bluuebunny/crossref_metadata_2025 huggingface dataset:
Binary Fe-Free Transition Metal Catalysts for the Oxygen Reduction Reaction
Authors: Martinez Ulises , Holby Edward F. , Dumont Joseph H , Zelenay Piotr
Published: February 2020

Platinum group metal (PGM)-free catalysts with high volumetric activity and low hydrogen peroxide yields are needed as replacements for expensive and scarce platinum-based catalysts for the oxygen reduction reaction (ORR). State-of-the-art PGM-free ORR catalysts are currently synthesized from a variety of carbon-nitrogen-iron (C-N-Fe) precursors. While these C-N-Fe catalysts have shown promising ORR activity and selectivity, a concern exists on the possibility of harmful Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) side reactions generating hydroxyl radicals risking the durability of polymer electrolyte fuel cells due to membrane degradation. Therefore, in an effort to mitigate that risk, development of Fe-free catalysts with similar ORR activity to the C-N-Fe system but with alternative transition metal precursors are being pursued.

Our previous results have shown improved ORR activity from (CM+PANI)-Co-C catalysts with a half-wave potential of 0.77 V nearing that of Fe-based catalysts [1]. While this improvement is significant, further development is necessary to enhance both activity and selectivity of Fe-free catalysts. In this work, we will exploit the synergism between theoretical and experimental approaches to develop binary Fe-free transition metal ORR catalysts. Earlier results from quantum-chemical models linking atomic scale structure to ORR activity based on density functional theory (DFT) suggest increased ORR activity for mixed-metal-species active site structures in the Fe-Co system [2]. The same effect was observed from the Mn-Co system. A Sabatier principle relationship between ORR activity and single-transition-metal active sites was observed in both theoretical and experimental studies. A similar experimental-theoretical relationship will be developed from our findings of binary Fe-free transition metal sites.

Acknowledgement

Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

[1] Martinez, U., Holby, E.F., Dumont, J.H., Chung, H.T., Zelenay, P. “Non-PGM ORR Catalysts Based on Transition Metals Alternative to Iron.” ECS Meeting Abstracts, 2016.

[2] Holby, E.F., Taylor, C.D. “Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands,” Scientific Reports, 2015, 5, 9286.
A Highly Active and Ultra-Durable Methanol Oxidation Electrocatalyst Based on the Synergy of Pt-Ni(OH)2-Graphene
Authors: Li Yanguang
Published: February 2020

Active and durable electrocatalysts for methanol oxidation reaction are of critical importance to the commercial viability of direct methanol fuel cell technology. Unfortunately, current methanol oxidation electrocatalysts fall far short of expectations and suffer from rapid activity degradation. Here we report platinum–nickel hydroxide–graphene ternary hybrids as a possible solution to this long-standing issue. The incorporation of highly defective nickel hydroxide nanostructures is believed to play the decisive role in promoting the dissociative adsorption of water molecules and subsequent oxidative removal of carbonaceous poison on neighbouring platinum sites. As a result, the ternary hybrids exhibit exceptional activity and durability towards efficient methanol oxidation reaction. Under periodic reactivations, the hybrids can endure at least 500,000 s with negligible activity loss, which is, to the best of our knowledge, two to three orders of magnitude longer than all available electrocatalysts.
Practical Considerations for Determining Thin Film Oxygen Surface Exchange Coefficients, Elastic Constants, Thermal Expansion Coefficients, Thermo-Chemically Induced Stresses, and Thermo-Chemically Induced Strains from Wafer Curvature Measurements
Authors: Nicholas Jason D.
Published: February 2020

Wafer curvature measurements have recently been developed as a new, electrode-free method for simultaneously measuring dense or porous thin film chemical oxygen surface exchange coefficients and stress states.1, 2 In addition to being one of today’s cheapest electrode-free oxygen surface exchange coefficient measurement techniques (and the only one presently yielding simultaneous surface exchange coefficient and stress data) these measurements allow for the in situ/in operando determination of thin film elastic constants, thermal expansion coefficients, and chemical expansion coefficients.3 Hence, wafer curvature measurements promise to be an important tool in establishing the links between the mechanical state and electrochemical performance of the materials used in solid state battery, fuel cell, memristor, catalytic reactor, and other solid state ionic devices.

This presentation will review the recent progress made in applying wafer curvature measurements to the study of oxygen ion conducting materials. Specifically, the presentation will provide 1) an overview of the fitting equations used to extract the aforementioned thin film materials properties from wafer curvature relaxation experiments, 2) materials case studies highlighting use of the technique, 3) a comparison of the technique’s benefits and limitations compared to alternative approaches, 4) a review of the sample geometric considerations and substrate material properties necessary to obtain reliable data, 5) a detailed description of the experimental setup used at Michigan State to conduct these experiments, 6) a breakdown of the system costs, and 7) a series of practical tips for successful implementation of the technique.

Acknowledgements

This work was supported by National Science Foundation Award Number CBET-1254453.

References

1. Q. Yang and J. D. Nicholas, Journal of the Electrochemical Society, 161, F3025 (2014).

2. Q. Yang, T. E. Burye, R. R. Lunt and J. D. Nicholas, Solid State Ionics, 249–250, 123 (2013).

3. J. H. Zhao, Y. Du, M. Morgen and P. S. Ho, Journal of Applied Physics, 87, 1575 (2000).

Figures

Figure 1.Schematics of the Wafer Curvature Setup used to perform measurements on dense and porous films.

Figure 1
Design-Led Solid Oxide Fuel Cell Manufacturing: Using 3D Imaging and Modeling to Optimize Electrode Performance
Authors: Kareh Kristina Maria , Ruiz-Trejo Enrique , Bertei Antonio , Tariq Farid , Yufit Vladimir , Kishimoto Masashi , Brandon Nigel P.
Published: February 2020

Solid oxide fuel cells are among the most thermodynamically efficient energy conversion devices. They are critical for the future if we are to meet rising energy demands and increasing selectivity over our future energy mix. Traditionally, solid oxide fuel cell performance has been assessed using bulk parameters, and the microstructure-bulk properties relationship is yet to be well understood.

Here, we use time-lapse 3D imaging to probe 3D electrode structure and move towards intelligently designing structures with specific performance attributes. Using 3D imaging allows for characterisation and quantification of parameters that are not well described in 2D, such as triple-phase boundary lengths, tortuosity and phase percolation.

In this work, the parameters for an optimised porous nickel-scandia stabilized zirconia anode (Ni-ScSZ) were calculated using an electrochemical model to maximise triple-phase boundary length and density, gas permeation and electronic and ionic transport. Ni-ScSZ scaffolds were then produced using screen-printing and impregnation and characterized with FIB-SEM to obtain 3D microstructural parameters such as actual percolation of the phases, tortuosity and connectivity of the phases, and the length and density of triple-phase boundaries (Figure 1). The experimental microstructural parameters were then compared to the modelled optimised microstructure, allowing for an examination of the accuracy of the manufacturing parameters.

Symmetrical cells were set up to compare the anode performance with the performance predicted by the electrochemical model. Early iterations of impregnated scaffolds show triple-phase boundary densities increased by approximately an order of magnitude and allowed for a critical assessment of the electrochemical model. The degraded electrode morphology was also characterized in 3D to link its changes during cycling to performance degradation. This approach enables us to move towards designing optimised electrodes with specific performance attributes.

Figure 1
Advanced Characterization of a Stabilized Solid Electrolyte Interphase on Silicon Anodes for Lithium-Ion Batteries By in-Situ Electrochemical Surfaces Forces Apparatus
Authors: Moeremans Boaz , Cheng Hsiu-Wei , Merola Claudia , Valtiner Markus , Zheng Yueming , Van Bael Marlies K , Hardy An , Renner Frank Uwe
Published: February 2020

The unsatisfactory behaviour of the solid electrolyte interphase (SEI) on silicon-based anodes still prevents the commercial introduction of silicon in lithium-ion batteries – a milestone which would be a huge leap forward towards a sustainable energy use.[1]

Our group has recently developed an electrolyte mixture improving the cycling performance of a silicon-based lithium-ion battery. For understanding the stabilizing effect of this novel electrolyte on the SEI, advanced characterization techniques had to be employed, such as a modified Surface Forces Apparatus (SFA) and synchrotron-based Hard X-ray Photoelectron Spectroscopy (HAXPES). So far, the SFA was used to research fundamental biologic and solution based interfacial processes.[2] Here we present a detailed investigation of the SEI on a silicon anode by designing a battery SFA cell for in-situ electrochemical measurements. This enabled us to monitor the SEI thickness during the different stages of the SEI formation on both silicon and graphite surfaces. Additionally, we report the mechanical properties of the SEI for different electrolytes which can also be addressed by the SFA setup.

HAXPES data collected on a modified SEI on silicon based anodes reveal a complex nanostructure and provide an additional insight into the stabilization mechanism of the electrolyte mixture. Coin-cell testing confirm the stabilizing effect of the novel electrolyte mixture on the battery performance.

The electrochemical battery SFA will be an important tool for evaluating novel electrolyte compositions and their effect on the mechanical properties and growth mechanism of the interfacial SEI. The introduction of this in-situ battery test cell for SFA opens the way for both fundamental interfacial insights as well as applied material studies in battery research.

REFERENCES

1. E.C. Evarts, To the limits of lithium, Nature, 2015, 526, 593-595.

2. J. Israelachvili et al., Recent advances in the surface forces apparatus (SFA) technique, Rep. Prog. Phys., 2010, 73, 1-16.

Figure 1
(Invited) Synthesis and Luminescent Characterization of Core-Shell Nanophosphors
Authors: Ha Jungmin , Han Jin Kyu , Zhou Chenhui , Novitskaya Ekaterina , Hirata Gustavo , Graeve Olivia A , McKittrick Joanna
Published: February 2020

Core/shell phosphors were synthesized and characterized for their structural and luminescent properties. Silicates phosphors were synthesized using a wet method as core materials and one of the possible shell materials, silica, was coated through Stöber process. SiO2 shells of 15- 90 nm were homogenously coated onto the nanophosphors, with the thickness controlled by the deposition time [1]. Core/shell particles show significant enhancement of the luminescence emission intensity over that of the core only particles. The luminescence intensity with thinner SiO2 shells (15-30 nm) and thicker shells (25-50 nm) is 72% and 25% higher than that of bare core particles. It has also been previously reported to show silimilar results that the inert shells mitigate the detrimental effect of the nanophosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-70%, depending on the core phase and shell thickness [2]. Another possible shell material is a polymer. Polymers have various refractive indices and scattering of the excitation light (reflectivity) will be reduced when the index of refraction of the suspension media is near that of the particle, or the index of refraction of the shells is between that of the suspension media and core particle. Therefore, the reflectivity which influences on the photoluminescent properties of core/shell phosphors can be adjustable when different polymers are coated. Silicate phosphors were used as cores and monomers were attached on the surface of cores using electrostatic force and then polymerization reaction occurred in order to coat on the cores. The change of emission intensity will be reported for various thicknesses of the polymers. The structural features (core and shell materials and order of deposition) will be related to the photoluminescence properties. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).

1. J. K. Han, G. A. Hirata, J. B. Talbot, and J. McKittrick, Mater. Sci Eng. B,
176, 436-441 (2011).

2. D. Cervantes-Vasquez, O. E. Contreras, and G. A. Hirata, J. Lumin.,
143, 226-232 (2013).
(Invited) Luminescent Metamaterials for Solid State Lighting
Authors: Gomez Rivas Jaime , Ramezani Mohammad
Published: February 2020

The introduction of white LEDs is leading to the solid state lighting revolution with the fast replacement of incandescent lamps by much more efficient light sources. In white LEDs, high efficiency UV or blue LEDs are used to excite the luminescence of high quantum efficiency (QE) materials called phosphors. Much effort is dedicated to the development of stable phosphors with the highest possible QE and with designed absorption and emission spectra. These efforts are also on the design of optical elements to couple light out of the devices and to beam this light in certain directions. Large improvements and control of the emission can be achieved with resonant nanostructures. This possibility that has been only recently proposed.

In this contribution we present results of our investigation of the emission of thin ﬁlms of dye molecules embedded in polymer layers (phosphors), on top of arrays of metallic nanoparticles. The emission couples to quasi-guided modes or to diffracted orders in the plane of the array that are efﬁciently coupled out to free space by scattering with the particles. This outcoupling provides a signiﬁcant enhancement of the emission in deﬁned directions. The exact position of the emitting layer, relative to the array, defines its coupling efficiency to defined optical modes. This coupling efficiency enables the precise tailoring of phosphor emission spectrum. The luminous efﬁcacy of the layer of dye can be also controlled by its thickness and the characteristics of the particle array. Also the absorption efficiency of the exciting blue light can be enhanced or reduced by controlling the illumination conditions onto the array of resonant nanoparticles, e.g., the angle of incidence and the relative phase of multiple incident beams.

The system formed by a phosphor layer and an array of nanoparticles can be regarded as a luminescent metamaterial with designed properties that can be exploited in solid state lighting applications. A visual example of these properties is presented in the figure, which displays a photograph of the luminescent emission of a layer of dye projected onto a screen (left) and the emission of a similar layer of dye on top of a nanoparticle array. The emission is clearly enhanced and beamed in the forward direction by the nanoparticles. This significant enhancement of the emission in defined directions can be used for the replacement of bulky optical components in LEDs by nanostructures.

Figure 1
On the Photoluminescence Linearity of Eu2+ Based LED Phosphors upon High Excitation Density
Authors: Jansen Thomas , Boehnisch David , Juestel Thomas
Published: February 2020

This work deals with the saturation behavior of Eu2+ doped luminescent materials. Eu2+ activated phosphors, excited by high radiance pump sources, like high power LEDs or Laser Diodes, offer considerable potential for high radiance conversion in Solid State Lighting. Remarkably, theoretical arguments suggest that the radiance of the luminescent spot should increase linearly with the excitation density of the incoming light source up to 1 kW/mm2. In practice, however, thermal quenching and (non-thermal) optical saturation limit the maximum attainable radiance of the luminescent material. We present experimental data of the widely applied red emitting LED phosphors (Ca,Ba)2SiO4:Eu2+ (OSE), Ba2Si5N8:Eu2+ (258:Eu), and CaAlSiN3:Eu2+ (CASN:Eu) in which these limits have been investigated. High excitation fluxes are achieved using laser pumping at 405 nm up to 800 W/mm2. In case of 258:Eu and CASN:Eu, optical pumping intensities have been shown to produce a significant efficiency depreciation already at low pump powers, which does not correlate with the relatively short Eu2+ luminescence lifetime (~ 1 μs). We assume a de-excitation mechanism that depletes the excited state [Xe]4f
65d
1 to the conduction band of the host structure, which bottlenecks the limit maximum pump intensities. We find that the investigated Eu2+ phosphors tend to show different efficiency depreciation. Finally, we use a rate equation model to simulate this nonlinear optical pumping.

Figure 1
Zinc Phosphate Glasses Doped Yttrium-Europium Oxide, a Luminescence Study
Authors: Mariscal B. L. , Carmona-Tellez S. , Murrieta H. , Falcony Ciro , Rivera-Álvarez Zacarias
Published: February 2020

Zinc phosphate glasses doped with yttrium-europium oxide, were obtained by melting at 1100 °C; suitable precursors of these glasses quantities was grinded mechanically and dried at 400 °C for 2hrs, then the temperature was raised to 800 °C for 2hrs again, finally the temperature was raised at 1100 °C for 3hrs until a liquid is achieved, this liquid is emptied in a copper block to produce a thermal shock and observe the formation of a glass; a final heat treatment at 300°C for 12hrs is practiced.

Luminescent studies were conducted in these glasses, it is observable, that when excited with λexc = 396nm are present the 5D0 to 7F1, 7F2, 7F3 y 7F4 transitions in 590, 616, 650, and 697 nm; the main emission is achieved at 616 nm and a high red light emission is observable at naked eye, due to the presence of europium ions. Absorption spectra, transmission and reflectance are obtained; these glasses are transparent in the region of 400 nm to 1100 nm UV; XRD indicates that samples are amorphous; the emission spectra of these glasses were doped with different amounts of yttrium-europium oxide; they depend on the amount of dopant.

The luminescent properties of Y2O3:Eu3+ powders have been studied, luminescent Y2O3:Eu3+ polycrystalline powders were synthesized by a simple evaporation method. The photoluminescence and cathodoluminescence emission spectra these samples show, luminescence peaks associated with transitions within the electronic energy levels of Eu3+ ions. The dominant peak is at 612nm corresponding to the 5D0 to 7F2 transition and present 5D0 to 7F1, 7F2, 7F3 y 7F4 transitions in 590, 616, 650, and 697 nm, when excited with λexc = 260 nm and λexc= 396at room temperature. The intensity luminescence Y2O3:Eu3+ powders with different dopant concentrations, Eu3+ ion dependent percentage, finding the optimal concentration is 17 mol%.

XRD of powders Y2O3:Eu3+ show these correspond to space group: Ia-3(206), with Cell: 10.6039 10.6039 10.6039 90.000 90.000 90.000, Volume: 1192.328 and whit Crystal System: Cubic (No: 01-075-3096); these powders were evaporated at 200 °C and then calcined for two hours at 1100°C. EDS analysis shows that the corresponding Y2O3:Eu3+ powders, showing that the achieved yttrium is stoichiometric according to general Y2O3 formula. According to the results of the photoluminescence of these powders Y2O3: Eu3+, to excite λexc = 396nm have the energy required for luminescence is less and therefore can obtain low-cost LEDs for red light; so it can be considered that this type of compound is a good candidate to have red light and its preparation is simple and inexpensive.
Investigation of Mechanoluminescent Light-Emitting Devices Based on ZnS:Cu Composite Embedded Elastomer Film
Authors: Heo Gi-Seok , Oh Jeung pyo , Kim Eun Mi , Kim Young Baek , Woo Jeong Ju
Published: February 2020

A mechanically driven light-generating composite flims consisted of ZnS:(Cu,Al) and polydimethylsiloxane (PDMS) were fabricated by spin coating method. Effects of mechanical stresses on the structural, optical properties of composite films were investigated. X-ray diffraction(XRD) measurements showed the ZnS:(Cu,Al) microparticle based composite films showed a hexaginal zinc blende type crystal peaks without any other distinguishable phase. Field emission scanning electron microsope (FE-SEM) images showed that the ~ 900 um thick composite films fabricated and the mixed ZnS:(Cu,Al) microparticles were mostly surrounded by PDMS matrix. The mechanoluminescence intensity and color of composite films were strongly related to the external mechanical stress. The mechanoluminescence intensity increased with increasing mechanical stress and a color of the ZnS:(Cu,Al) based composite films shifted from green to blue [Commission internationale de L'Eclairage (CIE) color coordinates of (0.225, 0.444) to (0.171, 0.304)] as the increased mechanically stress. The best brightness of the composite films was 140 cd/m2 when it was exposed to external gas flow of 700 kPa.
Radiation Dose Response of Ag-Doped Phosphate Glasses with Different Alkali Metal Compositions in the Host
Authors: Tanaka Hironori , Fujimoto Yutaka , Koshimizu Masanori , Yanagida Takayuki , Saeki Keiichiro , Asai Keisuke
Published: February 2020

Introduction

For many years, the radiophotoluminescence (RPL) of Ag-doped phosphate glass has been exploited in personal dosimeters. On exposure to X-ray, gamma ray, and high-intensity laser irradiations, the electrons and holes are captured by the Ag+ ions in the glass structure, thereby changing the Ag+ ions into Ag0 and Ag2+, respectively [1]. Thus, Ag-doped phosphate glasses enable the estimation of the exposure dose due to the correlation between the amount of irradiation and the relative intensity of luminescence of the Ag0 and Ag2+ ions excited with ultraviolet light. In a previous research, we found that the peak wavelengths of the RPL bands depend on the alkali metal species used [2]. In this study, we investigated the radiation dose response of various Ag-doped phosphate glasses, containing alkali metals as cations, to optimize their composition and develop a higher-performance dosimeter.

Experimental Methods

The glass samples were prepared according to a conventional melt-quenching method in air. The raw materials, AgCl and (LiPO3)n (Li/Ag), were mixed, loaded into an alumina crucible and melted at 1073 K, for 30 min, in an electric furnace. The melt was then quenched on a stainless steel plate at 573 K, which is below the glass transition temperature. The same operations were also performed for NaPO3 (Na/Ag), (KPO3)n (K/Ag)，RbH2PO4 (Rb/Ag)and CsH2PO4 (Cs/Ag) instead of LiPO3. The Ag concentration was 0.1 mol% for all samples. In addition, phosphate glasses with mixed alkali metals were prepared in the same manner Li/Na-Ag, K/Na-Ag, Rb/Na-Ag, and Cs/Na-Ag.

The samples were irradiated at room temperature with X-rays using an X-ray tube operating at 40 mA and 40 kV. The PL (photoluminescence) and RPL properties were analyzed using both PL and RPL spectra and the temporal luminescence profiles. The PL and RPL spectra were collected using an F-7000 (Hitachi) fluorescence spectrometer. The temporal profiles were recorded using a DeltaFlex 3000U-TMK2 (Horiba). The absorption spectra were measured using a spectrophotometer (Hitachi U-3500).

Results

The RPL spectra of the various Ag- doped phosphate glasses, irradiated with a dose of 50-Gy X-rays, are shown in Fig. 1. The sample K/ Na-Ag shows two emission band peaks, observed at 550 nm and 680 nm, with excitation at 310 nm. The peak of K is also detected at 550 nm with a line shapesimilar to that of the sample K/Ag. On the other hand, the peak of K/ Na-Ag observed at 680 nm shows a line shape similar to that of Na/Ag . These results indicate that Na-K/Ag is composed of K/Ag and Na/Ag domains and that Na and K phosphate layers are separately formed around fluorescent centers.

References

[1] Y. Miyamoto, et al, Radiation Measurements 45 (2010) 546-549.

[2] H.Tanaka, et al, Sensors and Materials (Submitted)

Figure 1
Radioluminescence Properties of Europium Doped Strontium Aluminum Borate Glass
Authors: Kawaguchi Noriaki , Okada Go , Yanagida Takayuki
Published: February 2020

Recent topics of scintillation materials were development of halide single crystals which exhibit high energy resolution such as divalent Eu doped strontium iodide and novel solid neutron scintillators which contains high efficiency luminescent centers and Li-6 or B-10 ions which convert neutron to charged particles. One of the most traditional neutron scintillator is Ce doped Li silicate glass. On the other hand, Eu doped glass scintillators were not almost studied.

 We studied radioluminescence properties of Eu doped strontium aluminum borate glass (Eu 0.1% : 35 SrO – 15 Al2O3 – 50 B2O3) in order to obtain divalent Eu doped borate glass. As a result of X-ray excited luminescence, emission peaks were observed around 600 nm; they are originated from trivalent Eu. Emission peak was also observed around 400 nm; it might be originated from defect or divalent Eu. Detail of X-ray excited luminescence around 400 nm and Eu doping concentration dependence of radioluminescence spectra will be discussed on the conference.
Novel Measurement Technique for Time Dependant Intensity Variations of AC-LEDs
Authors: Korte Simon Dominik , Juestel Thomas
Published: February 2020

LEDs have surpassed incandescent and compact florescent lamps for general lighting during the last 10 years.1 Nowadays, they show very high wall plug efficiency while  providing a good colour rendering index (CRI). However, flicker is still a perceivable drawback to these light sources.2 The impact and perception of flicker is increasingly investigated and its consequences for human beings range from headaches over migraines to severe neurological problems, including epileptic seizure.3 Evaluating these effects requires a number of factors  to be taken into account, for instance duration of exposure, stimulated area of the retina and brightness and colour of the flickering LED source. Flicker is defined as “the rapid variation in light source intensity”.4 To describe the flicker of a light source, two metrics are currently used, flicker percentage and flicker index. Both are mathematical approaches which use the overall emission intensity and compare the minimum and the maximum intensity within a single cycle or curve integrals to gain a key figure. They do not take the wavelength, the frequency, or the duty cycle into account. The presented, novel measurement technique processes the spectrally resolved emission intensity during an adjustable amount of duty cycles, shapes and frequencies. In order to verify this measurement technique, standard phosphors such as Y3Al5O12:Ce3+ (YAG:Ce), BaMgAl10O17:Eu2+,Mn2+(BAM:Eu,Mn) have been investigated with a rectangular pulsed 50 or 100 Hz LED as excitation source. YAG:Ce showed strong flicker while BAM:Eu,Mn exhibits a flicker reducing effect. The spectrally resolved measurement technique allows us to correlate the measurement data with the eye sensitivity curve resulting in a new kind of flicker index.

                                                                                     References

1.
M. Krames, O. Sheckekin, R. Mueller-Mach, G. Mueller, L. Zhou, G. Habers and M. Craford, “Status and Future of High-Power Light-Emitting Diodes for Solid-State Lighting,” J. Disp.
Technol.
3, (2) 160 (2007).

2.
J. Tan and N. Narendran, “Defining Phosphor Luminescence Property Requirements for White AC LED Flicker Reduction,” J. Lumin.
167, 21 (2015).

3.
A. Wilkins, J. Veitch and B. Lehman, LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update, 2010.

4.
M. Rea, IESNA Lighting Handbook, New York: Publication Department IESNA, 2000.
(Invited) Thermal Quenching of Phosphors: How to Reduce/Remove It?
Authors: Im Won Bin , Kim Yoon Hwa
Published: February 2020

The most significant revolution in artificial lighting is prompted by the work of 2014 Nobel laureates who developed efficient blue light-emitting diodes enabling bright and energy saving phosphor-converted white light-emitting diodes (pc-WLEDs). However, the most critical property is the thermal stability of phosphors, since, in general, emission losses occur during LED operation due to heat generation (~200˚C), which is detrimental to pc-WLEDs and this process is known as thermal quenching (TQ).

In this talk, different techniques have been employed to enhance the thermal stability of phosphor, such as making solid-solution of phosphors, applying ceramic coatings onto phosphor surfaces, and glass ceramic phosphor. Also we report the first of the self-healing blue phosphor that does not exhibit TQ, and sustains its emission intensity up to 200°C.
Optimization of Enzyme-Reconstituted Electrodes in Enzymatic Biofuel Cell for Low Power Applications
Authors: Parmar Sarthak , Durga Siddarth , Amaravati Sivakumar , Chittur Krishnaswamy Subramaniam
Published: February 2020

An enzymatic biofuel cell uses enzymes as a catalyst to oxidize its fuel, instead of precious metals like Platinum as in a conventional hydrogen fuel cell. Here to generate electricity chemical energy stored say in glucose is converted into electricity. Enzymatic oxidation from complex sugar is carried out by glucose selective enzymes such as gluco oxidase (Gox) and oxygen reducing enzyme namely laccase. These reactions are highly enzyme specific and occur at relatively mild conditions (Neutral pH and ambient temperature). It is necessary to thus to fabricate enzyme reconstituted electrode for the Membrane Electrode Assemble (MEA). The cell features (i) a 3-D meso/micro porous carbon electrode, for high surface area (ii) Cellophane paper, to immobilize the enzyme and mediators used (ferrocene) (iii) Perfluro sulphonic acid membrane to separate the potential developed between the enzymatic activity and the electron acceptor and to facilitate ion transfer (iv) Perspex glass cell structure (v) Copper micro mesh, as current collectors.

The electrochemical characteristics of MFC are studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) fluorescence imaging and polarization profiles. The achievable power density is still below theoretical value. A cell potential of around 0.7 to 0.8V is targeted.

Complete the characterisation and optimisation in terms of enzyme loading capability, conductive loss both electronic and ionic, direct charge transfer for improving charge transfer efficiency, and pore channel and size profile of the enzymatic cells, will be presented.

Low power applications like implantable devices (pacemakers) and other medical devices will be studied.
Synthesis of Fluorinated Triazole and Isoxazole Derivatives By Electrochemical Fluorination
Authors: Kuribayashi Shunsuke , Shida Naoki , Inagi Shinsuke , Fuchigami Toshio
Published: February 2020

Partially fluorinated triazole derivatives were synthesized through anodic fluorination of alkynes having arylthio group and following Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with benzyl azide. The other route toward the fluorinated triazoles, namely the anodic fluorination of triazole derivatives once prepared by advanced CuAAC of the alkyne and azide above was also investigated. Furthermore, Cu(I)-catalyzed isoxazole synthesis of fluorinated alkynes and imidoyl chloride was also successfully demonstrated.

Figure 1
Exploring Selective, Efficient 2 e- and 4 e- Electrochemical Oxygen Reduction Using Electrocatlayts Based on Reduced Graphene Oxide
Authors: Kim Hyo Won , McCloskey Bryan D
Published: February 2020

Recently, nitrogen-doped carbon materials, such as N-doped reduced graphene oxide (N-rGO), have been significantly studied due to their outstanding ORR performance, which some studies find rivals that of Pt. Generally the electroreduction of oxygen can proceed through one of two overall reactions: a 4e- process to convert from O2 to H2O, and a 2e- process to form H2O2. There is general agreement that nitrogen-defects selectively catalyze the more thermodynamically favored 4e- mechanism over the 2e-process. However, a distribution of different N-defect sites (pyridinic, pyrollic, graphitic) is typically observed in N-doped carbon materials and there is still no consensus regarding the role of each site on the ORR mechanism.

In this study, we use a straightforward, low temperature and pressure procedure to synthesize N-rGO and rGO and compare the resultant materials’ electrocatalytic behavior with rGO and N-rGO synthesized using more traditional high-temperature procedures. Briefly, the low temperature and pressure synthesis was conducted at 100 oC and atmospheric pressure using NH4OH as both the reducing and N-doping agent in a well-dispersed graphene oxide (GO) solution. This method results in materials with a distribution of the three nitrogen defect sites and reasonably high N-doping content (~6 atomic percent), as confirmed by structural analysis including XPS and TGA. The resulting materials could be further annealed at high temperatures (over 400 oC) under inert condition to modify the nitrogen and carbon defect distribution. Similar synthesis procedures were used to prepare non-N-doped rGO samples to elucidate the importance of N-sites.

We have characterized electrocatalytic selectivity by monitoring O2 pressure decay in well-stirred, modified electrochemical H-cells with a calibrated, known headspace volume. We also quantify H2O2 formation using a standard iodometric titration on the electrolyte. These techniques provide direct measurements of O2 consumption and H2O2 formation during ORR and are therefore more accurate than traditional rotating ring disk electrode measurements. Both acid (0.1 M H2SO4) and base (0.1 M KOH) conditions have been explored. We have found that certain variants of N-rGO and rGO display exceptionally selective (~100%) and efficient (nearly no onset overpotential) formation of H2O2 in basic conditions. Thermal annealing changes both the N-site distribution and reaction selectivity and efficiency. Furthermore, higher overpotentials for product formation are observed in acid solutions compared to basic solutions. Results will be discussed linking the selectivity and efficiency of the oxygen reduction reaction to the role of nitrogen and carbon defects in N-rGO and rGO.
Investigating the Photo-Electrochemical Properties of Quantum Rods Using Scanning Electrochemical Microscopy
Authors: Hapiot Philippe , Lhenry Sebastien , Boichard Benoit , Leroux Yann , Even-Hernadez Pascale , Marchi Valerie
Published: February 2020

In this presentation, Scanning Electrochemical Microcopy (SECM) is evaluated as a method for studying the intrinsic photo-electrochemical properties of nano-objects with the example of quantum rods that are CdSe/CdS core-shell anisotropic nanoparticles. Nanoobjects were deposited on a transparent and non-conductive glass plate and investigated by SECM in feedback and generator-collector modes using a series of redox mediators. The method allows the interrogation of the quantum rods under illumination without the interference of the substrate response notably the electron photo-ejection from the substrate, a process that is inherent to any polarized electrode material. Beside the methodological demonstration that could easily be extended to the investigations of the photo-redox properties of nanoparticles, studies highlight the strong reductive properties of quantum rods under illumination.

Figure 1
Modification of Microelectrode Surface with Hydrogel Layers and Determination of Pore Size in Layers
Authors: Kaniewska Klaudia , Karbarz Marcin , Hyk Wojciech , Stojek Zbigniew Jan
Published: February 2020

Hydrogels are three dimensional networks filled with water. Some of the gels can undergo fast, reversible volume phase transition (VPT) in response to a change in environmental conditions. During the transition the gels transform from one state to another (swollen/ shrunken) by changing content of water in the network. Interestingly, the gels have properties of both: solids and liquids. In the macroscopic scale the structure of the network is responsible for the mechanical energy storage. In the microscopic scale the gels exhibit the properties of water: their density is similar and diffusion processes occur in the network [1].

Pores and channels of nanometer size are employed to separate the analytes by size and to control their transport. The size of the pores could be easily changed in the hydrogel matrix by involving the shrinking and swelling process especially in the gels with continuous volume phase transition.

The main aim of this paper was to develop an electrochemical method of obtaining the NIPA- and NIPA-co-AA hydrogel films on the microelectrode surface without previous surface functionalization. Another aim was to determine the size of pores/channels in NIPA- and NIPA-co-%AA gels and to evaluate porosity of the gels. The hydrogel films were anchored to the microelectrode surface via electrochemically induced free radical polymerization (EIFRP) process with utilizing the chronoamperometric method. We found that cyclic voltammetry could be also successfully applied to obtain thin hydrogel layers. The electrochemical studies of the discontinuous volume phase transition and the determination of the channel size were done using the ferrocene molecules modified with polyethylene glycol units (PEG) of various length.

Figure 1. Woltamperograms obtained during the electrochemically induced free radical polymerization on platinum microelectrode This work was supported by a grant from the National Science Centre of Poland, Preludium 8, 2014/15/ST5/01980

[1] A. B. Imran, T. Seki, Y. Takeok, Polymer Journal, 2010, 42, 839–851

Figure 1
Electrocatalytic Alcohol Oxidation By a Ruthenium-Modified Covalent Triazine Framework
Authors: Yamaguchi Shingi , Kamiya Kazuhide , Nakanishi Shuji , Hashimoto Kazuhito
Published: February 2020

Ruthenium (Ru) based catalysts, such as RuO2 and Ru complexes, have been widely studied for various oxidation reactions, such as oxygen evolution reaction (OER) and alcohol oxidation reactions (AOR). For example, RuO2 is an efficient anode catalyst for OER, which is a key reaction for artificial photosynthesis. However, as OER competes with AOR under the range of operating potentials, the high activity of RuO2 for OER results in the low Faradaic efficiency for AOR. In contrast, some Ru complexes are known to catalyze AOR with high efficiency [1]. However, as these Ru complexes are homogeneous catalysts, they are fragile and are difficult to separate and recycle.

Recently, we have focused on covalent triazine frameworks (CTFs) as heterogeneous electrocatalysts. CTFs have 1,3,5-triazine units as linkers, and are representative microporous conjugated polymers. As CTFs possess abundant nitrogen (N) atoms with electron lone pair for metal coordination, CTFs are expected to stabilize Ru atoms through coordination with the N atoms like Ru complexes. Recently, we have indeed synthesized single-Pt atoms modified CTF hybridized with conductive carbon nanoparticles (Pt-CTF) as an electrocatalyst [2]. The Pt-CTF catalyzed the oxygen reduction with a high methanol tolerance, a unique property that was attributed to the atomic dispersion of Pt. In the present work, we successfully synthesized a Ru-modified CTF (Ru-CTF; Figure) and examined the electrochemical alcohol oxidation activity of this novel material. The Ru-CTF effectively oxidized alcohol with low OER activity.

[1] TJ Meyer, M. Huynh, Inorganic chemistry,
2003, DOI 10.1021/ic020731v.

[2] K. Kamiya, et al, Nat. Comm. 2014, 5, 5040.

Figure 1
Application of Electrochemically Deposited Cobalt Films in a Hydrogen Evolution Reaction
Authors: Abdel-Fattah Tarek M , Huff Clay , Dushatinski Thomas
Published: February 2020

Hydrogen gas production is a rapidly growing field of research due to its desirable properties from a sustainability viewpoint. The burning of hydrogen gas provides an environmental incentive as well, due to the lack of carbon-based byproducts [1-2]. Hydrogen gas is often evolved from water but is an energy intensive process. Solid chemical storage has been implemented through the use of metal hydrides, such as sodium borohydride. The oxidation reaction of sodium borohydride in water slowly evolves 4 moles of hydrogen gas. While a slow reaction is favorable for reduction, the use of NaBH4to produce hydrogen gas necessitates the use of catalysis to accelerate the reaction to an appreciable rate. A great deal of research has been conducted searching for catalysts of such reactions, often finding noble metals to be the most efficient. While less efficient than noble metals, cobalt materials have also demonstrated catalytic properties in a variety of hydrogen evolution reactions. Cobalt is more abundant in the earth’s crust than the noble metals, which makes it an arguably more attractive catalytic material due to a relatively lower cost and easier scalability [3-5].

Cobalt films deposited from aqueous (H2O/CoCl) and non-aqueous precursor (Ch:Ch/EG/CoCl) solutions were tested for catalytic activity in the hydrogen evolution reaction of aqueous NaBH4. The evolved gas was measured through the use of a water-displacement system, Ohaus microbalance, and mass logging software. The non-aqueously deposited films initially showed a higher reaction rate, but voids in the surface could prevent disassociation of the hydrogen, reducing the catalytic surface. The aqueously deposited films were largely amorphous, providing better active sites for the reaction than its non-aqueous counterpart. Both Co films outperformed the copper substrate (Cu).

Catalytic Surface

Rate Constant (10-3 min-1)

Aqueous Co Deposition
4.9

Non-aqueous Co Deposition
4.6

Original Copper Substrate
3.3

References:

Schlesinger, H.; Brown, H.; Finholt, A.; Gilbreath, J.; Hoekstra, H.; Hyde, E. Sodium Borohydride, Its Hydrolysis and its Use as a Reducing Agent and in the Generation of Hydrogen. 1952,
J. Am. Chem. Soc. 75(1) 215-219

Chinnappan, A.; Kang, H.; Kim, H. Preparation of PVDF nanofiber composites for hydrogen generationfrom sodium borohydride. 2011,
Energy 36(2) 755-759

Dushatinski, T.; Huff, C.; Abdel-Fattah, T. Synthesis and Characterizations of Cobalt Films Electrochemically Deposited from Aqueous and Non-Aqueous Media. 2014,
ECS Trans. 64(4) 487-491

Dushatinski, T.; Huff, C.; Abdel-Fattah, T. Optical Properties of Cobalt Films Electrochemically Deposited from Aqueous and Non-Aqueous Ionic Liquids. 2014,
ECS Trans. 61(10) 43-46

5. Damiano, B.; Wixtrom, A.; Abdel-Fattah, T. Electrochemical Deposition of Cobalt onto the Surface of Copper Using a Choline Chloride-Based Ionic Liquid.2012,
 
ECS Trans.
 50(11) 277-281
Electrochemical Synthesis of Tantalum Carbide in the NaCl-KCl-K2TaF7-K2CO3 Melt
Authors: Dolmatov Vladimir S. , Kuznetsov Sergey A.
Published: February 2020

The goal of this study was electrochemical synthesis of tantalum carbide in the NaCl-KCl-K2TaF7-K2CO3 melt. It was shown that tantalum carbide can be synthesized from the abovementioned melt under the certain conditions.

Alkali metal carbonates are subjected to thermal decomposition and appearance of oxygen anions led to the formation of tantalum oxofluorides complexes. Therefore, for understanding of electrode reactions during synthesis of tantalum carbide electrochemical behavior of tantalum oxofluorides complexes in the NaCl-KCl melt was studied. The titration of the NaCl-KCl-K2TaF7 melt was carried out by oxide ions as a Na2O. Formation of tantalum monooxofluoride complexes TaOF6
3- was found at the molar ratio of O2-/TaF7
2- = 1:1 that can be interpreted by the following interaction:

TaF7
2- + О2- ↔ TaOF6
3- + F-

Potentiostatic electrolysis at discharge potentials of TaOF6
3- complexes led to the tantalum formation, and this process can be expressed by the following electrochemical reaction:

TaOF6
3- + 5e
–
→ Ta + O2- + 6F
-

Appearance of tantalum dioxofluoride complexes TaO2F4
3- was observed in the melt at the molar ratio of O2-/TaF7
2- = 2:1, and potentiostatic electrolysis of such melt resulted to the formation of mixture tantalum oxides and oxofluorides.

Discharge waves of TaOF6
3-, TaF7
2- complexes and CO3
2- -ions were observed on cyclic voltammograms after addition of potassium carbonate to the NaCl-KCl-K2TaF7 melt. However, the electroreduction wave of CO3
2- disappeared during 40-50 min after addition, which can be explained by the following interaction:

TaF7
2- + CO3
2- → TaOF6
3- + F- + CO2↑

Therefore, the joint electroreduction of tantalum and carbon leading to the synthesis of tantalum carbide TaC was possible under the following conditions: potentiostatic electrolysis at discharge potentials of CO3
2- - ions during 40-50 min after addition of K2CO3 and the molar ratio of K2CO3/K2TaF7 ≤ 1.0.
Chopped-Illumination Pulse Frequency Effect on the Product Selectivity of CO2 Reduction at Si Photocathodes
Authors: Kumar Bijandra , Brian Joseph Patrick , Spurgeon Joshua M
Published: February 2020

The electrochemical carbon dioxide reduction mechanism is a complex reaction pathway dependent on the active catalyst surface and intermediate species binding energy, convoluted with the competing effects of kinetics and mass transport. The nature of the photoelectrochemical semiconductor/catalyst interface and the optical interactions occurring there provide a unique opportunity to possibly affect the carbon dioxide reduction mechanism and influence the reaction pathway. For CO2 reduction under continuous 1-Sun illumination, Cu-catalyzed p-Si photocathodes demonstrated the same general product faradaic efficiency trends as dark Cu electrocatalysts, but offset by the photovoltage of the photocathode. Under chopped illumination, however, the product distribution at a given potential changed significantly and depended on the chopping frequency.  The results are discussed along with the proposed effects of the chopped illumination on mass transfer and on the electrode interface which lead to the observed mechanistic shifts.