bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of Smart Au/TiO2 Nanotubes/Si Based Schottky-Tunneling Diode Sensors for Electrochemical Detection of Biomarkers
Authors: Bhattacharyya Dhiman , Misra Mano , Mohanty Swomitra K.
Published: February 2020

Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detection time, equipment portability, and performance. Detection of volatile organic compounds (VOCs) based disease biomarkers from the breath provides a potential solution to the aforementioned problems. One such tuberculosis (TB) biomarker identified from breath is methyl nicotinate. In this regard, development of smart sensor systems can provide an economically feasible solution and pave the way for rapid disease diagnostics.

In this paper, we present the fabrication of a smart sensor developed by synthesis of self-organized TiO2 nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) magnetron sputtering. Site-specific interdigitated patterned growth of gold electrode was achieved using photolithography techniques. The gold interdigitated electrodes behave as the working electrode while platinum deposited on the back surface of the Si wafer acts as the back contact. Au on TiO2 presents a Schottky junction due to differences in their work function and can be overcome by light irradiation. On the other hand, an ultra-thin, inherent SiO2 layer on Si aids in tunneling electrons across the TiO2 – Si junction. Thus, Au/TiO2/SiO2/Si behaves as a Schottky tunneling diode junction that electronically couples a VOC oxidation catalyst (Au) to a photovoltaic absorber (Si).

A sweep of the bias voltage (-5V to 5V) and associated sensor response at room temperature upon exposure to both air and biomarker vapors (~1000 ppm) was carried out. From the current-voltage plot (I-V), the operating voltage was chosen overcoming the negative differential resistance such that the sensor current response to the biomarker vapor would be maximized under forward bias condition. The sensor current when exposed to the biomarker vapor was higher than that in air. All sensor measurements were carried out under illuminated conditions.

The variation in the output current of the sensor biased at the chosen operating voltage (~ 0.7V) at room temperature was observed for the range of 0.01 ppm to 1000 ppm biomarker concentration. The sensor demonstrated a strong response and the results suggest that the sensor is capable of detecting extremely small concentrations of the biomarker in the vapor phase. This smart sensor presents significant enhancement in sensor response over previously reported metal functionalized TiO2 nanotube array based sensing platform developed in our group for electrochemical detection of similar disease biomarkers.
Carbon Nanofiber Nanoelectrodes for Neural Stimulation and Chemical Detection: The Era of "Smart" Deep Brain Stimulation
Authors: Koehne Jessica E. , Marsh Michael , Bennet Kevin E , Andrews Russell , Lee Kendall H , Meyyappan M.
Published: February 2020

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed.   Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes.  Here, we report two studies using vertically aligned CNF nanoelectrodes for biomedical applications. CNF arrays are investigated as neural stimulation and neurotransmitter recording electrodes for application in deep brain stimulation (DBS).  Polypyrrole coated CNF nanoelectrodes have shown great promise as stimulating electrodes due to their large surface area, low impedance, biocompatibility and capacity for highly localized stimulation.  CNFs embedded in SiO2 have been used as sensing electrodes for neurotransmitter detection.  Our approach combines a multiplexed CNF electrode chip, developed at NASA Ames Research Center, with the Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS) system, developed at the Mayo Clinic.  Preliminary results indicate that the CNF nanoelectrode arrays are easily integrated with WINCS for neurotransmitter detection in a multiplexed array format.  In the future, combining CNF based stimulating and recording electrodes with WINCS may lay the foundation for an implantable “smart” therapeutic system that utilizes neurochemical feedback control while likely resulting in increased DBS application in various neuropsychiatric disorders.  In total, our goal is to take advantage of the nanostructure of CNF arrays for biosensing studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.
Ruthenium-Modified Sensitive NO Sensors: Quantifying Nitric Oxide in the Pathobiology of Cystic Fibrosis
Authors: Bose Tiyash , Bayachou Mekki
Published: February 2020

This is a preliminary work towards preparing a device capable to measure nitric oxide levels in a cystic fibrosis cell line model. It has been found that exhaled NO levels remains unchanged or reduced in cystic fibrosis patients unlike other inflammatory lung diseases like asthma where it increases. However it is not clear whether the lower NO levels in cystic fibrosis correlate with lowered production of this metabolite in the bronchial epithelium. We will present preliminary results of our ruthenium oxide modified combined electrodes and how they can be applied to the study of cystic fibrosis at the cellular level.

In this work, we explore the performance of combined reference/working electrodes modified with ruthenium oxide and Poly(3,4-ethylenedioxythiophene) (PEDOT) in the detection of nitric oxide with the goal to measure nitric oxide at the level of single or collective cultured cells. The synergistic effect of the electrocatalytic activity of ruthenium oxide and the enhanced surface area for catalytic activity provided by the polymer greatly enhanced the analytical performance of our sensors in terms of sensitivity, selectivity and stability. With the incorporation of a layer by layer method of electrodeposition we attained a normalized sensitivity of 8.38E-4 pA/nM/μM2  and 1.16E-2 pA/nM/μM2 towards NO in the linear range of 0.2-1.6 mM and 2-16 nM respectively, at an applied potential of 0.8 V vs Ag/AgCl and a detection limit in the vicinity of 500 pM. In order to improve the selectivity of our sensors we coated the surface with nafion and also an ionic liquid composite and lowered the applied to 0.6 V vs. Ag/AgCl. We also measured the response to NO using Differential Pulse Amperometry to further decrease response from biological interferents especially nitrite and ascorbic acid.
Corrosion of Carbon Steel Wire Roads Containing Various Sulfur Content in Sour Solutions
Authors: Kim Su-Won , Park Chan-Jin
Published: February 2020

High strength carbon steel wire roads have been widely used in armor cables for offshore oil drilling plants. However, the materials can undergo some corrosions and hydrogen related damages such as hydrogen induced cracking (HIC) and sulfide stress cracking (SSC). In particular, it has been reported that HIC is highly influenced by content of MnS containing inside the steels. However, effects of sulfur content on the corrosion of carbon steel wire rod have scarcely been reported systematically. In this study, the effects of sulfur and propagation of corrosion in carbon steel wire rod were investigated in sour solutions with various pH.

 The carbon steel wire rods containing various sulfur content were used. All electrochemical tests were conducted using three-electrode system with a saturated calomel electrode (SCE) as the reference electrode and a Pt wire as the counter electrode. In addition, acetic acid based solution containing 95% CO2 and 5% H2S were used to adjust pH in the range of 2.5-6.5 at the room temperature for corrosion tests. Before testing, the carbon steel wire words were polished by abrasive papers and then washed with ethanol, and deionized water. The overall corrosion behaviors and corrosion rate of the samples were analyzed using potentiodynamic tests. In addition, the HIC characteristic of the steels was investigated by immersing the samples in the solution followed by observing the crack propagation inside the samples. Surface morphologies of the samples after tests were also observed by optical microscope (OM) and scanning electron microscope (SEM).

 The corrosion current densities (icorr
) of carbon steel increased with the increasing in sulfur contents in the steels. Further, from the polarization curves, it is observed that cathodic current density increased with sulfur content in steels. It is noticeable that the anodic current density rarely changes. This result indicates that the cathodic hydrogen evolution process on the surface of the steels was promoted by S content inside the steels. In addition, the samples without applied stress showed the internal macro-cracks in cross sections in pH 2.5~5.1, while only small micro-cracks were found in solution pH 5.1~6.5. The length of crack increased with increasing sulfur content except in the solution with pH 5.1~6.5. In particular, the micro-cracks by HIC appeared to initiate around inclusions. Some tracing of the cracks will be shown in this presentation.
Signal Amplification of a Universal Four-Way Junction Based Nucleic Acid Sensor through Modification of Electrochemical Technique Parameters
Authors: Mills Dawn M , Chumbimuni-Torres Karin Y.
Published: February 2020

Here, we report the characterization of a four-way junction (4J) universal electrochemical sensor that consists of an electrode-immobilized DNA stem-loop (SL) probe and two adaptor strands (m and f). The “m” adaptor strand was labeled with a methylene blue (MeB) redox marker. The adaptor strands hybridize to the DNA SL probe and target nucleic acid to form a 4J structure. In this orientation the MeB is in close proximity to the electrode’s surface thus enabling its reduction and subsequent electrochemical signal. The experimental timing for immobilization of the DNA SL probe and hybridization with adaptor strands and miRNA-122 was investigated. In addition, the density of the DNA SL probe coverage was evaluated using chronocoulometry to determine the ideal concentration of immobilized DNA SL probe. The sensor performance was investigated using cyclic voltammetry (CV), alternating current voltammetry (ACV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). Specifically, a single parameter from each voltammetric technique was modified to evaluate the sensor’s response. The DNA SL probe demonstrated an efficient immobilization after 30 minutes and optimal hybridization occurred at 1.5 hours. The 4J sensor was characterized with ACV at a frequency range from 1 to 5000 Hz and the current increased from 1 to 600 Hz where the threshold of the sensor was reached, followed by a drastic decrease in signal at higher frequencies. The 4J sensor was also characterized with SWV at frequencies ranging from 1 to 5000 Hz and exhibited an increase in signal from 1 to 1500 Hz, where the signal stabilized until reaching the threshold frequency of 4000 Hz, where the current then began to decrease. CV was used to evaluate the sensor’s performance at scan rates ranging from 0.1 to 800 V/s. The peak separation increased at faster scan rates (529 mV) and the signal was saturated after 500 V/s. Finally, the sensor performance was monitored using DPV at pulse widths ranging from 1 to 100 ms.  The current was highest at short pulse widths (1 ms) and the current decreased rapidly as the pulse width was increased. Amplification of the 4J sensor was achieved by modifying a specific parameter for each electrochemical technique which can provide insight into the sensor performance to facilitate lower limits of detection of nucleic acids.
Synthesis of Photocatalytic Nanocomposite Biomaterials for Enhanced Water Filtration Application
Authors: Murray Jacob , Senese Elizabeth , Rech Jeromy J , Keleher Jason J
Published: February 2020

Clean and drinkable water is a critical necessity for all human and economic development; unfortunately, millions of people do not have access to potable water, resulting in the death of over 2 million children every year. Over the past decade, emphasis has been placed on the synthesis and design of photocatalytic nanocomposites to enhance the chemical degradation of organic pollutants as a cost effective vehicle for clean water production.  Amongst the many semiconducting nanoparticles explored in literature, TiO2has stood out for its favorable physiochemical properties, low toxicity, easy availability, high stability, and low cost. When TiO2is irradiated by ultraviolet light, there is creation an electron-hole pair which provides sites for effective reduction or oxidization of the pollutant, converting the pollutant to carbon dioxide, water, and mineral acids. One major shortcoming of TiO2 is related to the efficiency of these systems to harness the entire solar spectrum; therefore, a main focus of this work is the modification of the TiO2 nanoparticles to increase the photon capture efficiency in the visible light region.  Of the various possible functionalization pathways, this work focuses on dye sensitization, noble metal deposition, and silane functionalization as well as understanding the synergy between all three. When looking at the rate of remediation of a organic dye pollutant in a simulated sunlight environment, the functionalized particles completely remediated an organic dye pollutant. These functionalized nanoparticles were then deposited into a cellulose matrix of highly absorbent beads in order to prepare a nanocomposite.  Results show there is a decrease in the chemical degradation of the pollutant when in the nanocomposite, but a significant increase in a physio-absorption capacity, thus maintaining the rate of  total remediation. In addition, the binding interaction between the dye and the particle is a major component in chemical degradation; an aminosilane can be covalently added to the surface of the nanoparticle, and increase the ability of various dyes to adhere to the surface of the TiO2.  The incorporation of Ag-functionalized nanocomposites resulted in a synergistic antimicrobial effect, which eliminated both E. coli and S. aureus from the water sample, in addition to increasing the photochemical degradation rate. The specific aim of this work was to create functionalized TiO2 particles with silane groups, organic dyes, and Ag, for the incorporation into a photocatalytic biomimetic nanocomposite membrane which utilizes sunlight to degrade pollutants and inhibit the growth of deadly bacteria.
Organic Single-Crystal Transistors Based on DBT3 Derivatives
Authors: Onozuka Tomoya , Tsutsui Masanori , Okamoto Kazuo , Kunugi Yoshihito
Published: February 2020

Heteroacenes that contain chalcogenophene have been actively investigated as semiconducting materials because they are more stable in air than acenes and various chemical modifications of the compounds are possible. While there have been many attempts to combine benzene with thiophene rings to produce higher-performance materials, only a few derivatives are known to show high mobilities above 1 cm2 /Vs. Also OFETs of high performance have been often achieved by using expanded heteroaromatic of π-conjugated including thiophene oligomers as the semiconducting materials.

In this work, we synthesize new type of fused chalcogenophene based transistor materials, 54DBTTT and 8-67DBTTT (Fig. 1), and investigate the characterization of organic single-crystal transistors based on the newly developed materials.

We made organic single crystals of 54DBTTT and 8-67DBTTT by physical vapor transport (PVT) and drop-cast method. We used an n
+-doped Si wafer with 220 nm thickness thermally grown SiO2, which was covered with a thin film (ca. 27.8 nm) of CYTOP insulator or a thin film (ca. 30 nm) of poly(methyl methacrylate) (PMMA) insulator. Source and drain electrodes were painted with a colloidal graphite paste. The field-effect mobility (μ) of the OFET devices were measured under vacuum from the saturation regime according to the equation: I
d=μC
i(W/2L)(V
g-V
th)2, where C
i is capacitance of the insulator, V
d and V
th are the gate and threshold voltages, respectively.

To investigate the molecular conformation and stacking of the molecules in the crystal states, single-crystal X-ray analysis was performed. In contrast to the herringbone structure 54DBTTT, 8-67DBTTT molecules exhibit a two-dimensional brick-wall packing arrangement (Fig. 2).

Organic single-crystal transistors based on DBTTT derivatives showed typical p-channel FET characteristic. The best field-effect mobility of 0.3 cm2 /Vs was obtained for 54DBTTT based single-crystal device with a CYTOP covered Si/SiO2 substrate. On the other hand, the mobility for the 8-67DBTTT based transistor was 8.1x10-3 cm2 /Vs. As shown above, molecular packing structure of the 8-67DBTTT is brick-wall packing. Acoording to the Fig. 2(d) alkyl chain placed between the DBTTT cores, which is not preferable to the high performance OFET device.

Figure 1
Si/SiGe Interfaces in Three-, Two-, and One-Dimensional Nanostructures and Their Influence on SiGe Light Emission
Authors: Lockwood David J , Wu Xiaohua , Baribeau Jean-Marc , Mala Selina A. , Wang Xiaolu , Tsybeskov Leonid
Published: February 2020

The development of a light emitter compatible with Si based complementary metal-oxide- semiconductor (CMOS) circuit technology and fast optical interconnects is important for the new generations of microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures (NSs) with light emission in the important optical communication wavelength of 1.3 – 1.55 μm are compatible with conventional CMOS processes. However, the predicted and experimentally confirmed long carrier radiative lifetimes in Si and Si/Si1-xGex NSs impede the demonstration of efficient light-emitting devices and lasers. Thus, engineering of Si/Si1-xGex heterostructures with controlled composition and interface abruptness is critical in producing the desired fast and efficient photoluminescence (PL) peaked around 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe NSs and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in one dimension (corresponding to the case of quantum wells), two dimensions (quantum wires), and three dimensions (quantum dots). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for NS confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 – 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex NSs incorporated into a Si0.6Ge0.4 wavy structure exhibit an intense PL signal with a characteristic decay time as much as 1000 times shorter than that observed in conventional Si/SiGe NSs. The experimentally observed non-exponential PL decay in Si/SiGe NSs is explained as being due to variations of the distances separating electrons and holes at the Si/SiGe heterointerface. The results demonstrate that an abrupt Si/SiGe heterointerface reduces the carrier radiative recombination lifetime and increases the PL quantum efficiency making these SiGe NSs promising candidates for applications in CMOS compatible light-emitting devices.
(Invited) Upconverting Fluoride Nanocrystals - Synthesis and Optical Properties
Authors: Noculak Agnieszka , Podhorodecki Artur
Published: February 2020

Over the past decade, high-quality lanthanide doped upconverting nanocrystals (UPCNCs) have been successfully synthesized with the rapid development of nanotechnology. Several materials (i.e. CaF2, NaYF4, NaGdF4) have been successfully applied so far as potential matrix for Yb3+-RE3+combinations, where the low crystal field symmetry and low phonon frequency are the main factors defining the best matrix selection. These materials have already found several potential applications in biology, medicine as well as in photovoltaics and photocatalysis – as the most common examples. However, to change the commercial potential of UPCNCs to real devices still a several problems must be solved, where week emission quantum efficiency (EQE typically < 2%) is one of the most important one. The EQE is directly related to other challenges in this field: growth of small size <10 nm UPCNCs, UPCNCs shape and architecture control and control of UPCNCs surface properties. To solve all abovementioned problems the correlation between technological, morphological and physical parameters is needed. This is however a difficult task because the system itself is very complicated and consist number of correlated parameters. Thus, still a better understanding of physical processes responsible for the optical properties of UPCNCs in needed to bring this fascinating material to commercial use.

In this work, we will discuss synthesis and optical properties of NaGdF4-based up-converting nanocrystals. We will discuss how to control size, shape and core-shell architecture of lanthanide doped NaGdF4 nanocrystals focusing mainly on Yb-Er co-doping. We will discuss how doping influencing the nanocrystals size, shape and their optical properties (Fig.1.). This will be done based on experimental results obtained from photoluminescence (PL) measurements, PL-excitation spectroscopy, PL-decay measurements, microscopic imaging and structural data obtained from HRTEM and XRD. Our conclusions will be supported by results obtained from numerical Monte Carlo modeling used to model the kinetic properties of nanocrystals emission and to model the ions distribution within the nanocrystals volume. Finally, based on our work on nanocrystals surface functionalization and their toxicity tests we will briefly discuss the potential use of UPCNCs in biology and medicine.

Figure 1. ß-NaGdF4:Yb, Er nanocrystals with different shapes and architectures.

Figure 1
(Invited) Plasmonic Hot Carrier Injection in Wide Bandgap Nitride Semiconductors
Authors: Narang Prineha
Published: February 2020

Despite more than a decade of intensive scientific exploration, new plasmonic phenomena continue to be discovered, including quantum interference of plasmons, observation of quantum coupling of plasmons to single particle excitations, and quantum confinement of plasmons in single-nm scale plasmonic particles. Simultaneously, plasmonic structures find widening applications in integrated nanophotonics, biosensing, photovoltaic devices, single photon transistors and single molecule spectroscopy. Decay of surface plasmons to hot carriers is a new direction that has attracted considerable fundamental and application interest, yet a theoretical understanding of ultrafast plasmon decay processes and the underlying microscopic mechanisms remain incomplete.

Recently we analyzed the quantum decay of surface plasmon polaritons and found that the prompt distribution of generated carriers is extremely sensitive to the energy band structure of the plasmonic material. A theoretical understanding of plasmon-driven hot carrier generation and relaxation dynamics at femtosecond timescales is presented here. We report the first ab initio calculations of phonon-assisted optical excitations in metals, which are critical to bridging the frequency range between resistive losses at low frequencies and direct interband transitions at high frequencies. We also present calculations of energy-dependent lifetimes and mean free paths of hot carriers, accounting for electron-electron and electron-phonon scattering, lending insight towards transport of plasmonically-generated carriers at the nanoscale. We will discuss calculations for multiplasmon and nonlinear processes in the ultrafast regime from the mid-IR to visible and in different geometries. Employing a Feynman diagram approach here has been critical to determine the relevant processes.

Based on these theoretical predictions, we designed a solid-state system with wide-bandgap semiconductors and studied the photocurrent generated upon plasmon decay across the extended UV and visible regime for different metals and plasmonic structures. Direct comparison with ab-initio calculations allow us to assess the contribution of direct and indirect transitions and identify guidelines for engineering the generation of plasmonic hot-carriers in the UV-VIS regime.
Reversible Magnetization Modulation in Ordered Mesoporous Mixed Metal Oxide Thin Films By Double Layer Charging and Topotactic Lithium Insertion
Authors: Reitz Christian , Brezesinski Torsten
Published: February 2020

Mesostructured metal oxide thin films have received much attention in recent years. The primary reason for this is the fact that many such materials have been shown to outperform their bulk counterparts. Energy storage and conversion is one of the fields where this is very evident. Advances in polymer templating over the past 10 years have enabled the preparation of various thin film materials with cubic and 2D-hexagonal pore structures and different ordering lenghts.[1] Their formation relies in principle on the coassembly of either sol-gel precursors or preformed building blocks with an amphiphilic polymer structure-directing agent. Despite the progress made so far, complex metal oxides (mixed metal oxides) often exhibit an ill-defined mesoporous morphology after removal of the polymer template and thermally-induced crystallization because of their limited stability.

Here, we describe the evaporation-induced self-assembly (EISA)[2] synthesis of cubic mesoporous mixed metal oxide thin films with >15 nm diameter pores and nanocrystalline walls by using a large polyisobutylene-block-poly(ethylene oxide) diblock copolymer. We focus specifically on perovskite-type La1–x
Sr
x
MnO3 (LSMO) and La1–y
Ca
y
MnO3 (LCMO) as well as spinel-type LiFe5O8. These materials were characterized by various state-of-the-art techniques, including electron microscopy, GISAXS, RBS, XRD and XPS, and were found to be of high quality after calcination at elevated temperatures. For LSMO and LCMO, we show that the charge carrier density, and therefore the magnetization, can be modulated through double layer charging (i.e., electrostatic hole- or electron-doping).[3] Magnetization modulation values of up to 10% have been achieved, the highest thus far reported for electrolyte-gated mixed-valence manganese oxides. Apart from that, we show that the room temperature magnetization of LiFe5O8 can be tuned by topotactic insertion/extraction of Li-ions into/from the spinel lattice and provide insights into the mechanism. Both processes allow for control of magnetism, are highly reversible, and strongly benefit from the high surface-to-volume ratio of the films.

[1] C. Sanchez, C. Boissiere, D. Grosso, C. Laberty, and L. Nicole, Chem.
Mater.20, 682 (2008).

[2] C. J. Brinker, Y. F. Lu, A. Sellinger, and H. Y. Fan, Adv. Mater. 11, 579 (1999).

[3] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn, and T. Brezesinski, Chem. Mater. 26, 5745 (2014).
The Promotion of the Methanol Electrooxidation Performance of Pt/CNTs By Lanthanide Oxides
Authors: Chu Haibin
Published: February 2020

The exploration of anode catalyst materials with low platinum loading, high catalytic activity and high CO tolerant ability is one the most important issues for the development of direct methanol fuel cell (DMFC). Recently, CeO2 are found to be an efficient promoter for the Pt/C catalysts towards methanol oxidation with both higher electro-catalytic activity and better stability [1, 2]. However, the poor conductivity of CeO2 is not benefit for the fast electron transfer on the electrode catalysts, which may lead to the poor performance of the catalysts. We have synthesized doped lanthanide oxides with different compositions, sizes and exposed facets, and combine them with Pt/MWCNTs [3] via different routes. Then the oxygen storage behaviors and variable valences of lanthanide ions are optimized to improve the electro-catalytic activities and CO tolerant abilities of Pt/nanocarbon in methanol oxidation. After the investigation of the relationship between the interface structures of lanthanide oxide- Pt/MWCNTs, the mechanisms about the promotion of the catalytic performance of Pt/MWCNTs by lanthanide oxides will be discussed.

Reference:

[1]  Kakati, N., Maiti, J., Lee, S. H., Jee, S. H., Viswanathan, B., Yoon, Y. S., Anode Catalysts for Direct Methanol Fuel Cells in Acidic Media: Do We Have Any Alternative for Pt or Pt-Ru?,
Chemical Reviews
2014, 114, 12397.

[2]  Chu, Y. Y., Wang, Z. B., Jiang, Z. Z., Gu, D. M., Yin, G. P., A novel structural design of a Pt/C-CeO 2 catalyst with improved performance for methanol electro-oxidation by β-cyclodextrin carbonization Advanced Materials
2011, 23, 3100.

[3] Chu, H. B., Shen, Y. H., Lin, L., Qin, X. J., Feng, G., Lin, Z. Y., Wang, J. Y., Liu, H. T., Li, Y., Ionic-Liquid-Assisted Preparation of Carbon Nanotube-Supported Uniform Noble Metal Nanoparticles and Their Enhanced Catalytic Performance. Advanced Functional Materials, 2010,20, 3747-3752.
Science and Technology of High Efficiency Solar Cells and Materials
Authors: Yamaguchi Masafumi
Published: February 2020

Solar photovoltaics are expected to contribute as one of major energy sources in the future. For this end, further development of high-efficiency, low-cost and high reliable solar cells, materials, modules and systems is necessary.

This paper reviews fundamentals of solar cells and materials and present recent R&D status of various solar cells and materials and their future. In order to realize high efficiency and highly reliable solar cells, understanding and controlling imperfections (defects) are very important. There are several loss mechanisms to be solved for realizing high-efficiency and highly reliable solar cells. 1) bulk recombination loss, 2) surface recombination loss, 3) interface recombination loss, 4) voltage loss, 5) fill factor loss, 6) optical loss, 7) insufficient –energy photon loss. Key technologies for reducing the above losses are high quality film growth, reduction in density of defects, optimization of carrier concentration in base and emitter layers, double-hetero (DH) junction structure, lattice-matching of active layers and substrate, surface and interface passivation, reduction in series resistance and leakage current, anti-reflection coating, photon recycling and so forth.

The multi-junction solar cells have high efficiency potential of more than 50% due to wide photo response, while limiting efficiencies of single-junction solar cells are 31-32%. In order to realize high efficiency multi-junction (MJ) solar cells, understanding and controlling imperfections (defects) are also very important. The key issues for realizing super-high-efficiency MJ solar cells are 1) sub cell material selection, 2) tunnel junction for sub cell interconnection, 3) lattice-matching, 4) carrier confinement, 5) photon confinement, 6) anti-reflection in wide wavelength region and so forth. For concentrator applications by using MJ cells, the cell contact grid structure should be designed in order to reduce the energy loss due to series resistance, and tunnel junction with high tunnel peak current density is necessary. Because cell interconnection of sub-cells is one of the most important key issues for realizing high-efficiency MJ solar cells, effectiveness of double hetero structure tunnel diode is also presented in this paper.

Present status of various solar cells efficiencies are presented: 46.0% for concentrator III-V compound 4-junction solar cell, 38.8% for 1-sun III-V compound 4-junctiion cell, 25.6% for single-crystal Si cell, 21.7% for CIGS cell, 21.5% for CdTe cell, 20.1% for Perovskite cell, 13.6% for a-Si based 3-junction cell, 11.9% for dye-sensitized cell and 11.1% for organic cell. Efficiency potential of various solar cells is also discussed.
Vertically Aligned Hollow TiO2 Shell Protected SnO2 Nanorods By Atomic Layer Deposition for Highly Stable Lithium Storage
Authors: Carvajal Christian G , Rout Sangeeta , Mundle Rajeh , Bahoura Messaoud , Pradhan Aswini K
Published: February 2020

Lithium-Ion batteries have shown a significant evolution in the last years regarding energy density and cycling life. Semiconductor nanomaterials such as tin oxide (SnO2) and similar metal-oxide materials such as titanium oxide (TiO2) are gaining significant attention for technologic innovations because of its Li storage stability. Our current study investigates vertically aligned SnO2 nanorods cycling stability for Li-ion batteries and TiO2 integration via atomic layer deposition (ALD) using the stop-valve configuration. 40nm film of ZnO was used as sacrificial layer to create in-tube SnO2 hollow TiO2 shell in vertically oriented nanorods configuration. Stainless steel battery spacer discs were used as substrates for the nanorods growth and coin cell half batteries were fabricated for the anodic Li storage studies. Li foil was used as the counter electrode and the batteries were charged and discharged from 0.1V to 2.5V for 75 cycles. Structural characterization along with the electrochemical study of the material demonstrated a higher capacity retention and improvement in cycling stability due to a better shape preservation during the lithiation process in comparison to the conventional vertical SnO2 nanorods anode configuration. Half battery cycling characterization and structural SEM comparisons and methods are described in detail.
Degradation and Stabilization of Lithium Cobalt Oxide in Aqueous Electrolytes
Authors: Ramanujapuram Anirudh , Gordon Daniel , Nitta Naoki , Magasinski Alexandre , Ward Brian , Huang Cindy , Yushin Gleb
Published: February 2020

Lithium cobalt oxide (LCO) has long been proven to be an excellent material for cathodes in organic electrolytes [1]. It has shown high volumetric capacity and good stability in non-aqueous environments of commercial lithium-ion (Li-ion) batteries. Unfortunately, the flammability of organic electrolytes in combination with a special propensity for batteries constructed with LCO to experience thermal runaway creates safety concerns [2].

Here we discuss the exceptional electrochemical performance characteristics and stability of LCO in aqueous electrolytes. Aqueous electrolytes offer greatly improved safety and lower cost. In addition, they exhibit higher ionic motilities for the Li+ions and thus can be potentially used for faster charging batteries [3] or batteries with thicker electrodes. While LCO has been demonstrated to cycle for 20-100 cycles in aqueous environments [4, 5], the causes of its degradation have not been investigated in detail.

In our previous work we have demonstrated promising characteristics of lithium iron phosphate (LFP) cathodes in aqueous electrolytes [6]. Here we further expanded our studies and demonstrated LCO cathodes with remarkably stable performance showing only 13 % fading after over 1500 cycles.

Post mortem analysis of the electrodes was conducted to understand the effect of cycling and the causes of degradation. A powerful combination of X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) have been utilized. Our systematic studies and post-mortem analyses of LCO cells reveal that the primary mechanism of LCO degradation in aqueous electrolytes is the formation of a resistive layer of cobalt (II) oxide on the particles’ surfaces. Electrolyte composition was found to have a dramatic impact on the electrochemical performance and stability of LCO in aqueous environments.

These results were recently accepted for publication in the Energy and Environmental Science Journal [7]. This talk will provide an overview of our findings and provide guidance for the future designs of aqueous electrochemical cells with stable cathodes.

References:

1.
J. Zhang, Y.J. Xiang, Y. Yu, S. Xie, G.S. Jiang, C.H. Chen
*, Journal of Power Sources 132 (2004) 187–194

2.
J.R. Dahn, E.W. Fuller, M. Obrovac, U. von Sacken, Solid State Ionics 69 (1994,) 265-270

3.
Y. Wang, J. Yi , and Y. Xia*, Advanced Energy Materials 2012, 2, 830–840

4.
G. Wang, L. Fu, N. Zhao, L. Yang, Y. Wu,* and H. Wu, Angew. Chem. Int. Ed. 2007, 46, 295–297

R. Ruffo, C. Wessells, R. A. Huggins, Yi Cui*,
Electrochemistry Communications 11 (2009) 247–249

6.
D. Gordon, Y. Wu, A. Ramanujapuram, J. Benson, J.T. Lee, A. Magasinski, N. Nitta, J. Huang and G. Yushin, Advanced Energy Materials (2015) 1501805

7.
A. Ramanujapuram, D. Gordon, A. Magasinski, B. Ward, N. Nitta, C. Huang, G. Yushin, Energy and Environmental Science (2016) [in press]
Carbon Nanotube Film Anodes for Flexible Li-Ion Batteries
Authors: Jeong Youngjin , Song Hyeonjun , Jun Jonghan , Oh Hyunwoong
Published: February 2020

In these days, IT devices such as smart card, flexible display and wearable devices requires flexible and high performances. To satisfy these demands, the battery also must be flexible and have high energy density. Lithium ion batteries(LIBs) with high energy density and long cycle performance are most promising candidate for wearable devices. However, the current collector which made of metal(Cu, Al) is an obstacle to flexibility of LIBs. For these reasons, many researches that replace metal current collector with flexible current collector had conducted. Nanocarbon materials such as carbon nanotube(CNT) and graphene have much attentions for using current collector of LIBs due to their high electrical conductivity. In addition, CNT and graphene also can perform as anode material of LIBs. Although nanocarbon materials have many advantages, they are suffered for the huge irreversible capacity and low coulombic efficiency at the initial cycling. This phenomenon is usually because of the formation of unstable solid electrolyte interface(SEI) due to nanocarbon materials’ large surface area. In this study, we tried to improve LIB’s reversible capacity and coulombic efficiency by forming stable SEI on CNT film’s surface. The CNT films were synthesized via direct spinning method. Stable SEI was formed by directly contacting CNT film with Li metal in electrolyte (1M LiPF6 solution in ethyl carbonate(EC) and diethyl carbonate(DEC) (1:1 v/v)) for 1h before cell assembled. The prelithiated CNT film was assembled to coin type half-cell without polymer binder and current collector under argon environment. According to the electrochemical analysis of the cells, directly prelithiated CNT film electrode didn’t show the SEI peak in the CV curve and very low surface resistance was measured in impedance test. After stabilization of a few initial cycles, the capacity increased up to 1300mAh/g at 300th cycle, which was higher than theoretical capacity of CNT. Pouch type cell assembled with the prelithiated CNT film was normally worked and maintained stable OCV during crumpled.
A New Method for Analyzing Transient Response of Hydrogen Permeation in Carbon Steel Sheet
Authors: Yamamoto Yudai , Jin Misako , Kitagawa Yuichi , Nakanishi Takayuki , Hasegawa Yasuchika , Fushimi Koji
Published: February 2020

In acidic media, corrosion of steel is accompanied by hydrogen evolution reaction and a part of adsorbed hydrogen atoms penetrates into the steel, causing hydrogen embrittlement. There are strong needs to elucidate mechanism and kinetics of hydrogen penetration for inhibiting hydrogen embrittlement. Conventionally, a diffusion coefficient of hydrogen atoms in steel sheet samples was estimated using so-called Devanathan-Stachurski (DS) cell.1 The authors have modified the DS cell with an electrolyte-flow channel in the entry side cell and discovered that the disturbance in a flow-rate causes a similar perturbation in hydrogen exit current i
exit as well as hydrogen entry current i
entry.2 When a sinusoidal wave perturbation was applied to flow-rate, i
entry and i
exit showed sinusoidal waveforms with phase shifts
θ
depending on the perturbation frequency. The phase shift was arisen from a diffusional delay in i
exit and could be utilized as a new parameter to discuss the diffusivity of hydrogen atoms in the sample sheets.

In previous researches, however, we only focused on the steady value of phase shifts and did not discuss about time-dependent information of the shifts in detail. In this study, we newly developed a method to realize a real-time evaluation of phase shift by fast-Fourier-transform (FFT). We also conducted transient analyses on phase shifts to elucidate more about hydrogen penetration mechanism in carbon sheet.

During a series of hydrogen permeation measurement of polycrystalline steel sheet samples, a phase shift obtained by the FFT calculation was gradually increased with measurement time. From an algebraic calculation on diffusion phenomena with sinusoidal perturbation and the previous report,3, 4 the value of θ depends on perturbation frequency f, sheet thickness L, diffusion coefficient D, showing a relationship of θ = tan-1(tan α tanh α) where α = (πfL2
/D)1/2. In the case where the values of f and L are fixed throughout the measurement, therefore, the experimental result indicates that the value of D is gradually decreased. This result suggests the existence and its effect of hydrogen trapping sites in the sample sheet.

References

1. M.A.V. Devanathan and Z. Stachurski, Proc. R. Soc. Lond. A,
270, 90 (1962).

2. K. Fushimi, M. Jin, T. Nakanishi, Y. Hasegawa, T. Kawano and M. Kimura, ECS Electrochem. Lett.,
3, C21 (2014).

3. K. Sekine, Chem. Lett.,
4, 841 (1975).

4. Y. Yamamoto, M. Jin, Y. Kitagawa, T. Nakanishi, Y. Hasegawa and K. Fushimi, ISIJ Int.,
56, 474 (2016).
Anodic Oxides Layers: Synthesis and Formation of Composites for Energy Storage Devices
Authors: Kowalski Damian
Published: February 2020

The anodizing is a high-voltage electrochemical conversion process that forms barrier-type oxides or nanoporous/nanotubular layers on valve metals and alloys mainly depending on the composition of electrolyte used.[1] The key to achieve the ordered nanoporous/nanotubular structures is a displacement of the film material above the original surface position due to synergistic effect of pits generation (field assisted oxide dissolution), stress generated at the metal-oxide interface including electrostriction and plastic oxide flow switching the growth of the barrier-film to nanotube/nanopore. Typically, the TiO2nanotube array formed in organic electrolytes such as glycerol, dimethyl sulfoxide, ethylene-glycol is obtained in the form of close packed structure in which the nanotubes nearly stick together with the tube walls. A fundamentally different nanostructure from that is obtained in diethylene-glycol electrolyte. The nanostructure is characterized by free standing nanotubes separated by an interconnecting space much bigger than the thickness of nanotube wall (Fig. 1). [2,3] Such geometry gives possibility for formation of composites with secondary materials using electrochemical deposition in view of improved wetting behavior for the nanostructure. [4] Herein we report on how to control the synthesis of nanotubes to achieve unique oxide geometries, we discuss functional properties of nanostructures and report an examples of composites formed between oxide layer and Si, CdSe, Au, Pt. An examples of the nanostructured energy storage devices will be demonstrated. [5]

References:

[1] D. Kowalski, D. Kim and P. Schmuki, Nano Today, 8(2013) 235.

[2] D. Kowalski, J. Mallet, J. Michel, and M. Molinari, J.Mater.Chem.A
3(2015) 6655.

[3] D. Kowalski, J. Mallet, S. Thomas, J. Rysz, B. Bercu, J. Michel and M. Molinari, Electrochim. Acta, (2016), 10.1016/j.electacta.2016.02.213.

[4] D. Kowalski, and P. Schmuki, Chem. Comm., 46(2010) 8585.

[5] D. Kowalski, J. Mallet, S. Thomas, A. Woreka, J. Michel, M. Molinari, C. Guery, and M. Morcrette Suubmitted (2016)

Fig. 1 SEM and TEM images for TiO2 nanotubes formed at 60V and 70V for 16h in diethylene glycol electrolyte containing 0.1M HF and H2O 2-4 wt.%. The right figure shows STEM and TEM images for Si electrodeposited on TiO2nanotubes and applied as negative electrode in lithium ion battery.

Figure 1
In-Situ Corrosion Monitoring of Iron and Zinc in Atmospheric Environments
Authors: Omoda Masataka , Mizuno Daisuke , Ishikawa Nobuyuki
Published: February 2020

Traditionally, for evaluating corrosion resistance of materials used in atmospheric conditions, exposure tests in the actual environment and accelerated corrosion tests in the laboratory have been widely used. Till now, it has been very difficult to estimate in detail corrosion rate variations caused by the change of each environmental factor such as temperature, relative humidity, amount of airborne sea salt during the test periods. Also, it requires a long time period to evaluate the corrosivity in actual corrosive atmospheric environments. For these reasons, an in-situ corrosion monitoring technique is useful. Time variation of corrosion rate has been successfully monitored by using an electrical resistance corrosion sensor, which converts the increase of electrical resistance caused by metal consumption to corrosion loss. Additionally, a new accelerated corrosion test was authorized as ISO 16539 Method B on March 1, 2013. This test has good correlation with corrosion behavior in an actual corrosive atmospheric environment. In this study, the details of the corrosion rate of steel and zinc were evaluated by the accelerated corrosion test (ISO 16539 Method B) and atmospheric exposure test. In addition, the relation between corrosion rate and each environmental factor was analyzed.

Two kinds of electrical resistance corrosion sensors, an Fe sensor (250 µm thick) and a Zn sensor (50 µm thick), were used. In the accelerated corrosion test (ISO16539-Method B), the corrosion depth as evaluated by the sensors displayed a good correlation with that of the exposure test samples. The variation in the corrosion rate could be evaluated by the sensors. And also, it was confirmed that the corrosion rate increased during the wet stage and decreased during the dry stage in both sensors. In exposure tests in Okinawa and Kawasaki, the variation of the corrosion rate due to the effects of changeable environmental conditions throughout the year could be evaluated by the sensors. Okinawa is seashore area at the s southern island in Japan, and Kawasaki is industrial area in Japan. The corrosion rate in Okinawa as evaluated by the Fe sensor was greater than that found in Kawasaki. However, the corrosion rate in Okinawa as evaluated by the Zn sensor was almost the same as that in Kawasaki. The corrosion sensors could clarify the difference in corrosion behavior between steel and zinc. Furthermore, the relationship between the corrosion rate and the environmental factors (temperature, relative humidity, amount of airborne sea salt, etc.) was analyzed. The corrosion rate of steel had a positive relation with temperature, relative humidity and airborne sea salt. The dependence of corrosion rate of zinc on environmental factors was also investigated. Comparison of corrosion behavior and its dependence of environmental factors between iron and zinc will be discussed.