Matching Items (11)
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- All Subjects: electrochemistry
- Creators: Chemical Engineering Program
- Creators: Torres, Cesar
- Resource Type: Text
Description
Within recent years, metal-organic frameworks, or MOF’s, have gained a lot of attention in the materials research community. These micro-porous materials are constructed of a metal oxide core and organic linkers, and have a wide-variety of applications due to their extensive material characteristic possibilities. The focus of this study is the MOF-5 material, specifically its chemical stability in air. The MOF-5 material has a large pore size of 8 Å, and aperture sizes of 15 and 12 Å. The pore size, pore functionality, and physically stable structure makes MOF-5 a desirable material. MOF-5 holds applications in gas/liquid separation, catalysis, and gas storage. The main problem with the MOF-5 material, however, is its instability in atmospheric air. This inherent instability is due to the water in air binding to the zinc-oxide core, effectively changing the material and its structure. Because of this material weakness, the MOF-5 material is difficult to be utilized in industrial applications. Through the research efforts proposed by this study, the stability of the MOF-5 powder and membrane were studied. MOF-5 powder and a MOF-5 membrane were synthesized and characterized using XRD analysis. In an attempt to improve the stability of MOF-5 in air, methyl groups were added to the organic linker in order to hinder the interaction of water with the Zn4O core. This was done by replacing the terepthalic acid organic linker with 2,5-dimethyl terephthalic acid in the powder and membrane synthesis steps. The methyl-modified MOF-5 powder was found to be stable after several days of exposure to air while the MOF-5 powder exhibited significant crystalline change. The methyl-modified membrane was found to be unstable when synthesized using the same procedure as the MOF-5 membrane.
ContributorsAnderson, Anthony David (Author) / Lin, Jerry Y.S. (Thesis director) / Ibrahim, Amr (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Microbial fuel cells (MFCs) promote the sustainable conversion of organic matter in black water to electrical current, enabling the production of hydrogen peroxide (H2O2) while making waste water treatment energy neutral or positive. H2O2 is useful in remote locations such as U.S. military forward operating bases (FOBs) for on-site tertiary water treatment or as a medical disinfectant, among many other uses. Various carbon-based catalysts and binders for use at the cathode of a an MFC for H2O2 production are explored using linear sweep voltammetry (LSV) and rotating ring-disk electrode (RRDE) techniques. The oxygen reduction reaction (ORR) at the cathode has slow kinetics at conditions present in the MFC, making it important to find a catalyst type and loading which promote a 2e- (rather than 4e-) reaction to maximize H2O2 formation. Using LSV methods, I compared the cathodic overpotentials associated with graphite and Vulcan carbon catalysts as well as Nafion and AS-4 binders. Vulcan carbon catalyst with Nafion binder produced the lowest overpotentials of any binder/catalyst combinations. Additionally, I determined that pH control may be required at the cathode due to large potential losses caused by hydroxide (OH-) concentration gradients. Furthermore, RRDE tests indicate that Vulcan carbon catalyst with a Nafion binder has a higher H2O2 production efficiency at lower catalyst loadings, but the trade-off is a greater potential loss due to higher activation energy. Therefore, an intermediate catalyst loading of 0.5 mg/cm2 Vulcan carbon with Nafion binder is recommended for the final MFC design. The chosen catalyst, binder, and loading will maximize H2O2 production, optimize MFC performance, and minimize the need for additional energy input into the system.
ContributorsStadie, Mikaela Johanna (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2015-05
Description
In this Honors thesis, direct flame solid oxide fuel cells (DFFC) were considered for their feasibility in providing a means of power generation for remote powering needs. Also considered for combined heat and fuel cell power cogeneration are thermoelectric cells (TEC). Among the major factors tested in this project for all cells were life time, thermal cycle/time based performance, and failure modes for cells. Two types of DFFC, anode and electrolyte supported, were used with two different fuel feed streams of propane/isobutene and ethanol. Several test configurations consisting of single cells, as well as stacked systems were tested to show how cell performed and degraded over time. All tests were run using a Biologic VMP3 potentiostat connected to a cell placed within the flame of a modified burner MSR® Wisperlite Universal stove. The maximum current and power output seen by any electrolyte supported DFFCs tested was 47.7 mA/cm2 and 9.6 mW/cm2 respectively, while that generated by anode supported DFFCs was 53.7 mA/cm2 and 9.25 mW/cm2 respectively with both cells operating under propane/isobutene fuel feed streams. All TECs tested dramatically outperformed both constructions of DFFC with a maximum current and power output of 309 mA/cm2 and 80 mW/cm2 respectively. It was also found that electrolyte supported DFFCs appeared to be less susceptible to degradation of the cell microstructure over time but more prone to cracking, while anode supported DFFCs were dramatically less susceptible to cracking but exhibited substantial microstructure degradation and shorter usable lifecycles. TECs tested were found to only be susceptible to overheating, and thus were suggested for use with electrolyte supported DFFCs in remote powering applications.
ContributorsTropsa, Sean Michael (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2014-05
Description
Microbial fuel cells (MFCs) facilitate the conversion of organic matter to electrical current to make the total energy in black water treatment neutral or positive and produce hydrogen peroxide to assist the reuse of gray water. This research focuses on wastewater treatment at the U.S. military forward operating bases (FOBs). FOBs experience significant challenges with their wastewater treatment due to their isolation and dangers in transporting waste water and fresh water to and from the bases. Even though it is theoretically favorable to produce power in a MFC while treating black water, producing H2O2 is more useful and practical because it is a powerful cleaning agent that can reduce odor, disinfect, and aid in the treatment of gray water. Various acid forms of buffers were tested in the anode and cathode chamber to determine if the pH would lower in the cathode chamber while maintaining H2O2 efficiency, as well as to determine ion diffusion from the anode to the cathode via the membrane. For the catholyte experiments, phosphate and bicarbonate were tested as buffers while sodium chloride was the control. These experiments determined that the two buffers did not lower the pH. It was seen that the phosphate buffer reduced the H2O2 efficiency significantly while still staying at a high pH, while the bicarbonate buffer had the same efficiency as the NaCl control. For the anolyte experiments, it was shown that there was no diffusion of the buffers or MFC media across the membrane that would cause a decrease in the H2O2 production efficiency.
ContributorsThompson, Julia (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The removal of support material from metal 3D printed objects is a laborious necessity for the post-processing of powder bed fusion printing (PBF). Supports are typically mechanically removed by machining techniques. Sacrificial supports are necessary in PBF printing to relieve thermal stresses and support overhanging parts often resulting in the inclusion of supports in regions of the part that are not easily accessed by mechanical removal methods. Recent innovations in PBF support removal include dissolvable metal supports through an electrochemical etching process. Dissolvable PBF supports have the potential to significantly reduce the costs and time associated with traditional support removal. However, the speed and effectiveness of this approach is inhibited by numerous factors such as support geometry and metal powder entrapment within supports. To fully realize this innovative approach, it is necessary to model and understand the design parameters necessary to optimize support structures applicable to an electrochemical etching process. The objective of this study was to evaluate the impact of block additive manufacturing support parameters on key process outcomes of the dissolution of 316 stainless steel support structures. The parameters investigated included hatch spacing and perforation, and the outcomes of interests included time required for completion, surface roughness, and effectiveness of the etching process. Electrical current was also evaluated as an indicator of process completion. Analysis of the electrical current throughout the etching process showed that the dissolution is diffusion limited to varying degrees, and is dependent on support structure parameters. Activation and passivation behavior was observed during current leveling, and appeared to be more pronounced in non-perforated samples with less dense hatch spacing. The correlation between electrical current and completion of the etching process was unclear, as the support structures became mechanically removable well before the current leveled. The etching process was shown to improve surface finish on unsupported surfaces, but support was shown to negatively impact surface finish. Tighter hatch spacing was shown to correlate to larger variation in surface finish, due to ridges left behind by the support structures. In future studies, it is recommended current be more closely correlated to process completion and more roughness data be collected to identify a trend between hatch spacing and surface roughness.
ContributorsAbranovic, Brandon (Author) / Hildreth, Owen (Thesis director) / Torres, Cesar (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Metal-organic frameworks (MOFs) are a new set of porous materials comprised of metals or metal clusters bonded together in a coordination system by organic linkers. They are becoming popular for gas separations due to their abilities to be tailored toward specific applications. Zirconium MOFs in particular are known for their high stability under standard temperature and pressure due to the strength of the Zirconium-Oxygen coordination bond. However, the acid modulator needed to ensure long range order of the product also prevents complete linker deprotonation. This leads to a powder product that cannot easily be incorporated into continuous MOF membranes. This study therefore implemented a new bi-phase synthesis technique with a deprotonating agent to achieve intergrowth in UiO-66 membranes. Crystal intergrowth will allow for effective gas separations and future permeation testing. During experimentation, successful intergrown UiO-66 membranes were synthesized and characterized. The degree of intergrowth and crystal orientations varied with changing deprotonating agent concentration, modulator concentration, and ligand:modulator ratios. Further studies will focus on achieving the same results on porous substrates.
ContributorsClose, Emily Charlotte (Author) / Mu, Bin (Thesis director) / Shan, Bohan (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Corrosion is one of the key failure modes for stainless steel (SS) piping assets handling water resources managed by utility companies. During downtime, the costs start to incur as the field engineer procures its replacement parts. The parts may or may not be in stock depending on how old, complex, and common the part model is. As a result, water utility companies and its resilience to operate amid part failure are a strong function of the supply chain for replacement piping. Metal additive manufacturing (AM) has been widely recognized for its ability to (a) deliver small production scales, (b) address complex part geometries, (c) offer large elemental metal and alloy selections, (d) provide superior material properties. The key motive is to harvest the short lead time of metal AM to explore its use for replacement parts for legacy piping assets in utility-scale water management facilities. In this paper, the goal was to demonstrate 3D printing of stainless steel (SS) 316L parts using selective laser melting (SLM) technology. The corrosion resistance of 3D printed SS 316L was investigated using (a) Chronoamperometry (b) Cyclic Potentiodynamic Polarization (CPP) and Electrochemical Impedance Spectroscopy (EIS) and its improved resistance from wrought (conventional) part was also studied. Then the weldability of 3D printed SS 316L to wrought SS 316L was illustrated and finally, the mechanical strength of the weld and the effect of corrosion on weld strength was investigated using uniaxial tensile testing. The results show that 3D printed part compared to the wrought part has a) lower mass loss before and after corrosion, (b) higher pitting potential, and (c) higher charge transfer resistance. The tensile testing of welded dog bone specimens indicates that the 3D printed parts despite being less ductile were observed to have higher weld strength compared to the wrought part. On this basis, metal AM holds great value to be explored further for replacement piping parts owing to their better corrosion resistance and mechanical performance.
ContributorsSampath, Venkata Krishnan (Author) / Azeredo, Bruno (Thesis advisor) / Torres, Cesar (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2021
Description
Ionic liquids boast a wide variety of application as modern electrolytes. Their unique collection of attributes, most notably insignificant vapor pressures, considerable ionic conductivity, and excellent thermal stability, prove ionic liquids excellent candidates for low-temperature electrolyte applications. This project focuses on the development of a low-temperature iodide-based ionic liquid electrolyte for a molecular electronic transducer (MET) seismometer. Based on ionic liquid 1-butyl-3-methylimidazolium iodide ([BMIM][I]), a functional electrolyte system is developed and optimized with addition of organic solvents, gamma-butyrolactone (GBL) and propylene carbonate (PC), and lithium iodide, showing the promise of operating at excessively low temperatures. The molecular interactions between [BMIM][I] and the organic solvents were classified using FTIR and 1H NMR spectroscopy. Specifically, the presence of hydrogen bonding between the carbonyl group on the organic solvents and the [BMIM]+ cation were captured. The effect of these interactions on several electrolyte properties were observed, including an extended glass transition temperature (Tg) of -120.2 °C and enhanced transport properties. When compared to the previous formulations, the optimized electrolyte exhibits a broader working temperature range, a higher fluidity over the temperature range from 25°C to -75 °C, and an enhanced ionic conductivity at temperatures below -70 °C as suggested by the Vogel–Fulcher–Tammann (VFT) model. Cyclic voltammetry (CV) confirmed the electrochemical stability of the electrolyte as well as the activity of the I3- / I- redox reaction for the MET sensing technology at room temperature. The presented works not only present a facile strategy of designing low-temperature electrolyte systems via design of molecular interactions, but also support future operations of MET seismometer.
ContributorsMacdonald, Shaun Michael (Author) / Dai, Dr. Lenore L. (Thesis director) / Lin, Wendy (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
As Energy needs grow and photovoltaics expand to meet humanity’s demand for electricity, waste modules will start building up. Tao et. al. propose a recycling process to recover all precious solar cell materials, a process estimated to generate a potential $15 billion in revenue by 2050. A key part of this process is metal recovery, and specifically, silver recovery. Silver recovery via electrowinning was studied using a hydrofluoric acid leachate/electrolyte. Bulk electrolysis trials were performed at varied voltages using a silver working electrode, silver pseudo-reference electrode and a graphite counter-electrode. The highest mass recovery achieved was 98.8% which occurred at 0.65 volts. Product purity was below 90% for all trials and coulombic efficiency never reached above 20%. The average energy consumption per gram of reduced silver was 2.16kWh/kg. Bulk electrolysis indicates that parasitic reactions are drawing power from the potentiostat and limiting the mass recovery of the system. In order to develop this process to the practical use stage, parasitic reactions must be eliminated, and product purity and power efficiency must improve. The system should be run in a vacuum environment and the reduction peaks in the cell should be characterized using cyclic voltammetry.
ContributorsTezak, Cooper R (Author) / Tao, Meng (Thesis director) / Phelan, Patrick (Committee member) / Chemical Engineering Program (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12
Description
Optimizing cathodes for microbial fuel cells is important to maximize energy harvested from wastewater. Cathodes were made by modifying a recipe from previous literature and testing the current of the cathode using linear sweep voltammetry. The cathodes contained an Fe-N-C catalyst combined with a Polytetrafluoroethylene binder. Optimizing the power resulting from the microbial fuel cells will help MFCs be an alternative energy source to fossil fuels. The new cathodes did improve in current production from −16 𝐴/𝑚 to −37 𝐴/𝑚 at -0.4 V. When fitted using a Butler-Volmer model, the cathode linear-sweep voltammograms did not follow the expected exponential trend. These results show a need for more research on the cathodes and the Butler-Volmer model, and they also show that the cathode is ready for further and longer application in a microbial fuel cell.
ContributorsRussell, Andrea Christine (Author) / Torres, Cesar (Thesis director) / Young, Michelle (Committee member) / School of Sustainable Engineering & Built Envirnmt (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05