bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Multiscale Modeling of Transport Phenomena in Ion-Conducting Membranes and Aqueous CO2 Reduction Cells
Authors: Weber Adam Z. , Crothers Andrew Robert , Singh Meenesh , Radke Clayton J. , Bell Alexis T. 
Published: February 2020

Transport phenomena is a critical component of electrochemical engineering of energy-conversion devices including fuel cells and solar-fuel generators. In fuel cells, ion-conducting polymers, such as perflurosulfonic-acid (PFSA) membranes, typically nanophase separate into conducting and nonconducting or structural domains that arrange together on the mesoscale and result in macroscopically observable properties. To examine these interactions, a multiscale model has been developed that includes a mean-field local-density theory at the nanoscale, a physically derived resistor-network for the mesoscale that leads up to macroscale. The nanoscale includes cation and water chemical potentials to model transport in the aqueous domains including cation-polymer electrostatic interactions, solvation energy, and a concentrated-solution transport theory to model transport and account for dielectric friction induced by the strong electrostatic fields of charged polymer groups. For the mesoscale, the model accounts for transport along the segments of the mesoscale network of the aqueous domains where mass and charge are conserved at each node (i.e. branching point) of the network. The difference in ionic potential and species chemical potentials between connected network nodes are driving forces for transport. The resistance of each segment of the network is determined from the nanoscale model. The results reveal nonlinear and nonintuitive transport pathways, where the overall properties agree with experimental property measurements.
In solar-fuel generators, including CO2 reduction cells, transport phenomena play a critical, yet not fully realized, role in controlling the overall reaction rate. To understand this interplay, multiscale modeling is used to examine the reaction mechanism of CO2 reduction to CO over a planar silver catalyst. Traditional Nernst-Planck expressions for ion and gas transport are coupled to a microkinetics model, where the reaction rates and barriers for the various reaction steps are taken from DFT calculations. The modeling approach helps to resolve the reaction mechanism and demonstrates good agreement with experimental data and trends without fitting parameters.

Acknowledgements

The fuel-cell work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract DE-AC02-05CH11231. The CO2 reduction was funded under the Joint Center for Artificial Photosynthesis (JCAP), a BES Energy Innovation Hub.
Water Phenomena in PEFCs As the Origin of the Pt Loading Effect: A Comprehensive Modelling Study
Authors: Muzaffar Tasleem Ahmad , Eikerling Michael Hermann 
Published: February 2020

The highly prioritized objective of research on polymer electrolyte fuel cells is to make highly performing and stable catalyst layers with drastically reduced platinum loading. Achieving this objective demands an understanding of the impact of composition and porous structure of the electrode layers on the water balance in the cell. Experimental studies
1-3
have shown a marked increase in the resistance to oxygen diffusion when the Pt content of the cathode catalyst layer was lowered
4
. We present a water balance model to explain these trends. Figure 1 illustrates modeling domain and processes considered. The set of 1D continuity and flux equations is formulated and solved for water distribution and fluxes in catalyst layers, diffusion media and flow fields. Model solutions reveal the impact of structure, composition, and operating conditions on the water transport phenomena and performance. Reducing the Pt loading induces a drastic shift of the balance between rates of water production and vaporization. This leads to a build-up of the liquid water pressure in catalyst layer and gas diffusion layer on the cathode side that raises the liquid water accumulation and thereby drastically diminishes the effective oxygen diffusivity. Our model unravels the fine details of this interplay and it helps identify strategies for minimizing the Pt loading without running into this water trap

References:

[1] A. Kongkanand et al., ACS Catal., 6, 1578-1583, (2016)
[2] J. Owejan et al. J. Electrochem. Soc. 160, F824-F833, (2013)
[3] M. Wilson, J. Electrochem. Soc., 139. L28-L39, (1992)
[4] T. Muzaffar et al., “Advanced Energy Materials”,
in Review

Figure 1
Influence of Size and Current Density on the Optoelectrical Properties of Green III-Nitride Micro-Light-Emitting Diodes
Authors: Kim Dae-Hyun , Seong Tae-Yeon 
Published: February 2020

High efficiency III-nitride light-emitting diodes (LEDs) have been applied to solid-state lighting. A luminous efficacy (about 150 lm/W) of InGaN/GaN-based LEDs is much higher than those of other self-emissive devices such as organic LEDs (OLEDs). As mobile electronics scale down, display technologies must also move to smaller form factors and ultra-high resolutions while maintaining high efficiencies to extend battery lifetime. III-nitride LEDs are an ideal candidate for achieving these goals. Current technologies including liquid crystal displays (LCDs) and organic light emitting diode (OLED) suffer from low efficiencies and brightness. For the realization of ultrahigh resolutions, around 10 μm or smaller light-emitting pixel sizes are required. In this regard, the InGaN/GaN μLED-based displays have emerged as a promising technology in terms of high brightness, contrast, luminous efficacies, resolution, compactness, operation under harsh conditions, and long lifetime, which cannot be satisfied by conventional LCD and OLED-based display technologies. Several groups have fabricated single-color μLED-based arrays with pixel dimensions as small as 12 μm. This self-emissive technology can be used in applications where high resolution, brightness, and efficiency are necessary such as smartphones, smartwatches, head-mounted and near-eye displays. In addition, μLEDs have exhibited improved thermal management, enhanced light extraction, and operation at higher current densities over their broad-area counterparts. Despite these benefits, surface recombination at small dimensions has been noted as a potential source for reducing device efficiencies.
We have investigated the effect of chip size on the forward voltage, light output, emission image and spectral shift of InGaN based green LEDs (518 nm) as a function of current density. The size of the chips was varied from 10 to 100 μm. The smaller chips exhibited higher light output power although the lower output powers were obtained at the higher current densities. Furthermore, the smallest devices showed the better current spreading at higher current densities. It was observed that green μLEDs underwent spectral shift more pronouncedly when dc drive current increased than when chip size increased. It was observed that variation of dc drive current more pronouncedly affected the spectral shift of green μLEDs compared with change of chip size. The relation between the electroluminescence characteristics and current density of different-size devices exhibited that the devices experienced more dominantly blue shift than red shift. However, at the same current density, the peak of the devices was not shifted when the device size changed. Dependence of size and current density on the spectral shift of green μLEDs will be described and discussed in terms of band-filling and stress relaxation effects.
(Invited) High Al-Content AlGaN for Power Electronics: A Fabrication Perspective
Authors: Douglas Erica A. , Klein Brianna , Allerman Andrew A. , Armstrong Andrew M. , Kaplar Robert J. , Baca Albert G. , Neely Jason C. 
Published: February 2020

Wide bandgap materials, such as GaN and SiC, have been rapidly maturing for use in power electronic applications. Recently, there has been a push to investigate materials with ultra-wide bandgaps (Eg > 3.4eV), such as Ga2O3 and AlGaN, in an attempt to achieve higher critical electric field, as it scales with the bandgap to the >2 power. Increasing the Al-content of AlGaN has been pursued for several applications, including both power electronics and UV optoelectronics, as the bandgap, and thus critical electric field, of the material increases with increasing Al-content. Though decades have been spent maturing GaN and low Al-content AlGaN for power, RF, and optoelectronic applications, the path for fabricating devices utilizing Al-rich AlGaN is not as straightforward as one may hope.
An overview of Sandia National Laboratories’ device development with Al-rich AlGaN will be presented. In addition, this talk will report on the intricacies faced during fabrication of Al-rich AlGaN devices, including both the challenges and advancements that AlGaN can present such as the effects of Al content on dry etch characteristics (e.g. surface morphology and etch rates), effects of surface cleaning and preparation, as well as metallization schemes and characteristics for both Schottky and Ohmic contacts.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Reliability of SiC Schottky Diodes with Mo2C Electrode
Authors: Saito Daiki , Muneta Iriya , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Iwai Hiroshi , Kakushima Kuniyuki 
Published: February 2020

Abstract

High current density electrical test was performed on SiC Schottky diodes. The shift in the Schottky barrier height was suppressed by adopting Mo2C as an electrode. Physical analysis revealed an epitaxial growth of Mo2C on SiC surface, which may be the origin of the stability.

Introduction

SiC Schottky barrier diodes (SBD) are used for high efficiency power conversion circuit owing to its high breakdown voltage, low ON-resistance and fast operation speed. However, pure metal and SiC surface reacts during high temperature annealing, forming an inhomogeneous interface [1]. Therefore, there is a concern in the diode characteristics change with time. We have shown diode characteristics with high temperature stability by using Mo2C as Schottky electrodes [2]. In this report, electric characteristics of SiC-SBD with Mo or Mo2C electrode when this devices is applied current of high current density and TEM analysis of Mo2C/SiC interface with high temperature stability are reported.

Experiments

A SiC wafer used in this study is an epitaxially grown 4°-off n-type 4H-SiC (0001) with a donor concentration of 1015cm-3 on a SiC substrate. Mo or Mo2C electrodes were sputter-deposited and patterned by reactive ion etching. The Mo and Mo2C samples were annealed in 500 or 850oC, respectively. Diode characteristics were measured before and after flowing a current density of 100A/cm2 for 500 s.

Results and discussions

The diode characteristics before and after the electrical current test are shown in fig. 1. Although increase in the Schottky barrier height was observed in both diodes, the amount of shift was suppressed with the Mo2C diode. This fact suggests that local interface reaction due to inhomogeneous current flow was suppressed. Moreover, only a slight degradation in the ideality factor was suppressed with the Mo2C electrode. Transmission electron microscope image of the diode, shown in fig. 2, revealed an epitaxial growth of a Mo2C layer on the SiC surface. The reliable diode characteristics might be originated from the sharp and uniform interface.

Conclusion

An electrical current test was performed on SiC Schottky diodes with Mo2C electrodes. A stable Schottky barrier height with a robust ideality factor was observed.
TEM analysis revealed an epitaxial growth of Mo2C on the SiC surface with a sharp and uniform interface.

References

[1] L. Kolaklieva, et al., ISBN 978-953-307-027-8, (2009) [2] T. Suzuki, et al., IEEE Electron Dev. Lett., 37, 618 (2016)

Figure 1
(Invited) Pixel-Parallel 3-D Integrated CMOS Image Sensors for Next-Generation Video Systems
Authors: Goto Masahide , Honda Yuki , Watabe Toshihisa , Hagiwara Kei , Nanba Masakazu , Iguchi Yoshinori , Saraya Takuya , Kobayashi Masaharu , Higurashi Eiji , Toshiyoshi Hiroshi , Hiramoto Toshiro 
Published: February 2020

Performances of image sensors including pixel counts, capturing speed, and dynamic range continue improving to meet the demands for high-reality video systems such as 8K/4K television and three-dimensional (3-D) imaging. Recent 3-D integration technology of silicon device has boosted sensor performances by using through-silicon vias (TSVs) and micro-bumps [1-2]. However, fully parallel signal processing has not been possible yet because the size of TSVs or micro-bumps is larger than the imaging pixel.
We have proposed a new 3-D integration technology without using TSV or micro-bumps but by using direct bonding of silicon-on-insulator (SOI) wafers, in which gold electrodes are embedded in the SiO2 intermediate layer. The gold electrodes formed by the damascene process with chemical mechanical polishing (CMP) can be reduced to 1 μm or less in diameter. This 3-D integration technology enables us to develop pixel-parallel 3-D integrated CMOS image sensors [3-5] as illustrated in Fig. 1. Two SOI wafers are stacked and directly connected by the embedded gold electrodes within every pixel. We have also developed novel in-pixel A/D converters (ADCs) with pulse frequency output, where signal charges generated in photodiodes (PDs) are converted into pulse signals at a frequency corresponding to the input illuminance. The ADC has an advantage of wide dynamic range of illuminance because the signal charge accumulated in the PD is never saturated in principle.
Prototype sensors of 128 × 96 resolution were developed with 80-μm square pixel each and 10-μm diameter gold electrodes. The upper layer was assigned for the PDs and ADCs, and the lower was for the 16-bit pulse counters. The two wafers were bonded by an image recognition of infra-red camera, where we achieved alignment accuracy as high as 1 μm or better. We evaluated the sensor and confirmed an excellent linear output with a wide dynamic range of 96 dB, which corresponds to the 16-bit output of the pulse counter. Fig. 2 shows an example image captured by the developed sensor. We successfully demonstrated the operation of the pixel-parallel sensor without any pixel defects.
In summary, a pixel-parallel 3-D integrated CMOS image sensor with pulse-frequency-output A/D converters was developed by using direct bonding of SOI wafers and embedded gold electrodes. The developed process is promising for image sensors with ultimate performances and various More-than-Moore type devices.

References

[1] T. Haruta et al., ISSCC, p. 76, 2017.
[2] T. Kondo et al., Symp. VLSI Tech. Dig., p. 90, 2015.
[3] M. Goto et al., IEEE Trans. Electron Devices, 62 (11), pp. 3530, 2015.
[4] M. Goto et al., ECS trans., 61 (6), p. 87, 2014.
[5] M. Goto et al., IEDM, 4.2, 2014.

Figure 1
Introduction to Performance Issues with Low Pt-Loaded Fuel-Cell Electrodes
Authors: Weber Adam Z. 
Published: February 2020

To commercialize successfully polymer-electrolyte fuel cells (PEFCs), the cost must be reduced. Such cost reductions come about through simplification of balance of plant, increasing cell and stack durability and lifetime, improving cell performance, and, decreasing the cost of the cell components without sacrificing performance and lifetime. Of particular importance is this latter issue, where cell developers are trying to reduce the cost of the relatively expensive platinum-group-metal (PGM) catalysts [1]. As discussed previously, it is thought that current architectures and materials reach a limit, below which unacceptable performance losses are realized as the PGM loading is decreased [2]. To understand the genesis of these limitations, one must understand the key processes that occur during PEFC operation and measure the local resistances. In this talk, performance issues with low Pt-loaded PEFC catalyst layers will be introduced and possibly ways to mitigate them discussed. This talk will serve to explore some of the relevant issues and set the stage for following, more specific talks.

Acknowledgements

This work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy.

References

[1] Fuel Cell Technologies Office Multi-Year Research, Development and Demonstration Plan, U.S. Department of Energy, 2013.
[2] A.Z. Weber and A. Kusoglu, ‘Unexplained transport resistances for
low-loaded fuel-cell catalyst layers,’ J. Materials Chemistry A, 2 (42), 17207-17211 (2014).
Identifying the Major Source of Oxygen Transport Resistance By Modeling Studies
Authors: Suzuki Takahisa , Yamada Haruhiko , Kudo Kenji , Jinnouchi Ryosuke , Morimoto Yu 
Published: February 2020

The interface between a perfluorosufonic acid ionomer like Nafion and platinum, the electrocatalyst, has been attracting more and more attention in the studies on PEFCs recently because experimental and theoretical studies have been revealing that the interface has the dominant impact on the PEFC performance in both the high and low current density regions.
This tutorial lecture reviews those studies especially focusing on the theoretical and modeling studies and suggests key areas for further improvement.
(Invited) B-Doped Pd Catalyst to Boost Formate Production in Electrochemical CO2 Reduction
Authors: Jiang Bei , Zhang Xia-Guang , Jiang Kun , Wu De-Yin , Cai Wen-Bin 
Published: February 2020

Facile interconversion between CO2 and formate/formic acid is important for energy storage and conversion and for neutral carbon emission. Boron-doped Pd catalyst (Pd-B/C), which was previously found in our group with a high CO tolerance to facilitate dehydrogenation of formic acid/formate to CO2[1-4], is now explored for electrochemical hydrogenation of CO2 with reference to Pd/C over a wide potential window [5]. Faradaic efficiency of formate (ηHCOO-) in the CO2 reduction reaction (CO2RR) reaches above 70% after 2 h of electrolysis in CO2-saturated 0.1 M KHCO3 at -0.5 V (vs RHE) on Pd-B/C, twelve times higher than that on homemade or commerical Pd/C, leading to a partial formate current of nearly 60 mA mg-1
Pd (ca. 300 mMHCOO- mg-1
Pd) without optimization of the catalyst layer and the substrate. Although the η
HCOO- decreases and the CO faradaic efficiency (η
CO) increases as potential goes more negatively, the competitive selectivity η
HCOO-/ηCO is always higher on Pd-B/C than on Pd/C at all the potentials examined. The density functional theory (DFT) calculation on energetic aspects of CO2RR on modelled Pd(111) surfaces with and without H-adsorbate confirms that B-doping in the Pd subsurface favors more the adsorption of HCOO*, an intermediate for the formic acid pathway than that of *COOH, an intermediate for the CO pathway. Our results reveal that Pd-B/C is a unique bifunctional catalyst for promoting the HCOOH « CO2 cycle [5].

Acknowledgements
：Financial support from the NSFC (grant No. 21733004 and 21473039）and the 973 Program (No. 2015CB932303) of MOST is highly appreciated

References
：

[1] J.Y. Wang, Y.Y. Kang, H. Yang, and W.B. Cai, J. Phys. Chem. C
,
113, 8366 (2009).
[2] K. Jiang, K. Xu, S.Z. Zou, and W.B. Cai, J. Am. Chem. Soc., 136, 4861 (2014).
[3] K. Jiang, J.F. Chang, H. Wang, S. Brimaud, W. Xing, R. J. Behm, and W.B. Cai , ACS Appl. Mater. Interfaces, 8, 7133(2016)
[4] J. S.Yoo, Z.-J. Zhao, J. K. Nørskov, and F. Studt, ACS Catal., 5, 6579 (2015).
[5] M.Z Wang, X.P. Qin, K. Jiang, Y. Dong, M.H. Shao, and W.B. Cai, J. Phys. Chem. C
121
, 3416(2017).
[5] B. Jiang, X.G. Zhang, K. Jiang, D.Y. Wu, W.B. Cai, to be submitted.
Catalysts for CO2 Electroreduction to Hydrocarbons and Oxygenates
Authors: Nwabara Uzoma , Verma Sumit , Gewirth Andrew A , Kenis Paul J.A. 
Published: February 2020

Rising atmospheric carbon dioxide (CO2) levels and the associated rise in global temperatures have been brought to light as major global concerns. In fact, annual atmospheric CO2 emissions have risen from about 2 Gt to 10 Gt in the last 5 decades.1 Electricity production (via fossil fuel, etc.) is a large contributor, accounting for 37% of total CO2 emissions, and therefore scientists have turned to renewable energy as a mitigation strategy.2,3 Another widely-studied approach has been to reduce CO2 to value-added chemicals and fuels (carbon monoxide, ethanol, formic acid, etc.). Previous works have aimed at increasing the feasibility of the CO2 electroreduction (CO2RR). Being able to improve and control the selectivity of CO2RR would greatly contribute to its industrial application.
Developing thermodynamically efficient and kinetically active catalysts is a key part of CO2RR. Depending on the catalyst or operating conditions, a variety of products can be formed.4 Hydrocarbons and oxygenates, such as ethanol and methanol, are attractive products because of their high-energy density and variability in application.5 For example, methanol is a feedstock for the industrially mature methanol to gasoline (MTG) process, which has a 95% thermal energy conversion efficiency.6 Although some state of the art electrocatalysts for CO2 electroreduction can produce CO and HCOOH at high selectivity (>80%) and energy efficiency (>60%), the selective production of higher hydrocarbons, especially oxygenates such as ethanol and methanol, is still lacking.7

In this talk, we will present examples of various catalysts for the selective electroreduction of CO2 to oxygenates and hydrocarbons using an alkaline flow electrolyzer at ambient conditions. These catalysts include copper supported on metal oxides (Cu/MxOy), copper-based alloys, etc. Electroanalysis results of the Cu/MxOy catalysts include selective production of C1 products (CO and methane) with traces of methanol when compared to copper nanoparticles. The copper-based alloys depict Faradaic efficiencies of up to 75% for C2 products (ethylene and ethanol).

Acknowledgement

We gratefully acknowledge financial support from I2CNER and the SURGE Fellowship for UN.

References

Hansen J., Kharecha, P., et al., PLoS One, 2013.

Oerlemans, J., Science, 2005, 308(5722), 675-677.

https://www.eia.gov Accessed 05/29/2017.

R.M. Jhong, S. Ma, P.J.A. Kenis, Curr. Opin. Chem. Eng., 2013, 2, 191-199.

Ma, M. Sadakiyo, R. Luo, M. Heima, M. Yamauchi, P.J.A. Kenis, J. Power Sources,
2016, 301, 219-228.

L. Spath, D.C. Dayton, NREL/TP-510-34929, 2003.

J. Martin, G.O. Larrazabál, J. Pérez-Ramírez. Green Chem., 2015.