>Magister Scientiae - MSc / This study focused on binary PtRu and PtSn electrocatalyst, synthesized using the polyol approach and supported on MWCNTs, TiO2 and MoO2 materials, after synthesis part of the resultant electrocatalyst was heat treated to improve alloying of the secondary metal to the primary platinum metal catalyst and also to enhance the stable distribution and uniform dispersion of the nanoparticles on the support material. Physical characterization of the supported catalyst was done using XRD, HRTEM, HRSEM and EDS for elemental analysis. For electrochemical characterization RDE-CV and RDE-LSV were employed. The homeprepared electro-catalysts were then compared to the Pt/C, PtRu/C and PtSn/C commercial electro-catalysts accordingly. XRD confirmed that the binary electro-catalyst for both the commercial and home-prepared display characteristic patterns similar to that of the standard Pt/C electro-catalyst, an indication that all catalysts have prevailed the Pt face-centred-cubic (fcc) crystal structure. Particle size and size distribution examined using HRTEM showed that Pt/C and PtSn/C was uniformly dispersed on the carbon support and that all electrocatalyst supported on MWCNTs showed small particle size known to enhance the activity of the catalyst. However, after heattreatment the particle size increased for all prepared supported electrocatalyst as was expected from literature. SEM micrographs showed that all electrocatalyst were decorated on the support material with agglomerates on some parts of the samples, agglomeration was more pronounced for catalysts supported on MoO2. The metal loading for the home- prepared electrocatalyst was examined using EDS and it was observed to be closer to that of the commercial catalysts. It was also observed that there were changes on the loading of the electrocatalysts after they were subjected to heat treatment and depending on the support material the metal loading of the catalyst was either more or less. This study found PtSn/C to be the most active commercial catalyst for methanol tolerant and oxygen reduction. For the home-prepared electrocatalyst supported on MWCNTs, PtSn/MWCNT-HT was found to be the most active catalyst while for catalyst supported on metal oxides PtSn/MoO2 was found to be more active than the rest of the Pt-based electro catalyst supported on metal oxides. Results showed that PtSn is more active than PtRu and could function as a methanol tolerant oxygen reduction electro-catalyst for the cathode of a direct methanol fuel cell. Furthermore, in terms of durability, the home-prepared electrocatalyst proved to be more durable than the commercial electro-catalyst supported on carbon black, with catalyst supported on MWCNTs showing more stability than other supported electro-catalyst. Multi-walled carbon nanotubes have therefore proven in this study to be the best supporting material for electro-catalyst as catalyst supported on them showed to be more stable than commercial catalyst supported on carbon black.

Philosophiae Doctor - PhD / High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC) have received renewed interest in recent years due to its inherent advantages associated with the limitations faced by Low Temperature Polymer Electrolyte Membrane Fuel Cells (LT-PEMFC). The high Pt loadings required for PEMFCs have significantly hindered its commercialisation. Electrophoretic Deposition (EPD) is a promising route to reduce the noble metal loading. EPD is a method in which charged colloidal particles are deposited onto a target substrate under the force of an externally applied electric field. To effectively study the EPD method, the methodology of this study was divided into two parts: (i) the EPD method was studied via known empirical methods to fabricate, test and characterise MEAs suitable for HT-PEMFCs. The feasibility of the EPD method was determined by comparing the performance of the fabricated EPD MEAs to MEAs fabricated via spraying methods, and (ii) due to the promising results obtained in part (i) of the methodology, a theoretical model was developed to obtain a deep understanding about nature of the interactions between the Pt/C particles in a colloidal suspension. The theoretical model will serve as a foundation for future studies. In part (i) of the methodology, the Pt/C particles were studied in organic solutions (i.e. Isopropyl Alcohol, IPA) via the Zetasizer Nano ZS instrument under various salt (NaCl) concentrations and pH conditions while introducing polymeric surfactants, i.e. Nafion® ionomer and Polytetrafluoroethylene (PTFE) to the suspension. The optimum catalyst suspensions were selected to fabricate GDEs via the EPD method. Physical characterisations revealed that the EPD GDEs exhibited cracked morphology with high porosity. Electrochemical characterisations revealed that the EPD MEA showed significantly better performance (i.e. 73% higher peak power) compared to the hand vi sprayed MEA due to lower charge transfer and mass transport resistance at high current densities. Compared to the ultrasonically sprayed MEA, the EPD MEA exhibited a peak power increase of ~12% at a slightly lower Pt loading (i.e. ~4 wt%). A comparative study between the Nafion® ionomer and PTFE in the CLs of two EPD MEAs revealed superior performance for the EPD MEA with the PTFE in the CLs. Part (ii) of the methodology deals with the electrical interfacial properties of the aqueous Pt/C suspension. The study consists of two sets of measurements (i.e. electrophoretic and coagulation dynamic studies) conducted for different electrolyte compositions. A theoretical background on determining the interfacial potential and charge from electrophoretic and coagulation dynamic measurements are provided. Detailed statements of the Standard Electrokinetic and Derjaguin, Landau, Vervey and Overbeek Models are given in the forms that are capable of addressing electrophoresis and the interaction of particles for an arbitrary ratio of the particle to Debye radius, interfacial potential and electrolyte composition. The obtained experimental data were processed by using numerical algorithms based on the formulated models for obtaining the interfacial potential and charge. While analysing the dependencies of interfacial potential and charge on the electrolyte compositions charge, conclusions were made regarding the mechanisms of charge formation. It was established that the behaviour of system stability is in qualitative agreement with the results computed from the electrophoretic data. The verification of quantitative applicability of the employed models was conducted by calculating the Hamaker constant from the experimental data. It was proposed how to explain the observed variations of the predicted Hamaker constant and its unusually high value.

This research explores the use of insulated electrodes to determine electrical impedance distributions within soil cores. It is used to infer the effect of roots on soil moisture which, in turn, can provide knowledge relating to crop breeding programmes. These programmes are becoming increasingly important in order to address challenges posed by global population growth and climate change. Direct contact electrical impedance measurements in soil are frequently used but these are vulnerable to electrochemical effects and corrosion. Insulated electrodes are used in the present work to overcome these difficulties and a modified electrode model has been proposed. Measurements require the acquisition of spectroscopic complex impedance and extraction of the real impedance to infer soil moisture content. Calculated and simulated impedance, from the analytical solution and an FEM model respectively, were compared to measurements performed within a parallel-plate test cell containing saline solutions. The effects of moisture, compaction and temperature on soil impedance measurements have been explored. Finally, two growth trials using maize plants and control vessels were performed to create 2D images of impedance distributions, from which moisture placement was inferred. Results show that for saline electrolytes, the insulated electrode method was capable of estimating the impedance of tap water to within 10% of calibrated laboratory equipment. For soil based measurements, the variation of moisture content from 5-30% resulted in a 1000-fold decrease in impedance. The change was most significant in drier soils. For compaction based testing, at 5% moisture content soil impedance decreased by approximately 40%, compared to only 20% in the wettest samples. Temperature testing revealed an impedance change of approximately 2%/ °C, in agreement with earlier reports. Plant growth trials revealed increases in electrical impedance due to soil drying from an initial value of 1-2kΩ when the soil was wetted to field capacity, to as much as 60kΩ when dry. Only small changes were evident in the control vessels. It was also found that areas exposed to potential evaporation, such as at the surface closest to the plant stem, suffered significant losses in moisture content, reaching as high as 15-20kΩ. This research utilises a measurement technique which has not previously been used to measure soil impedance to infer moisture content. The research also found that the scaling of a thin layer within an FEM model can significantly reduce computational demands, while retaining accuracy, and allow more complex FEM simulations to be performed on a less powerful computer.

Orientadores: Lauro Tatsuo Kubota, Graciliano de Oliveira Neto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-08T00:59:06Z (GMT). No. of bitstreams: 1 Ribeiro_PauloJoseFernandes_M.pdf: 3526765 bytes, checksum: d7527897c70e194a6207d1020f2ce8bc (MD5) Previous issue date: 2006 / Resumo: Nesse trabalho é apresentado o desenvolvimento de um eletrodo íon-seletivo para determinação de ibuprofeno, utilizando-se membrana do copolímero poli(etileno co-acetato de vinila) (EVA), tentando minimizar o uso de plastificantes. A membrana foi preparada diretamente sobre um suporte condutor constituído de uma mistura de resina epóxi, endurecedor e grafite. Na preparação da membrana foram estudadas diversas proporções de seus componentes, como concentração de par-iônico, influência do plastificante e quantidades de matriz polimérica. As melhores respostas foram obtidas com uma membrana composta de 115 mg do par-iônico aliquat-ibuprofeno, 170 mg de EVA e 150 mg do plastificante o-NPOE (orto-nitrofeniloctil-éter), não sendo possível eliminar o plastificante. Com o objetivo de otimizar as condições analíticas, foram feitos estudos da influência do pH, da natureza e concentração do tampão e de interferentes, além do tempo de reposta e de vida do eletrodo. As melhores respostas em estado estacionário foram obtidas em tampão Fosfato com concentração de 0,5 mol L a pH 7.0. Nestas condições foi verificado um bom desempenho do eletrodo na faixa de concentração de 2,93 10 a 10mol L, com limite de detecção de 8,7 10 mol L, sensibilidade de 127 mV década, tempo médio de resposta de 56 s e capacidade para aproximadamente 100 determinações. O eletrodo foi aplicado para determinação de ibuprofeno em amostras de medicamento obtendo bons resultados, sendo estes estatisticamente igual aos obtidos com o método de referência a um nível de 95% de confiança. / Abstract: In this work is presented the development of an ion-selective electrode for ibuprofen determination, using the poly(ethylene-co-vinyl-acetate) copolymer (EVA) membrane, trying to minimize the use of plasticizer. The membrane was prepared directly on a conducting support consisting of an epóxi resin, hardener and graphite mixture. In the preparation of the membrane several ratios of its components were investigated, such as concentration of ion-pair, influence of the plasticizer and polymeric matrix. The best performance was reached with a membrane composed with 115 mg of the ibuprofen-aliquat ion-pair, 170 mg of EVA and 150 mg of the o-NPOE (orto-nitrophenyloctyl-ether), being impossible to eliminate the plasticizer. Studies of the influence of pH, nature and concentration of the buffer and the interfering were carried out looking for the optimized conditions for the electrode performance like sensitivity, fast response and lifetime. The best response was obtained with Phosphate buffer in a concentration of 0,5 mol L at pH 7.0. In these conditions the electrode showed a good performance in the concentration range between 2,93 10 and 10 mol L, with a sensitivity of 127 mV/decade, a detection limit of 8,7 10 mol L, response time of 56 s and capacity for 100 determinations. The electrode was employed to determine ibuprofen in medicine samples obtaining good results, being statistically equal at 95% confidence level, when compared with the results obtained with the reference method for the same samples. / Mestrado / Quimica Analitica / Mestre em Química

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22794号 / エネ博第408号 / 新制||エネ||78(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー社会・環境科学専攻 / (主査)教授 石原 慶一, 准教授 奥村 英之, 教授 佐川 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Electropalatography (EPG) is a computer-based tracking system designed to provide real-time visual biofeedback of articulatory contacts occurring during speech production. Historically, EPG technology has proven functional within the treatment and assessment of speech disorders however, application of EPG technology to assist in second language learning has remained limited. The present thesis is part of a larger study examining the effectiveness of using EPG as an advanced instructional tool for assisting second language (L2) learners of German. Fricative productions ([ç], [x], /s/, and /∫/) within real words were gathered from 12 native English speakers enrolled in a second semester university level course to learn German. Speech productions from student participants were compared against native German speakers' productions collected in a previous study, using electrode mappings, percentages of regional contact, and center of gravity measures. These measures revealed different patterns of palatal contact between fricative sounds, between individual subjects, and cross-linguistically. Fricative sound mappings varied visually as speakers generally produced [ç] and [x] with significantly less palatal contact than when producing /s/ and /∫/. Variation across individual subjects was identified as some produced sounds with nearly no posterior palatal contact while others produced sounds asymmetrically or with decreased overall contact. Cross-linguistic differences were apparent as non-native German speakers frequently contacted greater numbers of electrodes with greater force, compared to the natives. It is anticipated that the information included in this thesis will provide insights into the role of EPG technology as an instructional tool for L2 learners.

The work deals with topic of bipolar electrodes of lead-acid accumulator. Theoretical part of the thesis presents of comtenporary knowledge of the topic as it is described in scientific literature. Experimental part deals with conductometric method that is used in corrosion rate measurement of experimental electrodes.

This Ph. D. thesis presents new methods for the determination of selected clinically relevant electrochemically active compounds. The first part deals with development of determination of tumour biomarkers homovanillic acid (HVA) and vanillylmandelic acid (VMA) in human urine with the use of hollow-fibre based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at cathodically pre-treated boron doped diamond electrode (BDDE). Optimum conditions for HF-LPME-DPV of HVA and VMA were as follows: butyl benzoate as supported liquid membrane formed on porous polypropylene hollow-fibre, 0.1 mol L−1 HCl as donor phase and 30 min extraction time. Optimum acceptor phases were 0.1 mol L−1 phosphate buffer of pH 6 with ionic strength set to 0.55 mol L−1 for HVAand 0.1 mol L−1 NaOH for VMA, respectively. HF-LPME-DPV concentration dependencies for HVA and VMAwere linear in the range from 0.4 to 100 µmol L−1 and 0.5 to 100 µmol L−1 . Limits of quantification (LOQ)/detection (LOD) were 1.2/0.4 µmol L−1 for HVA and 1.7/0.5 µmol L−1 for VMA, respectively. The applicability of the developed methods was verified by analysis of human urine. In the second part, voltammetric behaviour of heavy metal poisoning antidote 2,3- dimercapto-1-propane-sulfonic acid (DMPS) was investigated with the use...

Early and accessible diagnostics are important elements to reducing the negative side-effects of untreated disease. One key advancement in diagnostic monitoring is through the development of highly sensitive sensors that have the capability to detect lower concentrations, while still remaining accessible for point-of-care use. This dissertation characterizes electrochemical sensing platforms that are enhanced by convection and by 3D electrodes made from high surface area, vertically aligned carbon nanotubes (VACNTs). Free-standing VACNTs were patterned into microchannel arrays for flow-through amperometric sensing. Convective mass transfer enhancement was shown to improve sensor performance in amperometric sensing through the use of high surface area to fluid volume structures and concentration boundary layer confinement. Through-flow sensing of hydrogen peroxide produced drastically higher signals than stirred sensing, with over 90% of the hydrogen peroxide being oxidized as it passed through the channels. Non-enzymatic sensing of glucose was achieved by chemical reaction of glucose with methyl viologen to produce on average 3.4 electrons per glucose molecule, significantly higher than that obtained with enzymatic sensing with glucose oxidase. A scaled down sensor enabled detection from 200 μL of glucose by flow injection analysis with a limit of detection of 360 nM and a linear sensing range up to at least 150 μM glucose. Such sensing range offers the potential to measure glucose levels found in saliva. This work demonstrates the utility of high aspect ratio electrodes made of VACNTs. Convection and surface area are shown to enhance the sensitivity of flow-through VACNT amperometric sensors by effectively utilizing the available analyte to increase the measured current density. Advances in nanomaterials, combined with electrochemical impedance spectroscopy, have allowed impedimetric biosensors to have high sensitivity while remaining label-free, pushing towards enabling portable diagnosis at the point-of-care. Porous, 3D VACNT electrodes for impedance-based biosensing were fabricated with different electrode height, gap width, and configuration. Sensitivity was characterized by functionalizing the representative protein streptavidin onto VACNT electrodes for detection of biotin. Tall, closely-spaced VACNT interdigitated electrodes are shown to have the highest electroactive surface area (15x the 2D geometric area) and the highest sensitivity, allowing for a 1 ng/mL limit of detection. Aspect ratio and surface area are shown to be important factors in determining the sensitivity of 3D VACNT interdigitated electrodes for impedimetric sensing of biomolecules bound to electrode surfaces. Although this biosensing platform is shown with streptavidin and biotin, it could be extended to other proteins, antibodies, viruses, and bacteria.

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2021 / Recently, the use of electrochemical supercapacitors as energy storage devices has drawn great attention due to their high charge/discharge rate, long life span, high power and energy densities. However, the choice of electrode materials used is vital for the performance of supercapacitors. This study focused on the development of a low cost hybrid electrode based on reduced graphene oxide/metal organic framework composite (rGO/MOF) and a novel palladium (Pd) nanoparticles loaded on rGO/MOF termed Pd-rGO/MOF nanocomposite. The prepared nanocomposites were used for high performance electrochemical double layer capacitor-(EDLC) and battery-type supercapacitors known as supercabattery. The rGO material reported in this work was chemically derived through the oxidation reduction method using a hydrazine as a reducing agent. Furthermore, palladium nanoparticles were loaded on the rGO using the electroless plating method. The rGO/MOF and novel Pd-rGO/MOF nanocomposites were prepared using an impregnation method in dimethylformamide. The physical and morphological properties of the synthesised materials were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The XRD and FTIR analyses showed crystalline phases and vibrational bands for both parent materials, respectively. The TGA/DSC results showed enhancement of the thermal stability of the composite as compared to MOF material. The SEM/EDS and TEM/EDX confirmed the presence of octahedral structure of MOF in the rGO sheet like structure and elemental composition of the synthesised composite. The resultant of Pd-rGO/MOF nanocomposite showed a morphology in which a thin layer of rGO coating existed over MOF with unique bright spots indicating the presence of Pd nanoparticles. This observation agreed well with the structural properties revealed by both XRD and FTIR with the reduction of MOF intensities upon Pd-rGO loading as well as enhancement of thermal stability of the nanocomposites. The electrochemical properties of the prepared electrodes were determined using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). To evaluate the electrochemical performance of the prepared electrode materials, both two and three electrode cells were assembled. From the CV and GCD results, the nanocomposites demonstrated a battery-type behaviour and therefore asymmetric supercabattery cells were assembled using the composites as positive electrodes, and activated carbon as a negative electrode. The specific capacity of rGO/MOF in three electrode cell was found to be 459.0 C/g at a current density of 1.5 A/g in 3M potassium hydroxide. Furthermore, the asymmetric supercapacitor based on the rGO/MOF nanocomposite and activated carbon (AC) as a negative electrode exhibited a maximum energy density of 11.0 Wh/kg and the maximum power density of 640.45 W/kg. The loading of palladium nanoparticles on the nanocomposite was to improve the electrochemical active sites and the performance of the supercapacitor electrode. After incorporation of Pd nanoparticles, the specific capacitance in three electrode cell improved to 712 C/g at a higher current density of 2 A/g with the same electrolyte. The assembled supercabattery has shown improved maximum energy and energy density of 26.44 Wh/kg and 1599.99 W/kg, respectively. Based on these findings, the synthesised rGO/MOF and Pd-rGO/MOF nanocomposites are promising electrode materials for future supercabattery applications. / NRF (National Research Foundation) and SASOL foundation