PRISM :: Browsing by Author "Birss, Viola"

Browsing by Author "Birss, Viola"

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Open Access
Carbon Formation on Stainless Steel 304H in the Convection Section of an Ethane Cracking Plant
(Taylor & Francis, 2015) Ramezanipour, Farshid; Singh, Anand; Paulson, Scott; Farag, Hany; Birss, Viola; Thangadurai, Venkataraman
Open Access
Ceria-Based Anodes for Next Generation Solid Oxide Fuel Cells
(2015-05-01) Mirfakhraei, Behzad; Birss, Viola; Thangadurai, Venkataraman
Mixed ionic and electronic conducting materials (MIECs) have been suggested to represent the next generation of solid oxide fuel cell (SOFC) anodes, primarily due to their significantly enhanced active surface area and their tolerance to fuel components. In this thesis, the main focus has been on determining and tuning the physicochemical and electrochemical properties of ceria-based MIECs in the versatile perovskite or fluorite crystal structures. In one direction, BaZr0.1Ce0.7Y0.1M0.1O3-δ (M = Fe, Ni, Co and Yb) (BZCY-M) perovskites were synthesized using solid-state or wet citric acid combustion methods and the effect of various transition metal dopants on the sintering behavior, crystal structure, chemical stability under CO2 and H2S, and electrical conductivity, was investigated. BZCY-Ni, synthesized using the wet combustion method, was the best performing anode, giving a polarization resistance (RP) of 0.4 Ω.cm2 at 800 oC. Scanning electron microscopy and X-ray diffraction analysis showed that this was due to the exsolution of catalytic Ni nanoparticles onto the oxide surface. Evolving from this promising result, the effect of Mo-doped CeO2 (nCMO) or Ni nanoparticle infiltration into a porous Gd-doped CeO2 (GDC) anode (in the fluorite structure) was studied. While 3 wt. % Ni infiltration lowered RP by up to 90 %, giving 0.09 Ω.cm2 at 800 oC and exhibiting a ca. 5 times higher tolerance towards 10 ppm H2S, nCMO infiltration enhanced the H2S stability by ca. 3 times, but had no influence on RP. In parallel work, a first-time study of the Ce3+ and Ce4+ redox process (pseudocapacitance) within GDC anode materials was carried out using cyclic voltammetry (CV) in wet H2 at high temperatures. It was concluded that, at 500-600 oC, the Ce3+/Ce4+ reaction is diffusion controlled, probably due to O2- transport limitations in the outer 5-10 layers of the GDC particles, giving a very high capacitance of ca. 70 F/g. Increasing the temperature ultimately diminished the observed capacitance, likely as the chemical reduction of GDC at high temperatures is irreversible.
Open Access
Development and Mechanistic Analysis of Novel CO2 Reduction Electrocatalysts
(2023-01-13) Dubrawski, Zachary Sachiel; Piers, Warren; Roesler, Roland; Birss, Viola; Herbert, David; Ponnurangam, Sathish
The ever-growing anthropogenic concentrations of CO2 in our atmosphere has led to an entire industry centered around Carbon Capture and Utilization (CCU). One central pillar of the CCU ideology is the conversion of captured CO2 to “value-added” products such as carbon monoxide, formic acid, or commercial products such as plastics or vodka. However, the technologies that this industry rely on are not robust with suspect surface characterization and transient catalytically active sites. Solution phase molecular electrocatalysts are inherently impractical for industrial-scale CO2 conversion due to several complicating factors. However, the insights and knowledge developed from these homogeneous systems can often be directly utilized within industrial-scale heterogeneous electrolyzers with dramatic improvements to catalytic efficacy. Therefore, through the study of homogeneous systems, significant progress can be potentially made towards the effective valorization of CO2. With this in mind, the research outlined in this thesis details the development, exploration and mechanistic analysis of a range of novel CO2RR electrocatalysts with a special focus on earth abundant systems. Using ligand design principles developed through the literature, novel ligands were explored and CO2 reduction capabilities investigated. Once a promising target was identified, an intense mechanistic analysis was undertaken using spectroelectrochemistry and chemical reduction studies to identify and characterize key intermediates in the catalytic cycle. Through this analysis we have confirmed ideas on the importance of redox non-innocent ligands and developed new design principles centered around structural torsional strain. These insights provide value to developing next generation CO2RR electrocatalysts.
Open Access
Development and Microscaling of a Novel Glucose Biosensor for Application in a Minimally Invasive Sampling Platform
(2014-04-01) Jones, Tristan; Mintchev, Martin; Birss, Viola; Kaler, Karan
Diabetes Mellitus is approaching epidemic proportions in North America and many regions in the world. Current treatment involves self-monitoring of blood glucose levels by analysis of a blood sample obtained by "finger-pricking". This suffers from non-compliance, and samples at a rate much lower than the Shannon frequency of blood glucose levels. The e-Mosquito provides near-painless sampling, is apply-and-forget, and provides a higher sampling rate. This thesis concerns miniaturiziation of a novel glucose transducer, for integration in the e-Mosquito, that consists of iridium and glucose oxidase on a gold electrode, and which obeys Michaelis-Menten kinetics and were characterized using their Imax and Km values. The sensor includes this transducer, a micropotentiostat, a power supply, and an ADC that communicates with the e-Mosquito microprocessor. Testing of the transducer showed current densities of 250-400 uA/cm2, though with high inter-transducer variability. The potentiostat was also characterized and demonstrated to have adequate sensitivity and bandwidth.
Open Access
Development of Fuel Electrodes for Reversible Solid Oxide Fuel Cell Applications
(2017) Addo, Paul; Birss, Viola; Marriott, Robert; Thangadurai, Venkataraman; Shi, Yujun; Pagnier, Thierry
The stability, sulfur tolerance, and electrochemical performance of Ni-YSZ (yttria-stabilized zirconia) composites and single phase La0.3M0.7Fe0.7Cr0.3O3-δ (M = Sr, Ca, (LMFCr)) perovskites, for use as fuel electrodes for reversible solid oxide fuel cell (RSOFC) applications, were investigated in detail. RSOFCs are electrochemical devices that can be operated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. Although Ni-YSZ is the most common fuel electrode for RSOFC applications, it is prone to sulfur poisoning in ppm H2S levels at operating temperatures > 650 oC, thereby decreasing the rate of the hydrogen oxidation/reduction reaction (HOR/HER). It is shown that, at ≤ 650 oC, exposure of Ni-YSZ to ≤ 10 ppm H2S unexpectedly enhanced the HOR activity, while at higher temperatures, conventional Ni poisoning was seen. It was concluded that the activation behaviour at ≤ 650 oC was due to the formation of a catalytic Ni-S species (e.g., Ni3S2) at the triple phase boundary where the HOR/HER occurs. The sulfur tolerance of LCFCr electrodes was also investigated in H2 + low ppm H2S, with LCFCr showing the inverse behavior of Ni/YSZ. At > 700 oC, exposure of LCFCr to ≤ 10 ppm H2S activated the HOR/HER, while deactivation was seen at ≤ 700 oC. It was concluded that exposure of LCFCr to H2S at higher temperatures led to an increase in the density of surface FeO2 terminated species, the proposed active site for the HOR/HER. The LSFCr materials were also shown, for the first time, to be very active (comparable or better than other oxide materials (e.g., La1-xSrxCr1-yMnyO3-δ)) and stable electrocatalysts in CO/CO2 gas environments in both the SOFC and SOEC reaction directions at 600-800 oC. LSFCr was shown to be structurally stable in pure CO2 and 70% CO2:30% CO mixtures at 800 oC, with no major impurities detected. Also, extensive electrochemical characterization, based on both 2-electrode and 3-electrode full and half cell configurations, showed that LSFCr was more active as an electrocatalyst for the reduction of CO2 than for the oxidation of CO. Furthermore, it was found that the surface interaction of CO2 with LSFCr (adsorption, dissociation, electron transfer) was the slowest step in the reaction, relative to oxide ion transport processes.
Open Access
Development of Non-Noble Metal Oxygen Reduction Catalysts for PEM Fuel Cell Applications
(2014-06-27) Gharaibeh, Samar Ayesh Mousa; Birss, Viola
Proton exchange membrane fuel cells (PEMFCs) demonstrate great promise as low emission, high efficiency power sources. However, the sluggish kinetics of the oxygen reduction reaction (ORR) causes large voltage losses at the cathode. There is thus a need for an active ORR catalyst, preferably lower in cost than the most active catalyst known, Pt. Therefore, the primary goal of this work is the development of a low cost, non-noble metal-based ORR catalyst for PEMFC applications. The secondary goal of this work is to better understand and improve the ORR kinetics at these catalysts, as well as to gain insight into the nature of the active site. The catalysts investigated here have been formed using a modified sol-gel synthesis approach, in which carbon and nitrogen were introduced as specific ligands (ethylenediamine (EN) or o-phenylenediamine (oPDA)) to the metals (Co or Fe) used in the synthesis. After deposition on high surface area carbon supports and heat-treatment, these materials are found to be very active towards the ORR in both acidic and alkaline media. A wide range of methods were used to evaluate the catalysts, including cyclic voltammetry, quartz crystal microbalance, scanning electron microscopy (SEM), x-ray photoelectron microscopy (XPS), Auger Electron Spectroscopy (AES), and more. It was found that the best results were obtained when using oPDA and Fe as the precursors and then heat-treating at 900 oC for 2 h under N2, resulting in a catalyst only a little less active than Pt, with almost no H2O2 produced. It was also found that using the polymeric analogue of oPDA and supporting the precursors on acid leached carbon instead of as-received carbon gave the best ORR activity in both acidic and alkaline media. According to this thesis work, it was found that polymeric oPDA, formed either thermally or by pre-polymerization methods, decomposes at pyrolysis temperatures higher than 700 oC, forming ORR-active N sites that may also contain Fe. It was also found from XPS analysis that the N-species are in the form of graphitic and pyridinic sites embedded into the graphene structure, giving very good ORR performance. XPS also showed the presence of Fe2+/3+, which could be chelated to N as FeNx moieties. The microporosity of these types of catalysts was also shown to be essential, where high ORR catalytic activity was achieved for materials with a high micropore surface area. All of these results suggest that the FeNx moieties are hosted and stabilized in the micropores of the carbon support.
Open Access
Development of Novel Nanoporous Carbon Scaffolds for PEMFC Applications
(2021-03-26) Atwa, Marwa H; Birss, Viola I; Birss, Viola; Karan, Kunal; Roesler, Roland; Ponnurangam, Sathish; Gasteiger, Hubert
The microstructure of conventional polymer electrolyte fuel cell (PEMFC) catalyst layers (CLs) consists of a mixture of high surface area carbon powder, Pt or Pt alloy nanoparticles (NPs), and an ionomer, which acts as a binder and a proton-conducting electrolyte. These CLs contain complex pathways and a poorly controlled distribution of Pt NPs and ionomer, which can cause kinetic and transport limitations for the oxygen reduction reaction (ORR). Therefore, we have developed a self-supported, robust, and binderless carbon membrane with an ordered, tunable pore structure, namely the nanoporous carbon scaffold (NCS). The NCS films have a high surface area (200-610 m2/g), ultra-low tortuosity (close to 1), high porosity (ca. 90%) and electrical conductivity (? 2 S/cm), and excellent 3-dimensional scalability (1-150+ cm2 demonstrated area, 1-1000 µm thickness). Herein, the effect of the microstructure of various NCS materials, loaded with both catalytic Pt NPs and ionomer, on the kinetics of the oxygen reduction reaction (ORR), which is the rate limiting reaction in PEMFCs, was explored. Two different methods of Pt NP loading (wet impregnation and atomic layer deposition (ALD)) were examined and two types of NCS films with two different structures (monodisperse and bimodal pore size distributions) were prepared and then integrated into a membrane electrode assembly (MEA) as a PEMFC cathode. For the Pt-loaded NCS films with monodisperse pore sizes (uniform pore size distribution with a standard deviation of ± 10-15%) of either 22, 50, or 85 nm, it was found that ALD Pt loading results in a much narrower NP size distribution than wet impregnation, and that the ALD-Pt/NCS85 catalysts out-perform the ALD-Pt/NCS22 materials, likely as Nafion can better penetrate the larger pores to provide proton conductivity. The much smaller neck diameter may be the real problem, where it was shown that larger neck diameters, keeping all other factors constant, can significantly lower the mass transport resistance. The bimodal NCS12 films possess a Craspedia (flower)-like structure, with the spheres (~900 nm) fully saturated with close-packed 12 nm primary pores and connected to neighboring spheres through non-porous carbon fibers, leaving ~ 0.25 µm secondary pores between the spheres. It was found that the 12 nm pores contain the vast majority of the highly dispersed ca. 2-3 nm Pt NPs, and yet contain no Nafion, thus indicating that water must be conducting protons in these pores during the ORR. These Pt NPs also show signs of surface strain, perhaps contributing to their high ORR activity. These factors, including the absence of blocking or poisoning of the Pt NPs by Nafion, have resulted in an extraordinary ORR mass activity (0.58 ± 0.1 A/mgPt), retained after 10k ADT cycles, and a very high limiting current of close to 2.7 A/cm2 in MEA cathode studies.
Open Access
Development of Oxygen Electrodes for Reversible Solid Oxide Fuel Cells
(2017) Molero Sánchez, Beatriz; Birss, Viola; Trudel, Simon; Thangadurai, Venkataraman; Ponnurangam, Sathish; Barnett, Scott
The primary focus of this thesis has been to develop high performance stable oxygen electrodes, with a primary emphasis on a mixed conducting La0.3Ca0.7Cr0.3Fe0.7O3-δ (LCFCr) perovskite, for use in advanced reversible solid oxide fuel cells (RSOFCs). RSOFCs are single unit electrochemical devices that can operate in both the fuel cell (SOFC) and electrolysis (SOEC) mode, thus acting as flexible and efficient energy conversion systems. The interest in LCFCr arose from earlier work with LSFCr (La0.3Sr0.7Cr0.3Fe0.7O3-δ), shown to be a very promising SOFC cathode. Thus, this thesis began with a rigorous study of the oxygen evolution (OER) and reduction (ORR) reactions at the LSFCr material, including understanding how to interpret the electrochemical results. However, LSFCr has a thermal expansion coefficient (TEC) that does not match with common solid electrolytes and thus its long time stability is questionable. For this reason, the Ca analogue (LCFCr), a new electrode material, was synthesized and shown to have a much more suitable TEC. Extensive 2-electrode and 3-electrode half-cell studies revealed two slow steps during the OER and ORR, including oxygen/LCFCr surface reactions and O2- transfer at the LCFCr/electrolyte interface. It was also shown that LCFCr is more active in the electrolysis mode (OER) than in the SOFC mode (ORR). Further, the infiltration of ceria or co-infiltration of ceria+LCFCr led to substantial improvements in LCFCr performance, also providing further insights into the processes that control the reaction rates. It was shown that, after 200 h of operation in either the SOFC or SOEC modes, the main source of degradation was from the series resistance (the LCFCr/Au current collector interface), suggestive of Au sintering. The low frequency process, related to the LCFCr/air interface, also deteriorated somewhat, while the underlying LCFCr/electrolyte interface remained stable. This was confirmed from both electrochemistry and high-resolution TEM, showing the retention of a very high quality interface at the atomic level. A novel and very promising SOC powder and cell sintering methodology was also developed using microwave technology, significantly lowering the manufacturing temperature, processing, and energy requirements, due also to the much lower energy demand of the MW furnace. This translates to significant manufacturing cost savings, making MW processing of complete solid oxide cells a promising route for the future.
Open Access
Electrochemical Formation and Optimization of Ta-based Nanomaterials
(2015-09-28) Horwood, Corie; Birss, Viola
The primary focus of this research has been to develop simple and precise methods for the formation of novel Ta-based nanostructures, including Ta oxide nanotubes (NTs) and Ta-supported Au nanoparticle (NP) arrays. These nanomaterials are very useful for applications in sensing, electrocatalysis/catalysis, spectroscopy, and more. The Ta oxide NTs are formed by the electrochemical anodization of Ta, a process which can be modified to produce ordered nanoscale dimples that cover the Ta surface. These dimples can then be used as templates for the formation of ordered Au nanoparticle arrays. An in-depth study of the anodization variables showed that NT growth can be slowed down by decreasing the anodization time and HF concentration in the solution, allowing the controlled formation of short (50-1000 nm) NTs in under one minute. The charge passed during anodization was found to be directly proportional to the length of the NTs formed, making cross-sectional imaging unnecessary. A novel two-step anodization method, interspersed with a thermal annealing or negative polarization step, produced stable and well-ordered NTs free of a problematic thin surface oxide layer. These vertically oriented arrays of short NTs were found to have interesting optical properties, with visible structural colours that depend on NT length. The colour of the NT arrays was also found to depend on the medium inside the NTs (air, water, other solids), used for the first time to monitor NT filling, and to determine the refractive index and porosity of the Ta oxide nanotubular array, properties that are otherwise very difficult to obtain. Dimpled Ta was used to create ordered Au NP arrays using two thin film dewetting methods, thermal annealing and pulsed laser-induced dewetting. These methods yield Au NPs of predictable size, shape, spacing, and surface density, with these parameters varying predictably with the initial thickness of the Au thin film and the technique used for dewetting. The Au NPs formed particularly by thermal dewetting were found to be electrochemically addressable, giving another measure of Au surface area and serving as promising materials for future electrochemical applications.
Open Access
Enhancing the Durability of the Cathode Layer (Pt/C) in PEM Fuel Cells
(2017) Forouzandeh, Farisa; Birss, Viola; Creager, Stephen; Hinman, Scott; Thangadurai, Venkataraman; Welch, Gregory
Although proton exchange membrane (PEM) fuel cells are among the most advanced types of fuel cells, cost and durability are still hindering their deployment at a large scale. The durability of the catalyst layer (CL) components, including catalytic Pt nanoparticles (NPs) dispersed on a high surface area carbon support, is critical for the commercialization of this technology. However, conventional carbon supports are susceptible to corrosion during PEM fuel cell operation. Thus, the main goal of this thesis work was to understand and improve the durability of various novel carbon materials for their use in the cathode CL. Most of the durability testing carried out here was done on bare carbons, without interference from Pt, and thus the work also has relevance to other electrochemical devices (e.g., redox flow batteries, capacitors, etc.), which also employ carbon electrodes. The key contributions of this thesis work include the development of a reliable corrosion testing and evaluation protocol, applied initially to ordered mesoporous carbons (OMCs) and microporous Vulcan carbon (VC)). This involved the analysis of the current-time data collected during potential stepping in 0.5 M H2SO4, with continuous correction for the electrochemically accessible carbon surface area. The corrosion products include CO2, with no or very little O2 produced, as well as a passive oxide layer on the carbon surface. Cyclic voltammetry was also employed to reveal surface area changes, as well as the extent of surface oxidation as a result of the corrosion reactions. This thesis also focussed on increasing the corrosion resistance of colloid-imprinted carbon (CIC-x) powders (x=12-50 nm pore size) and VC. Heat-treatment of these carbons improved their corrosion resistance by 40-60%. Although the attachment of aminophenyl (–PhNH2) and nitrophenyl groups to the CIC-22 surface did not improve the corrosion resistance, –PhNH2 did help to nucleate the Pt NPs. In comparison, surface functionalization of VC and CIC-22 with pentafluorophenyl groups improved their corrosion resistance by ca. 50%. Heat-treatment of a self-supported nanoporous carbon scaffold (85 nm pore size, NCS-85) increased the corrosion resistance with/without Pt loading, with corrosion being more severe in 60 °C 0.5 M H2SO4 than at room temperature.
Open Access
Evaluation of MIEC Ce0.8Y0.1Mn0.1O2-δ Anode in Electrolyte-Supported SOFC
(Electrochemical Society, 2016) Handal, Hala T.; Addo, Paul; Buyukaksoy, Aligul; Birss, Viola; Thangadurai, Venkataraman
Open Access
Friction and Adhesion of Atomically Thin Films: A Study of Few-layer Graphene
(2017) Gong, Peng; Egberts, Philip; Egberts, Philip; Birss, Viola; Karan, Kunal; Federico, Salvatore
In order to gain better insight on the fundamental mechanisms governing friction and adhesion at the nanoscale, this thesis examines the friction and adhesion properties and mechanisms on the atomically-thin material, graphene. First, through conducting load dependent measurements of friction on mechanical exfoliated graphene samples, the dependence of the friction behaviour on graphene as a function of number of graphene layers, sliding history, environmental humidity, and air exposure time were examined. A mechanism was proposed to fully explain these experimental observations. Secondly, the finite element method (FEM) was applied to investigate the adhesion between a nanoscale tip and graphene covering a silicon substrate. The simulations, contrary to prior experimental results, showed a slight increase in the pull-off force as layer number increased. In addition, it was revealed that the layer-dependent pull-off forces result from the increasing tipgraphene interactions. This work contributes to gaining better insight on the applications to the lubrication mechanisms of graphene.
Open Access
Greenhouse Gas Detection Using Metal Oxides: Experiments and Challenges
(2016) Mulmi, Suresh; Thangadurai, Venkataraman; Etsell, Thomas; Birss, Viola; Shimizu, George; Almao, Pedro
The primary goal of this study has been to develop the mixed ion-electron conductors (MIECs) to illustrate their potential applications for real-time detection of CO2 and SO2 in ppm level. For this purpose, B-site substituted ordered perovskite-type MIECs Ba2(Ca0.66Nb1.34-xFex)O6-δ (x = 0, 0.34, 0.66, 1) (BCNF) and B-site disordered MIECs Ba(Mg0.33Nb0.67-xFex)O3-δ (x = 0, 0.17, 0.33, 0.50) (BMNF) were successfully synthesized by conventional solid state method in air at 1400 °C. Fe-substitution in BCNFs and BMNFs increased the total conductivity, while in-situ high temperature (25–800 °C) PXRD results under CO2 exhibited excellent chemical stability. The resistance of the MIEC ceramics significantly decreased upon exposure to CO2 gas in synthetic air. Response time (t90) of 4 min at 700 °C was obtained with higher Fe-content samples with thickness of 2 mm and diameter of 10 mm. To develop a fundamental understanding of the sensing mechanism, Fe-doped BCNFs were investigated. Firstly, p-type bulk semiconducting nature of BCNF was explored using AC impedance spectroscope and DC measurements using different p(CO2) and p(O2). Secondly, BCNFs were further studied using SEM coupled with EDX, 57Fe Mössbauer spectroscopy, Raman spectroscopy, TPO-MS. Upon CO2 exposure, CO2 was found to be catalytically reduced to C and can be explained using oxidation of Fe3+ to Fe4+/ Fe5+. Thus, the increase in total conductivity upon CO2 exposure is interpreted by the deposition of conducting graphitic C, which was confirmed using Raman spectra and TPO-MS. Furthermore; SEM/EDX results displayed the deposited C due to the reduction of CO2. For SO2 sensors, SnO2-TiO2 (S-T) composites with different molar ratios were also prepared at 700 °C in air to selectively monitor ppm level of SO2 in air. For S-T composites, the chemical stability were tested using PXRD, SEM and EDX, while the sensing performance was measured at different temperatures using various concentrations of SO2 (10-100 ppm). The highest sensitivity was obtained from a mixture of 25 mol.% of SnO2 and 75 mol.% ofTiO2 at 450 °C with t90 of ~5 mins. S-T composite sensors behave as a resistive-type SO2 sensor and sensing mechanism has been explained through the band structure model.
Open Access
Interweaving Computational Chemistry and Visualization: Explorations into Molecular Processes, Simulation Analysis, and Visualization Design
(2017) Hall, Kyle; Kusalik, Peter; Carpendale, Sheelagh; Birss, Viola; Molinero, Valeria; Ebert, David; Patey, Grenfell
This thesis is a three-part exploration of both chemistry and computer science through the interweaving of computational chemistry and visualization in a research context. Motivating overarching themes in this thesis include the use of chemical simulations to advance chemical understanding, and visualization as a tool to help bridge the gap between possessing chemical simulation data and advancing chemical understanding. In Part I of this thesis, a set of novel visualizations are introduced to address data analysis challenges in the context of Molecular Dynamics simulations. Through these visualizations, aqueous hydroxyl radical chemistry is advanced (e.g., through characterization of a hydroxyl radical reaction), and concepts relevant to future chemical visualizations are revealed. In Part II, extensive simulations, detailed data analysis, and visualization are then combined to probe gas hydrate formation (a crystallization process amenable to simulation, and yet not fully understood). This work demonstrates that gas hydrate formation involves funnel-shaped potential energy landscapes, that the evolution of nascent hydrate phases can be structurally biased, and that microscopic details (e.g., guest-host interactions) can apparently impact behavior and composition of nascent mixed hydrate phases. The concepts of funnel-shaped potential energy landscapes and biased evolution are relevant to scientific understanding of crystallization more broadly beyond formation of gas hydrates. In order to support others as they design visualizations, Part III explores the role of emphasis in visualization, and introduces an alternative design approach for problem-driven visualization work. In addition to advancing chemical understanding and visualization, this thesis provides evidence that novel visualizations can help bridge the gap between possessing chemical data and achieving chemical understanding. This thesis is thus a multifaceted interdisciplinary exploration and discussion of chemical processes, visualizations and their role in chemical research, and visualization design.
Open Access
Ir-core Pt-shell Nanoparticles for the Electro-oxidation of Ethanol
(2018-12-06) Slaby, Jachym; Birss, Viola; Shi, Yujun J.; Karan, Kunal; Heyne, Belinda J. M.
This work was conducted in order to establish the behavior of Ir@Pt core@shell nanoparticles (NPs) during the catalysis of the ethanol oxidation reaction (EOR). Ir@Pt catalysts with < 1 monolayer of the Pt shell were synthesized using the well-established polyol method, which involves the use of a capping ligand. The NPs were tested for the EOR at both room and elevated (70 ̊C) temperatures, as well as acetaldehyde oxidation at room temperature. Ir was found to be more active towards the EOR at lower potentials and Pt at higher potentials. The presence of the capping ligand made it difficult to establish any cooperativity between the two metals to catalyze the EOR. Thus, similar Ir@Pt NPs were also made without a capping ligand. Unexpectedly, little to no enhancement of the EOR catalytic activity was found for these core@shell NPs. The findings were compared to similar studies of methanol oxidation.
Open Access
Long-Term Electromethane Production in Continuous Flow Alkaline Microbial Electrolysis
(2018-09-14) Salehi, Vajiheh; Strous, Marc; Birss, Viola; Hubert, Casey R. J.; Larter, S. R.
Microbial Power to Gas (P2G) is a promising technology for storing renewable energy in the form of natural gas (methane). Energy storage is necessary because renewable energy is often produced at times when it is not demanded. Methane can be used as a transportation fuel in combustion engines due to its low energy density. Microorganisms can produce methane in a single compartment microbial electrolytic cell at room temperature and neutral pH. However, this technology faces several challenges, including anode corrosion, membrane failure, and the fact that the final product is a mixture of methane, hydrogen and CO2. Here, the performance of a continuous-flow MEC (without a membrane separator) was studied for microbial P2G, while monitoring hydrogen and methane gas production at the cathode, as well as microbial community changes over time, all in a pH 10 medium. A steel cathode was found to be preferred over various carbons, as the carbons changed their morphology and surface chemistry with time. Platinized titanium mesh was developed for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) carried out on stainless steel cathode in order to produce hydrogen necessary for biologically produce methane. The results showed that this alkaline environment is a superior alternative to neutral one for methane production. High rate of hydrogen production was observed in bicarbonate buffer with 97% columbic efficiency. Methane generation reached up to 17 µL/L reactor/day in 1.0 M bicarbonate buffer solution (BBS). Methanobacters a hydrogenotrophic methanogen along with Delta proteobacteria, and Archobacter, an aerobic sulfide, formate and acetate oxidizer, were significantly enriched in MEC. These results showed in this study indicates that inoculation and enrichment procedures are necessary to the initial success of larger-scale systems.
Open Access
Metal Oxide-Mediated Transformations of Small Molecules for Chemical Synthesis and Energy Storage
(2022-11-17) Jimenez Villegas, Santiago; Trudel, Simon; Siahrostami, Samira; Birss, Viola; Ponnurangam, Sathish; Kibria, Md Golam
To date, the ever-increasing global demands for energy and chemicals have been met primarily by utilizing fossil fuel resources. With the increase consumption of fossil resources, major concerns have been raised in terms of its detrimental impacts on the climate and public health. Accordingly, development of sustainable technologies are crucial to relieve the heavy dependence on fossil fuels and mitigate its adverse effects. This thesis focuses on such sustainable technologies involving electrochemical transformations of small molecules (e.g., O2 and H2O) for the production of H2, a storable chemical fuel, and H2O2, a valuable chemical oxidant. Using a combination of experimental and computational approaches, metal oxide electrocatalysts are investigated. In the first section (chapter 3), the effects of the synthetic route on the oxygen evolution reaction (OER) performance are explored using amorphous RuOx electrocatalysts; a benchmark catalyst for acidic OER. Structural, electrochemical, and spectroscopic analyses revealed a significant impact in performance by the deposition method, whereas the precursor used in the preparation of the catalyst had little influence. In the second section (chapter 4), the effects of heteroatom doping on the catalytic activity were explored via density functional theory. TiO2, a cost-effective, durable catalyst was doped with various amounts of Mn. DFT calculations showed optimal binding of reaction intermediates on the surface of the Mn-doped TiO2. As a result, the OER catalytic onset potential was decreased. The enhanced OER performance was corroborated by experimental studies, wherein a 370 mV reduction in onset potential was achieved through optimal amounts of Mn doping. Lastly, bifunctional catalysts to promote H2O2 production via the anodic two-electron water oxidation (2e-WOR) and cathodic two-electron oxygen reduction reaction (2e-ORR) were studied in the third section (chapter 5). Using DFT calculations, the catalytic activity, selectivity, and stability of SnO2-supported single atom catalysts were assessed. W:SnO2 was identified as a promising candidate for the 2e-ORR, while Ti:SnO2, Fe:SnO2, and Mn:SnO2 for the 2e-WOR. This thesis is another step in the collective effort to transition away from fossil fuels and creating economically-attractive, sustainable technologies for the future of clean energy and chemical production.
Open Access
Multiple-scale wettability and imbibition in engineered and natural nanoporous media
(2021-06) Pan, Bin; Clarkson, Christopher; Birss, Viola; Bryant, Steven; Marriott, Robert; Shimizu, George; Kovscek, Anthony
Wettability is an important parameter influencing imbibition into nanoporous media, and therefore, affects many processes in the fields of engineering and science. However, there are many challenges in quantifying wettability and imbibition in natural and heterogeneous nanoporous media. In order to provide fundamental understanding of wettability and imbibition in nanoporous media, in this dissertation, an engineered nanoporous carbon scaffold (NCS) with controllable wettability and pore geometry was used to investigate multi-scale wettability and imbibition (including spontaneous and electrocapillary) dynamics. The learnings obtained from studying this engineered material were subsequently applied to the evaluation of multi-scale wettability and spontaneous imbibition in unconventional hydrocarbon reservoirs. For spontaneous imbibition of nanoliter droplets in NCS and tight rocks, it was found that 1) spontaneous imbibition can take place in hydrophobic nanoporous media; 2) contact line remains pinned during the entire droplet lifetime; and 3) the estimated pore- contact angle (from new theoretical models) is larger than the measured macro- and micro- contact angles. For spontaneous imbibition of bulk liquid in NCS and shale/tight rocks, the following results were obtained: 1) a larger pore size leads to faster imbibition; 2) imbibition volume is linear with square root of time until front breakthrough; 3) a small amount of evaporation causes a deviation from this linear relationship; and 4) pore- contact angle is required for upscaling spontaneous imbibition data from laboratory to reservoir scales. Further, two theoretical models were developed to characterize these dynamics in the presence and absence of evaporation, respectively. Additionally, two new methods were developed to examine impacts of osmotic pressure and surfactant on fracturing fluid loss, respectively, which mitigated the effects of capillary pressure and rock heterogeneity. For electrocapillary imbibition of 1 M KCl electrolyte in hydrophobic NCS, two phenomena were observed: a dependence of electrocapillary imbibition on voltage polarity, and an appearance of electro-dewetting at negative voltages. Fundamentally, this dissertation advances the understanding of multi-scale wettability and imbibition physics in nanoporous media, and fracturing fluid loss mechanisms in unconventional reservoirs. Practically, this thesis provides useful guidance on fracturing fluid loss control and prediction in unconventional reservoirs, and on fluid manipulation at nanoscales.
Open Access
Nanoengineering of Bimetallic Materials for Electrocatalytic Applications
(2019-11) Hoang, Annie; Birss, Viola; Shi, Yujun; Kibria, Md. Golam; Thangadurai, V.
Fuel cells are electrochemical devices that cleanly convert fuel into electricity. However, the high cost of the catalyst materials and the lack of hydrogen fueling stations have led to the need for less costly catalysts, as well as the use of liquid fuels (e.g., ethanol, a highly accessible and renewable fuel for direct ethanol fuel cells (DEFCs)). In this work, Ru@Pt core@shell nanoparticles (NPs, 3-6 nm) supported on Vulcan Carbon (VC) powder were produced by two synthesis methods, and then compared for their catalysis towards the ethanol oxidation reaction (EOR). A stabilizer-based synthesis (Method I) produced NPs in a colloidal solution, prior to attaching the NPs to the carbon support. Method II was a stabilizer-free synthesis, involving nucleating Ru NPs on carbon, followed by thermal annealing, and then Pt shell deposition. Both synthesis methods successfully achieved Ru@Pt core@shell formation, although Method II generated larger and less agglomerated NPs that were also more crystalline after thermal annealing. Without annealing, the Method II Pt shell was not as uniform on the Ru cores as desired. These Ru@Pt core@shell NPs were examined for their activity towards the EOR in acidic conditions at room and elevated temperatures. The stabilizer-based Method I NPs exhibited lower EOR activity, perhaps due to some residual capping ligand blocking the NP surfaces. The Method II NPs with thermally annealed Ru cores exhibited greater EOR activity than their non-annealed analogues. For both types of NPs, those with Pt shell coverages < 1 monolayer (ML) were quite promising for the EOR, ascribed to the bifunctional effect. This work also focused on examining thermally annealed Au and Pt thin films (3-4 nm each) sputter-deposited sequentially on chemically polished (CP) Ta. Interestingly, Au always migrated to the outer surface, with Pt beneath, suggesting that Pt@Au core@shell thin films were formed, independent of the Au and Pt sputtering sequence. Also, the underlying Pt thin film prevents thermal dewetting of the thin Au film, playing an important role in stabilizing Au electrochemistry after long thermal annealing times.
Open Access
Nanopore Structure Analysis of Geological and Catalytic Materials
(2013-09-13) Aquino Carvelli, Samuel David; Clarkson, Christopher; Birss, Viola
The study of nanoporous materials is important due to their many applications, including gas sorption/storage and catalysis. In this thesis, two classes of materials have been studied: a hydrocracking catalyst (nickel (Ni)-containing zeolite, Ni/H-ZSM), prepared using two different methods, and naturally-occurring tight gas/shale core plugs from several North American reservoirs. The Ni/H-ZSM catalyst was used for the hydrocracking of toluene, while the tight gas/shale samples are from reservoirs with enormous potential for natural gas production. Because the storage and flow properties of both of these materials relate primarily to pores at the nanometer scale, these topics are connected through the multiplicity of powerful characterization techniques that have been employed, including high resolution imaging, gas sorption, and computational methods (e.g., DFT). It has been found that the two methods of Ni incorporation of the Ni/H-ZSM samples, which are catalytically similar, differ in the Ni nanoparticle size and distribution within the pores. For the tight-gas/shale reservoir samples, characteristic pore shapes and distributions have been identified, and comparisons between routine and non-routine characterizing methods were performed. Elemental compositions with depth in powdered samples were explored and their implications for distribution of organic and inorganic matter explored.