bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward Greener Lithium-Ion Batteries: Aqueous Binder-Based LiNi0.4Co0.2Mn0.4O2 Cathode Material with Superior Electrochemical Performance
Authors: Chen Zhen , Kim Guk-Tae , Chao Dongliang , Copley Mark , Passerini Stefano , Shen Zexiang
Published: February 2020

This work reports a strategy towards greener lithium-ion batteries, by employing the aqueous sodium carboxymethyl cellulose-based LiNi0.4Co0.2Mn0.4O2 (CMC/NCM) as cathode electrode. Compared with conventional organic PVDF-based electrodes, the CMC/NCM electrodes display very uniform distribution of NCM and carbon particles together with strong adhesion among the particles and with the current collector, leading to significantly mitigated crack formation and delamination of the electrode upon repeated delithiation/lithiation processes. As a result, CMC/NCM electrodes show good structural integrity. Additionally, these electrodes offer enhanced Li+ diffusion kinetics, reduced polarization, therefore, excellent high C-rate capability, and extremely stable cycling performance. In detail, CMC/NCM electrodes achieve capacity retention ratios as high as 96.4% (0.1 C), 102.9% (2 C), 111.8% (10 C), and 96.7% (at elevated temperature, i.e., 60 oC, 10 C) after 100 cycles. Moreover, benefiting from the features of low cost, environmentally friendliness, and easy disposability-recyclability, the water-soluble CMC is expected to be a promising binder for practical applicants in energy storage systems.
Catalytic Activities of MnO2/RuO2/Carbon Nanocomposites for Li-O2 Battery Application
Authors: Nahm Kee Suk , Arul Anupriya , Moon Kwang Uk , Park Hyosoek
Published: February 2020

We report the synthesis and electrochemical characterization studies of a bifunctional catalyst suitable for lithium air battery application. MnO2 and RuO2 are supported on two different carbon supports such as graphite nanofiber(GNF) and graphene oxide(GO) to employ oxygen cathode catalyst of lithium-air batteries. MnO2/GNF is first prepared by a simple hydrothermal synthesis and is then decorated with RuO2 using a redox reaction technique. The highest electrocatalytic performance is observed from a weight ratio of RuO2:MnO2/GNF=5:5 with good cyclability and high specific capacity. Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3(BSCF) decorated with palladium shows good ORR and OER activity when tested in aqueous medium (ORR onset potential : -0.072 V vs Hg/HgO, OER onset potential : 0.700 V vs Hg/HgO).
High-Energy Density LiNiO2 Core- Li[Ni0.87Co0.065Mn0.065]O2 shell Structured Li[Ni0.
95Co0.
025Mn0.
025]O2 Cathode for Lithium-Ion Batteries
Authors: Kim Un-Hyuck , Sun Yang-Kook
Published: February 2020

A core-shell (CS) structured cathode with a LiNiO2 core and Li[Ni0.87Co0.065Mn0.065]O2 shell, resulting in an average composition of Li[Ni0.95Co0.025Mn0.025]O2, was synthesized via the co-precipitation method. The core material, LiNiO2, designed to maximize the discharge capacity, was protected by a 500-nm-thick encapsulating Li[Ni0.87Co0.065Mn0.065]O2 shell layer to improve the structural stability. The CS cathode delivered an initial discharge capacity of 235.7 mAh g-1 at 0.1 C (18 mA g-1) and 90% of its initial capacity was maintained after 100 cycles at 0.5 C (90 mA g-1), whereas the capacity retention of the LiNiO2 cathode without the protective shell was limited to 74.2% after 100 cycles. The improved cycling stability of the CS cathode was also verified in a full cell test (against graphite anode) in which the cathode also clearly outperformed the LiNiO2 cathode. The improved cycling performance is mainly attributed to stabilization of the inherently reactive LiNiO2 surface by the Ni-depleted protective shell layer. The proposed CS approach allows harnessing of the high capacity of LiNiO2 and other extremely Ni-rich compositions with dramatically improved capacity retention, thus moving closer to satisfying the high energy density and long lifetime requirements for lithium-ion batteries for electric vehicles.

References

S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.

H. J. Noh, S. Youn, C. S. Yoon and Y.-K. Sun, J. Power Sources
2013, 233, 121.

C. S. Yoon, M. H. Choi, B.-B. Lim, E.-J. Lee, and Y.-K. Sun, J. Electrochem. Soc.
2015, 162, A2483.

Y.-K. Sun, S.-T. Myung, M.-H. Kim, J. Parakash, and K. Amine, J. Am. Chem. Soc. 2005, 127, 13411
Optimization of Li-O2 Batteries Using Bi Compartment Cells to Separate and Improve Each Electrode Condition
Authors: Kim Hun , Sun Yang-Kook
Published: February 2020

Despite theoretically high energy density of Li-O2 batteries, low energy efficiency, poor cycle life and Li-metal safety issues make the use of them yet impractical. Therefore, efforts are made to protect/block the lithium metal anode in these cells, in order to mitigate side reactions. However, new approach1-3 is required in order to solve the problems mentioned above, especially the irreversible reactions of the redox mediators which are mandatory to these systems with the Li anode.

Here, optimized bi compartment cells are proposed, in which detrimental crossover between the cathode and anode is completely avoided. The Li metal anode is cycled in electrolyte solution containing fluorinated ethylene carbonate, in which its cycling efficiency is excellent. The cathode compartment contains ethereal solution with redox mediator that enables oxidation of Li2O2 at low potentials. The electrodes are separated by a solid electrolyte membrane, allowing free transport of Li ions. This approach increases cycle life of lithium oxygen cells and their energy efficiency.1

References

W.-J. Kwak, H.-G. Jung, D. Aurbach, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1701232

S. H. Lee, J.-B. Park, H.-S. Lim, and Y.-K. Sun, Adv. Energy Mater. 2017
, 7, 1602417

W.-J. Kwak, S.-J. Park, H.-G. Jung, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1702258
Performance Study of Free-Standing Cathode Made with LiFePO4 and Sorted Single-Walled Carbon Nanotubes Composite Material
Authors: Adepoju Adewale A. , Searles Thomas A. , Fagan Jeffrey A. , Williams Quinton L.
Published: February 2020

A comparative study of free-standing LiFePO4/sorted single-walled carbon nanotubes (SWNTs) and conventional LiFePO4 cathode was carried out. The free-standing cathode was prepared by traditional slurry method followed by a surface peel-off technique. Our experiments revealed that the energy density of free-standing LiFePO4/sorted SWNTs cathode film having a trace amount (0.0075%) of sorted SWNTs is comparable to that of a conventional LiFePO4 cathode having 10% carbon black and a current collector foil. Both cathode types exhibit good cycling stability performance relative to each other. Moreover, the free-standing cathode exhibits good flexibility and robust mechanical strength which has the potential to be applied to flexible lithium ion batteries.
Π-π Interaction Enabling Highly Stable Li-Organic Batteries with Graphene Oxide – Based Separators
Authors: Fang Chun , Wang Yanjie , Zhao Ruirui , Huang Yunhui
Published: February 2020

CuTCNQ is a novel high capacity electrode material with three electrons transfer reaction. The main challenge of its practical application is the dissolution of the intermediate , which is similiar to the sulfur cathode in Li-S batteries. Here, we utilize graphene oxide (GO) coated separator to trap the dissolved aromatic active mateirals through charge transfer reaction by π-π interaction. Consequently, the CuTCNQ battery with GO separator is able to achieve a capacity of 252. mAh g-1 and show a high capacity retention of 81.3% over 100 cycles. Even at a higher current of 500 mA g-1, the cell still exhibits an outstanding cycle performance, delivering a capacity of 119.1 mAh g-1 with 75.8% capacity retention over 350 cycles. Not only for Li-organic battery, GO separator can also serve as a promising alternative separator in organic electrolyte based redox flow batteries.

Figure 1
MoS2 and MoO2 loaded Carbon Microfibers As Anode Materials for Lithium-Ion and Sodium-Ion Batteries
Authors: Valdez Alejandra , Zuniga Luis , Villarreal Jahaziel , Alcoutlabi Mataz
Published: February 2020

We present results on the Forcespinning (FS) of MoS2/PAN and MoO2/PAN solution precursors for the mass production of MoS2/C and MoO2/C composite fibers for use as binder-free and freestanding anodes for lithium-ion and sodium-ion batteries. The binary composite microfiber electrodes were prepared using a scalable technique (FS) and subsequent thermal treatment. Scanning Electron Microscope (SEM) images of the composite microfibers showed nanoparticles of the MoS2 and MoO2 active materials embedded in the surface of the fibers. The composite microfiber preparation process involved FS of the MoS2/PAN and MoO2/C solution precursors into microfibers and subsequent stabilization in air at 280oC and calcination at 700oC for MoO2/C and 810oC for MoS2/C under an inert atmosphere. The flexible composite microfibers were directly used as working electrode in lithium-ion and sodium-ion batteries without a current collector, conducting additives, or binder. The MoS2/C and MoO2/C composite fiber electrodes delivered a good electrochemical performance and Coulombic efficiency when used for lithium-ion batteries. The MoS2/C electrodes delivered an initial discharge (insertion) capacity of 650 mAhg-1, with a corresponding charge capacity of 425 mAhg-1 at a current density of 100 mAg-1. In the subsequent cycles, the MoS2/C electrodes stabilize at about 50 cycles and maintain a stable specific capacity of about 245 mAhg-1, in the last 5 cycles there is slight recovery with a final specific capacity of 255 mAhg-1. The MoO2/C composite anode delivered a reversible capacity of 356 mAhg-1 at 100 mAg-1, stabilizing at 245 mAhg-1 after 100 cycles. The results presented in this work showed that the MoS2/C and MoO2/C composite fibers have good reversible capacity, good capacity retention and acceptable rate performance when used as anode materials for rechargeable lithium ion batteries.
A Simple Metallic Coating on Separator for Lithium Dendrite Suppression
Authors: Lee Hongkyung , Ren Xiaodi , Niu Chaojiang , Yu Lu , Engelhard Mark H , Liu Jun , Xu Wu , Zhang Ji-Guang
Published: February 2020

Lithium (Li) metal has been considered as a very promising anode material for next-generation batteries because of its low electronegativity (-3.04 V), low gravimetric density (0.53 g cc-1) and ultrahigh specific capacity (3860 mAh g-1). The recent simulations forecast that the rechargeable Li metal batteries (LMBs) coupled with the conventional transient metal oxide cathodes and the Li metal anode can deliver a high gravimetric energy density of up to 500 Wh kg-1.[1] However, major challenges including low Coulombic eﬃciency (CE), short cycle life, and safety concerns have plagued the practical applications of Li metal as anode in recharge batteries.[2]

Here we present a simple approach to suppress dendritic Li metal growth by introducing a multifunctional Janus-faced separator. This separator is designed by coating metallic copper (Cu) thin film (CuTF) onto one side surface of conventional polyethylene (PE) membrane via simple sputtering technique. The CuTF of the obtained Janus separator (PE/CuTF) plays a crucial role of an additional conducting agent for facile Li metal deposition/stripping. Furthermore, its electrically conductive nature can guide the backside plating of Li metal and electrochemical Li metal merging, resulting in less dendritic Li metal deposition (Figure 1). The lifetime of Li metal anode is enhanced by preventing short circuit failures even under extensive Li metal deposition. LMBs with the PE/CuTF separator exhibit stable cycling performances and enhanced CE during extended cycles. Moreover, the CuTF coating can suppress the thermal shrinkage of the polymer separators and enable a current collector-less cell configuration for high energy density.

K.G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu, V. Srinivasan, Energy Environ. Sci.
7, 1555 (2014).

Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.-G. Zhang, Energy Environ. Sci.
7, 513 (2014).

Figure 1. Proposed working principle on Li dendrite suppression by using Janus-faced separator; (A) conventional PE separator and (B) Cu metal thin film (CuTF) coated Janus (PE/CuTF) separator.

Figure 1
Advanced Characterization and Quantification of Fuel Cell Electrodes Using Electron and X-Ray Microscopy Techniques
Authors: Jankovic Jasna , Susac Darija , Putz Andreas Michael Vincent , Kneer Alexander , Zhang Shawn
Published: February 2020

Performance and durability of proton exchange membrane fuel cells (PEMFC) very much depend on the composition, microstructure and spatial distribution of all components in the fuel cell electrodes, especially the metal catalyst, carbon support, ionomer and pores in the catalyst layer. This dependence is even more enhanced in the case of low Pt loading fuel cells, where high performance losses occur due to increased oxygen transport resistance [1, 2], and the design of the catalyst layer is of utmost importance. Understanding the electrode microstructure and component distribution at the beginning of life (BOL), as well as their change at the end of life (EOL), after running the cells at various operating conditions, is crucial for further development of fuel cells. Conventional imaging techniques offer limited information and can often be misleading. Novel and advanced methods for spatial structural characterization and component quantification are being developed, enabled by the rapid advancement of the microscopy techniques and computational power, offering a new level of understanding for processes in fuel cells.

This talk will give an overview of some of the advanced approaches reported in the literature, as well as describe novel fuel cell material characterization and quantification methods developed in our team. The topics will cover:

3D imaging and quantification of catalyst powders and resulting catalyst layers on a nano-scale using an electron tomography (ET) approach that enables spatial distribution of all phases, ionomer included, for the first time.

3D multi-scale imaging and quantification of membrane electrode assemblies (MEAs) correlatively utilizing ET, focused ion beam-scanning electron microscopy (FIB-SEM), and 3D X-ray microscopy (3D XRM), coupled with effective property simulation.

Applying a novel (all-in-one) approach to visualize and quantify a number of catalyst layer parameters in BOL and EOL samples, such as Pt loading, loss and distribution, ionomer loading and I/C ratio, as well as layer porosity using transmission electron microscopy with energy dispersive spectroscopy (TEM-EDX).

These advanced characterization approaches, coupled with targeted experimental testing and mathematical modeling, are key for further understanding and improving the performance and durability of fuel cells, bringing them closer to mass commercialization.

A. Kongkanand and M. F. Mathias, J. Phys. Chem. Lett., 2016, 7 (7), pp 1127–1137

P. Gazdzicki, J. Mitzel, A.M. Dreizler, M. Schulze, K. A. Friedrich, Fuel Cells, 2017, 17 (5)

Figure 1
(Invited) Nitrogenase Electrochemistry for Ammonia Production
Authors: Cai Rong , Milton Ross , Abdellaoui Sofiene , De Lacey Antonio L. , Pita Marcos , Sahin Selmihan , Minteer Shelley
Published: February 2020

The Haber-Bosch process, responsible for producing NH3 from H2 and N2, ranks as one of the most important discoveries in the history of chemistry. Its industrial application in synthetic fertilizers contributed to the continuously increasing population and their quality of life. The Haber-Bosch process, however, is a very energy-intensive process with high temperature (500 °C) and pressure (20 MPa) required for efficient NH3 production. Over 1 % of the world’s energy sources were consumed in order to produce ~140 megatons of NH3 in 2015. Additionally, 3 % of global CO2 emissions are due to the Haber-Bosch related technology. A renewable strategy for ammonia production would therefore be valuable.

In nature, the ability to reduce N2 to NH3 is limited to a group of bacteria and archaea classified as diazotrophs, all of which share an enzyme called nitrogenase. Using methylviologen (N,N’-dimethyl-4,4’-bipyridinium) to shuttle electrons to nitrogenase, N2 reduction to NH3 can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode which utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H2) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H2 and N2, while simultaneously producing an electrical current. To demonstrate this, 60 mC of charge was passed across H2/N2 EFCs, which resulted in the formation of 286 nmol NH3 mg-1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %. Importantly, this EFC produces NH3 and electrical energy in a carbon-neutral manner.

A protective FeSII protein, which can reversibly lock nitrogenase into a multicomponent protective complex upon exposure to low concentrations of O2, was incorporated into a nitrogenase bioelectrosynthetic cell whereby NH3 was produced using air as a substrate. This marks a significant step forward in overcoming the crippling limitation of nitrogenase’s sensitivity toward O2.
Microelectrode Arrays: Moving Toward the Synthesis of More Complex Surfaces
Authors: Moeller Kevin D , Yeh Nai-Hua , Nguyen Bichlien
Published: February 2020

Microelectrode arrays can be ideal tools for probing a host of biological interactions. Yet in spite of their general utility, their use is still limited by our ability to construct complex molecular surfaces that can spatially isolate molecules in specific locations proximal to specific electrodes.

With this in mind, we have been developing electrochemically based tools that allow for the placement of molecules by specific electrodes in an array and then probe the binding of those molecules with biological targets in “real-time”. Yet while those methods are very useful, they have limits. They enable the analysis of smaller libraries, but are not as effective if one wants to probe a receptor with even a medium size library. The problem is that the tools developed to date require a library to be synthesized at a remote site and then transfer that library to the array one molecule at a time. For larger libraries, this is time consuming and cumbersome. A better strategy would be to build the library directly on the array.

The approach to building a molecular library typically involves a diversification strategy like the one shown in Scheme 1. In the Scheme, P1-P4 represent protecting groups that can be orthogonally removed. But what are the orthogonal protecting groups that can be removed site-selectively on a microelectrode array so that such a strategy can be used to synthesize more complex molecular surfaces? Furthermore, are the current surfaces used on the arrays compatible with such an intensive synthetic effort?

In the talk to be given, we will describe initial findings that begin to address these questions as we push for the development of new methods that will allow for the greater community to take full advantage of what microelectrode arrays can offer.

Figure 1
Controlled Synthesis of Organic Frameworks of Pillar[6]Arene By Electrochemical Oxidation
Authors: Inagi Shinsuke , Tsuneishi Chiaki , Nishiyama Hiroki , Tomita Ikuyoshi , Ogoshi Tomoki
Published: February 2020

Recently, the novel synthesis of supramolecular 2D sheet materials composed of a pillar[6]arene (a cyclic hexamer of p-arylenemethylene), driven by charge-transfer (CT) interaction between its hydroquinone form and its benzoquinone form was reported [1]. When the hydroquinone form of pillar[6]arene was oxidized with an oxidant in a methanol solution, a generated partially oxidized benzoquinone form underwent CT complex formation with its pristine form to 2D-assemble with a hexagonal packing, followed by further assembly to form fibrils. In order to control the size and shape of the material, we investigated the electrochemical oxidation of a pillar[6]arene, and resulted in the successful formation of uniform hexagonal cylinder structures on an electrode surface (Figure 1) [2].

[1] T. Ogoshi, K. Yoshikoshi, R. Sueto, H. Nishihara, T. Yamagishi, Angew. Chem. Int. Ed. 2015, 54, 6466-6469.

[2] C. Tsuneishi, Y. Koizumi, R. Sueto, H. Nishiyama, K. Yasuhara, T. Yamagishi, T. Ogoshi, I. Tomita, S. Inagi, Chem. Commun. 2017, 53, 7454-7456.

Figure 1
Reactions Using Organo-Dications As Redox-Switchable Catalysts in Batch and Flow Systems
Authors: Suga Seiji , Kurihara Yuusuke , Hirata Takayuki , Tanaka Hiroki , Mitsudo Koichi
Published: February 2020

Organocations such as trityl cation effectively promote a variety of organic reactions. The electrochemically generated carbocations [1] can also be utilized for the efficient promoter of these reactions and are applicable to a redox-switchable system which involving entirely organic compounds. The transformation using a redox-switchable catalyst is an emerging research field that seeks to regulate chemical reactions by the simple reduction-oxidation manipulation. For example, when the solution of an aldehyde, enol silyl ether and a precursor of organo-dication were subjected to the electrochemical oxidation, the aldol reaction smoothly started. Subsequent electrochemical reduction of the solution brought the reaction to a stop. We would demonstrate the utility and applicability of the present investigation. Some preliminary applications to the electrochemical microflow system will also be discussed.

[1] M. Okajima, S. Suga, K. Itami, J. Yoshida, J. Am. Chem. Soc.
2005, 127, 6930.
Differences in Reactivity of Primary Amines, Diamines and Amino Acids with Orthophthalaldehyde – Spectroelectrochemistry and Structure of Products
Authors: Ludvík Jiří , Donkeng Joel , Kantnerová Kristýna
Published: February 2020

Orthophthalaldehyde (OPA) is used in analytical and biologically significant reactions for many years due to its specific reactivity with N-, S- and O- nucleophiles [1,2]. Besides the analytical method for determination of amino acids, the solution of OPA is broadly applied in hospitals as a disinfecting agent for surgery instruments made from plastics. In the literature, there is a simplified "traditional" description of main products and the expected mechanism related to the applications, however, our recent systematic research in this field revealed several unobserved phenomena showing that the mechanisms are not understood [3,4].

Due to the ortho-position of the two carbonyls, OPA contains a system of two communicating redox centers exhibiting very specific reactivity. The main feature of the OPA behavior is ability to fast intramolecular cyclization of primary intermediates of classic addition and condensation reactions of a carbonyl with a nucleophile. As a consequence, the reaction mechanism and formation of products strongly depends on the structure of the nucleophile itself, since the cyclization and inter-as well as intramolecular follow-up reactions offer a number of structural and stoichiometric possibilities.

In the present report (spectro)electrochemical monitoring of the reactions of OPA with various types of nucleophiles (water which is, in fact, the most abundant nucleophile in the system, primary amines, 1,2- and a,ω-diamines derived from aromatic, aliphatic or alicyclic species, amino acids, thiols and various molecules containing two different nucleophilic centers) will be discussed and the mechanistic conclusions will be supported by identification of products by MS, NMR and x-ray structural analyses [5-9].

Acknowledgments

The research was supported by GA CR (project No. 17-18108S) and by institutional support (RVO: 61388955).

References

[1] Roth, M. Anal. Chem.
1971, 43 (7), 880–882.

[2] Simoes, M.; et al. J. Basic Microbiol.
2007, 47, 230–242.

[3] Zuman, P. Chemical Reviews
2004, 104 (7), 3217–3237.

[4] Zuman, P.; et al. Electroanalysis
2009, 21 (3-5), 645–649.

[5] Kantnerová, K.; Donkeng Dazie, J.; Ludvík, ECS Transactions
2015, 60 (26), 13-22.

[6] Donkeng Dazie, J.; Liška, A.; Ludvík, J.; Fábry, J.; Dušek, M. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
2016, 72, 518-524.

[7] Donkeng Dazie, J.; Liška, A.; Ludvík, J. J. Electrochem. Soc.
2016, 163 (9), G127-G132.

[8] Donkeng Dazie, J.; Liška, A.; Ludvík, J.; Fábry, J.; Dušek, M.; Eigner, V.

Kristallogr.
2017, DOI: https://doi.org/10.1515/zkri-2016-2001

[9] Donkeng Dazie, J.; Liška, A.; Urban, J.; Ludvík, J. J. Electroanal. Chem. – submitted 2017.
Electrochemical Versus Photochemical: Mechanism of Radical Cation Cyclizations
Authors: Gonzalez Luisalberto , Graaf Matthew D. , Moeller Kevin D
Published: February 2020

Radical cations are key intermediate in oxidation reactions but their reactivity has not been explored in much detail. Our group has begun exploring these reactive intermediates through cyclizations that involve various radical cation trapping groups. Previously, we only utilized electrochemistry to probe the mechanism of these reactions but, recently, we have started to used photochemical methods to study the generality of the trapping groups. What we have seen is that it is important to include the steps in the cyclization mechanism that involve single electron transfers when considering radical cation cyclizations.
Electrochemistry of (Thia)Calix[4]Arenes Bearing Various Redox Probes
Authors: Liška Alan , Modi Krunal M. , Ludvík Jiří
Published: February 2020

Calixarene skeleton is a stable supramolecular frame which is, however, electrochemically inactive. Introduction of one or more electroactive substituents to the molecule enable its electrochemical investigation, moreover, the interpretation of series of electrochemical data can reveal the distribution of electrons in the molecule, their mutual communication, shape of the molecule, its dynamic behaviour etc. Suitable substitution on the upper and/or lower rim can influence not only geometry of the molecule, but also its reactivity and coordination ability. Generally, structure modification or introduction of heteroatoms lead to unusual and surprising properties of the whole supramolecule.

Thiacalix[4]arenes contain four aromatic units connected by sulphur atoms. This contribution will be focused first on two series of 1,3-alt-conformers bearing one or more nitro groups as electrochemical probes and on other calixarene derivatives bearing various redox probes..

The first series consists of eight para-tetranitro derivatives which resemble each other in their electrochemical response: first two two-electron reversible waves are followed by final step during which a tetrakis(hydroxylamino) derivative is formed. This reduction pattern is analogous to the “standard” methylene-bridged para-tetranitrocalix[4]arenes, where no mutual electron interaction takes place, all nitrogroups are totally independent and a stable tetraanion tetraradical is formed [1,2].

The second series includes four meta-nitro derivatives. Generally, the electroreductive behaviour of them is more complicated (except the first member which bears only one nitrogroup). Presence of two and three nitro groups in the same molecule in position meta towards the lower rim (that means in position ortho- and para- towards the thia bridges), exhibit clear intramolecular communication. [3,4]. This phenomenon was confirmed by quantum chemical calculations.

In the third series some newly synthesized derivatives with various redox probes are presented.

Acknowledgement: This work was supported by the GACR grant No. 17-18108S and by institutional support RVO: 61388955. The authors thank prof. Pavel Lhoták for granting the compounds.

Krunal M. Modi -

On leave from Chemistry Department, Gujarat University, Ahmedabad-380009 India

References:

[1] Alan Liška, Pavel Vojtíšek, Albert J. Fry, Jiří Ludvík: J.Org.Chem 78 (2013) 10651 – 10656.

[2] Alan Liška, Marco Rosenkranz, Jiří Klíma, Lothar Dunsch, Pavel Lhoták, Jiří Ludvík: Electrochimica Acta 140 (2014) 572 – 578.

[3] Alan Liška, Karolína Flídrová, Pavel Lhoták, Jiří Ludvík: Monatsh. Chem. 146 (2015) 857–862.

[4] Alan Liška, Jiří Ludvík: Current Opinions in Electrochemistry - submitted
Electrochemical Preparation of Aryl Mom Ethers
Authors: de Kruijff Goswinus H. M. , Waldvogel Siegfried R.
Published: February 2020

In organic synthesis, methoxymethyl (MOM) ethers are frequently used as acid-labile protecting group [1] or leaving group in aryl cross-coupling reactions [2]. Their preparation commonly involves MOM chloride, a carcinogenic liquid with high vapour pressure which should be avoided as much as possible [3].

Therefore, we started to synthezise aryl MOM ethers without the use of MOM chloride by application of sustainable electrosynthetic methods [4]. Anodic decarboxylation of 2-aryloxy acetic acids under non-Kolbe conditions and trapping of the corresponding cation with methanol gives the desired MOM ethers (Figure 1). Indeed, this pathway is described for few aliphatic α-alkoxyacetic acids [5] and unsubstituted phenoxyacetic acid [6], but scope of this transformation to prepare substituted aryl MOM ethers has not been investigated so far.

We now present our studies on the preparation of substituted aryl MOM ethers by anodic decarboxylation using an undivided cell setup. A wide range of substituents on the phenyl moiety is tolerated, giving access to valuable protected phenols [7].

References:

[1] P. G. M. Wuts, T. W. Greene, Greene's Protective Groups in Organic Synthesis, John Wiley & Sons, Inc,

Hoboken, NJ, USA, 2006.

[2] J. W. Dankwardt, Angew.
Chem. Int. Ed.
2004, 43, 2428-2432.

[3] Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, Ltd, Chichester, UK, 2001.

[4] B. A. Frontana-Uribe, R. D. Little, J. G. Ibanez, A. Palma, R. Vasquez-Medrano, Green Chem.
2010, 12, 2099-2119.

[5] H.-J. Schäfer in Topics in Current Chemistry, Vol. 152 (Ed.: E. Steckhan), Springer, Berlin Heidelberg, 1990.

[6] S. I. Rosca, E.-M. Ungureanu, M.-G. Alexandru, U. P. B. Sci. Bull., Series B, 2007, 69, 3-10.

[7] G. H. M. de Kruijff, S. R. Waldvogel, in preparation.

Figure 1
Electrochemical Synthesis of Azanucleosides
Authors: Okamoto Kazuhiro , Ishii Seika , Shoji Takao , Chiba Kazuhiro
Published: February 2020

Recently, the nucleic acid medicine receiving a lot of attention because of various drug targets and few side effects compared with conventional low molecular medicine. The numerous nucleoside analogues have been reported. Especially, azanucleosides, in which the oxygen atom of furanose ring has been replaced with a nitrogen atom, show anticancer, antivirus, and antileukemia activity. Furthermore, azanucleosides exhibit tolerance towards nucleases when their incorporate into oligonucleotides. However, the traditional synthetic strategy requires multiple steps and harsh conditions, thereby limiting to obtain desired product with high yield.

We developed mild condition and efficient synthesis of azanucleosides from prolinol derivative using by an electrochemical reaction in a 1.0 M lithium perchlorate-nitroethane and small amount of acetic acid mixture medium with a glassy carbon anode and platinum cathode. In this reaction, intermediate iminium cation was generated through anodic oxidation of N-α position. The nitroalkane solvent is suitable for cation-pool method because the cation intermediate species are stabilized at nearly room temperature. After 2.6 F of electricity, the nucleophiles were added into reaction medium and stirred overnight. We used each nucleobases (N6-benzoyl adenine: A(Bz), N4-benzoyl cytosine: C(Bz), N2-isobutyryl guanine: G(Ib)) as nucleophiles. The coupling with thymine (T) was carried out through silyl Hilbert-Johnson reaction from other prolinol derivative that has hydroxyl group in N-α position. It was also prepared by anodic oxidative C-H activation. As a result, desired deoxyribo-azanucleosides was obtained.

However, the desired azanucleosides was generated as α and β anomer by equally ratio in this reaction. The natural nucleic acids are composed by only β-anomer nucleosides. In this reason, to regulate the anomeric selectivity is very important. Now, we are challenging the stereoselective synthesis of these deoxyribo-azanucleosides. Furthermore, we are applying our electrochemical method for the synthesis of ribo-azanucleosides.
Electrocatalytic Hydrogenation of Toluene in a PEM Reactor As a Study of a Model Reaction for Hydrogen Storage
Authors: Fukazawa Atsushi , Takano Ken , Matsumura Yoshimasa , Nagasawa Kensaku , Mitsushima Shigenori , Atobe Mahito
Published: February 2020

Chemical conversion of toluene (TL) to methylcyclohexane (MCH) has been examined to develop a novel organic chemical hydride system. One of the most promising hydrogen storage techniques relies on the organic chemical hydride because of its safety and feasible handling. To produce methylcyclohexane effectively, we investigated electrochemical hydrogenation of toluene using PEM (Proton Exchange Membrane) reactor with various noble metal supported catalysts and found that PtRu/C catalyst afforded excellent current efficiencies for the hydrogenation. However, it has not been made clear whether by-products (e.g. partially hydrogenated products) are produced in the hydrogenation of toluene. In this work, we demonstrated a systematic study on the electrocatalytic hydrogenation of toluene to methylcyclohexane in order to clarify the above question.

As a results, Methylcyclohexane was obtained as a main product with high current efficiencies in all cases. However, small amounts of the partially hydrogenated product such as 1-methyl-1-cyclohexene (1-ene) was also produced. In addition, very small amounts of 3-methyl-1-cyclohexene and 4-methyl-1-cyclohexene were also detected by using the Ru catalyst. Among the all tested catalysts, the use of PtRu catalyst gave better selectivity and higher current efficiency (>99%) for the desired product like methylcyclohexane. Hence, it can be stated that PtRu is the most suitable catalyst for the electrochemical hydrogenation of toluene. Probably, PtRu/C catalyst exhibited dual functions such as the high catalytic activity of the rich Had on Pt and the strong toluene adsorption by Ru. This synergy would result in excellent current eﬃciencies for the hydrogenation of toluene to methylcyclohexane.

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Characterizing Bioconjugation and Electron Transfer at Coated Nanoparticles By Nano-Impact Electrochemistry
Authors: Kirk Kevin , Andreescu Silvana
Published: February 2020

Nanoparticle collision electrochemistry provides extensive capabilities for detection and characterization of nanoparticles. This presentation will describe development of an electrochemical nano-impact technique for evaluating the fundamental surface properties, functionalization and reactivity of metal and metal oxide nanoparticles and its use for quantifying biomolecule-nanoparticle conjugation and biomolecular recognition with a high degree of sensitivity in the absence of exogenous reagents. The presentation will demonstrate the potential of this method for the: 1) assessment of surface reactivity and electron transfer properties of coated nanoparticles, 2) monitoring surface adsorption/desorption and biorecognition events at single particle surfaces, and 3) as a method enabling rapid label free detection of biomolecular recognition targets. We will demonstrate capabilities of this method as a novel tool for characterizing fundamental properties of nanoparticles, and illustrate novel applications of this method for assessing bioconjugation for biosensing design, analytical and diagnostic applications. Potential advantages and limitations of this approach as a method for the routine study of nanoparticles and nanoparticle systems will also be discussed.
Redox Catalysis for Biomass Degradation
Authors: Stephenson Corey , Magallanes Gabriel , Yang Cheng , Kaerkaes Markus , Bosque Irene
Published: February 2020

Single electron transfer (SET) processes – frequently utilized by Nature to activate its substrates – significantly enhance the reactivity of organic molecules. These SET reactions provide facile access neutral radicals – reactive intermediates that are particularly attractive for use in complex settings as a consequence of their general lack of reactivity with polar functional groups. The use of redox catalysis (e.g. photocatalysis and electrocatalysis) furthers the benefits of SET processes enabling the reduction of stoichiometric waste byproducts and toxic or hazardous reagents compared with classical approaches. The development of methodologies involving organic free radicals underpinned on practicality and mechanistic understanding with applications in biomass conversion will be presented.

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Difunctionalization of Cyclopropylanilines and Cyclobutylanilines
Authors: Zheng Nan , Wang Jiang , Boateng Elvis
Published: February 2020

We have previously developed photoredox conditions for ring opening of cyclopropylanilines and cyclobutylanilines. Distonic radical cations are presumably the intermediates. Although commonly producing in gas phase such as in the ionization chamber of a mass spectrometer, in solution phase, the methods for generating them are quite limited. Bearing a spatially separated radical and cation within the same molecule, these species possess bimodal reactivities that are distinct from those of radicals, ions, or classical radical ions (the radical and the ion reside at the same atom). In the [3+2] annulation of cyclopropylanilines and the [4+2] annulation of cyclobutylanilines developed by us, only one pi bond of alkenes, alkynes, dienes, enynes, or diynes reacts with the radical and the cation moiety of the distonic radical cations sequentially to form a five-membered and six-membered carbocycle respectively. Therefore, the two reactions don’t maximize the distonic radical cations’ bimodal reactivity. We have recently focused on identifying a suitable nucleophile and a radical acceptor to orthogonally intercept the cation and the radical moiety, which allows us to capitalize the distonic radical cations’ bimodal reactivity fully. Herein, we report our efforts in harvesting the distonic radical cations' bimodal reactivity, which results in 1,3-difunctionalization of cyclopropylanilines and 1,4-difunctionalization of cyclobutylanilines.
Electrocatalytic Difunctionalization of Alkenes
Authors: Lin Song
Published: February 2020

Alkene difunctionalization represents one of the most efficient methods for the construction of highly functionalized products from simple and readily available starting materials. These transformations are usually promoted by a highly reactive electrophilic reagent (e.g., peracid, metal oxide, and hypervalent iodine), which engages the unactivated π electrons of the alkene to form two new vicinal chemical bonds in either a concerted or a stepwise fashion. The requirement for these highly reactive electrophiles can often lead to functional group compatibility issues, which may limit their broad use in late-stage synthesis. In addition, many of these reagents generate substantial amounts of byproducts upon reaction.

Herein, we describe the development of alkene difunctionalization reactions via electrochemical generation of radical intermediates. Electrochemistry allows for the generation of highly reactive intermediates in situ from simple and readily available feedstocks and with high atom economy. The heteroatom-based radical can be produced directly from the corresponding anion via anodic oxidation, and will add across a C=C bond in the alkene substrate to yield a carbon based radical. Due to the high reactivity and promiscuity of this carbon radical species, a variety of undesired pathways, including polymerization, dimerization, elimination, and over-oxidation, could follow. In order to realize difunctionalization with high selectivity in addition to high stereochemical control, we introduce a metal catalyst that could associate with the second heteroatom-based radical and deliver it to the carbon radical via a catalyst-controlled mechanism. The therefore reduced catalyst could then also be oxidized on the anode to complete the catalytic cycle. Judicious choice of catalyst and careful control of the applied electrochemical bias allow for the regulation of the reactivity and selectivity of the alkene difunctionalization process.
Thermally Activated Redox Conduction in Shewanella Oneidensis MR-1 Biofilms
Authors: Xu Shuai , El-Naggar Mohamed
Published: February 2020

Shewanella oneidensis MR-1 can gain energy by performing extracellular electron transport (EET) to external insoluble electron acceptors ranging from natural minerals to synthetic electrode surfaces when poised at proper potentials. Outer membrane c-type multi-heme cytochromes play a critical role in mediating this electron transport. The abundance of these cytochromes on the cell surface has also been hypothesized to facilitate long-distance electron transport along multicellular biofilms, in a manner similar to redox active polymers containing discrete redox moieties. Here we report measurements of electron transport in living S. oneidensis biofilms that bridged interdigitated array (IDA) microelectrodes. Electrochemical gating reveals a peak in the conduction current at the expected formal potential of the cytochrome conduits, consistent with redox conductivity where transport is driven by a multistep electron hopping mechanism through the heme network. The temperature dependency of the biofilm conduction is also consistent with such a thermally activated process, where conductivity increases with increasing temperature. In addition, the measured activation energy (0.315 eV) is consistent with the computationally-determined activation energy of the S. oneidensis Mtr decaheme cytochromes.
Mechanistic Studies on Photoredox-Mediated Organocatalyzed Ring-Opening Metathesis Polymerization
Authors: Boydston Andrew J
Published: February 2020

We have been investigating the application of photoredox catalysis in organocatalyzed ring-opening metathesis polymerization (ROMP). This metal-free variant enables unique synthetic capabilities in comparison with traditional metal-mediated ROMP methods, and offers distinct mechanistic considerations. We will discuss our recent results related to the polymerization mechanism. Specific focus is placed upon potential rate-determining steps in propagation, methods for controlling relative rates of propagation versus initiation, and hypothesized irreversible termination events. As a redox-mediated polymerization, electron transfer is central to each step in the process.
CdS As Holes Provider for Visible Light-Induced Urea Photo-Oxidation
Authors: Zhao Rong , Radich James
Published: February 2020

CdS is a semiconductor which can absorb visible light to generate electrons and holes. In urea solution, the holes are accepted by urea and oxidize urea while the electrons are accepted by water to reduce water to hydrogen. Photoluminescence of CdS QDs in urea showed lower amplitude as the quenching effect of urea on CdS QDs, which proves the holes transfer from CdS to urea. Photoelectrochemical test of TiO2/CdS electrode in urea solution showed photocurrent generated by the oxidation of urea and reduction of water. The decrease of photocurrent with time is because of photocorrosion of CdS, which is self-oxidation of CdS by holes generated after illumination. A dielectric layer ZnS was deposited on CdS by successive ionic layer absorption and reaction (SILAR) to passivate the CdS surface, which improved the intensity and stability of photocurrent.
Novel Electrochemical Cell Favorable for the Kinetic Studies of Highly Active Enzymes
Authors: Fadel Mariam
Published: February 2020

Rotating disk electrode is by far the most popular hydrodynamic electrode used for the kinetic studies of the chemical reactions. This is due to its great advantages, as a uniformly accessible electrode, makes it the most convenient for quantitative analysis. In our group, we are interested to study the mechanism of the enzymes using protein film voltammetry (PFV)1 in which the enzyme is absorbed at the electrode surface of the rotating disk electrode, where the electron transfer is direct (Figure). CO dehydrogenase, CODH, is a promising enzyme, that catalyzes the reversible reaction of reduction of carbon dioxide into carbon monoxide: CO + H2O ↔ CO2 + 2e- + 2H+, which is the first step to the production of fuel2,3. With the classical setup using the rotating disk electrode, the transport of chemical species toward the enzyme is insufficient to match its very high activity; this blurs the enzymatic response and prevents mechanistic studies. To enhance the transport toward the active sites of the enzymes at the electrode, we design a new type of a flow cell. We use fluid mechanics simulation to study a variety of geometrical configurations, to choose a suitable prototype of electrochemical cell. Based on our numerical simulations, we build this cell and we perform the experimental studies.

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A Modular Flow-through Platform for Spectroelectrochemical Analysis
Authors: Noyhouzer Tomer , Snowden Michael Edward , Tefashe Ushula M , Mauzeroll Janine
Published: February 2020

Electrochemical flow systems are broadly used in research and applied fields such as environmental, industrial and medical monitoring because they cost-effectively determine concentrations, yield energy data (redox potential) and elucidate reaction mechanism via kinetic analysis. The use of a flow system enables the automation of a process and can provide a much needed design flexibility. Moreover, the combination of reaction-oriented electrochemical flow systems with species-focused spectroscopy enables complete analysis of reactions involving multiple electron transfer steps, as well as unstable intermediates.

In this work, we present a new type of flow platform for electrochemical and spectroelectrochemical measurements is presented. Finite element method simulations confirm that the hydrodynamic profile within the device is not turbulent, and provides an analytical platform for the investigation of homogenous kinetics, radical lifetimes and reaction mechanisms. The modular “plug and play” configuration of the platform allows one to carry out electrochemistry and spectroscopy individually or simultaneously. Specific demonstrations of electroanalytical measurements using the flow system platform includes voltammetric analysis of organometallic compounds and quantitative analysis of ascorbic acid in commercial orange juice samples. Combined spectroelectrochemical (SEC) demonstrations include electrochemical luminescence of ruthenium compounds and ligand exchange reactions of iron complexes using UV-Vis spectroscopy.

Noyhouzer et al, Anal. Chem., 2017, 89 (10), pp 5246–5253

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