bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Mass Transfer Properties and Ionic Association in LiPF6 - Organic Carbonates Solutions from PFG-NMR and Specific Conductivity Data
Authors: Krachkovskiy Sergey A , Bazak J David , Fraser Sean , Goward Gillian R. , Halalay Ion C.
Published: February 2020

We derive herein several mass transport properties (diffusion coefficients for cations, anions, and neutral ionic aggregates; cation transference number; salt association constant) of LiPF6 solutions in binary mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC) or ethyl methyl carbonate (EMC) through an analysis of PFG-NMR and specific conductivity data. Results were obtained as a function of salt concentration for EC:DMC 1:1 v/v, also from 5 ºC to 35 ºC for 1M LiPF6 dissolved in binary mixtures of EC with DMC and EMC at 3:7, 1:1 and 7:3 volume ratios. Li+ transference numbers have significantly lower values than the transport numbers, ranging from 0.31 to 0.35, and decrease with concentration. Under the assumptions that the higher order neutral aggregates beyond ion pairs can be neglected and that the intrinsic diffusion coefficients of cations and ion pairs are the same (valid only for solutions containing LiPF6, LiBF4 or LiClO4salt and significant amounts of EC), one can determine the degree of ion pairing as well as the intrinsic diffusion coefficients for cations, anions and ion pairs. A high degree of ion pairing (from 36% to 67%) was observed for the solutions investigated in the present work.

Acknowledgements

The authors acknowledge funding through the NSERC APC program and GM of Canada.

Figure 1
Polymeric Gel Electrolyte Consisting of Network Polymer Using Tri-Functional Glycerol Ester for Li-Ion Batteries
Authors: Tanji Seiya , Yamabuki Kazuhiro , Fujii Kenta , Morita Masayuki , Yoshimoto Nobuko
Published: February 2020

Development of a safer electrolyte has become a key issue for realizing larger sizes of lithium-ion batteries (LIBs) for energy storage and transportation uses. Flame-retardant additives and/or ionic liquids are considered to be effective components that form safer electrolyte solutions. However, those systems still have risks coming from electrolyte leakage due to their liquid states. Solidification of the electrolyte is one of the effective ways to improve the safety of the battery system. In order to ensure sufficient ionic conductivity, a number of polymeric gel electrolyte systems have so far been proposed. We have investigated in this paper a novel polymeric gel electrolyte based on a network polymer having tri-functional glycerol ester for lithium-ion batteries.

A triply branched monomer possessing a terminal olefin unit was newly synthesized from glycerol ethoxylate (M
n~1,000) and 10-undecenoly chloride (3 eq.) (Fig. 1 (a)). The electrolyte consisting of 1 M LiPF6/ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1 by vol.) was added to a mixture of trimethylolpropane tris(3-mercaptopropionate) (Fig.1 (b)) and the triply branched monomer with a smaller amount of benzophenone sensitizer (1:1:0.05 by molar ratio). The resulting mixed solution was applied to a glass plate, and was broaden. Finally, the monomer-coated glass plate was exposed to UV irradiation to get a gel film. A transparent polymeric gel electrolyte was obtained as a self-standing film. The ionic conductivity of the gel electrolyte was measure by an AC method and found to be 5.2, 3.4, and 2.8 mS cm-1 (at 297 K) for the films containing 10, 20, and 30 wt% of polymer matrix, respectively. The electrochemical stability toward anodic oxidation was investigated for the gel electrolyte by linear sweep voltammetry (LSV). The anodic oxidation current was observed as a current peak at 4.2 V. This was attributed to the oxidative decomposition of the thiol group in the polymer matrix1). Thus, the present polymeric gel electrolyte can be used in a potential range up to 4.2 V. The application to the graphite negative and lithium iron phosphate (LiFePO4) electrodes will be reported in the presentation.

Reference

1) M.-H. Ryou, et al., Electrochim. Acta, 60, 23 (2012).

Figure 1
Optimizing Alkali Ionic Conductivity in Superionic Conductor Solid Electrolytes
Authors: Ong Shyue Ping , Meng Ying Shirley , Chu Iek-Heng , Nguyen Han , Hy Sunny , Zhu Zhuoying , Lin Yuh-Chieh , Deng Zhi , Xu Zihan , Wang Zhenbin , Kompella Christopher
Published: February 2020

The facile conduction of alkali ions in a crystal is of crucial importance in rechargeable alkali-ion batteries, particularly in all-solid-state architectures due to the longer diffusion length scales in the alkali superionic conductor solid electrolyte. Poor alkali transport in any part of the battery – electrode, electrolyte or the interfaces between them – leads to reductions in rate capability, practical capacity and cyclability. In this talk, I will present recent insights from integrated first principles and experimental studies into doping strategies to control levers such as alkali concentration, migration barriers, and percolation probability to enhance conductivity. A key focus will be on the tight integration of first principles computations with experiments, especially how theory can provide quantifiable insights that accelerate materials development. The materials chemistry covered in this talk includes both well-known superionic conductors such as alkali thiophosphates and NASICONs, as well as novel materials predicted by high-throughput screening.
Chemically Anchored Liquid-PEO Based Block Copolymer Electrolytes for Solid-State Lithium-Ion Batteries
Authors: Gohy Jean Francois
Published: February 2020

Solid-state electrolytes are being considered the keystone element for the development of safer all-solid-state lithium-ion batteries. While poly(ethylene oxide) (PEO) solid-state polymer electrolytes are known to support a lithium ions flux, satisfying conductivities are reached only above the melting point of the PEO crystallites rendering PEO unpractical. Herein, by means of block copolymer engineering, we design a mechanically clamped liquid-PEO electrolyte that combines the high ionic conductivity of a low molecular mass PEO while retaining the dimensional integrity of a solid material (1). Attractive ionic conductivities of about 0.01 mS/cm are attained at room temperature without compromising mechanical properties. The electrolyte shows a wide electrochemical stability window and help in building a stable interface with lithium metal. Competitive performances are attained when integrating the developed materials into operational/functional prototype batteries highlighting the provided potential.

Next, we discuss a three step synthesis procedure of self-doped solid block copolymer electrolyte, combining a single-ion poly(lithium methacrylate-co-oligoethylene glycol methacrylate) ion conducting block (P(MALi-co-OEGMA)) and a structuring polystyrene block (PS) (2). The macromolecular design allows the formation of a self-standing film with excellent mechanical properties provided by the PS anchoring nanodomains while attaining attractive ionic conductivities of up to 0.02 mS/cm at room temperature. Moreover, the single-ion configuration based on polyanionic backbone affords high transference numbers, close to unity, and alleviates the power limitation encountered in salt-doped solid polymer electrolyte (SPE). The electrolyte exhibits a wide electrochemical stability window up to 4.5 V vs. Li+/Li and promote the formation of stable interfaces at the electrodes.

(1) J. Rolland, J. Brassinne, J.-P. Bourgeois, E. Poggi, A. Vlad and J.-F. Gohy, J. Mater. Chem. A, 2014, 2, 11839–11846

(2) J. Rolland, E. Poggi, A. Vlad, J.-F. Gohy, Polymer
2015, 68, 344-352
Functional Design of Nitrile-Based Electrolyte Components
Authors: Grünebaum Mariano , Pelz Alexander , Rad Babak R. , Buchheit Annika , Krause Daniel , Pohl Benjamin , Winter Martin , Wiemhöfer Hans-Dieter
Published: February 2020

Introduction

One of the crucial points for next generation lithium batteries is the development of high performance electrolyte components (e.g. electrolyte solvents, conducting salts and additives) to replace current LiPF6-based liquid systems. Novel electrolytes should guarantee high thermal and electrochemical stability, high ionic conductivity, long term stability of anode and cathode interfaces as well as they should lead to stable SEI films.[1-2]
 On the other hand, electrolyte components should be nonflammable, nontoxic and environmentally friendly. This work is focused on applying basic chemical principles like inductive effects, sterical hindrance, increasing electronegativity and modification with fluoride splitting groups to model new nitrile-based electrolyte components (cf. Fig. 1).[3-4] The physicochemical properties of these new electrolyte components were investigated and different modification steps were compared.

Results and Discussion

Increasing the +I
effect, induced by electron donating substituents and the sterical hindrance of the nitrile-based electrolyte solvents led to highly cathodic stable nitrile-siloxane-solvents which are as well stable against metallic lithium in comparison to simple nitrile-based solvents like acetonitrile.[5] Additionally, they exhibit low vapor pressures and are in general nonflammable.

The here mentioned nitrile-based conducting salts show high anodic stabilities ranging from 4.5-5.6 V vs. Li/Li+ and in the cathodic region, they are stable down to the lithium metal stripping/plating process. In comparison to commonly used LiPF6, the lithium salts show very high thermal stabilities starting from 300 °C and raises to 500 °C with growing sterical hindrance.

Furthermore, BF3-modification of additive components led to stable passivation layers on aluminum current collectors and therefore to a better suppression of Al-dissolution, even in the presence of LiTFSI in carbonate type solvents. To sum it up, investigation and application of basic concepts on nitrile-based electrolyte components offer a simple tool for an easy tailoring.

 

References

[1] M. Winter, R.J. Brodd, Chemical Reviews, 104 (2004) 4245-4270.

[1] K. Xu, Chemical Reviews, 104 (2004) 4303-4418.

[3] M. Grünebaum, M.M. Hiller, S. Jankowsky, S. Jeschke, B. Pohl, T. Schürmann, P. Vettikuzha, A.-C. Gentschev, R. Stolina, R. Müller, H.-D. Wiemhöfer, Progress in Solid State Chemistry, 42 (2014) 85-105.

[4] J. Clayden, N. Greeves, S. Warren, P. Wothers, Organic Chemistry, Oxford University Press, United States, 2001.

[5] B. Pohl, M.M. Hiller, S.M. Seidel, M. Grünebaum, H.-D. Wiemhöfer, Journal of Power Sources, 274 (2015) 629-635.

 

Acknowledgements:

The author acknowledge the support of the Helmholtz-Institute Münster (HI MS) IEK-12 of Forschungszentrum Jülich.

Figure 1
Highly Dense Cu Nanowires for CO2 and CO Reduction
Authors: Raciti David , Wang Chao
Published: February 2020

Electrochemical reduction of CO2, an artificial way of carbon recycling, represents one promising solution for energy and environmental sustainability. Despite the many advantages, electrochemical reduction of CO2 is challenged by the absence of efficient catalysts for this reaction. Copper (Cu) is the most studied material capable of catalyzing CO2 reduction at significant rates, but it still requires large overpotentials; e.g., to reach a current density of 1 mA/cm2 on polycrystalline Cu electrode, it typically requires an overpotential of >0.5 V for producing CO and HCOOH (two-electron processes) and >0.8 V for further reduced products such as CH4 and C2H4. Moreover, hydrogen evolution competes with CO2 reduction, reducing the Faradaic efficiency (FE) towards carbon-containing compounds.

Here we report the synthesis of highly dense Cu nanowires and tailoring of their surface structures to achieve superior performance for electrocatalytic CO2 and CO reduction, with particular attention to low-overpotential conditions. CuO nanowires were first grown by oxidizing Cu mesh in air which were then subjected to electrochemical reduction or annealing in a reducing atmosphere to form Cu nanowires. By tailoring the conditions for the reduction, high activity and selectivity were achieved for the production of CO from CO2, and ethanol/acetate from CO, at E < 0.4 V. It was found that the catalytic performances of the Cu nanowires are strongly correlated to the crystalline and surface structures in the nanoscale, based on which the active sites capable of selective reduction of CO2 and CO were identified. Our work indicates the great potential of electrochemical conversion of CO2 for synthesis of fuel molecules and production of chemical feedstocks.
Influence of Alloying on CO2 Electroreduction on Ag-Zn System
Authors: Hatsukade Toru , Kuhl Kendra P , Cave Etosha R , Abram David N , Feaster Jeremy T , Hahn Christopher , Jongerius Anna L , Jaramillo Thomas F
Published: February 2020

Electrochemical reduction of CO2 is an attractive pathway for the sustainable production of fuels and chemicals, as it allows for the effective use of renewable energy sources while mitigating the effects of CO2 in the atmosphere. While significant decrease in overpotentials and increase in reaction rates have been reported for the two-electron reduction products, reports on improved activity and selectivity for the products that require more than two electrons (> 2 e- products) have been limited on monometallic transition metal catalysts. Recent theoretical work indicates that this difficulty of reducing CO2 to > 2 e- products is due to the linear scaling of the binding energies of CO2 reduction intermediates on transition metal catalysts, and the necessity of catalyst systems that can break such scaling has been emphasized.(1)

Alloys, which can provide bifunctional sites that selectively stabilize intermediates, are a promising class of materials, and a large amount of effort has been focused on the investigation of their effectiveness as CO2 reduction catalysts. Recent works have reported on improved CO2 reduction activity and selectivity on alloy systems, which were attributed to the synergy between the two metal atoms at the surface. However, most improvements reported in these works are pertaining to two-electron products, and alloy systems that demonstrate improvements for > 2 e- products remain elusive.

Here, we report on the investigation of polycrystalline AgZn foil, which resulted in the observation of enhanced activities and selectivities for methane and methanol productions compared to Ag and Zn foils. Although CO is the main CO2 reduction product as expected of an alloy between two metals active for CO production, the selective enhancement observed for the > 2 e- products is noteworthy, as it indicates that alloys are promising candidates in the development of effective CO2 electroreduction catalysts. The production of CO as major product is explained by the binding energies of intermediates, and the importance of optimal binding energies are discussed.

Reference

1. A. A. Peterson and J. K. Nørskov, The Journal of Physical Chemistry Letters, 3, 251 (2012).
(Invited) Proton-Conducting Ceramics for Fuels Synthesis
Authors: Sullivan Neal P , Ricote Sandrine , Ding Hanping , Rosensteel Wade , Le Long , Duan Chuancheng , O'Hayre Ryan
Published: February 2020

This presentation is centered on an exciting new class of proton-conducting ceramic materials that are emerging from the laboratory to play important roles in the commercial sector. While proton-conducting ceramics have been studied since the early 1980s, the unique properties of these materials are only now being harnessed to address societal challenges. Faculty and staff at the Colorado School of Mines (CSM) are actively developing protonic ceramics for use as fuel cells for efficient electricity generation (PCFCs), electrolyzers for energy storage (PCECs), and membrane reactors for fuels upgrading (PCMRs). Doped barium cerate-zirconate materials (BaCexZr1-x-yYyO3-d) are the focus of these efforts at CSM. The mixed ionic-electronic conductivity of these protonic ceramics can be exploited for developing cost-effective, novel solutions and new products.

Many previous approaches used to advance solid-oxide fuel cells are equally relevant for tuning the properties of protonic ceramics to meet the diverse needs of these different applications. In this talk, we will present several such efforts now underway at CSM.

As part of an ARPA-E-funded program, our team recently demonstrated a fuel-cell stack based on BaCe0.2Zr0.6Y0.2O3-d (BCZY26) protonic-ceramic materials. To the authors’ knowledge, this is the first reported result of a PCFC stack. The effort included a ten-fold scale up in cell size, and integration of these cells into a stack package. A three-cell stack achieved a power density of 180 mW cm-2 at 0.78 V under methane fuel at 550 ºC.

While this PCFC performance is encouraging, we found that similar protonic-ceramic materials demonstrated inefficient operation in electrolysis mode. Heightened electronic conductivity was observed under reverse bias, likely due to cerium reduction. By reducing the cerium content to below the percolation threshold, greatly improved Faradaic efficiency was confirmed. The team is now developing PCEC stacks using BaCe0.1Zr0.8Y0.1O3-d (BCZY18) electrolytes; 95% Faradaic efficiency was observed at 120 mA cm-2 and 600 ºC.

Electronic conduction is undesirable in fuel cells and electrolyzers; however, it may prove advantageous for hydrogen-separation membranes and membrane reactors. In an effort to increase flux through “passive” hydrogen-separation membranes, CSM is developing protonic-ceramic composites to increase membrane electronic conductivity. By mixing the BCZY material with an electronic conductor, a two-phase membrane with more balance between protonic and electronic conduction can be realized. Both ceramic (Ce0.8Y0.2O2-d) and metallic (Cu) electronic conductors are being explored as the second phase. While at an early stage of development, these two-phase hydrogen-separation membranes have demonstrated some of the highest thickness-normalized hydrogen fluxes ever observed through ceramic materials.

In this presentation, these efforts will be reviewed, with latest results presented.
(Invited) Degradation Mechanisms in Reversible Solid Oxide Cells
Authors: Barnett Scott A , Railsback Justin , Wang Hongqian
Published: February 2020

Reversible solid oxide cells (ReSOCs) have important applications for fuel production from renewable electricity and grid-scale electricity storage. However, in order to be economically viable, the cells should operate at high efficiency, in order to minimize the amount of electricity used, and should convert enough energy over the device lifetime to pay back capital cost. The latter issue makes long-term durability a key issue. A main focus of this talk is on recent measurements of ReSOC degradation rate, as a function of current density and electrode overpotential, during electrolysis and reversible operation. Measurements of LSM-YSZ, LSCF-GDC, and La2NiO4 oxygen electrodes are described. These electrodes appear to exhibit a similar behavior, where degradation rates are too low to measure (≲1%/kh) at low enough overpotential, but then increase rapidly when overpotential is increased above some critical value. Thus, operating at low overpotential (and hence low current density) is important not only for achieving high efficiency, but also for achieving viable total energy conversion over the useful device life. Results are also described on degradation of oxygen electrodes due to particle coarsening and Sr segregation.
Localized Carbon Deposition in Solid Oxide Electrolysis Cells Studied By Multiphysics Modeling
Authors: Navasa Maria , Graves Christopher , Frandsen Henrik Lund , Sundén Bengt
Published: February 2020

Modeling for optimizing performance has attracted substantial research efforts in the last twenty years with special focus on solid oxide fuel cells (SOFCs). However, limited amount of the modeling work has been focused on the solid oxide electrolysis cell (SOEC) operation mode and even less on degradation issues connected to SOEC operation. Despite the similarities between the two operation modes, the different operating voltage ranges and the gradients involved influence the long-term degradation and performance in different ways.

When performing co-electrolysis of CO2 and H2O at high current densities, which provides the highest syngas production rate, degradation at the interface between the Ni-YSZ electrode and the YSZ electrolyte has been reported due to the formation of small amounts of carbon. The formation of carbon at the active sites of the Ni-YSZ electrode may reduce the amount of active sites and, in the worst case, cause a delamination of the electrode/electrolyte interface due to the pressure exerted by the growth of carbon fibers. The Boudouard reaction (2CO(g) → C(s) + CO2 (g)) describes how carbon is formed. Carbon deposition could also occur by electrolysis of carbon dioxide to solid carbon (CO2(g)+ 4e-→ C(s) + 2O2-), which is thermodynamically equivalent to the two-step reaction of electrolysis of CO2 to CO followed by the Boudouard reaction. Although carbon deposition is thermodynamically favored only at higher reactant conversion than typically used in the operation of an SOEC, it has been observed at “safe” conversion conditions. Thus, understanding why the thermodynamic threshold is violated and where this happens locally in the cell would be of great interest when choosing operating conditions and to avoid possible degradation of the cell.

A three dimensional (3D) multiphysics model of an SOEC with cross-flows considering heat transfer is used to study and locate the degradation thresholds in these cells regarding carbon deposition at the Ni-YSZ electrode/electrolyte interface. The aim of this study is to show where and under which operating conditions the Boudouard reaction is locally induced. Only carbon dioxide electrolysis is considered as it is supposed to represent an extreme case compared with co-electrolysis, as the reverse water-gas shift reaction can mitigate carbon deposition. Moreover, possible solutions to the problem will be studied by varying structural parameters.
(Invited) Direct Conversion of Methane to Methanol and Other Value Products in SOFC
Authors: Marina Olga A , Polikarpov Evgueni , Zhong Lirong , Mitroshkov Alex , Pederson Larry , Coyle Chris , Coffey Gregory W
Published: February 2020

The direct conversion of methane to liquid fuels and chemicals is highly sought, especially at low-scale to more effectively utilize remote natural gas resources. Direct conversion has proven to be a very difficult problem, because methane is highly unreactive, though tends to over-oxidize once activated. Methanol is primarily produced today by the steam reformation of methane at high temperatures and pressures to synthesis gas (carbon monoxide plus hydrogen), followed by catalytic conversion at intermediate temperatures and high pressures. Though highly selective, this technology is not well suited for low production wellheads. The direct conversion of methane to methanol and other liquids would be a game changer, potentially leading to much lower production costs.

In our presentation we will be reporting the development of the metal oxide-based electrocatalysts, which provide an oxygen activity needed for the partial oxidation of methane to liquid fuels suitable for applications in intermediate temperature fuel cells. The tests were performed at atmospheric pressure at different CH4 flow rates and different temperatures in the 200-700oC range.The product analysis was performed by online quadrupole mass spectrometer as well as by GC-MS. Methanol is the primary product of methane conversion at temperatures below 400oC. At 600-700oC, ethane, ethylene, propane, propene, n-butane, iso-butane, 2-butyne, and benzene formation was observed. In all tests the formation of carbon oxides was observed as well. Separately, the catalysts were evaluated using diffuse reflectance infrared Fourier Transform Infrared Spectroscopy (DRIFTS), TGA and in operando XRD. The kinetics of oxygen gain appeared to be slower that the oxygen loss. Somewhat longer time was needed to re-oxidize the catalyst. Kinetics are faster and conversion of CH4 was greater at higher temperatures. The post-test analysis was done using SEM and XRD.

Figure 1. Methane conversion (right y-axis) and the rates of methanol, CO, and CO2 formation (left y-axis) at 300oC.

Figure 2. Relative hydrocarbon distribution at 700oC.

Figure 1
In Situ, Non-Contact Studies of Oxygen Exchange Kinetics in Thin Film Mixed Conducting Electrodes
Authors: Perry Nicola H. , Chen Ting , Sasaki Kazunari , Kim Jae Jin , Ma Yuxi , Nicholas Jason D. , Tuller Harry L.
Published: February 2020

More rapid and durable surface exchange kinetics at the oxygen electrode are desirable for long-term operation of reversible solid oxide cell (R-SOC) devices. Understanding and improving the oxygen exchange kinetics would benefit from measurement techniques that enable in situ and continuous evaluation of both the defect equilibria and kinetics of native electrodes (without potentially blocking or catalytic metal current collectors). The optical transmission relaxation (OTR) technique is one such approach, which relies on the change in optical absorption signatures of thin film electrode materials upon changing their oxygen contents, typically corresponding to changes in transition metal cation valence states. In this work, the OTR method was applied to thin film electrodes of Sr(Ti,M)O3-x (M=Fe, Co) to evaluate both point defect equilibria and surface exchange kinetics over a range of temperatures and oxygen partial pressures. While the thin film defect equilibria derived this way showed reasonable agreement to established bulk defect chemistry, the surface exchange kinetics were additionally compared to those measured by other methods (curvature relaxation, simultaneous ac-impedance spectroscopy, and simultaneous conductivity relaxation). Again reasonable agreement was found, though the rapid aging behavior of the films' surface exchange rate likely was the cause of some discrepancy. Additionally the surface exchange kinetics measured by ac-impedance spectroscopy were slightly slower than those measured optically, a result that may be attributed to a potentially blocking role of porous current collectors in the former approach. The benefits and limitations of the OTR approach will be discussed, including its particular utility in evaluating the impact of electrode microstructure on exchange kinetics.
Rare Earth Molybdate Nano-Rod Phosphor Self-Assembled without Organic Solvent By Dilute Acid Proton Exchange Method
Authors: Watanabe Mizuki , Kim Sun Woog , Uematsu Kazuyoshi , Toda Kenji , Sato Mineo
Published: February 2020

Nano-sized oxide phosphor has been actively investigated as transparent phosphors for use in solar energy converters [1], field emission applications [2] and bio-detectors [3]. In particular, oxide nanoscrolls, which is well-known as a one-dimensional (1D) materials prepared by rolling up the nanosheets, have been investigated because it is expected to exhibit unique and functional properties by structural distortion caused as a result of transformation from a nanosheet to a nanoscroll [4]. Some of the nanosheets raise the spontaneous transformation into nanoscrolls after exfoliation due to the difference of stress with asymmetric structure of the top and bottom [5].

Organization of 1D nanomaterials has attracted much attention because rational assembly of 1D building blocks into well-organized higher dimensional structures is extremely useful for the fabrication of nanodevises and open up many unique areas of nanoscience [6-7]. Up to now, organization control of nanosized 1D oxide has been succeeded by various methods, including Langmuir-Blodgett (LB) technique [8], and template-based method [9]. These methods require organic substance. However, the adsorbed organic substance on the surface of nano-sized 1D oxide and heat or UV treatments, removing the organic substance, result in the reduction of the opto-electric properties of these oxides. Therefore, new 1D materials synthesized without organic solvent is required in order to efficiently use the nanoscrolls in optical and opto-electric devices.

In our previous work, we have obtained organic-free HLn(MoO4)2 (Ln = rare earth metals) nanoscroll by the H+ exchanging of alkali rare earth molybdate ALn(MoO4)2 (A = alkali metals) using dilute nitric acid solution (0.01 M) for the first time [10]. In this study, we have found that HLn(MoO4)2 formed nanobundle structure assembled some nanoscrolls by a TEM observation. The detail of the nanobundle morphology will be given a presentation on.

[1] J.Y. Chen et al., Sol. Energy Mater. Sol. Cells, 2014, 120. 168.

[2] Z. Hou, C. Li, Jun Y, H. Lian, P. Yang, R. Chai, Z. Chenga, and J. Lin, J. Mater. Chem., 2009, 19, 2737.

[3] B. –K. Oh, J. –M. Nam, S. W. Lee, and C. A. Mirkin, Small, 2006, 2, 103.

[4] M. Kitano, K. Nakajima, J. N. Kondo, S. Hayashi and M. Hara, J. Am. Chem. Soc., 2010, 132, 6622.

[5] K. Maeda, M. Eguchi, W. J. Youngblood, and T. E. Mallouk, Chem. Mater., 2008, 20, 6770.

[6] K. Liu, N. Zhao and E. Kumachev, Chem. Soc. Rev., 2011, 40, 656.

[7] M. J. A. Hore and R. J. Composto, ACS Nano, 2010, 4, 6941.

[8] L.Mai, Y.Gu, C. Han, B.Hu, W.Chen, P. Zhang, L. Xu, W.Guo, and Y.Dai, Nano Lett., 2009, 2, 826.

[9] Virany M. Yuwono and Jeffrey D. Hartgerink, Langmuir, 2007, 23, 5033.

[10] M. Watanabe, K. Uematsu, S. Kim, K. Toda, and M. Sato, IEICE Trans. Electron., 2015, E9-C, 1063.
(Invited) Applications of Highly Bright PbS Quantum Dots to Non-Invasive Near-Infrared Fluorescence Imaging in the Second Optical Window
Authors: Jin Takashi , Imamura Yukio
Published: February 2020

Near-infrared (NIR) fluorescence imaging in the wavelength of 1000-1400 nm (2nd-NIR optical window) is expected to offer better spatiotemporal deep-tissue imaging due to the lower autofluorescence and scattering than that in the 1st-NIR optical window (700-1000 nm). During the past decade considerable progress has been made in the development of NIR fluorescent materials that emit over 1000 nm for non-invasive fluorescence imaging. Although single-walled carbon nanotube (SWNT), rare-earth metal ion doped nanomaterials and silver sulfide (Ag2S) quantum dots (QDs) have been reported as fluorescent probes in the 2nd-NIR optical window, their fluorescence brightness is relatively low, with quantum yields (QY) less than 6 %. To achieve deep-tissue imaging with high spatiotemporal resolution, we have developed fluorescent lead sulfide (PbS) QDs with high quantum yields (QY >10 %) in the 2nd-NIR region. We present the synthesis of 2nd-NIR emitting PbS QDs and their applications to the non-invasive fluorescence imaging of lymph nodes, cerebral blood vessels, breast tumors, and phagocytic cells in mice.
Gadolinium Doped NaLaF4 Nanocrystals in Glass-Ceramics and Polycrystalline Powders
Authors: Elsts Edgars , Antuzevics Andris , Kemere Meldra , Krieke Guna , Jansons Janis , Ignatans Reinis , Rogulis Uldis
Published: February 2020

Gadolinium doped scintillators could be efficient neutron detectors with a minimal residual radioactivity and good temperature stability [1]. In this research we analyze localization and properties of Gd3+ dopants in oxyfluoride glass-ceramics containing NaLaF4 nanocrystals and in polycrystalline NaLaF4 powders.

Glass samples with the composition 63SiO2-7Al2O3-16Na2CO3-9NaF-5LaF-0.1GdF3 were synthesized by the quench melting method and converted to glass-ceramics by the heat treatment technique. Heat treatment temperatures were selected according to the differential thermal analysis curves.

Polycrystalline samples were prepared by solid state reaction method from NaF, LaF3 and GdF3 batch materials. GdF3 concentrations were varied from 0.01 to 1 mol%.

NaLaF4 nanocrystals have been observed in glass-ceramics and polycrystalline samples by X-ray diffraction measurements. Photoluminescence and cathodoluminescence spectra show a peak around 315 nm, which originates from 6P7
/2 → 8S7/2 energy level transition of the Gd3+ ion. EPR measurements of the glass samples show the Gd3+ spectrum of disordered environment, however in glass-ceramics the EPR spectra have fine structure characteristic to the specific crystallite. EPR measurements of NaLaF4 powders with different concentrations of Gd3+ showed that the EPR spectrum consists of superposition of at least two paramagnetic centres.

Reference

[1] Watt, David Edwin, and Dennis Ramsden. High Sensitivity Counting Techniques: International Series of Monographs on Electronics and Instrumentation. Vol. 20. Elsevier, 2014.

Acknowledgement

Financial assistance to the first author from the Baltic-American Freedom Foundation is gratefully acknowledged.
(Invited) Exploiting Luminescence for Measurements of Temperature
Authors: Dramicanin Miroslav
Published: February 2020

Temperature is by far the most-measured physical quantity, and temperature sensors are

used by a large extent in daily life, industry, military, medicine, etc., with a market share of about 75%–80% of all sensors. Demands for temperature measurements of moving or contact sensitive objects, difficult to access bodies, objects in hazardous locations, at the nanoscale, in living organisms and cells, have stimulated research on the development of new temperature measurement concepts and temperature probes. Luminescence thermometry is among aspiring concepts capable of meeting aforementioned demands in the future. The changes of luminescence properties of materials with temperature allows some materials to act as sensitive thermometers. The phenomenon become the basis of a new arm in the field of luminescence spectroscopy commonly termed as a luminescence thermometry.

This lecture will present a brief introduction into the concept of temperature measurements via luminescence, with the description of the temperature quenching of emission. Then, an overview of different concept modalities of luminescence thermometry will be given including: the steady-state luminescence concepts (use of the emission band shapes and positions, emission intensity and intensity ratios, use of the materials with a single- or multi- emission centers) and concepts based on the temporal changes in emission (emission decay- and rise-times). The most important quantities used to characterize the performance of a measurements (such as temperature sensitivities, temperature and spatial resolution, measurement ranges) will be explained and compared between different measurements modalities as well as between different classes of materials utilized as temperature probes. Finally, several designs of temperature sensing by luminescence in a different application fields will be highlighted.
Optical, Scintillation and Dosimeter Properties of Ce-Doped and Eu-Doped LiCaAlF6 Crystals
Authors: Yanagida Takayuki , Fujimoto Yutaka , Okada Go , Kawaguchi Noriaki , Watanabe Kenichi , Fukuda Kentaro
Published: February 2020

Scintillators are one of the luminescent materials which have a function to convert the ionizing radiation to UV-NIR photons. Among such applications, scintillators for thermal neutron detectors have attracted much attentions in recent years since the lack of 3He gas causes some serious problems in this field. To develop the alternative to 3He gas, many groups are developing new scintillators containing 6Li or 10B since these elements have a high cross section against thermal neutrons. For this purpose, we have developed Ce- [1] and Eu-doped [2] LiCaAlF6 crystals. In addition to scintillators, dosimeter materials are also important, and these materials are used in the individual and environmental dose monitors. In dosimeters, optically stimulated luminescence (OSL), thermally stimulated luminescence (TSL), and radiophotoluminescence (RPL) have played an important role. In dosimeter materials, human tissue equivalency is one of the most important properties, and LiCaAlF6 crystals are interesting because the effective atomic number of this material is close to the human tissue. If the dosimeter materials have the same effective atomic number with the tissue, ideally no mathematical corrections are required to calibrate the dose. Furthermore, the complementary relation of scintillators and dosimeter materials was found by us [3, 4] so the investigation of these properties on the same material is important to develop high performance materials for ionizing radiation detectors and to understand the energy migration process from the host matrix to emission centers.

In this work, we have grown Ce and Eu differently doped LiCaAlF6 crystals to investigate optical, scintillation, OSL and TSL properties. In transmittance, absorption was proportional to dopant concentrations and typical optical quantum yield of Ce and Eu-doped LiCaAlF6 were 40 and 100%, respectively. Scintillation wavelength and decay time profiles were investigated under X-ray irradiation. Ce3+ and Eu2+ 5d-4f luminescence appeared around 300 nm and 370 nm with typical decay time of 40 ns and 1.5 ms, respectively. OSL of Ce-doped ones appeared under 405 nm stimulation and that of Eu-doped ones was observed under 470 nm stimulation. TSL of Ce- and Eu-doped LiCaAlF6 were enough strong and they exhibited good response function from 1 to 1000 mGy exposure. In Eu-doped LiCaAlF6, the clear relation between the scintillation and dosimeter properties were observe while it was not observed in Ce-doped ones.

[1] T. Yanagida, et al., Opt. Mater. 32 311 (2009).

[2] T. Yanagida, et al., Opt. Mater., 33 1243 (2011).

[3] T. Yanagida, et al., Rad. Meas., 71 162 (2014).

[4] T. Yanagida, J. Lumin., 169 544 (2016).
Crystal Structure Refinement of BaCaSiO4:Eu2+/Mn2+ and Its Tunable Luminescence
Authors: Park Jieun , Lee Choong Ki , Kim Young Jin
Published: February 2020

Color-tunable phosphors have been widely developed to enhance the luminous efficiency of phosphor-conversion white light-emitting diodes using near ultraviolet chips. For this application, the Eu2+ and Mn2+ ions are typically used as sensitizers and activators, respectively. One of suitable host materials is a (Ba,Ca)SiO4 system. For example, the tunable luminescence of Eu2+/Mn2+ co-doped Ba1.55Ca0.45SiO4, Ba1.3Ca0.7SiO4, and Ba1.2Ca0.8SiO4 compounds has been reported. However, the luminescence of BaCaSiO4:Eu2+/Mn2+ has rarely been studied.

In this study, BaCaSiO4:Eu2+/Mn2+ powders were prepared by a solid-state reaction process. And then the phase formation, the crystal structure, and tunable luminescence were investigated. The starting mixtures were fired at 1100−1300 °C for 4 h under a 5% H2 (+ 95% N2) atmosphere. Rietveld refinement was performed to verify the crystal structure. The crystal system of BaCaSiO4 is a hexagonal structure. It was most probable that both of the Eu2+ and Mn2+ ions were incorporated into the Ca2+ sites. The PL spectra exhibited two emission bands: green (A-band) and red (B-band) assigned to the Eu2+ and Mn2+ ions, respectively. The B-band occurred through an energy transfer (ET) from Eu2+ to Mn2+. The intensity ratio of the A- to B-band closely depended on the Eu/Mn ratio, resulting in a change in CIE chromaticity coordinates. Fluorescence lifetimes, multipolar interactions and critical distances between Eu2+ and Mn2+, ET efficiencies, and the evolution of the PL spectra were estimated and discussed.
Phellodendron Chinense Schneid: A Novel Yellow-Emitting Luminescent Materials for White Light-Emitting Diodes Applications
Authors: Lin Pin-Chun , Hsu Kuei-Ting , Liu Wei-Ren
Published: February 2020

Phellodendron chinense Schneid (Rutaceae) is a deciduous tree found widely in Southwest China. Rutaceae has attracted much attention due to its applications on various medical fields. In this study, we first report luminescent properties of Phellodendron chinense Schneid. NMR, PL, PLE, Thermal quenching as well as CIE coordinates and LED fabrication tests have been systematically carried out. Phellodendron give a intense yellow emission at 540 nm under optimal excitation wavelength of 460 nm. The absorption band of Phellodendron were in the range of 350-525 nm, which could be excited by both n-UV chips and blue chips. The CIE coordinate of Phellodendron is (0.3989, 0.5480). The LED package tests indicate the combining YAG phosphor and Phellodendron, the CCT could be dramatically decreased from 7623 to 3615 K. The result indicates that Phellodendron could be a potential yellow-emitting material for LED applications.
New Strategy for the Design of Yellow, Red and IR-Emitting LED Phosphors
Authors: Toda Kenji , Kim Sun-Woog , Uematsu Kazuyoshi , Sato Mineo
Published: February 2020

Typical white LEDs composed of blue light excitable LED phosphors and blue LED chip. Recently, long wavelength (yellow and red)-emitting Eu2+ or Ce3+-activated nitride phosphors have been usually used in the white LEDs as commercial phosphors. The excitation and emission band of Eu2+ or Ce3+-activated phosphors are due to the energy transitions between the 4f ground state and 5d excited state of Eu2+. Strong crystal field splitting of the 5d band in the nitrides lead to decrease the energy gap between the 4f ground state and the lowest level of the 5d excited state. On the other hand, the Eu2+ or Ce3+-activated oxide phosphors are also expected to be obtained the excitation and emission band in the longer wavelength region (yellow, red and IR), if the oxide host materials have small site for substitution of activator ions. Therefore, we focused on oxide materials including a compact octahedral sites in the host lattices.

As a result, we could successfully synthesize the novel long wavelength-emitting Eu2+ or Ce3+-activated phosphors such as NaMgPO4:Eu2+ and (Ba,Sr)3Sc4O9:Ce3+ [1,2]. The NaMgPO4:Eu2+ phosphor can be efficiently excited by blue light irradiation and presents red emission band centered at 628 nm due to the d - f transition of Eu2+. The internal quantum efficiency of NaMgPO4:2.5mol%Eu2+ at the excitation wavelength of 450 nm is estimated to be 81%. (Ba,Sr)3Sc4O9:Ce3+ shows orange to red emission peaking at 583(Ba) and 620(Sr) nm due to the 5d - 4f transition of Ce3+ under blue light excitation. Therefore, this new strategy (octahedrally coordinated sites for the Eu2+ or Ce3+) is a general and powerful tool for searching the long wavelength-emitting phosphors.

This work was supported by a project from NEDO, New Energy and Industrial Technology Development Organization (Rare Metal Substitute Materials Development Project Development of Technology for Reducing Tb and Eu Usage in Phosphors for Fluorescent Lamp by High-speed Material Synthesis and Evaluation).

References

[1] S-W. Kim, T. Hasegawa, T. Ishigaki, K. Uematsu, H. Takaba, K. Toda, M. Sato. “Efficient Red Emission of Blue-Light Excitable New Structure Type NaMgPO4:Eu2+ Phosphor”, ECS Solid State Lett
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2, (2013). R49-R51.

[2] T. Hasegawa, S-W. Kim, T. Ishigaki, K. Uematsu, H. Takaba, K. Toda, M. Sato. “Novel Ce3+-doped Ba3Sc4O9 Reddish Yellow-emitting Phosphors for Blue-light Based White LEDs”,
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Electrochemiluminescent Molecular Sensor for Point of Care Testing for Homocysteine Measurement
Authors: SHIN Iksoo
Published: February 2020

Homocysteine (Hcy) is a naturally occurring, sulfur-containing amino acid produced from demethylation of methionine, and an essential amino acid found in both animal and plant proteins. The level of plasma Hcy between 5 and 15 μM is generally considered normal. An elevated level of Hcy is, however, strongly linked to cardiovascular disease, Alzheimer’s disease, neural tube defects, and osteoporosis. Therefore a routine, easy-to-usable determination of Hcy is highly desirable. In the talk, an electrochemiluminescent (ECL) molecular sensor for simple Hcy determination will be discussed. Recently, we developed supramolecular probes which recognize Hcy in the solution by producing light emission under ECL process. The synthesized molecular sensor successfully monitors the level of Hcy in 99.9% aqueous media with a linear correlation between 0–40 µM. The method suggests a point-of-care testing of the Hcy level based on ECL analysis, and it is potentially useful for a routine, pre-cautious, and strip-based diagnosis for the cardiovascular diseases.
Morphology-Controllable Ni3Se2 Nanostructures; Synthesis, Characterization and Electrocatalytic Activity Towards Oxygen Evolution Reaction
Authors: Swesi Abdurazag T , Masud Jahangir , Nath Manashi
Published: February 2020

First raw transition metal-based chalcogenides (FRTMCs) are promising devices for next generation to serve as effective substitutes for the Pt-based electrocatalysts in fuel cell systems. OER and HER are considered to be clean and sustainable energy technology and an alternative for fossil fuels. However, OER involving a complex 4 electron process, has several steps that have large reaction barriers, which lead to large required overpotentials. Identifying more-efficient, stable and earth-abundant catalysts for water splitting has long been investigated. The planar configuration of FRTMCs could lead to robust integration for electronic devices. Nanostructured electroactive materials that are fabricated in-plane FRTMCs have attracted great attentions as a kind of storage energy material due to its electrochemistry properties. Recently we have observed that Ni-chalcogenide (Ni3Se2) is superior to the precious transition metal oxide-based electrocatalysts in terms of onset overpotential for O2 evolution as well as overpotential to reach a current density of 10 mA cm-2. With the onset of decreasing particle size to nanometric scale, electrodeposition techniques have provided an alternative route to obtain a variety of new nanomaterials with improved and well controlled properties. The improvement of properties of the metallic composites is dependent mainly on the morphology of materials. Morphology-controllable Ni3Se2 films were successfully prepared by electrodepositing Ni3Se2 film on Au substrate and following by electrochemical dissolution. In electrochemical dissolution process, Ni3Se2 phase is well-preserved and porous structure formed. This technology is a promising way to fabricate other porous materials. A porous Ni3Se2 film showed an enhanced OER catalytic performance in comparison with the as-deposited Ni3Se2 film. The results proved that the OER catalytic performance of porous Ni3Se2 film delivers the highest activity. Introduction of pores to the catalyst material by the electrochemical dissolution is availability for improve the electrochemical performance of the material for OER electrocatalysts.

The catalytic efficiency of the proposed catalysts was investigated through linear scan voltammetry (LSV), chronoamperommetry and double layer capacitance. Utilizing rotating ring disc electrode (RRDE) assemblies, the kinetics of OER process between various catalysts as well as the Faradaic efficiency were studied. The catalytic activity of the proposed novel compound (Ni3Se2) was also compared to the outstanding electrocatalysts for OER under conditions relevant to an integrated solar water-splitting device which have been reported so far. The synthesis, characterization, catalytic activity and advancement of the field will be presented in details.