bluuebunny/crossref_metadata_2025 huggingface dataset:
VOC Gas Sensors Fabricated with Graphene Oxide Composites for Food Safety and Quality
Authors: Park Hyejin , Lee Eunji , Chung Yoonsung , Lee Seokhee , KIM Dong-Joo
Published: February 2020

For food market, off-odors or flavors have become more than a quality issue with the increased awareness of food safety problems. This awareness to solve the safety problems, off-odor detection in foods, packaging materials, and their interactions involving scalping or other flavor system modification have been attracted. One of suggested methods is to use an electronic nose consisting of a gas sensor array to detect the volatile organic compounds (VOCs), released from foods as a byproduct of everyday physiological processes. Monitoring of the specific VOCs by a gas sensor can provide the information on both crop and field conditions. The array structure of gas sensors can enhance selectivity for in-situ detection [1, 2].

In this study, an array of sensors is investigated by employing graphene oxide and nanostructured metal oxide based on SnO2. Their composite films on a series of electrodes are prepared to create a high density of sensing array in a small size chip. A composition gradient sensing layers can produce  unique gas response patterns. Figure 1 shows surface morphology of compositionally gradient tin oxides (1:6 ratio of GO to SnO2) and structure property confirmed by XRD result. The results on the growth of nanostructured films using solution process and vacuum process are presented. Figure 2 also shows sensing properties of the composites to formaldehyde gas at room temperature. The combinatorial structure enhances the sensing properties of devices in terms of sensitivity, selectivity and response rate. Additionally, such a sensor can meet the proposed idea, in-situ detection, and also the requirements for low-cost and high-volume production as well as high gas analytical performance.

This research was partially supported by a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP.

[1]     A. D. Wilson and M. Baietto. Sensors. 2009, 9:5099-5148.

[2]     K. Arshak, E. Moore, G. M. Lyons, J. Harris, and S. Clifford. Sensor Review. 2004, 24(2):181-198.

Figure 1
Manipulation of Nanoscale 3 Dimensional Architecture: Graphitic Carbon/Nickel Core-Shell Structured Nanoparticles Dispersed on Carbon Black Support
Authors: Na Hyunwoong , Oh JI-Won , Cho Yong Soo , Choi Hanshin
Published: February 2020

Graphitic carbon and nickel core-shell structured nanoparticle was designed as a high surface area carbon with enhanced crystallinity and it was achieved by facile synthetic route. Nickel nanoparticle was directly deposited on mechanically agitating carbon black nanoparticle. After that, Ni/C was heated at high temperature and then cooled to room temperature. As a result, graphitic carbon layer covered Ni nanoparticles dispersed on carbon nanoparticle was obtained. In the suggested synthetic route, Ni acted as carbon transporter from support carbon black to surface graphite and also catalyst for graphitic layer on Ni surface by dissolution-precipitation reaction. Morphological evolution from the carbon black nanoparticle to graphitic carbon and nickel core-shell nanoparticle was shown. In addition, phase change of cored nickel nanoparticle and thickness of newly precipitated graphitic carbon layer were investigated. This study was focused on the validation for the particle design and however, it could be deduced that morphology and crystallinity of  GC/Ni core-shell nanoparticle are manipulated by Ni content and heat treatment temperature.
Formulation of Ionic Liquid Electrolyte to Expand the Voltage Window of Supercapacitors
Authors: Van Aken Katherine L , Beidaghi Majid , Gogotsi Yury
Published: February 2020

While their high-power performance exceeds that of batteries, supercapacitors lack the energy density capability for some energy storage applications. Since the energy density of the device is proportional to the square of operating potential window (OPW), an effective way to increase the energy density of the device is by increasing the potential window. Ionic liquid electrolytes are beneficial for this reason since they can theoretically operate at up to 6 V, though experimentally, this value is between 3-4 V depending on the properties of electrode materials. By employing a novel electrochemical technique to analyze symmetric supercapacitors of carbon electrodes and ionic liquid electrolytes, we have found one of the possible reasons for smaller OPWs of ionic liquids in practical applications.1 We observed that for a symmetric device with electrodes equal in size and weight, the different properties of cations and anions in the electrolyte results in an asymmetric performance of the two similar electrodes. By performing a systematic study with ionic liquid electrolytes and model electrode materials, we show that a symmetric behavior of the electrodes can be achieved by formulating an ionic liquid mixture containing different cations and anions. In our model electrochemical device, onion like carbon (OLC) was used to fabricate the device electrodes and two ionic liquids, EMI-TFSI and EMI-BF4, and their mixtures were used as electrolytes. This electrolyte mixing results in an extended OPW of the device and a higher energy density.

1.         Van Aken, K. L., Beidaghi, M. & Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie
127, 4888–4891 (2015).
Activated Graphene-Derived Porous Carbon with Exceptional Gas Adsorption Properties
Authors: Ganesan Aswathi , Shaijumon Manikoth M
Published: February 2020

Designing nanoporous materials with high surface area, large porosity, superior structural stability and amenability to various processing conditions, is important to meet the commercial demands of large-scale reversible gas storage systems.[1, 2] Carbonaceous porous materials are particularly interesting in this respect, due to its fascinating properties, which include high surface area, high amenability to pore structure modification and surface functionalization, relative ease of regeneration, high thermal stability etc.[3,4] Here, we demonstrate a simple approach to synthesize a highly porous activated graphene- derived carbon (a-GDC), with ultra-high surface area (~ 3240 m2g-1) and enhanced porosity characteristics, from thermally exfoliated graphite oxide (TEGO), through an efficient and finely controlled KOH chemical activation process. Various experimental techniques including Fourier Transform-Infrared spectroscopy, High resolution Transmission Electron Microscopy and Pore size analyser are employed to characterize the materials. Detailed studies on the gas adsorption behaviour of a-GDCs have been performed at different temperatures and pressures using a volumetric gas analyser. Highly interconnected network of micro and mesopores present in a-GDC acts as active sites for adsorption of different gas molecules and outstanding gas uptake values of 21.1 mmolg-1 (298 K, 20 bar), 11.3 mmolg-1 (298 K, 35 bar) and 3.8 wt% (77 K, 10 bar) are obtained respectively for CO2, CH4 and H2, superior to several of the other high surface area nanoporous carbon materials reported so far.[5,6] A comprehensive comparison on the gas adsorption potential of a-GDCs with  the existing previous reports on similar and other porous materials (MOFs, COFs etc ) is also presented. In addition, good kinetics of adsorption/desorption and moderate values of heat of adsorption obtained for the a-GDC samples are particularly interesting, while its large scale commercial applications are considered. The results will draw considerable attention towards developing such materials from other cheap and easily available carbon precursors, for more effective greenhouse gas capture and gas storage applications

References

R. E. Morris and P. S. Wheatley, Angew. Chem.  Int. Ed., 2008, 47, 4966-4981.

A. Stein, Adv. Mater., 2003, 15, 763-775.

J. Lee, J. Kim and T. Hyeon, Adv. Mater., 2006, 18, 2073-2094.

H. Marsh and F. Rodriquez-Reinoso, Activated carbon, Elsevier, Amsterdam, 2006

S. Himeno, T. Komatsu and S. Fujita, J. Chem. Eng. Data, 2005, 50, 369-376.

G. Srinivas, J. Burress and T. Yildirim, Energy Environ. Sci., 2012, 5, 6453-6459.

Figure 1
Anion Conductive Multiblock Copolymers with Long Side Chains for AEM Fuel Cells
Authors: Liu Lisha , Ahlfield John M. , Kohl Paul A
Published: February 2020

Anion Exchange Membrane (AEM) fuel cells are a possible route to overcoming fundamental issues with acid-based fuel cells. The issues include the high cost of platinum catalysts, complex water transport, and sluggish electrochemical reactions, etc. However, the performance of AEM fuel cells is not as good as that of Proton Exchange Membrane (PEM) fuel cells because of the limitations of current anion exchange membranes, such as low ionic conductivity, poor stability at high pH, and high water uptake.

A series of novel multiblock copoly(arylene ether)s with long side chains were synthesized for AEM fuel cells. The multiblock copolymers were synthesized by polycondensation of separately-prepared hydroxyl-terminated oligomers with fluoro-terminated oligomers. The resulting multiblock structure, in which one block is hydrophilic and one block is hydrophobic, was designed to ensure a nanophase-separated morphology. Multiblock copolymers with different block lengths and ion exchange capacities (IEC) were synthesized to maximize ion conductivity and explore the relationship between chemical structures and properties in anion exchange membranes. Furthermore, copolymers with long side chains exhibited higher stability in high pH environment than their counterparts without long side chains. The degradation mechanism was also studied for the long side chain block copolymers.

Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.
A New Silica-Based Anode Using Three-Dimensional Nanostructured Copper As a Current Collector for Lithium Ion Batteries
Authors: Ara Ryota , Arai Susumu
Published: February 2020

Introduction

Lithium ion batteries are widely used high energy density rechargeable energy storage devices, but there is great demand for batteries with higher energy densities. Consequently, new electrodes (or active materials) with improved capacities have been developed to replace current electrodes. Silicon and silica are promising candidates to replace the conventional graphite anode since their theoretical capacities (4200 mAhg-1 and 1965 mAhg-1, respectively 1)) are high compared to that of graphite (372 mAhg-1). Unfortunately, these active materials exhibit low cyclability due to degradation and separation of the silicon and silica from the current collector, caused by volumetric changes during alloying/de-alloying with lithium ions. Nanosized active materials have been examined as a means of mitigating this effect, and a three-dimensional (3D) network current collector has also been investigated to enhance the cyclability of lithium ion batteries using a silicon-based anode2). We previously reported a new and simple method of fabricating a 3D nanostructured copper layer by electrodeposition3).

Herein, we propose 3D nanostructured copper as a current collector using silica nanoparticles as the anode material for lithium ion batteries

Experimental

The composition of the 3D nanostructured copper plating bath was 0.85 M CuSO4{0.55 M H2SO4+3´10-4M polyacrylic acid (M.W. 5000). Electrodeposition was carried out under galvanostatic conditions at 25°C. A pure copper plate and a phosphorous copper plate were used as the cathode and anode, respectively. Silica nanoparticles were synthesized by the sol-gel method. 3D nanostructured copper was immersed into a solution of ethanol and tetraethyl orthosilicate. Ammonia water was added to this solution and silica nanoparticles were fabricated on/in the 3D nanostructured copper layer.

Electrochemical studies of the fabricated anode were carried out with coin cells assembled in an Ar-filled glove box. Each coin cell consisted of lithium foil as the counter and reference electrode and the fabricated anode as the working electrode. The electrolyte was 1 M LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 vol%). Cycling tests were performed between 0 - 3 V (vs. Li/Li+) at a constant temperature of 25°C.

Results and Discussion

 Figure 1 presents a cross-sectional SEM image of the fabricated anode and clearly shows uniform 200-300 nm diameter silica nanoparticles inside the 3D nanostructured copper layer.

Charge-discharge without conductive additive and binder was confirmed. The electrochemical performance of the anode will be discussed in detail at the meeting.

References

1)Young-Kuk Kim*, Jong-Woo Moon, Jung-Goo Lee, Youn-Kyung Baek, Seong-Hyun Hong, Journal of Power Sources, 272(2014) 689-695

2)Y. Liu, K. Huang, Y. Fan, Q. Zhang, F. Sun, T. Gao, L. Yang, J. Zhong, Electrochimica Acta, 88(2013) 766.

3) S. Arai, T. Kitamura, ECS Electrochemistry Letters,
3(5) (2014) D7.

Figure 1
Durability Study of Double Perovskite Cathode Materials for Intermediate Temperature-Solid Oxide Fuel Cells
Authors: Yang Ja-Yoon , Park Jun-Young
Published: February 2020

Solid oxide fuel cells (SOFCs) are the electrochemical power generation devices that convert chemical energy into electrical energy directly, providing several advantages of fuel flexibility, low pollutant emission, environmental friendliness, high power density, and high efficiency. Recently, the long-term durability has been major concerns for making commercialization of SOFC systems. One of methods to mitigate these issues is to decrease the high operation temperature to the low or intermediate temperature through the use of advanced electrolytes and electrodes. Lower operating temperature is possibly able to enhance stability and economic feasibility of SOFCs. In this work, hence, we investigate the durability of Ni-cermet anode-supported neodymium-doped ceria (Nd0.1Ce0.9O2-δ, NDC) electrolyte cells at the practical SOFC operating condition of 650 oC. In addition, double perovskite structure-based materials are considered as the candidate cathode materials, due to their high electrochemical properties with the excellent stability, and compared to that of single perovskite structured cathode materials. 

References

Lowering the temperature of solid oxide fuel cells, E. D. Wachsman, and K. T. Lee, Science
,
334, 935 (2011).

Fundamental mechanisms limiting solid oxide fuel cell durability, H. Yokokawa, H. Tu, B. Iwanschitz and A. Mai, J. Power sources, 182, 400 (2008).

Durability test of SOFC cathodes, M. J. Jørgensen, P. Holtappels and C. C. Appel, Applied Electrochemistry, 30, 411 (2000).

Keywords:
solid oxide fuel cells, cathode, double perovskite structure, durability, ceria.
Electrospun Porous Nanorod Perovskite Oxide/Ionic Conductor Composite As an Electrochemical Catalyst for Water Splitting
Authors: So In-Seop , Park Jun-Young
Published: February 2020

As the global energy demand increases rapidly, developments of cost-effective and highly active catalysts are of prime importance for the energy conversion and storage device in the pursuit of sustainable energy, such as the water splitting cells, rechargeable metal–air batteries, and regenerative fuel cells. In these electrochemical energy devices, the oxygen evolution reaction (OER) shows the considerable overpotential owing to the slow kinetics of OER, similar to the sluggish oxygen reduction reaction (ORR) in fuel cells. Noble metal-based catalysts such as RuO2 and IrO2 are still used, but the scarcity and high cost of the noble metal-based catalysts limit their wide application. In order to develop highly active, durable, and low-cost OER catalysts, the perovskite structure -based catalysts have been considered because of their highly electrocatalytic activity for the OER. Further, The core/shell-fiber-structure OER catalystswere prepared by the advanced electrospinning and Pechini process. The electrospinning process has various advantages, such as the fast, simple, the direct use of inorganic particles as precursors, to fabricate the inorganic core/shell fibers. Hence, in this work, perovskite structure -based catalysts with the morphology of core/shell-fibers are fabricated for highly effective OER catalysts and characterized by various physicochemical and electrochemical tools.

References

[1] J.A. Turner, Science 305 (2004) 972-974.

[2] A. Fujishima, K. Honda, Nature 238 (1972) 37–38.

[3] R. Cao, J.-S. Lee, M. Liu, J. Cho, Adv. Energy Mater. 2 (2012) 816–829.

[4] S. Park, Y. Shao, J. Liu, Y. Wang, Energy Environ. Sci. 5 (2012) 9331-9344.

[5] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Chem. Soc. Rev. 44 (2015) 2060-2086.

[6] H. Dau, C. Limberg, T. Reier, M. Risch, S. Roggan, P. Strasser, ChemCatChem, 2 (2010) 724-761.

Keywords:
electrochemical catalysts, electrospinning, Pechini method, Perovskite-based catalyst, Water splitting cells, Oxygen evolution reaction.
Synergistic Effect of Cobalt Nanoparticles Embedded in Nitrogen-Doped Carbon As a Pt Alternative Electrocatalyst for Dye-Sensitized Solar Cells
Authors: Ahn Sung hee
Published: February 2020

Dye-sensitized solar cells (DSSCs) are an attractive, innovative energy conversion device because of several distinctive benefits that are hardly obtainable from other next-generation solar cells. A typical configuration of DSSCs includes a nanoporous TiO2 anode sensitized with an inorganic complex, an electrolyte containing I-/I3-couple, and a counter electrode (CE). Platinum (Pt) has been preferred most as an electrocatalyst for the CE, because it possesses excellent properties such as a low charge-transfer resistance, a high electrical conductivity, high transmittance. However, the scarcity of Pt and the resulting cost issue has stimulated research to develop low-cost, earth-abundant materials as Pt alternatives in recent years. A wide variety of materials including metal chalcogenides, oxides, nitrides, and carbides have been explored to date.

In this work, we extend the choice of Pt alternatives up to a metal/carbon composite material and elucidate the hidden mechanism of electrocatalytic activity of this novel catalyst. A fast, large-scalable synthesis route via calcination of zeolitic imidazolate framework-67 (ZIF-67) is developed to obtain N-doped carbon incorporated with Co metals (Co/N-C). 2-methylimidazole coordinating to cobalt ions serves as an excellent carbon source that allows for high incorporation of N atoms within carbon lattice. In addition, in situ reduction of the cobalt ions aids in increasing graphitic nature of Co/N-C. Our in-depth electrochemical investigation including cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed that the electrocatalytic activity of Co/N-C catalyst toward the reduction of I3- is superior to that of traditional Pt counterpart. When employed for the CE material, the DSSCs equipped with the Co/N-C catalyst outperform those fabricated with Pt: the power conversion efficiency of 8.06% is obtained as compared to Pt CE (7.52%). Our study also provides a new sight into this metal/carbon composite catalyst: the Co nanoparticles embedded in the carbon significantly promote the electrocatalytic activity of N-doped carbon. The stability of the Co/N-C catalyst was investigated to ensure the long-term use, revealing that Co/N-C is substantially more resistive against corrosion by the I-/I3- couple, rendering excellent stability to Co/N-C.
Effect of Thermal Treatment of Poly(amide imide) Binder on Cycling Performance of Silicon Alloy-Based Anode for Lithium-Ion Battery
Authors: Kim Sang-Hyung , Yang Hwi Soo , Yook Seung Hyun , Kim Seon-Kyong , Park Cheol-Ho , Choi Hae Young , Kim Dong-Won
Published: February 2020

The growing demand for high-performance rechargeable lithium-ion batteries for applications such as portable electronic devices, electric vehicles and energy storage systems requires remarkable improvement in the energy density. It has led to the search for advanced materials with high theoretical specific capacities, which should be abundantly available for large-scale applications. Silicon-based anode materials with high theoretical capacity, low reduction potential and low cost satisfy these requirements for next-generation lithium-ion batteries.  However, the silicon materials undergo large volume changes during the alloying/de-alloying reaction, resulting in pulverization of the electrode. In addition, the large volume expansion results in the continuous breakdown and formation of solid-electrolyte interphase (SEI) layer during the repeated cycling.  To mitigate the volume change, many studies have been carried out by different approaches such as fabricating thin films, reducing particle size, employing Si alloy materials and using strong binder.  It is well known that binders are critical to maintain the electrode structure and capacity retention.  Different binders for Si-based anodes developed to date include carboxymethyl cellulose (CMC), poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), poly(amide imide)(PAI) and polyimide (PI).  Among them, thermally-treated PAI has high mechanical strength and good adhesion, enhancing the electric contact with current collector.  In this study, we report electrochemical characterization of Si alloy materials with thermally-treated PAI as a binder.  Furthermore, we analyzed binding mechanism of PAI, with changing heat treatment temperature. A detailed investigation and evaluation of cycling performances are performed by XPS, FT-IR, electrochemical impedance spectroscopy, peel test and galvanostatic cycling test.
Biomolecule Detection Using a Resonant Capacitive Sensor
Authors: Bane Danielle , Subramanyam Guru , Hansen Karolyn M.
Published: February 2020

Biomarker detection is of paramount importance to the medical community for the assessment of health and human performance.  Two biomarkers of interest are orexin A (a biomarker of cognitive function) and trimethylamine (a biomarker of the disease trimethylaminuria).  For the purpose of orexin A and trimethylamine detection, resonant capacitive sensors with a peptide functionalized guanine dielectric layer are designed and fabricated, Figure 1.  The molecular recognition peptides, Table 1, selectively capture the biomarkers.  The binding of the biomarkers to the peptides changes the permittivity of the dielectric layer resulting in a significant shift in the resonant frequency, amplitude, and phase of the sensors thereby indicating the biomarkers’ presence.  

Due to the limited utilization of guanine in electronics, the first objective in designing these sensors has been guanine characterization.  For characterization purposes, guanine was deposited as the dielectric layer in a capacitive test structure (CTS), and from these structures, the dielectric constant and loss tangent of guanine was determined by comparing the measured scattering-parameters (S-parameters) to an electrical model of the device.  Subsequently, guanine was deposited as the dielectric for the resonant capacitive sensor to determine the resonance of the guanine-integrated structure and to serve as the sensor platform. 

After guanine characterization, the next objective is to investigate methods for peptide functionalization.  The two methods of interest are spin-coating and chemical tethering (preferred).  In order to be successful, the peptides must adhere to the guanine in a manner that does not interfere with the biomarker binding sites.  The chemical tethering method offers a way to covalently cross-link the peptides to the guanine, but the spin-coating is less likely to interfere with the peptides’ binding sites. 

After determining a functionalization method, the guanine will be functionalized with peptides using this method. 

The final objective is to test the fabricated sensors.  For testing, the S-parameters are measured to determine the resonance of the sensors pre-exposure (baseline) and following exposure to positive (orexin A in aqueous phase and trimethylamine in vapor phase) and negative controls.

Acknowledgements:  Support was provided through the Dayton Area Graduate Studies Institute Fellowship, and the Air Force Research Laboratory (Human Effectiveness and Materials and Manufacturing Directorates).

References

[1] J. Hagen, W. Lyon, Y. Chushak, M. Tomczak, R. Naik, M. Stone, and N. Kelley-Loughnane, “Detection of orexin a neuropeptide in biological fluids using a zinc oxide field effect transistor,” ACS Chemical Neuroscience, vol. 4, no. 3, pp. 444–453, 2013.

[2] Y.-R. L. Tzong-Zeng Wu and E.-C. Chan, “Exploring the recognized bio-mimicry materials for gas sensing,” Biosensors and Bioelectronics, vol. 16, no. 9-12, pp. 945-953, 2001.

Figure 1
XPS and FTIR Studies of Dual Target Sputtered Bcn Thin Films
Authors: Prakash Adithya , Sundaram Kalpathy B
Published: February 2020

The ever increasing advancements in semiconductor technology and continuous scaling of CMOS devices mandate the need for new dielectric materials with low-k values. The interconnect delay can be reduced not only by the resistance of the conductor but also by decreasing the capacitance of dielectric layer. Also cross-talk is a major issue faced by semiconductor industry due to high value of k of the inter-dielectric layer (IDL) in a multilevel wiring scheme in Si ultra large scale integrated circuit (ULSI) devices. Recently it has been found that Boron Nitride (BN) films can achieve low-k values around and hardness comparable to diamond [1][2].  BN is hygroscopic in nature. In this respect carbon can be added to the BN structure to produce Boron Carbon Nitride (BCN) films as the possible substitute for BN. The minimum dielectric constant achieved by plasma assisted chemical vapor deposition for a BCN thin film was reported to be 1.9. [2] The BCN films are also instrumental in suppressing the Cu migration [3]. The Young’s modulus of BCN films are reported well above 20 GPa making it one of the suitable options for low-k materials [4].

In the present work, BCN films were deposited by dual target sputtering of boron carbide (BC) target (DC), boron nitride (BN) target (RF) in nitrogen ambient with argon. The films were deposited under various N­2/Ar gas flow ratios and temperature. XPS and FTIR measurements were performed to find the relative chemical compositions, chemical bonds and behavior of the deposited films with respect to change in N­2/Ar gas flow ratios and deposition temperature.

REFERENCES

[1] Jun Liu, Kian Ping Loh, Ming Lin, Yong Lim Foo, Wei De Wang, and Dong Zhi Ch, Journal of Applied Physics, 96 (2004) 6679.

[2] Riedel R., Advanced Materials, 4 (1992) 759.

 [3] M. K Mazumder, R. Moriyama, D. Watanabe, C. Kimura, H. Aoki, and T. Sugino: Jpn. J. Appl. Phys. 46 (2007) 2006.

[4] C. Morant, D. Caceres, J. M. Sanz, and E. Elizalde: Diamond Relat. Mater. 16 (2007) 1441.
Evaluation of Dynamic Hydrophobicity of Nanoporous Silicon Surfaces Prepared By Metal-Assisted Chemical Etching
Authors: Machida Kenta , Asoh Hidetaka , Yoshida Naoya , Okura Toshinori , Ono Sachiko
Published: February 2020

Wettability is one of the important properties of solid surfaces from both fundamental and practical aspects. Among various factors, surface energy and roughness are the dominant factors for the wettability. Static wettability, that is, water contact angle (WCA) has been commonly used as a criterion for the evaluation of hydrophobicity of solid surface. In recent years, WCA can be designed easily by controlling surface energy and roughness based on Young’s, Wenzel’s, and Cassie’s equations. On the other hand, dynamic wettabilities such as sliding property on the hydrophobic surface are poorly undersutood. Although water sliding angle (WSA: the critical angle where a water droplet with a certain weight begins to slide down the inclined plate) and contact angle hysteresis (the cosine of receding contact angle minus that of advancing contact angle) are often measured to evaluate the water-repellent property of the hydrophobic surface, comprehensive understanding of the water-repellent properties is still limited because the relationships between the WSA and the WCA are not clear [1-2]. In this study, we used nanoporous silicon surfaces with different surface morphologies, which were formed by metal-assisted chemical etching using Ag nanoparticles, as a solid surface. Static and dynamic wettabilities of their surfaces were investigated with focusing on the influences of pore size and surface roughness on wettability of porous silicon surfaces.

p-type silicon (100) substrates were immersed in a mixed solution of 2×10-2 mol dm-3 AgNO3 and 5 mol dm-3 HF to deposit Ag particles on the entire surface of silicon substrates. After deposition of Ag particles, silicon substrates were immersed in a mixed solution of 10 mol dm-3 HF and 1 mol dm-3 H2O2at room temperature at different time. SEM images of obtained porous silicon after etching with different surface roughness are shown in Fig. 1. WCAs (approximately 135°) of etched silicon were higher than that of flat silicon (75°), presumably due to decrease of contact area between porous structure and droplet based on Cassie’s model. Although surface roughness increased with increasing etching time, however, WCAs of etched silicon were about the same (135°) despite the difference in surface morphologies (Fig. 1a-c). On the other hand, WSAs increased with increasing surface roughness. The changes in WSAs were thought to be caused by the pinning effect generated by increase of pore diameter and surface roughness during chemical etching. These results indicate that WSA is affected more significantly by physical inhomogeneity such as surface roughness of the etched surface than WCA.

[1] M. Miwa, A. Nakajima, A. Fujishima, K. Hashimoto, T. Watanabe, Langmuir,
16, 5754-5760 (2000).

[2] S. Suzuki, A. Nakajima, Y. Kameshima, K. Okada, Surface Science Letters,
557, L163-L168 (2004).

Figure 1
Studies on the Effects of Angle of Incidence on the Optical Reflecftance Properties of Silicon Nanowires Grown By Electroless Etching
Authors: Velez Victor H. , Mertens Robert George , Sundaram Kalpathy B
Published: February 2020

Silicon nanowires (SiNW’s) arrays prepared by electroless etching method can significantly suppress light reflection across the visible spectrum [1]. The decrease in reflectivity is evidently due to optical absorption in the silicon. The nanowires scatter the incident light by reflection, refraction, and diffraction processes, and the light will interact with several nanowires until it is either absorbed by a nanowire or the substrate, or is reflected by the sample [2].  However, the Fresnel reflection predicts a large reflectance at a large angle of incidence (AOI) [3]. For effects of comparison, the reflectance versus wavelength data using visible light on SiNW’s grown by eletroless etching in three different concentrations of Hydrofluoric Acid (HF) and Silver nitrate (AgNO3) for different etching times at room temperature have been provided at different AOI values. In general, SiNW’s exhibit low reflectance over a wide range of AOI. SiNW’s etched with high concentration of AgNO3 produce low reflectance. These results are beneficial to the design and fabrication of nanowire-based optoelectronic devices.

In this experiment a Cary 100 UV-Visible Spectrometer was used for reflectance analysis and silicon (Si) wafers were dipped for 15, 30, 45 and 60 minutes at room in an electroless solution prepared in a petri dish containing silver nitrate (AgNO3) and hydrofluoric acid (HF) [4].
The Center for Electrochemical Energy Science (CEES): An Overview
Authors: Fenter Paul
Published: February 2020

The Center for Electrochemical Energy Science (CEES) seeks to develop a fundamental understanding of the lithium ion electrochemistry of oxides in lithium ion battery systems.  Controlling electrochemical reactions is a significant challenge, due to the extreme structural and chemical changes that take place as lithium ions are incorporated in the active electrode material.  We are approaching this through coordinated studies of three types of lithium ion chemistries with a focus on oxide electrodes: 1) Insertion reactions (e.g., Li + M-O ↔ LiM-O) into a host oxide matrix; 2) Conversion reactions (e.g., 2Li + M-O ↔ M + Li2O) that disrupt the oxide lattice upon lithiation, leading to phase separation of the metal and Li2O phases; and 3) “Hybrid” Li-O2/Li-ion reactions (e.g., 4nLi+ + nO2 + MOy ↔ (Li2O)2nMOy) that involve disruption of the host lattice, along with insertion of Li and O.  Specifically our primary focus is on studies of well-defined model systems that enable a fundamental understanding of these reactions.  One broad theme in these studies is the role of interfaces in these reactions.  I will also review recent work in which we seek to isolate and understand the role of interfacial reactivity in these systems through in-situ, real-time, observations of lithiation reactions of well-defined model electrode-electrolyte interfaces using X-ray reflectivity.  These results reveal novel insights into the role of interfacial reactivity in conversion reactions (e.g., Si, CrOx, NiO) that can be used to control the complex reaction lithiation pathway through the use of thin-film and multilayer electrode structures.

Acknowledgment: This work was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.  The work was done in collaboration with T. Fister, S. S. Lee (ANL), J. Esbenshade, B. Long, A. Gewirth (University of Illinois at Urbana-Champaign), X. Chen, G. Evmenenko, M. Bedzyk (Northwestern University).
Center for Mesoscale Transport Properties: Probing the Limits of Electron and Ion Transport over Multiple Length Scales
Authors: Marschilok Amy C
Published: February 2020

The mission of the EFRC is to understand and to ultimately control transport properties in complex battery systems with respect to multiple length scales, from molecular to mesoscale (m
2
m); to minimize heat and maximize work of electrical energy storage devices.  Thus, we are probing the factors limit of ion and electron transport and electron transfer over multiple length scales. 

This presentation will focus on several of the parameters affecting active materials. Several materials classes are under investigation including 1D, 2D and densely packed structures. The impact of the active material size and morphology on electrochemical behavior is probed through preparation of samples through direct synthetic manipulation of the material properties.  The intrinsic electrochemical properties of active materials without the complexities of composite electrodes were probed through development of electrochemical measurements of individual particles.  Additionally, the detailed analysis and role of structural defects on electrochemical performance will be presented.   The information gained will provide necessary information for the design of next generation energy storage devices.
Understanding the Layered Oxides for High-Voltage Intercalation in Alkaline Ion Batteries
Authors: Meng Shirley
Published: February 2020

Among all candidates of positive electrode materials for lithium ion batteries, the layered oxides have gained growing research interest in recent years, especially the Ni rich layered oxides and the mixed transition metal (Ni,Co,Mn) layered oxides. They can reach more than 220mAh/g capacity when charged above 4.5V, making them one of the highest energy density positive electrode materials among all known intercalation compounds for cathode materials. [1] Being the source of major capacity improvement, the high voltage operation (>4.5V), on the other hand, also cause unexplained phenomena in these layered oxides. In classical layered oxides, the transition metal (TM) oxide host TMO2should retain its host structure during initial discharging–charging, while lithium ions are intercalated–de-intercalated from the host. In contrast, recent studies suggested that after high voltage operation in layered oxides, certain amounts of transition metal ions migrate from the transition metal layers to lithium layers. Our previous work [2] has suggested that the migration may be assisted by oxygen vacancies generated in the late charging states (high voltages), but three critical questions remain unanswered: (1) how can we visualize and quantify the change in structure and chemical content at the atomic level (2) what is the oxygen activity upon high voltage and how does it assist transition metal migration and (3) what are the impact of these high voltage phenomena on rate capability and long-term cycling.

LiNi0.8Co0.15Al0.05O2 (NCA), LiNi1/3Co1/3Mn1/3O2 (NCM333) and LiNi0.5Co0.2Mn0.3O2(NCM523) are used as model compounds for the in-depth study. Figure 1 and Table 1 summarize the electrochemical properties of NCA and NCM333 and 532.

 A suite of powerful experimental tools and computational tools has been deployed. To probe the bulk structural change, morphological and chemical changes, we combined X-ray diffraction (XRD), Neutron diffraction (ND), Pair Distribution Function (PDF) analysis, Electron Energy Loss Spectroscopy (EELS) and Transmission X-ray Microscopy (TXM), analytical Transmission Electron Microscopy (TEM). We will reveal and discuss the factors that determining the high voltage stability of oxides materials in alkaline ion batteries.

Acknowledgements

This work is supported by the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences, with Award Number DE-SC0012583.   

Reference

1)     Z. H. Lu, D. D. MacNeil and J. R. Dahn, Electrochem. Solid- State Lett., 2001, 4, A191–A194

2)     K. J. Carroll, D. Qian, C. Fell, S. Calvin, … and Y. S. Meng, Phys. Chem. Chem. Phys., 2013 15, 11128

Figure 1
Center for Mesoscale Transport Properties: Molecular to Mesoscale (m2m)
Authors: Takeuchi Esther S
Published: February 2020

The mission of the m2m EFRC is to understand and to ultimately control transport properties in complex battery systems with respect to multiple length scales, from molecular to mesoscale (m
2
m); to minimize heat and maximize work of electrical energy storage devices.

In the context of energy storage the focus is on battery polarization (i.e. thermodynamic voltage - loaded voltage) under use conditions.  The determination of the factors that contribute to and control polarization at the material, electrode, and cell level will be explored under the program.  The organization of the center has been developed to facilitate investigation of the processes taking place over multiple length scales.  Additionally, as electroactive materials in the battery system are in complex environments, including multiple solid as well as liquid interfaces, the behavior of the materials in complex environments will be probed in detail.  Lastly, the impact of time and extended electrochemical activity (electron and ion flux) on the material and energy storage system behavior will be determined.

The efforts of the Center are unified through the investigation of model materials where the initial focus includes examples of 1D, 2D and densely packed materials.   Understanding the function of model materials from the atomic scale to the mesoscale to the systems level will reveal insight into the phenomena that control battery behavior, establishing the paradigms by which to explore and control other storage systems.  Examples of the research results from the Center will be described.
Computational Studies of Lithium Manganese and Nickel-Manganese Oxide Spinel Surfaces
Authors: Iddir Hakim , Lau Kah Chun , Curtiss Larry
Published: February 2020

LiMn2O4 is ideal as a high-capacity Li-ion battery cathode material by virtue of its low toxicity, low cost, and the high natural abundance of Mn. However, this material suffers from Mn dissolution problem that not only induces capacity fade, but can also poison the anode. Several approaches have been devised to mitigate Mn dissolution, including doping, coatings, and even particle shape control. Previous studies have shown that the electrochemical performance and cycling stability of these materials depend not only on the composition, but on the particle morphology as well. Simulations of the structure of low index surfaces of the spinel-structured LiMn2O4 and its derivatives, such as the high voltage LiNi0.5Mn1.5O4 spinel have been performed within the GGA+U approximation, and ab-initio molecular dynamics. New insights resulting from this work, including interactions with electrolytes, will be presented.

This work was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.
An Integrated First Principles and Experimental Approach to Enabling Multi-Electron Lithium-Ion Battery Cathodes
Authors: Ong Shyue Ping , Lin Yuh-Chieh , Huang Yiqing , Wen Bohua , Quackenbush Nicholas F. , Chung Youngmin , Chernova Natasha , Omenya Fredrick , Piper Louis F.J. , Whittingham M. Stanley
Published: February 2020

Today’s commercial lithium-ion battery cathodes function on the basis of a single-electron transfer per transition metal. In order to attain significantly higher capacities, particularly in polyanionic compounds with higher voltages, achieving reversible multi-electron transfer per transition metal is necessary. In this talk, we will discuss the efforts of the Northeast Center for Chemical Energy Storage (NECCESS), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001294, to identify crystal structures that can reversibly intercalate two lithium ions and understand the implications to the crystal lattice and its stability of inserting those two lithium ions. Specifically, we will present results from our combined first principles and experimental investigations into the thermodynamics, kinetics and electronic structure of ε-VOPO4 (theoretical capacity of 318 mAh/g) over two Li insertion. We find that density functional theory, X-ray photoelectron spectroscopy and cyclic voltammetry all provide evidence of two-phase behavior during the first Li insertion and multiple intermediate phases during the second Li insertion. We will also show that ε-VOPO4 and its lithiated compounds show extremely good thermal stability relative to other well-known cathodes, and discuss our findings on the ionic and electronic limitations in this material.
Hybrid Li-Ion/Li-Oxygen Battery Materials
Authors: Chan Maria K. Y. , Kinaci Alper , Yang Zhenzhen , Zhan Chun , Lin Chi-Kai , Maroni Victor A. , Trahey Lynn , Yao Zhenpeng , Wu Jinsong , Castro Fernando , Li Qianqian , Dravid Vinayak , Wolverton Chris , Johnson Christopher , Lu Jun , Amine Khalil , Thackeray Michael M.
Published: February 2020

In the Center for Electrochemical Energy Science (CEES) EFRC, we are investigating a new class of energy storage materials – hybrid Li-ion/Li-oxygen materials – that combine lithium ion and lithium oxygen capacity to deliver high energy storage capacity [1,2]. In this talk, we will discuss our synthesis, characterization, and first principles modeling efforts of these hybrid Li-ion/Li-oxygen materials, in an attempt to understand their electrochemical performance and reaction mechanisms. We will report on the in-situ observations of structural changes during electrochemical cycling, and accompanying first principles studies, in prototypical hybrid materials, Li5FeO4 and αMnO2 [3]. We will present results of high throughput computational searches for new hybrid materials [4]. Challenges and future prospects of hybrid materials will also be discussed.

[1] L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, M. M. Thackeray, “Activated Lithium-Metal-Oxides as Catalytic Electrodes for Li-O2 Cells,” Electrochemical and Solid-State Letters, 2011, 14, A64.

[2] M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, “Vision for Designing High-Energy, Hybrid Li Ion/Li-O2 Cells,” Journal of Physical Chemistry Letters, 2013, 4, 3607.

[3] Z. Yang, L. Trahey, Y. Ren, M. K. Y. Chan, C. Lin, J. Okasinski, and M. M. Thackeray, “In-Situ High-Energy Synchrotron X-ray Diffraction Studies and First Principles Modeling of α-MnO2 Electrodes in Li-O2 and Li-ion Coin Cells,” Journal of Materials Chemistry A, 2015, 3, 7389.

[4] S. Kirklin, M. K. Y. Chan, L. Trahey, M. M. Thackeray, C Wolverton, “High-throughput screening of high-capacity electrodes for hybrid Li-ion-Li-O2 cells,” Physical Chemistry Chemical Physics, 2014, 16, 22073.

Figure 1
Surface Segregation Phenomena in La0.6Sr0.4Co0.2Fe0.8O3-δ Subjected to Mechanical Stress
Authors: Araki Wakako , Tanii Wataru , Arai Yoshio
Published: February 2020

The present study reports on the surface segregation phenomena in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) subjected to mechanical stress. LSCF samples with mirror-polished surfaces were annealed under uniaxial compression and also four-point bending to investigate the effects of the compressive and tensile stresses on the surface segregation. The annealing was performed at up to 1173 K under up to 100 MPa of mechanical stress. The surface segregaion was examined by using SEM, EDX, and micro-Raman spectroscopy. The Sr-rich phase segregates on the surface, especially where specific surface area is large. The size of the segregated particles increases with increasing annealing time, whereas their number reveals no clear dependence. The number of the segregated particles is fewer, whilst the particle size is larger for the sample annealed under the uniaxial compression, compared to the one annealed without compression. There is a significant difference in the segregation phenomena between the tensile and compressive surfaces annealed under the bending. The effects of the stress distribution as well as the porous structure on the segregation are also demonstrated. In addition to the segregaion, high-temperature creep deformation due to Sr diffusion and grain boundary sliding is observed. Based on the above results, the mechanism for the Sr surface segregation in LSCF under mechanical stress is discussed, considering Sr diffusion under microscopic and macroscopic stress fields. The surface reactivity of LSCF under mechanical stress is briefly discussed.
Analysis of Performance Limiting Factors in Solid-Oxide Iron-Air Redox Battery Operated with Different Redox Couples
Authors: Jin Xinfang , Zhao Xuan , White Ralph E. , Huang Kevin
Published: February 2020

A new bi-functional fuel-cell/battery hybrid system has recently been developed in the presenter’s group for power generation and energy storage. The new system is comprised of a reversible SOFC as the electrical charger/discharger and a redox-active metal/metal-oxide chemical bed as the energy storage. During operation, the cathode of the system is constantly open to air, whereas the anode configuration defines the true functionality of the system: power generation when the anode chamber is open to a flowing fuel, and energy storage when the anode chamber is closed next to a neighboring multivalent metal/metal-oxide chemical bed.

The presentation highlights recent progress in computational analysis of physics and chemistry governing the performance of the fuel-cell/battery hybrid. These highlights include the identification of performance limiting factors, analysis of heat flow balance and proposal of strategies to achieve energy efficient hybrid system for simultaneous power generation and energy storage.