bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Rare-Earth Doping on Structural and Luminescent Properties of Screen-Printed ZnO Films
Authors: Khomenkova L. , Kushnirenko V.I. , Osipyonok N.M. , Singaevsky A.F. , Pekar G.S. , Avramenko K. , Strelchuk V.V. , Borkovska L.V. 
Published: February 2020

Over the past decades, zinc oxide has attracted considerable attention for its possible application in optoelectronics due to simultaneous observation of intense ultraviolet and visible emission offering the development of white light-emitting devices. However, in the most cases the native defects responsible for visible emission are not stable upon materials processing. Moreover, for white phosphors, efficient and controllable emission in specific spectral range is often required. This can be achieved in particular via materials doping with rare-earth (RE) ions.
In the present study the results on effect of doping of screen-printed ZnO films with Sm3+ and/or Ho3+ions are presented. Photoluminescence (PL) and Raman scattering spectra as well as the X-ray diffraction patterns of undoped and doped films are examined in details versus sintering conditions and doping level.
In the PL spectra of undoped ZnO films sintered at 400−700°C, the excitonic emission was observed only, whereas sintering at higher temperatures (up to 1200°C) resulted in the appearance of visible defect-related PL bands peaked at 540−600 nm. The most intensive defect-related emission was found in the films sintered at 1000°C and these latter were doped with rare-earth ions of different concentration in the range of 1·1019− 4·1020 cm-3.
In the PL spectra of the RE-doped films, the corresponding RE emission was observed at low temperatures, but not at room temperature. Since the defect-related PL band caused by intrinsic defects in ZnO overlapped essentially with corresponding Ho and Sm PL bands, the PL bands peaked at about 700 nm due to 4G5/2→6H11/2
transitions in Sm3+ ions were observed only. At the same time, simultaneous codoping with both Sm3+ and Ho3+ ions produced significant decrease in the intensity of the UV and visible defect-related PL bands as well as the increase in the intensity of Sm3+ and Ho3+ PL components. In the PL excitation spectra of the PL band peaked at about 720 nm in addition to excitation caused by ZnO band-to-band absorption and absorption involving intrinsic defects of zinc oxide, a new characteristic absorption band at about 410 nm appeared. The effect of RE doping on the PL and PL excitation spectra is discussed in terms of the formation of RE ions complexes as well as energy transfer from ZnO host to RE ions.
(Invited) Critical Metrics and Fundamental Challenges for Hydrogen and Fuel Cell Technologies
Authors: Randolph Katie , Peterson David , Sutherland Erika , Rustagi Neha , Studer Sarah , Stetson Ned T , Miller Eric Lars 
Published: February 2020

Research and development investments by the US Department of Energy’s (DOE) Fuel Cell Technologies Office have contributed to significant technological advancements leading to the cost reductions witnessed in hydrogen and fuel cell technologies over the past decade. The long-anticipated rollouts of fuel-cell electric vehicles (FCEVs) by major automotive manufacturers over the next several years provide clear evidence of this progress. At this tipping point when FCEVs are just entering the market, continued cost reductions sustained by ongoing scientific advances remain critical. Consumer acceptance will hinge not only on affordable cars, but also on the widespread availability of low-cost hydrogen. In the near term, hydrogen demand for early FCEV markets can be supplied through standard reforming of natural gas and biomass feedstocks. Emerging commercial technologies based on water electrolysis can also contribute. In the DOE’s longer term vision, a significant penetration of FCEVs into transportation markets coupled with an industrial-scale supply of renewable hydrogen could help the U.S. achieve its clean-energy and environmental goals. The continued development of enabling technologies for the widespread and affordable production, delivery, storage and utilization of renewable hydrogen is essential. Materials costs as well as system-level performance and durability issues all contribute to the cost barriers in these technologies. Quantifying these barriers and tying them to specific scientific and engineering metrics provides a powerful tool toward achieving needed performance enhancements and cost reductions. In the hydrogen and fuel cell space, DOE utilizes technoeconomic analyses to quantify key materials- and system-level cost drivers over a broad technology portfolio including fuel cells, hydrogen storage and compression, and hydrogen production by electrolytic, solar-thermochemical and photoelectrochemical water splitting, among others. In these technologies, the ultimate technical and economic viability can be linked to capital and operations costs, which are in turn impacted by fundamental materials properties, including thermodynamic and kinetic limitations. As discussed in this talk, technoeconomic sensitivity studies are invaluable in linking technology-dependent cost reduction targets with specific scientific and engineering metrics and goals. They also provide vital information for establishing research priorities for addressing the key cost drivers across all hydrogen and fuel cell technologies. Opportunities to exploit research synergies among these technologies in cross-cutting functionalities such as catalysis and separations will also be discussed.
(Invited) Benchmarking Transformational Energy Technologies
Authors: James Brian David , Colella Whitney G. , Moton Jennie M. 
Published: February 2020

Discussion of emerging energy conversion technologies is often made more difficult by conflicting terminology, assumptions, and perspectives of researchers who are often in different scientific specialty areas. Furthermore, researchers tend to describe their work in terms of the physical parameters they are able to measure in the laboratory, whereas policy developers and the general public tend to speak in terms of top-level system performance and economics. Consequently, there is often less than effective communication between researchers in different specialty areas, and between researchers and public policy developers. Development of a common framework to discuss all low-carbon energy conversion technologies would facilitate the transfer of ideas and foster more rapid development.
Strategic Analysis Inc. (SA) has conducted a variety of techno-economic analyses of emerging low-carbon energy conversion technologies for the Department of Energy covering a range of hydrogen production technologies including electrolysis (Alkaline, Proton Exchange Membrane (PEM), Solid Oxide (SO)), photo-electrochemical (PEC) (electrode and slurry based systems), biological, and solar to hydrogen conversion (STCH). Additionally, SA has examined fuel cell systems (PEM, SO) and fuel-cell/electrolyzer regenerative systems. Examination of these systems grants SA an excellent vantage point to classify the similarities and differences between the systems and their corresponding performance and economic metrics. For instance, all the solar systems utilize sunlight as the primary input energy source. However, performance is typically specified using the full light spectrum energy for photovoltaic (PV) arrays , using only the photosynthetically active radiation (PAR) spectrum for bio systems, and only the energy of direct light (not diffuse) for concentrating PV arrays. Thus all three systems would report a “% efficiency”, where the performance metrics are not directly comparable.
The objective of this presentation will be to discuss the common performance and economic metrics that apply to most/all low-carbon energy conversion technologies so as to allow easy and appropriate comparisons of the technologies. An effort will be made to chart a direct path between system level performance and economic parameters that policy makers and the general public find most useful, with the laboratory and scientific metrics that researchers typically use to discuss their work. From this, researchers will have a better holistic understanding of how their particular efforts would translate into system-level performance and a heighted awareness of negative factors that might sabotage the overall economics of the system.
(Invited) Performance and Durability of Solid Oxide Cells for Energy Storage
Authors: Barnett Scott A 
Published: February 2020

The first part of this talk will discuss the application of reversible solid oxide cells (SOCs) for grid-scale energy storage, focusing on pressurized reduced-temperature cell conditions where co-electrolysis yields methane-rich fuel. A full analysis of a storage system utilizing low-resistance thin Lanthanum Gallate electrolyte cells and large-scale underground caverns for gas storage indicates that round-trip storage efficiency > 70% can be achieved, along with storage capacity and operating cost values that are comparable or better than pumped hydroelectric storage.
The second part of the talk will describe results on degradation mechanisms, important for SOC storage technologies to achieve sufficient long-term durability for economic viability. LSM-YSZ and LSCF oxygen electrodes have been studied in both dc electrolysis and reversing-current (alternating between electrolysis and fuel cell operation) modes; similar delamination mechanisms are observed in both cases, although stability is improved by current cycling. A critical current density and overpotential is observed below which degradation is too slow to measure over ~ 1000 h, but above which degradation rate increases rapidly. High efficiency storage requires SOCs characterized by low resistance at intermediate temperatures. This makes it desirable to utilize nano-scale electrodes, but these may be susceptible to degradation by particle coarsening. Accelerated life test results for impregnated oxygen electrode materials are presented and fitted using a combined electrochemical/coarsening model, and the resulting expressions are used to predict long-term performance degradation. Life test results on Ni-based fuel electrodes are also discussed.
(Invited) Engineering the Microstructure and Atomic Arrangement of Pt-Based ORR Catalyst for High Activity and Durability
Authors: Yang Jun , Xu Chunchuan , Gath Kerrie , Pietrisz Patrick , Soltis Richard , Pence Benjamin , Jagnar Mark , Sun Kai , Meng Guangnan , Sohm Evan , Jia Qingying , Mukerjee Sanjeev 
Published: February 2020

Polymer Electrolyte Membrane Fuel Cells (PEMFC) have been developed for passenger vehicle applications for several decades. The durability and activity of the Oxygen Reduction Reaction (ORR) catalysts is one of the main obstacles to be overcome to make PEMFC vehicle commercially viable. Efforts have been focused on: 1) Developing non-precious metal catalysts. 2) Reducing the Pt loading and modifying the d-band structure of Pt by forming nano-sized core-shell structures on various cores including metallic materials, oxides, carbides and borides, and/or alloying Pt with transition metals (Cr, Ni, Co, Mn, etc.). 3) Stabilizing the Pt nano-particles by growing them larger and making the particle size more uniform. 4) Atomically engineering the Pt environment by using hybrid support of conductive metal oxide and carbon. Worldwide efforts have greatly improved the durability of the ORR catalysts, extending the life time of PEM fuel cell vehicles to about 2000 hours, which is still less than half of the required commercialization target of more than 5000 hours.
Pt-based ORR catalysts still dominate in PEMFC. The main requirements for an effective ORR catalyst are low Pt loading, high activity and durability. We used a PVD based method to engineer the microstructure and atomic arrangement of Pt into a 2-D connected network on worm-shaped islands of conductive metal oxides, which are deposited on graphitic carbon. A model catalyst was first developed on flat surface graphene, and it showed much improved activity and durability. Later, this desired Pt 2-D structure and morphology was replicated onto graphitic carbon powders. In this talk, we will discuss the catalyst, its development, and structural and electrochemical characterization using RDE and in-situ single cell experiments. A mechanistic understanding for the improvement in both activity and durability will be discussed.
Preparation and Performance Study of an Unsupported Pt Catalyst for Proton Exchange Membrane Fuel Cell
Authors: Ye Licheng , Zheng Junsheng , Tian Tian , Gao Yuan , Li Ping 
Published: February 2020

As the key material of proton exchange membrane fuel cell (PEMFC), the carbon supported Pt nanoparticles are the most widely used catalyst for cathode and anode of PEMFC1. Unfortunately, the corrosion of the carbon support can lead to a decrease of catalyst performance, stability and lifetime. And then, the research on unsupported Pt catalyst is very important for the commercialization of PEMFC.
We firstly prepared PtO2 colloidal solution and an unsupported Pt catalyst was obtained by the reduction of PtO2 colloidal solution. The microstructure and morphology of samples were characterized transmission electron microscopy(TEM). The electrocatalytic performances were measured by cyclic voltammetry(CV), linear sweep voltammetry(LSV) techniques. Reaction time, temperature and pH value have significant influence on catalyst performance. The results were compared with Pt/C-JM.TEM results show that average particle size of this catalyst is 2.46 nm. After treatment at 50 oC for 1h in H2 andN2 mixture (VN2:VH2=9:1), the ECA increased to 43.15 m2·g-1. It has high oxygen reduction reaction (ORR) onset reduction potential (0.98 V).

Acknowledgments

The authors acknowledge the support from the National Natural Science Foundation of China (21006073), the Scholarship Council and the Fundamental Research Funds for the Central Universities at Tongji University.

Reference

J.S. Zheng, X.Z. Wang, Fu R, D.J. Yang, P. Li, H. Lv, J.X. Ma. Int J Hydrogen Energy 37(2012) 4639.

J.S. Zheng, X.Z. Wang, Fu R, D.J. Yang, P. Li, H. Lv, J.X. New Carbon Materials 4 (2011) 262.

Figure 1
Effects on Wetting Agents in Cationic Contamination and Mitigation in PEFCs
Authors: Park Jaehyung , Uddin Md. Aman , Ganesan Selvarani , Pasaogullari Ugur , Bonville Leonard J. 
Published: February 2020

Effects of cationic impurities on performance loss are investigated by incorporation of foreign cation into the MEA in a form of salt solution. The hydrophobic property of the gas diffusion layer (GDL) acts as a barrier for transport of aqueous contaminant solution to reach the catalyst-coated membrane (CCM). In our previous work, the role of the GDL in cationic contamination and mitigation has been studied with isopropanol (IPA) as a wetting agent of the GDL [1]. Here, we present the effect of the added 15% IPA in the cationic solution to the overall fuel cell performance by an ex-situ soak method and an in-situ injection.
As shown in Figure 1(a), MEAs were disassembled from cell and exposed to further soaking test after preconditioning process for 24 hours. Two MEAs with same configurations have been subjected to ex-situ contamination with wetting agent (cell #1) and wetting agent alone itself (cell #2). The continuous voltage drop was observed in the case of cell #1, while there was no additional performance loss during the cell operation in the cell #2. Distributed Ca2+ ion in the membrane cross section after the soaking in the 15% IPA added cationic solution was gradually moved and accumulated in the cathode side due to migration under the potential gradients, resulting in performance degradation. Figure 1(b) shows the performance loss about 80mV by the only 15% IPA solution injection in both cases of the 400mA/cm2current density and at the OCV condition due to parasitic current of IPA oxidation in the cathode leading to a mixed potential.
To analyze the effect of IPA soaking on irrecoverable performance loss during soaking, the ion exchange capacitance (IEC) values are measured for fresh CCMs, IPA soaked CCM and re-protonated CCM. In Figure 2, the IECs of reinforced membranes show remarkably different behavior in compared to non-reinforced Nafion membranes. The IEC results reveal the IPA led to a strong impact on the proton conductivity of the membrane and catalyst layers that provides an irrecoverable performance in the fuel cell.

Acknowledg
e
ments

Financial support from the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI) is greatly acknowledged.

References

[1] M. Uddin, J. Park, X. Wang, J. Qi, U. Pasaogullari, L. Bonville and T. Molter, ECS Transactions, 64 (3) 537-544 (2014)

Figure 1
Polarization Induced Changes in LSM Thin Film Electrode Composition Observed by In Operando Raman Spectroscopy and TOF-SIMS
Authors: McIntyre Melissa D. , Traulsen Marie Lund , Norrman Kion , Sanna Simone , Walker Robert A 
Published: February 2020

For decades strontium doped lanthanum manganite (LSM) electrodes have been the material of choice for cathodes in high temperature solid oxide fuel cells (SOFCs). LSM has relatively high electrical conductivity at high temperatures and has mechanical properties that are well matched to yttria stabilized zirconia (YSZ), a common electrolyte material. Recently, LSM electrodes have been employed in lower temperature (300-500 °C) electrochemical gas purification applications. Several studies have attributed the electrochemical activation of LSM electrodes to changes in the surface stoichiometry under an applied potential.1-3 The presented work explores the polarisation induced changes in LSM electrode composition by utilizing in operando Raman spectroscopy and post mortem ToF-SIMS depth profiling on LSM thin film model electrodes fabricated by pulsed laser deposition on YSZ substrates with a thin (200 nm) CGO barrier layer. Experiments were conducted on cells with 200 nm thick (La0.85Sr0.15)0.9MnO3
±δ electrodes in 10% O2 at 500°C and 700°C under various electrical polarisations (-0.5V, ±1V and -2.5V). Raman spectra recorded continuously during polarisation showed evidence of shifts in band intensities that were both reversible and dependent on the direction of the applied potential (Figure 1). The spectral changes were assigned to changes in the LSM electronic structure and specifically to changes in the relative oxide concentration in LSM’s near surface region.

Ex situ ToF-SIMS depth profiles were recorded through the LSM thin film electrodes and revealed distinct compositional changes throughout the electrodes (Figure 2). The electrode elements and impurities separated into distinct layers that were more pronounced for the stronger applied polarisations. The mechanism behind this separation into “layers” in the LSM electrode poses interesting questions about mass transfer and ion migration in conducting materials subject to electrical polarisation.
Figure 1. Representative Raman spectra collected on an LSM electrode at 700 °C with the cell open at circuit voltage (OCV) and polarised at (a) -1 V and (b) +1 V. The peaks at 440 and 600 cm-1 are signatures from the CGO and YSZ electrolyte, respectively.
Figure 2. ToF-SIMS depth profile of LSM electrode polarised at -1V at 700 °C for 2 h. Stapled lines mark layers enriched in different species.

References

1 M. Backhaus-Ricoult, K. Adib, T. St.Clair, B. Luerssen, L. Gregoratti and A. Barinov, Solid State Ionics, 2008, 179, 891.
2 M. A. Haider and S. McIntosh, J. Electrochem. Soc., 2009, 156, B1369.
3 S. P. Jiang and J. G. Love, Solid State Ionics, 2003, 158, 45.

Figure 1
(Invited) Accurate Measurement of the Water Content of Proton-Exchange Membrane Fuel Cells Using Neutron Radiography
Authors: Hussey Daniel S , Jacobson David L 
Published: February 2020

The water sorption of proton-exchange membranes (PEMs) was measured in situ using high-resolution neutron imaging in small-scale fuel cell test sections. A detailed characterization of the measurement uncertainties and corrections associated with the technique is presented. With high-resolution neutron-imaging detectors, the water distributions across N1140 and N117 Nafion membranes are resolved in vapor-sorption experiments and during fuel cell and hydrogen-pump operation and measurements are in reasonable agreement with a 1-D macrohomogeneous model. The measured in situ water content of a restricted membrane at 80 °C is shown to agree with ex situ gravimetric measurements of free-swelling membranes over a water activity range of 0.5 to 1.0 including at liquid equilibration. Schroeder’s paradox was verified by in situ water-content measurements which go from a high value at supersaturated or liquid conditions to a lower one with fully saturated vapor. At open circuit and during fuel cell operation, the measured water content indicates that the membrane is operating between the vapor- and liquid-equilibrated states.
Electrocatalytic Aziridination of Alkenes in an Undivided Cell Mediated By Iodide
Authors: Zeng Chengchu , Chen Jie 
Published: February 2020

Abstract

Efficient synthesis of aziridines is of significant importance due to their various biological activities and potential application in organic synthesis. The most popular approach to construct aziridine ring is the reaction of alkene with nitrene or its precursors. To this end, a variety of chemical protocols have been developed using chloramine-T or N-aminoheterocycles as nitrogen source in the presence of chemical oxidant. On the other hand, an electrochemical process for aziridination of alkenes with PhthNH2 was also reported in a divided cell at a controlled potential using Pt as a working electrode.
Based on our previous work, we hypothesized that the electrochemically generated oxidative state of halide species may also apply to the catalytic aziridination reaction of alkene and PhthNH2. Herein, we reported an electrochemical approach for the efficient catalytic aziridination of alkenes using iodine ion as a redox catalyst. The process is conveniently carried out at constant current in an undivided cell.