bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress in HEXIS’ Development: Galileo 1000 N and HEXIS' Next Generation SOFC System
Authors: Mai Andreas , Fleischhauer Felix , Denzler Roland , Schuler Alexander 
Published: February 2020

HEXIS is developing and manufacturing SOFC-based micro-CHP systems for single-family or small multi-family houses. Galileo 1000 N with an output of 1 kW electrical power was brought into the market 2013. Since then, HEXIS together with other members of the Viessmann Group have been developing the next generation of the Viessmann/HEXIS SOFC system.
The paper and presentation will report on the newest results of the short-stack tests, fullscale-stack tests as well as on system tests based on the established Galileo systems as well as on Hexis’ next generation systems. These include results of Galileo tests running for more than 23’000 h, electrical efficiencies of the new generation of 40 % AC, net and total efficiencies of 95 % (LHV). An electrical efficiency of 54 % (DC) was demonstrated on fullscale-stack level with steam reforming.
The tests showed that the electrical efficiency is rather constant in the desired operation window. Degradation rates as low as approx. 0.3 % / kh, i.e. 10 mΩ cm² / kh could be shown on short-stack level over 19’000 h. As a consequence, the next generation will be operating at higher power densities, allowing a higher electrical power output at unchanged stack size. The results of tests concentrating on Redox and on-off cycles will be another topic of the contribution.
HEXIS’ next generation systems are being developed together with other group companies of the Viessmann Group leading to a new system architecture. The contribution will give a first glance into this new architecture and will show first test results obtained.
Durability of PEMFC Electrodes and Reduction of Pt Loading
Authors: Gazdzicki Pawel , Mitzel Jens , Sanchez Daniel G , Dreizler Andreas M. , Schulze Mathias , Friedrich Kaspar Andreas 
Published: February 2020

A particular challenge related to low temperature polymer electrolyte fuel cells (PEMFC) is to maintain high performance and long-term durability concurrently with the further reduction of Pt loading. These are conflicting goals because of a direct correlation of Pt surface with activity and Pt amount with durability. Moreover the lack of common procedures to reliably determine voltage loss rates leads to severe difficulties in the comparison of results obtained by different institutions or projects. Accordingly, special attention is devoted to the discrimination between irreversible and reversible voltage losses [1].
Regarding the influence of Pt loading on PEMFC performance and durability our recent rainbow stack study [2] performed in dynamic operation shows that for Pt/C based cathodes a sudden drop of performance is observed for loadings <=0.2 mgPtcm-2 and current densities >1 Acm-2. A similar threshold value is found for the increase of irreversible voltage losses which lead to a reduction of PEMFC durability for cathodes with <=0.2-0.3 mgPt/cm2 (see Fig. 1). Another durability issue at cathodic loadings <0.4 mgPt/cm2 is the acceleration of reversible degradation leading to a significant voltage drop at continuous fuel cell operation. The results show that the Pt loading of Pt/C based electrodes cannot be reduced below 0.2-0.3 mgPtcm-2 by just varying the thickness of the catalyst layers without suffering durability issue. To go below 0.2 mgPtcm-2 new electrode designs are needed. A special combination of coating techniques is also considered as promising approach to solve this issue.
The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303452 (Impact).
References:
[1] P. Gazdzicki, J. Mitzel, D. Garcia Sanchez, M. Schulze, K. A. Friedrich, J. Power Sources, 327, 85 (2016).
[2] P. Gazdzicki, J. Mitzel, A. M. Dreizler, M. Schulze, K. A. Friedrich, Fuel Cells, DOI: 10.1002/fuce.201700099

Figure 1
Surface Modification of Porous Foam Electrodes: Stabilization of Solid Electrolyte Interphase Formation in Li-Metal Batteries
Authors: Day Brian A , Gattu Bharat , Shanthi Pavithra Murugavel , Datta Moni Kanchan , Kumta Prashant N 
Published: February 2020

The formation of the solid electrolyte interphase (SEI) is critical to stabilization of lithium metal electrodes.1,2 When the electrodes contact electrolyte, a thin solid layer is immediately deposited on the surface. Ideally, this layer should be electronically insulating, while conducting Li-ions, and only a few nanometers thick to ensure that lithium can diffuse to the electrode surface without the reduction of any electrolyte components.2 Unfortunately, much research has shown that even after initial formation, the SEI layer continues to grow, and eventually leads to cell failure by limiting the ability of lithium to diffuse to the electrode surface.3,4 In order make electrodes practical for use in lithium metal batteries, the growth of the SEI needs to be well controlled and limited in thickness.
Previous work has shown that the use of high surface area porous metal anodes can prevent dendrite formation, another key barrier to commercialization of lithium metal batteries.5 However, as the number of cycles increases and the SEI layer on the electrode grows too thick, the pore network fills and lithium diffusion is limited, and plating subsequently reverts to unwanted dendritic growth.
In this work, a method for improving the cycling stability of these porous foam electrodes by controlling the SEI is examined. Accordingly, the work focuses on the utilization of novel surface additives to achieve this goal. The approach has shown to greatly increase the number of achievable cycles. The engineered systems already show ~99% efficiency over 100 cycles, far better than the 70 cycles at ~95% efficiency previously obtained using unmodified foams. By controlling the initial SEI formation and limiting its thickness, saturation of the pore network can be inhibited, thus extending the stable cycling window.

Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0007797, Edward R. Weidlein Chair Professorship funds, and the Center for Complex Engineered Multifunctional Materials (CCEMM).

References

Aurbach, E. Zinigrad, Y. Cohen, H. Teller, Solid State Ionics, 148, 405-416 (2002).

Peled, S. Menkin, J. Electrochem. Soc., 164 (7), A1703-1719 (2017).

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A. Day, P. Jampani, P. M. Shanthi, B. Gattu, P. N. Kumta. ECS 232, National Harbor Maryland (2017).
Novel Strategies to Interface Molecules and 2D Materials
Authors: Perez Emilio M 
Published: February 2020

One of the most attractive areas of research in Nanoscience is the combination of 2D materials through van der Waals forces to form heterostructures (Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H. Science 2016, 353, DOI: 10.1126/science.aac9439). Here, we present strategies beyond dispersion forces to interface 0D (molecules) and 2D materials.
We will show examples of 0D-2D heterostructures connected through covalent and noncovalent chemistry. In the first example, we will show a method to functionalize graphene covalently with exquisite atomic selectivity and yield (NanoLett. 2016, Chem. Commun. 2017). In the second example, we will show that the photoresponse of MoS2 photodetectors can be enhanced by simple and reversible supramolecular functionalization with organic dyes (Chem. Commun. 2016). We will also show the example of a naturally occurring van der Waals heterostructure, franckeite, an air stable, p-doped semiconductor with photoresponse in the far IR (Nat. Comms. 2017). Finally, we will present strategies for the self assembly of liquid-phase exfoliated 2D materials from suspension into functioning electronic devices (Chem. Commun. 2017).
(Invited) Exploitation of Nanomaterials and Interfacial Engineering in Perovskite Solar Cells
Authors: Jung Hyun Suk 
Published: February 2020

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues.
In this presentation, we introduce our recent efforts to facilitate commercialization of perovskite solar cells.1-5 For examples, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells.4 Moreover, we are going to discuss about stability issue of perovskite materials regarding charge generation and extraction.
(1) B. J. Kim, D.H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong, K. Mahmood, T. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee and H. S, Jung, Energy Environ. Sci., 2015, 8, 916.
(2) M.-C. Kim, B. J. Kim, J. Yoon, J.-W. Lee, D. Suh, N.-G. Park, M. Choi and H. S. Jung, Nanoscale , 2015, 7, 20725.
(3) S. Jang, J. Yoon, K. Ha, M.-C. Kim, D. H. Kim, S. M. Kim, S. M. Kang, S. J. Park, H. S. Jung, and M. Choi, Nano Energy, 2016, 22, 499.
(4) B. J. Kim, D. H. Kim, S. L. Kwon, S. Y. Park, Z. Li, K. Zhu and H. S. Jung, Nature Communications, 2016, 7, 11735.
(5) M.-C Kim, B. Jo Kim, D.-Y. Son, N.-G. Park, H. S. Jung, and M. Choi, Nano Lett., 2016, 16, 5756.
(Invited) Synthesis and Redox Property of Sumanenyl Trication
Authors: Sakurai Hidehiro , Ohigashi Yuya , Ikuma Naohiko , Yakiyama Yumi 
Published: February 2020

Sumanene, a bowl-shaped aromatic molecule, possesses the partial structure of C60 and shows unique structural and physical properties based on its curved pi-conjugated system. One of the characteristic features of sumanene is the presence of three benzylic carbons, which allow us to generate the corresponding cation, anion, and carbene species. Here we report the successful generateon, isolateon and redox property of sumanenyl tri-cations.
Sumanenyl tri-cations (1) were obtained in high yield by acid-triggered generateon o\from the corresponding hydroxyl-substituted sumanene derivative as a precursor. 1 reacted with the hydride donor, giving a tri-phenyl sumanene (2, 2’) and quinoidal sumanene (3’) in the presence and the absence of acid, respectively. Cyclic voltammetry revealed multi-step redox property of 1. Reductive wave at −1.28 V was observed as 2 electrons reduction without acid. In contrast, reductive wave at −1.17 V and −1.68 V were observed as 1 electron reduction with acid.

Figure 1
(Invited) Optical Phenomena in Bio-Assembled Nanostructures with Plasmonic and Excitonic Resonances
Authors: Govorov Alexander O. 
Published: February 2020

Metal nanocrystals and semiconductor quantum dots and have the ability to absorb and scatter light very efficiently. This study concerns special designs of hybrid nanostructures with electromagnetic hot spots, where the electromagnetic field becomes strongly enhanced. Overall plasmonic nanostructures with hot spots demonstrate strongly amplified optical and energy-related effects.

Using nanoparticle arrays made of different metals, one can transfer plasmonic signals coherently and with small losses [1].

Plasmonic hot spots efficiently generate energetic electrons, which can be used for photochemistry and photodetection [2,3].

Using nanostructures with hot spots, one can strongly enhance optical generation of heat and also confine high photo-temperatures in small volumes [4,5].

Colloidal nanocrystal assemblies with plasmon resonances allow us to strongly enhance chiral optical responses (circular dichroism) of biomolecules and drugs [6,7].

[1] E.-M. Roller, et al., Nature Physics 13, 761 (2017).
[2] A.O. Govorov, H. Zhang, H.V. Demir and Y. K. Gun’ko, Nano Today 9, 85 (2014).
[3] H. Harutyunyan, et al., Nature Nanotech. 10, 770 (2015).
[4] A. O. Govorov and H. Richardson, Nano Today 2, 20 (2007).
[5] C. Jack, et al., Nat. Commun. Volume:7, 10946 (2016).
[6] A. O. Govorov, et al., Nano Letters
10
, 1374–1382 (2010).
[7] A. Kuzyk, et al., Nature 483, 311 (2012).
A-Si Planarization By Inductively Coupled Plasma Etch with Advanced Process Control
Authors: Wang Yan , Zhang Dongping , Zhang Haiyang 
Published: February 2020

Since fin field effect transistors (FinFET) has been widely adopted in 16/14nm technology node and beyond, the process control becomes more and more critical. [1] A-Si thickness as well as uniformity control is rather rigorous.
In previous report, we have demonstrated the planarization of a-Si by inductively coupled plasma (ICP) with a fixed time [2]. Indeed, due to the process variation, the wafer level control of CMP cannot be too precise without specific process control. The temperature-only controlled etch amount to target thickness is limited and process window is restricted. Thus, one more etch factor need to be introduced for wider process window and more accurate control.
In this paper, a dynamic process time name as “trimming” function is simulated based on the incoming thickness and ‘trmming’ rate for better control the thickness after etching process. Trimming, namely time dependent etching, is more effective to the incoming thickness variation. In this planarization process, the process control focuses on two performances: the uniformity and the mean value. The uniformity is mainly control the “Hydra” parts, wlhich is equipped in the commercial ICP tools and can supply more than 100 temperature control units, while the mean value is mainly controlled by etching time. Our experimental results shows the temperature dependency of thickness control is -26.3Å/℃, while the trimming rate is -1.35 Å/s. Based on the experimental data, the time–dependent etching based on the input thickness is realized.
This work was partially sponsored by Shanghai Rising-Star Program(B type). The authors would like to thank Mr. Jiangang Liu, and Tongxun Guo from Lam research for the support of constructive discussion.

Reference:

[1] C. Auth et al., “A 22 nm high performance and low-power CMOS technology featuring fully-depleted tri-gate transistors, self-aligned contacts and high density MIM capacitors,” in VLSI Symp. Tech. Dig., pp. 131–132, 2012.
[2] Y. Wang et al., “Poly-Si Planarization by ICP Plasma Etch at FinFET Technology”, ECS Trans. 77(3), 71-76, 2017.
Phase Field Modeling of Eletrochemical Phenomena
Authors: Zerihun Nega Alemayehu 
Published: February 2020

Rational design of novel electrochemical energy storage systems with flexible designs, cheaper prices and more efficiency to meet the power storage needs of everything from handheld gadgets to electric cars heavily relies on the availability of advanced experimental and computational tools. One of the emerging computational tools in the discovery and design of materials is the phase field method. It is widely used for describing phase transformations and kinetics of microstructural evolution in materials sciences. One of its features is the diffuse interface, i.e. a region of space where two (or more) phases are assumed to mix. For electrochemical systems, the interface as the reacting zone plays a very important role. The diffusive nature of the electrical double layer across the electrode-electrolyte interface makes it more suitable for a description with phase field.
In this work, the phase field method is employed to study the kinetics of intercalation. The classical and the finite interface dissipation (FID) phase field methods are used. With the former, a systematic assumption of a linear temperature vs. concentration phase diagram for modeling the electrode-electrolyte coexistence is found to work well for higher partitioning coefficient. It was found that the rate constant is an exponential function of the partitioning coefficient. Moreover, it is possible to see that the activation energy required for intercalation is lower than the activation energy for de-intercalation, which is in agreement with both experiments and atomistic calculations. This work emphasizes on the non-equilibrium behavior especially at the beginning of interaction between electrode particles and electrolyte, with slow evolution of equilibrium. This was investigated using the FID model. One of its pivotal flux contributions is permeation which is caused by chemical potential difference across the interface. It is scaled by a material parameter dubbed “permeability”, which was originally estimated by the interdiffusion coefficient. A new approach to estimate this quantity for non-equilibrium electrochemistry is formulated based on the Butler-Volmer kinetics and its estimation from electrochemical measurement systems such as cyclic voltammetery and electrochemical impedance spectroscopy is shown. The simulation results on the influence of size, morphology and distribution of active particles on the kinetics of intercalation will be discussed. Furthermore, industrial exploitation of the simulation results for reverse engineering of electrode materials for high performance batteries will be described.
A Multiscale Method for Multiphase Pore-Scale Simulation of the Polymer Electrolyte Fuel Cell Catalyst Layer
Authors: Zheng Weibo , Kim Seung Hyun 
Published: February 2020

The cost and durability of polymer electrolyte fuel cells (PEFCs) are critical to their massive commercialization. To further reduce the cost of PEFCs, optimized catalyst layers (CLs) with low Pt loading and high performance are necessary. For the CL with low Pt loading, mass transport loss is a critical factor and limits the performance at high current density conditions. The micro-structure of a CL needs to be optimized to reduce the transport loss through heterogeneous porous structures and make reactants more accessible to the Pt sites. Pore-scale simulation directly computes detailed multiphysics phenomena occurring inside the heterogeneous nanoscale structure of the CL [1], thereby improving our understanding of micro-structural effects and guiding the design of an optimized CL. However, for the wide-spread use of pore-scale simulation in the design process, the computational cost needs to be reduced.
In this work, the multiscale method developed in Zheng and Kim [2] is used to accelerate multiphase pore-scale simulation, where water generation and liquid water transport processes in the CL micro-structure are explicitly computed. In the multiscale method, a physical quantity is decomposed into macroscopic and local variations. The macroscopic variations occur at the scale of the CL thickness, and are described by the volume-averaged equation as in the macroscopic method [3]. The local variations are due to the complex micro-structure of CL, and are captured by pore-scale simulation. The multiscale method is applied to the governing equations of electrolyte phase potential and gas phase oxygen concentration in the multiphase pore-scale simulation. The calculation of the electrolyte phase potential shows that the multiscale method substantially increases the convergence rate without sacrificing the accuracy. The application of the multiscale method to the oxygen concentration will be presented. The performance and computational cost of the multiscale method in simulating multiphase transport-electrochemistry coupling in the cathode CLs will be discussed.
Reference:
[1] J. Kang, K. Moriyama, S. H. Kim, An extended stochastic reconstruction method for catalyst layers in proton exchange membrane fuel cells, Journal of Power Sources 325 (2016) 752-761.
[2] W. Zheng, S. H. Kim, A multiscale approach to accelerate pore-scale simulation of porous electrodes, Journal of Power Sources 348 (2017) 21 - 29.
[3] D. M. Bernardi, M. W. Verbrugge, A mathematical model of the solid-polymer-electrolyte fuel cell, Journal of the Electrochemical Society 139 (9) (1992) 2477-2491.
Strain Engineering and Two-Dimensional Electron Gas in Polar ε-Ga2O3
Authors: Cho Sung Beom , Mishra Rohan 
Published: February 2020

As a wide gap semiconductor, Ga2O3 is rapidly emerging as a promising candidate for power electronics applications. While most of the studies have focused on its stable β-phase, there are a handful of reports on its metastable polar ε-phase having a spontaneous polarization. Numerous experimental groups have recently attempted to stabilize ε-Ga2O3 using epitaxial strain using substrates such as Al2O3(0001)1, GaN(0001)1, AlN(0001)1, MgO(111)2 and SiC(0001)3. However, due to the lack of an understanding of the stability of various Ga2O3 phases under epitaxial strain, these trial-and-error based attempts have been of limited success. All the films are observed to be of inherently poor quality. There are also diverging reports on the structure and properties of the deposited thin films. A recent experimental report of ε-Ga2O3 grown on Al2O3 substrate has even suggested the film to be ferroelectric, where the direction of the spontaneous polarization could be switched with an external electric field. It implies that the stabilization of ε-Ga2O3 will open new avenue of polarization engineering in Ga2O3 power electronics4.
We have used first-principles density-functional theory (DFT) calculations in combination with coincidence site lattice theory to develop a phase-diagram of Ga2O3 under epitaxial strain. We show that all the previously used substrates impose an epitaxial strain over 3% on ε-Ga2O3, which explains the poor structural quality of the deposited thin films. In this presentation, we will discuss promising commercially available substrates that can stabilize ε-Ga2O3 with epitaxial strain < 1 %. We will discuss the electronic structure of ε-Ga2O3 under epitaxial strain, including properties such as the band gap, polarization constants and its ferroelectric nature. We will theoretically demonstrate a way to achieve two-dimensional electron gas (2DEG) in ε-Ga2O3 heterostructure simply by using polarization engineering. The formation of 2DEG is due to the polar catastrophe, and the formation and sheet charge density 2DEG can be controlled by thickness of ε-Ga2O3 and its polarization direction. Our study highlights the potential of the polar behavior of ε-Ga2O3 and suggest pathway to realize its stabilize epitaxial growth.

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