bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Electrical and Structural Origin of Self-Healing Phenomena in Pentacene Thin Film Transistors
Authors: Kang Evan S. H. , Zhang Hongbin , Donner Wolfgang , von Seggern Heinz 
Published: February 2020

Despite the great potential for flexible large-area applications in organic electronics, electrical and structural instabilities have been widely regarded as an unavoidable weakness of organic semiconductors. Electronic components made of organic molecules are considered more fragile and sensitive to external conditions than their inorganic counterparts and the lifetime of them is shorter than that of conventional devices. Despite these shortcuts it is even more surprising that organic field-effect transistors (FETs) can undergo a self-healing process, i.e. their electrical characteristics can counter-intuitively improve over time, due to the unstable nature of weakly bound molecules. This remarkable phenomenon has never been understood completely.
In this work, we demonstrate that the self-healing in pentacene FETs is induced by a structural phase transformation and can be triggered by various extrinsic or intrinsic influences. We evaluate in detail the necessary conditions for electrical self-healing in pentacene FETs and reveal the structure-property relation at the heart of this phenomenon: a structural phase transformation from the metastable monolayer phase to the so called “thin film phase”. The transformation basically involves a tilt of the molecules against the surface normal near both interfaces of pentacene thin films (pentacene-dielectric and metal-pentacene) and has a profound influence on the electronic properties of pentacene FETs, which we demonstrate by way of electronic structure calculations using DFT and semi-classical transport theory. Finally, possible external triggers able to initiate the self-healing process are discussed. A case study adopting various fabrication procedures reveals that external triggers such as nitrogen gas or other organic compounds seem to be necessary to initiate the self-healing process.
Direct Determination of the Barrier Height of Au Contact on p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films
Authors: Hanada Takanori , Ohmagari Shinya , Zkria Abdelrahman , Yoshitake Tsuyoshi 
Published: February 2020

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films have a specific film structure, wherein a large number of diamond nanograins are embedded in an a-C:H matrix. The UNCD/a-C:H films possess large optical absorption coefficients of more than 106 cm–1 in the photon energy range between 3 and 6 eV. These optical features are profitable for the application of thin-film based solar cell and UV photodetectors. Although the Metal-Semiconductor-Metal (MSM) geometry is suitable for photodetection by using single-layered UNCD/a-C:H film, the property of film/metal interface hasn’t been investigated in detail. In this study, a direct determination of barrier height of metal contact on p-type UNCD/a-C:H film was performed using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). As a result, it was revealed that the down bending occurs on the film/metal interface, which indicates that depletion layer might appear on the surface of p-type UNCD/a-C:H by this structure. Whereas the surface of UNCD/a-C:H films is oxidized, that band-alignment of that does not change. It is possible that that different physical phenomena from that of single crystalline diamond occurs. There are numerous dangling bonds on the surface of UNCD/a-C:H film, therefore it is supposed that the dangling bonds have greatly affected the surface state.
Photoconduction of p-type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films in Metal-Semiconductor-Metal Geometry
Authors: Hanada Takanori , Ohmagari Shinya , Zkria Abdelrahman , Yoshitake Tsuyoshi 
Published: February 2020

Photovoltaics are representative renewable energy devices and the development of the next-generation photovoltaics have attracted considerable attentions. Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films, which possess large absorption coefficients of more than 106 cm−1 at photon energy range between 3 and 6 eV is one of the candidate materials to be employed as photovoltaic devices.
It has been theoretically predicted that additional energy states are introduced between the bandgap of diamond owing to a large amount of GBs. Here, GBs denote interfaces between UNCD grains and those between UNCD grains and an a-C:H matrix. Doped impurity atoms are preferentially incorporated into GBs. As a result, the production of p-type and n-type conduction with enhanced electrical conductivities is realized by boron (B) and nitrogen (N) doping, respectively.
Thus far, p-type UNCD/a-C:H films were deposited on n-type Si substrates, and it was confirmed that they exhibit typical rectifying behaviors. The UNCD/a-C:H films certainly act as drift layers in heterojunction diodes. Moreover, our recent studies have experimentally proved that UNCD/a-C:H can detect deep-ultraviolet (DUV) light with high external quantum efficiencies and the detectivity for 254 nm monochromatic light was enhanced at low temperatures. As for the photodetection of UNCD/a-C:H, spectral photoresponse measurements suggests that localized mid-gap states act as the generation centers of photocarriers. Although the peculiar photodetection properties might be attributable to GBs, the details were unknown.
In this study, the photovoltaic characteristics of UNCD/a-C:H films are experimentally demonstrated. The photovoltaic characteristics of UNCD/a-C:H films are discussed on the basis of photoconduction spectroscopic analysis data.
(Invited) Alkaline Water Electrolysis: Achieving High Current Densities
Authors: Carmo Marcelo , Tigges Fabian , Paciok Paul , Lüke Wiebke , Stolten Detlef 
Published: February 2020

The production of hydrogen via water electrolysis is currently recognized as the only option to store gigawatt electrical energy coming from renewable energy sources such as wind and sunlight. However, commercially available alkaline electrolyzers are still limited to low current densities (around 0.5 Acm-2), primarily due to its internal resistance losses. In order to reach the excellent current densities of acidic polymer electrolyte membrane (PEM) water electrolysis (ranging between 2 and 4 Acm-2), it is crucial to tailor electrolyte construction and cell design in order to overcome the high ohmic losses of conventional diaphragms and archaic cell designs used in alkaline electrolysis. Here, we demonstrate for the first time alkaline electrolysis achieving current densities as high as 2 A.cm-2 at 2 volts, not only well overcoming the performances of lab-scale and commercial alkaline electrolyzers, but also closely matching the performance of state-of-the-art PEM water electrolysis.
Investigation of a Correlation Between PEFC Operation Conditions and Electrocatalysts Degradation
Authors: Hayashi Akari , Kitamura Masahiko , Noda Zhiyun , Sasaki Kazunari 
Published: February 2020

One of the strategies to further increase PEFC performance is elevation of the operation temperature, reducing the reaction overvoltage of oxygen reduction reactions. On the other hand, durability of materials used in PEFC is assumed to be lowered at the higher temperature condition. In this study, understanding degradation phenomena of electrocatalysts at the higher temperature is particularly focused on in order to develop durable electrocatalysts at the elevated temperature.
MEAs were prepared using the standard catalyst and electrolyte, Pt/Ketjen black catalyst (TEC10E50E, TKK Corp.) and Nafion, respectively. Three different conditions of operation temperature and humidity (80 °C/RH100%, 105 °C/RH57%, and 80 °C/RH57%) were applied. Durability of MEAs in three conditions was studied through the potential cycles between 0.6 and 1.0 V assuming “load cycles” of FCVs.[1], [2]
Since Pt dissolution/re-precipitation is assumed to occur during the cycles, the changes in activation overvoltage and ECSA were carefully examined under three conditions. After 20000 potential cycles, activation overvoltage and ECSA increased and decreased, respectively, the most at 105 °C/RH57%. On the other hand, such degradation was much suppressed under the operation at 80 °C/RH57%. In order to understand the difference in degradation phenomena, the amount of water molecules was considered. With the presence of a large amount of water molecules, the rate of reducing ionized Pt (Pt2+) into Pt metal is assumed to be smaller. Then, in the case of 80 °C/RH57%, the amount of water molecules was smallest among three conditions, leading to fast and reversible reduction of Pt2+to Pt metal. Therefore, Pt particle growth was believed to be suppressed. However, if two factors, the amount of water and temperature, are considered, the temperature factor most likely influences more on Pt particle growth.
Reference
[1] A. Ohma et al., ECS Trans, 41 (2011) 755.
[2] M. Kitamura et al., ECS Trans, 69 (2015) 701.
Ionomer Layer Design of the Electrode Using PGM-Free Electrocatalysts for Anion Exchange Membrane Fuel Cells
Authors: Asazawa Koichiro , Takano Aoi , Nishino Eriko , Yamaguchi Susumu , Miyake Junpei , Uchida Makoto , Miyatake Kenji 
Published: February 2020

An anion exchange membrane fuel cell (AEMFC) using hydrazine hydrate liquid fuel has been investigated1 and the concept vehicle was exhibited at the 42nd and 43rdTokyo Motor Show.
For the improvement of the AEMFCs, technological breakthrough is necessary for anion exchange membranes. Especially, it is important to overcome the counteracting relationship of high ion conductance and low fuel permeability.
In addition, technology to optimize triple-phase interface formed by catalyst and ionomer is important to improve the performance.
Through many efforts to control the triple-phase interface, state-of-the-art proton exchange membrane fuel cell electrode that consists of platinum group electrocatalysts and perfluorinated ionomer has been investigated. However, the catalyst utilization is still insufficient. In addition, it is more challenging to control the triple phase interface for PGM-free electrocatalysts and anion exchange ionomers.
Our approach to develop the advanced AEMFC is using anion conductive quaternized aromatic multiblock copolymers, poly(arylene ether)s (QPEs)2as shown in Fig.1 and controling the interface and PGM-free electrocatalysts both for anode and cathode.
In this preliminary study, we focus on ionomer layer design for anode and cathode evaluated by ionomer thickness covered on the electrocatalysts. (TEM image shown in Fig.2)
MEA consisting of the QPE membranes and ionomers was fabricated with PGM-free electrocatalysts and subjected to performance evaluation. The MEA performance of direct hydrazine fuel cells will be shown and discussed in the meeting.

Figure captions

Fig. 1. Representative structure of QPEs.3

Fig. 2. TEM Image of ionomer layer (red line) on the cathode catalysts.

References

[1] K. Asazawa, K. Yamada, H. Tanaka, A. Oka, M. Taniguchi, and T. Kobayashi, Angew. Chem. Int. Ed., 46, 8024, 2007.
[2] M. Tanaka, K. Fukasawa, E. Nishino, S. Yamaguchi, K. Yamada, H. Tanaka, B. Bae, K. Miyatake, and M. Watanabe, J. Am. Chem. Soc., 133, 10646–10654, 2011
[3] R. Akiyama, N. Yokota, E. Nishino, K. Asazawa, and K. Miyatake, submitted.

Acknowledgements

This work was supported by CREST, JST.

Figure 1
(Invited) Genetic Algorithms and DFT for Accelerated Design of Nanoalloys
Authors: Jennings Paul C. , Lysgaard Steen , Tripkovic Vladimir , Hansen Heine A. , Vegge Tejs 
Published: February 2020

Binary and ternary alloys often show improved activity, selectivity or durability as electrocatalysts compared to elemental catalysts. For practical applications, nanoparticle catalysts are required to maximize utilization of precious metals such as platinum. Theoretical simulations based on density functional theory (DFT) have helped rationalize experimental observations and suggested new design directions for experimentalists.1 Commonly, theoretical studies are, however, limited to small clusters or extended surfaces under periodic boundary conditions. Although DFT simulations of nanoparticles with hundreds of atoms have become possible in recent years,2 prediction of properties such as morphology, atomic distribution and catalytic activity of nanoalloys remains a challenge.
Here, we report recent theoretical work on the global optimization of atomic distribution within nanoalloy catalysts using genetic algorithms and we predict their activity using density functional theory. We investigate the activity of Pt-Pd-Au binary and ternary alloys for the oxygen reduction reaction (ORR) and the stability of these ternary alloys under ORR conditions. Our findings suggest subsurface Pd, in binary Pt-Pd films, results in improved activity over pure Pt, while addition of small amounts of Au will hinder Pt dissolution and might also enhance activity. We study the ORR activity of 2 nm ternary Pt-Au-M Mackay icosahedral core-shell nano-particles in order to identify core elements, which increase activity and particle stability through strain and ligand effects.

Acknowledgements

Financial support from the European Commission under the FP7 Fuel Cells and Hydrogen Joint Technology Initiative grant agreement FP7-2012-JTI-FCH-325327 for the SMARTcat project is gratefully acknowledged.

References

1. I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy Environ. Sci., 2012, 5, 6744.
2. L. Li, A. H. Larsen, N. A. Romero, V. A. Morozov, C. Glinsvad, F. Abild-Pedersen, J. Greeley, K. W. Jacobsen and J. K. Nørskov, J. Phys. Chem. Lett., 2013, 4, 222–226.
(Invited) Engineering Modeling of PEM Water Electrolysis: A Survey
Authors: Bensmann Boris , Hanke-Rauschenbach Richard 
Published: February 2020

The conversion of electric energy into pressurized hydrogen by means of water electrolysis is currently discussed as promising option to handle intermittent electricity supply that occurs with the increasing use of renewable energy sources. Subsequently, this hydrogen could be (1) either reconverted into electricity, or (2) converted into other energetic molecules, such as methane (power to gas) or liquid fuels, or (3) utilized as a feed stock for the chemical industry.
Besides conventional alkaline water electrolysis, a water electrolysis technology based on a Polymer Electrolyte Membrane (PEM) is discussed since several years, which is the focus of the present contribution. The particular advantages of PEM water electrolysis are higher attainable current densities, higher voltage efficiency, and higher load flexibility. Current disadvantages include far lower technical maturity, shorter life time, and higher specific costs compared to alkaline water electrolysis.
The formulation of appropriate physico-chemical models for solid polymer electrolysis can help to contribute to the solution of the above mentioned problems. In the present contribution state of the art of modelling of solid polymer electrolyzers is summarized and discussed.
(Plenary) Electrochemical Diagnostics and Modeling in Developing the PEMFC Cathode
Authors: Kongkanand Anusorn , Yarlagadda Venkata , Garrick Taylor Reed , Moylan Thomas E , Gu Wenbin 
Published: February 2020

One key challenge to enable a wide spread adoption of proton-exchange membrane fuel cell vehicles is the reduction of Pt use to a level comparable to the incumbent internal combustion engine vehicles (<5 gPM/vehicle). Great progress in recent years in improving the activity and durability of Pt-based catalysts, particularly Pt alloy catalysts, has enabled a reduction of Pt loading in the cathode approaching 0.15 mgPt/cm2 or about 15 gPt/vehicle. However, as we attempt to go below 10-15 g/vehicle, a large performance loss is often observed at high-current density (high power).
In the cathode, where oxygen molecules meet protons and electrons to produce water, one must create as much interface as possible in order to minimize the transport resistances. As Pt loadings are reduced, performance losses due to these transport phenomena become more localized to the Pt and ionomer interface, posing new challenges to diagnose and understand these electrodes.
In this talk, we will discuss how we use in-situ electrochemical diagnostics and modeling to understand the performance of low-Pt electrodes, identify their key limiting factors, and guide our catalyst layer development. Diagnostics used to quantify the kinetic terms, proton conduction, oxygen transport resistance, and Pt-ionomer interaction will be introduced. Moreover, because non-noble metals leach out from Pt alloy catalysts and can replace protons in the ionomer, we will also consider the resulting impact on low-Pt electrode performance.
This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271.
Effect of Properties of Hydrophilic Microporous Layer (MPL) on PEFC Performance
Authors: Tanuma Toshihiro , Kawamoto Masako 
Published: February 2020

The effect of the microporous layer (MPL) on membrane electrode assemblies (MEAs) has been investigated. The performance of an MEA employing an MPL with a larger pore volume was better under 100%RH condition, which we reported in 2015 (1). Under 30%RH, no distinct relationship was found between the pore volume of the MPL and the MEA performance. However, the MEA employing an MPL with a larger median pore diameter showed higher cell voltage.

We reported that the MEA using a hydrophilic MPL showed much better performance in a wide range of pressure and humidity conditions than that using a conventional hydrophobic MPL. We applied our technique of preparing a carbon fiber dispersion to the fabrication of MPLs using carbon particles and carbon fibers with various fiber diameters. Properties of carbon materials and MPLs are shown in Table 1. The pore size distribution (Fig. 1) was measured using mercury intrusion porosimetry.
Figure 2 shows the surface SEM images of the MPLs: The MPL made of carbon black (Vulcan XC) has the smallest pore diameter (0.068 μm) and that made of carbon fiber (VGCF-H) has the largest pore diameter (0.77 μm). Although carbon fiber CF-X has the largest fiber diameter of 250 nm, the MPL made of it has the smallest pore volume. This is probably because fibers of CF-X are straight and longer than other carbon fibers, tending not to become tangled and form larger pores.

MEAs having an MPL made of four different carbon materials (Vulcan, 24PS, CF-X, and VGCF-H) were prepared, and polarization curves were measured under the conditions of 80 ºC, 30%RH. The IR free cell voltage (@0.1, 0.5, 1.0 and 2.0 A/cm2) for the four MEAs are plotted against the median pore diameter of the MPL in Fig. 3. The larger the pore diameter of the MPL, the higher the cell voltage becomes. The MEA employing an MPL made of VGCF-H, which has the largest median pore diameter, shows the best performance under the dry condition of 30%RH. This is probably because there is little liquid water in the MPL under the dry condition, and the cell voltage is largely dependent on the oxygen diffusivity of the MPL: The larger median pore diameter of the MPL, the better oxygen diffusivity and the higher the cell voltage.

References
1.　T. Tanuma and M. Kawamoto, ECS Transactions, 69, 1323 (2015).

Figure 1
Air Breathing PEM Fuel Cells in Aviation
Authors: Flade Steffen , Stephan Thomas , Thalau Oliver , Burberg Torben , Schirmer Johannes , Kallo Josef 
Published: February 2020

Aviation industry and governing bodies have set out to significantly reduce the environmental footprint of aviation. The visions brought forward request such low emissions that continuous optimization and advancement of current technology alone are not sufficient. This has led research groups to explore disruptive paths of innovation for aircraft and a trend to the electrification of onboard systems in more electric aircraft. Providing the required electric power using fuel cells and batteries not only promises the reduction of carbon emissions and noise but also allows for system level optimizations using synergy effects from a multi-functional system-integration that aircraft design could benefit from. At the same time using fuel cells in aircraft environments provides great challenges towards system design. System weight and size constraints require the use of air breathing fuel cells in commercial aircraft and airliners. This results in operation at low pressure and temperature which in term confronts the system design with two problems. First the low air density makes cooling of power systems difficult especially considering the low operating temperatures of PEM Fuel Cells. Second the low ambient temperature means the ingested air will heat up much more than during ground operation and in term will remove more water from the fuel cells, making water management and fuel cell operation strategies more important and complicated than in other applications. Also ambient conditions very rapidly change in air, adding even more complexity to the application.
Taking into consideration possibilities of advanced aerodynamic concepts like distributed propulsion and propulsion/wing vortex interaction, that electric propulsion could enable, Fuel cells could be of even larger benefit for aviation when considering a larger time-frame. All-electric aircraft could potentially be emissions-free and very low noise, thus enabling sustainable, environmentally friendly aviation. While not yet feasible for large passenger aircraft, application of such systems is currently being researched in aircraft like the HY4 enroute to this goal. This presentation will discuss the challenges of fuel cell operation in-flight, as well as introduce the concepts for multifunctional fuel cell APU replacements for A320 type aircraft and drive-trains for all-electric aircraft. Finally results from ground- and flight-testing of the all-electric fuel cell powered HY4 aircraft will be discussed.