Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 158-167).

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Ph.D. / This study explored the possible application of a relatively new electrode called exfoliated graphite electrode (EG electrode) in the electroanalysis of organic and inorganic water pollutants. This study also explored the applicability of this electrode in the removal of heavy metal pollutants in water. The EG material was successfully prepared by intercalating bisulphate ions into graphite flakes (>300 μm) followed by thermal shock at 800°C to obtain an exfoliated graphite. After compressing the EG at high pressure, the obtained circular sheets were used to fabricate electrodes. The electrochemical profiles of EG electrode and glassy carbon electrodes (GCE) were recorded and compared using cyclic voltammetryand square wave voltammetry in the presence of various supporting electrolytes and [Fe(CN)6]3-/4-, [Ru(NH3)6]2+/3+, ferrocene redox probes. In the supporting electrolytes (KCl, H2SO4, NaOH, tetrabutylammoniumtetraflouroborate, phosphate buffers), the potential windows of EG were found, in some cases, to be about 300 mV larger than that of GCE. The diffusion coefficients (cm2s-1) of the redox probes were calculated to be 3.638 x 10-6, 1.213 x 10-6 and 4.411 x 10-6 for [Fe(CN)6]3-/4-, [Ru(NH3)6]2+/3+ and ferrocene, respectively. These values are comparable to those obtained from GCE. Furthermore, EG was modified with various nanomaterials such as poly (propylene imine) dendrimer (PPI), gold nanoparticles, silver nanoparticles, dendrimer–gold nanoparticles composite, cobalt oxide and bismuth. The morphologies of the modified electrodes were studied using scanning electron microscopy and their electrochemical reactivities in the three redox probes were investigated. The current and the reversibility of redox probes were enhanced in the presence of modifiers in different degrees with dendrimer and gold nanoparticles having a favourable edge. The electrochemical determination of o-nitrophenol by square wave voltammetry using a nanocomposite of generation 2 poly(propyleneimine) dendrimer and gold nanoparticles modified GCEand EG electrode were compared. A characteristic reduction peak between -600 mV and -700 mV for o-nitrophenol was observed with enhanced current on both GCE and EG modified electrodes.

Cette thèse réalisée dans le cadre des projets PIE CNRS AMELI-0Pt et AMEPlas et ANR AMADEUS a regroupé plusieurs entités autour de la thématique des piles à combustible : Dreux Agglomération puis l’Agence Innovation Made In Dreux (MID), le GREMI, le LACCO et initialement l’industriel MHS Equipment. L’objectif de ce travail est l’élaboration par voie plasma et l’optimisation d’électrodes de piles à combustible de type PEMFC et SAMFC dans le but d’obtenir de bonnes performances avec des charges de platine ultra faibles ou sans platine. Le projet a été organisé en quatre étapes : l’étude de la croissance simultanée de platine et de carbone co-pulvérisés par plasma, la dispersion optimale de quantités ultra faibles de catalyseur, le remplacement du platine par un alliage bimétallique à base de palladium, et le dépôt direct du catalyseur sur la membrane par plasma. En utilisant un faisceau synchrotron de rayons X (Synchrotron SOLEIL), en collaboration avec le CRMD, l’étude GISAXS des couches minces Pt-C co-pulvérisés a révélé l’organisation particulière du platine dans ce type de nanostructure. Ces couches minces Pt-C offrent d’excellentes performances (20 kW.gPt-1) avec des charges de platine ultra faibles. Des électrodes PdPt (5 %at Pt) faiblement chargées permettent d’atteindre de bonnes performances en PEMFC quasiment sans platine (12,5 kW.gPd-1 et 250 kW.gPt-1). L’étude de l’activité de catalyseurs PdAu vis-à-vis de l’oxydation du glycérol a révélé l’origine des effets synergiques du palladium et de l’or en milieu alcalin. Le dépôt plasma direct de platine associé ou non au dépôt de carbone sur membrane a été optimisé. Les performances obtenues avec des CCM (Catalyst Coated Membrane) plasma démontrent l’intérêt de ce type d’architecture. / This research work has been achieved in the context of the PIE CNRS AMELI-0Pt and AMEPlas and ANR AMADEUS projects and has gathered several entities around the Fuel Cell research: Dreux Agglomération and Agence Innovation Made In Dreux (MID), the French national research laboratories GREMI and LACCO and initially the company MHS Equipment. The project aims at developing and optimising fuel cell electrodes (anode and cathode) for PEMFC (Proton Exchange Membrane Fuel Cell) and SAMFC (Solide Alkaline Membrane Fuel Cell) entirely by plasma in order to reach effective performances with ultra low platinum loadings or none at all. The project was divided into four stages: the study of the simultaneous growth of platinum and carbon co-sputtered by plasma, the optimum dispersion of a very small amount of catalysts, the replacement of platinum by a palladium based bimetallic alloy, and the direct deposition of the catalyst on the polymer membrane by plasma sputtering. By using an X-ray synchrotron beam light source (SOLEIL Synchrotron), in collaboration with the CRMD, the GISAXS study of co-sputtered Pt-C thin films has revealed the particular organisation of platinum inside this type of nanostructure. These Pt-C thin films offer excellent performances (20 kW.cm-2) with ultra low platinum amounts. Low loaded PdPt (5 %at Pt) electrodes offered good performances almost without platinum (12,5 kW.gPd-1 et 250 kW.gPt-1). The study of the activity of PdAu catalysts (plasma sputtered) on the glycerol electro-oxidation revealed the origin of the synergistic effects of palladium and gold in an alkaline medium. The direct plasma deposition of platinum associated or not with carbon deposition on membrane has been optimised. The performances of the plasma prepared CCM (Catalyst Coated Membrane) demonstrate the potential of this type of architecture.

As an efficient means of energy storage, rechargeable batteries, especially the lithium-ion batteries (LIBs) have been a vital component in solving the upcoming energy crisis and environmental problems. Recently, the development of electric vehicle market puts new requirement on the next generation LIBs, including superior energy density, safety and cycling stability, etc. Compared with experimental investigation, Physics-based models provide a surrogate method to not only tackle the underlying physics of the complex battery system, but also optimize the design of battery systems. In this thesis, I will show how I use the physics-based continuum model and cooperate with some experimental methods to understand the lithium transport phenomena inside the multiscale battery electrode systems, based on which the models are then applied to guide the experimental optimization of battery electrode design and to quantitively understand the degradation of high-performance electrodes. The thesis is divided into three parts. First part (Chapter 2) presents a systematical model selection study on the multiscale LiNi₀.₃₃Mn₀.₃₃Co₀.₃₃O₂ (NMC₁₁₁) electrode. Discharge and voltage relaxation curves, interrogated with theory, are used to distinguish between lithium transport impedance that arise on the scale of the active crystal and on the scale of agglomerates (secondary particles) comprised of nanoscale crystals. Model-selection algorithms are applied to determine that the agglomerate scale transport is dominant in the NMC₁₁₁ electrode studied here. This study not only discovers the dominant length scale for lithium transport, but also provide a validated model (the agglomerate model) for later study. The second part (Chapter 3 & 4) talks about understanding & optimization of ion transport in porous electrodes. In Chapter 3, multi-scale physics-based models for different active material systems, which have been parameterized and validated with discharge experiments, are optimized by varying porosity and mass loading to achieve maximum volumetric energy density. The optimization results show that with a re-scaling of the current rate, the optimal results follow a general design rule that is captured in a convenient correlation. Chapter 4 extends the model to simulate the performance of advanced electrode architectures utilizing aligned channels, by quantifying the impact of aligned channel electrode structures on cell rate capability. Then the optimization algorithm in Chapter 3 is applied to these aligned-channel electrodes. The final part (Chapter 5) shows how I use the physics-based model to quantitatively analyze the battery degradation. The validated model is applied to cycling data to obtain parameter estimates indicative of degradation modes. It’s found that growth rates of interfacial impedance and active material loss are greater at 4.5 V, as might be expected. However, when charged to 4.5V, degradation rates are lower at a cycling C-rate of 1.0 h⁻¹ than at 0.5 h⁻¹. Once performance changes are quantified, we use further simulation to evaluate the contribution of individual degradation modes to fade of cell performance metric such as capacity, power density, and energy density.

Thesis (Ph.D. (Physics)) -- University of Limpopo, 2020 / This work presents a computational modelling workflow that uniquely combines several techniques, proposed as a means for studying and designing high-energy-density electrodes for the next-generation of rechargeable batteries within the era of the fourth industrial revolution (4IR). The Self-Consistent Charge Density Functional-based Tight Binding (SCC-DFTB) parameterisation scheme for the Li-Si and Na-Si systems is presented. By using the Li-Si system, a procedure for developing the Slater-Koster based potentials is shown. Using lessons learned from the Li-Si framework, the parameterisation of the Na-Si is reported. The Li-Si SCC-DFTB parameter set has been developed to handle environments that consist of Si-Si, Li-Si and Li-Li interactions; and the Na-Si SCC DFTB parameter set is developed for Na-Na, Na-Si, and Si-Si interactions. Validations and applications of the developed sets are illustrated and discussed. By calculating equilibrium lattice constants, the Li-Si set is shown to be compatible with various phases in the crystalline Li-Si system. The results were generally within a margin of less than 8% difference, with some values such as that of the cubic Li22Si5 being in agreement with experiments to within 1%. The volume expansion of Si as a function of Li insertion was successfully modelled via the Li-Si SCC-DFTB parameter set. It was shown that Si gradually expands in volume from 53.6% for the LiSi phase composed of 50 atm % Li, to 261.57% for Li15Si4 with 78.95 atm % Li, and eventually shoots over 300% for the Li22Si5 phase with the expansion at 316.45%, which agrees with experiments. Furthermore, the ability of the Li-Si SCC-DFTB parameter set to model the mechanical properties of Si is evaluated by calculating the mechanical properties of pristine cubic Si. The parameter set was able to produce the mechanical properties of Si, which agree with experiments to within 6%. The SCC-DFTB parameter set was then used to model the volume expansion of amorphous silicon (a-Si) as a result of lithiation within concentrations ranging from 33 – 50 atm % Li. Consistent with experiments, the a-Si was found to marginally expand in a linear form with increase in Li content. a-Si was observed to exhibit a lower expansion compared to c-Si. Additionally, the structural stability of the amorphous Li-Si alloys was examined, and observations agree with experiments.vi The Na-Si SCC-DFTB parameter set produced equilibrium lattice parameters that agree with experiments to within 4% for reference structures, and the transferability was tested on three Na-Si clathrate compounds (i.e. the Pm-3n Na8Si46, the Cmcm NaSi6 and Fd-3m Na24Si136). By employing the approach used when lithiating Si, the sodiation of crystalline silicon (c-Si) was modelled. It was predicted that c-Si expands by over 400% at 77 atm% Na and shoots above 500% for concentrations exceeding 80 atm% of Na. By comparing how c-Si expands as a result of lithiation to the expansion consequent to sodiation for concentrations ranging from 66.6 – 81.4 atm%, c-Si is shown to be unsuitable for Na-ion batteries. As a test, the ability of the developed Na-Si SCC DFTB parameter set to handle large and complex geometries was shown by modelling the expansion of a-Si at 33 atm% Na. It was deduced that a-Si would be more preferable for Na-ion batteries since at 33 atm% Na, a-Si expanded a lot less than when c-Si was used. Using the Li-Si and the Na-Si SCC-DFTB parameter sets, it was noted that amorphisation appears to lower the magnitude by which Si expands, therefore agreeing with experiments in that amorphous structures are reported to exhibit a buffering effect towards volume expansion. The material space for the Li-Si alloy system is explored through crystal structure predictions conducted via a machine learning powered cluster expansion (CE). Using the FCC and BCC – based parent lattice in the grid search, 12 thermodynamically stable Li-Si alloys were predicted by the genetic algorithm. Viz. the trigonal Li4Si (R-3m), tetragonal Li4Si (I4/m), tetragonal Li3Si (I4/mmm), cubic Li3Si (Fm-3m), monoclinic Li2Si3 (C2/m), trigonal Li2Si (P-3m1), tetragonal LiSi (P4/mmm), trigonal LiSi2 (P-2m1), monoclinic LiSi3 (P2/m), cubic LiSi3 (Pm-3m), tetragonal LiSi4 (I4/m) and monoclinic LiSi4 (C2/m). The structural stabilities of the predicted Li-Si alloys are further studied. With focus on pressure, the thermodynamic conditions under which the Li-rich phase, Li4Si (R 3m), would be stable are tested. Li4Si (R-3m) was subjected to pressures during geometry optimization and found to globally maintain its structural stability within the range 0 – 25GPa. Hence, Li4Si was predicted to be a low pressure phase. In studying the PDOS, the Li4Si (I4/m) was noted to be more stable around 40GPa and vii 45GPa, which is consistent with the prediction made from other works, wherein intelligence-based techniques were used. A test for exploring the Na-Si material space was done using insights acquired from the Li-Si framework. Three thermodynamically stable Na-Si (i.e. the I4/mmm Na3Si, P4/nmm NaSi and Immm NaSi2) were predicted. Using the Na-Si SCC-DFTB parameter set, a correlation of the total DOS in the vicinity of the Fermi level (Ef) with the structural stability of the three Na-Si alloys is done. NaSi (P4/nmm) was shown to be unstable at 0GPa, NaSi2 (Immm) is found to be stable, and the Na-rich Na3Si exhibited metastability. The stability of Na3Si was seen to improve when external pressure ranging from 2.5 – 25GPa was applied; hence, suggesting Na3Si (I4/mmm) to be a high-pressure phase. Furthermore, expanding on the groundwork laid from the Li-Si and Na-Si CE, the Mg-Si system was tested to illustrate that the approach can be used to rapidly screen for new materials. The ground-state crystal structure search predicted 4 thermodynamically stable Mg-Si alloys. Viz. Mg3Si (Pm-3m), MgSi (P4/mmm), MgSi2 (Immm) and MgSi3 (Pmmm). Lastly, to highlight the power of combining various computational techniques to advance material discovery and design, a framework linking SCC-DFTB and CE is illustrated. Candidate electrode materials with nano-architectural features were simulated by designing nanospheres comprised of more than 500 atoms, using the predicted Li-Si and Na-Si crystal structures. The stability of the nanospheres was examined using SCC-DFTB parameters developed herein. The workflow presented in this work paves the way for rapid material discovery, which is sought for in the era of the fourth industrial revolution. / National Cyber Infrastructure System: Center for High-Performance Computing (NICIS-CHPC) for computing resources, the National Research Foundation (NRF) and the University of Limpopo

This research reports on the fabrication and characterization of integrated dual nanometer-sized electrodes. The electrodes are made of closely spaced nanometer-sized platinum and gold achieved by inserting and pulling platinum wire in cylindrical glass pipette plated with gold. Cyclic voltammetry has been used to characterize the electrodes. Our results show that both electrodes can work individually and can accomplish generation/collection experiments. Factors that may affect the performance of the electrodes as well as formation mechanism of the gold film by electroless plating are discussed.

Context: Electrodes play an important role in interfacing tissue with electrical stimulation devices. Manufacturers recommend that adhesive metallic mesh cloth electrodes be used no more than 10 times before they are discarded, however, clinically the electrodes are often used up to 30 times. Another concern is sanitation. When electrodes are used on different patients, there is a chance for cross-contamination and bacterial growth on the electrode. Objective: To compare amplitudes of perceived sensation, motor twitch and force produced at specific amplitudes using single-use electrodes that run no risk of cross-contamination, and multiple-use electrodes. Design: Mixed model ANOVA with the subject blocked. Setting: Therapeutic modalities research laboratory. Patients or Other Participants: 20 subjects comprised of 7 males (age 24.7 yrs ± 2.3 yrs, skin fold thickness 5.9 mm ± 2.4 mm) and 13 females (age 21.5 yrs ± 2.3 yrs, skin fold thickness 10.7 mm ± 4.1 mm) recruited by volunteer sample mainly from athletic and athletic training populations. They drew random numbers to determine which group they were assigned to. Interventions: Each subject had electrodes placed on their wrist extensors muscles. Measures were recorded of what intensity it took to achieve perceived sensation, motor twitch, and force produced at a specific intensity. To determine decay, multiple use electrodes were tested initially and on the 10th use. After the multiple use electrodes were tested initially, they were leached out. After eight uses, pretest procedures were repeated (10th use electrode) as the final trial on the subjects. Single use electrodes were tested one time. Main Outcome Measures: The dependent variables were sensation, motor twitch and force production. The experiment was a repeated measures study, using mixed models ANOVA with subjects blocked. Alpha was set at p<0.05. Data was analyzed using a SAS proc mixed 9.1. Results: There was no statistical difference between the measures taken during the initial trial and final trial of the multiple use electrodes for muscle twitch (FMUI MUF muscle twitch= 107.3, p= 0.09) and force production (FMUI MUF force production=28.7, p= 0.11). There was a significant difference between the single use and the multiple use electrodes for the initial and final trial. Average values in mA for perceived sensory were: single use 9.73, multiple use initial 16.70 , multiple use final 21.03; observed muscle twitch: single use 15.87, multiple use initial 29.16, multiple use final 31.78; and force produced: single use 22.8 Newtons, multiple use initial 10.0 Newtons, multiple use final 5.0 Newtons. Conclusion: Single-use electrodes produce more conductive power with fewer milliamps compared to multiple-use electrodes. Single use electrodes are just as, or more efficient as the multiple use electrodes and have the added advantage of eliminating the possibility of cross-contamination of bacteria from patient to patient.

The effect of ultrasonic vibration on the anodic oxidation of silver foil in KOH was studied. An increase in charging capacity of approximately 20% was found to be the result of cavitation erosion. Silver wire was exposed to tension and torsion during oxidation but no change in charge acceptance was caused by these stresses. The oxide growth rate on silver foil electrodes was compared to rate equations that have been proposed for other metals. Uhlig's equations for the growth of semiconductor oxides was found to describe most of the data. The data did not fit other rate equations. Determination of the location of radioactive Ag110 in the oxide layer indicated that silver oxide grows by direct transport of the silver ion through the oxide, if a uniform oxide thickness is assumed. However, the dissolution-precipitation-model of oxide growth describes the data better and allows for the non-uniform oxide thickness which is characteristic of silver.

No description available.