties. This material can potentially be used in the construction of novel Pelikan electrodes with enhanced integration functionalities, e.g. grafting non adhesive polymer coatings to assure that the poor performance in sensors as a result of impact of blood components can be mitigated. The final study included the development and optimisation of the reaction conditions for grafting a hyperbranched polymer onto the surface of the multi walled carbon nanotubes (MWCNT), using the A3 and B2 approach (described below). The aim of this work was achieving further increase in the sensitivity of Pelikan sensors.

This thesis describes a novel fabrication procedure for microelectrodes to be used with the scanning electrochemical microscope (SECM), the characterisation of a variety of novel impedance based immunosensors, and the characterisation of a novel oligonucleotide biosensor. The thesis firstly describes the development of a protocol for the fabrication of reproducible microelectrodes characterised to identify suitability in use with the SECM. The thesis then describes the use of SECM in feedback mode to interrogate a variety of antibody-polyelectrolyte films determining whether the changes observed by impedance were detectable by SECM. A screen printed carbon ink surface was patterned with an array of biotinylated polyethyleneimine (PEI) which was exposed to Neutravidin and then the biotinylated antibody of interest. Using ferrocenecarboxylic acid as the redox couple, the array was interrogated by SECM, scanning before and following exposure to a series of concentrations of the complementary antigen and a non-complementary antigen. Upon the exposure of the PEI/Neutravidin/biotinylated antibody array to the antigen, the feedback current over the functionalised region was observed to change. The change observed increased as the concentration of the antigen exposed to the array was increased showing linear correlation. On exposure of the array to a non-complementary antigen, only a small change in the feedback current was observed. NSE, PSA, Ciprofloxacin and NTx were all investigated with limits of detection of 0.5 pg ml-1, 1 pg ml-1, 0.1 ng ml-1 and 1 nM respectively. Finally using a similar method as employed above, SECM was utilised in the detection of binding events of short oligonucleotides. Once again scans were conducted before and after exposure to both complementary and non-complementary oligonucleotide sequences and by subtraction absolute changes in feedback current were determined. On exposure to the complementary oligonucleotide sequence a change in feedback was observed when the array was exposed to the non-complementary oligonucleotide sequence, as with the antibody/antigen array, only a small change in the feedback current was observed.

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