bluuebunny/crossref_metadata_2025_split huggingface dataset:
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
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.
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).