bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Cyclization of Brominated Allyl Ethers with the Aid of a Chiral Catalyst
Authors: Pasciak Erick , Rittichier Jonathan , Medeiros M. J. , VanNieuwenzhe Michael , Peters Dennis G 
Published: February 2020

Control over the stereochemistry of a desired product in chemical synthesis is an ongoing problem. Specifically, the selectivity of chiral molecules has been the most challenging problem in organic synthesis. Often, to overcome this problem, chiral catalysts are employed to induce preference for one chiral product over another. One catalyst, known as the Jacobsen catalyst, has been utilized for the enantioselective oxidative conversion of alkenes to epoxides in the presence of a large amount of an oxidizer.1

In the field of electrochemistry, Duñach and co-workers utilized nickel(II) and cobalt(II) complexes with a Jacobsen ligand (a chiral, substituted salen) in constant-current experiments for the electrochemical reductive cyclization of brominated allyl ethers at room temperature, for which they achieved an enantiomeric excess as high as 16%.2 In the present work, we have explored the use of the same cobalt(II) catalyst as Duñach and co-workers, but conducted the experiments under controlled-potential conditions in order to increase the enantiomeric excess. We expanded the study to more substrates to observe how ther products change as a function of structure. A generalized reaction is shown in Scheme 1 for the one-electron reductive cyclization of brominated allyl ethers to form the chiral product of interest. Experiments have been conducted to optimize reaction conditions such as temperature, concentration, and solvent. Finally, we changed the stereochemistry of the catalyst from the R species to the S species for the purpose of controlling the identity of our products.

1. Jacobsen, in: I. Ojima (Ed.), Catalytic Asymmetric Synthesis, VCH, New York, 1993 (Chapter 4.2).
2. Duñach, E.; Esteves, A. P.; Medeiros, M. J.; Pletcher, D.; Olivero, S. J. Electroanal. Chem.
2004, 566, 39–45.

Figure 1
Electrochemical Character and Application of Halide Mediators Using CF3CH2oh As Solvent
Authors: Lam Chiu Marco , Zeng Chengchu , Little R. Daniel 
Published: February 2020

The electrochemical characteristics of bromide and iodide in 2,2,2-trifluoroethanol (TFE) has been investigated and studied by cyclic voltammetry.
TFE is a protic solvent that has different nucleophilicity compared to other common alcohol solvents. Based on the experimental results, iodide and bromide lose two electrons and form a triiodie/tribromide system in one oxidation wave in TFE. The processes were found to be diffusion-controlled.
Different types of electrochemical reactions were attempted and studied in TFE. TFE found to be useful for the synthesis and benzylic C-H bond activation.
Electrochemical Reduction of Flavones
Authors: Medeiros M. J. , Pasciak Erick , Mubarak Muhammad , Peters Dennis G 
Published: February 2020

Flavone and its derivatives comprise an important class of compounds due to their diverse biological properties and therapeutic applications. They are commonly used as precursors in the preparation of various biologically active compounds, such as anticancer pharmaceuticals [1]. Dimerization of flavone may lead to new and alternative drug candidates with improved pharmacological profile.
In this work, we report electrochemical results obtained by means of cyclic voltammetry and controlled-potential electrolysis for the reduction of flavones in both aprotic and protic media containing tetraalkylammonium salts, under various experimental conditions, including an aprotic solvent (DMF) with an added proton donor. We have identified and quantitated the various electrolysis products with the aid of GC–MS and GC. A mechanistic pathway is proposed to account for the formation of products.

ACKNOWLEDGMENT

We are grateful to the Fundação para a Ciência e Tecnologia (PestC/QUI/UI0686/2013 and FCOMP-01-0124-FEDER-037302) for financial support of this work.

REFERENCE

[1] R. H. Greg, R. H. James, J. Biol. Chem. 1997, 272, 5396.
Electronic Structure Effects on Electron Transfer Controlled Hydrogen Bonding in Substituted Dinitrobenzene Electrogenerated Anions As Receptors for 1,3-Diethylurea
Authors: Martinez-Gonzalez Eduardo , Frontana Carlos 
Published: February 2020

In Electron Transfer Controlled Hydrogen Bonding (ETCHB), switching molecules experiment changes in their reduction potential values as hydrogen bond donor species (DH) are added to the solution. ETCHB is the basis of operation of many molecular switches [1-3]; therefore a comprehensive understanding of the mechanistic routes that govern electron transfer in these systems would allow the design of devices with more specific applications. These processes have been extensively studied employing model molecules, such as nitrocompounds as receptor species [1-3]. In the case of complexes formed via ETCHB with electrogenerated anions from dinitrobenzene isomers [3-7], proton transfer reactions were also observed, thus diminishing the stability of these intermediates. Therefore, in this work, a similar electrochemical analysis was performed using 1,3-diethylurea to avoid protonation. The results showed two sequential reversible voltammetric signals, from which Kb (binding constant) values were calculated. The experimental behavior suggest that the mechanistic routes for ETCHB depend on the relative position of the nitro groups within the molecule: For o- and p-dinitrobenzenes radicals, a reduction involving an Erev Erev C mechanism occurs while for with m-dinitrobenzene radicals, the reaction evolves by an Erev C Erev route. By employing m-dinitrobenzenes substituted in 5 position as receptors, results revealed an inductive effect on Kb values in the formation of the anion radical binding complex.

Acknowledgments

E. M.-G. thanks CONACYT for support his M. Sc. Studies (scholarship no. 270926). C. F. thanks CONACYT for support through project 107037.

References

[1]. E. Martínez-González, C. Frontana. J. Org. Chem. 2014. 79, 1131-1137.
[2]. J. Bu, N. D. Lilienthal, J. E. Woods, C. E. Nohrden, K. T. Hoang, D. Truong, D. K. Smith. J. Am. Chem. Soc. 2005, 127, 6423-6429.
[3]. C. Chan-Leonor, S. L. Martin, D. K. Smith. J. Org. Chem. 2005, 70, 10817-10822.
[4]. M. A. Syroeshkin, A. S. Mendkovick, L. V. Mikhal chenco, A. Rusakov, V. P. Gultyai. Russian Chemical Bulletin, International Edition. 2009, 58, 468-472.
[5]. A. S. Mendkovich, M. A. Syroeshkin, L. V. Mikhalchenko, A, I. Rusakov, V. P. ultyai. Russian Chemical Bulletin, International Edition. 2008, 57, 1492-1495.
[6]. M. Mohammad, A. Rauf, S. Rauf, M. Tariq. J. Phys. Org. Chem. 2012, 25, 1269-1274.
[7]. M. F. Nielsen, V. D. Parker. Acta Chemica Scandinavica B. 1988, 42, 93-100.
Simulation and Mechanism Analysis of Electrochemistry of the Vanadium Redox Couples By a Rotating Disk Electrode
Authors: Pan Jianxin , Li Xue , Zhao Yubin , Xie Xiaofeng , Ramani Vijay K 
Published: February 2020

A redox flow battery is the one of most potential and commercial electrochemical energy storage technologies. During all types of redox couples, the vanadium couples received the remarkable attention and wildly investigated in the past two decades. Usually, the electrochemistry of vanadium redox couple is experimentally studied by electrochemical methods such as cyclic volt-ampere measurement, linear voltage scanning, electrochemical impedance spectroscopy, and rotating disk electrode. Beside those methods, rotating disk electrode is the most complicated and contains a large amount of electrochemical information.
A mathematical mechanism model has been developed based on the physical phenomenon and equations of diffusion, convection, electro-migration, and electrochemical reaction dynamic. The effect of rotating rate on the performance of vanadium couples is simulated, analyzed and comprised with the experimental data. The distributions of velocity, concentration, potential, and current have been provided while the traditional experimental methods could not been done. The simulation technique not only can provides more electrochemical information, but also gives a better understanding of the electrochemical process for the teaching and research.
Key words: redox couples, flow battery, simulation, mechanism model
Acknowledgment: This work was supported by the National High Technology R&D Program of China (2012AA053401)
Modeling and Analysis of All-Vanadium Redox Static Cells
Authors: Lee Seong Beom , Soundappan Thiagarajan , Suthar Bharatkumar , Sonawane Dayaram , Subramanian Venkat R. 
Published: February 2020

Progress made in renewable energy technologies (e.g. solar, wind and tidal energy) has fueled the research in energy storage technologies which are indispensible for the success of these intermittent sources of energy. Electro-chemical energy storage systems specially redox flow batteries (RFB) offer modular and scalable energy storage systems for large scale energy storage1.
Research in different RFBs has been pursued to improve the efficiency, cost and safety aspects of these systems. While research on most aspects requires small scale (lab-scale) redox flow battery, research on some aspects can be performed and analyzed using a static cell set up (e.g. cross contamination, characterization of membrane and electrolyte etc.).
These static cells (H cell) can be used to quickly estimate the performance of redox flow batteries (at least at the lab scale) including capacity loss due to cross contaminations2. Use of static cell with simplified modeling approach (including capacity loss) to validate experimental data is demonstrated by Tang et. al.2 on vanadium redox flow battery. This approach can be made more robust and general to be useful for any redox couple by combining electrochemical models and robust optimization framework (parameter and state estimation techniques) to increase the confidence in predictions made by static cell.
This presentation will focus on electrochemical models for static cell with parameters and state estimation framework to increase the fidelity of results obtained by experiments performed.

Acknowledgements

The authors acknowledge financial support from the U.S. Department of Energy’s Advanced Research Projects Agency- Energy (ARPA-E), and the Solar Energy Research Institute in India and the United States (SERIIUS), as well as, Washington University in St. Louis’ McDonnell Academy Global Energy and Environmental Partnership (MAGEEP) and SunEdison Grant.

References

1. B. R. Chalamala, T. Soundappan, G. R. Fisher, M. R. Anstey, V. V. Viswanathan and M. L. Perry, Proceedings of the IEEE, 102, 976 (2014).
2. A. Tang, J. Bao and M. Skyllas-Kazacos, J. Power Sources, 196, 10737 (2011).
Investigation on the Microfluidics in PEM Water Electrolyzers
Authors: Mo Jingke , Steen Stuart M. , Barnhill William , Zhang Feng-Yuan 
Published: February 2020

A sustainable and robust electrochemical energy storage and/or a hybrid system to accommodate daily, even hourly changes of renewable resources becomes more critical. An advanced polymer electrolyte membrane water electrolyzer (PEMWE) has been shown to be effective energy storage medium by producing hydrogen/oxygen from water with electricity from renewable sources. When the renewable resources are available, hydrogen will be produced and stored, such that it can later provide a constant power supply with a PEM fuel cell, which is a reverse device of the electrolyzer. This entire portfolio will make renewable and hybrid energy systems effective to provide reliable and multiscale energy whenever needed.
In proton exchange membrane water electrolyzers (PEMWEs), water is electrochemically splitting into oxygen and hydrogen. The oxygen generated at the anode side and the circled water flowing over the liquid/gas diffusion layer yield two-phase transport conditions in micro-channels and pores of LGDL, which significantly impact the performance. Due to limitations of the design of conventional PEMWEs and LGDLs, the in-situ phenomena of two-phase flow has few been explored in operating PEMWEs. In this research, an innovative design of a transparent PEMWE is developed coupled with the thin and well-tuned titanium LGDLs with straight pores. The high-speed and micro-scale visualization system (HMVS), and electrochemical impedance spectroscopy will be used for in-situ characterizations. Visualization results are used for better understanding the behavior of two-phase flow and its effects on the PEMWE performance. Patterns of gas-bubble formation, evolution, departure and transport are identified. The effects of property of materials, including LGDL pore sizes, channel dimensions, are also investigated.
Development of High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 fuel Cells
Authors: Yarlagadda Venkata , Nguyen Trung Van , Lin Guangyu , Chong Pau Ying 
Published: February 2020

The H2-Br2 system is considered as one of the viable options for large scale electrical energy storage due to faster H2 and Br2 reaction kinetics, low cost, and high round-trip efficiency. Since the bromine reactions in this fuel cell system do not need any precious metal catalysts, plain porous carbon paper can be used as an electrode material. However, these porous carbon electrodes have low surface area and hence multiple electrode layers are employed to improve the active surface area. While the active surface area is enhanced by using multiple electrode layers, it could lead to mass transport limited performance at higher current densities. To overcome this problem, porous carbon electrodes with multi-wall carbon nanotubes grown directly on their surface were developed. The cross section of a carbon nanotube based electrode is shown in Figure 1. In this presentation, we will discuss the synthesis and characterization of carbon nanotube based electrodes as well as their durability and actual performance in a H2-Br2 fuel cell. Also, the advantages of these carbon nanotube based electrodes over conventional porous carbon electrodes will be highlighted.

Acknowledgements

This work was funded by NSF through grant number EFRI-1038234 and DOE/ARPA-E under award number DE-AR0000262.

References

Haley Kreutzer, Venkata Yarlagadda, and Trung Van Nguyen, J. Electrochem Soc., 159(7), F331 (2012).

Venkata Yarlagadda and Trung Van Nguyen, J. Electrochem. Soc., 160(6), F535 (2013).

Cheng Wang, Mahesh Waje, Xin Wang, Jason M. Tang, Robert C. Haddon, and Yushan Yan, Nano Letters, 4(2), 345 (2004).

Chunyu Du, Baorong Wang, and Xinqun Cheng, J. Power Sources, 187, 505 (2009).

Venkata Yarlagadda and Trung Nguyen, ECS Transactions, 58(36), 25 (2014).

Figure 1
(Invted) Catalytically Accelerated Hydrogen Gas Detection at Electrodeposited Pd@Pt Nanowires
Authors: Penner R. 
Published: February 2020

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with control of the Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 60 nm(h) × 200 nm(w) × 20 μm(l) are first prepared using lithographically-patterned nanowire electrodeposition (LPNE). A thin Pt surface layer is elec- trodeposited conformally onto a Pd nanowire at coverages, θPt , of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements are consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.04 to 5.0 vol%. Both Pd nanowires and Pd@Pt nanowires show a prompt increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. The Pt surface layer present at Pd@Pt nanowires modifies the response to H2 in two ways: First, the amplitude of the resistance change is reduced as θPt is increased, and second, the rate at which the nanowire resistance attains a new steady-state value upon a change in the H2 concentration - characterized by the response time and the recovery time - is accelerated. An optimum Pt coverage of θPt = 1.0 ML is seen for which nanowire response is accelerated by a factor of 2-3 while the recovery from H2 exposure is faster by an order of magnitude as compared to a pure Pd nanowire operating at the same elevated temperature.
(Invited) Fluorescence-Enabled Electrochemistry of Single Molecules and Nanoparticles
Authors: Zhang Bo , Oja Stephen , Lu Jin 
Published: February 2020

We are developing a new electrochemical detection method to study redox properties of single molecules. This method relies on the use of fluorescence to amply the signal of single electron-transfer events at the electrode/solution interface. A bipolar electrode mechanism is used to couple a redox reaction of interest to a fluorogenic reaction. The oxidation or reduction of the redox species at the bipolar electrode results in the generation of a highly fluorescence product at the opposite pole of the same bipolar electrode, which is optically monitored with total-internal reflection fluorescence microscopy (TIRFM). The use of this method allows one to resolve single redox events in an electrolyte solution at room temperature. In this talk, I will first discussion some of our recent results on the detection of single redox molecules, including ferrocene and ferricyanide, and single nanoparticles. I will then discussion some of our new experiments on electrochemical coupling at single nanoparticles. I will also discuss a couple of experiments focusing on imaging and resolving single redox events with very large electrochemical arrays.
(Invited) Dendrite-Free Rechargeable Zinc-Based Batteries: Solving a Chronic Impediment through Architectural Design in 3D
Authors: Rolison Debra R. , Parker Joseph F. , Pala Irina R. , Chervin Christopher N. , Nelson Eric S. , Long Jeffrey W. 
Published: February 2020

The international effort to move beyond lithium-ion batteries—present-day’s ubiquitous electrochemical energy storage (EES) device—arises from the unending safety threat posed courtesy of flammable electrolytes and oxygen-releasing cathodes. The oft-posited “Beyond Lithium” as an R&D rationale for next-generation batteries needs to bypass not just lithium-ion, but Li-based batteries. Zinc-based batteries offer a compelling alternative thanks to nonflammable aqueous electrolytes augmented by the high domestic abundance of Zn and the high energy density of Zn-based batteries (comparable to or greater than Li-ion). The present performance, however, of traditional Zn-based batteries is hindered by suboptimal Zn utilization (typically <60% of theoretical capacity) and poor rechargeability—thanks to the complex dissolution/precipitation processes that accompany Zn/Zn2+cycling in alkaline electrolytes. We adapt the promise of three-dimensional (3D) battery architectures [1–3] to address these limitations by redesigning the zinc anode as a porous, highly conductive, and 3D-wired “sponge” architecture. These aperiodic electrode architectures achieve >90% Zn utilization when discharged in primary Zn–air cells, while retaining the 3D monolithic framework and exhibiting an impedance characteristic of the metal with uniform deposition of charge/discharge products at the external and internal surfaces [4]. We further show that the structural characteristics of the Zn sponge promote greater rechargeability when cycled in prototype Ag–Zn and Ni–Zn cells, even thwarting dendrite formation when cycled in a symmetric Zn–Zn cell at an applied current density twice that of the critical current density necessary to form dendrites [5]. Our results show that all Zn-based chemistries can now be reformulated for next-generation rechargeable, Li-free batteries.
The information, data, or work presented herein was funded in part by the Office of Naval Research and by the Advanced Research Projects Agency–Energy (ARPA–E), U.S. Department of Energy, under Award Number DE-AR-0000391; the work has been Approved for Public Release, Distribution Unlimited.
[1] R.W. Hart, H.S White, B. Dunn, D.R. Rolison, Electrochem. Commun.
5(2003) 120–123.
[2] J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Chem. Rev. 104(2004) 4463–4492.
[3] D.R. Rolison, J.W. Long, J.C. Lytle, A.E. Fischer, C.P. Rhodes, T.M. McEvoy, M.E. Bourg, A.M. Lubers, Chem. Soc. Rev.
38(2009) 226–252.
[4] J.F. Parker, E.S. Nelson, M.D. Wattendorf, C.N. Chervin, J.W. Long, D.R. Rolison, ACS Appl. Mater. Interfac., in the press.
[5] J.F. Parker, C.N. Chervin, E.S. Nelson, J.W. Long, D.R. Rolison, Energy Environ. Sci.
7 (2014) 1117–1124.
Electrolytic and Electroless Fabrication of Al-Sc Alloys in KF-Naf-AlF3 Electrolytes
Authors: Tkacheva Olga , Suzdaltsev Andrey , Nikolaev Andrey , Zaikov Yurii , Shtefanyuk Yuriy , Pingin Vitaliy , Vinogradov Dmitriy 
Published: February 2020

The Al-Sc alloys were obtained in the KF-NaF-AlF3 electrolyte containing Sc2O3 and Al2O3 at 800 oC by chemical and electrochemical techniques. Electrolysis was performed in a 20 A lab-scale cell with graphite anode and aluminum cathode. An impact of the cathode current density (0-1 A∙cm-2), the Sc2O3 content (1, 2, 4, and 8 wt%) in the KF-NaF-AlF3 electrolyte, the rate of the molten aluminum agitation (0, 100 rotates/min), and the synthesis duration (30-210 min) on the Sc content in the Al-Sc alloy was studied. The Al-Sc alloys with the Sc content of 0.30-1.80 wt%, depending on the synthesis conditions, and with the uniform Sc distribution throughout the aluminum matrix were produced. The peculiarities of the electrolytic and electroless fabrication of the Al-Sc alloys in the KF-NaF-AlF3-Al2O3-Sc2O3 electrolytes at 800 oC in comparison with the processes occurred in the NaF-AlF3-Al2O3-Sc2O3 melts at 980 oC are discussed.
Monitoring Mechanical Modulation of Reactivity in Electrocatalysis
Authors: Deng Qibo , Weissmueller Joerg 
Published: February 2020

Many modern catalyst materials exploit a strained surface layer as the active component, exploiting that reaction rates in heterogeneous catalysis vary when the substrate is elastically strained in the tangent plane. Here we report a direct and quantitative experimental monitoring of the modulation of the electrocatalytic reaction current while the electrode is strained. The hydrogen evolution reaction (HER) on Au and Pt electrodes in H2SO4 is studied as a model process.
Our experiment uses a lock-in technique for following the modulation of the electrocatalytic reaction current in situ while a small cyclic elastic strain (~ 10-4) is imposed on the electrode material. The approach yields well-defined and precisely quantifiable coupling coefficients linking the reactivity to strain. The coefficients are measured as the function of the overpotential. We advertise the fact, ignored in previous work on strained-layer catalysis, that the coupling strength depends on the overpotential by magnitude and, as we show, even by sign. Specifically, tensile strain enhances the reactivity at low overpotential, whereas the trend is inverted and the reactivity diminished at higher overpotential. Furthermore, we show that the data affords a quantification of strain-dependence of the adsorption and barrier energies. This quantification is another distinguishing feature of our approach.
The overpotential-dependent coupling is readily modeled by kinetic rate theory. To this end, we take the impact of strain for, e.g., Heyrowsky kinetics to be mediated by (i) a strain dependence of the activation enthalpy for the ion + atom reaction step, and (ii) an independent strain dependence of the hydrogen adsorption enthalpy. In agreement with experiment, the rate equation predicts the reaction current-strain coupling coefficient to invert its sign upon transition from dilute to concentrated hydrogen adsorbate layer.
Our method appears applicable quite generally to electrocatalytic reactions. Therefore it promises a new tool for studying strain-dependent catalysis and for identifying the underlying microscopic processes.