bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorinated Solvent Based Electrolytes for Lithium-Sulfur Batteries
Authors: Bouchal Roza , Boulaoued Athmane , Johansson Patrik
Published: February 2020

The lithium-sulfur battery is a promising next generation battery (NGB) technology, but with a common major complication of irreversible loss of active material (S) from the composite cathode (C/S). Elemental sulfur and polysulfides (Li2Sx, 4 ≤ x ≤ 8, PS) generated during the charge/discharge process are both dissolved into the electrolyte and the PS shuttle between the anode and the cathode without performing useful work. This shuttling results in low Coulombic efficiency, low cycling capacity, and increased internal cell resistance.1, 2

One way to reduce the PS shuttling is to employ electrolytes that only sparsely dissolve sulfur and PS.3, 4 Here we have employed several such electrolytes based on fluorinated carbonates and ethers and studied the resulting performance including the cycle life of the Li-S battery cells made. By combining physico-chemical characterization, electrochemical performance assessments, and operando confocal Raman spectroscopy we gain a better understanding of the PS formation. The overall outcome can be used to guide the selection of solvents for more performant Li-S batteries.

The research presented has received funding through the HELIS project (European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 666221).

References

1 Q. Pang, X. Liang, C. Y. Kwok and L. F. Nazar, Nat. Energy, 2016, 1, 1–11.

2 P. Bonnick, E. Nagai and J. Muldoon, J. Electrochem. Soc., 2018, 165, A6005–A6007.

3 S. Drvarič Talian, S. Jeschke, A. Vizintin, K. Pirnat, I. Arčon, G. Aquilanti, P. Johansson and R. Dominko, Chem. Mater., 2017, 29, 10037–10044.

4 S. Gu, R. Qian, J. Jin, Q. Wang, J. Guo, S. Zhang, S. Zhuo and Z. Wen, Phys. Chem. Chem. Phys., 2016, 18, 29293–29299.
Highly Enhanced Cycleability from High Crystalline Biaxially Aligned CNT Web for Li-Air Cathode Applications
Authors: Kim Hyunjin , Cho Youngshik , Byeon Minhu , Baek WoonJoong , Kwon Hyuk Jae , Lee Dong Joon , Lee Hyunpyo , Jung Yeonsu , Park Chong Rae , Im Dongmin
Published: February 2020

In recent years, Li-O2 batteries have attracted a great deal of attention due to the high theoretical capacity for applications as electronic vehicles. Carbon nanotubes are widely used as cathode materials for Li-O2 batteries because of their high conductivity, high surface area and low density. However, due to their hydrophobic surface properties and the high van der Waals interaction between their walls, they tend to aggregate on their own, failing full use of the CNT surface. Therefore, it is necessary to engineer the nanoscale space between the CNTs such that each CNT aligns with each other and the nanoscale spacing lies between them. In this way, it is possible for the ionic liquid electrolyte and oxygen to access individual CNTs and enable uniform Li2O2 formation.

In this research, we developed a one-step process for biaxially oriented, highly crystalline CNT fabrics using a combination of floating catalyst chemical deposition (FCCVD) and one-step direct spinning technology. A highly crystalline DWCNT with a diameter of 6 nm was synthesized by FCCVD using ferrocene, thiophene, and methane, as precursors, and as-spun CNTs were woven into fabric by 2-directional spinning process. The intensity ratio between D and G bands (ID/IG) of 0.06 showed high crystallinity of CNT surface. The microscopic architectures of randomly oriented CNT fabric and biaxially oriented CNT fabric were investigated using a high-resolution scanning electron microscope (See Figure 1.(a) and (b)). The biaxial orientation was reconfirmed using a polarized Raman spectroscopy.

In order to investigate the effect of the microscopic structure on the performance of the Li-O2 battery, we have assembled Li-O2 cells using a random CNT fabric and a biaxially aligned CNT fabric as a cathode. In the random CNT cathode, the charging overpotential gradually increases, leading to rapid decay of capacity upon cycling (Fig. 1(c)). The increase in overpotential is typically associated with the accumulation of insulating byproducts due to parasitic reactions involving the electrolyte or the carbon electrode. However, in the biaxially aligned CNT electrode, a much improved cycle stability and small charging overpotentials are demonstrated (Fig. 1.(d)). This dramatically improved cycling performance might result from the increase in the surface area corresponding to mesopores, providing more effective sites capable of carrying discharge products such as Li2O2. In addition, Li-O2 cathode using biaxially aligned CNT fabric can offer open framework in which O2 and electrolytes can access to the individual CNTs, facilitating reversible Li2O2 formation and removal, and consequently exhibiting enhanced cyclability.

Figure 1
Biological Redox Mediation for Oxygen Reduction Reaction Catalysts in Lithium–Oxygen Batteries
Authors: Ko Youngmin , Park Hyeokjun , Kim Jinsoo , Lim Hee-Dae , Lee Buyngju , Kwon Giyun , Kang Kisuk
Published: February 2020

Governing the fundamental reaction of oxygen and lithium in lithium–oxygen batteries is vital to realizing their potentially high energy density. Here, we report novel oxygen reduction reaction (ORR) catalysts that are capable of mediating the lithium and oxygen reaction within a solution-driven discharge, which promotes the solution-phase formation of lithium peroxide (Li2O2), thus enhancing the discharge capacity. The new ORR catalysts are derived from mimicking the biological redox mediation occurring in the respiration system of a bacteria, where biomolecule mediates the oxidation of reduced flavin mononucleotide and the reduction of cytochrome b in the cell membrane. The redox potential of the molecule in the biological environment is demonstrated to coincide with the suitable ORR potential range of lithium–oxygen batteries in aprotic solvent, thereby enabling its successful functioning as a redox mediator (RM) that triggers the solution-based discharge. The use of the catalyst prevents the growth of film-like Li2O2 even in an ether-based electrolyte, which has been reported to induce surface-driven discharge and early passivation of the electrode, thus boosting the discharge capacity by ~30 times. The similarity of the redox mediation in the biological cell and lithium–oxygen ‘cell’ inspires the exploration of various redox active bio-organic compounds for potential high-performance RMs toward achieving high theoretical specific energies for lithium–oxygen batteries.
Hexacyanoferrate Cathode for Superior Na-Ion Batteries
Authors: Zhang Wuxing , Wan Min , Tang Yang , Liu Yang , Huang Yunhui
Published: February 2020

Sodium iron hexacyanoferrate (Fe-HCF) is regarded as a potential cathode material for sodium-ion batteries (SIBs) due to its high specific capacity, low cost, facile synthesis and environmentally friendly. However, Fe-HCF always suffers from poor electronic conductivity, low crystallinity and side reactions with electrolyte, leading to poor rate performance, low coulombic efficiency and deterioration of cycling stability. Herein, we report the green and facile synthesis to encapsulate Fe-HCF microcubes with potassium nickel hexacyanoferrate (Ni-HCF) and PPy, separately, the surface modified Fe-HCF can exhibit excellent electrochemical performance as cathode in SIBs (Fig. 1).

Firstly, the Fe-HCF@PPy composite exhibits a discharge capacity of 113.0 mA h g-1 at a current density of 25 mA g-1 and 75 mA h g-1 at 3000 mA g-1. Greatly improved cycling stability is attained with 79% capacity retention over 500 cycles at 200 mA g-1. The superior rate capability and excellent cyclability can be ascribed to the effects from PPy as both electronic conductor to enhance the conductivity and protective layer to prevent the side reactions.

Secondly, the core-shell Fe-HCF@Ni-HCF composite delivers a reversible capacity of 79.7 mAh g-1 at 200 mA g-1 after 800 cycles and a high coulombic efficiency of 99.3 %. In addition, Fe-HCF@Ni-HCF exhibits excellent rate performance, retaining 60 mAh g-1 at 2000 mA g-1. The results show that Fe-HCF@Ni-HCF integrates the advantages of both Fe-HCF and Ni-HCF, making it electrochemically stable as cathode material for SIBs.

Figure 1
Glyme-Na Salt Equimolar Complex Electrolytes for Sodium Ion Batteries
Authors: Dokko Kaoru , Terada Shoshi , Susa Hiroko , Ueno Kazuhide , Watanabe Masayoshi
Published: February 2020

Physicochemical and electrochemical properties of glyme-Na salt equimolar complex electrolytes were investigated. The pentaglyme (G5) forms complexes with Na salts in 1:1 molar ratio.1,2 The structures of complexes of G5-Na[TFSA] (TFSA: bis(trifluoromethanesulfonyl)amide) and G5-Na[FSA] (FSA: bis(fluorosulfonyl)amide were investigated using single crystal X-ray diffraction and ab initio calculations. In the crystals of G5-Na[TFSA] and G5-Na[FSA], G5 molecules wrap around Na+ ion and form [Na(G5)]+ complex cations. The melting points of [Na(G5)][TFSA] and [Na(G5)][FSA] are 32 °C and 41 °C, respectively.1 To apply the G5-Na salts complexes to sodium ion batteries as electrolytes at room temperature, the complexes were mixed with a low polar solvent, HFE (HFE: 1,1,2,2–tetrafluoroethyl 2,2,3,3–tetrafluoropropyl ether (CF2H−CF2−O−CH2−CF2−CF2H)). The liquid structures of [Na(G5)][TFSA]/HFE and [Na(G5)][FSA]/HFE were elucidated using Raman spectroscopy. The complex structure of [Na(G5)]+ complex cation were kept in the liquids, and the HFE hardly participate in the solvation of Na+ in the solutions.3 [Na(G5)][FSA]/HFE showed higher ionic conductivity than [Na(G5)][TFSA]/HFE owing to the higher mobility of FSA than that of TFSA.

The reversibility of the Na metal deposition/dissolution changed greatly depending on the electrolyte composition. The Coulombic efficiency of Na metal deposition-dissolution in [Na(G5)][FSA]/HFE reached to 95 % while the efficiency in [Na(G5)][TFSA]/HFE was much lower. X-ray photoelectron spectroscopy (XPS) revealed that a thin and compact SEI layer was formed on the Na metal in [Na(G5)][FSA]/HFE, and the SEI was effective in suppressing the reductive decomposition of the electrolyte.

The charge and discharge properties of hard carbon (HC) anode and Na0.44MnO2 cathode of sodium ion batteries in [Na(G5)][FSA]/HFE electrolyte were characterized. Highly reversible charge-discharge of HC anode was possible in [Na(G5)][FSA]/HFE with a high Coulombic efficiency of 99.9%. In addition, the discharge capacity of HC negligibly decreased during 300 charge-discharge cycles. Na0.44MnO2 cathode also showed highly stable charge-discharge behavior in [Na(G5)][FSA]/HFE owing to the good oxidative stability of the electrolyte.

Acknowledgements

This study was supported in part by the MEXT program “Elements Strategy Initiative to Form Core Research Center” of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan and JSPS KAKENHI (No. 15H03874) from the Japan Society for the Promotion of Science (JSPS).

References

T. Mandai, R. Nozawa, S. Tsuzuki, K. Yoshida, K. Ueno, K. Dokko, M. Watanabe, J. Phys. Chem. B, 117, 15072-15085 (2013).

S. Terada, T. Mandai, R. Nozawa, K. Yoshida, K. Ueno, S. Tsuzuki, K. Dokko, M. Watanabe, Phys. Chem. Chem. Phys., 16, 11737-11746 (2014).

S. Terada, H. Susa, S. Tsuzuki, T. Mandai, K. Ueno, Y. Umebayashi, K. Dokko, M. Watanabe, J. Phys. Chem. C, 120, 23339-23350 (2016).
(Invited) Integration of Thin Film Wavelength Converter on III-V Blue LED
Authors: Kundaliya Darshan , von Malm Norwin , Mishra Kailash C.
Published: February 2020

The concept of micron-sized emitter (µ-emitter) arrays in a LED chip for advanced displays has been envisioned and realized about a decade and half-ago [1-3]. Since then, these arrays have been fabricated in smaller dimensions of a chip with a very high density. While there has been a significant progress in the fabrication technology of pixelated LEDs of InGaN blue LEDs, there has been scant research addressing the pixelation of LEDs with a phosphor layer for down-conversion of the LED emission.

In this talk, we will describe an approach where an ultra-thin inorganic phosphor layer is fabricated and transferred onto both pixelated as well as non-pixelated LEDs. We will also explain the importance of developing a suitable sacrificial layer while maintaining the desired photoluminescence quantum yield of the phosphor for its successful integration on a LED. It will be shown how important it is to consider the melting temperature, bonding energy, thermal conductivity and optical bandgap of the sacrificial layer to enable successful integration of phosphor thin films to LEDs for solid state lighting applications [4].

S.-X. Jin et al., Appl. Phys. Lett. 76, 631 (2000).

H.X. Jiang et al., Appl. Phys. Lett. 78, 1303 (2001).

H.X. Jiang et al., US Patent 6,410,940 (2002).

D.C. Kundaliya et al., ECS Journal of Solid State Science and Technology, 7, R3046 (2018).
Monitoring Acidithiobacillus Thiooxidans Biofilm Formation on Graphite Surface
Authors: Méndez-Tovar Marcela , García-Meza J Viridiana , González I
Published: February 2020

Biofilm formation has been studied to understand modifications in electrode interface to create new monitoring devices related with different fields as medical, environmental and industrial. In biomining industry, specifically in bioleaching processes, Acidithiobacillus
thiooxidans is an acidophilic bacterium that enhances bioleaching as it biooxidizes sulfur which normally passivates ores surfaces and diminishes the bioleaching efficiency. In this work, cells of Acidithiobacillus thiooxidans colonized a graphite surface during seven days in acidic culture medium contained elemental sulfur as nutrient, resulting in bioelectrode. In order to monitor the biofilm formation as bioelectrode, microscopic and electrochemical characterization was performed. Confocal laser scanning microscopy images show biofilms formation since first day of graphite immersion in medium, exopolymeric substances (EPS) becomes hydrophobic after 3 days of immersion which is related with lipidic exopolymers, while on day 5 there is an important change in EPS composition resulting in a higher proportion of exopolysaccharides than lipidic substances. This shift on the EPS composition was related to the analysis of EIS spectra obtained for bioelectrodes: An increase of electrochemical resistance of biofilm at the initial 3 immersion days, meanwhile the presence exopolysaccharides decreased such resistance. Cyclic voltammetry characterization of bioelectrodes using culture medium as electrolyte, shows an irreversible reduction process since day 1, which increases in longer exposure times, even when the characterization was performed with agitation. This suggests the reduction process is associated to the adsorbed S0 on graphite bioelectrode. The cathodic peak is near to the calculated reduction potential in acid media (0.1 to 0.2) V vs. NHE. It is known that the sulfur oxidation in acidithiobacilli as A. thiooxidans and A. caldus, initiated via S8 reduction after its activation (protonation) by the GSH and sulfonate (-SH) groups found in an outer-membrane protein [1-4].

M. Méndez-Tovar acknowledges to Universidad Autónoma Metropolitana-Iztapalapa and CONACYT for PhD grant 212534.

References:

[1] Mangold S., Valdés J., Holmes D.S., Front Microbiol, 2011,2,1

[2] Bobadilla R.A., Cortés M.P., Padilla L., Biotechnol. Bioeng., 2013,110, 2242

[3] Yin, H.,Zhang, X., Li X.,BMC Microbiol. 2014,14,179

[4] López‐Cázares I.,Patrón‐Soberano O.A.,García‐ Meza J.V.,Minerals, 2017,7,156

Figure 1
(Invited) Hydrogen Bonding Effects at the Organic-Water Interface of Aqueous Toluene Droplets Investigated By Particle Collision Electrochemistry
Authors: Alvarez Julio C , Paul Dilip K , Meng Kejie
Published: February 2020

This work reports on the hydrogen bonding effects induced by water solvation in aqueous toluene droplets studied by Particle Collision Electrochemistry (PCE). The latter approach is an emerging methodology employed to characterize microscopic particles that collide with the surface of an ultramicroelectrode as a result of Brownian motion. The ability of PCE to yield in-situ kinetic and thermodynamic information from single collision events has led to fundamental studies of nanoparticle electrochemistry which now is recognized as a sub-field in electrochemistry dubbed as single entity electrochemistry, due to the wide range of probes that can be investigated.

Herein, the reversal of hydrogen bonding affinity between quinone phenolate di-anions (Q2-) and carboxylic acids, induced by water in micrometer-size droplets of toluene is reported. Such an effect is revealed by the two-electron reduction of the hydrophobic quinone (Q) tetrachoro-1,4-benzoquinone to Q2- inside the toluene droplets, when performed in the presence of carboxylic acids that partition differently between the aqueous and organic phases. In bulk toluene, the hydrogen bonding affinity of Q2- for acetic acid (pKa = 4.8) is higher than for oleic acid (pKa = 9.9). However, such trend is reversed in emulsified toluene droplets due to preferential solvation of acetic acid by the surrounding water. The goal of this work is two-fold: first, to illustrate a subtle yet consequential water effect that arises from heterogeneous micro-confinement of organic-water phases, and second, to demonstrate how mechanistic information in such interfaces can be extracted from PCE.
Electrochemical and Circular Dichroism Study of the Interaction of Cu(II) Coordination Compounds with BSA
Authors: Ocampo Janet , Moreno Rafael , Cruz Marisela , Ortiz Luis Antonio
Published: February 2020

Because to the redox properties, the Cu(II) coordination compounds have been used as potential antineoplastic agents. However these may have their bioavailability compromised by interaction with biological components, depending on their chemical structure. This fact motivates us to demonstrate the effect of ligand type on interaction of a BSA plasma protein with two coordination compounds [Cu(1,10-phenanthroline)2(NO3)]+ y [Cu(Bztpen)]2+, (Bztpen=N-benzyl-N,N’,N’-tris (pyridin-2-ylmethyl) ethylenediamine), by means of electrochemical and spectroscopics thechniques of circular dichroism.
Go in and Go out — Change in Local Structure and Diffusivity in Monoclinic Li3+X
V2(PO4)3 upon Li Insertion and Extraction
Authors: Brinek Marina , Lunghammer Sarah , Hanzu Ilie , Rettenwander Daniel , Wilkening Martin
Published: February 2020

The use of Li-ion batteries in our daily life has become vital and is going to increase further as the demand for portable energy storage systems will continue to rise in the future. Considering advanced anode and cathode materials a fundamental understanding is needed to visualize the electrochemical processes, local changes in structure and diffusivity upon insertion and extraction of Li ions.

Monoclinic α-Li3+x
V2(PO4)3 (LVP), crystallizing with the space group P21
/n, serves as a very attractive model compound to study these changes. As a chameleon-like electrode material it can be used as both the anode and cathode active material [1]. The Li ions in LVP (x = 0) are equally distributed over 3 crystal sites, which are clearly resolved in high-resolution 7Li magic angle spinning (MAS) nuclear magnetic resonance (NMR). As has been shown earlier by the Goward group [2], 1D and 2D exchange NMR spectroscopy is an excellent tool to identify site-specific ion mobilities and to identify the electrochemically active Li positions. Less attention has, however, been paid to LVP with x > 0. Although the topic has been addressed earlier [2,3], a complete picture about the correlation of local magnetic structures with macroscopic phase transitions is still missing.

Here, we used 7Li MAS NMR, combined with both X-ray and neutron diffraction to throw some light on the changes LVP undergoes during Li uptake and release (− 2 < x < 2). As an example, Li insertion causes a drastic change of the original 7Li NMR spectrum of LVP. For Li3.5V2(PO4) the spectrum recorded at ambient bearing gas temperature consists of at least 4 distinct NMR signals being sharper than those of the starting materials with x = 0. Further increase of x to values larger than 1 reveals a second change leading a quite complex NMR signal with many overlapping lines. For Li3.5V2(PO4) and Li4.0V2(PO4) 2D 6Li MAS NMR will help us to understand the elementary hopping processes in the vanadium phosphate.

Financial support by the Austrian Federal Ministry for Science, Research and Economy as well as the Christian-Doppler Forschungsgesellschaft is highly appreciated.

[1] W.-F. Mao, H.-Q. Tang, Z.-Y. Tang, J. Yan, and Q. Xu, ECS Electrochem. Lett., 2 (7), A69-A71, (2013).

[2] L. S. Cahill, R. P. Chapman, J. F. Britten, and G. R. Goward, J. Phys. Chem. B, 110, 7171-7177, (2006).

[3] C. Liu, R. Massé, X. Nan, G. Cao, Energy Storage Mater., 4, 15-58, (2016).

[4] S.-C. Yin, P. S. Strobel, H. Grondey, L. F. Nazar, Chem. Mater., 16, 1456-1465, (2004).
Improvement in Cycling Performance of Rechargeable Metal Hydride/Air Laminate Cell
Authors: Fukumoto Tatsuya , Kawaguchi Kenji , Morimitsu Masatsugu
Published: February 2020

A metal hydride (MH)/air secondary battery is one of the next generation energy storage devices, since a high energy density and a high power density are expected from its unique property that the active mass of the positive electrode is oxygen in air. We have developed this type of battery and demonstrated that a non-packaged cell fabricated using PTFE container has about 900 Wh/L [1] and a laminate cell using polyethylene film about 772 Wh/L [2], which are beyond the energy density of lithium ion secondary batteries. However, the laminate cell also indicated some issues on the structure and components of the cell, causing the electrolyte’s leakage and a poor cycleability. This work was done to improve the charge-discharge performance of the MH/air laminate cell, especially the cycling performance, and evaluated the charge-discharge behaviors of the cell obtained with some modification in the process and materials.

The laminate cell consisted of an MH electrode (23 mm x 23 mm), an air electrode (23 x 23 mm), and a separator with 6 mol/L KOH solution between the electrodes, which were thermally sealed and packed in polyethylene (PE) film having an open area (13 x 13 mm) on the air electrode. All the components were the same as those used in our previous work [1]. We examined the design, size, and thickness of PE film to improve the adhesion to the electrode and between PE films and to inhibit the leakage of the alkaline solution. A water repellent film attached to the air electrode to prevent the flooding of the solution was also modified to suppress the increase in internal pressure by oxygen generated during charge. The cell was operated with constant current (0.05 C) at room temperature in a desiccator, and the cell voltages during charge and discharge were measured, in which charge was limited for 2 hours and the cut-off voltage of discharge was 0.5 V.

Some modifications in the structure and components of the laminate cell, e.g., the change in the electrode’s tab from Ni ribbon to Ni mesh and the optimization on the thickness of PE film and the thermal bonding conditions such as heating temperature and time, resulted in no leakage of the electrolyte during charge-discharge cycles and no expansion of the laminate package by oxygen, and the cycling performance was significantly enhanced compared to our previous cell [2]. The cell presented very stable charge and discharge voltages for 20 cycles and the current efficiency was more than 90 %. More detailed results will be shown in this paper.

This work was financially supported by “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST). The authors acknowledge FDK Corporation for supplying the MH negative electrode.

Reference

[1] T. Gejo, K. Kawaguchi, M. Morimitsu, 2017 TMS Annual Meeting & Exhibition, Pan American Materials Congress, San Diego, USA (2017).

[2] S. Kino, M. Morimitsu, The 232th ECS Meeting, Abs#104870, Washington, D. C., USA (2015).
Optimization of a Novel All-Vanadium Hybrid Redox Flow Battery/Mediator Supercapacitor
Authors: Narasimhan Swati , Pape Marie , Zhou Xiangyang
Published: February 2020

The increasing demand for renewable energy is reliant upon progress in energy storage, which is essential in smart-grid and transportation applications. Redox flow batteries have been a promising path for these applications with their very high specific energy, but they suffer from low specific power, slow response, and a low charge rate. In contrast, mediator supercapacitors display high specific power and a fast response rate with a high charge rate, but relatively low specific energy. A hybrid flow-battery/supercapacitor is fabricated and operated under different conditions to provide high specific energy and power along with performance capabilities across a wide range of charge rates, utilizing both physical and chemical charging methods within the cell. The porous electrodes of the electrochemical cell consisted of the Vanadium mediators (VOSO4 and VCl3), supercapacitor carbon black powder, and a polymer binder. A commercial ion exchange membrane was used as the separator. This investigation focuses on the effects of flow rate, charge rate, and mediator concentration on the performance of the hybrid device. Potentiostatic EIS (EIS), Cyclic Charge Discharge (PWR), and Cyclic Voltammetry (CV) measurements were conducted under a wide range of flow rates and mediator concentrations. The electrochemical kinetics of the mediators were evaluated using linear polarization methods. The results indicate that at a given current for PWR tests and scan rate for CV tests, both the flow rate and mediator concentration greatly impact the charge/discharge behavior, the total energy, and the efficiency of the hybrid system. The system performs over a wide range of currents with repeated cycling. A transition between capacitor-like behavior and battery-like behavior is observed.
Fine Regulate the Process of Exfoliation of Graphite to Prepare Graphene
Authors: Chen Duhong , Zhan Dong Ping
Published: February 2020

The use of graphene (Gr) has led to great breakthroughs because of its excellent mechanical strength, high electric and thermal conductivity, catalytic properties, etc. Industrial applications of this material are hindered by the absence of high-volume production method of high-quality Gr. Electrochemical exfoliation of graphite is a promising method for mass production of Gr. The key issue is the difficulty of controlling the intercalation and tailing processes, which occur in almost the same potential region. Nevertheless, we realized that these processes are different kinetically and designed various programmed strategies of potential modulation for electrochemical exfoliation. High-quality Gr (≤ 5 layers) was obtained from highly oriented pyrolytic graphite (HOPG), with a yield of 96% and an average area greater than 230 μm2. The programmed electrolysis applies to commercial graphite rods with a yield of 58% (≤ 5 layers) and an average area about 50 μm2. The molecular ratio of carbon over oxygen (C/O) was confirmed as 22.7, indicating an oxidation degree as low as 4.4 %, and excellent electron transport and electron transfer properties. The specific capacitance of the prepared layer Gr by commercial graphite rods was 135 F g-1. The programmed electrolysis opens a promising route to the mass production of Gr, which is crucial for the follow-up modification and assembly of graphene for industrial applications.
Aluminium Corrosion in Bioethanol/Gasoline Blends
Authors: Brito Franco Alfredo
Published: February 2020

In this work, the corrosion behavior of aluminum in different types of bioethanol/gasoline blends has been evaluated by using electrochemical techniques. Evaluated bioethanols included bioethanol from Apple, mango, orange and sugar cane in concentrations of 10 and 20%, whereas employed techniques included electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and linear polarization resistance (LPR) during 90 days. Corroded samples were analyzed in a scanning electronic microscope (SEM). Obtained results have shown that orange, apple and mango bioethanols/gasoline, in both concentrations, there is a decrease in the impedance value as compared to that for pure gasoline, with the highest corrosion rate exhibited by the sugar cane bioethanol. LPR results indicate that the mango bioethanol/gasolina blends exhibited similar corrosion rates to that exhibited by gasoline. On the other hand, EN measurements showed that in both pure gasoline and the 10% concentration noise reading showed indicating a high susceptibility towards localized type of corrosion, whereas those exhibited by th 20% concentration indicated a susceptibility towards uniform type of corrosion or passivation, which was corroborated by the SEM micrographs.
Effects of Severe Plastic Deformation and Interstitial Carbon on Corrosion Resistance of Steel
Authors: Komura Tomoki , Muto Izumi , Sugawara Yu
Published: February 2020

For the improvement of mechanical properties of steels, nanocrystallization is a center of interest. Nanocrystallization greatly influences on the mechanical properties such as tensile strength, ductility, and wear resistance. Severe plastic deformation (SPD) is one of the effective methods to generate the nanocrystalline structure. It was reported that nanocrystallization also affects corrosion behavior of steels. When the grain size of stainless steels is less than 1 μm, it would appear that the grain boundaries act as barriers against the growth of pitting corrosion1). Interstitial carbon atoms also affect the corrosion behavior2). In this study, the SPD layers were fabricated on Fe plates by ball-milling, and electrochemical measurements were conducted to investigate the corrosion behavior of the SPD layers.

Planetary ball-milling was applied to fabricate the SPD layers on Fe and stainless steel plates. The Fe and type 304 stainless steel plates were polished by SiC paper through a 1500 grid and put into a stainless steel pot with Fe powders, and mechanical alloying of Fe and C powders was accomplished. Grinding balls were made of stainless steel. In the milling process, the SPD layers of Fe-C alloy were fabricated on the Fe and stainless steel plates. To investigate the effect of the carbon concentration, the amount of the carbon powders put into the pot was changed.

Potentiodynamic anodic polarization curves were measured in deaerated H3BO3-Na2B4O7-1 mM NaCl solution (pH 8.0) at 298 K to elucidate the influence of the SPD and the carbon concentration on the corrosion resistance of the Fe-C steels. With the exception of the electrode area (ca. 5 mm × 5 mm), the surfaces of the specimen were coated with an epoxy resin and paraffin. The measurements were performed in a conventional three electrode cell. The reference electrode was Ag/AgCl (3.33 M KCl) and the counter electrode was a Pt plate.

The results of potentiodynamic anodic polarization for the SPD layers on the Fe plates are shown in Fig. 1. In the case of pure Fe, the increase of the anodic current density at ca. -0.5 V was due to the anodic oxidation and/or dissolution of Fe. In the potential range of -0.3 to 0 V, the current density decreased by passivation. And then, the current density drastically increased. This appeared to be attributed to localized corrosion. On the other hand, at around -0.5 V, the current densities for Fe-0.1mass%C and Fe-0.5mass%C were higher than that of pure Fe. However, the passivation current density of Fe-0.5mass%C specimen was the lowest. Therefore, the increase of carbon concentration possibly causes the improvement of corrosion resistance.

References

1. A. Chiba, I. Muto, Y. Sugawara, and N. Hara, J. Electrochem. Soc., 159, C345 (2012).

2. A.Chiba, S. Shibukawa, I. Muto, T. Doi, K. Kawano, Y. Sugawara, and N. Hara, J. Electrochem. Soc., 162, C278 (2015).

Figure 1
Change in pH and Chloride Concentration inside Crevice of Stainless Steels
Authors: Matsumura Kengo , Muto Izumi , Sugawara Yu
Published: February 2020

Stainless steels sometimes suffer from crevice corrosion in chloride environments. The pH value and Cl- concentration are important factors in the initiation and growth of crevice corrosion. Nishimoto et.al.[1] fabricated a glass plate with a sol-gel SiO2 sensing layer, which contains a pH indicator and a Cl- sensitive florescent dye, and the pH and Cl- distributions in the crevice solution for stainless steel were visualized simultaneously.

The specimens used in this study were cut from a Type 430 stainless steel sheet (0.035%C, 0.20%Si, 0.38%Mn, 0.019%P, 0.005%S, 0.19%Ni, 15.9%Cr in mass%). The specimens were heat-treated at 1123 K for 600 s and water-cooled. The size of the specimen was 4 mm×3 mm×20 mm. The specimen surfaces were polished by a 1 μm diamond past.

To fabricate the sensing plate for the simulations measurements of pH and Cl- concentration, Terbium-dipicolinic acid complex (Tb-DPA) and quinine sulfate as the fluorescent dyes were chosen. Tb-DPA was used as the sensing dye for the pH measurements, and quinine sulfate was used to measure the Cl- concentration. Tb-DPA was formed by mixing Tb­­2(SO4)3 and dipicolinic acid. A sol-gel method was used to make the sensing layer, which contained two fluorescent dyes, onto one side of a quartz glass plate.

Figure 1 shows the illustration of a crevice corrosion test cell. In crevice corrosion tests, the crevice was formed between the sensing plate and specimen. Potentiostatic polarization was performed at 0.15 V (vs. Ag/AgCl, 3.33 M KCl) in 10 mM NaCl (pH 3.0). During crevice corrosion tests, the surface images of the specimen were taken under UV irradiation, and pH and Cl- values were calculated from the fluorescence images. The details were described in the literature. [1]

Figure 2 shows the surface appearance and the images of pH and Cl- distributions at the initiation point of the crevice corrosion at 1500 s. The pH and Cl- were calculated by the brightness of fluorescence images. A pit was initiated inside the crevice. Before the initiation of crevice corrosion, it was elucidated that the pH at the initiation point of gradually decreased with time, and that the Cl- concentration increased with time. On the basis of time variations of the pH and Cl- concentration, the initiation and growth mechanims of the crevice corrosion of stainales steels were determiend.

References;

Nishimoto, J. Ogawa, I. Muto, Y. Sugawara, N. Hara: Corros. Sci.,
106, 298-302(2016)

Figure 1
Under-Deposit Corrosion (UDC): The Hidden Cause of Major Asset Failures in the Oil and Gas Industry
Authors: Shamso Ahmed Nabil , Abdullah Aboubakr Moustafa , Laycock Nick , Ryan Mary P
Published: February 2020

With the continued need for fossil fuels, even as we enter energy transitions, the extraction of oil and gas from significantly abundant sour fields is increasing globally. Sour i,e, H2S –containing gas environments present several challenges to system integrity, including an accelerated rate of localized corrosion, and potential catastrophic premature failures in fluid handling equipment. This creates a risk to asset integrity, leading to financial losses, and significant risk to both human health and the environment. A major problem in sour systems is ‘underdeposit corrosion (UDC)’ which is a type of extremely rapid, localized attack observed under deposits (in this case typically iron-sulfides); it is extremely difficult to both predict and monitor. The mechanism of both iron sulfide formation and UDC in pipeline is not fully understood: the complex nature of iron sulfides along with the dynamic changes of their physical and chemical properties during the corrosion process entails that multiscale correlative investigations are needed.

1-dimensional artificial pit experiments are developed in order to study localised corrosion with the use of multi-electrode arrays; this allows high-throughput measurements such that different variables can be studied simultaneously. The artificial pit acts as an anode in a three-electrode electrochemical cell, simulating an actively dissolving pit, but with reduced dimensionality that allows quantitative extraction of kinetic data as a function of the various system parameters- essentially the deposit physical and chemical properties. Data on the role of deposit chemistry and morphology on the electrochemical dissolution behaviour are presented, and discussed in terms of a transport-controlled model for pit propagation. Complementary planar (2D) surface experiments were performed under deposits; using this blended approach, both general and localized corrosion can be assessed and related to provide a comprehensive understanding of the overall performance of steel under deposits. The dynamic physicochemical variations (surface morphology and chemical composition) in both metal and deposit are related to the electrochemical findings to explain the metal-deposit interdependent physicochemical interactions.

The findings of the study paved the way towards innovating experimental methods for example the use of micro-pH electrodes to provide real-time data on the chemistry inside actively dissolving pits under representative deposits. This study provides insights into the different scenarios of UDC phenomenon and potential protocols to develop monitoring probes for industrial application.
Fast 2D Diffusion in Nanocrystalline RbSn2F5 as Seen By Impedance and 19f NMR Spectroscopy
Authors: Gombotz Maria , Lunghammer Sarah , Breuer Stefan , Preishuber-Pflügl Florian , Wilkening Martin
Published: February 2020

The functionality of sensors or batteries relies in many cases on mobile ions such as Li+, Na+, O2- or F-, which are subjected to rapid self-diffusion processes. The dynamic parameters as well as the shape of the underlying motion correlation function depend on the dimensionality of the diffusion pathways. Model compounds help to unambiguously proof the concepts and models developed to describe low dimensional diffusion.[1-3] The pseudo-binary fluoride RbSn2F5 with trigonal symmetry constitutes such a model substance.

Here, we present a new mechanochemical route to synthesise nanocrystalline RbSn2F5 via a one-pot reaction in a planetary mill. Soft annealing transforms the as prepared product into microcrystalline RbSn2F5. We used X-ray diffraction, thermal analyses and high-resolution 87Rb, 19F , and 119Sn NMR spectroscopy to characterize structure and ion dynamics in detail. In particular, we took advantage of AC impedance spectroscopy and time-domain NMR measurements to record diffusion-induced spin-lattice-relaxation rates in both the laboratory and rotating frame of reference to monitor long-range as well as short-ranged F anion transport processes in RbSn2F5. It turned out that only an NMR spectral density function developed for 2D diffusion yields an activation energy being in accordance with that derived from conductivity measurements. Our results confirm Richards[4,5] semi-empirical NMR relaxation model for 2D uncorrelated jump diffusion, not only for microcrystalline RbSn2F5 but also for the nanocrystalline, mechanosynthesized sample.

Financial support by the Austrian Federal Ministry for Science, Research and Economy as well as the Christian-Doppler Forschungsgesellschaft is highly appreciated.

References

[1] M. Wilkening, W. Küchler, and P. Heitjans, Phys.
Rev. Lett.
97, 065901 (2006).

[2] A. F. McDowell, C. F. Mendelsohn, M. S. Conradi, R. C. Bowman, and A. J. Maeland, Phys. Rev. B.

51, 6336 (1995).

[3] V. Epp and M. Wilkening, Phys. Rev. B
82, 020301 (2010).

[4] P. M. Richards, Solid State Commun.
25, 1019 (1978).

[5] P. M. Richards. In Topics in Current Physics (Ed. M. B. Salamon), Band 15, Springer, Berlin (1979).
Atomistic State of Absorbed Hydrogen in Electrodeposited Platinum Films
Authors: Kinoshita Takeshi , Yokoyama Ayano , Matsumoto Ayumu , Fukumuro Naoki , Yae Shinji
Published: February 2020

Hydrogen absorption into electrodeposited metal films is largely influenced by the depositing conditions. We have been investigating the hydrogen absorption into electrodeposited platinum (Pt) films that depends on a change in hydrogen adsorption state with applied potential.1 The microstructure of electrodeposited Pt films was affected by the absorbed hydrogen.2 In this study, we investigate an atomistic state of absorbed hydrogen in electrodeposited Pt films.

Pt films were potentiostatically deposited on a gold foil from a solution containing 0.024 mol dm-3 K2PtCl4 at pH of 0.8. A Ag/AgCl electrode was used as the reference electrode and a Pt plate was used as the counter electrode. The amount of hydrogen in samples was measured by thermal desorption spectroscopy (TDS) in a temperature range between 300 and 1100 K. The amount of hydrogen in deposited Pt films was calculated by subtracting the total amount of desorbed hydrogen of the gold foil substrates from that of the samples.

The amount of hydrogen in potentiostatically deposited Pt films (+0.1 ~ -0.3 V vs. Ag/AgCl) as a function of film thickness is summarized in Fig. 1. The amount of hydrogen was nearly 0 for Pt films deposited at +0.1 V (Fig. 1 ●). It was 1 ~ 2×10-7 mol cm-2 and independent of the film thickness at 0 V (Fig. 1 ◇). For the Pt films deposited at -0.1 and -0.2 V, a positive correlation was observed between the amount of hydrogen and the film thickness (Fig. 1 ○ and △), respectively. The positive correlation of ca. 1.7×10-7 mol cm-2 µm-1 indicates that hydrogen was uniformly contained at atomic ratio ([H]/[Pt]) of 0.015 in the Pt films. For the Pt films deposited at -0.3 V, the positive slope, that is, content of uniformly absorbed hydrogen was much larger than that for the films deposited at -0.1 and -0.2 V (Fig. 1 □). Positive vertical intercepts of 2 ~ 6×10-7 mol cm-2 for -0.1 ~ -0.3 V indicate that a certain amount of hydrogen was contained even in the initial deposits. Pt deposition at +0.1 V onto the Pt film deposited at 0 V reduced the amount of hydrogen to nearly 0. The Pt deposition at 0 V onto the Pt film deposited at +0.1 V increased the amount of the hydrogen to ca. 1×10-7 mol cm-2. These results suggest the possibility that the certain amount of hydrogen indicated by the vertical intercepts of Fig. 1 exists near film surface.

Acknowledgements

The present work was partly supported by JSPS KAKENHI (JP26289276 and JP17K06864).

References

A. Yokoyama, S. Karatsu, M. Sumikawa, N. Fukumuro, and S. Yae, ECS Trans., 75(52) 55 (2017).

N. Hisanaga, N. Fukumuro, S. Yae, and H. Matsuda, ECS Trans., 50(48), 77 (2013).

Figure 1
Electrically Conductive Polymer Composites for Injection-Molded Bipolar Plates
Authors: Sander Meredith L , Pritts James T , Young Brian A , Santamaria Anthony D. , Hollinger Adam S
Published: February 2020

This presentation reports the development of electrically conductive polymer composites as an alternative to the traditional metal alloys commonly used for fuel cell bipolar plates. Polymer composites can reduce both the cost and weight of the bipolar plate, while still providing sufficient electrical properties. Several factors impact the ability of a polymer composite to conduct electricity. The geometry, filler weight percent, and the physical properties of the fillers are crucial to forming an electrical pathway through the composite. In this study, carbon black and carbon fiber were added to nylon 6,6 at various weight percentages, ranging from 0 to 50%, in order to determine the optimal filler-to-polymer ratio. Samples were injection-molded and then compared by measuring the electrical conductivity using a four-point probe method. Conductive filler was added to the polymer with and without a compounding process prior to injection molding. Results show that compounding the additives via a twin-screw extruder helps to disperse the filler within the polymer but decreases conductivity due to shearing of the conductive carbon fibers. When the compounding process was removed, the conductive pathways from intact fiber bundles were maintained. Conductivities greater than 40 S/cm were achieved, nearing the United States Department of Energy technical target of 100 S/cm for bipolar plate electrical conductivity.
Lanthanum Nickelate Cathode Materials for Low and Intermediate Temperature for Solid Oxide Fuel Cells
Authors: Lee John In , Park Ka-Young , Park Jun-Young
Published: February 2020

Solid oxide fuel cells (SOFCs) are a clean electrochemical conversion devices from chemical energy of fuel to electrical energy. SOFCs are considered as future green energy devices because of their diverse advantages including high energy conversion efficiency, various fuel acceptance, and negligible gas pollutants [1]. Now, the performance of SOFCs is highly affected by the oxygen reduction reaction (ORR) in the cathode of SOFCs. Until now, the major materials of cathode are cobalt-contained perovskite oxides because they show a low over-potential for ORR with the high SOFC performance [2]. However, cobalt-contained perovskite cathode materials also have several technical issues, such as expensive price, low chemical stability, and big difference of thermal expansion coefficient (TEC) to the zirconia-based electrolyte. The TEC of cobalt-contained perovskite oxides is 20-25×10-6K-1, whereas the yttria-stabilized zirconia and lanthanide-doped ceria electrolytes are 11-13×10-6K-1. This can results in the delamination of cell components during high temperature operation [3]. On the other hand, the TEC of lanthanum nickelates (Lan+1NinO3n+1) is 11-12×10-6K-1, which is similar to that of electrolyte materials and thus high thermal stability is expected for the SOFC[4]. Hence. in this work, the characteristics of lanthanum nickelates in terms of performance and durability are investigated.

References

[1] K.T. Lee, E.D. Wachsman, Science 334 (2011) 935.

[2] W. Zhou, Z. Shao, J. Power Sources 192 (2009) 231.

[3] S. Pang, X. Xi, J. Power Sources 326 (2016) 176.

[4] R.K. Sharma, E. Djurado, J. Power Sources 325 (2016) 337.

[5] C. Nicollet, J. Grenier, ECS Trans (2015) volume 68,issue 1, 837-845.

[6] C. Laberty, A. V. Virkar, Electrochem. Solid-State Lett (2007) volume 10, issue 10,B170-B174.
Low Loading Pt/Rgo Composite for Oxygen Reduction Reaction
Authors: Pérez-Zúñiga Germán , Rosado Gabriel , Verde Gómez Ysmael , Valenzuela-Muñiz Ana Maria
Published: February 2020

The synthesis and evaluation of low platinum loading-reduced graphene oxide (Pt/rGO) electrocatalyst with high surface area and electrochemical activity for the oxygen reduction reaction (ORR) is presented in this work. Pt nanoparticles were synthesized via colloidal method by simultaneous chemical reduction of metallic salts in presence of poly (N-vinyl-2-pyrrolidone). First he GO was obtained by exfoliation of graphite layers using the modified Hummers methodology. The exfoliation process allowed getting GO of a few layers (around 5). The well dispersed Pt particles (around 10 nm) were deposited in small amounts (1 to 10%) over the GO using incipient wetness in an ultrasonic bath. It is expected that due to the surface functionalization (side step during the exfoliation process); the anchorage sites for the Pt particles between layers are created facilitating the deposition. Afterwards, the material obtained was treated at different temperatures (300, 500 y 800 °C) under inert atmosphere in order to improve the reduction degree and the electrical conduction of the rGO layers. The obtained electrocatalysts were characterized physically and chemically using X-ray diffraction (including Rietveld analysis), Raman and UV-Vis spectroscopies as well as scanning electron microscopy. The electrochemical performance of low loading Pt/rGO materials towards the ORR was studied using cyclic and linear voltammetry with a rotating disk electrode, in a typical three electrode cell using O2-satured acid solution as electrolyte, glassy carbon as substrate for the working electrode, Ag/AgCl (KCl sat) as reference and a Pt wire as counter electrode. Low metal loading materials exhibited interesting behaviors and will be presented and discussed at the conference.