bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tunnel Structural Heterogeneity in MnO2 Polymorphs: Origins and Effect on Ion Transport
Authors: Yuan Yifei , Yao Wentao , Byles Bryan , He Kun , Liu Cong , Song Boao , Cheng Meng , Huang Zhennan , Amine Khalil , Pomerantseva Ekaterina , Lu Jun , Shahbazian-Yassar Reza 
Published: February 2020

The establishment of an accurate synthesis-structure-property relationship is the central scheme of materials science, which is particularly important for polymorphic materials possessing various structural forms with different properties. Manganese dioxide (MnO2) is a typical polymorphic material exhibiting various one-dimensional tunnel phases that are constructed by [MnO6] octahedra units, enabling its extensive applications in water desalination, (electro)catalysis and energy storage. Despite the long-range [MnO6] ordering confirmed by conventional diffraction tools, surprisingly, the electrochemical energy storage properties of a specific MnO2 tunnel phase still vary significantly in literature with unclear structural origins.
Here, we demonstrate the existence of tunnel heterogeneity featuring localized tunnel intergrowths within single MnO2 nanoparticles via atomically-resolved imaging. Furthermore, combining both ex situ and in situ transmission electron microscopy, the tunnel heterogeneity within one MnO2 nanoparticle is demonstrated to significantly affect the energy storage kinetics in sodium ion battery even down to sub-nanometer scale.
The origins of such tunnel structural heterogeneity in MnO2 are explored further, where a layer-to-tunnel (L-T) transition mechanism is identified to be responsible. The L-T transition is the essential step for the MnO2 layered precursors to gradually transform to tunnel polymorphs during the hydrothermal synthesis. The intermediate state during the L-T transition is successfully obtained and analyzed to extract the critical information regarding the atomic reconfiguration, compositional evolution and electronic structure change during this transition. It is found that the L-T transition is not homogeneous but rather topotactically happening from the layer edges into the body, which leads to the gradual splitting of 2D MnO2 layers into 1D nanowires possessing tunnel structure. The layers are transformed to 3×3 tunnels in multisteps via formation of intermediate tunnel phases exhibiting much larger openings. The transition starts by macroscopic layer distortion from adjacent Jahn-Teller active [Mn3+O6] octahedra, experiences Mn3+ disproportionation reaction and layer-interlayer Mn migration, expels doped Mg2+ out of the openings, and gradually builds the tunnels by reconstructing the Mn-O bonds.
Findings in this work could guide the controlled synthesis and selective size-engineering of MnO2 tunnels for specific applications in various fields. We also expect it to call for renewed attention to the controlled synthesis of homogeneous tunnel-specific phases with predictable properties, and to yield a more precise structure-property relationship in polymorphic materials.

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(Invited) Multi-Functional Flexible Physical and Chemical Sensor Sheets
Authors: Takei Kuniharu 
Published: February 2020

Mechanically flexible and stretchable devices have been attracted much attention for a next class of electronics such as flexible photovoltaics, flexible displays, and wearable electronics. In particular, multiple sensors for potential applications such as wearable healthcare devices and Internet of Things (IoT) concepts are one of the most important components for moving forward to building the flexible sensor system platform. For healthcare application, chemical information such as pH, glucose, sodium ion, and pattaisum ion levles are very important to monitor as well as physical information such as activity, skin temperature, heartbeat, and electrocardiogram (ECG) signals. Furthermore, simultaneous multiple condition monitoring including physical and chemical information is a next class of wearable devices for convienient and safe human life. To address these challenges, in this talk, flexible physical and chemical sensor sheets using mainly inorganic nanomaterials will be introduced by proposing low-cost, macroscale, and multi-functional device integrations. Especially human-interactive flexible sensors to detect human motion, health condition, and room environment information are mainly discussed. In addition to the fundamental sensor characteristics of a strain sensor, a temperature sensor, an ultraviolet sensor, a tactile pressure sensor, and a chemical sensor, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional flexible healthcare sensor sheets.
Although a lot of investigations and developments are still required for practical application as products, these studies may help to open a door for the next step of flexible electronics.
(Invited) Hybrid Nanomanufacturing of Heterostructured Wearable Devices for Self-Powered User Interface
Authors: Wu Wenzhuo 
Published: February 2020

The seamless and adaptive interactions between functional devices and their environment (e.g., the human body) are critical for advancing emerging technologies, e.g., wearable devices, consumer electronics, and human-machine interface. The state-of-the-art technologies, however, require a complex integration of heterogeneous components to interface the environmental, mechanical stimulus, which is ubiquitous and abundant in the above applications. These limitations have severely hampered the advancement and broader utilization of related technologies. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes.
In this talk, I will discuss our recent progress in developing self-powered human-integrated nanodevices through the hybrid nanomanufacturing of heterostructured nanodevices. This new class of wearable devices are conformable to human skins and can sustainably perform self-powered, non-invasive functions, e.g., physiological monitoring and gesture recognition, by harvesting the operation power from the human body. Such an operation scheme is fundamentally hinged on the polarization induced current term in Maxwell’s displacement current. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g., biomedical monitoring, consumer electronics, and intelligent robotics.
(Invited) Tunable and Efficient Hot Carrier Generation from Plasmonic Au-Pd Nanoalloy Photocatalyst
Authors: Stofela Sara K.F. , Kizilkaya Orhan , Taheri Mohammad , Leite Tiago R , Shelton William A , Baxter Jason B , Sprunger Phillip T , McPeak Kevin Michael 
Published: February 2020

Noble metals are the most studied plasmonic materials due to their chemical stability, small ohmic losses and high DC conductivity. However, the majority of electronic states in the valence band of these metals require at least 2 eV to excite. Therefore, even Au, which is often used for near-infrared hot carrier applications, has a band structure that is not ideal for this low energy wavelength regime. One possible route to improving the efficiency of hot carrier generation in noble metals at near-infrared wavelengths, is to shift their electronic density of states (EDOS) closer to the Fermi level via alloying with a transition metal.
Here, we present the tuning of optical and electronic properties of co-evaporated Au-Pd alloy thin films at different compositions by taking ultraviolet photoelectron spectroscopy (UPS) measurements to represent the EDOS, ellipsometry measurements to show the modulated dielectric function and the calculated plasmonic quality factors, and infrared-pump/THz-probe spectroscopy measurements for studying the dynamics of the hot carrier generation in the near-infrared regime. For comparison, calculated EDOS and hot carrier distributions for these alloys are also shown. Furthermore, we characterized the alloy thin film structural properties by grazing incidence x-ray diffraction (GIXRD).
Our GIRXD results show that all Au-Pd alloy thin films are true alloys (single phase). UPS data supports our initial hypothesis that adding Pd to Au considerably increases the EDOS in the near-infrared region. The calculated hot carrier distribution show that adding Pd to Au increases the number of carriers generated, and that the Au-Pd alloys thin films generate hotter holes than electrons. Finally, time-dependent changes in ∆E/E from 1550 nm-pump/ THz-probe spectroscopy illustrate that for Pd and Au-Pd alloys there is a change in the conductivity attributed to contributions arising from both thermal and nonthermal electron distribution, while for Au there is no evidence of transitions under 1550 nm pump-excitation. We hypothesize this is due to a lower generation rate of hot carriers in Au than for Pd and Au-Pd alloys in the near-infrared regime.
(Invited) Toward Highly Efficient Solar Water Splitting: A Concurrent Electrical, Optical, and Catalytic Design
Authors: He Jr-Hau 
Published: February 2020

Energy crisis is a broad and complex global topic. Natural resources such as gas and oil are in limited in supply. Development towards renewable resources is one of the most important technologies in the world. Currently, photocatalytic and photoelectrochemical (PEC) water splitting devices under the irradiation of sunlight have received much attention for the production of renewable hydrogen from water. Solar energy conversion and storage through photoelectrolysis of water using semiconductors as both light absorber and energy converter to store solar energy in simple chemical bond, H2, become highly desirable approaches to solving the energy shortage challenge.
We focus on the effort to develop an efficient Si-based PEC water splitting device. We introduce the surface textured Si heterojunction PEC cell consisting of ultrathin amorphous Si/crystalline Si as efficient and robust photoelectrodes. The solar to hydrogen conversion efficiency has been improved to 13.26%, which is the highest ever reported for Si-based photocathodes. Later on, we design the cascading energy band structure in Si via doping for facilitating carrier separation and novel electrode structures for 360° light harvesting for hydrogen generation with ultrahigh current densities of 61.2 mAcm-2. The cells have been further demonstrated with excellent hydrogen production rate. In addition, our method can significantly improve the stability of Si-based solar cells in water to sustain up to 300 hr. These multifunctional designs provide the potential for the future development in the renewable energy market.
(Invited) Modeling Mechanical Behaviors and Lifetime of a Polymer Electrolyte Membrane in Fuel Cell Dynamic Operations
Authors: Hasan Morshed , Goshtasbi Alireza , Chen Jixin , Santare Michael H , Ersal Tulga 
Published: February 2020

Mechanical failure of a polymer electrolyte membrane (PEM) such as pin-hole and delamination has been identified as a major degradation source in a PEM fuel cell. The hydration/dehydration cycles of a membrane during the fuel cell operation, and the resulted mechanical stress, are in general responsible for the mechanical failures. For example, the cyclic mechanical stressor has shown a significant role in propagating a crack through the thickness of a membrane [1], although there is also the synergistic acceleration from the chemical stressor [2]. It is of interest to thoroughly investigate the mechanical behaviors of a membrane under in-situ cyclic conditions, so that alleviating strategies focusing on the fuel cell operating conditions could be developed.
We have interfaced a two-dimensional transient fuel cell transport/performance model in Comsol [3] with a viscoelastic-plastic membrane mechanical model in the fuel cell geometry [4]. Using the combined model we have studied the impacts of dynamically cycling hydration, current and voltage on a membrane [5]. Furthermore, we have developed a model-based method to predict the crack propagation rate. It is expected that the crack propagation rate could be used as a metric to differentiate various dynamic driving cycles from the mechanical durability aspect, thereby creating a pathway to a transfer function for mechanical durability. The modeling results will be validated with RH cycling data. The role of the chemical stressor will also be discussed in using this mechanical durability transfer function.

References:

[1] G, Ding, M. Santare, A. Karlsson, and A. Kusoglu, “Numerical evaluation of crack growth in polymer electrolyte fuel cell membranes based on plastically dissipated energy”, Journal of Power Sources 316, 114-123 (2016).
[2] A. Kusoglu and A. Weber, “Electrochemical/Mechanical Coupling in Ion-Conducting Soft Matter”, Journal of Physical Chemistry Letters 6, 4547−4552 (2015).
[3] A. Goshtasbi, P. Garcia-Salaberri, J. Chen, K. Talukdar, D. Sanchez, and T. Ersal, "Through-the-Membrane Transient Phenomena in PEM Fuel Cells: A Modeling Study." Journal of The Electrochemical Society, Under Review.
[4] N. Khattra, A. Karlsson, M. Santare, P. Walsh, and F. Busby “Effect of time-dependent material properties on the mechanical behavior of PFSA membranes subjected to humidity cycling”, Journal of Power Sources 214, 365-376 (2012).
[5] M. Hasan, A. Goshtasbi, J. Chen, M. Santare, and T. Ersal, "Model-Based Analysis of PFSA Membrane Mechanical Response to Relative Humidity and Load Cycling in PEM Fuel Cells." Journal of The Electrochemical Society, 165(6), F3359-F3372 (2018).
Investigation of Gas Transport Properties of PEMFC Catalyst Layers by Using a Microfluidic Device
Authors: Suzuki Takahiro , Nakata Yasuhiro , Tsushima Shohji 
Published: February 2020

Gas transport properties of catalyst layers (CLs) used in proton exchange membrane fuel cells (PEMFCs) are one of the important factors which affects cell performance. The gas transport properties are strongly affected by the porous structure of the CLs. In this study, a measurement system of gas diffusion flux through the CLs by using a microfluidic device was developed. Parallel channels were made on a Si chip by microfabrication techniques. Air and nitrogen were supplied to the two parallel channels in the device, respectively. Oxygen was transferred to a nitrogen flow channel through the CL under a rib between the two channels. Oxygen partial pressure in the nitrogen flow channel was measured at the outlet of the channel by using an optical oxygen sensor. The porous structure of the measured CLs was characterized. Effective gas diffusivity and tortuosity factor of the CLs can be calculated based on the measured gas transfer and porous structure properties.
Several types of CLs were fabricated and characterized. The thickness and overall porosity of the CLs were evaluated from scanning electron microscopy and weight measurement. Pore size distribution and effective porosity were evaluated by using nitrogen physisorption measurement. Then effective diffusivity of CLs can be calculated by measuring oxygen partial pressure at the inlet and outlet of the flow channel. The CL, which has 1.0 of ionomer to carbon ratio, was evaluated. Oxygen partial pressure at the outlet of the nitrogen flow channel decreases with flow rate as shown in Figure 1. Effective gas diffusivities obtained from each flow rate showed almost constant value. Tortuosity factor was calculated from the effective diffusivity and measured structural properties and indicated around 3. This evaluation method was applied to the CLs containing a different type of carbon materials, which show different porous structure. Adding multi-walled carbon nanotube in the CL(1) instead of carbon black resulted in an increase of effective gas diffusivity, while geometrical porosity was decreased.
Acknowledgments
A part of this work was financially supported by JSPS KAKENHI Grant Number 16K18028. This study was supported by Osaka University Nanofabrication Platform [F-18-OS-0006] in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
References

T. Suzuki, R. Hashizume and M. Hayase, J. Power Sources, 286, 109 (2015).

Figure 1
Structuring GDL’s for Improved Water Management
Authors: Csoklich Christoph , Schmidt Thomas J. , Büchi Felix N. 
Published: February 2020

In polymer electrolyte fuel cells, at high current densities, water management in gas diffusion layers (GDL) is a potentially limiting process. Liquid water present in the void space of the GDL increases the tortuosity of the gas transport path from channel to catalyst layer and thus the mass transport overvoltage increases. The concept of improving water management in GDL by mechanical structuring is already 10 years old1, though it’s potential has not been systematically assessed, and therefore not been exploited yet. This work aims at exploring the fundamental understanding of regularly perforated GDL’s (see Figure 1a/b) by a systematic performance analysis under different cell operating conditions. Figure 1c shows an exemplarily cell performance analysis for different operating conditions for Toray 060 TGPH GDL with the perforations given in Figure 1 a/b. Experiments shown are for GDL without MPL, more conditions and underlying systematics will be discussed in the presentation.
1. Gerteisen, D., Heilmann, T. and Ziegler, C. Enhancing liquid water transport by laser perforation of a GDL in a PEM fuel cell. J. Power Sources,
177, 348–354 (2008).

Figure 1
PEMFC Catalyst Testing: From RDE to GDE Setup
Authors: Arenz Matthias , Inaba Masanori , Du Jia , Zana Alessandro , Jensen Anders Westergaard , Sievers Gustav Wilhelm , Escudero-Escribano María 
Published: February 2020

The thin film-rotating disk electrode (TF-RDE) method is the standard method for screening the performance of electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). It is fast and requires only small amount of catalysts, however, the measured activity not only depends on the intrinsic catalyst properties, but also ink and catalyst film properties, respectively [1, 2]. In addition, the RDE method has an inherent limitation of low reactant mass transport, which limits the accessible reaction rates and potential ranges. This limitation makes it difficult to predict the performances of the catalysts in membrane electrode assembly (MEA) where much higher mass transport is required and higher overpotentials are applied.
Recently, we introduced a new half-cell configuration aiming to bridge the gap between the RDE method and MEA, a gas diffusion electrode (GDE) setup [3, 4] that combines the strength of TF-RDE method and at the same time alleviates its weakness (i.e. low reactant mass transport).
In the presentation, the two approaches, TF-RDE and GDE measurements are compared and their weaknesses and strengths in measureing activity and stability of PEMFC catalysts discussed. Benchmark data and best practise guidlines are given.
[1] M. Inaba et al., Journal of Visualized Experiments, 2018, e57105
[2] M. Inaba et al., Journal of Power Sources, 2017, 353, 19-27
[3] G.K.H. Wiberg et al., Review of Scientific Instruments, 2015, 86 (2), 024102

[4] M. Inaba et al., Energy & Environmental Science, 2018, 11, 988-994
Kinetic Isotope Effect of the Oxygen Reduction Reaction on Carbon-Supported Platinum Electrocatalysts
Authors: Rezaei Talarposhti Morteza , Asset Tristan , Dai Sheng , Artyushkova Kateryna , Zenyuk Iryna V. , Atanassov Plamen 
Published: February 2020

Proton exchange membrane fuel cells (PEMFC) can partially satisfy the energy need with the least anthropogenic impact on nature. However, they suffer from great costs, partly induced by their expensive catalytic material, platinum, necessary to catalyze the oxygen reduction reaction (ORR) occurring at the cathode. Hence, it becomes essential to either synthesize electrocatalysts without platinum1, or to maximize the performance of the fuel cell per unit mass of platinum2 by increasing the exposure of its active sites for the ORR.3 We studied the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) supported on several Vulcan-type carbon blacks with various physicochemical characteristics. Those materials were thoroughly investigated by various microscopic, spectroscopic and electrochemical methods, such as kinetic isotope effect (KIE) studies. KIE studies were used to assess an eventual change of the rate determining step (RDS). The rate constants of the RDS were calculated in 0.5M H2SO4 and 0.5M D2SO4 at the onset potential. The KIE values are reported in Figure 1, as a function of Scarbon/SPt,H
. Scarbon/SPt,H
corresponds to the ratio between the carbon specific surface and the platinum electrochemically active surface and acts as an indicator of the Pt NPs density onto the carbon surface. A low Scarbon/SPt,H
shows KIE = 1, which corresponds to what is commonly observed on Pt electrocatalysts for the ORR and implies that the rate determining step is proton independent.4 An identical value was observed on the commercial Pt/C (40 wt. % on Vulcan XC72R carbon, i.e. with the high density of Pt NPs), i.e. KIE = 1.11 ± 0.08. At high Scarbon/SPt,H
a KIE = ca. 1.5 is observed, hence, providing evidence for a shift from a proton independent to a proton dependent mechanism with the increase of the Scarbon/SPt,H
: the involvement of the proton in the ORR RDS is dependent on the density of Pt NPs on the electrocatalyst surface.
(1)Chen, Y.; Asset, T.; Lee, R.; Artyushkova, K.; Atanassov, P. J. Phys. Chem. C 2019, acs.jpcc.9b01480.
(2)Robson, M. H.; Serov, A.; Artyushkova, K.; Atanassov, P. Electrochim.
Acta 2013, 90, 656–665.
(3)Matanović, I.; Garzon, F. H.; Henson, N. J. J. Phys.
Chem. C 2011, 115 (21), 10640–10650.
(4)Tse, E. C. M.; Varnell, J. A.; Hoang, T. T. H.; Gewirth, A. A. J. Phys. Chem. Lett. 2016, 7 (18), 3542–3547.

Figure 1