bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of Hydroxide-Stable Anion-Conducting Functional Groups
Authors: Weissbach Thomas , Wright Andrew G. , Holdcroft Steven 
Published: February 2020

Immobilized benzimidazolium cations as functional groups in anion exchange polymers can be used in alkaline anion exchange membrane fuel cells (AAEM-FCs), electrolyzers, or water purification systems, but are prone to hydroxide attack. Steric protection by proximal methyl groups has been shown to drastically increase hydroxide stability (A. Wright, S. Holdcroft ACS Macro Lett. 2014, 3, 444-447.). To further improve stability, model compounds, representing the ion exchange sites of AAEMs, were investigated for their hydroxide stability. By means of density functional theory (DFT), we studied degradation mechanisms, such as de-methylating SN2 reaction of methylated benzimidazolium cations with hydroxide ions and the attack of hydroxide on the C2 position of the benzimidazolium. Some of these results have also been compared to experimental stability tests of model compounds and polymers (A. G. Wright, T. Weissbach, S. Holdcroft Angew. Chem. Int. Ed.
2016, 55, 4818-4821.). The findings of this study enable the design of new materials for AAEM-FCs.
Decoupling the Influences of Molecular- and Mesoscales on Macroscopic Transport Properties in Perfluorosulfonic-Acid Membranes
Authors: Crothers Andrew Robert , Shi Shouwen , Radke Clayton J. , Weber Adam Z 
Published: February 2020

Performance of polymer-electrolyte-fuel-cells (PEFCs) links strongly to thermodynamic and mass-transport properties of the polymer membrane. The quintessential PEFC-membrane material is perfluorosulfonic-acid (PFSA) polymer, which phase separates into nanoscale hydrophilic water-filled domains through which ions and water transport and into hydrophobic polymer-matrix domains that provide structural integrity and durability. Although considerable progress has been made to reduce reactant mass-transport limitations in PFSA membranes, mass-transport is still a critical area of concern. Aqueous electrolyte transport across a phase-separated membrane is inherently a multiscale problem with aqueous-dissolved species moving through nanoscale domains that are connected to form a transport network at the intermediate mesoscale. To guide the optimization of PEFC material design and operation, we decouple the impact of micro and macro length-scale on mass transport in PEFC membranes.
Specifically, molecular-scale interactions between aqueous-electrolyte and polymer in hydrophilic domains of PFSA membranes are modeled with mean-field local-density theory aligned with an experimentally consistent 3D domain geometry. Our molecular-scale description of membrane conductivity accounts for solvation, electrostatics, solvent dielectric saturation, finite size, and confinement effects. The microscale framework is validated against atomistic simulations and, subsequently, up-scaled to predict macroscale conductivity and solvent absorption by accounting for the interconnectedness of the hydrophilic domains. Excellent agreement is found with experimental data, as shown in Figure 1. Our proposed multiscale model for membrane conductivity and solvent sorption provides a new tool to explore potential avenues for improving PFSA membrane performance.

Acknowledgements

This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231 and by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400

Figure 1.3M PFSA membrane conductivity of proton-form membranes as a function of water content as determined from the model (open) and experiments (filled, with lines to guide the eyes) for equivalent weights of 1100 (circles), 1000 (squares), and 825 g/mol (SO3-) (diamonds)

Figure 1
Metal Oxide Nanocrystals Supported on Carbon Nanotubes As Bifunctional Electrocatalysts in Reversible Alkaline Membrane Fuel Cells
Authors: Zhao Shuai , Rasimick Brian , Mustain William E , Xu Hui 
Published: February 2020

Hybrid structure of Co3O4 nanocrystals supported on carbon nanotubes (CNTs) was previously synthesized in our lab, and it exhibits excellent bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activities in alkaline media. More importantly, the hybrid nanomaterials showed great durability in a broad cycling potential range, from 0.0 V to 1.9 V (vs. RHE), which is a harsh environment that no previous hybrid structure reported has demonstrated stability in.
In this study, we further explored other types of structure using similar synthesizing procedure, but different metal precursors (forming single, binary or ternary oxide solid solution with cobalt acetate, nickel acetate, manganese acetate, iron acetate or copper acetate) and solvents to pursue better performance. Other parameters such as CNT size and post-treatment conditions were also altered to optimize the synthesis procedure.
The CNT-based hybrid electro-catalysts were made into membrane electrode assemblies (MEAs) to be tested in reversible alkaline fuel cells. The MEA fabrication was optimized in aspects of: catalyst ink preparation (by tuning the ionomer type, ionomer/catalyst ratio, and sonication length), membrane selection (alkaline membrane types, pre- and post- activation), catalyst-coated membrane fabrication (painting, spraying, hot pressing condition) and cell assembly. The MEAs were then tested in fuel cell mode and electrolyzer mode intermittently. MEA structural characterizations were carried out before and after these tests to study catalyst degradation mechanisms.
This work may provide perspectives for bifunctional catalyst synthesis and MEA design for reversible alkaline fuel cells.

Acknowledgement:The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.
Platinum Based Catalysts for Direct Alcolhol Oxidation and Oxygen Reduction Reaction
Authors: Man Tran Van 
Published: February 2020

In this study, we report about the activity of different catalysts based on nanoplatinum and/or platinum alloys and nanocarbons for alcolhol oxidation.
Firstly, we introduce about the synthesis of nanocatalysts by reduction in aqueous solution using NaBH4 and Ethylene Glycol as reductant. Then we present the synthesis of thin films of Platinum and bimetallic platinum-ruthenium on carbon paper and fluorine-doped tin oxide coated glass (FTO) by electrostatic spray deposition (ESD). The alcolhol electro-oxidation in acidic and alkaline media were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Oxygen reduction reaction was investigeted using a rotating disk electrode and the three-electrode cell operating MetrOhm AutoLab-302N. Compared to Pt, the bimetallic catalysts displayed an enhanced activity toward alcolhol electro-oxidation reaction and some for oxygen reduction reaction. The beneficially effect of combination Ru with Pt was also found to be influenced by the nature of metallic precursors and substrates used in the ESD technique.
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.
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