No description available.

Magister Scientiae - MSc / The particles of the Pt metal were well dispersed on carbon nanotubes when EG was used and in isopropanol poor dispersion was observed and no further investigation was done on them. The platinum wt% on the supports observed from EDS was 21.8, 19.10 and 16.74wt% for Pt/EMWCNT, Pt/LPGCNT and Pt/ commercial CNT respectively. Pt/LPGMWCNT showed high electro-catalytic activity of 2.48 mA and active surface area of 76 m2/g, toward oxygen reduction, observed from cyclic voltammogram in iv sulfuric acid. Pt/LPGMWCNT also showed better tolerance toward methanol, however it was not highly active towards methanol, and hence the methanol oxidation peak current observed between 0.75 and 08 potential was the smallest. In this study a wide range of instruments was used to characterize the properties and behavior of Platinum nanoparticles on multi-wall carbon nanotubes. To add to the already mentioned, Scanning electrochemical microscopy (SEM), proton induced x-ray emission (PIXE), scanning electrochemical microscopy (SECM) and Brunauer-Emmett Tellar (BET) were also used. / South Africa

Electrochemical Supercapacitors (ES), also known as Supercapacitor or Ultracapacitor, has been regarded as an advanced electrical energy storage device for decades. Fabrication of advanced electrode materials is of critical importance for advanced ES. Among various materials used for ES electrode, polypyrrole (PPy) is found to be a promising material due to high specific capacitance, good electrical conductivity, low cost and ease of processing. The use of advanced anionic dopants and addition of multiwall carbon nanotube (MWCNT) have been proved an .effective approach towards advanced PPy based ES with improved electrochemical behaviors. In this research, chemical polymerization of PPy powders and PPy/MWCNT composite materials have been successfully accomplished in presence of advanced anionic dopants, including chromotrope families, amaranth, pyrocatechol violet, eriochrome cyanine R and acid fuchsin. The influence of polyaromatic dopants with different molecular size, charges and charge to mass ratios on the microstructure and electrochemical characteristics has been discussed. PPy coated MWCNT with uniform microstructures was successfully achieved in simple chemical methods. The results showed PPy powders with enhanced microstructures and electrochemical behaviors can be obtained by using such advanced anionic dopants. Multi-charged polyaromatic dopants with larger molecular size benefitted PPy powders with smaller particle size, improved specific capacitance, and enhanced cycling stability, at high electrode mass loadings. Moreover, advanced aromatic dispersant and chemical synthesis was proved a simple and effective method for fabrication of PPy/MWCNT composite materials at different PPy/MWCNT mass ratio, among which the powder with PPy/MWCNT mass ratio of 7:3 showed optimum electrochemical performance. Last but not the least, the use of advanced high porosity current collector (Ni foam) allowed high electrode mass loading and good electric conductivity. As a result, advanced PPy/MWCNT composite materials which allows improved electrochemical behaviors, especially at high mass loading, are promising electrode materials for ES. / Thesis / Master of Applied Science (MASc)

This thesis delivers an in-depth investigation into electrochemical carbon dioxide reduction (CO2R), a process with the potential to convert CO2 gas into value-added chemicals and fuels. However, the efficiency and operational durability of current CO2 reduction processes are limited by catalytic performance. To address this, the thesis focuses on gaining a deep understanding of the transformations that CO2R electrocatalysts undergo under realistic conditions, such as morphological, phase structure, and compositional changes. These insights inform the design of next-generation materials by identifying performance descriptors and degradation patterns. A key aspect of this thesis is the development and application of in-situ liquid phase transmission electron microscopy (LP-TEM), an advanced platform that directly correlates nanoscale changes in catalyst materials under the influence of electrode potentials in CO2R reactive environments. Despite its potential, the use of in-situ LP-TEM presents a range of challenges, which this thesis addresses alongside exploring potential advancements for enhancing its accuracy and applicability. With the evolution of nanofabricated liquid cells, dynamic nanoparticle tracking, and high-resolution imaging in a liquid medium, this technology can more accurately mimic realistic exposure conditions. Cumulatively, this thesis systematically navigates the technical hurdles, advancements, and future prospects of in-situ LP-TEM in the context of electrochemical CO2R. The findings not only advance our understanding of the in-situ LP-TEM technical process but also guide new researchers in the field of in-situ TEM of electrocatalyst materials, aiding in the optimization of catalyst design, and paving the way for more sustainable and economically competitive CO2R technologies. The application of in-situ LP-TEM extends to the examination of two specific catalysts: Palladium (Pd) and a bi-metallic alloy of Copper (Cu) and Silver (Ag). By employing in-situ LP-TEM and selected area diffraction (SAD) measurements, we trace the morphological and phase structure transformations of the Pd catalyst under CO2R conditions. Interestingly, our findings indicate that alterations in reaction energetics, rather than morphological or phase structure changes, chiefly govern catalyst selectivity. This provides invaluable insights for designing more efficient catalysts. Further, we observe the morphological transformation of a metallic copper catalyst structure into a Cu-Ag bimetallic alloy during a galvanic replacement method. We then investigate the stability of both catalyst structures under operational CO2R conditions. Our results reveal that the metallic Cu structure undergoes significant morphological deformation during CO2R, leading to migration, detachment, and recrystallization of the catalyst surface. Contrarily, the Cu-Ag bimetallic alloy demonstrates notable thermodynamic stability under a similar applied potential. / Thesis / Candidate in Philosophy / This PhD thesis focuses on the development and implementation of cutting-edge technologies to address the climate change implications of CO2 emissions - a potent greenhouse gas. CO2 molecules could be electrochemically converted into various chemical feedstock and fuels. This process involves the development of efficient catalyst designs that can reduce CO2 gas at high conversion rates. Acquiring mechanistic insights on the behavior of the developed catalysts under reaction conditions would significantly assist on producing performance descriptors for catalyst design in CO2 conversion approach. Among a range of different advanced techniques, in-situ liquid phase transmission electron microscopy (LP-TEM) technology is selected for this study. This technique is capable of correlating dynamic nanoscale compositional and morphological changes with the electrochemical response of the catalysts. The primary focus of the thesis is on developing and implementing in-situ LP-TEM techniques to achieve electrochemical CO2 conditions while tracking particle morphology and phase structures as functions of electrochemical potential and time. Furthermore, the thesis investigates the performance of different catalyst designs under CO2 reduction (CO2R) operational conditions, which includes palladium (Pd) nanoparticles and copper–silver (Cu–Ag) bimetallic alloys. On a fundamental level, these studies provide a detailed understanding of the phase transformation and structural changes of these catalysts during CO2R that contributes valuable knowledge to the field and can be used to design next-generation CO2R catalysts.

Hepatocyte transmembrane potential (V(m)) during osmotic stress responds as an osmometer, in part because of changes in membrane K+ conductance. This may contribute to the electromotive force that drives transmembrane Cl- fluxes. To test this, double-barreled ion-sensitive microelectrodes were used to measure changes in steady-state intracellular Cl- activity (a(Cl)/(i)) during osmotic stress applied to mouse liver slices. Hyperosmotic and hyposmotic conditions were created by rapidly switching to a solution in which sucrose concentrations were increased or reduced, respectively. Hyperosmotic stress [1.4 x control osmolality (280 mosmol/kgH2O)] decreased hepatocyte V(m) 46% from -39 ± 1 to -21 ± 1 mV (SE; n = 16 animals). Corresponding a(Cl)/(i) increased twofold from 19 ± 2 to 38 ± 3 mM. This shifted the Cl- equilibrium potential (E(Cl)) 19 mV, from -38 ± 0.3 to -19 ± 2 mV. Hyposmotic stress [0.71 x control osmolality (290 mosmol/kgH2O)] increased hepatocyte V(m) 64% from -28 ± 1 to -46 ± 1 mV (SE; n = 13 animals). Corresponding a(Cl)/(i) decreased 0.53-fold from 17 ± 1 to 8 ± 1 mM. This shifted the E(Cl) 20 mV from -26 ± 2 to -46 ± 3 mV. Thus hepatocyte a(Cl)/(i) is in electrochemical equilibrium with V(m). The paired measurements above were repeated after addition of K+-channel blockers quinine or Ba2+. Ba2+ (2 mM) had no effect on either V(m) or a(Cl)/(i) during hyperosmotic stress; however, Ba2+ significantly inhibited changes in V(m) and a(Cl)/(i) during hyposmotic stress. Effects of quinine (0.5 mM) on V(m) and a(Cl)/(i) during both hyperosmotic stress and hyposmotic stress were similar to those of Ba2+. A previous report shows that inhibition of hyposmotic stress-induced V(m) changes results in loss of hepatocyte volume regulation and greater swelling. Thus osmotic stress-induced changes in a(Cl)/(i) are nowhere near those predicted by cell water volume changes based on transmembrane osmotic pressure differences. We conclude that these larger changes in a(Cl)/(i) resulted from voltage-driven transmembrane Cl- fluxes.

Early detection is crucial in delivering timely treatment and improving patient outcomes. Point-of-care (POC) biosensors play an essential role in early detection, allowing for rapid and accurate diagnosis of diseases at the patient’s bedside without the need for expensive equipment or specialized personnel. By performing the analysis on-site, POC diagnostics can offer continuous monitoring and real-time data acquisition of a patient's health status. Thus, there is strong incentive in creating POC biosensors to provide healthcare professionals with greater access to diagnostic information, ultimately improving outcomes and reducing healthcare costs. Herein, the development of a POC lab-in-a-tube biosensor that utilizes simple and scalable fabrication techniques is presented. Electrodes are patterned on low-cost plastic substrates, which can be subsequently rolled and heat-shrunk into miniaturized tubing for flow-through analysis of liquid samples. Heat-shrinking of the device results in 3-dimensional, hierarchically wrinkled electrodes with morphological feature that span several orders of magnitude in size. These wrinkled electrodes demonstrate dramatically increased surface area in a given footprint compared to traditional planar electrodes. Incorporation of modified gold and silver wires allows for sensitive and stable electrochemical detection, enabling fast and quantitative results. These devices are capable of millilitre-per-minute flow rates to allow for rapid sample processing and for increased mass-transport to the electrode surface. The ability to capture analytes was characterized with nucleic acid sequences using pump-driven and blood-collection tube induced flow for rapid and accurate detection. Overall, this work demonstrates the successful development of an electrochemical platform integrated into a plastic tubing capable of rapid detection of flowing analytes. With its ease-of-use and compatibility with a wide range of flow rates, the device has the potential to be incorporated with existing medical tubing and procedures to achieve POC diagnostics. / Thesis / Master of Applied Science (MASc) / Early detection is critical for timely treatment and better patient outcomes. Point-of-care (POC) biosensors allow for disease diagnosis and real-time monitoring of a patient's health status directly at the patient's bedside without the need for expensive equipment or specialized personnel. A lab-in-a-tube biosensor was developed using sensing surfaces on low-cost plastic that is rolled and heat-shrunk into miniaturized tubing for analysis of liquid samples. The wrinkled sensing surface that results from heat-shrinking dramatically increase surface area and interaction with the sample, enabling sensitive detection that is fast and quantitative. These devices are capable of capturing samples at high flow rates, allowing for rapid analysis of large samples. Overall, this work demonstrates the successful creation of a biosensor platform that could be incorporated with existing medical tubing for POC diagnostics.

No description available.

No description available.

No description available.

No description available.