bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Analysis of Graphene-Based Nanoelectromechanical Switch
Authors: Lee Eunae , Kang Jeong Won
Published: February 2020

We present simple schematics for a three-terminal nanoelectromechanical switch using a vertical carbon nanotube tip and planar graphene. We investigated its operational dynamics via classical molecular dynamics simulations combined with classical electrostatic theory and found that the key operation of the proposed graphene-based nanoelectromechanical switch is based on the following two characteristics. First, it has a low mass density, large area, and a flexible deflection of the graphene, and second, the carbon nanotube tip is narrow and sharp. The electromechanical dynamics of the graphene switch are well-balanced by five forces, with a capacitive force between the bottom electrode and the graphene, the van der Waals force between the bottom electrode and the graphene, the capacitive force between the carbon nanotube tip and the graphene, the van der Waals force between the carbon nanotube tip electrode and the graphene, and the elastic force of the graphene. ACKNOWLEDGEMENTS : This research was partially supported by the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the C-ITRC (Convergence Information Technology Research Center) (IITP-2015-H8601-15-1008) supervised by the IITP (Institute for Information & communications Technology Promotion), and partly supported by Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2015R1A1A1A05027643).
Enzymatic Glucose Biofuel CELL Based on Graphene
Authors: Bagheri Samira
Published: February 2020

Nowadays, by increasing the amount of implantable devices with high variety of applications, supplying their required energy to sense, monitor, vibrate, pump and report the collected data, has concerned the scientists and engineers around the world. This power source should be environmentally friendly with long life time and even implantable as well as capable of producing energy from the living organisms’ fluids. These required properties, light up the idea of using enzymatic biofuel cells (EBFCs) to generate the power. Unfortunately, EBFCs are limited by their short life time and poor electron transfer from the enzyme active site to the electrode surface. Recent studies have indicated that 3D graphene is a relatively novel material with unique properties that could make it useful in enzymatic biofuel cells. The graphene offers high electrical conductivity and high porous structure. According to recent studies carbon nanostructures can be used widely to immobilize the enzymes and transfer the electron from enzyme active site to the electrode surface as well. In this proposed research project, graphene oxide will be synthesised via the simplified Hummers method and then reduced into three dimensional graphene.  However, the high efficiency of 3D graphene-enzyme biocomposite in a biofuel cell requires a suitable porous architecture that maximizes the enzyme immobilization at nanostructure and increase the electron transfer. In order to further increase the efficiency of biofuel cell, considerable effort has to be exerted to improve the enzyme lifetime and the amount of transferred electron. It has been well-established that immobilizing the redox enzyme using the carbon nanostructures hold a number of advantages such as increasing the lifetime of enzyme, decreasing the enzyme leaking as well as enhanced electrical charge transfer properties. In this contribution, graphene hydrogel has been synthesized and used to immobilize the enzyme on the surface of the electrode for enhancement of the EBFCs generated power.
(Invited) Chalcogenide Glasses for Planar Devices
Authors: Novak Spencer , Lin Pao-Tai , Li Cheng , Sisken Laura , Deng Weiwei , Hu Juejun , Agarwal Anuradha , Richardson Kathleen A
Published: February 2020

Semiconducting chalcogenide glasses (ChGs) are well known for their amenability to film fabrication and intriguing optical properties, namely transparency in key mid-infrared wavelength regimes where target analytes have fundamental molecular fingerprints. To realize next generation photonic sensing devices, high production and low cost is sought by leveraging the existing capabilities and knowledge-base of microelectronics, such as through the compositional design of materials that are compatible with CMOS manufacturing techniques. Subsequent improvements in overall device performance through reduced optical loss, and increased accuracy, sensitivity, and specificity enables these sensors to rival the capabilities of larger and costlier sensing technologies such as Fourier transform infrared (FTIR) spectroscopy. Thus, ChGs are poised to play a leading role in miniaturized chemical sensing technology, which is enabled through various techniques of film deposition on Si substrates and post-processing to precisely fabricate micron-scale structures and components. Amongst these techniques, this presentation highlights recently developed 2-D and 3-D printing of ChG films from solution by electrospray, a process which is compatible with continuous manufacturing, engineered non-uniform thickness films, and direct writing of coatings with compositional gradients. In addition, this work has also advanced the controlled crystallization of both bulk and film forms of ChG by laser exposure and heat treatment, which allows further tunability of the material properties and an additional strategy to obtaining spatial gradients in material properties. This presentation will discuss the development of the ChG materials processing “toolbox” in light of the oncoming maturation of microphotonic chemical sensors.
(Invited) Plasmon-Induced Deposition of Conductive Polymer on Au Nanostructured TiO2 Electrode
Authors: Murakoshi Kei , Minamimoto Hiro , Toda Takahiro , Li Xiaowei
Published: February 2020

The plasmon-induced photo-polymerization of molecules was observed at the gold nano structures on TiO2 electrodes in an electrolyte. Spatially confined electromagnetic fields generated by the excitation of localized surface plasmon resonance leads to highly localized deposition of conductive polymer at the edge of Au nanostructures on TiO2 electrodes. Characteristics on the deposition rate depending on the Au nanostructures provide the information on the mechanism of plasmon-exciton conversions.
(Invited) Effect of Ionomer Structure for Oxygen Reduction Reaction in Acidic Media and Fuel Cell Performance
Authors: Fujigaya Tsuyohiko , Nagashima Akiyo , Nakashima Naotoshi
Published: February 2020

Polymer electrolyte fuel cell (PEFC) using liquid phosphoric acid (PA) as polymer electrolyte membrane has poor durability due to leaching of PA from the membrane, resulting to the deterioration of PEFC performance during long-term operation. To overcome this issue, poly(vinylphosphonic acid) (PVPA) was used for electrolyte instead of PA. Although this PEFC showed high durability, this catalyst had large overpotential in the area of low current density, probably due to the poisoning of Pt by PVPA. In this study, we studied an effect of ionomer chemical structure for oxygen reduction reaction.
Electronic Properties of Various B-Doped Diamond(111)// Dye Molecule Interfaces
Authors: Larsson Karin Margit Eleonora
Published: February 2020

Diamond is a widely known material for its many excellent properties (e.g., high thermal conductivity, high break down voltage, transparency, chemical intertness and bio-compatability). A B-doped diamond is an excellent  p-type material for solar cell usage. Due to some specific properties (e.g., large chemical inertness, very high carrier mobility for both electron and holes, and high transparency), it is considered as one of the strongest candidates for photovoltic electric generation. However, in order to implement the usage of diamond in solar energy applications, properties like the i) electrochemical window, ii) possibility for interfacial charge transfer, and iii) stability of functionalized surface, have to be further studied and optimized.

In the present investigation, the adsorption of different dye molecules onto H-terminated diamond (111) surfaces, have been theoretically studied using Density Functional Theory (DFT) calculations under periodic boundary conditions. The diamond surfaces were B-doped in order to make them p-type semi-conducting. The choice of dyes was based on the match between the electronic structures of these H-terminated B-doped diamond surfaces, and the respective dye molecules. The dye molecules in the present study included C20H13NO3S4 (A), C35H37NO2S3 (B),  C34H38OS2(C), C32H36OS2(D), and C31H35S3Br(E). These dyes differ in the various functional groups, which have the role as electron acceptors. The main goal with the present study was thereby to investigate and compare the photovoltaic efficiency of the various dyes when attached to B-doped and H-terminated diamond (111) surfaces. Of a special interest was to study the i) absorption spectra of the dye, ii) degree of electron transfer over the diamond//dye interface, iii) electron transfer rate,  iv) electron-hole recombination, and v) diamond//dye bond strength.

The calculated absortion spectra for in principle all of the different dyes were shown to be located in the most intense part of the sunlight spectrum. For the E dye, the spectrum were more positioned towards the UV light range. The usage of a combination of these different dyes would, hence, be an optimal choice in order to improve the light harvesting in a photovoltaic process.

Furthermore, the calculations identified the LUMO´s for the B, C, and D dyes to be positioned on the upper end of the molecules, which also will be the position of the electron acceptor when being excited by light. For the dyes A and E, there were though  certain extentions of the LUMOs to the lower end of the molecules (i.e., towards the diamond surface), which will also increase the electron-hole recombination rates.

Calculation of electron transfer was to ensure that the HOMO of these dyes were positioned at a lower energy compared to the upper edge of the valence band of the B-doped diamond surface. Moreover, all dyes were found to bind with strong C-C covalent bonds to the diamond (111) surface.
(Invited) Artificial Photosynthesis Using All-Soild-State Photocatalysts -Photocatalytic Conversion of CO2 By H2O As an Electron Donor
Authors: Teramura Kentaro
Published: February 2020

The reduction in human-induced emissions of CO2 from automobiles, factories, power stations, etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock in order to build a sustainable society in the near future. These days, we found that Ag-modified ZnGa2O4/Ga2O3, LiTi2O7, ZnGa2O4, and SrO/Ta2O5 exhibits activity and good selectivity toward CO evolution for the photocatalytic conversion of CO2 by H2O as an electron donor. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of evolved O2 were generated together with CO. In this study, we focus on how to suppress the H2 evolution derived from overall water splitting to enhance the selectivity toward CO evolution.
(Invited) Photophysics of Hybrid Semiconductor Nanostructures in Photocatalytic Hydrogen Generation
Authors: Kuno Masaru
Published: February 2020

Semiconductor nanostructures possess a number of applications in solar energy conversion.  This includes using colloidal quantum dots in solar cells and, more recently, using analogous nanostructures such as nanowires (NWs) and nanosheets (NSs) in photocatalytic applications.  Here we describe recent work to understand the photocatalytic response of solution-synthesized cadmium chalcogenide NWs and NSs within the context of hydrogen generation.  Various CdX (X = S, Se) systems such as core/shell NWs and hybrid metal nanoparticle decorated NWs and NSs have been studied.  In all cases, femtosecond transient differential absorption spectroscopy has been used to reveal relevant carrier relaxation processes in these materials as well as the flow of charges across the different heterointerfaces that are present.  By correlating these transient absorption results to results from accompanying hydrogen generation efficiency measurements, we have, in turn, rationalized the response of these materials, clarifying the role that different heterojunctions play in establishing both charge separation and hydrogen generation efficiencies.
Investigation of Graphene Oxide-TiO2 Photoelectrodes with Different Compact Layers and Counter Electrodes
Authors: Devarepally Kishore Kumar
Published: February 2020

Modified Hummer’s method was adopted for the preparation of graphene oxide (GO) using graphite flakes. Graphene-oxide was incorporated in the TiO2 paste and the films are prepared by screen printing on FTO glass (TEC8) substrates. The screen printed films were subjected to heat treatment cycle at 375°C for 5 min, 375 °C for 5 min, 450°C for 15 min and finally at 500°C for 15 minutes. The crystallinity and phase purity of the GO samples were characterised by X-ray diffraction using Cu-Kα radiation. The morphology of the GO is investigated using transmission electron microscopy and the chemical structures of GO are analysed by XPS.

Photovoltaic properties were measured by a computer-controlled digital source meter (Keithley 2400) under simulated one sun illumination at AM 1.5G (100mW/cm2) from a solar simulator (92250 A, Newport, USA). The electrochemical impedance spectroscopy (EIS) is carried out using Metrohm Autolab in the frequency range of 1MHz to 0.1Hz with amplitude of 20 mV under dark conditions. The device was assembled by coupling GO-TiO2 films soaked in N719 dye with Surlyn as the spacer between the electrodes. The performance of the GO-TiO2 composite photoelectrodes were tested with different compact layers and different counter electrodes. The DSSC fabricated with graphene oxide as counter electrode exhibited photoconversion efficiency of 4.6% whereas, platinum based devices showed photoconversion efficiency of 4.7%. The present study suggests that graphene oxide counter electrodes can be considered as a promising alternative to platinum, with further optimisation, which clearly has advantages in terms of its abundance and low cost processing towards industrial prospects.
(Invited) Electrochemistry of Nitrophenylcorroles in Nonaqueous Media
Authors: Jiang Xiaoqin , Shan Wenqian , Pacquelet Sandrine , Desbois Nicolas , Gros Claude , Kadish Karl M.
Published: February 2020

Nitrocorroles have recently been studied as potential agents against human cytomegalovirus infection for their antiviral activity.1 They have also been incorporated into triple-decker complexes containing phthalocyanine macrocycles.2 The nitrophenyl corroles can undergo multiple redox reactions at the conjugated macrocycle in addition to one or more reductions at the meso-nitrophenyl groups. Metal-centered reactions can also occur for some transition metal corroles. As part of our continuing studies into elucidating the electrochemistry of porphyrins, corroles and related macrocycles, we have synthesized a series of free-base and metallated nitrophenylcorroles which were electrochemically characterized in a variety of nonaqueous solvents. The structures of the investigated compounds are shown in Chart 1. The redox potentials for each electrode reaction of the above compounds were measured by cyclic voltammetry and spectra of the electroreduced and electroxidized forms of the corrloles were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution condition. This data was then analyzed as a function of the solvent properties, the number and position of the meso-nitrophenyl substituents and the type or oxidation state of the central metal ion. Protonation and deprotonation constants of the free-base corroles were also determined by monitoring changes in the UV-visible spectra during titrations with different acids or bases. The free-base corroles can add one proton to form CorH4
+ and they can also lose one or two protons to form CorH2
- and possibly CorH-. These positively and negatively charged corroles are also electroactive and were characterized as to their electrochemistry and spectral properties.

1. Gros, C. P.; Desbois, N.; Michelin, C.; Demilly, E.; Tilkin-Mariame, A.-F.; Mariame, B.; Gallardo, F. ACS Infect. Dis.
2015,
1(8), 350-356.

2. Lu, G.; Li, J.; Jiang, X.; Ou, Z.; Kadish, K. M. Inorg. Chem.
2015,
54 (18), 9211-9222.

Figure 1
(Invited) Phthalocyanine Monolayer Nucleation of Gate Oxide ALD on Single Layer Graphene and TMD Surfaces
Authors: Kummel Andrew , Park Jun Hong , Kwak Iljo , Chagarov Evgeniy , Movva Hema , Chou Harry , Banerjee Sanjay K , Fathipour Sara , Seabaugh Alan , Fullerton Susan , Vishwanath Suresh , Xing Huili Grace , Choudhury Pabitra
Published: February 2020

Several proposed beyond-CMOS devices based on two-dimensional (2D) heterostructures require the deposition of thin dielectrics between 2D semiconductor layers as an interlayer, or on the 2D semiconductor as a gate. However the direct deposition of dielectrics on 2D materials is challenging due to their inert surface chemistry. To deposit subnanometer EOT dielectrics on 2D semiconductors, a flat lying titanyl phthalocyanine (TiOPc) monolayer was employed to functionalize the 2D materials via non-bonding interaction for atomic layer deposition (ALD), and the initial stage of growth was probed using in-situ STM. ALD pulses of trimethyl aluminum and H2O resulted in the uniform deposition of AlOx on the TiOPc/HOPG via dissociative chemisorption onto TiOPc reactive sites. The uniformity of the dielectric is consistent with DFT calculations showing multiple reaction sites on each TiOPc molecule for reaction with TMA.

In order to deposit dielectrics with low leakage and low equivalent oxide thickness (EOT) on WSe2, a flat-lying titanyl phthalocyanine (TiOPc) monolayer (ML), deposited via molecular beam epitaxy (MBE), was integrated to create a seed layer for atomic layer deposition (ALD) on WSe2 surfaces. TiOPc molecules formed a flat lying monolayer on WSe2 ML, with four fold crystal structure in scanning tunneling microscopy. ALD pulses of trimethyl aluminum and H2O resulted in the uniform deposition of Al2O3 on TiOPc/WSe2, confirmed by AFM and cross sectional TEM. After deposition of 50 cycles of the Al2O3 onto the TiOPc/multilayer WSe2, top gated FETs were fabricated. The top gated leakage current was measured 0.046 pA/µm2 at 1 V gate bias with 2.4 nm EOT, which is lower leakage current than previous results. A subthreshold swing of 80 mV/dec was measured in n-branch of dual gated device.

Figure 1
(Invited) Applications of the Orthogonal Reactivity for the Functionalization of the Bodipy CORE
Authors: Peña-Cabrera Eduardo , Gómez-Durán Cesar F. A. , Valois-Escamilla Ismael
Published: February 2020

Herein, we report the synthesis of polyfunctional BODIPY building blocks suitable to be subjected to several reaction sequences with complete chemoselectivity, which allowed the preparation of complex BODIPY derivatives in a versatile and programmable manner. The reactions included: the Liebeskind-Srogl cross-coupling reaction (LSCC), SNAr, Suzuki, Sonogashira, and Stille couplings and a desufitative reduction of the MeS- group. This novel synthetic protocol is a powerful route to design a library of compounds with tailored photophysical properties for advanced applications. In this context, it is noteworthy the straightforward and cost-less strategies to shift the BODIPY emission deep into the near infrared spectral region but retaining high fluorescence quantum yields.
(Invited) Electrogeneration and Electrochemistry of Sigma-Bonded Cobalt Porphyrins with Pi-Extended Systems and/or Highly Electron-Withdrawing Pyrrole Substituents
Authors: Kadish Karl M. , Ke Xiangyi , Cong Lei , Kumar Ravi , Sankar Muniappan
Published: February 2020

A series of cobalt β-substituted nitroporphyrins were investigated as to their electrochemistry, spectroelectrochemistry and reactivity with alkyl halides in nonaqueous media. Selected structures of the examined compounds are shown in Chart 1. Each porphyrin contains cobalt(II) in its neutral air-stable form and is characterized by multiple redox reactions, some of which involve the conjugated π-ring system and others, the central metal ion which can be converted to its Co(III) and Co(I) forms under the application of an applied oxidizing or reducing potential. The half-wave potentials for each redox reaction were measured by cyclic voltammetry and spectra of the oxidized and reduced compounds were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution conditions. The electrogenerated Co(I) porphyrins are highly reactive in the presence of methyl iodide and a rapid reaction occurs to generate a new series of σ-bonded Co(III) methyl derivatives, which were also characterized as to their electrochemistry and spectroscopic properties in nonaqueous media. These data were then analyzed as a function of the solvent properties, the nature of the β-pyrrole substituents and the oxidation state of the central metal ion.

Figure 1
(Invited) Carbon-Rich Porphyrins
Authors: Jux Norbert , Lungerich Dominik , Hölzel Helen , Reger David , Ruppel Michael , Martin Max
Published: February 2020

We will present new carbon-rich porphyrins and tetrabenzoporphyrins some of which carry hexabenzocoronene units as well as other aromatic species.

We report on the synthesis, characterization, and properties of some of these novel systems.[1,2]

References

[1]        J. M. Englert, J. Malig, V. A. Zamolo, A. Hirsch, N. Jux, Chem. Commun. 2013, 49, 4827 – 4829.

[2]        D. Lungerich, J. F. Hitzenberger, M. Marcia, F. Hampel, T. Drewello, N. Jux, Angew. Chem. Int. Ed..
2014,
53, 12231-12235.

Figure 1
(Invited) Controlled Growth of Porphyrin Based Nano/Micro Coordination Polymers and Their Use in Olefin Oxidation
Authors: Lee Kyung Yeon , Lee Suk Joong
Published: February 2020

Porous coordination polymers (PCPs), also called metal–organic frameworks (MOFs) for three-dimensional (3D) PCPs, have received much attention due to their potential applications. Currently, nano- and microsized PCPs (nPCPs or mPCPs) have often been reported with their promising applications. They could possess numerous advantages over both the PCPs and inorganic nanomaterials, and their novel and/or enhanced performances are frequently reported with potential applications in catalysis, separation, gas storage, drug delivery, biosensing, and imaging. Although a variety of nPCPs or mPCPs can be successfully obtained by controlling the growth conditions, their fabrication is still a major challenge because of lack of information regarding the crucial factors for the precise control of particles during the synthesis. Furthermore, the translation of building blocks into well-defined structures, whose properties and functions are regulated in the building block level, still remains very challenging. In this regard, metalloporphyrins would be good building blocks for the construction of such functional materials witnessed by a wide range of molecular architectures, such as molecular boxes, self-assembled arrays, and CPs, and MOFs with various applications in catalysis, gas storage, and separation. Particularly, Mn(III)- and Fe(III)-containing metalloporphyrins are often used to fabricate various functional molecular architectures and to mimic the extraordinary behavior of enzymes in both homogeneous and heterogeneous catalysis. In the case of homogeneous catalysis, these materials have frequent trouble with fast catalytic degradation because of µ-oxo dimer formation or ligand oxidation. To avoid the catalyst degradation, the heterogenization of homogeneous catalysts, such as immobilization and site-isolation of homogeneous catalysts on polymers, membranes, and MOF supports, is widely used alternative strategy. Here I like to present the preparation and heterogeneous catalytic uses of Mn(III)–porphyrin that contain size-controlled amorphous and crystalline nano- and microsized CPs. Particularly, I like to focus on the conversion of kinetically controlled amorphous assemblies into thermodynamically controlled crystalline structures based on the self-assembly of Mn(III)–porphyrin biscarboxylic acid and Co(OAc)2.
Modeling and Experimental Study of Micro Enzymatic Biofuel Cells
Authors: Song Yin , Wang Chunlei
Published: February 2020

Miniaturized enzymatic biofuel cells (EBFCs) converting biological energy into electrical energy by using enzyme-modified electrodes are considered as a candidate to power implantable medical devices and portable electronics. In this study, modeling of the EBFC system has been conducted using finite element analysis based on COMSOL Multiphysics 4.3a in terms of cell performance, efficiency and optimum cell configurations. Two modules have been applied to obtain the maximum theoretical cell performance of on-chip microelectrodes: 1) diffusion module to incorporate the mass transport and enzymatic kinetics; 2) conductive module to integrate concentration and potential. The design rule has been developed in the steady state. The effect of orientation of the microelectrode arrays in blood artery has been studied. In the experimental part, integration of the high surface area nanomaterials such as carbon nanotubes (CNTs) and graphene could be one of the effective solutions to further improve the performance of current EBFCs. The EBFC systems employing 3D carbon micropillar arrays integrated with different nanomaterials, such as graphene, reduced graphene oxide (rGO) and rGO/CNTs composite have been investigated. The fabrication process of this micro-system combined top-down carbon microelectromechanical system (C-MEMS) technology to fabricate the 3D micropillar arrays platform and bottom-up electrophoretic deposition (EPD) to deposit various carbon based nanomaterials onto the 3D micropillar arrays. The materials characterization, electrochemical characterization and device evaluation have been conducted. Upon comparison among bioelectrodes integrated with different nanomaterials, the amperometric response of the rGO/CNTs based bioelectrodes exhibited the best electrochemical performance and the as-resulted 3D micro EBFC generated a maximum power density of 196.04 µWcm-2 at 0.61 V. In addition, modeling of the rGO/CNTs EBFC system based on finite element analysis has also been conducted to predict the theoretical cell performance.  The power density of actual device has been noted to be 71.1% of the modeling result.
Porous Carbon Interdigitated Electrode Arrays for Electrochemical Biosensors
Authors: Ibrahim Fatimah , Selvarajan Reena Sri , Yafouz Bashar , Madou Marc J , Azari Pedram , Abd Hamid Sharifah Bee , Gan Seng Neon
Published: February 2020

In this paper, three-dimensional (3D) porous carbon interdigitated electrode arrays (IDEAs) are developed utilizing standard photolithography of electrospun mats of SU-8 photoresist nanofibers. Porous IDEAs have the potential to produce higher aspect ratio than non-porous electrode due to the reduced stress at the interface between the substrate and the carbon structure [1]. In a first step, a layer of polymeric nanofibers is deposited on a silicon substrate by optimizing the conditions for far-field electrospinning of SU-8 photoresist. Subsequently, the SU-8 mat is patterned using conventional photolithography to generate the polymer precursor for the carbon electrode structure. Finally, the polymer precursor is pyrolysed at 900°C in an inert atmosphere to produce a porous carbon IDEA [2]. The porous carbon IDEAs were optimized as a function of the nanofibers diameter, thickness of the electrospun SU-8 mat and width/gap ratio of the IDEAs. To characterize the porous carbon IDEAs, electrochemistry studies (cyclic voltammetry and electrical impedance spectroscopy) were conducted and the results were compared with traditional flat carbon IDEAs (the latter was fabricated by spin coating a non-porous SU-8 film on a silicon substrate).  The redox amplification factor of both porous and flat carbon IDEAs was studied to gain an understanding of the effect of electrode porosity on the redox amplification. This factor was optimized for width and gap of the IDEAs and the nanofibers diameter.

 

Acknowledgments

This research is supported by Flagship grant project number FL001A-14AET, Transdisiplinary Research Grant Scheme (TRGS TR002A-2014B) from University of Malaya and Ministry of Science Technology and Innovation (MOSTI) Science Fund (SF-020-2014).

 

References

1.         Sharma, C.S., A. Sharma, and M. Madou, Multiscale carbon structures fabricated by direct micropatterning of electrospun mats of SU-8 photoresist nanofibers. Langmuir, 2010. 26(4): p. 2218-2222.

2.         Kamath, R.R. and M.J. Madou, Three-Dimensional Carbon Interdigitated Electrode Arrays for Redox-Amplification. Analytical chemistry, 2014. 86(6): p. 2963-2971.
Environmental Friendly Fluorine Mixture for CVD Cleaning Processes to Replace C2F6, CF4 and NF3
Authors: Wieland Robert , Boudaden Jamila , Pittroff Michael
Published: February 2020

Since the beginning of the 1980’s per fluorinated carbons (PFC’s) such as C2F6 and CF4 have been used as cleaning gases in thin film deposition technology and since the 1990’s NF3 has been used in the same way. PFC’s and NF3 have long atmospheric lifetimes and therefore high global warming potentials. The main applications of these gases are to remove residual films left behind after a chemical vapor deposition process (CVD). The most important materials to remove are dielectric layers like silicon oxides (SiO2), carbon-containing silicon oxides, silicon nitrides (Si3N4) and, to a certain extent, conducting films like doped poly-silicon and silicide layers. According to the World Semiconductor Council the semiconductor industry in 2013 used 7512 t NF3, 1133 t CF4 and 708 t C2F6 on a global basis. Approximately 72% of all semiconductor industry gaseous emissions are caused from these three gases (C2F6, CF4 and NF3). Fraunhofer EMFT and Solvay Special Chem have developed an alternative cleaning process, which can be a replacement for the currently used PFC’s and NF3in semiconductor CVD tools.

The target of this work was to find viable alternative gas mixtures for the semiconductor industry, which could be used as a “drop in” to avoid additional high investment costs from equipment modification. Our study has demonstrated that these more environment friendly gas mixtures also provide a more efficient and faster cleaning behavior for most applications. A cleaning efficiency gain of a factor 1.3 up to 17 can be expected, relative to the F2-amount required for cleaning; this gain in efficiency depends on the cleaning gas to be replaced and on the reactor type. A shorter cleaning time can lead directly into a higher equipment throughput and more cost effective usage of thin film tools. To generate data on particle and tool attrition, a first “mini marathon” test run has been performed. The test reactor, a 200mm wafer size CVD tool, was equipped with a mass spectrometer, to verify the end point of the chamber cleaning and to gain an overview of the waste gases going into the abatement system.

Figure 1
In Operando Studies of Electrode-Electrolyte Interfaces for Magnesium Batteries
Authors: Hahn Nathan T , Zavadil Kevin R
Published: February 2020

The development of rechargeable Mg batteries, driven by the desire to overcome the limiting specific energy density and high cost of Li ion batteries, is currently frustrated by the lack of stable, functional electrolytes compatible with high voltage cathodes.  Successful electrolytes have typically employed chloride complexes as the Mg cation delivering species in order to avoid the formation of Mg cation blocking films on the anode surface.  However, such electrolytes exhibit questionable compatibility with the high voltage cathodes and current collector materials needed to attain large energy density and low cost in a complete magnesium battery system. Motivated by this problem, novel “conventional” electrolytes resembling those used in Li-ion batteries have been proposed, including those based on the weakly coordinating bis(trifluoromethylsulfonyl)imide (TFSI) and monocarborane (CB11H12
-) anions.  The electrochemical behavior and stability of such electrolytes is not well understood, and their study is necessary in order to guide magnesium battery development efforts.    

In this presentation we describe the results of in operando studies focused on evaluating the relationship between interfacial speciation and electrochemical behavior from the perspective of the efficiency of magnesium electrodeposition and dissolution in novel electrolyte chemistries. The techniques utilized by these studies include Raman spectroscopy and X-ray absorption spectroscopy, conducted in such a way as to provide interfacial or near-interfacial information concerning the interactions of the Mg cation with the solvent and anion species in the presence of the electrified interface. We demonstrate that these in situ experiments provide a level of insight that is not attained by bulk or otherwise ex situ electrolyte characterization techniques.  In particular, we find that interfacial changes in MgTFSI2/glyme electrolyte speciation promote instability in the TFSI anion contributing to the poor reversibility of the Mg metal deposition process.  We further demonstrate that the addition of chloride species to the TFSI-based electrolyte modifies these interfacial processes, suppressing the TFSI decomposition pathway.  We will also discuss how the nature of the specific ether solvent employed influences these findings.  We believe that this information provides important insight into the design and implementation of electrolytes for future magnesium batteries.

This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.

Figure 1
Mesoscale Interplay of Physicochemical Processes in Li-S Battery Electrodes
Authors: Mistry Aashutosh , Liu Zhixiao , Chen Chien-Fan , Mukherjee Partha P.
Published: February 2020

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density [1-6]. A typical Li-S battery operation includes multi-step electrochemical reactions and transport phenomena relevant to the “internal shuttle effect”. The insoluble final product, such as Li2S, can passivate the active cathode surface, block mass transfer channels and induce mechanical degradation, all of which negatively impact the cell performance. Each of these phenomena takes place at different spatial and temporal scales which necessitates a mesoscale approach to understand the implications of physicochemical coupling.

In this regard, a coupled mesoscale model has been developed in order to study physicochemical interactions in the cathode microstructure. At the interface level, the mechanism of chemical interactions between discharge products and cathode surface is fundamentally investigated. The growth rates of precipitation thickness and coverage are predicted. At the cathode microstructure level, the surface passivation and pore blockage induced by Li2S precipitation are systematically studied. At the cell level, the mechanisms of discharge capacity loss are revealed.

In summary, this mesoscale modeling framework can be employed to quantify the capacity loss due to the internal shuttle effect and other electrochemical degradation mechanisms and understand the effect of cathode microstructure (i. e. sulfur loading, specific surface area, pore size distribution) on the electrochemical performance.

Acknowledgement:

Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Tien Duong) is gratefully acknowledged.

References:

P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat. Mater., 11(1), 19-29 (2012).

F. Y. Fan, W. C. Carter, and Y. M. Chiang, Adv. Matter., 27, 5203-5209 (2015)

R. Cao, W. Xu, D. Lv, J. Xiao, and J. G. Zhang, Adv. Energy Matter., 5, 1402273 (2015)

Y. X. Yin, S. Xin, Y. G. Guo, and L. J. Wan, Angew. Chem., 52(50), 13186-13200 (2013)

Y. Yang, G. Y. Zheng, and Y. Cui, Chem. Soc. Rev., 42(7), 3018-3032 (2013).

Z. Liu, D. Hubble, P. B. Balbuena, and P. P. Mukherjee, Phys. Chem. Chem. Phys., 17, 9032 (2015).

Figure 1
Diffusion Barriers and Structural Evolution in Alpha-Sulfur for Lithium-Sulfur Batteries
Authors: Arneson Claire , Ma Ying
Published: February 2020

Lithium-sulfur (Li-S) batteries are a promising alternative to the Li-ion technology due to their high theoretical capacity and low cost. However, unlike intercalation compounds that are currently used in commercial lithium ion batteries, the sulfur cathode undergoes a series of complex electrochemical reactions with substantial structural and morphological changes during charge and discharge. Various lithium polysulfides are formed that may shuttle between the electrodes, resulting in poor Coulombic efficiency. In this work, first principles calculations based on the density function theory are performed to study the structural evolution of alpha-sulfur during discharging. First, the surface energies of a few low index surfaces are obtained, and the lithium diffusion barriers into those surfaces are calculated. While clear driving force is observed for both the (001) and the (010) surfaces, a diffusion barrier exists for the (100) surface. Then, the structural evolution is studied with ab initio molecular dynamics by adding lithium ions at a specific rate. The effects of electrolytes are also studied, and the interface diffusion barrier of lithium from the electrolyte into the cathode are calculated. Finally, the elementary process that leads to the formation of soluable polysulfide is also simulated. These calculations help to reveal an atomistic understanding of the complex electrochemical reactions that take place in the sulfur cathode.
Charging Mechanism of Lithium-Sulfur Batteries: Insight from Spatially Resolved Operando X-Ray Absorption Spectroscopy
Authors: Gorlin Yelena , Patel Manu U. M. , Freiberg Anna Teresa Sophie , He Qi , Piana Michele , Tromp Moniek , Gasteiger Hubert A.
Published: February 2020

A major barrier toward to the development of cost-effective lithium-sulfur (Li-S) batteries with sufficient energy densities to meet the requirements of battery electric vehicles is the lack of a mechanistic understanding of the processes occurring inside the battery. Motivated by improving the mechanistic understanding of lithium-sulfur batteries, we focus on the charging process of the Li2S cathode, a possible alternative to the conventional S8 cathode, with a potential to enable batteries with silicon or tin rather than lithium anodes.(1) Li2S presents an interesting system for mechanistic characterization, because the first charge of the cathode requires an application of a high overpotential, while each subsequent charge can be performed at a lower overpotential.(2) The presence of the high overpotential in the first charge has been hypothesized to relate to a charge transfer step that leads to a lithium-deficient surface on the surface of large Li2S particles.(2) This mechanism, however, does not provide a sufficient explanation for how an activation of less than 10% of the volume of the particle could lead to an extraction of the entire capacity.

To clarify the charging process of Li2S cathode, we have performed X-ray absorption spectroscopy (XAS) characterization of Li2S-Li battery using a spectro-electrochemical cell designed in our laboratory (Fig. 1a),(3) which is capable of spatially resolved measurements (Fig. 1b). Our experiments demonstrate which solid and solution phase intermediates are produced in two locations of the cell, the Li2S cathode and the separator, and thus generate a unique set of spatially resolved data, which we use to identify a plausible charging mechanism. Because the intermediates forming during the first charge of Li2S cathode have so far only been characterized using X-ray diffraction (XRD),(2, 4) a technique that is capable of detecting crystalline solids, but cannot provide information about amorphous species, our combination of XAS with spatial resolution facilitates a significantly improved mechanistic understanding of the operation of Li-S batteries.

References

1. J. Hassoun and B. Scrosati, Angew. Chem., 49, 2371 (2010).

2. Y. Yang, G. Zheng, S. Misra, J. Nelson, M. F. Toney and Y. Cui, J. Am. Chem. Soc., 134, 15387 (2012).

3. Y. Gorlin, A. Siebel, M. Piana, T. Huthwelker, H. Jha, G. Monsch, F. Kraus, H. A. Gasteiger and M. Tromp, J. Electrochem. Soc., 162, A1146 (2015).

4. H. Jha, I. Buchberger, X. Cui, S. Meini and H. A. Gasteiger, J. Electrochem. Soc., 162, A1829 (2015).

Figure 1
Direct Visualization of the in-Plane and out-of-Plane Electrostatic Competition in P2 Type Na2/3TMO2
Authors: Qian Danna , Seo Joon Kyo , Xu Jing , More Karren L. , Chi Miaofang , Meng Ying Shirley
Published: February 2020

Na-ion batteries are important to develop lower cost batteries that deliver safe, reliable storage with long calendar life. Among various studied cathodes, layered P2-NaxTMO2 (TM -- 3d transition metal ions) compounds, exhibiting comparable performance as compared with Li-ion cathodes, are attractive candidates.1-3However, they suffer from capacity loss and poor reversibility upon cycling, which results from two determinative factors structurally: oxygen layer shifts and Na-ion in-plane ordering transitions during Na insertion/extraction. The oxygen layer shifts usually happen at low Na contents and the ordering transitions form at particular Na stoichiometry. A throughout understanding of the Na/Vac ordering is necessary.

Herein we present the first atomic scale visualization of the Na-Na in-plane and out-of-plane distribution variations due to the competitions of the in-plane Nae/f-Nae/f interactions and the out-of-plane Naf-TM-Naf electrostatic forces. An alternative Na concentration distribution along the c axis has been identified in the P2-Na2/3[Ni1/3Mn2/3]O2 where (Ni are all 2+ and Mn are all 4+), while not for P2-Na2/3[Fe1/3Mn2/3]O2(both Fe and Mn are mixture of 3+ and 4+). This study visualizes for the first time the electrostatic-interaction-induced Na ordering in both ab plane and c directions. Our work demonstrates the strong interaction between alkali ordering and electronic, magnetic structure, and underlines the important role that structure plays in determining electronic behavior and electrochemical performance, opening up the new design approach for energy storage materials.

1. J.   Electrochem. Soc.
2015, 162, A2589.

2. Functional Materials Letters
2013, 06, 1330001.

3. Nat. Mater.
2012, 11, 512.
One-Dimensional Nanomaterial for Energy Storage
Authors: Mai Liqiang , Tian Xiaocong , Xu Lin , Wei Qiulong
Published: February 2020

One-Dimensional nanomaterials with large surface area, more surface active sites and better permeability can significantly increase the energy density, power density and cycling performance for the energy storage. Such hierarchical structure can also be used as targeted intracellular recording for its facile synthesis route. In our present work, a series of hierarchical nanomaterials have been obtained, including kinked hierarchical nanowires, hierarchical heterostructured nanowires and hierarchical scrolled nanowires which shows great electrochemical.

To increase the stability of Li-ion battery, V3O7 nanowire templated semi-hollow bicontinous graphene scrolls architecture is designed and constructed through “oriented assembly” and “self-scroll” strategy. The V3O7 nanowire templated semi-hollow bicontinous graphene scrolls with interior cavities provide continuous electron and lithium ion transfer channel and space for free volume expansion of V3O7 nanowires during cycling, thus representing a unique architecture for excellent lithium ion storage capacity and cycling performance. 1 Besides, we have designed and synthesized hierarchical MnMoO4/CoMoO4 heterostructured nanowires by combining "oriented attachment" and "self-assembly". The asymmetric supercapacitors based on the hierarchical heterostructured nanowires show a high specific capacitance and good reversibility with a cycling efficiency of 98% after 1,000 cycles. 2 Recently, we also constructed the hierarchical zigzag Na1.25V3O8 nanowires, 3 K3V2(PO4)3 bundled nanowire, 4 and Li3V2(PO4)3 mesoporous nanotubes 5 with enhanced electrochemical performance. Our work presented here can inspire new thought in constructing novel nanofiber/nanowire structures and accelerate the development of energy storage appilications.

References

(1) Yan, M. Y. et al., J. Am. Chem. Soc. 2013, 135, 18176-18182.

(2) Mai, L. Q. et al., Nature Commun. 2011, 2, 381.

(3) Dong, Y. F. et al., Energy Environ. Sci. 2015, 8, 1267.

(4) Wang, X. P. et al., Adv. Energy Mater. 2015, 5(17).

(5) Niu, C. J. et al., Nature Commun. 2015, 6, 7402.
Development of Novel Noncarbonate Electrolytes for Silicon Alloy Anodes
Authors: Zhu Ye , Cheng Gang , Strand Dee , Yang Johnny
Published: February 2020

Wildcat Discovery Technologies is developing novel electrolyte additives and noncarbonate solvent formulations that yield improved solid electrolyte interphase (SEI) layers on silicon alloy anodes. The large volumetric changes in silicon during charge/discharge cycles result in mechanical disruption of conventional SEI's leading to rapid capacity fade as the cell cycles. Novel additives are demonstrated to improve cycle life of silicon based materials by forming less brittle, more mechanically robust SEI passivation layers. Since propylene carbonate (PC) is not expected to form an effective SEI layer, the additives are tested with PC to determine their efficacy. Wildcat's high throughput electrolyte formulation, cell assembly, and test capabilities enable the evaluation of hundreds of additives in a very short timeframe.

Once effective SEI additives are identified in a PC-based formulation, other non-SEI forming solvents can be evaluated. Since the additives are effective without solvent participation in SEI formation, solvents can be considered that may not be reductively stable on the anode - and also opens the possibility to more oxidatively stable or less flammable solvents. Wildcat has evaluated hundreds of combinations of noncarbonate solvents with its initial silicon anode SEI additives. This presentation will focus on the results of the additive improvement to cycle life in NMC//Si full cells, and illustrate the opportunities for novel solvent combinations.