bluuebunny/crossref_metadata_2025 huggingface dataset:
Strategies and Tactics in Electroorganic Synthesis: Electroauxiliary, Cation Pool, and Flow Microreactor
Authors: Yoshida Jun-ichi
Published: February 2020

The electrochemical method serves as one of the most straightforward methods for electron-transfer-driven reactions that have been widely used for various transformations in organic synthesis, although its potential has not yet been fully utilized. To meet future demands for producing desired compounds in a highly efficient and environmentally benign way, the power of electroorganic synthesis should be greatly enhanced. We have developed some strategies and tactics for organic electrochemical reactions over the past few decades, and this presentation will provide an outline of their principles and applications.
Paired Electrochemical Reactions of a Fluorene-Based Conjugated Polymer
Authors: Inagi Shinsuke , Nagai Hiroyuki , Tomita Ikuyoshi , Fuchigami Toshio
Published: February 2020

Bipolar electrochemistry using a wireless electrode driven by an external electric field from feeder electrodes is attractive because electrochemical oxidation and reduction takes place simultaneously on the same surface of the bipolar electrode with a potential slope between both poles. The redox ability of parent polymer P1 containing fluorenol moiety to form P2 (fluorenone) and P3 (fluorene), which is accompanied by a drastic color change, is expected to exhibit a multi-colored gradient film by the application of a potential slope on the bipolar electrode according to the bipolar polymer reaction. A BDD plate (3 × 3 cm2) covered with P1 was placed between driving stainless electrodes (1 × 4 cm2) in a bipolar cell and a constant current (0.1 mA/cm2) was passed between them in 5 mM Et4NOTs/i-PrOH. After the electrolysis, the emission color of the polymer film under UV-irradiation was a gradation with yellow-blue-dark orange from the cathodic pole to the anodic pole. The gradient polymer film was peeled off from the BDD plate with scotch tape, and divided into three pieces for PL measurements. The PL spectra corresponded well to those of P1-P3. Previous reports on the bipolar electrolysis for producing gradient materials focused only on anodic reaction with sacrificial cathodic reaction or vice versa. This paired bipolar electrolysis successfully provided a new class of composition-gradient polymer film.
Electrolysis of Trichlomethylated Compound Under Aerobic Condition Catalyzed by B12 Model Complex
Authors: Shimakoshi Hisashi , Inaba Takuya , Hisaeda Yoshio
Published: February 2020

Reductive dehalogenation reactions are presently of great interest, primary because of their potential use in the treatment of halogenated solvent wastes as well as in remedial approaches to remove such chemicals from contaminated soils. A Co(I) species of cobalamin emerged in the active site of B12-dependent enzyme is a supernucleophile and reacts with an alkyl halide to form an alkylated complex with dehalogenation. Thus, the superior ability of cobalamin for reductive dehalogenation prompted us to investigate the catalysis of a cobalamin derivative for degradation of various halogenated compounds such as 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT), perchloroethelene (PCE), chloroform and so on.

Electrolysis of such organic halides mediated by cobalt complex usually achieved in anaerobic condition to avoid loss of reactive Co(I) species by autooxidation. Carbon center radical formed by homolysis of cobalt-carbon bond in alkylated complex generally coupled to form dimerized compound or abstract hydrogen to form simply reduced product. Here we reported electrolysis of organic halide under aerobic condition and conducted the reaction of in-situ generated substrate radical with oxygen to form more valuable compound such as ester.

Electrolysis of trichloromethyl benzene at -0.9 V vs. Ag/AgCl in the presence of heptamethyl cobyrinate perchlorate (1) in ethanol under anaerobic condition using undivided cell equiped with Pt mesh cathode and Zn plate anode to yield Z and E forms of 1,2-dichlorostilbene with 49% and 7%, respectively. In contrast, the same reaction was carried out in an aerobic condition, ethyl benzoate was selectively produced in 61 % yield based on initial concentartion of substrate. When the electrolysis was carried out in methanol or isopropano, methyl benzoate and isopropyl benzoate were formed, respectively. As for mechanism, primary formed radical species from homolysis of alkylated complex may reacts with oxygen to form peroxy species. Homolysis of O-O bond of peroxy species should produce oxyl radical. Following disproportionation and isomerization may produce benzoyl chloride as key intermediate in this reaction. Reactive benzoyl chloride could reacts with solvent ethanol to yield ethyl benzoate. Application of this aerobic electrolysis with colalamin derivative toward various trichloromethylated compounds will be reported.
Vanadium Flow Battery Performance Improvement through Electrode Modification
Authors: Brooker R. Paul , Bell Curtis , Bonville Leonard J. , Kunz H. Russell , Fenton James M.
Published: February 2020

Flow battery performance has recently been significantly improved through the use of carbon papers, adopting a so-called “zero-gap” architecture.[1] The benefits of the carbon paper, as opposed to carbon felt, are increased rigidity for reduced contact resistance, high surface area, and low compression. These combinations lead to an improved flow through the high surface area electrode, and enhanced high current performance through increased mass transport.

Much attention has been devoted to improving the V(IV)-V(V) couple at the positive electrode.[2] However, a need exists to increase the reversibility of the vanadium reactions at the negative electrode. For example, Aaron et al. have demonstrated[3] that on discharge, V(II) oxidation appears to have slower kinetics than V(V) reduction, resulting in high overpotentials at the negative electrode. Therefore, in addition to the improvements gained by the use of carbon paper, increased performance may be obtained through increasing the oxidation kinetics of the negative electrode. This paper will demonstrate some efforts aimed at reducing the discharge overpotentials at the negative electrode through electro-deposition of metals.

An all-vanadium cell was utilized in these tests, with single-carbon papers used as electrodes. For all tests, a fresh carbon paper was utilized at the positive electrode, while the negative electrode was either plain carbon paper, or metal-coated carbon paper. The results indicate that performance of the cell improved dramatically by adding metal to the surface of the negative electrode.

This presentation will discuss the approach employed herein for improved performance, as well as its limitations.

[1] D.S. Aaron, Q. Liu, Z. Tang, G.M. Grim, A.B. Papandrew, A. Turhan, T.A. Zawodzinski, M.M. Mench, J Power Sources, 206 (2012) 4-4.

[2] C. Flox, M. Skoumal, J. Rubio-Garcia, T. Andreu, J.R. Morante, Appl Energ, 109 (2013) 344-351.

[3] D. Aaron, C.N. Sun, M. Bright, A.B. Papandrew, M.M. Mench, T.A. Zawodzinski, Ecs Electrochem Lett, 2 (2013) A29-A31.
Phase Stability of Li-Mn-O Oxides As Cathode Materials for Li Ion Batteries
Authors: Longo Roberto C , Kong Fantai , KC Santosh , Park Min-Sik , Yoon Jaegu , Yeon Dong-Hee , Park Jin-Hwan , Doo Seok-Kwang , Cho Kyeongjae
Published: February 2020

The over-lithiated-oxides (OLOs) are a composite material of layered structures of Li2MnO3 and LiMO2 (M = Mn, Fe, Co, Ni). Their main advantage over current layered oxides is that they show much higher storage capacity as cathode material for Li-ion batteries, due to the presence of Li2MnO3 phase. However, experimental results indicate that Li2MnO3 is an almost inert material from an electrochemical point of view, and that it partially transforms into layered LiMnO2 after the first charge/discharge cycle, thus forming a phase that is a mixture of both Li2MnO3 and LiMnO2. During the subsequent charging cycles, OLO capacity is known to reduce gradually in connection with Mn spinel phase formation. To improve the OLO cathode material performance, it is desirable to suppress such spinel phase formation. In order to address the stability of Mn layered oxides, we have examined the phase diagram of the Li-Mn-O system on both physical and chemical (as a function of two chemical potentials, μ(Li) and μ(O)) potential space, using ab initio density-functional theory (DFT) simulations. These DFT findings will provide conceptual guidance in the experimental search for the mechanisms driving the structural transformation into the spinel phase, in an attempt to solve such structural instability problem and, thus, improving the performance of the OLO cathode materials.

This work was supported by Samsung GRO project.
Electrochemical Analysis and Interfacial Stability of Carbon-Overlay LiNi0.5Mn1.5O4 Cathode Material for High Potential Lithium Ion Battery
Authors: Jin Yi-Chun , Duh Jenq-Gong
Published: February 2020

Recently, researches in lithium ion battery have focused on interfacial properties of various cathode materials. The interfacial reaction on the electrode material greatly dominates its electrochemical performances and thermal stability, especially manganese-type spinels. The deteriorated cyclability of LiNi0.5Mn1.5O4cathode at elevated temperature greatly hinders its realistic applications. One of the reasons is that the high surface reactivity with the electrolyte at an ultimate operating voltage around 4.7V, associating with the dissolution of Mn and the formation of SEI layer.

A proper SEI-layer can not only facilitate lithium intercalations but also provides a good protection from the undesired electrolyte invasion. This study demonstrates the carbon-overlay on the surface of LiNi0.5Mn1.5O4 electrode through atmosphere-controlled sputter techniques. The advantage of sputtered carbon layer on the electrode surface is without the degrading of pristine spinel structure. The carbon-overlay with the appropriated thickness was found to extend the cycle life and suppress the swelling behavior of LiNi0.5Mn1.5O4 cathode material. The essential beneﬁts of carbon-overlay is to stable the SEI layer on LiNi0.5Mn1.5O4 cathodes, retarding the severe capacity decay at elevated temperatures. Charge transfer kinetics and failure mechanisms involving the high-voltage oxidation and high temperature degradation are also detailed discussed.
Nitrogen-Doped Graphene-Wrapped Mn3O4 Nanoparticles As High-Performance Anode Materials for Lithium Ion Batteries
Authors: Park Seung-Keun , Piao Yuanzhe
Published: February 2020

Lithium ion battery (LIB) is one of the most important power sources due to its high energy density [1]. To meet the increasing demands associated with the use of LIB in hybrid electric vehicles, many researches are focused on improving their electrochemical properties in term of materials. Graphite is commonly used as an anode material in commercial LIB. However, as it deliver a low specific capacity, its application in LIB is limited

Graphene has awakened a tremendous interest due to its very large surface area (~2600 m2 g-1), excellent electronic conductivity and stability. These properties allow graphene a promising electrode material for LIB. However, graphene exhibits rapid capacity decay during cycling.

Nitrogen doping of carbon materials has been studied as an effective way to solve the limitations and improve the electrochemical properties. Actually, nitrogen doping of graphene allows for enhanced interaction with lithium ions and the formation of a greater number of active sites through modulation of the band structure of graphene [2]. However, very few studies have been reported on the use of nitrogen-doped graphene/Mn3O4composite as the LIB anode material.

In this study, we have developed a simple hydrothermal method for the well-deposition of Mn3O4 nanoparticles onto nitrogen-doped graphene. Hydrazine plays an important role in the formation of such nanocomposites since it can act as both a nitrogen source and a reducing agent. In the SEM and TEM images, we have confirmed that highly crystalline Mn3O4 nanoparticles are well-dispersed on the N-doped graphene. The Mn3O4/N-doped grapheme nanocomposites show excellent electrochemical performance, including outstanding cycling stability, high reversible specific capacity and improved rate capability. The enhancement in the electrochemical properties of the material can be attributed to N-doped graphene, which acts as both a conductive substrate and a volume buffer layer, and also nitrogen doping allows for the fast electron moving and ion transfer by decreasing the energy barrier.

Reference

[1] M. Winter, R.J. Brodd, Chem. Rev., 104,4245 (2004).

[2] H.B. Wang, C.J. Zhang, Z.H. Liu, L. Wang, P.X. Han, H.X. Xu, K.J. Zhang, S.M. Dong, J.H. Yao, G.L. Cui, J. Mater. Chem. 21, 5430 (2011).

Acknowledgement

This work was supported by the Center for Integrated Smart Sensors funded by the Ministry of Science, ICT & Future Planningas Global Frontier Project (CISS-2012M3A6A6054193) and partial support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (no. 2013-053595)
Novel Co-Precipitation Method for Synthesis of Carbon-Free LiFePO4
Authors: Feng Hai , Milev Adriyan S , Kannangara G.S. Kamali
Published: February 2020

Lithium iron phosphate (LiFePO4) is an important alternative cathode material to LiCoO2, which applications are limited by resource availability and safety issues. However, the full potential of the material is sometimes difficult to achieve due to its limited electrical conductivity and low rate of Li+ ion diffusion that together may limit the battery performance. One strategy is to manufacture LiFePO4 particles coated with a conductive phase, such as carbon, which improves the electronic contact between the LiFePO4 particles. However, the carbon seems to modulate not only the electric conductivity but also the reduce crystallite sizes and thus reduces the distance for Li+ transport in the LiFePO4 structure. Furthermore, carbon may improve the phase purity of the final product because during high temperature synthesis, carbon acts as a reducing agent and thus minimizes the likelihood of oxidation of Fe2+ to Fe3+. Despite these advantages, the role of different forms of carbon on the synthesis of LiFePO4 and the electrochemical performance of the materials is yet to be fully understood. This could be because the synthetic methods reported in the literature employ carbon containing precursors or solvents and therefore the LiFePO4 product always contain some form of residual carbon. This complicates the analysis of the effect of a specific carbon type on the electrochemical performance of the cathode material.

Carbon-free LiFePO4 material has been synthesised by a novel single-step co-precipitation method from aqueous solutions of LiOH∙H2O, NH4H2PO4 and FeSO4.7H2O precursors. The precipitation sequence and methodology, reaction atmosphere and the role of intermediate phases on the purity of LiFePO4 product has been investigated. The mechanism of formation of phase-pure carbon free LiFePO4 is also investigated and the role of synthesis atmosphere on the phase transformations and the effect of evolving gaseous species on the likelihood of oxidation of Fe2+ to Fe3+ are discussed. The lowest temperature to synthesise phase pure carbon-free LiFePO4 is 550 oC which remains phase pure during further heating up to 750 oC. The novel carbon-free method is suitable for investigation of the effect various forms of carbon (carbon black, nanotubes, meso-porous carbons, etc.) on the electrochemical performance of the cathodes containing LiFePO4.
All Polythiophene Redox Flow Battery
Authors: Yang Jung Hoon , Jeon Jae-Deok , Shim Joonmok
Published: February 2020

Surge in demand for electrical energy has been a common phenomenon around world. In addition, greenhouse gas emission is another challenge. As a solution to these problems, large-capacity energy storage system have been proposed. This energy storage system can manage the increasing energy demand more efficiently in conjunction with renewable energy and smart grid.

Among various large energy storage systems, the redox flow battery (RFB) is one of the most viable alternatives. In particular, RFB in the range of 10 kW-10 MW is the most competitive in terms of cost, flexibility, rapid response and safety over other secondary batteries such as lithium ion and sodium sulfur batteries [1].

RFB can be simply classified into aqueous and organic redox flow batteries. Of the aqueous RFBs, all vanadium RFB and zinc/bromine RFB are the most representative ones. Many companies have been considering the commercialization of those flow batteries based on their high energy density and low cost. However, the aqueous redox flow battery is limited by water electrolysis which prevents from increasing the cell potential out of the hydrogen or oxygen evolution voltage.

Organic redox flow battery, which is free from the water electrolysis problem, has been studied extensively. Organic molecules can be synthesized from low-cost, lightweight, widely available materials. In addition, their electrochemical properties can be easily adjusted using the well-established knowledge of organic chemistry [2]. By taking these attributes of organic materials, it may be possible to make a redox flow battery with very high energy densities and power densities.

Polythiophene is a representative conjugated polymer. It has received a lot of attention due to its various availability as nonlinear optics and electronic device [3].

In this study, we investigated the possibility of polythiophene as a redox couple in organic redox flow battery. Polythiophene shows electrochemical redox activities at two different potentials of about -2.0 V and +0.5 V versus Ag/Ag+ (figure 1). The polythiophene is reduced at -2.0 V (n-doping) and oxidized at +0.5 V (p-doping). To investigate the charge-discharge characteristics, a single cell with the active electrode area of 7.0 cm úI 5.0 cm was used.

References

1. P. Leung, X. Li, C.P. de León, L. Berlouis, C.T. John, and F.C. Walsh, RCS Advances, 2, 10125 (2012).

2. S.E. Burkhardt, M.A. Lowe, S. Conte, W. Zhou, H. Qian, G.G. Rodriguez-Calero, J. Gao, R.G. Hennig, and H.D. Abruna, Energy Environ. Sci., 5, 7176 (2012).

3. S. Jin, S. Cong, G. Xue, H. Xiong, B. Mansdorf, and S.Z.D. Cheng, Adv. Mater. 14, 1492 (2002).
Amorphous Soft Carbon Coated Graphite As Anode Material for Lithium Ion Battery
Authors: Kim Byung-Ryang , Hong Young Kyu , Kang Hye-Joung , Choi Nak-Mo , Shin Sang-Yong , Lee Jong-hyuk , Kim Sun Ah , Lee Ki-Tae , Shin Jin-Koog
Published: February 2020

The natural graphite was used without a purification process and processing step that results in the folding of the graphite fragments into small spheres. It is well known that spherically shaped anode material is preferable as a means of improving the anode characteristics due to its high tapping density [1]. To reduce movement of impurities and side reaction with electrolyte impurities [2], the amorphous soft carbon was coated on the spherical graphite surface.

In this study, we report the characteristics of anode which is made from the amorphous soft carbon coated natural graphite and charge-discharge behavior of half cells. The electrodes were prepared by pasting an aqueous slurry with styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

The charge–discharge tests were performed in CR2032 coin cell. Half cells consisted of the working electrode to be studied, Li metal as the counter electrode, and Celgard 2400 separator. 1 M LiPF6in ethylene carbonate and dimethyl carbonate (1:1 by volume) was used to electrolyte. Anode half-cells were tested between 1.5 V and 5 mV at a C-rate of 0.1 C. Microstructure of the amorphous soft carbon coating layer on graphite particle was observed using TEM to examine the cycle stability. Fig. 1 shows structural stability of carbon layer after charge-discharge cycles and thickness of carbon layer was about 50nm. Fig. 2 shows the charge(Li insertion)-discharge(Li extraction) curves of the amorphous soft carbon coating sample versus non-coating sample for the first cycle, charged in CC-CV mode and discharged in CC mode. The discharge capacity obtained at carbon coated sample is about 330 mAh/g and the columbic efficiency is about 90 %.

This research was financially supported by the Ministry of Trade, Industry and Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT) through the Promoting Regional specialized Industry

References

[1] Y. Chen, G.X. Wang, J.P. Tian, K. Konstantinov, H.K. Liu, Electrochim. Acta 50 (2004) 435–441.

[2] C. Wang, X. Zhang, A.J. Appleby, X. Chen, F.E. Little, J. Power Sources 112 (2002) 98-104.
Electrochemical Characteristics of (Li0.33La0.56)1.005Ti0.99Al0.01O3 Ceramic As a Solid Electrolyte for Lithium-Oxygen Batteries
Authors: Le Hang T.T. , Park Chan-Jin
Published: February 2020

To date, lithium lanthanum titanate (LLTO) of the nominal formula Li3xLa2/3-x
1/3-2xTiO3 with perovskite structure have been considered to be promising solid electrolyte materials for lithium batteries due to a numerous outstanding advantages such as: (i) a high lithium conductivity at room temperature, (ii) a high lithium diffusion coefficient, (iii) a low electronic conductivity, (iv) an electrochemical window larger than 4 V. However, the LLTO materials have also suffered from a few disadvantages such as insufficient total conductivity due to the large grain boundary resistance and difficulty in controlling Li+ content and Li+ conductivity of the materials especially after exposure to high annealing temperature. In addition, when LLTO contacts directly with Li metal, Ti4+ in LLTO can be reduced into Ti3+ by metallic Li leading to increase in the electronic conductivity of LLTO.

In this study, we focused on enhancement of the total conductivity of LLTO ceramics by improving the bulk conductivity using Al3+ dopant and the grain boundary conductivity using excess Li2O. Al-doped LLTO powders of (Li0.33La0.56)1.005Ti0.99Al0.01O3 with a various amount of 10-35% excess Li2O in stoichiometry were synthesized using sol-gel modified Pechini method, and then pelletized and sintered at 1350 oC.

The XRD patterns on the synthesized powders were compared and matched with Li0.33La0.56TiO3 (PDF#01-087-0935; Tetragonal) confirming pure tetragonal crystalline structure (P4/mmm space group) of perovskite phase without secondary phases. With the amount of excess Li2O 15%, crystal grains grew significantly. The largest grain size reached 100 m. The grains with typical rectangle shape were connected together closely.

The ionic conductivity of the obtained materials was measured using electrochemical impedance spectroscopy (EIS). Obviously, the bulk and grain boundary conductivities increased with the addition of excess Li2O. A maximum total conductivity of 3.17 10-4 S/cm was achieved for the sample with 20% excess Li2O, which is 4 times higher than that of the sample without excess Li2O. The high conductivity of the sample with 20 % excess Li2O is attributed to the minimum total activation energy of 0.358 eV and the somewhat large crystal grain size, 50 m.

To realize the application of LLTO materials as a solid electrolyte separator in Li-air batteries, a lithium phosphorous oxynitride (LIPON) interlayer fabricated using sputtering method was employed to prevent direct contact between Li metal and LLTO. The Li-O2 cells employing the LLTO ceramic electrolytes were tested in galvanostatic mode. Initial results showed that the Li-O2 cell employing LLTO electrolyte layer exhibited the satisfactory performance.
Diverse Pyrochlore Materials for Oxygen Reduction and Evolution Reaction in Alkaline Medium
Authors: Manivannan A. , Abreu-Sepulveda Maria , Quesnel David J
Published: February 2020

The oxygen reduction and evolution reactions (ORR and OER) have proven to be the limiting factors on the development of rechargeable metal-air batteries. Numerous research work has been carried out on the improvement of cathode technologies in order to reduce the voltage loss associated with the oxygen reactions. ORR and OER have proven to be a catalytic electrochemical process, and thus, the catalytic material in the cathode plays an important role in the performance of such batteries.

Current catalysts used for air cathodes can be classified into noble metals and metal alloys, carbons, and transition metal oxides. Platinum and platinum-based electrodes such as Pt-nanopartices dispersed on a carbon support have been the primary choice to catalyze the ORR because of their known superior electrocatalytic activity. Other Pt-based alloys, Pt3M (where M can be Fe, Co among others) have also shown superior ORR activities. Carbonaceous materials have also emerged as an alternative for metal-free electrodes. Some of the best performing carbonaceous materials are vertically aligned nitrogen doped carbon nanotubes (VA-NCNT), nitrogen doped porous carbons and graphenes which have exhibit comparable activity to that of the Pt-based electrodes [1]. However, in order to fully develop the applicability of metal-air batteries, bifunctional electrodes are essential.

In the present research, a group of pyrochlore materials, A2B2O7-δOδ, have being synthesized, characterized and studied for bifunctional oxygen electrode applications. Among the characteristics that make pyrochlores attractive for air cathodes, is the unusual framework containing oxygen vacancy ordering. Lanthanum, lead and bismuth-based pyrochlores has been synthesized by the well-known Pechini, solid state, and stearic acid methods.

All the samples were characterized by XRD for phase analysis, and electrochemical performance has been investigated by means of cyclic voltammetry. The effect of dopant concentration on the electronic conductivity as well as oxygen activity will be presented.

Acknowledgements

This work is supported by the IGERT-NSF fellowship and partially funded by the US Dept. of Energy/NETL, Oak Ridge Institute for Science and Education (ORISE) fellowship.

References

[1] Y. Lu, z. Xu, H.A. Gasteiger, S. Chen, K. Hamad-Schifferli, Y. Shao-Horn, J. Am. Chem. Soc. 2010, 132, 12170-12171.

[2] D. Geng, et al. Energy Environ. Sci., 2011, 4, 760-764.
Electroless Sn-Cu Alloy Electrodes for Li-Ion Batteries
Authors: Gomez Jamie , Telama Wete , Kalu Egwu Eric
Published: February 2020

Cu was electrolessly deposited onto an activated carbon cloth. To prepare the Sn-Cu alloy material, the Cu coated cloth was immersed in a tin bath of composition 28 g/L of stannous sulfate (SnSO4), 80 g/L of sodium hypophosphite (NaH2PO2), and 80 g/L of thiourea (Tu) for 30 seconds or more. A partial dispalcement of Cu and subsequent formation of Sn-Cu alloy resulted from the dispalcement step. The Sn-Cu alloy sample was used in a Li cell in which polytetrafluoroethylene (PTFE) membrane was sandwiched between the cathode and a lithium foil. The Sn-Cu alloy electrode cell was charged and discharged by applying a constant current at different current rates including 0.25 mA, 0.5 mA, 1 mA, and 2 mA, respectively. The results of the cell performance evaluation as a battery will be presented and the overall concept of the electrode material fabrication discussed.
Electrode Materials for Lithium-Ion Batteries with Surface Modification by Advanced Hybrid Polymers
Authors: Bittner Andreas , Guntow Uwe , Schulz Jochen , Olsowski Birke-Elisabeth , Lorrmann Henning , Sextl Gerhard
Published: February 2020

The main challenges in the development of lithium-ion batteries for automotive applications are the improvement of energy density and cycling stability. For this purpose the electrodes have to be protected from irreversible reactions with the electrolyte which occur especially at high operating voltages.

A very promising approach to prevent this degradation process is the surface coating of electrode materials with protective layers. To achieve these protective layers a new nanosized multifunctional coating was designed. The coating (shown in Fig. 1) consists of an inorganic-organic hybrid polymer, named ORMOCER® (trademark of Fraunhofer ISC). Due to its specific design of inorganic and organic networks on the molecular level, several remarkable material properties could be generated. These properties include an electrochemical stability up to at least 5.0 V. This enables the stabilization of high-voltage materials like LiMn1.6Ni0.4O4. The hybrid polymer also displays a high elasticity, which provides a long-term mechanical stability of the coating during cycling. Moreover, the coating material has a good ionic conductivity of 10-4 S/cm to facilitate the ion transport into the electrode material.

Based on these properties, the new core-shell nanocomposite approach can be applied to various electrode materials to improve their cycling performance, especially on materials with high operating voltages to achieve a high energy density of the batteries. Fig. 2 shows such an improvement, expressed in a significantly reduced capacity fade of coated LiMn1.6Ni0.4O4 electrodes during cycling.

This work was supported by the Bavarian State Ministry of Economics, Infrastructure, Traffic and Technology.
Investigation of the Active Thickness of Solid Oxide Fuel Cell Cathode
Authors: Zheng Keqing , Ni Meng
Published: February 2020

In solid oxide fuel cell (SOFC) electrode, electrochemical reaction only occurs in a narrow region near the interface of electrode and electrolyte, which is regarded as the “active thickness”. However, as a key parameter for SOFC electrode microstructure design and optimization, the active thickness of SOFC cathode reported by different research groups vary significantly (from 13 μm [1] to 253 μm [2]) due to different measuring conditions or simulation assumptions.

In this study, a detailed SOFC model is developed, in which the dusty gas model (DGM), Ohm’s law and the concentration related Butler-Volmer equation are used to describe the gas diffusion in pores, ion and electron conduction in electrolyte and electrodes, and electrochemical reaction kinetics, respectively. The effective ionic conductivity, electronic conductivity and the TPB length are calculated with the percolation theory and coordinate number theory [3]. Current density distribution in cathode is investigated under various operating conditions and 99% total current density is used as the indicator of the active thickness. This work could provide useful information for SOFC cathode microstructure optimization and for performance enhancement.

Keywords: Solid oxide fuel cell; Cathode thickness; Triple phase boundary length

[1] Lu, Z., Hardy, J. S., Templeton, J. W., & Stevenson, J. W. (2012).Extended reaction zone of La0.6Sr0. 4Co0.2Fe0. 8O3 cathode for solid oxide fuel cell. Journal of Power Sources, 198: 90-94.

[2] Jiang, Z. Y., Xia, C. R., & Chen, F. L. (2010). Efficient thickness of solid oxide fuel cell composite electrode. Chinese Journal of Chemical Physics, 23(2), 217.

[3] Chen, D., Bi, W., Kong, W., & Lin, Z. (2010). Combined micro-scale and macro-scale modeling of the composite electrode of a solid oxide fuel cell. Journal of Power Sources, 195(19), 6598-6610.
Redox Mediators of Shewnella Bacterial Biofilms Using SECM
Authors: Cliffel David , Crisostomo David
Published: February 2020

With help from Dr. Sean Elliott of Boston University, we have obtained samples of Shewnella for scanning electrochemical analysis. These are samples of S. Oneidensis (shewie). We were able to learn to grow shewie bacterial films on our transparent electrodes. We also were able to do some basic electrochemical characterization of these films which confirmed their surface redox activity. Our initial SECM results would be the first attempts at using a SECM to study a biofilm of any type, but unfortunately the tip electrodes kept being coated by the sticky protein layer of the biofilm, which then fouled the electrochemical signals. Our newest attempts are going to keep the tip electrode farther from the biofilm, but close enough to map the redox activity of the shewie bacteria. This has led to our first manuscript using SECM to measure the amount of redox agents, specifically identified as riboflavin, coming out of the bacteria, and also confirmed by mass spectrometry.
Practical Implementation of Nano-Electrochemistry
Authors: Freeman Neville J , Kay Nicola J , Sultana Reshma , Hick Camilla
Published: February 2020

Many papers have been published on the use of nanoelectrodes fabricated by a wide range of techniques. However these electrodes have not been available to the wider electrochemical community (who do not necessarily have access to sophisticated fabrication facilities) until recently. As a result there are a number of preconceptions about the use and utility of nanoelectrodes. In our laboratory we have extensive experience of the practical use of nanoband electrodes over a significant period of time and much of what we observe is at odds with the ‘received wisdom’ regarding their practical value. In this paper we describe the nanoband structures we are using and discuss their performance in terms of repeatability, reproducibility, durability and longevity. We believe these observations have a material bearing on the future scope and practicality of such electrodes and provide examples which are germane to biosensing and environmental analysis.
Infrared Spectroscopy As a Probe of Water Structure and Content in Fuel Cell Membrane Materials
Authors: Korzeniewski Carol , Zheng Shu , Aquino Adelia , Kabrane Joseph
Published: February 2020

Vibrational spectroscopy techniques are being applied to gain insights at the molecular level into processes that control charge transfer and energy conversion efficiency in fuel cells and related electrochemical technologies (i.e., batteries and charge storage systems). In one direction under investigation, the structure of water confined to nanoscale pore and channel regions of ion conducting polymer membranes is being investigated. The high internal surface area of materials, such as Nafion 112, enables water interacting with interfaces inside membrane pores and channels to be detected with the use of simple infrared sampling methods. The structure of interfacial water in Nafion membrane determined through measurements on H2O/D2O mixtures in combination with electronic structure simulations will be discussed. Additionally, infrared spectroscopy is being investigated as a straightforward method for determining membrane water content. A combination band associated with vibrations of -CF groups is used as an internal standard. Application of the approach to compare differences in water uptake by fluorinated ionomer materials prepared with and without inorganic filler materials will be presented.
Infrared Spectroscopy of Thin Organic Films Adsorbed at a Gold Electrode Surface
Authors: Lipkowski Jacek
Published: February 2020

This lecture will review our research involving IR spectroscopy at the solid –liquid interface. After a brief review of basic principles of IR spectroscopy and the laws of reflection of light at interfaces, three methods of Infrared Reflection Absorption Spectroscopy (IRRAS) will be described. The first is subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) or in short potential difference IR spectroscopy. This technique finds application to study reversible adsorption of soluble molecules at electrode surfaces. The methods of optimisation of the SNIFTIRS experiment will be discussed. Its application will be illustrated by the case of adsorption of a soluble surfactant such as sodium dodecyl sulphate (SDS) at a gold electrode surface.1 The second technique to measure IR spectra at interfaces is the photon polarization modulation infrared reflection absorption spectroscopy (PM IRRAS). This technique is used to study films of insoluble molecules a various interfaces. I will discuss application of this technique to study model biological membranes supported at a gold electrode surface.2 The third technique is the surface enhanced infrared reflection absorption spectroscopy (SEIRAS). It is performed using attenuated total internal reflection (ATR) element covered by nanoparticles of gold. The intensity of the IR signal is then enhanced by a factor of 100. In addition, since the film of metal nanoparticles is conductive it is used to study phenomena at electrified interfaces. I will describe application of this technique to study structure of water in model biological membrane supported at a gold electrode surface.3 I will emphasize complementarity of SEIRAS and PMIRRAS in application to bio-electrochemical research.

Literature

1.Jay Leitch, John Collins, K. Andreas Friedrich, Ulrich Stimming, John R. Dutcher, Jacek Lipkowski “Infrared Studies of the Potential Controlled Adsorption of Sodium Dodecyl Sulfate at the Au(111) Electrode Surface”, Langmuir,
2012,28,2455-2464.

2. Jacek Lipkowski, “Building model biomimetic membrane at a gold electrode surface”, Phys. Chem. Chem. Phys., 2010,12,13874-13887.

3. Taro Uchida, Masatoshi Osawa and Jacek Lipkowski, “SEIRAS studies of water structure at the gold electrode surface in the presence of supported lipid bilayer”, J.Electroanal.Chem. DOI:10.1016/j.jelechem.2013.10.015
In-Situ Surface-Enhanced Raman Scattering Observation of Intermediate Species at Plasmon-Induced Water Oxidation Process Using Au Nanostructures on Titanium Oxide Single Crystal
Authors: Suzuki Kentaro , Nagasawa Fumika , Yasuda Satoshi , Murakoshi Kei
Published: February 2020

Recent attempts to use localized surface plasmon resonance (LSPR) for photoexcitation of molecules suggests the possibility to modify the excitation processes and the selection rule of electrons [1, 2]. Among several choices of the applications of LSPR, the system of Au-nanostructured titanium dioxide (TiO2) is one of promising approaches for plasmon-enhanced photoenergy conversion under illumination of visible and near infrared light . It has been suggested that photo-induced electron injection from the Au structure into the TiO2 conduction band occurs by localized surface plasmons excitation. In this system, Au-nanostructured TiO2 enabled efficient water oxidation owing to the excitation of multiple electrons and holes generated by near-infrared light, and the evolution of O2 via four-electron oxidation of water. In this work, size-controlled Au-nanostructures was fabricated on a TiO2 single crystalline by means of angle-resolved nanosphere lithography (AR-NSL) to measure surface-enhanced Raman scattering (SERS) from the intermediate species at water oxidation process at the electrode-electrolyte interface under near-infrared light irradiation. SERS spectra were obtained from the size-controlled Au nano-dimer (Au-NSL) arrays on a single crystalline TiO2 immersed in 0.1 M NaF solution. For comparison, we also measured SERS spectra from Au-NSL on indium tin oxide (ITO). Observed spectral feature at ~580 cm-1 can be attributed to Au-O stretching vibrations of adsorbates. This wavenumber suggests that adsorbed hydroxide anion with Au-O bonding are produced as intermediate of water oxidation reaction at Au/TiO2. It should be noteworthy that Au-O vibration was observed at more negative potential on Au/TiO2 than that of Au/ITO. Negative shift is attributed to the water oxidation on Au/TiO2 is assisted by electrons and holes generated by plasmon-induced excitation.

References

[1] M. Takase et al., Nature Photonics, 7, 550 (2013).

[2] F. Nagasawa, M. Takase, H. Nabika, K. Murakoshi, "Depolarization of Surface-Enhanced Raman Scattering Photons from a Small Number of Molecules on Metal Surfaces", in Vibrational Spectroscopy at Electrified Interfaces, Eds. C. Korzeniewski, B. Braunschweig and A. Wieckowski: Wiley, NY (2013).

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The Role of Well-Defined Surfaces in Electrocatalysis
Authors: Markovic Nenad M , Stamenkovic Vojislav R
Published: February 2020

The progress in electrocatalysis over the last two decades has been achieved primarily through the fundamental understanding of electrochemical processes that are taking place at well-defined surfaces. Fine tuning of the surface properties has led towards unprecedented improvements in functionality of practical materials for energy conversion and storage applications. This presentation is an overview of the most relevant studies related to well-defined surfaces in ultra-high vacuum (UHV) and at solid-liquid interfaces that have revealed the structure-function relationships in electrocatalysis and established principles for the design of advanced electrocatalysts. The following topics will be discussed: 1) well-defined surfaces in UHV; 2) atomic/molecular insight into electrified interfaces; 3) modeling of electrochemical processes; 4) identification of the active sites under reaction conditions; 5) insight into chemical bonds between the surface atoms, and molecular species in the electrolyte; 6) design and synthesis of practical catalyst with desired size, shape and composition profile; and 7) fine tuning of the activity and durability in electrocatalysis.
Oxygen Reduction at Model Pt Single Crystal Surfaces
Authors: Gomez-Marin Ana María , Rizo Ruben , Herrero Enrique , Feliu Juan
Published: February 2020

Oxygen reduction reaction ORR is the main cathodic problem in electrochemistry and has a deep influence in the development of technologically relevant applications such as fuel cells. It is a complex reaction involving a nonpolar molecule with double bond breaking, 4 electron transfer and 4 O-H bond formation in different scenarios. In the reaction mechanism a possible important role can be played by intermediate peroxo species, after the exchange of only 2 electrons. To enhance reactivity, the understanding of the reaction mechanism at the Pt surfaces is necessary. Models can be used to simplify the complex reaction and from the experimental point of view such models are related to the use of single crystal surfaces with well defined orientations. For Pt(111) electrodes, the activation region is quite narrow despite the high overpotential and the process readily becomes transport controlled. Moreover, in the activation region the platinum electrode is covered by oxygenated species and it is well known the influence that these species can play in the electrode surface order, the surface stability being dependent a structure sensitive process. Possible influence of the surface oxygen-containing species, particularly as intermediates in the ORR is not clearly understood and only has been addressed at Pt(111), which likely is the most stable surface upon oxidation . On the other hand the ORR is structure sensitive, the Pt(111) being the most active in alkaline media [1] in contrast to that observed in acidic solution in which Pt(110) and Pt(hkl) surfaces with small two-dimensional domains are able to reduce oxygen at lower potentials. It is obvious that surface effects play an important role in the activation region as deduced from the marked anion effect that should be less important in alkaline solutions due to the shift in the surface charge on the metal. Another aspect that should be considered is the reactivity of hydrogen peroxide at these platinum surfaces, because its possible role as reaction intermediate [2]. In this respect if the ORR necessarily took place through the peroxo intermediate, a possible strategy would be based in the inhibition of peroxide oxidation while keeping constant ORR.

Acknowledgements

Financial support from MICINN (Spain) through project CTQ2010-16271 and Generalitat Valenciana (PROMETEO/2009/045, FEDER) are greatly acknowledged.

References

1. Rizo R, Herrero E, Feliu JM (2013) Phys Chem Chem Phys 15:15416-15425

2. Gomez-Marin AM, Feliu JM (2013) Chemsuschem 6:1091-1100
Cytochrome C Mutants with Enhanced Capabilities in Multi Layer Arrangements
Authors: Weber Dennis , Turano Paola , Allegrozzi Marco , Lisdat Fred
Published: February 2020

In the field of biosensors it is important to increase the surface concentration of the selected biological recognition elements for a higher sensitivity. Based on cytochrome c, a small heme containing electron carrier protein from the respiratory chain, fully redox active multi layer assemblies have been developed by using the layer by layer technique, where every immobilized protein contributes to the electron transfer with the electrode. This provides the basis for integrating catalytically active enzymes into the layers, giving the opportunity of tuning the sensitivity by the number of layers deposited. This was shown already e.g. for bilirubin oxidase (BOD) and sulfite oxidase (SOX). However, one limiting factor for the effective coupling of proteins in those multi layer systems is the electron self-exchange rate of the cytochrome c molecules. In order to follow the applied potential but also the enhanced conversion at the embedded enzymes, a rather high exchange rate between the immobilized proteins is necessary.

Based on the hypothesis, that the electron transfer happens via hopping between the heme-centers which are embedded in a protein-pocket that is mainly positively charged at neutral pH, we tried to engineer human cytochrome c mutants with increased electron self exchange rates. By replacing some of the positively charged surface lysines around the heme pocket with uncharged alanines via site directed mutagenesis, repulsion between cytochrome c molecules should be decreased and ease the charge transfer.

Six different mutants have been designed, expressed and evaluated. The electrochemical properties of the cytochrome c mutants have been analyzed by cyclic voltammetry at self assembling mono layers (SAMs) of 11-mercapto-1-undecanol (MU) and 11-mercapto-1-undecanoic acid (MUA) on gold. In a second step cytochrome c mutant multi layers have been prepared and analyzed with respect to different rates of the potential sweep in order to elucidate how the systems can follow the driving force.
Photocurrent Generation by Immobilized Nostoc Sp. Via Direct Electron Transport
Authors: Sekar Narendran , Umasankar Yogeswaran , Ramasamy Ramaraja P
Published: February 2020

Photosynthesis based energyconversion is an effective way of utilizing the most abundant solar energy for the benefit of mankind. Photosynthetic energy conversion processes have enormous potential towards energy and environmental sustainability. Among the various photosynthetic microorganisms, cyanobacteria possess exciting features for energy conversion. This study focuses on production of direct electricity from a cyanobacterium called Nostoc sp. (NOS). By illuminating with white light (of intensity 76 mW cm-2), the NOS immobilized on multi-walled carbon nanotubes (MWNT) modified electrodes generated a photocurrent density of 30 mA m-2 at an applied potential of 0.2 V (vs. Ag/AgCl). The contribution of different photosynthetic pigments of NOS to the photocurrent generation was analyzed by measuring the current density produced by MWNT/NOS upon illuminating with monochromatic lights of different wavelengths. Phycocyanin was found to be the major pigment greatly contributing to the photocurrent. Further investigation using a set of inhibitors1 revealed that the plastoquinones were primarily responsible for the electron transfer between the cyanobacteria and the electrode. Finally a rudimentary design photosynthetic electrochemical cell2 has been constructed with MWNT/NOS on the anode and MWNT/laccase on the cathode. The cell generated a maximum current density of 250 mA m-2 and a peak power density of 35 mW m-2 without any mediator. With the addition of benzoquinone as a redox mediator, the electricity generation capability was significantly enhanced to a current density of ~2300 mA m-2 and power density of 100 mW m-2, which is the highest among such systems reported thus far in literature.

References

Torimura M, Miki A, Wadano A, Kano K and Ikeda T (2001) Electrochemical investigation of cyanobacteria Synechococcus sp. PCC7942-catalyzed photoreduction of exogenous quinones and photoelectrochemical oxidation of water. Journal of Electro-analytical Chemistry, 496, 21–28.

Calkins J, Umasankar Y, O'Neill H and Ramasamy R (2013) High photo-electrochemical activity of thylakoid–carbon nanotube composites for photosynthetic energy conversion. Energy Environ. Sci., 2013, 6, 1891-1900.