bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability of Octahedral-Shaped Pt-Ni Nanoparticles for Electrochemical Oxygen Reduction
Authors: Kühl Stefanie , Gocyla Martin , Heyen Henner , Beermann Vera , Heggen Marc , Dunin-Borkowski Rafal E. , Strasser Peter 
Published: February 2020

In case of polymer electrolyte fuel cells (PEFCs) Platinum is still the most used catalyst for the oxygen reduction reaction (ORR) at the cathode – where PtNi alloys are the state of the art [1, 2]. Following a study by Stamenkovic et al. in 2007 [3] several groups dealt with octahedral shaped nanoparticles (NPs) during the last decade to enhance both specific and mass activity [4]. Well-defined octahedral shaped NPs can be obtained e.g. by solvothermal synthesis using DMF as solvent and reduction agent [5]. Unfortunately, such PtNi octahedra show a major disadvantage in lacking of morphological stability during electrochemical cycling [6]. In the present work, we combine the DMF-based synthesis with a thermal post-treatment as annealing step toward an improved PtNi alloy structure with higher stability. The study is primarily based on the morphological investigations by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray analysis (EDX), both ex situ as well as in situ mode, to gain insights into the structure-activity-stability relationship.
In detail, based on a previous work [7], we exposed octahedral PtNi particles (supported on carbon) to a post-treatment in hydrogen using a tubular furnace. First off all, an increased annealing temperature results in a better defined PtNi alloy – proven by XRD. Whereas after 300°C mainly octahedral NPs were present, a complete loss of shape was observed after annealing at 500°C, where nearly spherical particles resulted. Additionally, the morphological changes during heating were also observed in situ using a TEM heating nano-chip (i.e. heating in vacuum). Both annealing in hydrogen as well as in vacuum show indications for Pt diffusion to (111) facets before the octahedral shape collapsed. Indeed, a rather mild treatment in hydrogen can improve the alloy structure and, thus, lead to higher activity in ORR, whereas a complete PtNi alloying at higher temperatures is diminishing the ORR activity due to the loss of octahedral shape and, accordingly, (111) facets.

References

[1] Y. Bing et al., Chem. Soc. Rev
39 (2010) 2184-2202.
[2] H. A. Gasteiger, N. M. Marković, Science
324 (2009) 3791.
[3] V. R. Stamenkovic et al., Science
315 (2007) 493.
[4] P. Strasser, Science
349, 379-380 (2015).
[5] M. K. Carpenter et al., J. Am. Chem. Soc.
134 (2012) 8535-8542.
[6] L. Gan et al., Science
346 (6216) (2014) 1502-1506.
[7] M. Ahmadi et al., ACS Nano 7 (2013) 9195-9204.
Combined Modeling and Experimental Analysis of Direct Methanol Microscale Fuel Cells
Authors: Hollinger Adam S , Doleiden Daniel G , Argun Nazlihan O , Miller Kelly L 
Published: February 2020

With the advancement of portable technology, suitable power sources must be developed. Alternatives to standard battery technology, such as fuel cells, have shown promise; however such fuel cells are in their infancy with regards to industrial and consumer adoption [1-3]. In order for fuel cells to become a feasible alternative to traditional dry-cell alkaline and lithium-ion batteries, their performance must be optimized for their intended application via manipulation of parameters such as fuel molarity, flow rate, temperature, and electrode geometry. Here, we present a mathematical model of a microscale direct methanol fuel cell (DMFC), validated with experimental data. In the past, an iterative fabrication approach was undertaken to optimize DMFC performance, involving the fabrication and testing of many individual components to assess the effects of individual parameters. This model provides a means to automate the design process and remove the fabrication requirement.
Prior parametric studies by Thorson et al. [4] show that shorter and wider electrodes yield higher current densities, however a recent review by Goulet et al. [5] highlights the need for a combined modeling and experimental approach to evaluating electrode design in a microscale fuel cell. Here we present a mathematical model to analyze the fuel flow pattern and performance of a direct methanol microscale fuel cell as a function of electrode geometry. Localized current densities are calculated over the electrode surface to elucidate the differences between electrode geometries. In the present work, the dimensions of the fuel channel are constant (0.5 cm (L) x 1.0 cm (W) x 0.125 cm (H)), while the length and width of the catalyst deposition region are varied. The model is validated with experimental data taken as a function of electrode geometry, fuel concentration, fuel temperature, and fuel flow rate. The performance of our experimental fuel cell is consistent with our modeling studies, achieving a maximum power density greater than 25 mW/cm2 at room temperature with 1 M methanol. The model presented here, in conjunction with the supporting experimental data, expands prior parametric studies [4] to predict optimal electrode design with regard to methanol concentration, temperature, and flow rate.
[1] C.K. Dyer, Fuel Cells Bulletin, 2002 (2002) 8-9.
[2] E. Kjeang, N. Djilali, D. Sinton, Journal of Power Sources, 186 (2009) 353-369.
[3] A.S. Hollinger, P.J.A. Kenis, Journal of Power Sources, 240 (2013) 486-493.
[4] M.R. Thorson, F.R. Brushett, C.J. Timberg, P.J.A. Kenis, Journal of Power Sources, 218 (2012) 28-33.
[5] M.A. Goulet, E. Kjeang, Journal of Power Sources, 260 (2014) 186-196.

Figure 1
(Invited) Tomographic Analysis of Fuel Cell Catalyst Layers - Methods, Challenges and Validity
Authors: Thiele Simon , Vierrath Severin , Zielke Lukas 
Published: February 2020

The catalyst layer (CLs) are the central part of Polymer Electrolyte Fuel Cells. Consisting of catalyst particles, ionomer, carbon black plus numerous gases and liquid water during operation, the CL contains not less than five different phases with a plethora of mutual physical interactions. Further, all these phases have characteristic length scales in the nanometer range. Due to its nanoscale, multi-phase nature the CL bears complex physical phenomena that are very challenging to describe and understand.
The precise morphology of all phases within a CL plays a key role for reactant transport and thus performance: Platinum catalyst particles with poor connection to ion conducting, electron conducting or gas transporting phases cannot contribute to the fuel cell reaction. Also, the precise shape of the pathways of the reaction species determines their effective transport properties. Wetting or non-wetting pore wall areas influence water precipitation and therefore the generation of liquid water networks. Such networks both improve ionic transport and adulterate gas transport.
Facing the tremendous influence morphology has on PEMFC performance, cost and durability, tools to image morphology are an obvious necessity. While there is a variety of imaging methods that allow three-dimensional reconstructions, only few are able to resolve the nanostructure of CLs: x-ray tomography (Xt), focused ion beam / scanning electron microscopy tomography (FIB-SEMt) and transmission electron microscopy tomography (TEMt) [1].
Both Xt and FIB-SEMt have been proven to enable differentiating porous and solid phase within PEMFC CLs [2,3]. TEMt allows imaging with resolutions below 1 nm and can be directly used to image Platinum particles [4]. To image all important phases multiple tomographic techniques must be used. In this talk we give an overview on the latest tomographic analysis techniques for PEMFC CL reconstruction with a particular emphasis on FIB-SEMt, multi-scale imaging approaches and validity of the existing reconstruction methods.

References

[1] G. Möbus, B.J. Inkson, Materials Today 10 (2007) 18–25.
[2] C. Ziegler, S. Thiele, R. Zengerle, J. Power Sources 196 (2011) 2094–2097.
[3] W.K. Epting, J. Gelb, S. Litster, Advanced Functional Materials (2012).
[4] H. Uchida, J.M. Song, S. Suzuki, E. Nakazawa, N. Baba, M. Watanabe, The Journal of Physical Chemistry B 110 (2006) 13319–13321.
[5] S. Thiele, T. Fürstenhaupt, D. Banham, T. Hutzenlaub, V. Birss, C. Ziegler, R. Zengerle, J. Power Sources 228 (2013) 185–192.
Development of Sulfonated Poly(Arylene Ether Sulfone) Multi-Block Membranes for Low RH PEMFC Operation
Authors: Bae Byungchan , Lee Sojeong , Lee Hyejin , Shin Dongwon 
Published: February 2020

Perfluorosulfonic acid (PFSA) polymers are the most promising state-of-the-art materials as proton exchange membranes (PEM) for fuel cells, however, there are some drawbacks such as high production cost and hydrothermal stability. Aromatic membranes based on hydrocarbon polymers have been studied as alternatives. Among them, multi-block copolymers seem to be promising to compete with PFSA resulting high proton conductivity even under low RH conditions.[1, 2]
In this report, novel sulfonated poly(arylene ether sulfone)s multi-block copolymer membranes containing highly sulfonated hydrophilic blocks were synthesized.[3] Different local concentration of sulfonic acid in their hydrophilic blocks affected chemical and physical properties of the SPAES. To investigate the effects of chemical composition on their membrane properties, different hydrophilic oligomers sharing same hydrophobic blocks gave us exact comparison of effect of hydrophilic blocks. The higher concentration of sulfonic acid groups resulted in higher proton conductivity under certain relative humidity conditions than that of the state-of-the-art perfluorinated sulfonic acid membrane and showed that the well-developed phase separation of SPAES. Moreover, physical properties of theses SPAES including water behavior, humidity dependence of proton conductivity were investigated along with morphology characterizations by transmission electron microscopy (TEM) for PEMFC application. Two types of oligomers, F-terminated and OH-terminated telechelic oligomers, were synthesized by controlling the feed ratio of dihydroxyl- and difluoro-monomers. Their number of repeating unit (X and Y) was analyzed by GPC and 1H NMR. Copolymerization with F-terminated and OH-terminated telechelic oligomers via nucleophilic aromatic substitution, gave high-molecular-weight multi-block PESs. Each block length was controlled to have different values with X5Y10, X10Y10, X20Y10 and X20Y20.
The SPAES X10Y10 membrane showed highest proton conductivity than that of our previous random and block copolymers at wide range of humidity. The best balanced membrane was SPAES X10Y5 membrane with high proton conductivity and lower water uptake. Consequently, the SPAES X10Y5 membrane showed high cell performance under various conditions (510 mA/cm2, 290 mA/cm2 @ 0.6V under 80% and 50 % RH conditions at 80℃, respectively). Systematic approaches for developing alternative block SPES membrane for low RH condition will be discussed.
References

[1] H.-S. Lee, A. Roy, O. Lane, J.E. McGrath, Polymer, 49 (2008) 5387-5396.
[2] B. Bae, T. Yoda, K. Miyatake, H. Uchida, M. Watanabe, Angew. Chem. Int. Ed., 49 (2010) 317-320.
[3] S. Lee, J. Ann, H. Lee, J.-H. Kim, C.-S. Kim, T.-H. Yang, B. Bae, J. Mater. Chem. A, 3 (2015) 1833-1836.
Tensiometric, IR- and 19f-NMR Analysis of Nafion Solutions for PEMFCs and PEMELs
Authors: Schulz Anne , Luehmann Nicole , Stähler Markus , Lüke Wiebke , Lehnert Werner 
Published: February 2020

In the construction of polymer electrolyte membrane fuel cells (PEMFCs) and polymer electrolyte membrane electrolyzers (PEMELs), Nafion® (sulfonated tetrafluorethylene) is used as a membrane material and as proton conductor in the porous catalysts layers of membrane electrode assemblies (MEAs). Efficiency can be increased and costs reduced by optimizing and controlling the porous catalyst layer in MEAs. It is important to understand the polymer properties, which can be achieved by using different solutions and varying concentrations of one mixture for manufacturing the dispersion. Furthermore, the findings are of particular importance for the coating process. The efficiency of the PEMFCs and PEMELs depends on the number of active centers in the porous catalyst layer. The formation of the triple phase boundary is of great importance. This can be ensured by controlling the structural properties of the dispersion. Thereby, the static and dynamic surface tensions are analyzed. Surface tension and interfacial tension are necessary for understanding the coating process and adhesion to a transfer layer. The complex system was simplified and research on the surface properties performed with an aqueous Nafion® solution in an alcohol concentration series. Hence, the only aspect that changed was the alcohol, while the dynamic surface tension was measured with a bubble pressuretensiometer (BP100, KRÜSS GmbH). The static surface tension and interfacial surface tension were carried out with a force tensiometer (K100, KRÜSS GmbH) after Wilhelmy plate respectively the duNouy Ring method. In addition the solution was analyzed by means of IR- and 19F-NMR- spectroscopy.
It will be demonstrated in this contribution that the static and dynamic surface tensions differ significantly at lower alcohol concentrations in solution series with and without Nafion®. While at higher alcohol concentrations the static surface tension between both series is similar, the dynamic surface tension shows a different trend with varied bubble age. This can be explained by the interaction between alcohol and Nafion®. In accordance with the previous interface outcomes, the 19F-NMR- and IR- spectra are analyzed. According to the first results, it is also apparent that there are interactions between Nafion® and alcohol. The application of these methods provides an understanding of the interaction between the molecules in the catalyst dispersions. This information is essential for understanding the interactions between the components of catalyst dispersion during electrode manufacturing.
Conductive Si-B-C Ceramics As Durable Catalyst Supports
Authors: Smith Graham , Jackson Colleen , Kramer Denis , Levecque Pieter 
Published: February 2020

Long recognised as key to the reduction of precious metal loading in PEMFC is the use of small catalyst nanoparticles (c.a. 3nm) stabilised by supporting them on high surface area carbon. However, PEMFCs using this technology achieve only 50% of the lifetime required by the US DOE’s target [1] with the oxidation of carbon supports a major lifetime limitation [2]. We have previously reported that catalysts on composite boron carbide, graphite supports show an increased durability to potential cycling below 1V and remarkably high ORR specific activities, 85% higher than commercial Pt/C [3]. Despite their excellent performance at low potentials, the presence of carbon in these catalysts still limits their durability during cycling to high potentials.
We will present our latest work on catalyst supports in the Si-B-C system with the focus on eliminating carbon. Hybrid DFT/HF calculations were used to highlight boron doped boron carbide and boron doped silicon carbide as ceramics with intrinsic conductivity [Figure 1a]. To synthesise these doped ceramics with high purity, low temperature synthetic routes based on the carbo-thermal reduction of polymers were developed. These routes gave carbides with low levels of carbon impurities and provided control over the morphology of the support. This allowed the creation of high surface area supports on which platinum nanoparticles have been deposited [Figure 1b]. Electrochemical characterisation (ORR activity, accelerated degradation, etc) of the produced catalysts will also be presented.
[1] Fuel Cell Technical Team Roadmap, 2013, US DOE
[2] E. Antolini, and E. R. Gonzalez. Solid State Ionics, 2009, 180.9, 746
[3] C. Jackson et al. 18th Topical ISE Meeting 2016. [Manuscript in preparation]

Figure 1
Evaluation of La3Ta0.5Ga5.3Al0.2O14 and Sr3NbGa3Si2O14 Piezoelectric Crystals on Scintillation Properties
Authors: Yanagida Takayuki , Fujimoto Yutaka , Futami Yoshisuke , Okada Go , Kawaguchi Noriaki 
Published: February 2020

Piezoelectric materials are one of the functional materials which convert the energy of stress to electric energy and widely used for sensors. Up to now, many materials were investigated for this application. Among them, LTGA (La3Ta0.5Ga5.3Al0.2O14) and SNGS (Sr3NbGa3Si2O14) single crystals have langasite type structures and they are famous for their piezoelectric characteristics even in high temperature more than 1,000 degrees [1]. Recently, we studied optical properties such as photoluminescence (PL) and radioluminescence (RL, scintillation in other words) of other langasite crystals including Ca3NbGa3Si2O14 (CNGS), La3Ga5SiO14 (LGS), La3Nb0.5Ga5.3Al0.2O14 (LNGA), and LTGA [2, 3]. In previous studies, we found that these langasite crystals exhibited quite interesting feature of very fast sub-ns decay time in visible wavelength and detectable scintillation signal [2, 3]. Therefore it was proved that langasite crystals can be potentially applicable for scintillator applications.
In this work, optical and scintillation properties of Sr3NbGa3Si2O14 (SNGS) single crystal were evaluated for the first time, and compared with those properties of La3Ta0.5Ga5.3Al0.2O14 (LTGA) which was previously reported. Although these materials are a type of piezoelectric materials, significant optical and scintillation properties were observed. SNGS showed ~80% optical transmittance in wavelength longer than 250 nm. Under 250 nm excitation, strong photoluminescence appeared at 400 nm with a primary decay time of 1.4 ns. In X-ray induced radioluminescence spectrum, intense emission peak at 400 nm was observed and primary scintillation decay time resulted ~ 1.37 ms. Finally, the absolute scintillation light yield of SNGS turned out to be 850 photons/MeV under 137Cs 662 keV gamma-ray excitation and it was largely brighter than LTGA.
[1] I.H. Jung, K.H.Auh, Mater. Lett., 51 (2001) 129.
[2] Y. Futami, T. Yanagida, Y. Fujimoto, V. Jary, J. Pejchal, Y. Yokota, M. Kikuchi, M. Nikl, A. Yoshikawa: Opt. Mater., 34 (2012) 1513.
[3] Y. Futami, Y.Yokota, M. Sato, T. Yanagida, N. Kawaguchi, Y. Fujimoto, K. Tota, K. Onodera, A.Yoshikawa, J. Cryst. Growth, 352 (2012) 129.
(Invited) Efficient Phosphor Materials: The Fundamental Physics
Authors: Happek Uwe 
Published: February 2020

The advent of solid state lighting has resulted in great achievements in the development and refinement of phosphor materials during the last two decades. While novel phosphors are developed at a rapid pace even today (often driven by patent constraints or production cost demands), we have come to a point where we can, with the advantage of hindsight, have a close look at the requirements for an efficient phosphor.
An overview of the underlying solid state physics will be given, and this physics will be applied to explain, in a number of examples, the advantages of efficient phosphors and the shortcomings of inferior ones.
(Invited) X-Ray-Induced Changes in Spectroscopic Properties of LuPO4:Eu and LuPO4:Sm Ceramic Phosphors
Authors: Zych Eugeniusz , Zeler Justyna , Meijerink Andries 
Published: February 2020

Rare earth (RE)-activated orthophosphates were thoroughly investigated for their luminescent properties years ago. However, it is only recently as the singly-activated LuPO4:Eu was reported to show efficient thermoluminescence when exposed to ionizing radiation. In this presentation we shall compare and discuss X-ray induced profound changes in spectroscopic properties of the two high-temperature sintered ceramics: LuPO4:Eu and LuPO4:Sm.
After exposure to ionizing radiation, both Eu- and Sm-activated LuPO4 ceramics show an efficient orange-red thermoluminescence (TL) with a maximum signal around 200°C and covering ~130-280 °C range of temperatures (see Fig. 1). The mechanism of the energy storage involves the Eu3+→Eu2+ or Sm3+→Sm2+ transformation due to trapping an electron from the conduction band. Spectroscopic effects related to the generation of Eu2+ or Sm2+will be presented and compared for both compositions.
Fig. 1. Temerature- and wavelength-resolved thermoluminescence of LuPO4:Eu and LuPO4:Sm sintered ceramics.

Figure 1
New Red-Emitting Boronitrides: Ca3(BN2)2:Eu2+ and Sr3(BN2)2:Eu2+
Authors: Dierkes Tobias , Juestel Thomas 
Published: February 2020

The first boronitrides of this relatively new class of materials have been reported as early as the 1960ties by Gobeau and Anselment [1]. In the meantime, due to their versatile chemistry a wide variety of very different materials has been reported, including boronitrides of alkali metals, alkaline earth metals, and lanthanides [2-4]. These materials have been investigated thoroughly with respect to their magnetic and electronic properties. For instance, La2Ni2(BN2)2N exhibits supra conductivity.
The potential of boronitrides for luminescent applications, i.e phosphors in phosphor-converted light emitting diodes (pc-LEDs) on the other hand has almost not been researched at all, up to now [5-8]. The title compounds Ca3(BN2)2 and Sr3(BN2) doped by divalent europium exhibit luminescence in the red spectral range, when excited by near-uv radiation. In the present study we provide the first comprehensive investigation of the luminescence of the aforementioned materials. This includes excitation, emission and reflection spectra as well as measurements of the decay constants.

References

[1] J. Gobeau and W. Anselment, Z. Anorg. Allg. Chem. 310 (1961) 248-260
[2] C. Koz, S. Acar, Y. Prots, P. Höhn and M. Somer, Z. Anorg. Allg. Chem. 640 (2) (2014) 279-285
[3] S. A. Kulinich, L. G. Sevast’yanova, G. N. Bondarenko and K. P. Burdina, Russ. J. Gen. Chem. 69 (4) (1999) 530-533
[4] B. Blaschkowski, H. Jing and H.-J. Meyer, Angew. Chem. Int. Ed. 41 (2002) 3322-3336
[5] Y. Q. Li, C. M. Fang, Y. Fang, A. C. A. Delsing, G. de With and H. T. Hintzen, J. Solid State Chem. 182 (2009) 3299-3304
[6] J. Schölch, T. Dierkes, D. Enseling, M. Ströbele, T. Jüstel and H.-J. Meyer, Z. Anorg. Allg. Chem. 641 (5) (2015) 803-808
[7] M. Ströbele, K. Dolabdjian, D. Enseling, D. Dutczak, B. Mihailova, T. Jüstel and H.-J. Meyer, Eur. J. Inorg. Chem. 10 (2015) 1716-1725
[8] Q. Long, C. Wang, J. Ding, Y. Li, Q. Wua and Y. Wang, Dalton Trans. 44 (32) (2015) 14507-14513

Figure 1