The electrochemistry of planar and porous lead dioxide electrodes has been investigated using the techniques: linear sweep voltammetry, potentiostatic pulse experiments and Faradaic (a.c.) impedance studies. The first two techniques were digitally controlled and the data were acquired at high speed and could be easily retrieved after storage. A morphological examination on the electrodes was also carried out using scanning electron microscopy. The electrochemical behaviour of flat lead in sulphuric acid at concentrations in excess of 5 mol dm-3 has been studied. Various solid lead alloys in different sulphuric acid concentrations were investigated together with porous PbO2 on different lead alloy supports. It was found that the acid concentration had a marked effect on the electrochemistry of the electrodes. The current transients obtained from potentiostatic step experiments with the porous PbO2 electrodes were nearly all of a complex nature and some attempt was made to match the data with established mathematical relationships for electracrystallisation processes. The alloys used were of industrial importance and they were lead-antimonyp lead-tin-calcium and lead-tin-bismuth-calcium. Also various automotive positive pastes were employed to form the porous PbO2 structure. A.C. impedance studies were carried out on the porous PbO2 electrodes. An analogue was found which described the discharge process of Pb02.

The work undertaken involved the exploration of CO2 electroreduction systems, focussing heavily upon electrocatalysis utilising an array of electrochemical, spectroelectrochemical and spectroscopic techniques. The identification and characterisation of a relatively inexpensive and simple electrocatalyst for CO2 reduction was achieved, with the optimisation and development undertaken in such a manner that not just the electrocatalytic species, but also the entire electrochemical system was investigated, in order to determine and better understand the roles played by the various components. The complex of interest, Mo(CO)4bpy, represents the first molybdenum based molecular electrocatalyst reported to be active toward CO2 reduction, despite the prominence of Mo in enzymes with analogous function. The electrochemical characterisation of the complex in the both the presence and absence of CO2 was undertaken, yielding valuable information on the redox behaviour of the complex within the non-aqueous system in which it was employed and highlighting previously unreported features such as a third reduction and new reoxidation attributed to the reoxidation of a tricarbonyl anionic species. Non-aqueous solvents were chosen as they provide greater CO2 solubility than water with portions of the investigation undertaken in tetrahydrofuran, THF, then moving to the less widely used N-methylpyrrolidone, NMP. NMP is significantly less volatile than THF and has a large negative electrochemical window so is ideal for looking at reduction processes and, importantly, is also used as a commercial CO2 scrubbing solvent. Upon addition of CO2 to the Mo(CO)4bpy system there was an observable lowering of the overpotential by over 300 mV, and significant increase in CO2 associated current when compared to that for ‘direct’ CO2 reduction within the same system, at the reduction potential associated with the first reduction of the tetracarbonyl bipyridyl species. The confirmation of the anionic radical as the active species was attained through DFT calculation and EPR spectroelectrochemistry. Under inert gas the spectrum rapidly generated upon application of the first reduction potential is consistent with the expected response for the radical anionic [Mo(CO)4bpy] •−. When the system is saturated with CO2 this radical is no longer detectable. This supports the idea that the unpaired electron is transferred from the [Mo(CO)4bpy]•− to the CO2 molecule and also suggests that this transfer is rapid as no adduct is detectable via EPR even at reduced temperature (240 K). This is in keeping with the rate constants calculated from the voltammetric measurements made. The stability and activity toward CO2 reduction exhibited by Mo(CO)4bpy displayed a strong dependence on working electrode material, with gold proving optimal, indicative of adsorption being significant in the process. Optimisation of both the catalyst structure and the solvent and electrolyte system were also explored, as well as the (somewhat less directly related) comparison of various sources of diffusivity data.

No description available.

The oxygen pressure leaching of pyrite has been studied in sulfuric and perchloric acid using an oxygen-18 tracer technique. The results are consistent with an entirely electrochemical mechanism. The leaching potential of a pyrite pulp has been measured as 0.699V SHET*(110°C, 1M H2S04, 176 psi 02) and potentiostatic experiments at that potential have yielded the same reaction product ratios as observed in oxygen pressure leaching. The ratio of sulfate to elemental sulfur produced during pyrite leaching has been found to be a function of the leaching mixed potential. The yield of sulfate is increased with increasing potential until all the mineral sulfur is converted to the sulfate form at potentials above 1.0V. A mechanistic model of pyrite leaching has been advanced, which includes the electrochemical formation of a protective sulfur film as its basis. The theory has been supported by polarization studies in combination with Eh-pH diagrams. Chalcopyrite leaching has been studied using the same 0¹⁸ technique. Again the results are consistent with an electrochemical mechanism. The ratio of the sulfate to elemental sulfur in the reaction products has been observed to increase with higher oxygen pressures. The mixed potential of leaching is also increased at higher pressure indicating that the same type of mechanism observed in the pyrite work is operational for chalcopyrite. Molybdenite leaching has also been discussed in terms of the electrochemical model derived for pyrite with good results, and the mechanism therefore appears to have applications in many, if not most, sulfide systems. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The fundamental process that lies at the foundation of batteries, capacitors, and solar cells is the electron transfer process. This takes place at an interface or boundary in each device and is governed by its corresponding chemical reaction. Making these devices more efficient can help decrease our negative impact on the environment. Recent experiments in the field of Electrochemistry demonstrate that sound waves act as a catalyst for these electron transfer reactions. A model is developed using an Euler equation (conservation of momentum), conservation of mass equation, boundary motion equation, and surface tension equation. Chemically, it is clear that the catalytic phenomenon is derived from the sound waves and how they are affected by the top boundary. When combining these four equations we arrive at a boundary condition involving the top boundary only. We place this condition and the other contributing boundary and initial conditions on the wave equation to understand the interaction that occurs between the waves and the cell. We establish a self-adjoint operator and further use its inverse. Overall, using the Variational form and the Galerkin Method an approximation converges to the solution of the wave equation. With the help of MATLAB these eigenfunctions can be articulated as standing waves.

The focus of this work was to examine the direct plating of Cu on Ru diffusion barriers for use in interconnect technology and the substrate mediated growth of graphene on boron nitride for use in advanced electronic applications. The electrodeposition of Cu on Ru(0001) and polycrystalline substrates (with and without pretreatment in an iodine containing solution) has been studied by cyclic voltammetry (CV), current-time transient measurements (CTT), in situ electrochemical atomic force microscopy (EC-AFM), and X-ray photoelectron spectroscopy (XPS). The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. XPS measurements confirmed the presence and stability of adsorbed I on the Ru surface following pre-treatment in a KI/H2SO4 solution and following polarization to at least −200 mV vs. Ag/AgCl. CV data of samples pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD peak. The kinetics of the electrodeposited Cu films was investigated by CTT measurements and applied to theoretical models of nucleation. The data indicated that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. A novel method for epitaxial graphene growth directly on a dielectric substrate of systematically variable thickness was studied. Mono/multilayers of BN(111) were grown on Ru(0001) by atomic layer deposition (ALD), exhibiting a flat (non-nanomesh) R30(3x3) structure. BN(111) was used as a template for growth of graphene by chemical vapor deposition (CVD) of C2H4 at 1000 K. Characterization by LEED, Auger, STM/STS and Raman indicate the graphene is in registry with the BN substrate, and exhibits a HOPG-like 0 eV bandgap density-of-states (DOS).

Thesis advisor: Matthias M. Waegele / The properties of electrified interfaces, such as surface structure of metal catalyst, local pH, coverage of surface-adsorbed intermediates, interfacial electric field, and water structure, influence the activity and selectivity of electrocatalytic reactions. Because these interfacial properties often influence each other and undergo changes with applied potential, it is very challenging to identify the key characteristics of the interface that directly modulate electrocatalytic reactions. In this thesis, we demonstrate in-situ probing of electrochemical interfacial properties by employing surface-enhanced infrared (IR) absorption spectroscopy (SEIRAS) in conjunction with surface-adsorbed CO (COads) as a molecular probe of the Cu/aqueous electrolyte interface. This interface shows potential for the reduction of CO2 and CO to a wide variety of hydrocarbons. The CO and CO2 reduction reactions (CO/CO2RR) feature COads as an intermediate; therefore, this interface is conveniently probed by COads. In the first part if this thesis, we focus on investigating the dynamics of the surface morphology of the electrode during electrocatalysis. We found that the surface morphology of polycrystalline Cu undergoes reconstructions during CO/CO2RR. We determined that these reconstructions can be induced by COads and the local pH. As a result of the surface reconstructions, new specific surface sites form that can effect catalytic activity. For example, we detected an electrochemically inert COads population that appears as a result of reconstruction processes. Further, to form a rigorous connection between the product formation and the atomic-level surface morphology of rough polycrystalline Cu electrodes, we combined SEIRAS with differential electrochemical mass-spectrometry (DEMS). We established the potential-dependence of the line shape of the C≡O stretch band as an indicator of the atomic-level surface morphology. The last part of the thesis focuses on the determination of properties of the electrochemical double layer. Specifically, we elucidated the effects of cation identity on the electrochemical double layer. By evaluating the C≡O stretch frequency in the presence of alkali metal cations (Li+, K+, and Cs+), we determined that the promotion of the CO reduction reaction is associated with a cation-dependent interfacial field. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Jeffery A. Byers / This dissertation discusses the development of an electrochemically switchable system for copolymer synthesis as well as surface modifications. In Chapter one, the usage of electrochemistry to control polymerization reactivities is introduced. In Chapter two, an electrochemically redox switchable polymerization for lactide and cyclohexene oxide will be presented. In Chapter three, a surface modification method based on the electrochemically redox switchable catalysis is discussed. The surface-anchored catalyst responds to applied electrochemical potentials towards two different ring-opening polymerizations to generate binary polymer patterns in one step. The method represents a facile way to generate polymer coatings on surfaces. In Chapter four, a discussion on the detailed kinetic analysis of an iron-catalyzed epoxide polymerization will be presented, the study allows us to unveil the importance of entropy-controlled reactions. In Chapter five, future perspectives on the electrochemically redox switchable catalysis will be discussed. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

In this research, electrochemical methods are used to synthesize the inorganic fraction of bone, hydroxyapatite, for application in biological implants and as a calibration material for elemental analysis in human bone. Optimal conditions of electrochemically deposited uniform apatite coatings on stainless steel were investigated. Apatite is a ceramic with many different phases and compositions that have beneficial characteristics for biomedical applications. Of those phases hydroxyapatite (HA) is the most biocompatible and is the primary constituent of the inorganic material in bones. HA coatings on metals and metal alloys have the ability to bridge the growth between human tissues and implant interface, where the metal provides the strength and HA provides the needed bioactivity. The calcium apatites were electrochemically deposited using a modified simulated body fluid adjusted to pH 4-10, for 1-3 hours at varying temperature of 25-65°C while maintaining cathodic potentials of -1.0 to -1.5V. It was observed that the composition and morphology of HA coatings change during deposition by the concentration of counter ions in solution, pH, temperature, applied potential, and post-sintering. The coatings were characterized by powder x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The precipitated powders from the experiment were also characterized, with results showing similarities to biological apatite. There is a need for quantitative elemental analysis of calcified biological matrices such as bone and teeth; however there are no suitable calibration materials commercially available for quantitative analysis. Matrix-matched standards are electrochemically synthesized for LA-ICP-MS analysis of human bone. The synthetic bioapatite is produced via a hydrothermal electrochemical process using a simulated body fluid solution to form hydroxyapatite. Additional bioapatite standards are synthesized containing trace amounts of metals. The x-ray diffraction of the synthesized standards shows an increase in cell volume for the crystal structure from 0.534 to 0.542 nm3 with the substitution of metals into the crystal structure. The analyte concentration and recoveries for the synthesized standards and reference materials were determined by ICP-MS with % RSD below 6.3% and limits of detection below 1.2 ng/mL for trace metals. The electrochemically synthesized bioapatite was also compared to standard reference materials with X-ray diffraction, FTIR, and Raman spectroscopy. Optimum laser ablation parameters were determined for the standards and human bone. The synthesized standards were homogeneous and the reproducibility for the isotope concentrations determined by LA-ICP-MS was between 3-10 % compared to 10-35% for SRM 1486 Bone Meal and SRM 1486 Bone Ash. A quantitative method has been developed for 2D mapping using LA-ICP-MS and the matrix-matched standards of metal-doped biopaptite to characterize metal concentrations in human bone. Laser ablation parameters for the method are refined resulting in concentration (ug/g) contour map measurements for each isotope measured in the human bone. Essential and non-essential metals, Al, Ca, Cu, Fe, Pb, and Zn are quantitatively mapped using these parameters. Limit of detection for the metals in the bone range from 0.001 to 0.08 ug/g. The LA-ICP-MS analysis method developed proves to be a straightforward and simple method for quantitative analysis of human bone.

A Thesis submitted to the Faculty of Science University of the Witwatersrand, Johannesburg, for the Degree of Doctor of Philosophy. / Student and pupil difficulties relating to the qualitative interpretation of microscopic processes which take place in operating electrochemical cells were determined. The subjects were studying electrochemistry at either high school, college of education or University. The investigation followed a stage process which involved the identification of misconceptions, further inquiry into the nature and possible causes of these as well as the development and evaluation of a teaching method aimed at alleviating the identified problems. The interview and the pencil and paper methods were employed to elicit the misunderstandings and simple experiments provided the focus of discussion. From the relatively broad base of the initial stages in which open-ended questions were used, the problem areas narrowed progressively as the stud difficulties became clarified. The tape recorded interviews as well as the responses from the pencil and paper test were analysed for apparent misconceptions. Four areas emerged as problematic among the majority of the subjects. (Abbreviation abstract) / Andrew Chakane 2019