bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study on the Relaxation Process in 4H-SiC Homoepitaxy Growth
Authors: Guo Jianqiu , Yang Yu , Wu Fangzhen , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael 
Published: February 2020

BPD half loops arrays (HLAs) present in the homoepitaxial layers of 4H-SiC are responsible for introducing an increase in the forward voltage drop via the electron-hole Recombination Enhanced Dislocation Glide (REDG) and therefore are harmful to the device operation. Different sources are observed to form HLAs and interfacial dislocations (IDs) including surface, scratch, micropipe, 3C inclusion. Recent observation was made in a 100mm 4H-SiC wafer where a short edge-oriented BPD segment in the substrate was drawn towards the interface during the epitaxy growth producing screw-oriented segments intersecting the growth surface. These screw segments of BPDs subsequently glide under the mismatch stress when the critical thickness is reached. HLAs and IDs are subsequently formed. We believe that the formation of HLAs and IDs is driven by the mismatch stress brought by the doping concentration difference between the substrate and the epilayer. To verify this, we first estimate the amount of mismatch strain caused by the epi/substrate doping concentration difference according to Sasaki’s work [1]. Then Matthews-Blakeslee’s model [2, 3] is used to predict the value for critical thickness corresponded to such amount of mismatch strain. The predict value is then compared to the critical thickness that we measured via Synchrotron X-ray study and they are found to have a good agreement with each other. This indicates that mismatch strain brought by the doping concentration is sufficient for relaxation process to occur.
[1] S. Sasaki, J. Suda, and T. Kimoto, Materials Science Forum 717-720, 481 (2012).
[2] J. W. Matthews, Journal of Vacuum Science and Technology 12(1), 126 (1975).
[3] J. Matthews and A. Blakeslee, Journal of Crystal Growth 27, 118 (1974).
(Invited) Triboelectric Nanogenerators Harvesting (Bio)Mechanical Energy for Self-Powered Systems
Authors: Wang Sihong 
Published: February 2020

The fundamental science and applicable technologies for harvesting environmental energy are not only essential in realizing the self-powered systems, but also tremendously helpful in meeting the rapid-growing world-wide energy consumptions. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. The triboelectric effect is a universal phenomenon that can generate electrostatic charges from mechanical contact. Here, a new type of technology—triboelectric nanogenerators (TENGs)—has been developed to efficiently convert mechanical energy into electricity, based on the coupling of triboelectrification and electrostatic induction. In order to develop TENGs of different structural designs for harvesting various types of mechanical energies existing in the natural environment, we established three basic modes/mechanisms of TENGs that serve as the basis for most of the TENG structures: (1) vertical contact-separation mode [1]; (2) lateral sliding mode [2]; (3) freestanding-triboelectric-layer based mode [3]. All of the three modes of TENGs are shown to be effective electrical sources that are capable of generating a voltage over hundreds of volts and a power density larger than 10 W/m2, and also instantaneously driving hundreds of electronic devices (such as LEDs). Based on these fundamental modes, a number of different structural designs for harvesting different types of mechanical energy have been developed. For the storage of the electricity generated by triboelectric nanogenerators, we further developed the self-charging power unit (SCPU) by hybridizing a TENG with a flexible Li-ion-battery into as a single device, which allows a battery to be charged directly by ambient mechanical motion. This physical hybridization enables a new operation mode: the “sustainable mode”, in which the environmental mechanical energy is scavenged to charge the battery while the battery keeps driving an external load. In this mode, the demonstrated SCPU can provide a continuous and sustainable DC current at a stable voltage for as long as there is mechanical motion/agitation. It can be used to continuously drive a UV sensor for extended period of time. Thus, the SCPU can serve as an independent and sustainable power unit, which will meet the general requirement of almost any electronic device. [4] This technology has shown the potential to utilize (bio)mechanical energy to realized self-powered systems.
[1] Wang, S. H.; Lin, L.; Wang, Z. L. Nano Lett. 2012, 12, 6339-6346.
[2] Wang, S. H.; Wang, Z. L. et al.
Nano Lett. 2013, 13, 2226-2233.
[3] Wang, S. H.; Wang, Z. L. et al.
Adv. Mater. 2014, 26, 2818-2824.
[4] Wang, S. H.; Wang, Z. L. et al.
ACS Nano 2013, 7, 11263-11271.
Durability Improvements in PBI Membranes
Authors: Qian Guoqing , Fishel Kayley , Chen Xiaoming , Mao Yating , Ploehn Harry , Benicewicz Brian C 
Published: February 2020

Phosphoric acid (PA) doped polybenzimidazole membranes made by the PPA process have been the main focus of our research efforts for more than a decade.1 These membranes exhibit an excellent combination of properties including high proton conductivities, excellent fuel cell performance, and long-term durability. For both fuel cell and hydrogen pump devices, the improvement in membrane mechanical properties at high temperatures could lead to further increases in durability and lifetimes of the membranes and resulting devices. We have been particularly interested in membrane compressive creep properties and have developed test protocols which are being used to understand the compressive creep properties and develop structure-property relationships for PPA processed membranes. In this work, we have investigated PBI copolymer membranes that showed higher mechanical properties (in particular, creep resistance) than homo-para-PBI membranes, and still possessed good proton conductivities at 180˚C under anhydrous conditions. Membrane electrode assemblies were prepared and tested in single cells to demonstrate long-term durability at different current densities and low phosphoric acid leaching rates. We will also discuss recent investigations in terms of hydrogen pumping applications, which may have broad applications in both emerging energy applications and current industrial gas markets.
1. L. Xiao; H. Zhang; E. Scanlon; L.S.Ramanathan; E.-W. Choe; D. Rogers; T. Apple; B.C. Benicewicz. Chem. Materials, 2005, 17, 5328-5333.
Organic/Inorganic Composite Membrane Using a Proton-Conducting SnP2O7 Electrolyte and PFSA Polymers for Intermediate Temperature PEMFC
Authors: Lee Kwan-Soo , Kim Yu Seung , Kreller Cortney R , Wilson Mahlon S. , Mukundan Rangachary 
Published: February 2020

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C.
Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs this relies on the development of membranes that process the desired electrochemical and mechanical properties in dry (< 30% RH) hot (> 100 oC) conditions.
In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various condition. Figure 1 illustrates the conductivity of this membrane under anhydrous conditions at various temperatures. The conductivity is a strong function of the % of TPP in the composite and reach as high as 0.1 S/cm at T ≥ 250oC using ≈ 90wt % TPP.
Membrane electrode assemblies (MEA) were prepared from these membranes using either standard PEMFC Gas diffusion electrodes or Pt/C/TPP based electrodes painted into to the membrane. The performance of one of these MEAs is shown in Figure 2. A maximum power density of 300mW/cm2 (not shown) has been obtained for fuel cell operation at ≈ 250 oC and < 5 % relative humidity. While these preliminary results are promising, there are still challenges with low open circuit voltage (OCV) due to membrane porosity and high kinetic losses due to insufficient electrode morphology optimization. In this talk we will address these issues and discuss the progress made towards better performing intermediate temperature fuel cells.
[1] Nagao et al., J Electrochem Soc, 2006
[2] Nagao et al. Electrochem Solid State Lett, 2006.

Figure 1
Tomographic Analysis of Polymer Electrolyte Fuel Cell Catalyst Layers: Methods, Validity and Challenges
Authors: Thiele Simon , Vierrath Severin , Klingele Matthias , Zengerle Roland 
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.
Preparation Procedures of Pt-Decorated SnO2 Electrocatalysts on Conductive Fillers
Authors: Horiguchi Dai , Noda Zhiyun , Hayashi Akari , Sasaki Kazunari 
Published: February 2020

For polymer electrolyte fuel cells (PEFCs), the electrocatalysts with Pt nano-particles homogeneously dispersed on carbon black (Pt/C) are widely used. However, during the fuel cell start-stop cycles, the potential of the cathode can reach up to ca. 1.5V, resulting in a severe carbon corrosion. Tin oxide (SnO2) has been studied as an alternative support material because of its thermochemical stability. Takasaki et al. [1] have demonstrated negligible degradation within 60,000 cycles in a half-cell test, indicating that Pt/SnO2 electrocatalyst can exhibit an excellent voltage cycle durability. However, relatively low electrical conductivity in such semiconducting oxides often leads to poor cell performance. In the previous PEFC Symposium in Cancun, we reported higher activity of Pt/SnO2 electrocatalysts on conductive fillers acting as the backbones of the electrocatalysts [2]. We selected vapor grown carbon fibers (VGCF) and acetylene black (AB) as possible conductive fillers, and Pt/SnO2/VGCF and Pt/SnO2/AB were synthesized. Their electrochemical surface area (ECSA) was about three times as large as that of Pt/SnO2. However, they are slightly inferior to the ECSA of Pt/C. Here, we aim to improve the electrochemical activity of Pt/SnO2electrocatalysts on conductive fillers approaching that of the state-of-the-art Pt/C electrocatalyst.
First, we have reexamined the procedure for the preparation of SnO2. Previously, SnO2/VGCF and SnO2/AB were synthesized via the ammonia co-precipitation. In this process, due to heat treatment required at a high temperature (e.g. 600oC), the particles of SnO2 were agglomerated. We thus introduced a homogeneous precipitation procedure using microwaves which requires no heat treatment at a high temperature. Consequently, the BET specific surface area of SnO2becomes one order of magnitude larger.
Second, we have adjusted the loading of SnO2 for the conductive fillers. The BET specific surface area of SnO2/VGCF becomes larger with increasing SnO2 loading. However, their electrochemical activity decreased for too high SnO2 loading, due to its lower electrical conductivity. In addition, the catalytic activity was improved by heat treatment to 200 or 400oC. The details on the catalytic activity increase by optimizing SnO2loading and heat treatment temperature will be presented at the meeting.
[1] F. Takasaki et al., J. Electrochem. Soc.,
158(10) B1270 (2011).
[2] D. Horiguchi et al., ECS Trans., 64(3) 215 (2014).

Figure 1
Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction
Authors: Zhu Chengzhou , Zhou Yazhou , Fu Shaofang , Du Dan , Lin Yuehe 
Published: February 2020

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. Although great progress has been made on ORR catalysts in recent decades, the further development of PEMFCs is severely restrained by high-priced Pt in the cathode catalysts and the slow kinetics of the ORR. Control of nanostructures at the atomic level can precisely and effectively tune catalytic properties of materials, optimizing the structural and compositional effect and further enabling enhancement in both activity and durability. Besides, most electrochemical systems consist of porous electrode materials. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. Fabricating interconnected mesoporous arrays/superstructures is critical to achieve both high surface area and fast mass transfer. Under the circumstances, constructing novel 3D porous nanostructures with non- and low Pt group metal (PGM) nanocatalysts have received significant attention to further enhance ORR electrocatalytic performance.
Supercritical CO2 (sc-CO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials, consisting of active nanocarbon and nanocrystals. Herein, we developed the sc-CO2 technique to synthesize boron-doped 3D graphene and low PGM-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability toward the ORR, holding great promise for the development of PEMFCs.
Imaging Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells by X-Ray Tomographic Microscopy
Authors: Eberhardt Sebastian H. , Marone Federica , Stampanoni Marco , Büchi Felix N , Schmidt Thomas J. 
Published: February 2020

High temperature polymer electrolyte fuel cells (HT-PEFC) use phosphoric acid (PA) as the proton conducting electrolyte, which is imbibed in a polybenzimidazole (PBI) membrane. The low vapour pressure of PA allows for increased operating temperatures of up to 200°C. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels up to 3% and H2S up to 10 ppm can be achieved.1 Phosphoric acid doped PBI membranes are therefore ideal candidates for cost-efficient combined heat and power (CHP) as well as hydrogen separation, purification and pumping applications. Unlike low temperature sulfonic acid based PEFC, the electrolyte is not covalently bound to the polymer backbone of the membrane and migration of anions in the electric field can occur similar to what has been observed in phosphoric acid fuel cells (PAFC).2,3 We have recently demonstrated how X-ray tomographic microscopy (XTM) can be applied for imaging electrolyte migration in HT-PEFC under dynamic operation.4 It was shown, for the first time, that PBI based membrane systems exhibit extensive PA migration from cathode to anode under high current operation. PA flooding of the anode gas diffusion layer (GLD) and flow field channel was observed.
In this contribution, the application of synchrotron based XTM for in-operando imaging and quantification of migrated phosphoric acid in HT-PEFC will be presented. The influence of current density, temperature, membrane material (conventional m-PBI film casted5 and sol-gel based6 membranes) and phosphoric acid loading will be discussed.
[1] T. J. Schmidt and J. Baurmeister, ECS Trans., 3, 861–869 (2006).
[2] H. R. Kunz, ECS Trans., 11, 1447–1460 (2007).
[3] H. R. Kunz, Electrochem. Soc. Proc., 99-14, 191–207 (1999).
[4] S. H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F. N. Büchi, and T. J. Schmidt, J. Electrochem. Soc., 162, F310–F316 (2015).
[5] R. Savinell, E. Yeager, D. Tryk, U. Landau, J. Wainright, D. Weng, K. Lux, M. Litt, and C. Rogers, J. Elelectrochemical Soc., 141, L46–L48 (1994).
[6] L. Xiao, H. Zhang, T. Jana, E. Scanlon, R. Chen, E.-W. Choe, L. S. Ramanathan, S. Yu, and B. C. Benicewicz, Fuel Cells, 5, 287–295 (2005).
Enhanced Ir-Ru-Ox Electro-Catalysts for Oxygen Evolution in Proton Exchange Membrane Water Electrolysis
Authors: Monforte Giuseppe , Siracusano Stefania , Baglio Vincenzo , Aricò Antonino S. 
Published: February 2020

Interest in water electrolysis has recently increased with the large diffusion of renewable energy sources and the perspective to produce hydrogen with a very low environmental impact [1-2]. In this regard, hydrogen appears a promising energy carrier that can be produced by cost-effective electrolysis of water using renewable energy sources and it can be used to store energy in grid-balancing services. A challenging problem to the development of such process is the substantial energy loss associated with the oxygen evolution during electrochemical water splitting. High surface area nanostructured (2-10 nm) IrRu-oxide electro-catalysts can substantially reduce this loss allowing to achieve efficient hydrogen production. IrOx and Ir0.7Ru0.3Ox nanosized materials of similar crystallite size (mean size 5 nm) were prepared for application as oxygen evolution electro-catalysts in solid polymer membrane water electrolysers (PEMWEs). The physico-chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and X-ray-Photoelectron Spectroscopy (XPS). Particular efforts were addressed to tailor the crystallographic characteristics and the surface properties. The electrochemical properties were investigated in an electrolysis cell, based on Nafion 115 and 30% Pt/C as cathode catalyst, by using linear sweep voltammetry, electrochemical impedance spectroscopy and Tafel curves. The Ir0.7Ru0.3Ox-based electro-catalyst showed a performance of 3.2 A cm-2 at 1.85 V at 90°C which corresponds to a voltage gain of 0.1 V as compared to the IrOx catalyst at the same current density. A similar Tafel slope with a decrease of charge transfer resistance for IrRuOx compared to IrOx would indicate the same mechanism for these materials and higher intrinsic activity for the mixed oxide. The present study indicates that Ir0.7Ru0.3Oxcan be an excellent electro-catalyst for the oxygen evolution in PEM-based water electrolysis provided that structure, morphology and surface characteristics are properly tailored.

Acknowledgements

The authors acknowledge the financial support of the EU through the FCH JU Electrohypem Project. ‘‘The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2010-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement Electrohypem n 300081.’’

References

Siracusano, S.; Van Dijk, N.; Payne-Johnson, E.; Baglio, V.; Aricò, A.S.; Applied Catalysis B: Environmental,
2015, 164:488. DOI:10.1016/j.apcatb.2014.09.005

Aricò, A.S., Siracusano, S., Briguglio, N., Baglio, V., Di Blasi, A., Antonucci, V. Journal of Applied Electrochemistry,
2013, 43:107. DOI:
10.1007/s10800-012-0490-5