bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbonate Fuel Cell Anode: A Review
Authors: Hilmi Abdelkader , Yuh Chao-Yi , Farooque Mohammad
Published: February 2020

Introduction

The molten carbonate fuel cell (MCFC) has emerged as one of the leading devices to convert chemical energy into power. To date 1.9 GWh of electricity has been produced commercially using this new technology. The molten carbonate fuel cell uses a mixture of alkali carbonates as the electrolyte and operates in the temperature range of 550-650°C. The high operating temperature dramatically improves the reaction kinetics and eliminates the need for a noble metal catalyst. During cell operation, hydrogen is oxidized at the anode and oxygen is reduced at the cathode, equations (1) and (2)

H2 + CO3
2- → H2O + CO2 + 2e- (1)

1/2O2 + CO2 + 2 e- → CO3
2- (2)

The current carbonate fuel cell design (illustrated in figure 1) has evolved over many years from extensive research conducted in fifteen companies and many prestigious laboratories. The cell hardware is made from stainless steel, the electrodes are nickel based, and the separator called matrix is a porous ceramic. The anode design is an important consideration from both performance and cost considerations.

The state of the art MCFC anode is a porous Ni electrode stabilized against sintering by Cr and/or Al additives. Typical anodes have porosities of 40-60% and 3-6 µm as average pore diameters. To ensure long-term stability against creep, corrosion and oxidation, major considerations need to be taken into account in material selection. Mechanical and chemical stability as well as the electrochemical activity for anode are key factors for performance and life stability.

Accelerated lab-scale technology stacks (30kW) and long-term field tests have shown that the current anode materials have the desired performance and stability of the useful life of >5-7 years. As shown in figure 2, anode maintains stable pore structure and morphology over long-term operation. Parameters such as conductivity, pore size distribution, wetting and electrolyte fill level affect anode performance and its stability. To achieve an
New Visible Light Absorbing Materials for Solar Fuels, Ga(Sbx)N1-X
Authors: Sunkara Swathi , Vendra Venkat Kumar , Jasinski Jacek B , Deutsch Todd G , Menon Madhu , Rajan Krishna , Sunkara Mahendra Kumar
Published: February 2020

In this work large band gap bowing of dilute antimonide alloys of gallium nitride, Ga(Sbx)N1-x has been investigated. Our computational calculations using first principles density functional theory2 revealed that a small amount of Sb incorporation is sufficient to achieve a significant band gap reduction in GaN from 3.4eV to 2eV. Theoretical calculations predicted that Ga(Sb)xN1-x alloys with 2 eV band gap straddle the electrochemical potentials of the hydrogen and oxygen evolution reactions. Theoretical computations with Sb composition beyond 7% change the electronic band gap from direct to indirect.

Synthesis of crystalline GaSbxN1-x alloys were carried out using metal organic chemical vapor deposition using trimethyl gallium (TMGa) and Trimethyl Antimony (TMSb) and ammonia at x values ranging from 0-8%. Synthesis was carried out on different planar substrates and GaN nanowires. X-ray diffraction measurements showed a monotonic increase in the lattice with increase in antimonide composition which corroborates with theoretical calculations. Optical measurements like UV-Vis spectroscopy and photocurrent spectroscopy suggested a rapid decrease in band gap from 3.4 to 2 eV with small concentration of antimonide incorporation. Experimental data from optical measurements indicated direct band gap transition for alloys less than 7at% and an indirect band gap transition for alloys beyond 7% as shown in fig. 1. In addition Mott Schottky measurements showed that Ga(Sb)xN1-x alloys ranging from 0-8% straddle the water oxidation and reduction potentials in agreement to computational calculations. Moreover, the photo-electrochemical data on activity and stability suggest that these alloys are highly suitable for solar water splitting under visible light irradiation.

Fig. 1 Tauc plots for direct transition and indirect transition for 2 % Sb (a,b) and 8 % Sb (c,d).

Acknowledgements: Financial support from US Department of Energy (DE-FG02-07ER46375) and NSF (DMS1125909).

References:

1. S. Sunkara, V. Vendra, J. Jasinski, T. Deutsch, A.N. Andriotis, K. Rajan, M. Menon and M.K. Sunkara, “New Visible Light Absorbing Materials for Solar Fuels, Ga(Sbx)N1-x”, In Review (2013)

2. R.M. Sheetz, E. Richter, A.N. Andriotis, C. Pendyala, M.K. Sunkara and M. Menon, “Visible light absorption and large band gap bowing in dilute alloys of gallium nitride with antimony”, Phys. Rev. B, 84, 075304 (2011)
Solar Fuel Generation By Semiconductor-Graphene Heterogeneous Photocatalysts
Authors: Wu Nick , Meng Fanke
Published: February 2020

Semiconductors have been extensively used as photocatalysts and photoelectrodes for solar fuel generation. Currently single semiconducting material cannot suffer from low efficiency of conversion of solar energy to chemical energy. An alternative to overcome this barrier is to the development of hetero-structured photocatalysts.

This presentation shows that integration of semiconductors with graphene can significantly improve the photocatalytic activity. First, hematite (a-Fe2O3) nanocrystals have been deposited on the reduced graphene oxide (rGO) sheets to form the hematite/rGO heterogeneous photocatalyst, which shows much higher photocatalytic activity toward water oxidation.1 The photocatalysis enhancement is due to the fact that facilitates the charge migration and reduces the charge recombination rate.

In addition, we have developed a heterogeneous photocatalyst based on the nanoscale p-n junction of p-type molybdenum disulfide/n-type nitrogen-doped reduced graphene oxide.2 It is interesting that MoS2 alone exhibits negligible photocatalytic activity. In contrast, the MoS2/rGO p-n junction photocatalyst show significant photocatalytic activity toward hydrogen generation.

References

[1] F. Meng, J. Li, S. K. Cushing, J. Bright, M. Zhi, J. Rowley, Z. Hong, A. Manivannan, A. D. Bristow, N. Q. Wu, ACS Catalysis, 3 (2013), 746–751.

[2] F. Meng, J. Li, S. K. Cushing, M. Zhi, N. Q. Wu, J. Am. Chem. Soc., 135 (2013), 10286-10289

Acknowledgement:

The resource and facilities used were partially supported by NSF (EPS 1003907), the West Virginia University Research Corporation and the West Virginia EPSCoR Office. The use of WVU Shared Facility was appreciated.
Branched Nanowire Heterostructures for Efficient and Durable Solar-Driven Hydrogen Production
Authors: Kargar Alireza , Kim Sung Joo , Choi Chulmin , Allameh Paniz , Jeong Huisu , Jung Gun Young , Jin Sungho , Pan Xiaoqing , Wang Deli
Published: February 2020

Branched nanowire (NW) heterostructures have recently been attracted considerable attention for solar water splitting and clean hydrogen production due to their unique properties such as nanoscale integration of different functional materials, greatly enhanced junction and surface area, enhanced gas evolution efficiency, broadband light absorption, etc. Moreover, branched NWs can be fabricated using facile and scalable fabrication methods such as hydrothermal or solvothermal growth methods. In this presentation, we show branched NWs of different compositions for core (or trunk) and branch NWs which were fabricated with facile and low-cost synthesis methods using cheap, non-toxic, and earth abundant materials including Si, CuO, Cu2O, ZnO, TiO2, and Fe2O3. The branched NW structures and the heterostructures’ interfaces are investigated in detail using different characterization techniques such as SEM/HRSEM, TEM/HRTEM, STEM/HRSETM, etc. The photoelectrochemical (PEC) performances including photocurrent turn-on potential, photocurrent, solar conversion efficiency, and incident photon-to-current efficiency (IPCE) are studied systematically and optimized, based on different core and branch NW dimensions, for each specific branched NW heterostructure to provide efficient water splitting in a neutral medium. The electrode stability of different branched NWs is also investigated and long-term stability of over one day or several hours using a thin passivation layer or robust branched NWs are presented. The achieved results pave the way for accomplishing spontaneous overall solar water splitting for clean, efficient, cost-effective and durable solar hydrogen generation at large scales.
Water Oxidation and CO2 Reduction Catalyst for Artificial Photosynthesis
Authors: Jia Hongfei , McDonald Kenneth J , Gower Mitchell , Zhou Li Qin , Ling Chen
Published: February 2020

Photocatalytic or photoelectrochemical processes that couple water oxidation and CO2 reduction are currently under intense investigation for solar fuel production. As these so called “artificial photosynthesis (AP)” systems are expected to remediate the issue of ever increasing CO2 level in the atmosphere, it is necessary to construct them using cheap and efficient materials for large scale deployment. The importance of water oxidation and CO2 reduction catalysis for AP has been well recognized in recent years, yet significant challenges still remain to find low cost materials that are both efficient and stable [1]. Towards the search for catalyst based on earth abundant materials, we previously investigated transition metal tungstates as water oxidation catalysts [2] and nickel macrocycles for CO2 reduction [3]. In this work, perovskites-type of metal oxides is further studied to improve catalyst performance at neutral pH as oxygen evolution catalyst. We also report a new strategy of ligand modification to silver surface, which allows the control of product selectivity for electrochemical CO2 reduction. Details about materials synthesis, characterization of physiochemical properties and evaluation of catalytic performance will be discussed in this presentation, as well as studies on catalyst stability and the influences of electrolytes.

(1) J. R. McKone, N. S. Lewis and H. B. Gray, Chem. Mater., 2013 ASAP

(2) H. Jia, J. Stark, L. Q. Zhou, C. Ling, T. Sekito, Z. Markin. RSC Adv. 2012, 2(29), 10874-10881

(3) J. Schneider, H. Jia, K. Kobiro, et al. Energy Environ. Sci. 2012, 5, 9502-9510.
Gas Cross-over and Durability of Membrane Electrode Assemblies
Authors: Büchi Felix N. , Kreitmeier Stefan
Published: February 2020

Durability of the membrane electrolyte is a key factor for the longevity of polymer electrolyte fuel cells. A loss of gas separation is the most detrimental failure mode of perfluorosulfonic acid membranes. Mechanical formation of micron sized membrane defects is the main degradation process during fuel cell operation. This process is accelerated by variations in the operating conditions, such as humidity and temperature, and by imperfections and local defects of the gas diffusion electrodes.

The impact of these local defects, termed pinholes is studied by implementing artificial micron sized defects in the membrane by focused ion beam (FIB) milling. Such membranes were then operated in different accelerated stress tests to study the development of chemical, mechanical and thermal degradation processes. Degradation at membrane defects was investigated post mortem using synchrotron based X-ray tomographic microscopy (XTM) and FTIR spectro-microscopy (see Figure 1) [1]. Gas cross-over, a key function for degradation, is controlled by operating conditions and material characteristics and was measured in-situ by mass spectrometry using a tracer gas concept [2, 3].

From the results an overall degradation mechanism at membrane defects can be thus formulated [4].

[1] S. Kreitmeier, M. Michiardi, A. Wokaun, F. N. Büchi, Factors determining the gas crossover through pinholes in polymer electrolyte fuel cell membranes, Electrochim. Acta, 80, 240-247 (2012)

[2] G. A. Schuler, A. Wokaun, F. N. Büchi, Local online gas analysis in PEFC using tracer gas concepts, J. Power Sources, 195, 1647–1656 (2010)

[3] S. Kreitmeier, G. A. Schuler, A. Wokaun, F. N. Büchi, Investigation of membrane degradation in polymer electrolyte fuel cells using local gas permeation analysis, J. Power Sources, 212, 139-147(2012)

[4] S. Kreitmeier, P. Lerch, A. Wokaun, F.N. Büchi, Local degradation at membrane defects in polymer electrolyte fuel cells, J. Electrochem. Soc. 160, F456-F463 (2013)
The Graphitization-Stability Relation of High Surface Area Carbons
Authors: Stamatin Serban Nicolae , Nørgaard Casper Frydendal , Andersen Shuang Ma , Skou Eivind Morten
Published: February 2020

Fuel cells have benefited from increasing attention for the last two decades. They have shown their ability of producing both electrical energy and heat with high efficiency and low environmental pollution. One of the main challenges which need to be addressed before commercialization is the durability and activity of the membrane-electrode assembly (MEA). This is formed of proton exchange membrane sandwiched between two catalytic systems. The catalyst in form of 2-3 nm particles is supported on a high surface area active carbon. The most used catalyst is Pt and its alloys which carry a large contribution to the total cost associated with a fuel cell [1]. However, Pt activity is lost during fuel cell operation due to the contribution of a matrix of phenomenon such as dissolution[2], particle agglomeration, particle detachment, Ostwald ripening and carbon support corrosion[3].

This work focuses on how the overall catalyst durability depends on morphological and chemical properties of the catalyst support material. Morphological and chemical changes have been induced in a high surface area carbon by heat treatment at different temperatures. The resulting samples, along with the pristine material, have been characterized by Raman spectroscopy, XRD and XPS. Furthermore, all these support materials have been platinized and tested for activity in the oxygen reduction reaction as well as their stability under potential cycling in acidic environment The degradation was done according to the FCCJ degradation protocol and took place in a two compartment – three electrode cell setup.

Fig. 1 TG-DSC curve of the initial high surface area carbon

Acknowledgement

This work has been supported by the Danish PEMFC Catalysts for Boosted Activity and Enhanced Durability (Energinet. dk project no. 2011-1-10669).

References

[1] H. A. Gasteiger, D. R. Baker, R. N. C. Hydrogen Fuel Cells: Fundamentals and Applications; Wiley: Copenhagen, 2010

[2] Topalov, A.; Katsounaros, I.; Auinger, M.; Cherevko, S.; Meier, J. C.; Klemm, S. O.; Mayrhofer, K. J. J. Angewandte Chemie (International ed. in English) 2012, 51, 12613–5.

[3] Meier, J. C.; Galeano, C.; Katsounaros, I.; Topalov, A. A.; Kostka, A.; Schu, F.; Mayrhofer, K. J. J. ACS Catalysis 2012, 2, 832–843.
Glycosylation of a Novel Sugar Orthoester Under Electrochemical Conditions
Authors: Kawa Kohei , Saitoh Tsuyoshi , Nishiyama Shigeru
Published: February 2020

Glycosylation is one of the important synthetic methodologies to generate glycoside antibiotics and sugar chains, which tightly interact with living body. A number of condensation methodologies to acquire glycosidic linkages with efficient selectivity and yields, have been developed during the last century, and related investigation is powerfully promoting even today. Among such efforts, electrochemical procedure for oxidation-potential differentiation of anomeric substituents, has been exploited by Yoshida et al. to generate oxocarbenium cation intermediates.

We present another electrochemical glycosylation by using an extremely stable sugar orthoester derivative, which is intact under standard work-up and chromatographic conditions. Thus, the orthoester, prepared by the standard Koenig Knorr reaction of the corresponding glucose tetra-O-benzoyl bromide, was reacted with the 6-hydroxyl glucoside in the presence of EGA (electrochemically generated acid) to give the desired b-glycoside in 90% yield. EGA was produced by anodic oxidation of cyclohexanol under CCE conditions (6 mA, 3 F/mol, supporting salt Bu4NClO4 in (ClCH2)2, divided cell, anode: GC plate, cathode: Pt wire). Detailed synthetic process will be discussed.
The Addition of ArSSAr to Alkenes: The Implications of a Cationic Chain Mechanism Initiated by Electrogenerated ArS(ArSSAr)+
Authors: Matsumoto Kouichi , Sanada Tomonari , Shimazaki Hayato , Shimada Kazuaki , Hagiwara Shino , Fujie Shunsuke , Ashikari Yosuke , Suga Seiji , Kashimura Shigenori , Yoshida Jun-ichi
Published: February 2020

Organosulfur compounds have received much attention because they serve as useful building blocks in organic synthesis and exhibit interesting physical properties in materials chemistry. To synthesize such compounds, the addition of ArSSAr to carbon-carbon multiple bonds is one of the most efficient methods.

We have recently reported the reactions of alkenes with a stoichiometric amount of ArS(ArSSAr)+, which is generated by electrochemical oxidation and accumulated as a cation pool of ArSSAr.1) Thiiranium ions are generated as initial intermediates. Quenching with hard nucleophiles such as MeOH and H2O leads to the addition of an ArS group and RO group (R = Me or H) across the carbon-carbon double bond. In contrast, the use of soft nucleophiles such as ketene silyl acetals, allylsilanes, and Et3N leads to the addition of two ArS groups across the carbon-carbon double bond. Presumably, soft nucleophiles assist nucleophilic attack of ArSSAr on the thiiranium ion intermediate. We envisioned that the addition reaction of ArSSAr to alkenes may proceed with a catalytic amount of ArS(ArSSAr)+ if another molecule of ArSSAr plays a role of a soft nucleophile. This is indeed the case, if we use Bu4NB(C6F5)4 as a supporting electrolyte, and herein, we report this chemistry (Scheme 1).2)

We focused on the reaction of ArSSAr (Ar = p-FC6H4) and (E)-β-methylstyrene with a catalytic amount of electrochemically generated ArS(ArSSAr)+ (Ar = p-FC6H4), as a model reaction. The reaction gave the addition product in 78% yield (Scheme 1). The addition took place anti-selectively, which was confirmed by the comparison of the NMR spectra of the product with those reported in the literature.1a) The present reaction seems to proceed by a cation chain mechanism.

In the prsentation, the details of optimization conditions and the scope and limitations of the present reaction will be discussed.

References

1) (a) Fujie, S.; Matsumoto, K.; Suga, S.; Nokami, T.; Yoshida, J. Tetrahedron
2010, 66, 2823-2829. See also, (b) Matsumoto, K.; Suga, S.; Yoshida, J. Org. Biomol. Chem.
2011, 9, 2586-2596.

2) Matsumoto, K.; Sanada, T.; Shimazaki, H.; Shimada, K.; Hagiwara, S.; Fujie, S.; Ashikari, Y.; Suga, S.; Kashimura, S.; Yoshida, J. Asian J. Org. Chem.
2013, 2, 325-329.
Redox Behavior and Reactions of Cobalt Porphycene Derivatives
Authors: Hisaeda Yoshio , Hashimoto Koichi , Saeki Tatsuya , Shimakoshi Hisashi
Published: February 2020

Tetrapyrrole compounds are very important for the biological system, and these are pigments of life. Heme protein has an iron porphyrin, and chlorophyll contains a magnesium porphyrin derivative. And vitamin B12 has a cobalt corrin. These tetrapyrrole compounds have various functions.1 Inspired by the significance of the porphyrins, a new research direction has emerged that is devoted to the preparation and study of non-porphyrin tetrapyrrolic macrocycles. In this symposium, we will present photochemical and electrochemical reactions of porphycene derivative, which is a porpyrin isomer.

We prepared various brominated porphycenes.2 The singlet oxygen production ability via energy transfer from the triplet state of the porphycene was controlled by the number of bromine. And then, the porphycene having an ionic liquid tag was synthesized and the photo-oxidation reaction in ionic liquid was investigated.3

Tetrapropyl porphycene (H2TPrPc) was synthesized according to the reported procedure.4 A hydrogenated porphycene was obtained by a hydrogenation of H2TPrPc in the presence of zinc and hydrochloric acid.5 Cobalt complexes (cobalt porphycene and cobalt dihydroporphycene) were synthesized by the reaction with [CoII(acac)2] as a metal source. Redox properties were examined by cyclic voltammetry and controlled potential electrolysis. UV-vis spectra of controlled-potential electrolysis revealed that spectra of cobalt porphycene and cobalt dihydroporphycene were quite different in the reduced conditions. These data indicate that the cobalt porphycene was reduced to form a ligand reduced anionradical, but cobalt dihydroporphycene was reduced to form Co(I) species. It suggests the ligand hydrogenation can change the redox behavior.

It is known that cobalt porphyrin can form a Co-C bond by the oxidative addition with Co(I) species and an alkyl halide. Cobalt porphycene is not reduced to form the corresponding Co(I) species unlike cobalt porphyrin. We found that Co-C bond formation is mediated by the reduced ligand of cobalt porphycene. This new reaction, “redox-active ligand-mediated Co-C bond formation of porphycene”, will be reported.

Reference

(1) Hisaeda, Y.; Tahara, K.; Shimakoshi, H.; Masuko, T. Pure Appl. Chem., 2013, 85, 1415.

(2) Shimakoshi, H.; Baba, T.; Iseki, Y.; Aritome, I.; Endo, A.; Adachi, C.; Hisaeda, Y. Chem. Commun., 2008, 2882.

(3) Shimakoshi, H.; Sasaki, K.; Iseki, Y.; Hisaeda Y. J. Porphyrins Phthalocyanines, 2012, 16, 530.

(4) Vogel, E.; Balci, M.; Pramod, K.; Koch, P.; Lex, J.; Ermer, O. Angew. Chem. Int. Ed. Engl., 1987, 26, 928.

(5) Okawara, T.; Hashimoto, K.; Abe, M.; Shimakoshi, H.; Hisaeda, Y. Chem. Commun., 2012, 48, 5413.
Phosphorus: An Alternative for High Capacity Li-Ion Battery Anodes
Authors: Nitta Naoki , Magasinski Alexandre , Yushin Gleb
Published: February 2020

Greater gravimetric and volumetric electrode capacities could result in battery technologies finding greater use in transportation, industrial equipment, electronics, and electric grid applications. Currently, the volumetric capacities of graphite electrodes used in commercial Li-ion cells approach 500 mAh/cm3, while the volumetric capacities of commercial cathodes approach 700 mAh/cm3. Thus, there is a pressing need to develop high capacity anodes to match or exceed the volumetric capacities of cathodes. Tin (Sn) and silicon (Si) – based anodes have been heavily investigated in recent years, while many other materials have received significantly less attention (1). Phosphorus (P) had attracted very little interest until recent years, perhaps due to its difficulty in handling, but has since been shown to offer high gravimetric capacity and rate capability (2). Furthermore, the theoretical volumetric capacity of P is higher than that of Si (2266 mAh/cm3 for Li3P vs. 2190 mAh/cm3 for Li15Si4) (3,4), and Li3P is known to have high Li+conductivity (5).

Here we report on our early investigations of P-based anodes produced using various polymeric binders. The choice of binder material is key to the development of well performing electrodes (6,7). A broad range of binders were tested and analyzed for their impact on the stability and rate performance of phosphorous-carbon composites. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to analyze both the structure and chemistry of the anode materials before and after cycling. Atomic force microscopy (AFM) was used to test mechanical properties of polymer binders (such as swelling and stiffness) in electrolyte solvent solution. Cyclic voltammetry (CV) at different rates was used to test both the electrochemical stability of the polymers and performance of P-based anodes, while electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge cycling at different current densities were additionally used to test the electrochemical performance of the final electrodes in half cells. Our results indicate significant promise for P-based anodes in select applications.

REFERENCES

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A. Jain, S.P. Ong, G. Hautier, W. Chen, W.D. Richards, S. Dacek, S. Cholia, D. Gunter, D. Skinner, G. Ceder, K.A. Persson, APL Materials, 1, 01002 (2013).

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A. Magasinski, B. Zdyrko, I. Kovalenko, B. Hertzberg, R. Burtovyy, C. F. Huebner, T. F. Fuller, I. Luzinov, and G. Yushin, ACS Appl. Mater. Interfaces, 2, 3004 (2010).

I. Kovalenko, B. Zdyrko, A. Magasinski, B. Hertzberg, Z. Milicev, R. Burtovyy, I. Luzinov, and G. Yushin, Science, 334, 75 (2011).
Highly–stable Ternary Si/Carbon Nanotube/Carbon Nanofiber Anodes for Li-Ion Batteries
Authors: Kim Yong Seok , Joo Yong Lak , Cummins Jamie , Patel Bharat , Chakrapani Srinivasan , Lee Sangho
Published: February 2020

Despite the highest theoretical capacity, silicon anodes for Li-ion batteries have two critical drawbacks of (i) severe volume expansion leading to electrical disconnection and (ii) formation of poor electronic conductive solid–electrolyte interface caused by deformation of electrolyte at low potential,[1,2
] leading to a poor cycle performance. Herein, we fabricated ternary silicon nanoparticles (Si NPs) /carbon nanotube (CNTs) /carbon nanofibers (CNFs) via water-based electrospinning process, followed by carbonization. Since CNTs provide excellent electrical and electronic properties from their one–dimensional (1–D) feature, they could be easily assembled with Si NPs into nanofibers and improve the charge conductivity and structural stability for our anodes. Furthermore, the carbon nanofibers made from polyvinyl alcohol polymer can make Si NPs connected each other to form networking electrodes. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests of this ternary anode demonstrated better activity and smaller charge transport resistance than pure SiNPs and our previous Si rich carbon nanofibers[3]. Furthermore, more than two-fold increase in the capacity retention was achieved for the ternary anode compared to that of Si rich carbon nanofibers after 100 cycles. In addition, our ternary anodes exhibited about 1,000 mAh/g even at high charging rates after 150 cycles. This improvement of cycle life should be attributed to facilitating charge transport and distribution of Si NPs by employing 1–D CNTs and carbon nanofibrous networks, and our ternary SiNPs/CNTs/CNFs system provided by scalable water-based spinning should overcome current barriers to commercializing Si-based anodes such as pulverization and low production rate.

References

[1] H. Wu, Y. Cui, Nano Today
2012,
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[2] Wu H.; Chan G.; Choi J. W.; Ryu I.; Yao Y.; McDowell M. T.; Lee S. W.; Jackson A.; Yang Y.; Hu L.; Cui Y. Nature Nanotech.
2012, 7, 310.

[3] Y.S. Kim, K.W. Kim, D. Cho, N.S. Hansen, J. Lee and Y.L. Joo, ChemElectroChem
2013, (in press).
Synthesized Dense and Nanostructured Lithium-Beta-Alumina for Solid-State Li Conductor
Authors: Liu Bo , Ji Liwen , Liu Jun , Xiao Jie
Published: February 2020

Solid state electrolyte has gained much attention because of durability, reliability, no flammable component. As a good candidate, high dense Li-β-Al2O3 electrolyte materials have been synthesized via multiple methods. Direct synthesis was reported to prepare pure Li-beta-alumina ion conductor. Many attempts were investigated to lower sintering temperature. And the effect of the microstructure and oxygen deficiency to ionic conductivity was also studied. The properties and microstructures of the prepared samples were studied by X-ray diffraction (XRD), scan electron microscope (SEM) and ionic conductivity tests.
Studying Rare Earth Surface Treatment for Magnesium Using Scanning Electrochemical Microscopy
Authors: Wallace Gordon G , Jamali Sina S , Moulton Simon E , Weber Jan , Forsyth Maria
Published: February 2020

Rapid dissolution of magnesium alloys in biological solutions limits its successful application as a biodegradable implant where a controlled dissolution/corrosion of magnesium along with healing of tissue is required. Treatment of magnesium surface with rare earth conversion layers has been subject of several studies 1–4 revealing its potential as a passivating layer. Given the biocompatibility properties of such surface treatments, two type of rare earth conversion layers based on Ce(NO3)3 and Pr(NO3)3 have been studied in this present work as surface treatment for AZ80X in simulated biological (buffered) solution. Conversion layers were formed by acid etching the Mg samples in 15mM HCl followed by immersion in 0.05 M Pr(NO3)3 or Ce(NO3)3solutions. Morphology and elemental composition of the conversion layers were characterized by SEM-EDXS.

Scanning electrochemical microscope (SECM) was used to investigate protective properties and degradation behaviour of Ce and Pr conversion layers on a local scale. Surface generation/tip collection (SG/TC) mode was used to study the hydrogen evolution rate and localization while AC mode was used to resolve the resistive/capacitive behaviour of conversion layer. Figure 1 represents the schematic SG/TC mode for probing the local hydrogen evolution. Self-healing properties of the conversion layer in presence of Ce3+ and Pr3+was also studied using SECM. Electrochemical impedance spectroscopy (EIS) was used to look at the changes in charge transfer and diffusion phenomena due to the formation of conversion layer and its degradation in the long term. Preliminary results have shown that Ce and Pr conversion layers improve corrosion resistance in the short term by producing an electrochemically stable surface. In the long term, however, conversion layer shows instability in simulated biological fluid and tends to degrade locally exposing the magnesium substrate to corrosive media.

1. A. Rudd, C. Breslin, and F. Mansfeld, Corrosion Science, 42, 275-288 (2000).

2. M. F. Montemor, a. M. Simões, and M. J. Carmezim, Applied Surface Science, 253, 6922-6931 (2007).

3. K. Brunelli, M. Dabalà, I. Calliari, and M. Magrini, Corrosion Science, 47, 989-1000 (2005).

4. M. Dabalà, K. Brunelli, E. Napolitani, and M. Magrini, Surface and Coatings Technology, 172, 227-232 (2003).

Figure 1 Schematic representation of SG/TC mode SECM for probing hydrogen evolution
Electrochemically Modulated Extraction of Neodymium
Authors: Kalu Egwu Eric , Anderson Shannon , Nilsson Mikael
Published: February 2020

The separation of lanthanides and actinides using the liquid-liquid extraction technique poses a major challenge due to the chemical similarities of the two groups of metals. Hence, interest exists in devising a technique to improve the separation factor. The use of an imposed external field (electrochemical) to improve the liquid-liquid extraction has been explored in the literature with limited success due to conductivity issues. In this work, the use of reverse micelle solutions containing water/AOT-HDEHP/n-dodecane for improved electrical conductivity will be explored. The results of a feasibility study of electrochemical modulation of neodymium extraction using the reverse micelles/microemulsions will be presented.

Electrochemical impedance technique was used to determine the effect of molar content of water, Wo, on the reverse micelle solution conductivity. The distribution ratio of Nd in an electrochemically modulated liquid-liquid extraction containing reverse micelles will also be presented. The mechanism of electrochemical modulated liquid-liquid metal ion extraction will be explored.
Characterization of Nanocomposite Based on Carbon Nanotubes and Conducting Polymers with Different Dopants for Obtaining of Modified Electrodes
Authors: Branzoi Florina , Branzoi Viorel , Pahom Zoia
Published: February 2020

Nanocomposite films of functionalized single-walled carbon nanotubes (SWCNTs), 3,4-ethylene dioxythiophene (PEDOT) and different dopants (sodium dodecyl sulphate-SDS, tiron, 3-methylthiophene) were grown electrochemically from aqueous solutions such that constituents were deposited simultaneously onto substrate electrodes. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) revealed that the composite films consisted of nanoporous networks of SWCNTs coated with polymeric film. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated that these composite films had similar electrochemical response rates to pure polymeric films but a lower resistance and much improved mechanical integrity. The negatively charged carbon nanotubes (CNTs) served as anionic dopant during the electropolymerization to synthesize polymer/CNTs composite films. The specific electrochemical capacitance of the composite films is a significantly greater value than that for pure polymer films prepared similarly.

The higher capacitance of the composite films results obviously from the contribution of the embedded SWCNTs that provide interconnected pathways for electrons through the SWCNTs and ions through the pore network or the direct interaction between the delocalised electrons on polymer chains and the SWCNTs.

Using these composite films, the modified electrodes with improved properties were obtained.
Photoenergy Transfer in SWCNT Mesomaterials
Authors: Parra-Vasquez A. Nicholas G. , Subbaiyan Navaneetha K , Tian Yongming , Montano Gabriel , Doorn Stephen K. , Duque Juan G
Published: February 2020

Individual single-walled carbon nanotubes (SWCNTs) have interesting optoelectronic properties that have shown potential uses in photovoltaics, transparent conducting films and sensing devices. However, due to the extreme sensitivity of their optoelectronic properties to environmental stimuli, engineering SWCNT materials is complex. The key ingredient is maintaining a relatively interaction-free local environment during the material synthesis. Toward this end, selection of the correct protective wrappings (i.e. surfactants, polymers, DNA, etc) and added materials (i.e. porphyrin, salts, acids, etc) to maintain or tune the tubes optoelectronic properties for a desire application is crucial. We will highlight some of our recent SWCNT mesomaterials and discuss the effects each of the matrixes has on SWCNT optoelectronic properties. We will introduce photoactive molecules and discuss the electronic interactions we observe with SWCNTs and how these various additives can be used to control the final material properties for targeted applications such as sensors and photovoltaics.
(Invited) Tuning Dielectric Properties of Epitaxial Lanthanide Oxides on Silicon
Authors: Osten H. Joerg , Schwendt Dominik , Chaudhuri Ayan Roy , Fissel Andreas , Shekhter Pini , Eizenberg Moshe
Published: February 2020

A very promising way to realize advanced future devices is using single-crystalline, closely lattice matched oxides, which will be grown on the substrate of choice. The dielectric properties of such oxides are sensitive to small variations in structure and symmetry. It is known that thin layers of crystalline binary rare earth oxides can exhibit significant larger dielectric constants compared to bulk materials. For example, thin crystalline Gd2O3 films epitaxially grown on silicon exhibit dielectric constants up to 20 although the known bulk value is only around 13. The reason for that “enhancement effect” is not fully understood yet. Here, we will report about different investigations on strain-induced effects on dielectric properties. As model systems, we chose Gd2O3 and Nd2O3 having very similar bulk dielectric constants and band gaps. The crystalline structures are also identical. On the other hand, the lattice spacing in Nd2O3 is larger while that of Gd2O3 smaller than the lattice spacing in silicon; i.e. one layer should be under compressive strain and the other under tensile strain. First, we report on the dependence of the dielectric constant on layer thickness for epitaxial Gd2O3 on Si(111). The K-value strongly decreases with increasing layer thickness and reaches the bulk value at around 8 nm. Controlling the oxide composition in ternary (Gd1-xNdx)2O3 thin films enables us to tune the lattice mismatch to silicon, and thus the strain-induced variation in the dielectric constants of the layer from 13 (close to the bulk value) up to 20. Finally, we will show that solely tetragonal distortion of the cubic lattice is not sufficient to explain the huge lattice-mismatch induced enhancement in K-values. Thus, we will explain these effects by more severe strain induced structural phase deformations. Further, dielectric properties of epitaxial oxide thin films grown on Si have been found to improve significantly by incorporation of suitable dopants. We observe substantial reduction of the leakage current density in nitrogen-doped Gd2O3 layers. To achieve optimum electrical properties from such doped oxides it is important to understand the correlation between doping and the electronic structure of the material. X-ray photoelectron spectroscopy investigations revealed band gap narrowing in epitaxial Gd2O3 due to nitrogen doping, which leads to reduction in the valence band offset to Si. The observed reduction of the leakage current densities in the these layers with increasing nitrogen content suggests that nitrogen doping can be an effective route to eliminate the adverse effects of the oxygen vacancy induced defects in the oxide layers.
Development of in Situ Electrochemical Small-Angle Neutron Scattering (eSANS) for Simultaneous Structure and Redox Characterization of Nanoparticles
Authors: Prabhu Vivek , Reipa Vytas , Bonnesen Peter , Rondinone Adam J
Published: February 2020

The demand for engineered nanomaterials in expanding research sectors, such as energy and healthcare, require materials with widely disparate physicochemical properties. The oxidation and reduction (redox) properties of nanomaterials are crucial for catalysis, matching semiconductor band gaps for photovoltaics, as well as toxicology, since they may cause oxidative stress by generating reactive-oxygen species. Optical spectroscopy analysis of molecular and nanomaterials undergoing redox reactions quantifies the electron transfer and energetics of the reaction via potential control and are the most common analytical techniques employed for this purpose. However, with conjugation to organic ligands and smaller, well-defined particle sizes, engineered nanomaterial redox characterization would benefit by techniques that provide nanometer sensitivity to nanoparticle core and ligand structure. We developed an in situ electrochemical small-angle neutron scattering (eSANS) method to measure simultaneously the redox properties and size, shape, and interactions of solution-dispersed nanomaterials [1]. By combining multi-step potentials and chronocoulometry readout with SANS, the structure and redox properties of engineered nanomaterials are followed, simultaneously in one experiment. Specifically, ZnO nanoparticles were examined as dilute dispersions in pH buffered deuterium oxide solutions under negative electrode potentials. The ZnO disk-shaped nanoparticles undergo an irreversible size transformation upon reduction at the vitreous carbon electrode. The decrease in average nanoparticle size near a current maximum shows the reduction reaction from ZnO to Zn occurs. The eSANS method provides nanometer scale sensitivity to the nanoparticle size and shape changes due to an electrochemical reaction that is crucial to understand in energy, healthcare, and other applications. These experiments utilized the EQ-SANS beamline at the Spallation Neutron Source, Oak Ridge National Laboratory that uniquely provides the ability to follow the redox kinetics under quasi-stationary potential step-scans. The methodology, contrast variation, and scattering properties of the micro and nanoporous carbon electrodes will also be described.

[1] V.M. Prabhu and V. Reipa, J. Phys. Chem. Lett. 3, 646 (2012)
Improving Selectivity on Ge CMP Applications
Authors: Karagoz Ayse , Basim G. Bahar
Published: February 2020

In this study, slurry formulations are evaluated to enhance selectivity for germanium silica planarization systems. Initial selectivity analyses were studied by material removal rate responses measured at a single particle-surface level through atomic force microscopy (AFM) wear tests using both anionic (sodium dodecyl sulfate-SDS) and cationic (cetyl trimethyl ammonium bromide-CTAB) surfactants at their sub-micelle and above critical micelle concentrations (CMC) as a function of pH and oxidizer concentration [1]. CMP performances of Ge and SiO2 wafers were evaluated in terms of material removal rates, selectivity and surface quality [2]. The surfactant adsorption characteristics were studied through surface wettability (measured by contact angle technique) and FTIR analyses. It was determined that the very strong or loose self-assembled surfactant structures can help obtain selectivity on the silica/germanium systems and good defectivity control with a sufficient material removal rate values yet the surface charge of the wafer and the hydrophobic nature of the germanium surface add to the complex surface assembly of the surfactant systems. In addition, since the slurry stability is necessary to prevent unacceptable levels of surface roughness and defects, the impact of adding surfactants on particle-particle interactions is investigated in the paper.

References:

Vakarelski I. U., Brown, S.C, Basim G.B, Rabinovich, Y. I., and Moudgil B.M., "Tailoring Silica Nanotribology for CMP Slurry Optimization: Ca2+ Cation Competition in C12TAB Mediated Lubrication", ACS Applied Materials & Interfaces, Vol. 2, No 4, pp. 1228-1235, 2010.

Basim, G.B., Vakarelski, I.U. Karagoz, A. Chen, L., “Surfactant Mediated Slurry Formulations for Ge CMP Applications” MRS Proceedings, MRS Spring Meeting, San Francisco, CA, April 2013, V. 1560, DOI http://dx.doi.org/10.1557/opl.2013.971.
(Invited) Material Engineering for 7nm FinFETs
Authors: Moroz Victor , Huang Joanne , Choi Munkang , Smith Lee
Published: February 2020

Recently, several enabling technologies have become available for integrating non-Si channels on Si wafers, including HKMG with acceptable trap densities, aspect ratio trapping, and low temperature epitaxy with in-situ doping. This considerably broadens the list of potential candidate materials for the 7nm technology node in search of exceeding performance of Si FinFETs.

The search for the alternative channel materials is often motivated by high levels of carrier mobility in bulk material. Some promising demonstrations have been done with long channel transistors. However, the bulk carrier mobility is not relevant for performance of the short channel transistors. The target channel length for the 7nm node is about 15 nm, with most of the carriers exhibiting ballistic transport without experiencing scattering events when moving from source to drain. The ballistic transport favors materials with lighter effective carrier mass in terms of the driving current strength. On the flip side, such materials exhibit higher off-state leakage currents via band-to-band tunneling and direct source-to-drain tunneling mechanisms. So, instead of being guided by the bulk carrier mobility numbers, a more appropriate approach is to evaluate the trade-off between the on-state and the off-state current levels for the particular combination of material properties and transistor design rules.

In this work, we assume that the process-related issues such as defects can be resolved over time and focus on performance of defect-free materials, with performance determined by fundamental material properties. This way, we can get the upper bound on performance for each candidate material and see if it is worth pursuing in terms of struggling through laborious process integration.

Besides the on-state and off-state currents, several other key metrics are included into the trade-off analysis, such as self-heating and the ability to withstand and dissipate the heat, and parasitic R and C of the MOL.

The comparative analysis of several candidate channel materials is performed considering four technology flavors: HP, SP, and LP logic, and the I/O transistors. The appropriate modeling methodologies are introduced to cover these materials and the target design rules.
Back Gate Bias Stressing on Extremely Thin SOI (ETSOI) MOSFETs with Gate Last Process Integration
Authors: Tang Zhaoyun , Tang Bo , Zhao Lichuan , Wang Guilei , Xu Jing , Xu Yefeng , Wang Hongli , Wang Dahai , Li Junfeng , Yan Jiang , Zhao Chao
Published: February 2020

Full depleted extremely thin SOI (ETSOI) is viewed as a promising device due to its excellent immunity to short channel effect (SCE) especially with applying of back gate bias stressing. In this paper, SOI transistors fabricated with gate last process scheme with thin channel layers of 4 to 11nm are provided with superior device performance. For a given gate length less than 30nm, DIBL and Swing are achieved with 40mV/V and 78mV/Dec respectively with stressing of back gate bias. Threshold voltage can be tuned within range of 0.8 volts (Vdd=-0.05v). It is large enough for adjusting device performance. Also, from our results, it is shown that device with thicker channel layer of 11nm are more sensitive to back gate bias comparing with that with thinner channel layer of 4nm. It demonstrates electrical characteristic of ETSOI with thicker channel layer is propitious to be adjusted, while that is more convergent with thinner channel layer.

Figure.1. shows the detail integration flow of ETSOI with HKMG and TEM of cross section of gate structure. In Fig. 2, Id-Vg curves for different channel thickness are plotted. It can be seen that shift of voltage with thicker channel layer of 11nm is larger than that with thinner channel layer of 4nm. Fig. 3 displays Vt difference under back gate bias stressing for different channel thickness.

In conclusion, we have successfully fabricated extremely thin SOI (ETSOI) devices with both HK and MG last integration scheme. Excellent device performances are achieved and back gate bias stressing on device characteristic is analyzed. With thicker channel layers, devices are more sensitive to back gate bias, while with thinner channel layers; devices are more convergent for electrical characteristic.

References

[1] K. Cheng, etc. in IEDM Tech. Dig., Dec. 2012, pp. 419-422.

[2] A. Ohata, etc. IEEE Electron Device Lett., vol. 33, no. 3, pp. 348–350, March. 2012.

[3] A. Majumdar, etc. IEEE Electron Device Lett., vol. 30, no. 4, pp. 413–415, Apr. 2009.

[4] A. Majumdar, etc. IEEE Trans. Electron
Devices, vol. 56, no. 10, pp. 2270–2276, Oct. 2009..

[5] A. Khakifirooz, etc. IEEE Electron Device Lett., vol. 33, no. 2, pp. 149–151, Feb. 2012.
Single Crystalline Beta-FeSi2 Nanowires: Growth and Their Physical Properties
Authors: Yang Chih-Yung , Huang Wei-Jie , Lu Kuo-Chang
Published: February 2020

In this work, self-catalyzed beta-FeSi2 nanowires were synthesized via chemical vapor deposition method where the fabrication of beta-FeSi2 nanowires occurred on Si(100) substrates through the decomposition of the single-source precursor of anhydrous FeCl3 powders at 650-850℃. We varied temperatures, duration time and the flow rates of carrier gases to control and investigate the growth of the nanowires. The morphology of the beta-FeSi2 nanowires was observed with scanning electron microscopy (SEM) and the structure of them was analyzed with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Additionally, we have measured and discussed the properties of the silicide nanowires, including field emission, magnetism and photoluminescence. The study on beta-FeSi2 nanowires, featuring a high optical coefficient, a direct band gap of ~0.85 eV and an optical wavelength of 1.5μm, supports the development of infrared light detectors, opto-electric devices, and photovoltaics.