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- Title
- PHYSICOCHEMICAL AND THERMOCHEMICAL PROPERTIES OF SULFONATED POLY(ETHERETHERKETONE) ELECTROLYTE MEMBRANES.
- Creator
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Rhoden, Stephen, Diaz, Diego, University of Central Florida
- Abstract / Description
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Fuel cells have long been seen as an alternative to combustion powered and diesel powered engines and turbines. Production of energy via a fuel cell conversion method can generate up to 60% efficiency in comparison to 30% using a combustion powered engine, with low co-production of harmful side-products. The polymer electrolyte membrane (PEM) adapted for the fuel cell application is one of the main components that determines the overall efficiency. This research project was focused towards...
Show moreFuel cells have long been seen as an alternative to combustion powered and diesel powered engines and turbines. Production of energy via a fuel cell conversion method can generate up to 60% efficiency in comparison to 30% using a combustion powered engine, with low co-production of harmful side-products. The polymer electrolyte membrane (PEM) adapted for the fuel cell application is one of the main components that determines the overall efficiency. This research project was focused towards novel PEMs, such as sulfonated poly(etheretherketone) or SPEEK, which are cost-efficient and robust with high proton conductivities under hydrated conditions. The degree of sulfonation (DS) of a particular SPEEK polymer determines the proton conducting ability, as well as the long term durability. For SPEEK with high DS, the proton conduction is facile, but the mechanical stability of the polymer decreases almost proportionally. While low DS SPEEK does not have sufficient sulfonic acid density for fast proton conduction in the membrane, the membrane keeps its mechanical integrity under fully saturated conditions. The main purpose of this work was to address both issues encountered with SPEEK sulfonated to low and high DS. The addition of both solid acids and synthetic cross-links were studied to address the main downfalls of the respective SPEEK polymers. Optimization of these techniques led to increased understanding of PEMs and notably better electrochemical performance of these fuel cell materials. Oxo-acids such as tungsten (VI) oxide (WO3) and phosphotungstic acid (PTA) have been identified as candidate materials for creating SPEEK composite membranes. The chemistry of these oxo-acids is well known, with their use as highly acidic catalyst centers adopted for countless homogeneous and heterogeneous, organic and inorganic reactions. Uniform dispersion of WO3 hydrate in SPEEK solution was done by a sol-gel process in which the filler particles were grown in an ionomer solution, cast and allowed to dry. PTA composites were made by adding the solid acid directly to a solution of the ionomer and casting. The latter casting was allowed to dry and Cs+- exchanged to stabilize the PTA from dissolution and leaching from the membrane. The chemical and physical properties of these membranes were characterized and evaluated using mainly conductometric and X-ray photoelectron spectroscopic methods. Composite SPEEK/ PTA membranes showed a 50% decrease in PEM resistance under hydrogen fuel cell testing conditions, while SPEEK/ WO3 composites demonstrated a ten-fold increase in the membrane's in-plane proton conductivity. The chemical and physical properties of these composites changed with respect to their synthesis and fabrication procedures. This study will expound upon their relations.
Show less - Date Issued
- 2010
- Identifier
- CFE0003470, ucf:48976
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003470
- Title
- COMPARATIVE STUDY OF ETHANOL AND METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE AND ACID SOLUTIONS: ELECTRO-CATALYTIC PERFORMANCE AND REACTION KINETICS.
- Creator
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Hidalgo, Carlos, Diaz, Diego, University of Central Florida
- Abstract / Description
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A comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by...
Show moreA comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by potentiodynamic and potentiostatic methods in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions at various concentrations of ethanol and methanol. The kinetics of ethanol and methanol on a Pt/ceria composite electrode were measured in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions using a rotating disk electrode (RDE). Cyclic voltammetry was employed in temperatures ranging from 15 to 55°C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. The temperature dependence of the electro-catalytic activities afforded the determination of apparent activation energies for ethanol and methanol oxidation.
Show less - Date Issued
- 2011
- Identifier
- CFE0003628, ucf:48853
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003628
- Title
- INVESTIGATION OF NANOCERIA-MODIFIED PLATINUM-GOLD COMPOSITE ELECTRODES FOR THE ELECTROCHEMICAL REDUCTION OF OXYGEN IN ALKALINE MEDIA.
- Creator
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Hegishte, Rahul, Diaz, Diego, University of Central Florida
- Abstract / Description
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Platinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO2 electrodes while the total concentration of the metals was maintained at 2 x 10-3M and the concentration of nanoceria was maintained constant at 5 x 10-3M. The electrodes were characterized by their cyclic voltammetry curves in...
Show morePlatinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO2 electrodes while the total concentration of the metals was maintained at 2 x 10-3M and the concentration of nanoceria was maintained constant at 5 x 10-3M. The electrodes were characterized by their cyclic voltammetry curves in 0.5M sulfuric acid solution. The electrochemically active area of the electrodes was determined using the copper underpotential deposition method. The linear sweep voltammograms of the PtAu and PtAu/CeO2 electrodes were plotted from -1V to 0V vs. Ag/AgCl, 3M KCl reference electrode using the rotating disk electrodes for the rotation speeds from 200 to 3600rpm in an oxygen saturated 0.1M sodium hydroxide solution. The values of the kinetic controlled current density were determined from the rotating disk voltammetry. The values of the limiting current density for each rotation speed were used to plot the Koutecky-Levich plots for the electrodes. The rate constants were obtained from the Koutecky-Levich plots for each composition of the electrode. The values of kinetic current density and the rate constants indicated that the addition of Au enhances the ORR rates in both the PtAu and the PtAu/CeO2 electrodes. The values of the kinetic current densities of the PtAu/CeO2 were lower than that of the PtAu electrodes owing to the poor electrical conductivity of ceria. The Koutecky-Levich plots for the PtAu and the PtAu/CeO2 electrodes are linear for the four-electron reduction of oxygen in the alkaline media, which indicates that the overall reaction follows the first order kinetics. The electron transfer rate constants obtained from the Koutecky-Levich plots for the PtAu and the PtAu/CeO2 electrodes both were found to increase in values with the addition of Au. The Tafel plots were plotted for the PtAu and PtAu/CeO2 electrodes and the values of Tafel slopes were found to be in a small range for lower amounts of Au which indicated that the ORR rates were enhanced in lower amounts of Au. The values of Tafel slopes were found to be much higher for the ceria-modified PtAu electrodes as compared to the PtAu electrodes, which indicate the lower rates of ORR after the modification with ceria. Also, the ORR rates for the electrodes with smaller amounts of Au in PtAu/CeO2 were higher than those in the larger amounts of Au.
Show less - Date Issued
- 2011
- Identifier
- CFE0003639, ucf:48860
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003639
- Title
- INFRARED SURFACE PLASMON POLARITONS ON SEMICONDUCTOR, SEMIMETAL AND CONDUCTING POLYMER.
- Creator
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Shahzad, Monas, Peale, Robert, Heinrich, Helge, Coffey, Kevin, Diaz, Diego, University of Central Florida
- Abstract / Description
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Conductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a...
Show moreConductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a heavily doped semiconductor, a semimetal, a conducting polymer and its composite.Heavily doped silicon was investigated by tuning its plasma frequency to the infrared region by heavily doping. The measured complex permittivity spectra for p-type silicon with a carrier concentration of 6 (&)#215; 1019 and 6 (&)#215; 1020 cm-3 show that these materials support SPPs beyond 11 and 6 ?m wavelengths, respectively. SPP generation was observed in angular reflection spectra of doped-silicon gratings. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 ?m wavelength for the heaviest doped, and the observed resonances were confirmed theoretically using analytic calculations. The permittivity spectra were also used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range of 6 to 10 ?m. The semimetal bismuth (Bi) has an infrared plasmon frequency less than the infrared plasma frequency of noble metals such as gold and silver, which is one order of magnitude lower than their plasma frequencies. The excitation of IR surface plasmons on Bi lamellar gratings in the wavelength range of 3.4 (&)#181;m to 10.6 (&)#181;m was observed. Distinct SPP resonances were observed although the usual condition for bound SPP is not satisfied in this wavelength range because the real part of the permittivity is positive. The excitation of these resonances agrees theoretically with the electromagnetic surface waves called surface polaritons (SPs). The measured permittivity spectra were used to calculate the SP mode heights above the bismuth surface and SP propagation length, which satisfied our criteria for sensors.A conducting polymer and its composite with graphite were also investigated since their plasma frequency may lie in the infrared region. Polyaniline was chemically synthesized and doped with various acids to prepare its salt form. A composite material of polyaniline with colloidal and nano-graphite was also prepared. Optical constants were measured in the long wave infrared region (LWIR) and were used to calculate SPP propagation length and penetration depth. SPP resonance spectra were calculated and suggested that polyaniline and its composite can be used as a host with sufficient mode confinement for IR sensor application.
Show less - Date Issued
- 2012
- Identifier
- CFE0004598, ucf:49215
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004598
- Title
- Development of Novel Redox Sensors and Processes Towards Biological Applications.
- Creator
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Patel, Jigna, Yestrebsky, Cherie, Clausen, Christian, Hampton, Michael, Harper, James, Diaz, Diego, University of Central Florida
- Abstract / Description
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Research on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by...
Show moreResearch on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by this, many researchers today have developed numerous types of sensing devices that can detect various physiological and biological compounds. However, most of these sensors are enzyme based. They have several setbacks such as the lack of sensitivity, restricted selectivity, short shelf life, and biological fouling. To overcome these obstacles, we examine the use of nanoceria modified Pt and Au electrodes for the detection of glucose and reactive oxygen species such as hydrogen peroxide. Amperometric detection of glucose and hydrogen peroxide is critical for biological applications for diabetes and possible Alzheimer's and Parkinson's patients. This dissertation focuses on the exploration of non-enzymatic detection of glucose and reactive oxygen species which has the prospective to be used for biological applications, in addition to an investigation of an odor control technology that uses these reactive oxygen species for the treatment of wastewater plants. The combination of bi-metallic composites with nanoceria showed increased oxidation ability towards glucose and hydrogen peroxide. The following dissertation expands on the relationship between bi-metallic nanoceria composite materials and its electro-oxidation of glucose and hydrogen peroxide towards biological sensing along with an investigation of an odor control technology that utilizes generates hydroxyl radical fine particle mist for the degradation of hydrogen sulfide odor in wastewater treatment plants.
Show less - Date Issued
- 2013
- Identifier
- CFE0005227, ucf:50585
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005227