bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemically-Induced Radical Cation Diels-Alder Reactions Assisted By "Redox Tag Strategy"
Authors: Yamaguchi Yusuke , Okada Yohei , Chiba Kazuhiro 
Published: February 2020

Diels-Alder (DA) reaction is among the most important reaction for constructing carbon-carbon bond in organic chemistry. The mechanisms into it are well understood; diene and dienophile should have complementary electronic characters for smooth reaction. In the situation where both substrates are electron-rich, significantly higher temperature or longer time are required.
One of the most effective solution for such electronically-mismatched DA is umpolung process, which can give highly electrophilic radical cation from otherwise nucleophilic electron-rich starting substrates by one electron oxidation. Namely, the radical cations generated from electron-rich olefins can readily afford the DA adduct with nucleophilic electron rich dienes.1 Since electrochemical method has proven to be the simplest approach for the umpolung reaction, anodic method has been developed for the radical cation-mediated DA (rDA).2

Our group have been focused on the anodically-induced C-C bond forming reactions using lithium perchlorate nitromethane electrolyte solution system.3 In particular, [2 + 2] cycloaddition reaction4 between enol ether and unactivated terminal olefin is initiated by one electron oxidation of enol ether to give corresponding radical cation. The reaction allow for the mechanistic study of radical cation species, providing information, for example, intramolecular electron transfer properties5 and functionality of aromatic radical cation intermediates.6

In the talk to be presented, anodically-induced rDA (Scheme 1) will be reported especially to electrochemical condition, scope and limitations, and new design of the rDA based on the previous study of radical cation properties.
References:

Bellville, D. J.; Wirth, D. D.; Bauld, N. L. J. Am. Chem. Soc.
1981, 103, 718.

Mlcoch, J.; Steckhan, E. Tetrahedron Lett.
1987, 28, 1081.

Chiba, K.; Tada, M. J. Chem. Soc., Chem. Commun.
1994, 2485.

Chiba, K.; Miura, T.; Kim, S.; Kitano, Y.; Tada, M. J. Am. Chem. Soc.
2001, 123, 11314.

Yamaguchi, Y.; Okada, Y.; Chiba, K. J. Org. Chem.
2013, 78, 2626.

Okada, Y.; Nishimoto, A.; Akaba, R.; Chiba, K. J. Org. Chem.
2011, 76, 3470.

Figure 1
All Vanadium Redox Flow Battery Development for Stationary Energy Storage Applications
Authors: Sprenkle Vincent , Reed David , Thomsen Ed , Wang Wei , Li Bin , Nie Zimin , Koeppel Brian J , Recknagle Kurt P , Viswanathan Vilayanur , Crawford Alasdair 
Published: February 2020

The DOE Office of Electricity’s – Energy Storage program at Pacific Northwest National Laboratory (PNNL) has been focused on the development of cost effective energy storage technologies to improve the grid reliability, power quality, and adoption of the intermittent renewable energy. Among the most promising large-scale energy storage technologies are redox flow batteries (RFBs). RFB’s are electrochemical devices capable of storing up to multi-megawatt-hours (MWhs) of electrical energy via a reversible electrochemical energy conversion. Unlike traditional batteries in which the electrodes serve as the supply/sink of ionic charge, RFB’s store electricity in liquid electrolytes that flow on either side of a membrane. As such, the power and energy of a RFB can be separately designed, offering greater flexibility for a greater selection of stationary applications.
All-vanadium RFB system enlists the same element, vanadium, in both the catholyte and anolyte. Researchers at PNNL have revisited the standard vanadium sulfate electrolyte chemistry used in this system and developed an novel mixed acid electrolyte (sulfate and chloride) that can stabilize all four vanadium cations at concentrations ≥ 2.5M within a temperature range of 5~50oC. Recently, PNNL recently demonstrated a kW/kWh scale prototype battery utilizing this electrolyte system in order to better understand the system benefits of the mixed acid electrolyte. The system consisted of ~ 20 cell stack with 780cm2 of active area/cell, ~ 30 liter electrolyte tanks, pumps and associated piping. The stack incorporated new interdigitated flow fields for reduced pressure drop and thinner Nafion membranes for improved performance. Results of stack testing under a wide range of current densities and temperature conditions will be reported along with resulting energy efficiencies.
Building a Better Redox Flow Battery - Innovative Diagnostics to Visualise Reactant Transport
Authors: Rubio-Garcia Javier , Kucernak Anthony R. J. 
Published: February 2020

While the optimization of PEMFCs and RFBs require addressing multiple issues, both systems share an operation mechanism based on pumping a fluid (a gas or a liquid) containing chemically reactive species across the face of an electrode. As a consequence of this characteristic, a significant source of inefficiency is linked to mass transport limitations including high pressure drop or inhomogeneous reactant flow distribution across the electrode. Previously, strategies including infrared mapping, (1) magnetic resonance imaging (2) or neutron radiography (3) were employed in an attempt to investigate fluid transport phenomena (predominantly for fuel cells). However, although those studies rendered valuable results, the measuring procedures can be considered as expensive and require delicate equipment.
In this contribution, a simple and low cost methodology to study the mass transport processes in RFBs is presented. This approach relies on the instantaneous electrochemiluminescence of Luminol. By simply recording the emitted light with a low cost camera,(4) concentration profiles at the surface of the electrode were obtained presenting high temporal and spatial resolutions. In addition, modifications on the electrolyte formulation and flow rate permitted identifying turbulent flow areas located at the turn of the flow field (Fig. 1) as well as leading to the design of improved components.

References:

(1) Wang et al., Journal of Power Sources, 157, 181–187 (2006).
(2) Tsushima et al., Magnetic Resonance Imaging, 23, 255-258 (2005).
(3) Trabold et al., International Journal of Heat and Mass Transfer, 49, 4712–4720 (2006).
(4) Lopes et al., Journal of Power Sources, 274, 382–392 (2015).

Figure 1
Determination of Inorganic Arsenic As(III) in Water By Anodic Stripping Linear Sweep Voltammetry Using Gold Ultra-Microelectrode Array
Authors: Duong Quyet Nguyen , Le Nghiem Van , Le Thuong Dinh , Nguyen Hoang Thai , Tong Hien Duy , Nguyen Thoa Thi Phuong 
Published: February 2020

A sensitive electrode has been developed for the determination of arsenic As(III) ions by anodic stripping linear sweep voltammetry (ASLSV). The method shown in this work for the electroanalytical speciation of inorganic As(III) in water used a gold ultra-microelectrode array, consisted of 100 gold wires; each sized of 1 µm width and 1000 µm long. The sensor from gold band microelectrode arrays was made on a silicon wafer by the deposition and etching under angles (DEA) technique.
The parameters of ASLSV, such as deposition potential (Edep) and time (tdep) and potential scan rate, were investigated. Different acidic solutions (HNO3, H2SO4, HClO4, H3PO4, HNO3/KCl, H2SO4/KCl and HClO4/KCl) with various concentrations were tested as a supporting electrolyte for arsenic analysis, from which the 0.1 M H3PO4 solution was chosen due to its medium acidity and being environmental friendly. Well defined voltammetric waves at Edep = -0.450 V (vs. Ag/AgCl reference electrode), tdep = 100 s and 1.000 V/s scan rate are found with peak currents proportional to the concentration of As(III) in the range of 10 to 100 ng.L-1. The limit of detection was 2 ng.L-1(signal-to-noise ratio = 3). These results well satisfy the requirements given by the World Health Organization (WHO). The repeatability, linearity and accuracy of the proposed method were evaluated. This method was applied for analysis of As(III) in natural water samples and the obtained results suggested that the fabricated gold chip would facilitate monitoring of As(III) in water.
This research was part of the project ĐTĐL.2011-G/76, granted by the Ministry of Science and Technology (MOST) Vietnam.

Keywords: anodic stripping voltammetry, arsenic, gold, ultra-microelectrode.
Non-Precious Metal Catalysts for the Oxygen Reduction Reaction
Authors: Varnell Jason A. , Tse Edmund C. M. , Gewirth Andrew A. 
Published: February 2020

We report on our efforts to characterize the active site of Fe-based non-precious metal (NPM) catalysts for the oxygen reduction reaction (ORR). Acid leaching using aqua regia significantly decreases the amount of Fe present in the catalyst material to levels below 1 wt% with the lowest Fe content observed at 0.34 wt%. However, no change in the ORR onset is observed following catalyst treatment with acid when tested in acidic media. This indicates that some Fe centers are buried within the carbon material making then inaccessible to the acid treatment. These remaining Fe sites are accessible to oxygen and are catalytically active to the ORR.
To further remove Fe from NPM ORR catalysts we exposed them to chlorine gas at high temperature (600- 1000 °C). Through this treatment Fe content as low as 0.16 wt% is achieved. After the demetalation with chlorine gas the ORR onset is seen to shift to more negative potentials by as much as 250 mV when tested in acidic media. Remetalation by exposure to FeCl3 results in partial recovery of ORR activity.
We also summarize our efforts examining multinuclear copper complexes inspired by laccase, a class of blue copper oxidases that efficiently mediate the four-electron four-proton reduction of dioxygen to water.(1) We first prepare Cu complexes of 2,2'-dipicolylamine (DPA) and test its electrocatalytic activity towards the ORR. To investigate the effect of multinuclearity on the ORR, we connect two DPA units together with a flexible linker and installed a third metal-binding pocket in the ligand framework (Figure 1).
The ORR onset potentials and the diffusion-limited current densities of [Cu(1)]2+ are comparable to that of [Cu(TPA)(H2O)]2+ previously reported by our group. However, the electron transfer rate between [Cu(1)]2+ and carbon electrode surface is low, indicating that more intimate coupling to the electrode may be required for efficient ORR. Covalently linking two [Cu(DPA)]2+ cores together results in ORR activities no better than [Cu(1)]2+ alone.
This study highlights the viability of Cu complexes of DPA to mimic the T3-site of laccase and serves as a guide for designing future laccase models. The relationship between inter-site flexibility and cooperativity is long recognized; it is insufficient to simply connect reactive Cu sites. To ensure cooperativity comparable to that of metalloproteins, future catalysts will require more sophisticated designs.
Reference
1. E. C. M. Tse, D. Schilter, D. L. Gray, T. B. Rauchfuss and A. A. Gewirth, Inorg. Chem., 53, 8505 (2014).

Figure 1
NO Electrochemical Reduction on Pt Electrocatalysts: A DFT Approach
Authors: Chun Hee-Joon , Clayborne Andre , Rankin Rees , Greeley Jeff 
Published: February 2020

Electrochemical denitrification is a promising technology for the removal of toxic nitrate and nitrite species from groundwater due to the process’s environmental compatibility, energy efficiency, safety, and product selectivity. The adsorbed NO is generally considered to be a selectivity-determining species during this electrochemical potential dependent reaction. Atomic-scale studies using density functional theory (DFT), in turn, can provide powerful molecular-level information about the elementary mechanisms of reductive NO electrocatalysis. These basic building blocks can further serve as a starting point for future trends-based analysis on different transition metal surfaces.
In this work, we employ periodic, self-consistent DFT calculations to clarify the adsorption structures and thermochemistry of NO and its related reaction intermediate species on different Pt single crystal surfaces ((111) and (100)). Kinetics are further determined by calculating the activation barriers for N-O dissociation, protonation, and N-N bond formation. We begin by describing results for the reaction at low NO coverage (ca. 0.11 ML). After describing the thermodynamics (the adsorption) and kinetics (N-O bond breaking and protonation barrier) for the dentirification reaction scheme, a plausible mechanistic reaction pathway is proposed. Water-assisted protonation barriers are generally shown to be lower than barriers for non-electrochemical reactions, such as surface hydrogenation or N-O bond breaking. Consistent with available experimental evidence, from the most probable reaction pathway, we conclude that ammonium ion would be the most favorable product that would evolve. There is no evidence for the formation of hydroxylamine (H2NOH) at low coverage. At higher NO coverages (ca. 0.45 ML), the relative energy states of the intermediates show a similar trend for the energetics when it is compared with the study with lower NO coverage.
Finally, N2O formation is examined. We find that trans NO dimer species could be a precursor state for the N­2O formation due to its lower kinetic barrier than barriers that are found for cis-type NO dimers. The simulation demonstrates that N2O could be formed at higher potentials through two protonations of trans NO species, and the reaction is thermodynamically more favorable at higher NO coverage. This barrier could be surmountable at room temperature, and these mechanistic conclusions hold on both the (111) and (100) surfaces.
Based on our study, we find that reduction of NO proceeds through the water-assisted protonations which will finally lead to ammonia. The primary pathway for N2O formation occurs through trans-type NO dimer species. The proposed pathways occur with different applied electrochemical potentials and NO coverages.
Electrocatalytic Oxidation of Ethanol and Formic Acid on Bimetallic Nanoalloys and Core-Shell Nanoparticles
Authors: Lewera Adam , Gorzkowski Maciej T. , Piwowar Justyna , Jablonski Andrzej , Gralec Barbara , Jurczakowski Rafal Robert 
Published: February 2020

Mechanism of ethanol electrooxidation on numerous materials has been widely investigated in the past. It is well known that in acidic conditions the electrooxidation of ethanol on platinum surface leads to strongly adsorbed surface groups (i.e. CO), poisoning the surface of catalyst and inhibiting further reactions. Presence of metals other than platinum will make it possible to oxidize adsorbed CO by surface OH groups, present on the other metal (so called “bi-functional mechanism”). Such bi-metallic surface is more resistant to poisoning and as a result more catalytically active. Hovewer it is still not well understood, how the presence of the other metal influences the surface’s electronic properties, which in turn alter adsorption properties, and reaction mechanism.
Electronic properties of the catalyst can be modified by the following methods: they can be related directly to charge transfer from other component of the system, such as another component of the alloy, from substrate, or they can be induced by geometric factors, such as change in lattice parameter. Change in lattice parameter influences the degree of overlapping of valence orbitals forming the conduction band. When lattice is contracted, the conduction band becomes broader. When the conduction band is filled in more than half the broadening of the conduction band leads to shift of the d-band center towards Fermi edge. The lattice parameter can be (to some degree) modified, and as a result, the degree of orbital overlapping can be changed, for instance by alloying. It is known that in alloys the atom-atom distance changes linearly as a function of composition, in the range determined by inter-atomic distances of the pure elements (Vegard’s law). Similarly, when thin layers are formed, the layer forming metal will exhibit the lattice parameter of the substrate (so called “pseudomorphic monolayer”). Consequently experimental investigation of materials, where lattice parameter has been intentionally modified, allows for experimental determination of the relation between reaction mechanism and electronic properties of the material used.
Study of the Supported Catalysts Core-Shell Type of Gold and Palladium: Analysis of the Reaction Products and Mechanism for the Electrooxidation of Ethanol in Alkaline Medium
Authors: Ruiz Montoya José Gabriel , Chávarri Marín Violeta Herminia , Ocón Esteban Pilar , Morales Gomero Juan Carlos 
Published: February 2020

One of the main disadvantages to the development of fuel cells direct ethanol (DEFCs) is the synthesis of catalysts which are able to break the C-C bond in the molecule of ethanol. In this context, Xu et al.,[1] compares the activity of palladium and platinum for ethanol oxidation reaction (EOR) in alkaline medium, showing that the onset of ethanol oxidation on palladium occurs to potential more negative compared to platinum, and the oxidation current density is higher for the palladium.
One way to study the reaction and propose a reaction mechanism for an electrochemical process is using in situ FTIR spectroscopy. For example Tremiliosi-Filho et al., [2] propose an accepted mechanism of ethanol oxidation on gold by FTIR in situ, while Zhou et al., [3] studied the adsorption and oxidation of ethanol on polycrystalline Pd. Since, palladium is more electroactive for ethanol electrooxidation than gold, in this work, the effect of a supported catalyst core-shell Au-Pd, in different proportions were studied.
In this work, the preparation of core-shell catalysts supported Au-Pd/C, in different ratios detailed. The characterization of the catalysts was performed using X-ray diffraction, Energy Dispersive Spectrometer (EDS), transmission electron microscopy (TEM), and electrochemical tests, to calculate the real electroactive area. Cyclic voltammetry tests showed that for the case of Au-Pd catalysts, the parameters like onset and density current oxidation of ethanol were better in relation to gold and palladium alone. This is due largely to the gold produces a stable nucleus where Pd nanoparticles can be dispersed better. On the other hand, the in situ FTIR studies showed an identical oxidation of Au and Pd in an alkaline medium with acetate ion with main product, but variations are also observed in the symmetry and intensity of the collected peaks, this has to see strongly with different intensities bond between ethanol and Pd onset of oxidation.
In conclusion, in this study it was found that the Au-Pd catalysts show better electrocatalytic properties that gold and palladium catalysts. This leads to a more efficient oxidation of ethanol, and use less amount of Pd in the anode catalysts.

References:

[1] Xu, Changwei, et al. "Methanol and ethanol electrooxidation on Pt and Pd supported on carbon microspheres in alkaline media." Electrochemistry Communications 9.5 (2007): 997-1001.
[2] Tremiliosi-Filho, G., et al. "Electro-oxidation of ethanol on gold: analysis of the reaction products and mechanism." Journal of Electroanalytical Chemistry444.1 (1998): 31-39.
[3] Zhou, Zhi-You, et al. "In situ FTIR spectroscopic studies of electrooxidation of ethanol on Pd electrode in alkaline media." Electrochimica Acta 55.27 (2010): 7995-7999.

Figure 1
Improving Activity and Stability of ORR Electrocatalysts with Pt-Rich Hollow Nanostructures
Authors: Dubau Laetitia , Asset Tristan , Chattot Raphaël , Maillard Frederic 
Published: February 2020

The ever-growing energy demand worldwide and the announced end of the so-called “fossil fuel era” are currently boosting the development of electrochemical energy technologies, such as fuel cells, batteries and supercapacitors. In proton-exchange membrane fuel cells (PEMFC), special effort has been paid to improve the catalytic activity for the oxygen reduction reaction (ORR) of the cathodic material, its stability and to decrease its precious metal content.
This study describes the advantages of hollow nanostructures composed of a Pt-rich outer-layer surrounding a central void. Pt-rich hollow nanoparticles with different Pt-shell thicknesses were synthesized via a method involving the galvanic replacement of Ni atoms by Pt atoms, and the nanoscale Kirkendall effect [1]. Increasing the Pt:Ni stoichiometry from 1:1 to 1:5 in the initial metal precursor solution resulted into a thinner Pt-rich shell and an increased Pt lattice contraction. The specific activity and the mass activity for the ORR at E = 0.95 V vs. RHE of the most active hollow electrocatalyst were 9-fold and 3.6-fold that of a reference solid carbon-supported Pt nanocrystallites with a comparable crystallite size (Figure 1). Their structural stability was investigated at different temperatures ranging from T= 293 to 353 K by identical-location and conventional transmission electron microscopy.
Acknowledgements
This work was performed within the framework of the Centre of Excellence of Multifunctional Architectured Materials "CEMAM" n° AN-10-LABX-44-01 funded by the "Investments for the Future" program. The authors acknowledge financial support from University of Grenoble-Alpes through the AGIR program (grant # LL1492017G), and from the French national Research Agency through the HOLLOW project (grant # ANR-14-CE05-0003-01).
References
[1] L. Dubau, M. Lopez-Haro, J. Durst, L. Guétaz, P. Bayle-Guillemaud, M. Chatenet, F. Maillard, “Beyond conventional electrocatalysts: Hollow nanoparticles for improved and sustainable oxygen reduction reaction activity”, J. Mater. Chem. A. 2 (2014) 18497-18507.

Figure 1
(Invited) Electrocatalysis on Tailored Electrochemical Interfaces
Authors: Kang Yijin , Li Dongguo , Strmcnik Dusan , Markovic Nenad M , Stamenkovic Vojislav R 
Published: February 2020

The primary barrier to broad applications of electrocatalyst for electrolyzers, fuel cells and metal-air batteries is lack of fundamental understanding of processes that are taking place at solid-liquid interfaces. Moreover, the cost, performance and durability of the current state of the art electrocatalysts are still not at level that would warrant commercialization of these technologies.
This presentation will bring the most recent progress in the development of advanced interfaces for electrochemical energy conversion and storage. The structure-function relationships in electrocatalysis that led to establishment of principles for the design of advanced electrocatalysts will be particularly discussed. It will be also demonstrated that fine tuning of the properties of solid and liquid components at the interfaces can led towards unprecedented improvements in functionality of practical materials for energy conversion and storage applications.
(Invited) Epitaxial Oxide Surfaces: New Insights in Oxygen Electrocatalysis
Authors: Stoerzinger Kelsey A. , Shao-Horn Yang 
Published: February 2020

Fundamental understanding of transition metal oxides for oxygen electrocatalysis is often hampered by heterogeneity of oxide powder surfaces and the composite nature of electrodes used for electrochemical measurements. Surfaces of epitaxial thin films, with well-defined crystallographic orientations and strains offer an excellent opportunity to develop insights into what parameters can govern catalytic activity and deduce active sites for oxygen electrocatalysis. In addition, these surfaces allow spectroscopic study of the chemical speciation and electronic structure in an aqueous reaction environment, using ambient pressure X-ray photoelectron and absorption spectroscopy coupled with mass spectrometry to analyze the reaction productions. Here, control of the surface homogeneity is critical for quantifying the adsorption of intermediates and comparing the reactivity between surfaces. The insights obtained from study of these epitaxial surfaces build fundamental understanding of the mechanisms of oxygen electrocatalysis, as well as guide the rational design of high surface area oxide catalysts for technical application.