bluuebunny/crossref_metadata_2025_split huggingface dataset:
Umpolung Diels-Alder Reactions By Electrocatalysis
Authors: Okada Yohei , Ozaki Atsushi , Yamaguchi Yusuke , Chiba Kazuhiro 
Published: February 2020

Although the Diels–Alder reaction is a classic reaction, it is still at the forefront of the carbon–carbon bond formation toolbox in synthetic chemistry. In particular, the mechanism of the reaction has been well studied, and the scope has been expanded to a wide variety of diene/dienophile combinations. However, electronic matching needs to be considered; more specifically, that one reaction partners should be electron-rich and the other electron-deficient. To overcome this hurdle, "umpolung" strategy has been proven to be powerful approach. In this context, single electron transfer (SET) would be the most simple and straightforward process. For example, electron-deficient radical cation species can be produced from electron-rich reactant via SET oxidation. A typical example of the umpolung Diels-Alder reactions is the reaction between an electron-rich diene and a dienophile. These combinations are electronically mismatched, however, SET oxidation can produce a radical cation of one component, which is then able to be trapped by the other component.
In addition to the use of chemical redox agents, photocatalysis and electrocatalysis are currently recognized as effective approaches to induce SET processes. Umpolung Diels-Alder reactions have also been extensively studied for almost half a century, however, scope of the reactions has been limited. In many cases, the reactions were triggered by SET oxidation of diene components, generating the radical cation species, and which were then trapped by dienophiles. In 2011, Yoon elegantly demonstrated the opposite version, namely, the reaction triggered by SET oxidation of dienophile components using photocatalysis.
We have been developing carbon-carbon bond formations by electrocatalysis in lithium perchlorate (LiClO4)/nitromethane (CH3NO2) electrolyte solution.1 In most cases, the use of LiClO4/CH3NO2 electrolyte solution is critical, which exhibits remarkable property as a Lewis acid to facilitate the reactions of carbon-centered radical cations with carbon nucleophiles. We also have shown that the electrocatalysis in LiClO4/CH3NO2 electrolyte solution is effective to induce umpolung Diels-Alder reactions.2 In this talk, recent advancement of the umpolung Diels-Alder reactions by electrocatalysis will be discussed in details.
(1) Imada, Y.; Yamaguchi, Y.; Shida, N.; Okada, Y.; Chiba, K. Chem. Commun.
2017, 53, 3960–3963.

(2) (a) Ozaki, A.; Yamaguchi, Y.; Okada, Y.; Chiba, K. ChemElectroChem
2017, 4, 1852–1855. (b) Okada, Y.; Yamaguchi, Y.; Ozaki, A.; Chiba, K. Chem. Sci.
2016, 7, 6387–6393.

Figure 1
Cycloaddition Reaction Assisted By Photoinduced Electron Transfer in a Lithium Perchlorate-Nitromethane System
Authors: Nagahara Shingo , Wakamatsu Hiroki , Okada Yohei , Chiba Kazuhiro 
Published: February 2020

Photochemical and electrochemical processes both have proven to be powerful tools that enable unique bond formations to construct various carbon skeletons. In this context, we have been developing electrochemical reactions in lithium perchlorate/nitromethane (LiClO4/MeNO2) electrolyte solution. This solvent system possibly stabilizes the anodically-generated cation species and acts as a Lewis acid catalyst. The feature of the LiClO4/MeNO2 allows effective syntheses of various compounds, such as dihydrobenzofuran derivatives formed via phenoxonium cation intermediates [1] and azanucleoside derivatives formed via iminium cation intermediates.[2] Furthermore, it is also demonstrated that the LiClO4/MeNO2 is effective for several [2+2] cycloaddition reactions between enol ethers and unactivated olefins,[3] affording cyclobutane products, and electrocatalytic Diels-Alder reactions[4]. In this way, our reaction development is governed by the use of a high concentration LiClO4/MeNO2 electrolyte solution. Recent 7Li NMR and calorimetric studies showed that Li+ is weakly coordinated in the solution to exhibit Lewis acidity, which we termed entropic effect.[5]

During such reaction developments, we serendipitously found the [2+2] cycloaddition reactions in LiClO4/MeNO2 also proceed under UV (365 nm) irradiation without any other reagents such as photo-catalyst. UV-Vis spectra study suggested that MeNO2 would absorb UV light and drive the reaction. This could be reasonably understood based on energy transfer mechanism, namely, irradiation of the MeNO2 with UV light produces the excited state, which then generates the excited state of the enol ether that undergoes the reaction. Molecular oxygen must also be involved in the overall process, since Ar bubbling had a negative impact on the reaction. . The reaction was also dramatically suppressed in other solvent systems Furthermore, we found this photo-induced reaction in LiClO4/MeNO2 system also can be applied to [4+2] and [3+2] cycloadditions. Details of reaction mechanism and scope & limitation would be discussed in the presentation.

Reference

[1] Kim, S.; Hirose, K.; Uematsu, J.; Mikami, Y.; Chiba., K. Chem.
Eur.
J.,
2012, 18, 6284–6288.
[2] Shoji, T.; Kim, S.; Chiba, K. Angew. Chem. Int. Ed., 2017, 56, 4011-4014.
[3] Okada, Y.; Nishimoto, A.; Akaba, R.; Chiba, K. J. Org. Chem., 2011, 76, 3470-3476.
[4] Okada, Y.; Yamaguchi, Y.; Ozaki, A.; Chiba, K. Chem. Sci., 2016, 7, 6387-6393.
[5] Imada, Y.; Yamaguchi, Y.; Shida, N.; Okada, Y.; Chiba, K. Chem. Comm., 2017, 53, 3960-3963.
Non – Linear Electrochemical Impedance Spectroscopic Analysis of Instabilities in Electrochemical Systems
Authors: Pachimatla Rajesh , Srinivasan Ramanathan 
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is one of the principle technique which is capable of in situ analysis of electrode – electrolyte interface and of probing electrochemical reaction mechanism. Typically, small amplitude perturbations are employed and the response is analyzed assuming that the system behavior is linear and stable [1, 2]. If large amplitude perturbations are employed, the resulting current will have significant higher harmonic signals, which can provide more information about the system examined [3]. This is often referred to as nonlinear EIS (NLEIS).
In this work, we present NLEIS analysis of an unstable system, where potential drifts and concentration changes are introduced. The classical Fe2+/Fe3+ redox couple is chosen for experimental and numerical analyses. A setup comprising of three instruments (Potentiostat, Lock-in amplifier and signal analyzer from Stanford Research System) to acquire the NLEIS data with the help of an in-house developed software was established. The applied perturbation frequency was varied from 100 kHz to 125 mHz and the amplitude was varied from 20 mV to 100 mV. The current magnitude and phase at fundamental and higher harmonics were measured using FFT analyzer. Instabilities were introduced by continuously changing the dc potential or the active species concentrations, during the NLEIS measurements. All the solution contained 100 mM Na2SO4 as supporting electrolyte. The initial concentration of Fe2+/Fe3+ species was 5 mM each. Figure 1 shows the experimental results with fixed as well as changing concentrations. In case of experiments denoted as ‘changing concentration’, the active species concentrations at any time ‘t’, min, were given by C = (200+ 3 t)-1 M. The governing equations were solved without linearization, using numerical methods. Both mass transfer and reaction kinetics effects were taken into consideration and the experimental results were compared with the numerical solutions.

Keywords: nonlinear EIS, system instabilities, potential drift, mass transfer effect

References

[1]. Orazem, M., Tribollet, B., Electrochemical Impedance Spectroscopy, John Wiley & Sons, NJ, (2008)
[2]. Wilson, J. R., Sase, M., Kawada, T. Adler , S.B., Electrochem. Solid-state Lett. 10 (5) (2007) B81-B86.
[3]. Fathima Fasmin and Ramanathan Srinivasan, J Electrochem. Soc., 164 (7) H443-H455 (2017)

Figure 1
Optical Direction of Morphological Complexity of Periodic Semiconductor Nanoarchitectures Deposited Via Templateless Photeolectrodeposition
Authors: Carim Azhar I , Batara Nicolas A. , Thompson Jonathan R , Atwater Harry A , Lewis Nathan S 
Published: February 2020

Electrodeposition of Se-Te alloy films under illumination spontaneously generates nanopatterned films with significant periodic order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern are a function of the exact nature of the optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Additoinally, the anisotropies, subwavelength feature size and periodic nature of the deposits enables the fabrication of optical elements with significant wavelength and polarization discrimination.
The nanopatterning process occurred without the use of any type of physical or chemical templating agents: no photomask, patterned substrate nor surfactants/ligands were used to influence the morphology. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was a consequence of the fundamental light-matter interactions during growth.
Methane Pulse and in-Situ Raman Study of Impregnated Ni/CGO As Anodes of SOFC
Authors: Ouyang Mengzheng , Boldrin Paul , Maher Robert C. , Brandon Nigel P. 
Published: February 2020

Nickel/gadolinium doped ceria (Ni/CGO) has been a popular SOFC anode material for decades for its superior mix conductivity and excellent oxygen storage capacity. However, the study of Ni/CGO in a realistic working condition is still lacking. Also, not much research has linked the chemical properties of CGO with the carbon resistance which is essential when using hydrocarbon as fuels.
In this research, Ni/CGO powder was prepared via impregnation-calcination method. A novel pulse experiment has been conducted on impregnated powder. We did certain pulses of a fixed amount of methane into the sample at 600℃.The outlet gas was monitored by a quadrupole mass spectrometer.
The product gas was composed of several species including hydrogen, steam, carbon monoxide, carbon dioxide, and methane that was not participated to the reaction.
The major reaction was the partial oxidation of methane.
With the increase of pulsing number, the product and shape of product peak changed a lot. Also, we observed a “tail” after each carbon monoxide production peak which was deduced to be the self-oxidation of carbon by the bulk migrated oxygen.
After detailed quantitative analysis of the shape and intensity of the peaks and tails. We came up with a model in which the mechanism of methane partial oxidation was confirmed and so was the relation between carbon self-oxidation rate, surface oxygen and bulk oxygen migration rate of CGO.
In-situ Raman spectroscopy was performed during the pulse experiment to monitor the change of CGO surface oxygen stoichiometry and deposited carbon. Thus we can confirm the conclusion deduced by pulse experiments and directly relate the carbon self-oxidation rate with bulk oxygen migration of CGO.
The results would provide an insight into the design and modification of SOFC anode materials.
(Invited) Development and Application of Core-Shell Cathode Catalysts in PEM Fuel Cell
Authors: Yang Lijun , Banham Dustin , Markiewicz Matthew , Knights Shanna , Ye Siyu 
Published: February 2020

Platinum group metals (PGM) catalysts are presently the most promising catalysts for the oxygen reduction reaction (ORR). However, the total PGM content in the PEM fuel cell should be reduced. To meet longer term passenger vehicle automotive targets, catalyst with at least 4 times higher mass activity over the currently available commercial Pt/C is required. One promising approach to meet this goal is the development of Pt monolayer core-shell catalysts through electro under-potential deposition of Cu onto a core (Pd, PdAu, etc.), followed by galvanic replacement of the Cu by Pt salt [1]. It is widely accepted that Pt monolayer catalysts exhibit at least 4-8 times higher mass activity vs. Pt/C, while also demonstrating excellent durability during accelerated stress testing on rotating disk electrodes (RDE) [2]. However, the scale-up synthesis of the platinum monolayer core-shell catalysts and the retention of favorable catalytic performance in the membrane electrode assemblies (MEA) are still quite challenging [3].
In this work, we will present the results of Pd@Pt/C core-shell catalysts successfully scaled up (in-house) from a conventional synthetic approach (micro gram level) to a large 3-electrodes reactor (gram level). It is demonstrated that this scale up is successful, with the gram level batch showing comparable activity to the small scale batch, based on RDE testing. In addition, preliminary in-situ MEA tests of commercial core-shell catalysts will be presented, demonstrating the performance and durability of these monolayer core-shell catalysts under fuel cell operating conditions.
[1] R. R. Adzic. Electrocatalysis, 2012, 3 (3-4):163-169.
[2] J. Hu, L. Wu, K. A. Kuttiyiel, K. R. Goodman, C. Zhang, Y. Zhu, M. B. Vukmirovic, M. G. White, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 2016, 138: 9294-9300.
[3] L. L. Zhang, S. Zhu, Q. Zhang, D. Su, J. Yue, Z. Du, M. Shao. ACS Catal. 2016, 6: 3428 −3432.
(Keynote) Correlating Fundamental Properties of Materials to Fuel Cell Catalysts
Authors: Lopes Pietro Papa , Strmcnik Dusan , Markovic Nenad M , Stamenkovic Vojislav 
Published: February 2020

Fuel cells technology rely on electrochemical processes that need to provide satisfactory energy density in order to be used in applications for transportation; however, a major challenge lies in the insufficient activity and durability of materials that are currently employed as cathode catalysts for electrochemical reduction of oxygen. These limitations inevitably lead to a lower operating efficiency of the devices, which highlights the need for development of more active and durable oxygen reduction reaction (ORR) catalysts. Consequently, the majority of research efforts are placed on the catalyst design and synthesis aiming to improve their efficiency. It has been found that properties such as surface structure, surface and subsurface composition are determining electronic properties and have distinguished roles in defining the functional properties of electrocatalysts 1. The material-by-design-approach, would be used here as an example to emphasize the transfer of the knowledge obtained from the well-defined systems towards tailor-made real-world catalysts 2. Considering current state-of-the-art in fuel cells, most of the research is centered on platinum, which is the best monometallic catalyst for the ORR. Special emphasis will be placed on utilization of multimetallic systems that could provide additional benefits by bringing together highly diverse constituents to alter and tune both catalytic activity and durability 3.
[1] Stamenkovic et al. Science 315 (2007) 493.
[2] Stamenkovic et al. Nature Materials 6 (2007) 241.
[3] Wang et al. Nano Letters 11 (2011)919.
(Invited) Solar Fuel Production for a Sustainable Energy: Water Splitting to Hydrogen and CO2 to Fuel
Authors: Chu Deryn , Li Jiangtian 
Published: February 2020

Chemical fuel generation by solar driven water splitting to hydrogen and CO2 reduction to hydrocarbons is attractive to supply the sustainable energy. The design and fabrication of photoelectrode materials that are able to harvest sunlight and then produce excitons for chemical reactions is an important scientific undertaking. In this presentation, we will present our recent experimental and theoretical efforts to engineer both photoanode and photo/cathode materials from the perspectives of light absorption improvement by forming heterojunctions, electronic band structure manipulation by controlling the surface states and energetic level alignment, as well as surface catalysts optimization with the aim to improve their capability in the sunlight harvesting range, charge carrier transport efficiency, and the product selectivity. The resultant nanostructures could be employed as photocathode and photoanode separately in a photoelectrochemical tandem cell for unbiased solar fuel generation.
Keywords: Solar fuels, Water Splitting, CO2 Reduction, Photoelectrochemical Tandem Cell.
Electrochemical Reduction of Aqueous CO2 to Synthesis Gas Using β Palladium Hydride
Authors: Sheng Wenchao , Kattel Shyam , Yao Siyu , Chen Jingguang G 
Published: February 2020

Electrochemical reduction of CO2 (CO2RR) to value-added liquid fuels or chemical feedstocks using off-peak electricity or intermittent renewable energy sources is a green approach for energy storage and carbon recycling. However, the difficult activation of CO2 to form the CO2
∙−
intermediate and the competitive hydrogen evolution (HER) in aqueous electrolytes make the Faradaic efficiency and selectivity for the CO2RR remain very low. From another perspective, CO2 reduction to CO, with co-production of H2 from water, is very appealing as the mixture of CO and H2 with controlled ratio can be used as syngas for methanol synthesis and Fischer-Tropsch reactions. In this approach, catalyst search is therefore no longer limited to metals with low HER activity such as Au and Ag. Materials with fair HER activity can be potentially considered for the CO2RR. Interestingly, Pd, a good HER catalyst, has been found to continuously produce CO in the CO2RR, which is however counterintuitive to that Pd is prone to CO poisoning.[1] In this work, we have re-examined Pd for the CO2RR using in situ XAS and in situ XRD, and have found that Pd transforms into β-PdH under the CO2RR condition. DFT calculations suggest that CO adsorption energy on the PdH surface is greatly reduced compared to that on the Pd surface, which is most likely the cause for high selectivity of CO2RR to CO when using Pd as the electrocatalyst.[2]
[1] Y. Hori, Modern Aspects of Electrochemistry, Springer, New York, 2008, vol. 42, ch. 3, pp. 89–189.
[2] Wenchao Sheng, Shyam Kattel, Siyu Yao, Binhang Yan, Zhixiu Liang, Christopher J. Hawxhurst, Qiyuan Wu and Jingguang G. Chen, Energy & Environmental Science, 10, 1180-1185 (2017)
(Keynote) Tuning the Properties of Biological Catalysts for Biofuel Cells Applications: From Site-Directed Mutagenesis to the Design of Macroscopic Redox Matrices
Authors: Léger Christophe , Fourmond Vincent , Dementin Sébastien 
Published: February 2020

Microorganisms make large metalloenzymes which catalyse the production and recycling of biological "solar fuels" such as O2, H2 and CO2. Using these enzymes in biotechnological applications requires that they be selected according to their particular properties or that these properties be tuned. It may be important for example that a particular enzyme resists inhibition by oxygen or work with high efficiency in one particular direction of the reaction (e.g. H2 oxidation versus H2 production). Here we shall summarise our efforts to understand the molecular determinants of catalytic bias and oxygen sensitivity in hydrogenases and CO-dehydrogenases (enzymes that catalyse the H+/H2 and CO2/CO conversion), and explain why and how these properties are affected when the enzymes are incorporated in a redox hydrogel that allows mediated electron transfer to the electrode.
References:
http://bip.cnrs-mrs.fr/bip06/~leger/
http://orcid.org/0000-0002-8871-6059

Figure 1
Electrical Response of a New Lipophilic Ionic Liquid and the Effect of CO2 on Its Conductivity Mechanism
Authors: Bertasi Federico , Vezzù Keti , Pagot Gioele , Pace Giuseppe , Negro Enrico , Abu-Lebdeh Yaser , Armand Michel , Di Noto Vito 
Published: February 2020

Ionic liquids (ILs) have drawn sustained attention in the last twenty years due to their unique combination of intrinsic conductivity, very low vapour pressure and their ability to be tailored to an application via facile chemical modification [1].
As a consequence, the development of new ILs with improved properties and an in-depth understanding of the interplay existing between structures and properties are particularly active research fields.
In this report preparation and study of a new lipophilic tetraoctyl-formamidinium bis(trifluoromethanesulfonyl) imide (TOFATFSI) ionic liquid [2], will be discussed.
Tetraoctyl-formamidinium (TOFA) TFSI proved to be a water-insoluble IL that is completely miscible with the lower alkanes and the solutions are ionic conductors. Therefore, we were intrigued if conductivity could be induced in an even more demanding medium, i.e. supercritical carbon dioxide (scCO2) [3,4].
Following this, the conductivity and relaxation phenomena of this new IL are revealed through the analysis of the broadband electric spectra with a particular emphasis on the effect of temperature and CO2 pressure on the IL conductivity.
It is found that temperature boosts the conductivity via an increase in the charge carrier mobility. Also, CO2 absorption affects both the conductivity and the permittivity of the material due to the presence of CO2–IL interactions that modulate the nanostructure and the size of the TOFATFSI aggregates, which increases both the mobility and the density of the charge carriers.

Acknowledgements

The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence).

References

[1] F. Bertasi, K. Vezzù, G. Nawn, G. Pagot, V. Di Noto, Interplay Between Structure and Conductivity in 1-Ethyl-3-methylimidazolium tetrafluoroborate/(δ-MgCl2)f Electrolytes for Magnesium Batteries, Electroch. Acta, 219, 152-162 (2016).
[2] Federico Bertasi, Guinevere A. Giffin, Keti Vezzù, Pace Giuseppe, Yaser Abu-Lebdeh, Michel Armand, Vito Di Noto, A lipophilic ionic liquid based on formamidinium cations and TFSI: The electric response and the effect of CO2 on conductivity mechanism, PCCP, 19, 26230 – 26239 (2017).
[3] V. Di Noto, K. Vezzù, F. Conti, G.A. Giffin, S. Lavina, A. Bertucco. Broadband electric spectroscopy at high CO2 pressure: Dipole moment of CO2 and relaxation phenomena of the CO2 - poly(vinyl chloride) system. J. Phys. Chem. B, 115, 9014-9021 (2011).
[4] S. Kitajima, F. Bertasi, K. Vezzu’, E. Negro, Y. Tominaga, V. Di Noto. Dielectric relaxations and conduction mechanisms in polyether-clay composite polymer electrolytes under high carbon dioxide pressure. Phys. Chem. Chem. Phys., 15, 16626-16633 (2013).

Figure 1