While thermodynamic reference electrodes with known and stable potentials are common in traditional aqueous systems, the high temperature and corrosive environment of a molten fluoride salt makes achieving long term stability with a thermodynamic reference electrode challenging, especially at temperatures of 600°C or higher. In this work, a thermodynamic reference electrode consisting of U(IV)/U(III) in a boron nitride compartment was evaluated for use in FLiBe at temperatures ≥ 600°C. FLiBe used in the study was purified by AlphaTech’s proprietary process and characterized by ICP-MS and square wave voltammetry. The free oxide concentration was <2 ppm. Using the purified FLiBe, the U(IV)/U(III) thermodynamic reference electrode was shown to provide a stable, well-defined, and reproducible potential for more than 600+ hours of use in different tests. Moreover, the thermodynamic reference electrode showed a consistent potential with no signs of failure, even after being cooled between tests and then reheated for reuse. Thus, the U(IV)/U(III) reference electrode is suitable for use in rigorous electrochemical studies in molten fluoride salts. It may be useful as a common standard, facilitating the advancement of nuclear applications such as isotope separation or online monitoring of reactor systems through improved certainty in the measurement of thermodynamic potentials.

An analytical model of shunt currents in a bipolar stack is presented. The analysis assumes linear kinetics and treats the stack as a continuum. The model results in three principal design equations: port current density, manifold current, and drain current due to shunts. These design equations use well-defined stack geometric parameters and physico-chemical properties and are suitable to introduce learners to the topic of shunt currents. The connection between corrosion and shunt currents is shown. The simplified model qualitatively explains the general behavior of corrosion, providing important insights. However, linear kinetics are not appropriate for accurate work detailing the susceptibility to corrosion. The role of the analytic model is to help newcomers develop an understanding and some intuition into the behavior of shunt currents.

NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Session 3431 Maximizing the Benefit of Developing an Educational Plan to Meet the ABET 2000 Criteria W.V. Wilding, J.N. Harb, R.E. Terry, W.C. Hecker Department of Chemical Engineering Brigham Young University Provo, Utah 84602 Abstract This paper documents our experience with the development of an educational plan designed to satisfy the requirements of ABET 2000. The paper first presents the overall structure of the plan which includes both a process loop and a product loop, with assessment and feedback at multiple levels. Our progress on the initial pass through the process loop is then described. This description begins with a procedure developed and used for definition of learning outcomes in the form of attributes and competencies. Also documented are the methods used for successfully promoting faculty involvement in and ownership for the process. Mastery levels have been defined in order to quantify the relative importance of individual competencies. Based on these levels, a core set of outcomes targeted for mastery by all graduating students was identified. These core outcomes will impact the structure of our curriculum and influence instruction and evaluation at all levels. Introduction ABET 2000 provides an excellent opportunity to improve engineering education by focusing on the product (student attributes) rather than the process (teaching). Although the formality of outcomes-based education may be unfamiliar to some, the fundamental ideas are not new, and are routinely incorporated into our day-to-day efforts to improve student learning. ABET 2000 provides the formal context needed for broad application of these ideas and, of course, the driving force needed to facilitate change. At issue, then, is how we will respond to this opportunity. On one hand ABET 2000 may be viewed as an unpleasant and perhaps unnecessary task that must be accomplished to achieve accreditation. Alternatively, it may be viewed as a catalyst for making significant improvements to engineering education. It is our opinion that the second outlook is essential in order to maximize the benefits of implementing ABET 2000. Otherwise, it is unlikely that the full benefits will be achieved. Our experience has shown that the approach used to implement an educational plan consistent with the ABET 2000 criteria has a significant impact on the attitude of the faculty towards the process. Based on this experience, we have developed an approach to maximize faculty interest in and ownership for the process in our department. The purpose of this paper is to share our approach and to discuss some of the results and benefits that we have observed to date.

Among nerve agents, V-series nerve agents are some of the most toxic, making low-concentration detection critical for the protection of individuals, populations, and strategic resources. Electrochemical sensors are ideally suited for the real-time and in-field sensing of these agents. While V-series nerve agents are inherently nonelectroactive, they can be hydrolyzed to electroactive products compatible with electrochemical sensing. Zr(IV) MOFs are next-generation nanoporous materials that have been shown to rapidly catalyze the hydrolysis of nerve agents. This work makes use of these nanomaterials to develop, for the first time, an MOF-enabled electrochemical sensor for V-series nerve agents. Our work demonstrates that the VX thiol hydrolysis product can be electrochemically detected at low concentrations using commercially available gold electrodes. We demonstrate that low-concentration thiol oxidation is an irreversible reaction that is dependent on both mass transport and adsorption. Demeton-S-methylsulfon, a VX simulant, is used to demonstrate the full range of sensor operation that includes hydrolysis and electrochemical detection. We demonstrate that MOF-808 rapidly, selectively, and completely hydrolyzes demeton-S-methylsulfon to less-hazardous dimethyl phosphate and 2-ethylsulfonylethanethiol. Low-concentration measurements of 2-ethylsulfonylethanethiol are performed by using electrochemical techniques. This sensor has a limit of detection of 30 nM or 7.87 mu g/L for 2-ethylsulfonylethanethiol, which is near the nerve agent exposure limit for water samples established by the United States military. Our work demonstrates the feasibility of rapid, robust electrochemical sensing of V-series nerve agents at low concentrations for in-field applications.

Directed placement of DNA origami could play a key role in future integrated nanoelectronic devices. Here we demonstrated the site-selective attachment of DNA origami on gold dots formed using a pattern transfer method through block copolymer self-assembly. First, a random copolymer brush layer is grafted on the Si surface and then poly (styrene-b-methylmethacrylate) block copolymer is spin-coated to give a hexagonal nanoarray after annealing. UV irradiation followed by acetic acid etching is used to remove the PMMA, creating cylindrical holes and then oxygen plasma etching removes the random copolymer layer inside those holes. Next, metal evaporation, followed by lift-off creates a gold dot array. We evaluated different ligand functionalization of Au dots, as well as DNA hybridization to attach DNA origami to the nanodots. DNA-coated Au nanorods are assembled on the DNA origami as a step towards creating nanowires and to facilitate electron microscopy characterization of the attachment of DNA origami on these Au nanodots. The DNA hybridization approach showed better DNA attachment to Au nanodots than localization by electrostatic interaction. This work contributes to the understanding of DNA-templated assembly, nanomaterials, and block copolymer nanolithography. Furthermore, the work shows potential for creating DNA-templated nanodevices and their placement in ordered arrays in future nanoelectronics.

Bottom-up fabrication using DNA is a promising approach for the creation of nanoarchitectures. Accordingly, nanomaterials with specific electronic, photonic, or other functions are precisely and programmably positioned on DNA nanostructures from a disordered collection of smaller parts. These self-assembled structures offer significant potential in many domains such as sensing, drug delivery, and electronic device manufacturing. This review describes recent progress in organizing nanoscale morphologies of metals, semiconductors, and carbon nanotubes using DNA templates. We describe common substrates, DNA templates, seeding, plating, nanomaterial placement, and methods for structural and electrical characterization. Finally, our outlook for DNA-enabled bottom-up nanofabrication of materials is presented.

Molten salt mixtures have important applications in, for example, industrial metallurgical processes, energy storage for solar plants, and the development of advanced nuclear reactor systems. Several unanswered questions in these systems involve the thermodynamics of minor components in the molten salt solution. Consequently, we examine molten salt systems using electrochemical thermodynamics, published experimental data, and atomistic simulations to accurately characterize interactions between a minor component and the base salt for multiple salts. The utility of an infinite dilution reference state is demonstrated and used to characterize the range over which solute-solvent interactions dominate over solute-solute interactions for minor components. Under such conditions, the activity is readily defined and cell potential can be easily determined as a function of concentration with use of an appropriate standard potential. Experimental data show that reactions can proceed at very different potentials in different salt melts, and molecular dynamics simulations are used to quantify differences between salts. Simulations show that the chemical potential of an anion varies between melts as influenced by the different cations present in each melt. Hence, attempts to use a common reference reaction for different salt mixtures are at best an approximation. Simulations also demonstrate that solute-solute interactions become significant at lower concentrations if the minor component includes an anion that is different from that of the base salt. This work helps to enhance our understanding of the behavior of minor components in molten salts, which is important for the development of future energy technologies.

DNA origami-assembled metal-semiconductor junctions have been formed as a step toward application of these nanomaterials in nanoelectronics. Previously, techniques such as electroless plating, electrochemical deposition, or photochemical reduction have been used to connect metal and semiconductor nanomaterials into desired patterns on DNA templates. To improve over prior work and provide a more general framework for the creation of electronic nanodevices as an alternative nanofabrication step, we have developed a method to connect gold (Au) and tellurium (Te) nanorods on a single DNA origami template without electroplating by annealing after coating with a heat-resistant polymer. Bar DNA origami templates (17 nm x 410 nm) were seeded site-specifically with Au and Te nanorods in an alternating manner. These templates were then coated with a polymer and annealed at different temperatures. At 170 degrees C, the Au and Te nanorods were best connected, and we hypothesize that the junctions were established primarily due to the atomic mobility of gold. Electrical characterization of these Au/Te/Au assemblies revealed some nonlinear current-voltage curves, as well as linear plots that are explained. This annealing method and the metal-semiconductor nanomaterials that are formed simply through controlled seeding and annealing on DNA origami templates have potential to yield complex nanoelectronic devices in the future.

Aqueous redox flow batteries (ARFBs) with neutral electrolytes show promise for large-scale energy storage owing to their relatively low cost and inherent safety. However, the performance of these ARFBs has been limited by the low solubility of electroactive species and/or low cell voltages. In this study, an asymmetric viologen-based compound called MMV (1-Methyl-4,4 '-bipyridylium iodide) was assessed as the redox active compound in the negolyte of ARFBs. Inexpensive starting materials and a simple synthesis route yielded MMV at a low cost. MMV exhibited a solubility of similar to 3 M in water, and electrochemical measurements confirmed that the reaction of MMV involves the transfer of a single electron with relatively fast kinetics. Importantly, MMV with an asymmetric structure demonstrated a redox potential of -1.05 V vs SCE, one of the most negative potentials reported for an electroactive organic compound in neutral electrolytes. MMV, however, showed poor cycling performance at high concentrations. Signs of dimerization and precipitation were observed, resulting in measured capacities significantly lower than theoretical values and a rapid fade rate. It should be possible to avoid these problems by synthesizing asymmetric MMV derivatives with a higher charge to preserve high solubility and low redox potential.

The dissolution and deposition behavior of molybdenum in a deep eutectic solvent was examined to assess the possibility of molybdenum electrorefining. When added to the ethaline, MoCl5 exhibited electrochemically irreversible behavior and appeared to be reduced via a two-electron reaction. However, Mo metal deposition was not observed, even after an extended period at high cathodic overpotentials. Deposition of molybdenum from ethaline at 80 °C was enabled by adding fluoride ions to the liquid to alter the speciation of the metal complex. Fluoride changed the electrochemical behavior of Mo in solution determined by cyclic voltammetry. Mo was successfully deposited from ethaline onto a nickel substrate at constant potential in the presence of fluoride ions, as confirmed analytically. The impact of fluoride ions on the anodic dissolution of molybdenum in ethaline was also found to not significantly hinder the dissolution process. Thus, both dissolution and deposition of molybdenum are possible in a DES, opening the way for possible development of a Mo electrorefining process.

DNA-based nanofabrication of inorganic nanostructures has potential application in electronics, catalysis, and plasmonics. Previous DNA metallization has generated conductive DNA-assembled nanostructures; however, the use of semiconductors and the development of well-connected nanoscale metal-semiconductor junctions on DNA nanostructures are still at an early stage. Herein, we report the first fabrication of multiple electrically connected metal-semiconductor junctions on individual DNA origami by location-specific binding of gold and tellurium nanorods. Nanorod attachment to DNA origami was via DNA hybridization for Au and by electrostatic interaction for Te. Electroless gold plating was used to create nanoscale metal-semiconductor interfaces by filling the gaps between Au and Te nanorods. Two-point electrical characterization indicated that the Au-Te-Au junctions were electrically connected, with current-voltage properties consistent with a Schottky junction. DNA-based nanofabrication of metal-semiconductor junctions opens up potential opportunities in nanoelectronics, demonstrating the power of this bottom-up approach.

Glucose is a potential source of energy for fuel cell applications. However, its complete oxidation has been a challenge. Dimethyl viologen, as an electron mediator, has been shown to promote high levels of glucose oxidation under aerobic conditions. Nevertheless, the efficiency of viologen-mediated glucose oxidation has been low in electrochemical experiments. In this study, viologen-mediated oxidation of glucose was investigated under anaerobic electrochemical conditions to understand the factors that impact the oxidation efficiency. Of particular interest was the improvement of electrochemical oxidation for glucose fuel cell applications. An experimental cell was developed to electrochemically reoxidize the mediator as it was homogeneously reduced by glucose under anaerobic conditions. In contrast, the mediator was reoxidized by direct reaction with oxygen under aerobic conditions. The aerobic oxidation efficiency was 75%, three times larger than the maximum efficiency in the electrochemical cell. C-13-NMR results show that the main product formed under aerobic conditions was formic acid, whereas glycolic acid was the principal product formed in the electrochemical cell. Carbonate was only formed under aerobic conditions. Therefore, the use of oxygen to reoxidize the mediator also directly influenced the glucose oxidation pathway. In the electrochemical cell, the oxidation efficiency depended on the electrochemical reaction rate of the mediator and was higher at faster rates. The efficiency also depended on the initial molar ratio of the mediator to glucose. The maximum oxidation efficiency of glucose in the electrochemical cell was approximately 22%, which is about three times larger than the maximum efficiency for precious-metal-based anodes.

aDepartment of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29208, USA bDepartment of Chemical Engineering, Texas A&M University, College Station, Texas 77843, USA cLawrence Berkeley National Laboratory, Berkeley, California 94720, USA dEnerVault Corporation, Sunnyvale, California 94089, USA eDepartment of Energy, Environment and Chemical Engineering, Washington University, Saint Louis, Missouri 63130, USA

The objective of this work is to advance the mechanistic understanding of cathodic electrocoating. These efforts focus on the initial processes responsible for deposition, which are examined through direct experimentation and simulation. Electrocoating is a global industrial process providing a corrosion-resistant, base-paint layer to automobile bodies. Presently, empirical models are used to model coating thickness; these models tend to overpredict deposition in occluded areas. Convection is implemented to study electrochemical mechanisms at the surface of the coated part. The impact of surface H-2 bubbles and early e-coat deposition on the local current density is studied using current distribution simulations. Results show an increase in current density locally around surface H-2 bubbles and early e-coat deposition influences film growth. When surface H-2 bubbles are displaced by convection before sufficient e-coat is deposited, deposition is slowed under lower local current density. However, when the e-coat covers sufficient surface area, and convection is then applied, the induction period is unaffected, implying the early deposition is sufficient to keep the local current density high enough to drive deposition. These results provide an increased understanding of fundamental processes responsible for e-coat deposition, which is the foundation needed for advanced physics-based models of the electrocoating process. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Self-assembly nanofabrication is increasingly appealing in complex nanostructures, as it requires fewer materials and has potential to reduce feature sizes. The use of DNA to control nanoscale and microscale features is promising but not fully developed. In this work, we study self-assembled DNA nanotubes to fabricate gold nanowires for use as interconnects in future nanoelectronic devices. We evaluate two approaches for seeding, gold and palladium, both using gold electroless plating to connect the seeds. These gold nanowires are characterized electrically utilizing electron beam induced deposition of tungsten and four-point probe techniques. Measured resistivity values for 15 successfully studied wires are between 9.3 × 10−6 and 1.2 × 10−3 Ωm. Our work yields new insights into reproducible formation and characterization of metal nanowires on DNA nanotubes, making them promising templates for future nanowires in complex electronic circuitry.

Glucose is a desirable source of energy for fuel cell applications. However, its slow oxidation rate on nonprecious metal electrodes has been a challenge. Viologens can potentially mitigate this challenge as they homogeneously oxidize glucose and then transfer electrons to inert electrodes with fast kinetics. This study aims to better understand the factors that determine the effectiveness of viologen as a mediator for glucose oxidation. The relative significance of the key physical processes including homogeneous reaction, mass transfer, and electrochemical reaction was evaluated by dimensional analysis and detailed simulations. While all processes were important under certain conditions, mass transfer was the principal limiting step. Mass transfer was initially improved by flow; however, this impact was counterbalanced by the decreased concentration of the reduced mediator at high flow rates. The maximum obtainable current density was close to 200 mA cm−2, which corresponded to a predicted anode polarization of 300 mV. This current density is noticeably higher than rates available from biological cells and comparable to values for precious-metal-based cells. Thus, viologen-mediated fuel cells offer high rates without the additional cost associated with precious metal electrodes. Finally, the approach presented can be used for process development and optimization of any mediated system.

Redox flow batteries have been recognized as a promising option for energy-storage purposes, mitigating the intermittency of renewable sources of energy such as solar, wind, and hydroelectric power. In particular, aqueous redox flow batteries (ARFBs) are very attractive owing to high conductivity, relatively low cost, and safe nature of aqueous electrolytes. Performance of ARFBs can be further improved with developing new electroactive species. Viologens are a group of organic compounds with great tunability, making them appealing for flow battery applications. In this study, a viologen-based electroactive compound called MMV is proposed with the potential of improving performance of aqueous flow batteries. The potential of MMV as an anolyte was investigated for developing a neutral aqueous flow battery. MMV required a simple synthesis procedure with inexpensive starting materials, resulting in a low cost. MMV showed solubility of almost 3 M that is relatively high compared to other organic electroactive compounds, such as quinones, especially in neutral electrolytes. The electrochemical reaction of MMV involved the transfer of one electron at fast kinetics. Additionally, MMV demonstrated a redox potential of -1.05 V vs. SCE that is one of the most negative redox potentials reported for organic electroactive species under neutral conditions. These characteristics indicated that MMV is a promising anolyte candidate. Such a very negative redox potential and high solubility provide MMV the potential to significantly improve performance of a flow battery in terms of capacity, energy density, and cell potential. Despite these interesting properties, MMV exhibited a poor cycling performance. MMV underwent irreversible reactions at elevated concentrations. Signs of dimerization and also precipitation were observed during cycling. The irreversible reactions led to a high capacity fade rate (2.1%/cycle). Approaches to improve the cycling performance include synthesizing MMV-derivatives that possess a higher charge compared to that of MMV to possibly limit the extent of both dimerization and precipitation.

One area of exploration for renewable energy is the development of fuel cells, including carbohydrate fuel cells that can extract energy from carbohydrates. Viologen electron mediators have been shown to enhance energy extraction and improve carbohydrate conversion efficiencies, although the limiting step appears to be the homogeneous rate at which electrons are first transferred from the carbohydrate to the viologen. In this work, electron transfer rates for various monosaccharides in the presence of methyl viologen were studied in the absence of a fuel cell to isolate the homogeneous rate. Using glucose as the model carbohydrate, a rigorous mechanistic model of the homogeneous electron transfer rate was developed and showed a first-order dependence on OH- concentration, a first-order dependence on carbohydrate concentration, a zero-order dependence when the methyl viologen concentration was >> 0.4 mM, and an increasing rate with incubation time when glucose was incubated in a buffer solution prior to exposure to methyl viologen. The incubation effect had a strong dependence on pH and was consistent with interconversion between glucose and fructose. The mechanistic model, which agreed well with experimental data, can be useful for identifying process improvements to carbohydrate fuel cells, especially when the homogenous rate is a limiting step. (c) 2019 Elsevier Ltd. All rights reserved.

DNA origami-templated fabrication enables bottom-up fabrication of nanoscale structures from a variety of functional materials, including metal nanowires. We studied the impact of low-temperature annealing on the morphology and conductance of DNA-templated nanowires. Nanowires were formed by selective seeding of gold nanorods on DNA origami and gold electroless plating of the seeded structures. At low annealing temperatures (160 °C for seeded-only and 180 °C for plated), the wires broke up and separated into multiple, isolated islands. Through the use of polymer-constrained annealing, the island formation in plated wires was suppressed up to annealing temperatures of 210 °C. Four-point electrical measurements showed that the wires remained conductive after a polymer-constrained annealing at 200 °C.