bluuebunny/crossref_metadata_2025 huggingface dataset:
Process Parameters Effect on Deep Silicon Etching for High Density Capacitor Structure
Authors: Meng Lingkuan , Yan Jiang , Li Chunlong , Li Junjie , Hong Peizhen , Luo Jun , Li Junfeng , Zhao Chao
Published: February 2020

In deep silicon etching process, there have been many investigations on etching rate. However, only few published papers mentioned the sidewall roughness, which is a critical issue for NMES/MEMS application. In this work, we encountered a special phenomenon: sidewall damage, which was firstly observed during deep silicon etching. Various process parameters such as chamber pressure, bias power, passivation gas flow and etch time have been investigated using a conventional two steps Bosch process for high density Metal-insulator-metal (MIM) capacitor application. During the etching, obvious sidewall damage can be observed in the etched trench sidewall. It can be noted its starting depth has a close dependence on process parameters such as chamber pressure and bias power, which play a significant role influencing etching profile and trench depth. At a lower pressure, a smooth sidewall without any damage can be achieved. With pressure increasing above a certain value, sidewall damage has almost occurred in the full trench, which will lead a series of severe issues such as poor conformal deposition of high-k insulation film, discontinuity of the electrode layer, and reliability failures in MIM capacitor structure.

On the other hand, at a given pressure, bias power has a direct effect on etching profile and sidewall damage. As bias power increases, etching profile becomes more negative from vertical one. In particular, sidewall damage is not located in certain depth range but distributed in almost whole trench sidewall and, multi-bowing profile can be seen with increasing etching depth.

According to the experimental results, an etching mechanism has been presented to explain the etching phenomena by the ion angular distribution function (IADF) fundamental. Finally, by optimizing process parameters, a perfectly smooth profile without any sidewall damage can be obtained having an aspect ratio as high as 30 with 5μm width.
Monolithic Entangled Photon Sources Using Second Order Optical Nonlinearities
Authors: Helmy Amr S
Published: February 2020

Entangled photon sources play a pivotal role in most of the optical systems that utilize quantum effects. Those include quantum key distribution, quantum computing, metrology, sensing and imaging. Photon pair generation using spontaneous parametric down conversion (SPDC) is one of the most popular routes for producing entangled photons. While SPDC has become more popular, the creation of entangled photon pairs in a degree of freedom, such as polarization, is more challenging. The difficulty is related in no small part to the birefringence of the structure where the generation takes place. Birefringence results in distinguishing information that hinders the production of entanglement in the platforms where SPDC has been most popular including ferroelectric crystals.

Despite this limitation, entangled sources have been realized in bulk crystals via well designed interference techniques, which often include additional compensating optics. As the boundaries of optical quantum information science continue to be extended, multi-photon entanglement is now required. Solutions based on SPDC have been attempted, and while some outstanding results have been achieved, the interferometers and compensation procedures become increasingly complex as the size of the entangled state grows. Such scalability and stability issues are directly addressed by integrated entangled photon sources, and while still in their infancy, they promise to help a great deal towards the practical utilization and the production of entanglement on a larger scale.

Semiconductors are an ideal platform to fabricate such integrated entangled photon sources. Recently, it was demonstrated that the gallium-arsenide (GaAs) based Bragg refection waveguide (BRW), could efficiently produce photon pairs via SPDC. This platfrom was shown to have a distinct advantage over other semiconductor sources, due largely to its monolithic architecture and its layered epitaxy, which underpins many photonic devices. In this work we demonstrate yet another advantage: the intrinsic capability of the BRW to directly produce polarization entangled photon pairs, without any additional interferometry, spectral filtering, compensation or post-selection. Not only do we show that the BRW can produce entangled photons, but we wish to emphasize that the traditional compensation and interferometric methods used to create entanglement, which presumably would have occurred on chip, may no longer be necessary. Our experimental results confirm that the BRW has the potential to be one of the very first self-contained integrated room temperature resources of entanglement.

In this talk various approaches for utilizing SPDC processes in various integration platforms will be discussed. The root cause of entanglement generation is the lack of birefringence in these material systems, which otherwise makes exact phase matching impossible in bulk crystals. Because of this, cross-polarized photons propagate at almost identical group velocities, making off-chip path compensation unnecessary.
Phosphorus-Doped P-Type ZnO Nanowires and Their Electrical Properties
Authors: Li Wei-Che , Huang Chun-Wei , Chan Jui-Yuan , Wu Wen-Wei
Published: February 2020

Among variety of 1-D materials, ZnO nanowires (NWs) has attracted extensive attention due to its specific physical properties. For wide-ranging applications in nanoscale electronic devices, p-type ZnO NWs even have excellent electrical properties. In this work, ZnO NWs were synthesized with P2O5 as a dopant source via the hydrothermal method which used zinc acetate and hexamethylenetetramine (HMTA) mixed solution as the precursor. The morphology and aspect ratio of aligned phosphorus-doped ZnO NWs arrays were examined by field emission scanning electron microscope (FESEM). The effect of various phosphorus-doped concentration were systematically discussed. The X-ray diffractometer (XRD) and the high resolution transmission electron microscope (HRTEM) image indicated that the NWs are single-crystalline with <0001> growth direction. The results of temperature-dependent photoluminescence (PL) spectra revealed that both phosphorus-doped and undoped ZnO NWs show a UV light emission (370–380 nm) and a defect-related emission (400–750 nm). The phosphorus-doped ZnO NWs enhanced defect-related emission intensity. The electrical transport properties and field effect transistors (FETs) confirmed that p-type conductivity of the single phosphorus-doped ZnO NW. The phosphorus-doped ZnO NWs were successfully synthesized by hydrothermal method and showed characteristics of the p-type conductivity.
Correlation Between CD Bias and Fwhm Bandwidth on Immersion Exposure Systems
Authors: Jung Juyoung , Roh Yonghan
Published: February 2020

Immersion lithography has been developed with great speed. This technology moved to volume production of memory devices about 7 years ago. As immersion lithography developed, various and unexpected problems occurred under 30nm devices. In the act of investigating these problems, it was discovered correlation between Critical Dimension (CD) bias and full-width-at-half-maximum (FWHM). The relationship between wavelength and focus are well known issue [Fig. 1]. Also deviation of wavelength was become a crucial factor on CD bias. These similar phenomena will be frequently happened despite meeting the specification. Therefore this correlation will be able to be a solution for the similar cases.

CD bias issue was occurred in 2x nm node production. This phenomenon was expected an aberration problem, presented equation like below. For improving CD bias, chromatic distortion (aberration) had to be minimized by reducing (λ-λo). (λ-λo) is a kind of bandwidth. Also it is called a FWHM.

Correlation between aberration and laser wavelength

δx(x) = (λ-λo) x dSx/dλ + (λ-λo) x3 dE/dλ

where, [δx(x) : chromatic distortion]

[(λ-λo) : laser wavelength deviation]

[dSx/dλ, dE/dλ : distortion coefficient]

[x : slit position]

The test of narrowing FWHM is done successfully from 0.3pm to 0.25 pm [Fig. 2]. As a result it is obtained better aberration values (coma Z7_0 0.7 nm à 0.4 nm). and CD bias issue was under controlled by E95 (FWHM). Although It is impossible for revealing the exact information about CD in this paper, this problem still occurred similar phenomena. CD bias issue was not easy to solve, However equation and simulations [Fig. 3, Fig. 4] could be explained clearly. Wavelength deviation caused best focus shift, which led to CD bias issue.

References

[1] Armen Kroyan et al., “Effects of 95% Integral vs. FWHM Bandwidth Specifications on Lithographic Imaging” Proc. SPIE Vol. 4346(2001)

[2] Kevin Huggins et al., “Effects of laser bandwidth on OPE in a modern lithography tool.” Proc. of SPIE Vol. 6154(2006)

[3] R. C. Peng et al., “Effects of laser bandwidth on Iso-Dense Bias and Line End Shortening at sub-micron process nodes” Proc. of SPIE Vol. 6520, 65203S, (2007)
Optical Studies of Reactively Co-Sputtered Bcn Thin Films
Authors: Prakash Adithya , Sundaram Kalpathy B
Published: February 2020

The motivation behind the boron carbon nitride (BCN) ternary compounds is their similarities in the structure and difference in properties between graphite and hexagonal boron nitride (h-BN). Both theoretical calculations and experimental studies show that BCN compounds exhibit excellent mechanical, optical and electrical properties [1], [2]. In particular, the possibility to control the band gap (EG
) by atomic composition and structure makes them good candidates for the application in electronic and photonic devices [3], [4].

The optical characteristic like transmittance is improved with initial incorporation of nitrogen into the film composition and has a stable trend with further increase in nitrogen concentration. Also the optical band gap of BCN (2.2eV-3eV) increased with incorporation of nitrogen and said to follow a linear trend between B4C (2eV) and BN (4eV) [5]. The co-sputtering helps in creation of films with graded indexes of refraction as well. It gives more freedom to vary the composition as when compared to single target sputtering. Thickness uniformity and the film quality are better when using co-sputtering.

Dual target approach will be conducted to prepare BCN tin films. In this work we are depositing BCN thin films on quartz substrates using two targets namely B4C and BN using RF power and DC power respectively at different N2/Ar gas flow ratios. Also the input power for B4C and BN are varied to achieve different composition of the BCN thin films to control the optical properties. The optical properties like transmission and reflectance are studied using the UV-visible spectrophotometer. The optical absorption is studied by Tauc plot which is instrumental in finding the optical band gap of the material and the refractive index.

REFERENCES

[1] I. Caretti, J.M. Albella, I. Jiménez, Diamond Relat. Mater., 16 (2007), p. 1445

[2] A. Perrone, A.P. Caricato, A. Luches, M. Dinescu, C. Ghica, V. Sandu, A.Andrei , Appl. Surf. Sci., 133 (1998), p. 239

[3] M.O. Watanabe, S. Itoh, K. Mizushima, T. Sasaki, J. Appl. Phys., 78 (1995), p. 2880

[4] P.R. Fitzpatrick, J.G. Ekerdt, J. Vac, Sci. Technol. A, 26 (2008), p. 1397

[5] Optical characterization of BCN films deposited at various N2/Ar gas flow ratios by RF magnetron sputtering

.
Investigation of Electroless-Electrolytic Ni-Mo Binder-Free Electrode for Ultracapacitor Applications
Authors: Stephens Jamal Frederon , Kalu Egwu Eric , Gomez Jamie , Weatherspoon Mark H , Zheng Jim P
Published: February 2020

This paper provides results of a thin film binder-free Ni-Mo electrode ultracapacitor that was fabricated by using electroless-electrolytic (EE) technique with a glass fiber separator and 0.5M Na2SO4electrolyte solution.

Galvanic cycles were performed to characterize the charge/discharge curves of the Ni-Mo ultracapacitor at different currents as shown in figures 1 & 2. The capacitance was then analyzed by using equation (1).

where C is the capacitance normalized by the geometric area of the electrode, I is the current set to the cell and Ais the geometric area.

Figure 3 illustrates the capacitance relationship between 0.1 and 0.5 mA. From the plot it seems that at 0.1 mA the capacitance is more consistent and larger than at 0.5 mA. This can be because looking at the galvanic cycles for 0.5 mA we see a bend in the curve which can occur from the internal resistance being large. [1]

We will explore options and approaches to smoothing the curves to not only get a better capacitance values but obtained more consistent capacitance over different current rates.

References

Steven Risser, Elvin Beach, Megan Moore and Olga Koper, “Application of Metal Oxide Supercapacitor for Naval Applications”, ASNE Proceedings (2012)
Characterization of Reaction Products on the Surface of Li/Air Battery Electrodes
Authors: Lee Chan Kyu , Park Yong Joon
Published: February 2020

Recently, the Li/air batteries have received a lot of attention as an alternative of lithium ion batteries (LIB), since they provide higher energy density than LIB. The Li/air batteries are composed of air electrode, separator, electrolyte, and anode electrode. Among them air electrode plays a key role because the capacity and cycle life of the Li/air batteries are highly dependent on the air electrode. Therefore many studies have focused on the development of air electrode with enhanced electrochemical performances. During the discharge, lithium ions and oxygen dissolved in electrolyte have a reaction on the surface of air electrode and forms reaction products like Li2O2. Interestingly, it has been reported that the morphology of the reaction products can affect the electrochemical property of the Li/air cell such as cyclic performance and overpotential [1, 2]. Our study gives importance to characterize the morphology of reaction products. To achieve the image of morphologies on the surface of air electrode, we have composed the air electrode on the nickel grid for TEM and manufactured cell. After test of cell using the grid, we could take the TEM images of reaction products. In addition, it is observed that morphologies have difference according to several conditions like the presence of a catalyst or the rate of discharge/charge. It is expected that observation of morphologies in our approach could signpost for development of enhanced air electrode for Li/air batteries.

Reference

[1] Y. Shao-Horn, B. M. Gallant, R. R. Mitchell, D. G. Kwabi, J. Zhou, L.Zuin, C. V. Thompson, J.Phys. Chem. C 2012, 116, 20800-20805

[2] Y. shao-Horn, B. M. Gallant, D. G. Kwabi, R. R. Mitchell, J. Zhou, C. V. Thompson, Energy Environ. Sci. DOI: 10.1039/c3ee40998h
Doped Carbonate Alkaline Battery Cathodes
Authors: Hertzberg Benjamin Joseph , Sviridov Lev , Stach Eric A. , Mehra Aashna , Steingart Daniel A.
Published: February 2020

There is a need for reliable, low-cost energy storage for electric vehicle applications. While advanced Li-ion batteries may possess sufficient power and energy density to be useful for electric vehicles, their high manufacturing and materials costs make them unsuitable outside of a relatively small market niche. Alkaline batteries, one of the most common modern forms of primary battery, are potentially ideal for electric vehicles. These cells depend on a reaction between zinc (Zn) and manganese dioxide (MnO2) to generate energy. This reaction gives alkaline batteries a relatively high energy density and a low cost per kilowatt-hour, but phase transformations occurring during deep discharge prevent recharge. In a typical alkaline battery, useful rechargeability with minimal capacity losses can only be achieved if no more than 10% of the cells capacity is used. [1]

We have developed a new family of electrode materials, new to the literature, which consist of aragonite- or calcite-type carbonates with extensive substitution of manganese atoms on carbon sites. These materials are produced by a simple one-step hydrothermal process, which transforms the surface of a carbon precursor material into an manganese-doped carbonate. Permanganate salts used in the synthesis process result in extensive substitution of manganese atoms into the crystal structure without significant changes in long-range order. These materials have superior capacity, rate capability and cyclability compared to gamma MnO2, with comparable cost. In this presentation, we will describe these materials as we have characterized them via electroanalytical, X-ray and electron microscopy techniques.

References:

1. Shen, Yuwei, and Karl Kordesch. "The mechanism of capacity fade of rechargeable alkaline manganese dioxide zinc cells." Journal of power sources 87.1 (2000): 162-166

Acknowledgements:

This work was performed with financial support from the National Science Foundation CMMI 1402872, Department of Energy ARPA-E RANGE DE-AR0000400, and the Laboratory Directed Research and Development Program of Brookhaven National Laboratory (LDRD-BNL) under Contract No. DE-AC02-98CH 10866 with the U.S. Department of Energy. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Image Captions:

Fig. 1: Structure of manganese-doped barium carbonate (witherite). Barium is represented as green, oxygen as red, manganese as magenta, and carbon as black.
Stability Investigation of Inorganic Li Conductors As Protective Layers for Li-Air Batteries
Authors: Fung Kuan-Zong , Ni Chung-Ta , Tsai Shu-Yi , Chen Mei-Han
Published: February 2020

The development of Li-air battery has received great attention recently. However, using metallic lithium directly as an anode has been challenging due to the high reactivity of Li. Protective coatings with ionic conduction on metallic Li has be proposed to overcome this problem.Inorganic Li ion conductors may be suitable for being used as the protection layer.

NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 are known to be inorganic solid electrolytes with adequate conductivity in a range of 10-3 S/cm after required modification. However, Li tends to react with La0.56Li0.33TiO3 due to the incorporation of the released electrons with Ti+4 ions. Simultaneously, Li+ ions will migrate into the vacant sites in the cation sublattice. As a result, La0.50Li0.50TiO3 perovsikte becomes a mixed ionic/electronic conductor after reacting with Li. On the other hand, limited reaction was observed on the Li1+xAlxTi2-x(PO4)3 electrolyte when the metallic Li was used as the anode.

In order to improve the stability of Li1+xAlxTi2-x (PO4)3, a concept of composite electrolyte based on NASCION-type LiTi2(PO4)3 and perovsikte-La0.50Li0.50TiO3 is proposed. With proper mixing and distribution of these two electrolytes, a better stability from the composite electrolyte is expected.

Thus, the objective of this work is (1) to develop a composite electrolyte based on the mixture of Li1+xAlxTi2-x (PO4)3, and La0.50Li0.50TiO3, (2) to analyze the interface reaction between two components of composite cathode, (3) to investigate the electrical conduction/stability of composite as a function of volume fraction, grain size, and thickness, (4) to evaluate the feasibility of using composite electrolyte for Li-Air battery. The stability of composite electrolyte will be determined based on the measurement of the induced electronic conductivity and the open circuit voltage after a Li-air cell is assembled.
NaCrO2-Based Batteries: Effects of Processing
Authors: Sawicki Monica , Shaw Leon
Published: February 2020

Na-ion batteries (NIBs) have attracted substantial attention lately as an alternative electrochemical energy storage technology. In this study, we report the effects of processing conditions on the electrochemical properties of Na-ion batteries made of the NaCrO2 cathode. NaCrO2 is synthesized via solid state reactions. The as-synthesized powder is then subjected to high-energy ball milling under different conditions. The CR2032 coin cells made using the as-synthesized NaCrO2 powder exhibit a specific capacity of 110 mAh/g in the first discharge at 0.3C rate. The specific capacity decreases gradually in the subsequent charge/discharge cycles. The observed electrochemical properties are similar to those reported previously [1,2].

High-energy ball milling has reduced the particle size drastically. However, after subjecting to high-energy ball milling the specific capacity for NaCrO2 degrades significantly. X-ray diffraction reveals that the lattice distortion has taken place during high-energy ball milling, likely forcing some Cr ions into the tetrahedral site and thus blocking the pathway for Na intercalation and de-intercalation. This study shows that a balance between reducing the particle size and maintaining the layered structure is essential to obtain high specific capacity for the NaCrO2 cathode.

References:

S. Komaba, C. Takei, T. Nakayama, A. Ogata and N. Yabuuchi, “Electrochemical intercalation activity of layered NaCrO2 vs. LiCrO2,” Electrochem. Commun., 12, 355-358 (2010).

S. Komaba, T. Nakayama, A. Ogata, T. Shimizu, C. Takei, S. Takada, A. Hokura and I. Nakai, “Electrochemically reversible sodium intercalation of layered NaNi0.5Mn0.5O2 and NaCrO2,” ECS Transactions, 16, 42, 43-55 (2009).
Reversible Conversion Reaction of Tin Monosulfide/Graphene Nanocomposite As a Negative Electrode Material for Na-Ion Battery
Authors: Kim Joo-Hyung , Jung Young Hwa , Kim Do Kyung
Published: February 2020

To date, there has been much research on electrochemical study of lithium ion batteries. However, the question has also been raised for depletion of lithium resources, causing interest in sodium ion batteries. While extensive investigations on conversion reactions of various metal oxides as lithium electrode materials have been carried out, conversion reactions in sodium-based systems have been rarely reported. Here we have synthesized Tin monosulfide with graphene oxide nanocomposites by simple hydrothermal reaction and annealing for reduction of graphene oxide in successive process. The phase and morphology of SnS/rGO nanocomposites have been investigated by XRD, SEM, and TEM, respectively. The electrochemical performances of SnS/rGO nanocomposites were tested in sodium nonaqueous electrolytes. It delivers 588mAh/g at a rate of 50 mA/g, indicating relatively higher capacity compared to previous reports. This material also shows stable capacity retention with 396mAh/g at 100mA/g after 100cycles. Furthermore, we conduct ex-situ XRD measurements on the initial stage of cycles to investigate the structural differences during the conversion reactions in sodium system. Finally, we demonstrate which electrochemical reaction has directly affected on the cause of capacity fading during cycles.
A New Approach to the Lithium-Oxygen Cell Via the Utilisation of Redox Shuttles
Authors: Frith James T , Garcia-Araez Nuria , Owen John R.
Published: February 2020

Lithium-O2 cells, with a theoretical specific energy of around 5 times higher than lithium-ion cells have the potential to become the technology powering tomorrow’s electric vehicles. However, since they were first reported by Abraham and Jiang[1] they have faced problems and setbacks. The principal problem was of instability of organic non-aqueous electrolytes to the superoxide ion formed as an intermediate discharge product [2]. Ionic liquids are a promising alternative to traditional carbonate based electrolytes, and indeed recent works have shown that Pyr14TFSI is relatively stable to superoxide [3–5]. Having identified a stable electrolyte we have then looked at the problem of electrode passivation by the insoluble and insulating discharge product lithium peroxide [6], which produces a significant reduction on the practical capacity.

This work continues our previous study on the use of ethylviologen triflate as a mediator/redox shuttle for the discharge reaction [7], with a study of mediator action by the shuttle molecule to achieve a 2-electron reduction of oxygen to form lithium peroxide away from the electrode surface. This eliminates electrode passivation as shown in Fig. 1. We will also present an in-depth study into the mechanism of oxygen reduction by ethylviologen triflate and other candidate mediators.

The need for mediators for the charge reaction has also been stated by Bruce et
al.,[8] who found TTF to be a redox mediator in DMSO. Our own studies of TTF have found it to be unsuitable for use in in Pyr14TFSI due to its lower oxidation potential, so we have focused on the use of other compounds to carry electrons back to the electrode while the charge reaction converts the lithium peroxide back to oxygen.

[1] K.M. Abraham, Z. Jiang, J. Electrochem. Soc.143 (1996) 1–5.

[2] F. Mizuno, S. Nakanishi, Y. Kotani, S. Yokoishi, H. Iba, Electrochemistry. 78 (2010) 403–405.

[3] J.T. Frith, N. Garcia-araez, A.E. Russell, J.R. Owen, Prep.(n.d.).

[4] I.M. AlNashef, M. a. Hashim, F.S. Mjalli, M.Q.A. Ali, M. Hayyan, Tetrahedron Lett.51 (2010) 1976–1978.

[5] S. Randström, G.B. Appetecchi, C. Lagergren, A. Moreno, S. Passerini, Electrochim. Acta. 53 (2007) 1837–1842.

[6] V. Viswanathan, K.S. Thygesen, J.S. Hummelshøj, J.K. Nørskov, G. Girishkumar, B.D. McCloskey, et al., J. Chem. Phys.135 (2011) 214704.

[7] M.J. Lacey, J.T. Frith, J.R. Owen, Electrochem. Commun.26 (2013) 74–76.

[8] Y. Chen, S.A. Freunberger, Z. Peng, O. Fontaine, P.G. Bruce, Nat. Chem. 5 (2013) 489–94.
Characterization of Polymerized Sulfur Cathodes upon Cycling
Authors: Schaefer Jennifer L. , Kim Jenny , Oleshko Vladimir P. , Char Kookheon , Pyun Jeffrey , Soles Christopher L.
Published: February 2020

Rechargeable Li-S batteries offer an unprecedented opportunity for energy storage technology. Sulfur is a very cheap material with remarkably high energy storage density when used as a cathode. Sulfur cathodes have historically suffered from a myriad of problems, including low active material utilization due to low electronic conductivity and significant capacity fade upon cycling due to polysulfide dissolution and cracking of the cathode. The main approach for improving active material utilization and maintaining capacity has been to sequester sulfur within various forms of electronically conductive, nanostructured carbons.

Recently, researchers have developed a copolymer with a very high sulfur content via a process termed inverse vulcanization.1 The sulfur-containing polymer is inexpensive to produce, and full Li-S cells utilizing this copolymer in the cathode achieve capacities of 635 mAhr/g after 500 cycles at a rate of C/10.2

This talk will focus on results of characterization studies to determine the morphology and composition of the sulfur copolymer cathode and electrolyte solution during the cycling process. Microscopy studies show that the sulfur copolymer cathode maintains greater uniformity and shows less cracking upon cycling than an elemental sulfur cathode. We will also report on results of in-situ Raman and XPS studies to identify the products present in the cathode and in the electrolyte at various potentials during cycling.

1. J. Pyun et. al., Nature Chemistry, 5:518-524, 2013.

2. J. Pyun, et. al., ACS Macro Letters, 3:229-232, 2014.
Sn-Polyacrylate Composite Electrode for Advanced Na-Ion Batteries
Authors: Fukunishi Mika , Yabuuchi Naoaki , Kuze Satoru , Son Jin-Young , Cui Yi-Tao , Oji Hiroshi , Komaba Shinichi
Published: February 2020

Na-ion batteries are attractive rechargeable batteries as Li-free batteries. Sodium resources are abundant, inexpensive elements and unlimited everywhere, unlike lithium availability. Additionally, relatively low redox potential of sodium is slightly higher, 0.3 V, than that of Li/Li+. Therefore, many researchers extensively study about Na-ion batteries nowadays and the electrode performance is significantly improved, which is being competitive for Li-ion batteries. We have demonstrated approximately 300 mAh/g discharge capacity after 50 cycles by using hard-carbon electrodes in Na cells.[1] In order to achieve higher energy battery, electrode materials with high reversible capacity is needed. Thus we have examined group 14 elements (C, Si, Ge, Sn, and Pb) as the potential negative electrodes materials for Na-ion batteries.[2] In our previous report, we demonstrated acceptable electrode performance with tin, approximately 500 mAh/g of reversible capacity after 30 cycles.[2] However, reversible capacity was lower than that of expected capacity (847 mAh/g based on the formation of Na15Sn4).[3]In this study, the factors affecting electrode performance of tin electrochemically alloying with Na are described; slurry conditions, cut-off voltages and so on. After the optimization of tin composite electrodes, finally, we have demonstrated more than 650 mAh/g of reversible capacity with good capacity retention.

Nanosized tin powder (<150 nm, Sigma-Aldrich Co., Ltd), graphite, and sodium polyacrylate (PANa) were mixed with 80:10:10 (wt%) to prepare slurry with deionized water mixed with or without methanol (5 vol%) and were cast onto Al foil to make composite electrodes. The electrode was tested in aprotic Na cell with NaPF6PC solution with FEC (2 vol%) additive. As shown in Fig.1, the higher reversible capacity (approximately 700 mAh/g) is obtained by addition of 5% methanol to the slurry. Approximately 200 mAh/g discharge capacity is increased compared with the slurry prepared without the addition of methanol. Change in the electrode morphology prepared with or without methanol in the slurry was observed by SEM (Fig. 2). SEM observation reveals that the uniform morphology and better dispersion of the active materials for the composite electrode prepared with methanol-added dispersant. It indicates that methanol additive is effective to improve the dispersion of tin and carbon materials in the aqueous slurry, resulting in better electrochemical properties in Na cells. Based upon these results, we will discuss the effects of cut-off voltages in relation to the changes in the surface of tin electrodes characterized by secondary ion mass spectroscopy and photoelectron spectroscopy in synchrotron facility.

References
:

[1] M. Dahbi, N. Yabuuchi, K. Kubota, K. Tokiwa, S. Komaba, submitted.

[2] S. Komaba et al., Electrochem. Commun., 21, 65 (2012).

[3] L. D. Ellis et al., J.

Electrochem.Soc., 159, A1801 (2012).
Advanced 3D Imaging and Analysis of SOFC Electrodes
Authors: Tariq Farid , Yufit Vladimir , Kishimoto Masashi , Cui Guansen , Somalu Mahendra , Brandon Nigel P.
Published: February 2020

Meeting increasing energy demands, storage demands and energy portability in a clean efficient manner will be expedited through an ability to directly image solid oxide fuel cell (SOFC). Tomographic techniques allow for the 3D imaging and chracterisation of complex microstructures down towards tens of nanometers; which are inadequately described in 2D. The performance of the SOFCs is dependent on nano/micro-structure as the electrochemical reactions and transport phenomena are strongly affected by the complex porous microstructure, where important reactions occur. Furthermore, during processing or operation microstructural evolution may degrade electrochemical performance

Here we use tomographic techniques to probe the 3D electrode structure at micro-nanometer length scales. Subsequently, micro/nano structural changes are followed to facilitate understanding the differences which occur with shape, structures and morphology at high resolution. Additionally the quantification of electronic, ionic and gas interfaces are also correlated with observed differences in electrode behaviour. When coupled with electrochemical and thermo-mechanical computational models, the results show nano/microstructural and compositional variations can significantly affect performance of SOFC electrodes. Altogether this provides important insights for electrode design and understanding sources of performance degradation.
Effect of Heat Treatment on Thermal Sprayed Protective Oxides for SOFC Metallic Interconnects
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Ni Chung-Ta , Ho Hsin-Chia
Published: February 2020

For the stack design of solid oxide fuel cells (SOFC), metallic interconnects such as Crofer 22H is widely used to replace ceramic interconnects. Most metallic interconnects use chromium-containing alloy that form chromia scales to suppress further oxidation at high temperatures. Since chromia may react with cathode and cause degradation, a protective oxide may be used to suppress the growth of chromia. Although several techniques have been adopted to deposit oxides on metallic interconnects, the thermal spray is found to be an appropriate technique. Thermal spray coating process has been widely used to produce a high quality coating by a combination of high temperature, high energy heat source, a spraying gas medium, such as argon, and high particle velocities. This process allows the spraying of various types of metallic or ceramic coatings on to a wide range of substrate materials. As a result, uniform coating layer with excellent bond strength to substrate is obtained without noticeable distortion.

For metallic interconnects used for SOFC applications, several oxides such as LaMnO3 and LaCrO3-based perovskite oxides and (Mn,Co)3O4, (MCO), with spinel structure have been used to form protective layer for metallic interconnects. However, the temperature during thermal spraying may be high enough to change the crystal structure and conductivity of protective oxides. The heat treatment is believed to be an appropriate method to obtain adequate properties for protective oxide. Thus, the after-spray treatment will play an important role for metallic interconnects to obtain desired electrical properties. In this study, the high-temperature ferritic stainless steel Crofer 22H and nickel-chromium alloy Inconel 625 were first thermally sprayed with oxides with perovskite and spinel structures.

The objective of this work is to investigate the effect of after-spray treatment on the crystal structure and conductivity of the sprayed oxide. The crystal structure, morphology and electrical conduction of interconnect with sprayed oxide films will be examined by using XRD, FESEM and resistance measurement.
Study on Protocols for Evaluating Durability of PEFC Electrolyte Membranes
Authors: Oono Yuka , Kobayashi Kenji , Hori Michio
Published: February 2020

Introduction

Under the NEDO Project called Cell Evaluation Project, Daido University(DU) decided the evaluation protocol of membrane chemical and mechanical durability based on the protocol recommended by FCCJ and DOE. Table1 and Table 2 shows the OCV and Dry-wet cycle test protocols were decided by DU. Using these protocols, chemical durability and mechanical durability of fluorine based and hydrocarbon membranes from all over the world have been evaluated with single cells.

Regarding to OCV test protocol, the criterion of this test is set which quantity of cross leak current reached at 10 times of the initial current. As the OCV test is going, chemical degradation of membranes are caused by hydrogen peroxide is produced, and then membranes are gradually broken and finally hydrogen leak current larger increase.

Recently, the protocol that combined a OCV test and a Dry-wet cycle test has been suggested by ENE-FORM companies to evaluate and accelerate membranes chemical and mechanical durability of membranes.

In this study, to clarify the degree of the chemical degradation of hydrocarbon-based membranes in the OCV test, DU examine a newly protocol of evaluating for membrane’s chemical durability by OCV test with the new diagnosis method to use dry-wet cycle test.

Experimental

Table3 shows DU newly protocol for membrane chemical durability based on the protocol recommended by ENE-FORM companies. As seen this table, OCV tests with diagnosis method of membrane’s chemical durability were conducted on single cells with Nafion HP membrane and hydrocarbon-based membranes. Dry-wet cycle test was conducted for diagnosis method to evaluate degree of membrane chemical durability.

Acknowledgement

This research was performed under a grant from the Cell Evaluation Project from the New Energy and Industrial Technology Development Organization (NEDO) .
Invited: Confinement Effects on the Structure and Transport of Nafion Ultrathin Films
Authors: Stafford Christopher M. , Page Kirt , Davis Eric M. , Kim Sangcheol , Dura Joseph , Yager Kevin , Kusoglu Ahmet , Soles Christopher L.
Published: February 2020

Polymer electrolyte membrane (PEM)-based fuel cells are being aggressively targeted as an alternative energy source for transportation and stationary power due to their high charge density and low operating temperatures. While the structure, transport and mechanical properties of bulk PEMs have been extensively studied, there is increasing interest on the behavior of these materials at interfaces and under confinement, since there exist many heterogeneous interfaces within an actual fuel cell assembly. One could argue that the performance and ultimate failure of the membrane electrode assembly is greatly impacted by the structure and transport of ionomers confined to extremely small length-scales.

Using a combination of neutron and x-ray reflectivity, grazing-incidence small-angle x-ray scattering (GISAXS), quartz crystal microbalance (QCM), polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), as well as measurements capable of measuring thin-film mechanics we have studied the water transport and mechanical behavior as a function of humidity and initial film thickness (< 220 nm). Our previous work has shown that when the polyelectrolyte is confined to thin films there is suppression in both swelling and water diffusivity in addition to considerable changes in the nano-scale structure.

More recently, we have developed methods to measure the mechanical properties of these systems, as well as extended our PM-IRRAS method to attempt to answer questions about the roles interfacial mass transport and polymer chain relaxations. The mechanical methods reveal an effect of confinement on the measured stiffness of the material. Specifically, we observe an increase in the modulus with decreasing film thickness and, in the beginning of the hydration process, a visco-plastic response due to swelling. These results lend some explanation to the observed decrease in water uptake with decreasing film thickness.

Moreover, we have extended our use of PM-IRRAS to include in-situ vapor switching between H2O and D2O. In this approach, we measure the time-resolved diffusion of H2O into the film (swelling), followed by the diffusive exchange of D2O for H2O (switch), and then then loss of H2O upon drying (deswelling). The experiments enable us to (1) eliminate contributions of swelling and relaxation to the measured transport of water and (2) measure the transport in a pseudo-steady state manner. This method shows promise in answering questions about the dominant mechanism for transport in confined thin films.

Collectively, our program aims to provide a comprehensive understanding of the effect of confinement on the structure and transport of ionomer-based materials, and how these effects manifest themselves in the performance and mechanical response of such membranes.
Validation of the Influence of Test Parameters in Performance Measurements of a PEMFC Stack
Authors: Harms Corinna , Köhrmann Frank , Dyck Alexander
Published: February 2020

Uniform testing procedures for the characterisation of PEMFC stacks are important due to the necessity to achieve comparable and reliable results. The comparability of different stacks is relevant for stack manufacturers as well as for system integrators and for academic research. Results generated in different laboratories can be influenced by different test stands, test procedures and diverse environmental conditions.

Harmonized testing procedures for PEMFC stacks were developed within the EU project “Development of PEM Fuel Cell Stack Reference Test Procedures for Industry” (Stack-Test) regarding performance, durability and safety aspects for automotive, portable and stationary applications. The testing procedures for performance measurements were developed in order to investigate the sensitivity of stacks to the operating parameters.

The testing procedures for performance measurements developed by the project partners were validated using a set of PEMFC stacks. For the measurements the input parameters have to be defined and controlled in a precise way. By varying the input parameters like temperature, relative humidity and stoichiometry the effect on the main output parameters like the single cell voltages and the overall stack voltage is monitored. The effect on the voltage was evaluated by the variation of the electrical load. Additionally, current voltage curves at different parameters e. g. with a set of temperatures were generated.

An overview on the achieved results will be given, to describe the optimization pathway for stack characterization under manufacture defined conditions. With these procedures it is possible to achieve reproducible and stable results to be applied by stack manufactures and system integrators for reliable fuel cell stacks.

The research leading to these results is part of the EU project Stack-Test which has received funding from the European Union´s Seventh Framework Programme (FP/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° [3034445]. We acknowledge the preparation of the test modules used for this validation by the project partners within the Stack-Test project. The test modules are available for further revision on the project website: stacktest.zsw-bw.de
Fabrication and Cell Analysis of a Pt/SiO2 Platinum Thin Film Electrode
Authors: Inaba Masanori , Suzuki Takahisa , Hatanaka Tatsuya , Morimoto Yu
Published: February 2020

Platinum thin film electrodes, such as nanostructured thin film (NSTF) by 3M [1], have attracted much attention as alternative catalysts for polymer electrolyte fuel cells (PEFCs). Although NSTF electrodes showed higher efficiency and power density than conventional Pt/C electrodes under suitable operating conditions, it has been reported that they tend to show larger performance decline under dry or wet conditions [2]. To examine all those properties of NSTF on other thin film electrodes and reveal their general features, in this research we fabricated a platinum thin film electrode on the surface of SiO2 nanofibers. Performances of the cell with the electrode were studied and its various properties were analyzed.

Platinum was deposited on a SiO2 nanofiber web (Japan Vilene Company, Ltd., 200 nm in fiber diameter and 6 mm in web thickness) by atomic layer deposition. An SEM image of the cross section of the Pt/ SiO2 nanofiber electrode is shown in Fig. 1. The SiO2 nanofibers are covered with a platinum thin film of 3 nm in thickness. Nafion membrane was sandwiched between the Pt/SiO2 nanofiber electrode as a cathode and a conventional Pt/C electrode as an anode to form an MEA. Note that no ionomer was impregnated on the Pt/SiO2 nanofiber electrode. Fuel cell polarization curves were obtained using 1 cm2 single-cell hardware with cross-flow flowfields under various conditions. The electrochemical surface area (ECSA), proton conductivity and oxygen transport resistance were analyzed by cyclic voltammetry, electrochemical impedance measurement, and diffusion-limited current measurement using diluted oxygen, respectively.

Polarization curves and analyzed results were shown in Fig. 2 and Table 1, respectively, in comparison with those of conventional Pt/C electrode. The Pt/SiO2 cell showed comparable performance to the Pt/C cell at 100% RH in spite of the much smaller ECSA. At 40% RH, however, the Pt/SiO2 cell showed lower performance than the Pt/C cell.

A transmission line model of the electrode was applied to the Pt/SiO2 nanofiber electrode to analyze the performance loss. By following the model, the reaction resistance was calculated using values of the cathode resistance and the ohmic resistance, which were obtained from slopes of the polarization curves and the proton conductivity, respectively. The analyzed results under various RH conditions are shown in Fig. 3. The reaction resistance significantly increases with decreasing RH, while the ohmic resistance increase is limited. This indicates that the performance loss of the Pt/SiO2 nanofiber electrode under dry condition is mainly due to the increase in the reaction resistance.

Oxygen transport resistance, performances in wet conditions, and the effects of ionomer impregnation on the Pt/SiO2 electrode will also be discussed.

[1] M. K. Debe, J. Electrochem. Soc., 2013, 160, F552

[2] A. Kongkanand, et al., J. Electrochem. Soc., 2012, 159, F405
Water/Methanol Transport in Polyethylene Based Block Copolymers as Anion Conductors for Applications in Fuel Cells
Authors: Sarode Himanshu N , Yang Yuan , Herring Andrew M
Published: February 2020

Anion exchange membranes have been a central point of focus for the low temperature fuel cell application. The primary goal of AEMs in fuel cells is to transport hydroxide (OH-) ions from cathode to anode and to act as a separator between the electrodes.

In this work we have studied a block copolymer of polyethylene and polyvinyl benzyl trimethyl ammonium bromide (PE-b-PVBTMA[Br], Fig. 1) for various transport properties. By using the dynamic vapor sorption apparatus we were able to study water and methanol uptake dynamics for this AEM. Fickian diffusion coefficients for both water and methanol were calculated during this study giving idea about the solvent uptake kinetics.

We also measured the conductivity of the AEM under 95% relative humidity (Figure 2). It was found that the AEM followed VFT theory behavior for transporting ions through it as opposed to the classical Arrhenius behavior. VFT behavior suggests that ion transport in the membrane is facilitated by the polymer chain motion as opposed to ion transport in water which is governed mainly by the Arrhenius type of behavior.

We also report methanol/water ion transport using the pulse gradient stimulated spin echo (PGSTE) NMR technique to determine the tortuosity of the membrane along with self diffusion of each species.

Acknowledgements:

We would like to thank the Army Research Office for funding this Multidisciplinary University Research Initiative under contract #W911NF-10-1-0520 and the Colorado School of Mines NMR facility, funded by National Science Foundation under the grant CHE-0923537. We would like to thank Yifan Li, D M Knauss for providing with the polymer for this study.