Browsing by Subject "Electrochemistry"
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Item Design and Fabrication of High Capacity Lithium-Ion Batteries using Electro-Spun Graphene Modified Vanadium Pentoxide Cathodes(2019-08) Ahmadian, Amirhossein; Agarwal, Mangilal; Xie, Jian; Dalir, HamidElectrospinning has gained immense interests in recent years due to its potential application in various fields, including energy storage application. The V2O5/GO as a layered crystal structure has been demonstrated to fabricate nanofibers with diameters within a range of ~300nm through electrospinning technique. The porous, hollow, and interconnected nanostructures were produced by electrospinning formed by polymers such as Polyvinylpyrrolidone (PVP) and Polyvinyl alcohol (PVA), separately, as solvent polymers with electrospinning technique. In this study, we investigated the synthesis of a graphene-modified nanostructured V2O5 through modified sol-gel method and electrospinning of V2O5/GO hybrid. Electrochemical characterization was performed by utilizing Arbin Battery cycler, Field Emission Scanning Electron Microscopy (FESEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), Mercury Porosimetry, and BET surface area measurement. As compared to the other conventional fabrication methods, our optimized sol-gel method, followed by the electrospinning of the cathode material achieved a high initial capacity of 342 mAh/g at a high current density of 0.5C (171 mA/g) and the capacity retention of 80% after 20 cycles. Also, the prepared sol-gel method outperforms the pure V2O5 cathode material, by obtaining the capacity almost two times higher. The results of this study showed that post-synthesis treatment of cathode material plays a prominent role in electrochemical performance of the nanostructured vanadium oxides. By controlling the annealing and drying steps, and time, a small amount of pyrolysis carbon can be retained, which improves the conductivity of the V2O5 nanorods. Also, controlled post-synthesis helped us to prevent aggregation of electro-spun twisted nanostructured fibers which deteriorates the lithium diffusion process during charge/discharge of batteries.Item Electrochemical Tape-and-Paper-Based Sensor for the Quantification of Potassium(2023-08) Zhang, Tommy; Deiss, Frédérique; Webb, IanPotassium levels in serum are used in the diagnosis of diseases involving cardiac arrhythmias, neuromuscular weakness, and chronic kidney diseases. These illnesses are becoming more prevalent, therefore, developing new potassium quantification methods would aid in advancing preventative care. Current methods of quantifying potassium mainly rely on the use of glass ion-selective electrodes which are costly, fragile, and requires frequent maintenance and recalibration. For faster and more accessible quantification of potassium, we are developing low cost, portable, and easy to fabricate electrochemical tape-and-paper-based devices. Our sensor bypasses the inconveniences of ion-selective electrodes and could ultimately serve as a point-of-care device to allow for regular monitoring or even home-use. Our sensing method relies on Prussian blue immobilized on the surface of electrodes as a potassium recognition element. Potassium ions intercalate into the Prussian blue lattice and subsequently changes the electrochemical characteristics of Prussian blue such as the redox peak potentials. These devices are highly robust, feature a limit of detection of 1.3 mM potassium and the response is linear to at least 100 mM, which contains the clinically relevant ranges required for diagnostics. Quantification was developed using cyclic voltammetry, demonstrated in Chapter 3. We observed changes in Prussian blue redox peak potentials at different concentrations of potassium and followed the expected Nernstian response. We investigated multiple methods of immobilizing Prussian blue onto the electrode surfaces to investigate stability and reproducibility in Chapter 4. Adsorption, in-situ synthesis, and carbon paste incorporation of Prussian blue was tested. Prussian blue-carbon paste devices had reproducibility issues and featured broad reduction peaks. In-situ synthesis of Prussian blue directly onto the surface of the electrodes also featured broad reduction peaks but the Prussian blue response was reproducible. The issue with in-situ synthesis was the stability of the Prussian blue layer, which was susceptible to degradation after repeated use of the device, which is required for evaluating the performance of the device. Although adsorption using Prussian blue in water had some reproducibility issues as well, this method led to the most stable Prussian blue layer, had distinct reduction peaks, and was simple to perform. Various solvents were used to dissolve Prussian blue in Chapter 5 to investigate methods of increasing device reproducibility when using adsorption. A few organic solvents were able to dissolve Prussian blue to form a stable solution with the goal of forming a more uniform Prussian blue layer and potentially improving consistency of the layer immobilization. While these alternative solvents were able to dissolve Prussian blue, they also damaged the graphite electrodes on the devices, which altered the electrochemical responses of the devices to the point where potassium quantification was no longer possible. Due to incompatibility between these alternative solvents and the devices, adsorption of Prussian blue in water continued to be used. Different modes of adsorption were explored and was optimized in Chapter 6. By altering the adsorption setup and allowing the Prussian blue particles to settle evenly onto a level electrode surface, device reproductivity increased substantially. To understand the applicability of the devices in real samples, interferent studies were performed in Chapter 7. Other cations such as Na+, Li+, Ca2+, Mg2+, and Ba2+ were not observed to enter the Prussian blue lattice in the cyclic voltammograms. Monovalent cations that share the same charge as K+ but have smaller ionic radius, Na+ and Li+, were able to decrease K+ sensitivity. Divalent cations that had a smaller ionic radius than K+ did not alter sensitivity. The exception was Ba2+, which also decreased K+ sensitivity. These results suggested that both ionic radius and charge of a species were important factors in impacting K+ intercalation into the Prussian blue lattice. Other interferents such as sulfates, phosphates, carbonates, urea, and lactic found in serum and sweat samples were tested. The presence of these interferents decreased the current intensity of the reduction peak of Prussian blue, which resulted in less definition in the peaks. For the future of this project, the effects of interferents found in serum and sweat must be investigated further. Additionally, reproducibility of the devices could be improved further if less harsh organic solvents are tested for adsorption, square wave voltammetry could be used for quantification to evaluate the viability of alternative voltametric techniques, and Prussian blue analogues could be implemented into the devices for quantification of other cations.Item LAYER BY LAYER NANOASSEMBLY OF COPPER INDIUM GALLIUM SELENIUM (CIGS) NANOPARTICLES FOR SOLAR CELL APPLICATION(2011-12) Hemati, Azadeh; El-Mounayri, Hazim; Agarwal, Mangilal; Varahramyan, KodyIn this research thesis, copper indium gallium selenium (CIGS) nanoparticles were synthesized from metal chlorides, functionalized to disperse in water, and further used in layer by layer (LbL) nanoassembly of CIGS films. CIGS nanoparticles were synthesized through the colloidal precipitation in an organic solvent. The peak and average sizes of the synthesized particles were measured to be 68 nm and 75 nm in chloroform, and 30 nm and 115 nm in water, respectively. Two methods were used to disperse the particle in water. In the first method the stabilizing agent oleylamine (OLA) was removed through multiple cleaning processes, and in the second method ligand exchange was performed with polystyrene sulfonate (PSS). Zeta potential of CIGS nanoparticles dispersed in water was measured to be +61 mV. The surface charge of the nanoparticles was reversed by raising the pH of the solution, which was measured to be −43.3 mV at 10.5 pH. In a separate process, the CIGS nanoparticles dispersed in water were coated with PSS. The resulting dispersion was observed to be stable and the surface charge was measured to be −56.9 mV. The LbL deposition process of CIGS nanoparticles was characterized by depositing thin films on quartz crystal microbalance (QCM). LbL depositions was conducted using (i) oppositely charged CIGS nanoparticles, (ii) positively charged CIGS nanoparticles and PSS, and (iii) PSS-coated CIGS (CIGS-PSS) and polyethyleneimine (PEI). The average thickness of each bi-layer of the above mentioned depositions were measured to be 2.2 nm, 1.37 nm, and 10.12 nm, respectively. The results from the QCM have been observed to be consistent with the film thickness results obtained from atomic force microscopy (AFM). Various immersion times versus thickness of the film were also studied. For electrical characterization, the CIGS films were deposited on indium tindioxide (ITO)-coated glass substrates. Current versus voltage (I/V) measurements were carried out for each of the films using the Keithley semiconductor characterization instruments and micromanipulator probing station. It was observed that the conductivity of the films was increased with the deposition of each additional layer. The I/V characteristics were also measured under the light illumination and after annealing to study the photovoltaic and annealing effects. It was observed that under light illumination, the resistivity of a 12-layer CIGS film decreased by 93% to 0.54 MΩ.m, and that of the same number of layers of PSS-coated CIGS and PEI film decreased by 60% to 0.97 MΩ.m under illumination. The resistivity of an 8-layer CIGS and PSS film decreased by 76.4% to 0.1 MΩ.m, and that of the same layers of PSS-coated CIGS and PEI decreased by 87% to 0.07 MΩ.m after annealing. The functionalized nanoparticles and the LbL CIGS films were implemented in the solar cell devices. Several configurations of CIGS films (p-type), and ZnO and CdS films (n-type) were considered. Poly(3,4-ethylenedioxythiophene) (PEDOT), molybdenum (Mo), and ITO were used as back contacts and ITO was used as front contact for all the devices. The devices were characterized the Keithley semiconductor characterization instruments and micromanipulator probing station. For a CIGS and n-ZnO films device with PEDOT as back contact and ITO as front contact, the current density at 0 V and under light illumination was measured to be 60 nA/cm2 and the power density was measured to be 0.018 nW/cm2. For a CIGS and CdS films device with ITO as both back and front contact, the current density at 0 V and under light illumination was measured to be 50 nA/cm2 and the power density was measured to be 0.01 nW/cm2. For a drop-casted CIGS and CdS films device with Mo as back contact and ITO as front contact, the current density of 50 nA/cm2 at 0 V and power density of 0.5 nW/cm2 under light illumination was measured. For the LbL CIGS and chemical bath deposited CdS films device with ITO as both back and front contact, the current density of 0.04 mA/cm2 at 0 V and power density of 1.6 μW/cm2 under light illumination was measured. Comparing to Device-III, an increase by 99% in the power density was observed by using the CIGS LbL film in the device structure. The novel aspects of this research include, (i) functionalization of the CIGS nanoparticles to disperse in water including coating with PSS, (ii) electrostatic LbL deposition of CIGS films using oppositely charged nanoparticles and polymers, and (iii) the utilization of the fabricated LbL CIGS films to develop solar cells. In addition, the n-type cadmium sulfide film (CdS) and zinc oxide (ZnO) buffer layer were also deposited through LbL process after the respective particles were functionalized with PSS coating in separate experiments.Item Study of catalysts with high stability for proton exchange membrane fuel cells(2015-08) Yang, Fan; Xie, JianThe innovation and investigation of catalysts in proton exchange membrane fuel cells are included in this thesis. In the first part of this work, stability of the catalyst support of PEMFC catalyst is investigated. Nanoscale platinum particles were loaded on two different kinds of carbon supports, nano graphene sheets and functionalized carbon black/graphene hybrid were developed by the liquid phase reaction. The crystal structure of two kinds of catalysts was characterized by X-ray diffractometer (XRD). The morphology and particle size were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Pt loading was measured by thermal gravimetric analysis (TGA). The Brunauer, Emmett and Teller (BET) method was applied to test the surface area of the catalysts. The electrochemical surface area (ECSA) and mass activity during oxygen reduction reaction (ORR) process for two kinds of catalyst were tested by cyclic voltammetry method under different conditions. The stability of the catalysts were tested by accelerated durability test (ADT). The results show that although the mass activity of Pt/graphene is much lower, the stability of it is much better than that of the commercial catalyst. After adding functionalized carbon black (FCB) as spacer, the stability of the catalyst is preserved and at the meantime, the mass activity becomes higher than 20% Pt/XC72 catalyst. The lower mass activity of both catalysts are due to the limitation of the electrolyte diffusion into the carbon support because of the aggregation nature of graphene nano-sheets. After introducing functional carbon black as spacer, the mass activity and ECSA increased dramatically which proved that FCB can be applied to prevent the restacking of graphene and hence solved the diffusion problem. In the meantime, the durability was still keeping the same as Pt/graphene catalyst. In the second part of the work, the restacking problem was solved by introducing FCB as spacers between functionalized graphene nanosheets. The same measurement was applied to test the electrochemical performance of Pt/FCB/FG catalyst. The new catalyst showed a higher mass activity compared to Pt/graphene catalyst which meant the restacking problem was partially solved. The durability of the Pt/FCB/FG catalyst was still excellent.Item Towards commercialization of self-healing technology in epoxy coating(2014) Ye, Lujie; Jones, Alan S.; Zhang, Jing; Zhu, Likun; Chen, JieThis work is focused on developing viable self-healing coatings, especially considering the viability of the coating in a commercial context. With this in mind, finding low cost healing agents, with satisfactory healing and mechanical properties as well as adapting the healing system for use in coatings was required. Seven potential healing agents were evaluated and an air-drying triglyceride (linseed oil) was identified as the candidate healing agent. Different encapsulation techniques were evaluated and ureaformaldehyde microcapsules were chosen as the candidate encapsulation technique. Self-healing coatings were fabricated using urea-formaldehyde encapsulated linseed oil. EIS, SEM and TGA technologies were used to evaluate mechanical performance, corrosion resistance, and self-healing performance.Item Two-Dimensional Titanium and Molybdenum Carbide MXenes as Electrocatalysts for CO2 Reduction(Elsevier, 2020-06-26) Handoko, Albertus D.; Chen, Hetian; Lum, Yanwei; Zhang, Qianfan; Anasori, Babak; Seh, Zhi Wei; Mechanical Engineering and Energy, School of Engineering and TechnologyElectrocatalytic CO2 reduction reaction (CO2RR) is an attractive way to produce renewable fuel and chemical feedstock, especially when coupled with efficient CO2 capture and clean energy sources. On the fundamental side, research on improving CO2RR activity still revolves around late transition metal-based catalysts, which are limited by unfavorable scaling relations despite intense investigation. Here, we report a combined experimental and theoretical investigation into electrocatalytic CO2RR on Ti- and Mo-based MXene catalysts. Formic acid is found as the main product on Ti2CTx and Mo2CTx MXenes, with peak Faradaic efficiency of over 56% on Ti2CTx and partial current density of up to −2.5 mA cm−2 on Mo2CTx. Furthermore, simulations reveal the critical role of the Tx group: a smaller overpotential is found to occur at lower amounts of –F termination. This work represents an important step toward experimental demonstration of MXenes for more complex electrocatalytic reactions in the future.