bluuebunny/crossref_metadata_2025 huggingface dataset:
Pt Nanowires with High Catalytic Activity and Durability Towards Methanol Oxidation Reaction
Authors: Liu Yongqiang , Geng Dongsheng , Meng Xiangbo
Published: February 2020

Direct Methanol fuel cells (DMFCs) have been attracting great research interest because of their cleanness and high-efficiency in energy conversion1
,
2. Pt catalysts have been used extensively for helping oxidize methanol on the anode side with high catalytic activity and efficiency. However, Pt catalysts are expensive and also suffering from insufficient durability3. To this end, substantial efforts have been devoted to design structure-controllable Pt catalysts. In our recent study, we developed Pt nanowires as electrocatalysts in DMFCs with high catalytic activity and durability for methanol oxidation reaction (MOR) (see Figure 1). Using N, N-Dimethyl form amide (DMF) and N-butanol as both solvent and reductant synergistically, we found that the growth of Pt nanowires highly depends on reaction time and solution ratio. Experimental results showed that all the obtained networked Pt nanowired catalysts exhibit improved durability over those of commercial Pt/C. After 2000 accelerated degradation cycles, the commercial Pt/C electrocatalysts lost ~ 95% of their specific MOR activities, while the Pt nanowired membrane shows only ~70 % loss. Our results suggest that the networked Pt nanowires with high surface areas are promising for MOR of DMFCs.

B. C. Steele and A. Heinzel, in Materials For Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, World Scientific, 2011, pp. 224-231.

X. Zhao, M. Yin, L. Ma, L. Liang, C. Liu, J. Liao, T. Lu and W. Xing, Energy & Environmental Science, 2011, 4, 2736-2753.

J. N. Tiwari, R. N. Tiwari, G. Singh and K. S. Kim, Nano Energy, 2013, 2, 553-578.

Figure 1
Using an Ultrasonic Input for Ammonium Persulfate Electrosynthesis and Advanced Oxidation Processes
Authors: Wallace Alexander George , McHugh Patrick James , Symes Mark
Published: February 2020

The persulfate anion is a powerful oxidant that can be used for effective degradation of persistent organic pollutants. In this work, it is shown that low-power ultrasonic irradiation does not adversely affect Faradaic yields of persulfate electrosynthesis from ammonium sulfate solutions, and that a combined sono-electrochemical treatment of sulfate solutions containing exemplar pollutant naphthol blue-black provides swift degradation of dye solutions as compared to treatments where the sonochemical and electrochemical steps are performed separately. The implications for the degradation of persistent organic pollutants are discussed.
Disentangling Thermodynamic and Kinetic Effects at Photoelectrochemical Interfaces Via Intensity-Modulated High-Frequency Resistivity (IMHFR)
Authors: Pekarek Ryan T , Christensen Steve , Liu Jun , Neale Nathan
Published: February 2020

Photoelectrochemically (PEC) driven reactions are an attractive approach to the capture and storage of solar energy. The quest for efficient and robust solar fuel formation motivates the development of increasingly complex semiconductor surface architectures with correspondingly intricate interfacial energetics, such as oxide deposition, catalyst incorporation, or surface texturing. PEC performance is a function of kinetic and thermodynamic aspects at the semiconductor/liquid junction, and deconvoluting these elements is therefore critical to understanding and improving interfacial dynamics. The flatband potential is one measure of thermodynamics at the semiconductor surface and – when compared with voltammetric data – also allows for an indirect assessment of interfacial kinetics. While electrochemical impedance spectroscopy (EIS) and subsequent Mott–Schottky analysis is the historical standard for flatband potential measurements, additional capacitive elements from surface oxides, catalysts, or other deviations from ideal semiconductor/liquid junctions complicate this analysis. Accordingly, we developed the Intensity-Modulated High-Frequency Resistivity (IMHFR) apparatus to study dynamic and complex semiconductor/liquid junctions. In this method we use a large AC frequency (100 kHz) to measure the space–charge resistance (RSC
) of a semiconductor/liquid junction under chopped light as a function of potential. We then isolate potential regimes where RSC
is dependent and independent of illumination and extract the potential at the boundary between the two regimes, which we define as the flatband potential.

We apply this technique to nanoporous ‘black’ silicon in order to demonstrate its utility and characterize the thermodynamic and kinetic effects of surface treatments at a complex semiconductor/liquid junction. Black silicon is an exciting improvement upon traditional silicon for its large surface area and increased light absorption. We form organic/inorganic films– known to favorably shift proton reduction onset potentials – on black silicon by first covalently binding organic monolayers to nucleate inorganic film growth by atomic layer deposition (ALD). After depositing TiO2 and Pt we collected voltammograms and IMHFR data in acidic media to characterize proton reduction behavior. We find that while the flatband potential shifts positively (favorable for proton reduction), interfacial kinetics are limiting as thicker TiO2 layers are deposited. To circumvent the kinetic limitation, we bury Pt nanoparticles directly into the silicon and form the organic/inorganic film around the nanoparticle. We find the direct Si/Pt contact improves interfacial kinetics but at the cost of the positive shifts to the flatband potential we observed previously. This analysis on a textured and layered semiconductor interface demonstrates the analytical power of the IMHFR technique.
High Performance Li-Ion Battery Electrode with Hierarchical Ordered Porous Microstructure
Authors: Azami-Ghadkolai Milad , Creager Stephen E , Bordia Rajendra
Published: February 2020

Rechargeable batteries are important components of many systems and devices and a high capacity battery that can be rapidly charged remains a top research and development priority. Important performance factors like capacity, energy density, and power density strongly depend on chemical nature and the microstructure of the porous electrodes. Highly tortuous porous electrodes and long lithium ion pathway due to pore blockage by inactive material are detrimental to the energy and power density.

Our goal is to investigate the potential of fabricating low tortuosity, controlled porosity Li-ion battery electrodes by taking advantage of the hierarchical ordered porous microstructure, which can be obtained using freeze tape casting technique.

For this research, Lithium titanate (Li4Ti5O12) powders with and without molybdenum doping (LTO and MoLTO respectively) were synthesized by a solid-state method and used to fabricate electrodes on Cu foil using a normal tape-cast method and a novel freeze-tape-cast. Modest molybdenum doping produces a significant electronic conductivity increase (e.g. 1 mS cm-1 for MoLTO vs 10-7 mS.cm-1 for LTO) that is thought to reflect a partial Ti4+ reduction to Ti3+ with charge compensation by the Mo6+ dopant, producing a stable mixed-valent Ti4+/3+ state. Freeze-tape-cast electrodes were fabricated by a variant of the normal tape-cast method that includes a rapid freezing step in which the solvent in the Cu-foil-supported slurry is rapidly frozen on a cold finger then subsequently sublimed to create unidirectional columnar macropores in the electrode. The effect of Mo doping, freezing rate, electrode thickness on electrochemical behavior of electrodes were investigated.

The resulting freeze tape cast electrodes exhibit high porosity and low tortuosity which enhances electrolyte accessibility throughout the full electrode thickness. Freeze-tape-cast electrodes subjected to galvanostatic charge-discharge testing as cathodes in cells vs. a lithium metal anode exhibit higher specific capacity and lower capacity loss at high discharge rates compared with normal-tape-cast electrodes of the same mass loading, despite the fact that the freeze-tape-cast electrodes are nearly twice as thick as the normal tape cast electrodes.

We show that these engineered porous electrodes of MoLTO have improved energy and power density compared with randomly oriented uniform porosity electrodes – feature of the current generation of battery electrodes.
Improving Reversibility of Anionic Redox Reaction of NaVO3 By Metal Doping for Sodium-Ion Batteries
Authors: Su Bizhe , Yu Denis Yau Wai
Published: February 2020

Traditionally, positive electrode materials in lithium/sodium-ion batteries (LIBs/NIBs) undergo charge and discharge through redox reaction of the transition metal (TM) within the structure. As a result, the number of electron transfer is limited by the available valence states of the TM. Recently, there is an increased interest in solid-state anionic redox reaction (ARR) in positive electrode materials that compensates the charge transfer by the oxygen atoms. ARR can potentially increase the capacity of the active material with the additional charge-transfer site. It can also open the door to more transition-metal compounds that are originally thought to be inactive.

Our previous work has shown that NaVO3 (NVO) can undergo anionic redox reaction while the oxidation state of V remains 5+ between 1.5 and 4.9 V vs. Na/Na+.[1] It can give a capacity of more than 100 mAh g-1, though its capacity fades with cycling. Here, we aim at improving the stability and capacity of the material by incorporating other transition metals into the structure to utilize both the anionic and cationic redox reactions. As a start, we synthesized a single phase Na1.3Co0.1V0.9O3 (NCVO) with Co2+ doping by a typical solid-state method. Both NVO and NCVO materials were first discharged to 1.2 V to investigate the amount of V5+/4+ redox reaction that is available in the material and then charged to 4.7 V. Figure 1a shows the first and second charge-discharge curve of the two materials. Interestingly, the incorporation of Co into the structure reduces the activity of V5+/4+ during initial discharge, with a smaller capacity of 38 mAh g-1 for NCVO as opposed to 94 mAh g-1 for NVO to 1.2 V. Though, the amount of charge and discharge capacities during 2nd cycle are the same, suggesting changes in reaction mechanism of the material with Co2+ addition. The available capacity of about 180 mAh g-1 is higher than that can be obtained from Co and V redox reactions alone, so part of the capacity comes from oxygen redox reaction.

Figure 1b shows the cycle performance of NCVO and it gives good stability. In addition, NCVO can delivers better rate performance with a discharge capacity of 130 mAh g-1 at 50 mA g-1. Further works with techniques such as ex-situ XRD, XPS and GITT to characterize the material and understand the reaction mechanism are underway. More results on the effect of the metal dopant will be presented at the meeting.

[1] J. Zhang, B. Su, A. Kitajou, M. Fujita, Y. Cui, M. Oda, W. Zhou, P. H.-L. Sit, D. Y. W. Yu, J. Power Sources 400, 377 (2018).

Figure 1. (a) Initial discharge and second charge-discharge curves of NVO and NCVO electrodes at 10 mA g−1 between 1.2 and 4.7 V vs. Na/Na+; (b) Cycle performance of NCVO between 1.2 and 4.7 V.

Figure 1
Polymeric Coating on Lithium Metal Surface for the Stabilization of Electrode-Electrolyte Interface
Authors: Zhou Hongyao , Liu Haodong , Liu Ping
Published: February 2020

Lithium (Li) metal is believed as a promising anode material taking over the conventional graphite, because of the higher energy density. However, non-uniform electroplating (dendrite growth) of Li metal leads to a short circuit inside the battery and hinders Li metal battery from the practical use. The dendrite growth is often resulted from uneven flux of Li cation near the surface of the Li metal. Here we present the design and the constructing methods of polymeric coating on the Li metal to regulate the ion flux and stabilize the electrode-electrolyte interface. The methods include; (1) in situ formation of soft and rigid solid electrolyte interface (SEI) layer composed of poly(vinylene carbonate) (polyVC) and lithium carbonate (Li2CO3); (2) the direct polymerization of polyVC on Li metal surface. The method (1) also focuses on the study of cycle life of Li metal under fluorine-free environment by using lithium iodide (LiI) as the lithium salt. The method (2) enables the direct formation of an uniform and dense polymeric layer on Li metal in a scalable fashion.
Correlation between Pulse Charging, Volume Expansion and Structural Degradation in Silicon Electrodes for Li-Ion Batteries
Authors: de Vasconcelos Luize Scalco , Zhao Kejie
Published: February 2020

Silicon electrodes experience substantial volume expansion upon lithium insertion. The volume change is approximately linear with Li concentration which leads to a constant rate of expansion under galvanostatic charging. Interestingly, recent experiments have revealed that the rate of expansion (or contraction) spikes immediately following the application of a constant current, before converging to the lower, steady state value. This effect is seen throughout the entire range of charge and slowly fades away in the course of electrochemical cycles. The volumetric shock can have important implications on the structural stability of strain-rate sensitive materials during pulsed charging. In this work, we use operando nanoindentation to study the effect of the pulse frequency on the rate of expansion and structural evolution of silicon thin films. The electrode is subjected to intermittent step galvanostatic (dis)charge, and the volumetric response is recorded in the course of multiple cycles. The structural degradation is characterized via in-situ optical microscopy and possible mechanisms leading to experimental observations are discussed accordingly.
Understanding the Effects of Structural Water in Tungsten Oxide for High Power Electrochemical Capacitor Applications
Authors: Mitchell James Brooks , Geise Natalie R , Paterson Alisa R , Ko Jesse S. , Long Jeffrey W. , Toney Michael F , Augustyn Veronica
Published: February 2020

Typically, high surface area electrodes and low active material mass loadings are required to obtain both high power and energy in electrochemical devices. Structural water in bulk, hydrated oxides exists as a 2-D layer and could lead to enhanced interfacial charge transfer and solid-state ion transport for high-power applications. The use of bulk hydrated oxides and high mass loadings could also result in high areal capacitance, which is an important metric for energy storage applications. This research investigates the role of interlayer structural water in bulk, crystalline WO3·nH2O (0 ≤ n ≤ 2) for high power and high areal capacitance energy storage. WO3·2H2O was synthesized via precipitation of a tungstate salt in acid, and the structural water content was further controlled through thermal dehydration to yield anhydrous WO3. Morphology and structure of the obtained materials were characterized through electron microscopy, X-ray diffraction, and Raman spectroscopy. Electrochemical characterization was performed with slurry-cast electrodes and high mass loadings (> 4 mg cm-2) using three-electrode cyclic voltammetry at charge/discharge times ranging from minutes to seconds. These results show that hydrated WO3 exhibits excellent capacity retention, and more importantly, improved energy efficiency compared to the anhydrous material. We attribute the excellent high rate capability of hydrated WO3 to the presence of interlayer structural water. To further understand the role of structural water, three-dimensional Bode impedance analyses, electrochemical quartz crystal microbalance, and operando X-ray diffraction studies were investigated and will be presented. Overall, these studies aim to elucidate the role of structural water to present a new design strategy for high power and energy density storage based on bulk, hydrated transition metal oxides.
Modeling and Simulation of Fiber-Based Electrodes for Li-Ion Batteries
Authors: Grazioli Davide , Zhuo Mingzhao , Goudarzi Mohsen , Simone Angelo
Published: February 2020

Fiber-based electrodes represent viable solutions for high-performance and multifunctional batteries. Thanks to the establishment of production techniques such as electrospinning, batteries can nowadays be devised using a fiber-reinforced composite material in which active and conductive material fibers are dispersed in a solid polymer electrolyte matrix.

In order to maximize the active material utilization in fiber-based electrodes, the most suitable fiber arrangement can be identified so that internal pathways for electrons and ions are ensured. In particular, the optimal mixture of fibers (active and conductive) and electrolyte in structural batteries is a compromise between several requirements. First, conductive fibers have to form a conductive network for electrons. Second, the space left for the active material must be sufficient to guarantee a reasonable energy storage capacity. Third, mechanics requires enough fibers to attain a specific load bearing capacity without additional electrochemically-inactive reinforcement. Fourth, the solid polymer electrolyte must provide mechanical connection between fibers and, at the same time, the path for ionic conduction.

The electrode design-battery performance relationship is investigated by means of numerical simulations. Three-dimensional composite structures are generated by randomly distributing fibers in the electrolyte hosting matrix. Effective electrode properties and charge/discharge performance are evaluated by means of Monte Carlo and finite element simulations. To ease the generation of the finite element mesh, fibers are reduced to mathematically equivalent one-dimensional objects using a mesh-independent embedded fiber method. In the numerical simulations, results of the dimensionally-reduced model are validated against reference finite element solutions.
Molecular Modeling of Reaction and Diffusion Processes at Electrochemical Interfaces in Lithium Ion Batteries
Authors: Boyer Mathew J , Hwang Gyeong S
Published: February 2020

Lithium batteries are well-known as a critical technology, but they are also a fundamentally interesting chemical system do to the presence of complex phenomena such as chemical and electrochemical reactions, phase changes, and ion transport across interfaces, to name a few. Such complexity, however, provides opportunity for computational approaches which are able to resolve size- and time-scales unreachable through experimental methods. Many of the practical hurdles moving forward in battery technologies lie at the interfaces between the electrolyte and the electrodes, making study of these interfaces an important application of computational tools. However, no single computational approach is robust enough to encapsulate the entirety of the interface while also providing the appropriate resolution to study charge transfer and chemical bond breaking/formation. For this reason, it is critical that a multi-scale approach is taken in order to incorporate both accurate models and accurate methods into the characterization of important interfacial phenomena. Our work focuses on the formation of the so-called solid electrolyte interphase (SEI) by the reductive decomposition of ethylene carbonate (EC) at a graphite electrode surface prior to the initial lithiation during its first charge cycle. The SEI is a solid film consisting of decomposed electrolyte which permits the conduction of Li+ ions to and from the electrode, while passivating further electron transfer. Thusly, its formation process consists of electrochemical reduction, subsequent chemical reactions, reactant/intermediate/product transport, and solid precipitation onto the electrode surface. In order to encapsulate all of these phenomena, multiple simulation tools must be used. In particular, we utilize molecular dynamics (both classical force field and ab initio), enhanced sampling techniques, and mixed MD/Monte-Carlo methods to model reaction, transport, and phase transformation phenomena which contribute to the formation of the SEI. In this talk, we will present some of our recent findings from our investigation of the SEI and the methods we use to study it. In particular, we will discuss our framework for modeling reactions and diffusion processes near the electrode and the importance of explicit consideration of the electrolyte in predicting kinetics. Interfaces are critical to electrochemical systems from lithium ion batteries, to electrocatalysts, to sensors and computational methods possess great potential in shaping our understanding of them.
Single Mo Atom Supported on N-Doped Black Phosphorus As an Efficient Electrocatalyst for Nitrogen Fixation at Ambient Conditions
Authors: Ou Pengfei , Song Jun
Published: February 2020

Ammonia (NH3) is one of the most significant industrial chemical products due to its wide applications in various fields. However, production of NH3 from nitrogen (N2), (i.e., nitrogen fixation) at ambient conditions is one of the most important issues but a coveted goal for chemists. Here, we propose Mo@N3-embedded black phosphorus (BP) as the electrocatalyst for nitrogen fixation from density functional theory calculations. Results show that in view of the chemical coordination, the Mo@N3 center is highly spin-polarized with a localized magnetic moment substantially to promote N2 adsorption and activate its inert N≡N triple bond, as well as selective stabilization of *N2H species, or destabilizing *NH2 species. Mo@N3 center can catalyze nitrogen fixation through the distal mechanism with an ultralow overpotential of 0.02 V which is lower than any previously reported values, and the removal of the produced NH3 is relatively rapid with a free energy uphill of only 0.56 eV. In addition, the coordination effect on activity is further evaluated (Mo@N2P1, Mo@N1P2, and Mo@P3 centers), confirming that the Mo@N3 center possesses the highest catalytic performance. These findings provide a rational paradigm for catalytic nitrogen fixation by single-atom catalysts at ambient conditions.
(Invited) Nanofibrous Doped Tin Oxide As Electrocatalyst Support for PEM Fuel Cells and Electrolysers
Authors: Cavaliere Sara , Jiménez-Morales Ignacio , Haidar Fatima , Jones Deborah J. , Rozière Jacques
Published: February 2020

In the way towards the reduction of noble metal loading in electrodes for proton exchange membrane fuel cells (PEMFC) and electrolysers (PEMWE), the use of metal oxides as support materials offers electronic electrocatalyst-support interactions beneficial for their activity and durability [1]. The morphology of the supports also plays a crucial role. Nanofibrous webs prepared by electrospinning provide a way to achieve increased performance when used in electrodes by the control of nanostructure and porosity [2].

Tin oxide loose-tubes doped with a range of elements (niobium, antimony and tantalum) were prepared by single-needle electrospinning and subsequent calcination leading to a fibre-in-tube morphology [3]. The doping allowed to increase the electrical conductivity of tin oxide, typical of a semiconducting material. In particular, Sb-SnO2 presented a conductivity similar to that of carbon (1 S cm-1 at 20 °C) [4]. The hollow morphology of doped SnO2 allowed the access of electrocatalyst as well as ionomer and gas, improving the triple phase boundary. The electrochemical stability of the different supports was evaluated in acidic medium at low and high potentials coupling electrochemistry and spectroscopic methods to investigate the specific degradation mechanism occurring.

Pt and IrO2 nanoparticles synthesized by a microwave-assisted polyol method were deposited onto the SnO2-based loose-tubes. The resulting materials were characterised for their morphology and structure. Their electrochemical activity towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as their durability upon accelerated stress tests were evaluated by electrochemical analysis. X-ray photoelectron spectroscopy was a useful tool to demonstrate the strong metal-support interaction leading to improved electroactivity towards ORR and OER [5].

The obtained electrocatalysts were used to prepare PEMFC cathodes and PEMWE anodes and assembled with commercial electrodes and membranes and characterised in membrane-electrode assemblies. Their performance and stability were investigated in different operating conditions and will be discussed.

References:

[1] H. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Arauj́o, E. Willinger, R. Schlögl, D. Teschner, P.Strasser, J. Am. Chem. Soc., 138, 12552 (2016).

[2] S. Cavaliere, S. Subianto, I. Savych, D.J. Jones, J. Rozière, Energy Environ. Sci., 4, 4761 (2011).

[3] S. Cavaliere, S. Subianto, I. Savych, M. Tillard, D.J. Jones, J. Rozière, Phys. Chem. C, 117, 18298 (2013).

[4] S. Cavaliere, I. Jiménez-Morales, G. Ercolano, I. Savych, D. Jones, J. Rozière, ChemElectroChem, 2, 1966 (2015).

[5] I. Jiménez-Morales, S. Cavaliere, D. Jones, J. Rozière, Phys. Chem. Chem. Phys., 20, 8765 (2018).
Rapid and Low-Cost Field Detection of Marine Toxins
Authors: Argun Avni , Weber Andrew , Manoukian Mourad , Rana Muhit , Pierce Richard , Lovko Vincent , Henry Michael
Published: February 2020

Brevetoxins (PbTx) are a group of marine algal toxic compounds that are produced by the bloom-forming dinoflagellate Karenia brevis. During harmful algal blooms (HAB), brevetoxins can reach concentrations high enough to cause human neurological and gastrointestinal illnesses through inhalation of the airborne toxins or consumption of contaminated shellfish. The timely recognition of this toxin in marine environment is of great importance for public safety, human health, human recreation, marine ecology, and the marine economy.

We present the development of a low-cost and easy-to-use electrochemical test for rapid and quantitative detection of brevetoxin species in seawater. Specifically, we utilize an assay to enable measurement of PbTx-2 and PbTx-3 with high specificity while lowering the field detection limits to sub-parts-per-billion (ppb) levels via unique use of disposable electrode chips. Key sensor specifications include PbTx-2 detection limit of 0.25 ppb, a linear range of 0.25 - 50 ppb, and sample-to-result turnaround time of < 5 minutes. The assay also works interference-free; the measured electrochemical signal maintains 90% of its magnitude in seawater in the presence of other aquatic toxins.

This versatile field sensor will allow near real-time monitoring of brevetoxin levels in seawater throughout the progression of a red tide bloom. Additionally, our platform technology has the potential to monitor shellfish toxins and could find applications in seafood safety where rapid, accurate, and selective detection of toxins is needed.
Millimetre-Wave Bow-Tie Reconfigurable Antenna for 5G Applications
Authors: Saha Tonmoy Kumar , Riheen Manjurul Ahsan , Sekhar Praveen K.
Published: February 2020

In order to keep pace with the growing research and development on next-generation reconfigurable 5G wireless devices, this research presents a new design of flexible and low-cost 5G antenna. Instead of a conventional design, two identical back to back bow-tie antenna elements have been used on the same side of the Polyethylene terephthalate (PET) substrate with a dielectric permittivity of 3.2, loss tangent of 0.022, and a thickness of 135μm. The proposed coplanar waveguide (CPW) fed antenna is fabricated by inkjet printing using silver nanoparticles ink. The designed single element antenna is of dimensions 18.5 mm x 9.4 mm. The proposed antenna shows that it operates over a 24.2-31.5 GHz (26% fractional bandwidth, FBW) range with a return loss of 10 dB or less. The solo-element exhibits an average 5dB peak gain within the entire frequency spectrum and 99.34% of radiation efficiency with the consistent radiation pattern. The fabricated antenna was tested under different bending conditions and showed satisfactory performance. Based on the mentioned attractive results and reconfigurable characteristics of the PET substrates, the proposed antenna was found to be suitable for the 5G flexible, conformal, and body-centric applications.
Development of a Wireless Surface Acoustic Wave Methane Sensor Using a Metal-Organic Framework As a Sensing Layer for Natural Gas Pipelines
Authors: Devkota Jagannath , Hong Tao , Culp Jeffrey , Ohodnicki Paul R
Published: February 2020

Methane emission from the processing and transportation of fossil fuels can create serious environmental and safety issues as well as a financial burden. The need to monitor the energy infrastructure creates an opportunity for developing low-cost and robust sensors with wireless options. Wireless surface acoustic wave (SAW) devices, which are highly sensitive, cost-efficient, and passive, are a potential candidate for these applications. Nanoporous metal-organic frameworks (MOFs), which can selectively adsorb large amounts of gases in engineered pores at ambient conditions, are potential sensing layers. Here, we present on the development of a wireless and passive SAW sensor using the MOF zeolitic imidazolate framework-8 (ZIF-8) as the sensing layer for methane detection at ambient conditions.

The SAW delay lines (nominal operating frequency = 436 MHz) were custom fabricated on Y-Z LiNbO3 piezoelectric substrates and coated with a 500 nm thick ZIF-8 layer using a dip coating method. The devices were excited by 428 MHz RF pulses to test for various concentrations of CO2 and CH4 in N2 background at a constant gas flow rate. Wireless measurements were performed via dipole antennas of nominal resonant frequency 433 MHz. When the sensor was exposed to the gases, surface acoustic wave phase shifted in a negative direction relative to the N2 baseline. This shift was attributed to the decrease in SAW velocity due to the increased mass of the MOF film upon gas adsorption. The CO2 and CH4 sensitivities extracted as the slopes of the respective calibration curves were 1.26 deg/vol-% and 0.03 deg/vol-%, respectively. It is important to note that currently tested minimum concentrations of CO2 and CH4 were 1% and 20%, respectively. Also, the wireless measurements were highly affected by the housing and metal reflectors around it. The demonstration on wireless methane sensing is of great importance for remote monitoring of methane emission sites and transmission pipelines. Our current investigations are focused in advancing the detection limit for leak detection and addressing the electromagnetic interferences in wireless measurement caused by the housing.
Redox Active Molecule Induced Metal-Organic Framework Thin Film on Optical Fiber Towards Chemical Sensing of Carbon Dioxide
Authors: Kim Ki-Joong , Culp Jeffrey , Ohodnicki Paul R , Cvetic Patricia , Goodman Angela
Published: February 2020

Sensing of carbon dioxide (CO2) has proven to be a challenging area of research over the few last decades. Although nondispersive infrared absorption sensors are widely used as gas sensors, these are unsuitable for mobile sensing applications due to the necessity of a bulky and expensive optical system. In the case of chemi-resistive sensors based on metal oxides, elevated temperatures are required to promote reaction of surface-bound chemical species and they exhibit cross-sensitivity and significant baseline drift over the life of the sensors. Therefore, it is necessary to explore new types of sensing materials and systems that provide a sensitive, selective, and stable response for CO2 gas as well as sensing at atmospheric conditions.

Waveguide-based optical fiber sensors have unique characteristics and flexible designs which make them well-suited to remote monitoring applications due to their inherent long- range transmission of light. Integrating functional materials such as metal-organic frameworks (MOFs) into optical fibers enable the measurement of optical property changes by adsorbing guest molecules and has led to the potential approach for the fabrication of chemical sensors due to their exceptional sorption capacity and high degree of reversibility even at near-ambient temperatures. Recently, efforts have also demonstrated the ability to infiltrate guest molecules into the pores of MOFs to induce emergent properties (guest-host interaction) which are important advantages for MOFs for use in optoelectronic devices such as chemical sensors. Examples of such properties include enhanced electronic conductivities compatible with chemi-resistive sensing platforms as well as increased optical absorption relevant for optical waveguide-based sensors.

In the present work, MOF thin films were coated on an uncladded optical fiber through a simple solution method at room temperature, which is critical for manufacturability of optical fiber-based sensor devices. Then, the redox-active molecules, 7,7,8,8-tetracyanoquinodimethane (TCNQ), was introduced into MOF pores, achieving enhanced electronic conductivity and optical absorption as well as selective closing of MOF pores and enhanced stability in water. It is observed that the activation of pristine MOF at different temperatures greatly affects the coordination of TCNQ guest molecule into pristine MOF pores.

Sensing responses of TCNQ infiltrated MOF deposited on optical fibers showed a linear relationship between partial pressure of CO2 gas and the light transmission, indicative of a guest molecule-induced optical response modification. Furthermore, the sensors show high sensitivity to CO2 with rapid response time and excellent reversibility. A method for fabricating guest molecule induced MOF films on optical fibers and the capabilities of these sensor to reversibly detect a wide range of concentrations of CO2 gas will be presented.
Ethanol Sensing Characteristics of Nitrogen Doped ZnO and in2O3 Thin Films
Authors: Shihabudeen P K , Roy Chaudhuri Ayan
Published: February 2020

Gas sensing characteristics of semiconducting metal oxides (SMOs) are often modulated by incorporation of suitable dopants that influences oxygen vacancy formation, bang gap and crystal structure of SMOs. Impact of dopant incorporation at the cation site in diverse SMOs has been extensively investigated, whereas the anion site doping is less explored. In this work we report the impact of anion site substitution on the VOC sensing characteristics of SMOs. As a case study ethanol sensing characteristic of nitrogen doped ZnO and In2O3 thin films have been compared. The films were synthesized using spin coating of corresponding sols. Pure ZnO and In2O3 thin films were also synthesized as control samples. The structural and morphological features have been analyzed using XRD and SEM respectively. Presence of nitrogen in the thin films has been confirmed using XPS. The nitrogen substituted sensors exhibited enhanced sensing response towards ethanol in comparison to the pristine oxide films. Nitrogen substituted ZnO film exhibited highest response of 99.6 % at 225 °C, whereas the nitrogen incorporated In2O3 film exhibited a highest response of 99.5 % at 250 °C. Both the samples have shown fast response time of one second up to 200 °C and exhibited excellent long-term stability in their response. Further, nitrogen substituted ZnO has shown better selectivity towards ethanol compared to doped In2O3 thin film.

Figure 1
Structural Properties and Sensing Characteristics of YbTaO4 Sensing Membranes
Authors: Chen Ching-Hung , Pan Tung Ming , Her Jim Long
Published: February 2020

In this paper, we developed YbTaO4 sensing membranes for use in a solid-state electrolyte–insulator–semiconductor (EIS) pH sensor. Impact of rapid thermal annealing (RTA) treatment on the structural and sensing properties of the YbTaO4 sensing membranes deposited through reactive co-sputtering onto Si substrates was investigated. X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy were employed to examine the structural, morphological, and chemical features, respectively, of the YbTaO4 sensing films annealed at three RTA temperatures (700, 800 and 900 °C). The YbTaO4 EIS sensor annealed at the 800 °C exhibited a super-Nernstian response of 71.17 mV/pH within the pH range of 2–12. It also showed the lowest hysteresis voltage (<1 mV) and the lowest drift rate (0.22 mV/h) among the these RTA temperatures. Presumably, the optimal annealing temperature improved the stoichiometry of YbTaO4 film and increased its (-131)-oriented nanograin size.

Figure 1
(Invited) Role of Carbons in Electrochemical Applications
Authors: Wampler Wesley A
Published: February 2020

Carbon has played an important role in many electrochemical applications. This perspective review will focus on selective applications and how carbon has been found to be more important as time goes on. While not always completely understood there is no doubt that it is an essential component of many electrochemical reactions. A few of the applications to be considered will be Lithium ion batteries, fuel cell catalysts and environmental remediation.
Microfluidic Chemotaxis Assay through Stable Chemical Gradient
Authors: Lee Chang-Soo
Published: February 2020

The diffusion-based method can create a non-flow environment for the bacteria, so chemotaxis response can be observed in gradients that evolve only by diffusion, in the absence of flow. Recently, we have reported a convenient and reliable diffusion-based microfluidic device for nonlinear gradient generation. Stable and rapid diffusion of chemicals was successfully generated by direct contact of two fluids manipulated by control of capillary action. In our design, the height of the junction channel is very critical because the junction channel play key roles in diffusion-based gradient generation and physical prevention of bacterial movement toward the chemoeffector channel in analysis of positive chemotactic response. In this study, to improve the height accuracy of the junction channel, we propose a new alternative microfabrication method using thick silicon oxide deposition and reactive ion etching. The height of the junction channel within 1% accuracy could be precisely fabricated by the newly-proposed microfabrication. As a proof-of-concept, we conducted experiments with bacterial chemoeffectors with Pseudomonas aeruginosa PAO1 based on fluorescent observation in a concentration-dependent manner. We easily achieved chemotaxis index of each chemoeffector and it was in a good agreement with our previous result while the variation of chemotaxis index is reduced to be half. We envision that our proposed fabrication will guide microfluidic fabrication to techniques for reproducibility for various field.
(Invited) Gamma Irradiated WO3 Nanostructures for Electrochemical Sensing of Multiple Depression Biomarkers
Authors: Sekar Chinnathambi , A C Anithaa
Published: February 2020

Ability of smart sensors to monitor critical biomarkers even at very low concentration paves the way for further progression in precision medicine initiatives. Hence, many attempts have been made to improve sensing performances by suitably modifying the electrode materials. Surface modification by radiation (e.g. neutrons, ions, electrons and γ-rays) leads to production of lattice defects such as vacancies, defect clusters and dislocations and these induced defects act as recombination centres by trapping the generated carriers. In the present work, we report the synthesis of nanostructured WO3 and its surface modification by gamma ray and swift heavy ion irradiation with different doses and its application for electrochemical sensors applications.

Identification and detection of easily obtainable biomarkers that accurately diagnoses depression are imperative for improving mental health of patients. Here, the gamma and swift heavy irradiated WO3 nanoparticles have shown very high electrocatalytic activity towards a number of neurochemicals including dopamine, serotonin, epinephrine, norepinephrine, acetylcholine, and melatonin [1-4]. For example, nicotinamide adenine dinucleotide (NAD) immobilized gamma irradiated WO3 NPs modified glassy carbon electrode has exhibited simultaneous electrochemical determination of NEP and MEL with the lowest detection limits of 1.4 nM, and 2.6 nM respectively over a wide dynamic range of 0.010 to 1000 µM in phosphate buffer solution at physiological pH of 7.0. The major improvements in the electrocatalytic activity of the fabricated electrode towards the oxidation of analytes is due to the induced high surface density defects, larger electroactive surface area, higher conductivity and fast electron kinetics. Interestingly, these electrodes exhibited excellent anti-interference 5ability against a number of active biological species and metal ions with good stability and reproducibility. Furthermore, fabricated sensors could be successfully applied for real sample analysis with human blood serum, and pharmaceutical samples and the results will be discussed in detail.

References

AC. Anithaa, K. Asokan, C. Sekar, Biosensors and Bioelectronics (2019)

AC Anithaa, K Asokan, C Sekar, J. Taiwan Inst. Chem. Eng. 84 (2018) 11-18

AC. Anithaa, K. Asokan , C. Sekar, Sens.Actuators B: Chem. B 238 (2017) 667–675

AC. Anithaa K. Asokan, C. Sekar, Electrochim. Acta, 167 (2015) 294; 237 (2017) 44-53
Multiplexed Surface Plasmon Imaging of Circulating Biomarkers
Authors: Krishnan Sadagopan , Premaratne Gayan , Al Mubarak Zainab Hussain , Dharmaratne Asantha
Published: February 2020

In vitro diagnosis is a rapidly growing research field to meet the unmet needs of early disease prediction, treatment, and prevention. Among many target analytes, circulating biomarkers facilitate a minimally invasive diagnostic approach. Biomarkers are molecular indicators that can vary widely in concentrations between normal and abnormal conditions (either up or down regulated). Nevertheless, they are typically present at very low levels in complex clinical matrices (e.g., whole blood, serum, saliva, and urine). Hence, bioassays that are selective, sensitive, and offering a wide dynamic range of detection are ideal. Furthermore, multiplex assay platforms are expected to increase the probability of in vitro diagnostics for specific and successful identification of desired abnormalities. We present herein a multiplex surface plasmon resonance imaging microarray that employs citrate-stabilized Fe3O4@Au core/shell nanoparticles as the plasmon signal amplification label for ultra-low detection of serum proteins and microRNA markers.
Study on the Structural and Surface Changes during Lithiation/Delithiation Processes in Copper Sulfide
Authors: Nam Jae Seok , Lee Jung-Hun , Hwang Soo Min , Kim Young-Jun
Published: February 2020

Rechargeable batteries have been considered as one of efficent routes for energy conversion and storage. Li-ion batteries (LIBs) have been empolyed as major power sources for both mobile and stationary and applications. However, the energy densities of conventional, intercalation-based LIBs are insufficient to meet the demands for high-energy-densities enabling long distance driving electric vehicles and large-scale energy storage [1]. Transition metal sulfides based on conversion and/or alloying reactions have drawn considerable interest due to their abundance and high specific capacities [2]. Among them, copper sulfide (CuS) has a theoretical capacity of 560 mAh g-1 (CuS + 2Li+ + 2e‒ ↔ Li2S + Cu) and good electronic conductivity of ~10-3 S cm-1 [3,4]. Nevertheless, CuS shows poor cycling stability, owing to the dissolution of lithium polysulfides (Li2Sn, 2<n≤8) in the organic electrolytes and the insulating nature of Li2S products. To improve the irreversibility issues, it is highly required to understand the electrochemical behavior of CuS during lithiation and delithiation processes.

In this work, we conducted in-situ and ex-situ analysis studies to investigate the electrochemical behavior of CuS during lithiation and delithiation in a carbonate-based electrolyte in the potential range of 0.05 – 3.0 V vs. Li+/Li. The structural and phase evolution of the CuS electrode were in-situ monitored by X-ray diffraction (XRD) and Raman spectroscopy during the lithiation and delithiation processes. In addition, the ex-situ XRD measurement was carried out to probe the phase transition of the CuS during the electrochemical processes and the result was correlated to the in-situ XRD patterns for characteristic lithiation/delithiation potentials. Furthermore, the changes in the chemical binding energies and the formation of the solid-electrolyte interphase layer on the CuS surface were analyzed by ex-situ X-ray photoelectron spectroscopy. It was found that CuS experiences a two-step lithiation reaction of insertion, followed by conversion; however, from the in-situ data, the CuS appears to convert into Li2S and Cu phases without forming distinct intermediate phases, such as Cu1.8S, Cu1.96S, and Cu2S, by lithiation process, which is contrast from the ex-situ data. Based on the above results, we showed the improved battery performance in the carbonate-based electrolyte through nano-engineering of CuS electrode, demonstrating the promise as a high-capacity LIB electrode.

[1] O. Grӧger, H. A. Gasteiger, and J.-P. Suchsland, J. Electrochem. Soc., 162, A2605‒A2622 (2015).

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9, 604‒630 (2014).

[3] J.-S. Chung and H.-J. Sohn, J. Power Sources
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Highly Stable Silver Nanowires Based Bilayered Flexible Transparent Conductive Electrode
Authors: Shinde Mahesh Ashok , Koduru Mallikarjuna , Rakibuddin Md , Kim Haekyoung
Published: February 2020

A flexible transparent conductive electrode (TCE) with silver nanowires (AgNWs) is an essential component in flexible optoelectronic devices. Considerable efforts have been made to improve the transmittance and sheet resistance of AgNWs TCE for large area applications. However, long-term usages of AgNW TCEs are limited by their poor thermal and chemical stabilities under different atmospheric conditions. In this work, we propose to improve the opto-electrical properties by fabricating AgNWs layer on a metal mesh (MM) polyethyleneterephthalate (PET) substrate (AgNW/MM/PET). A bilayer structure of the AgNW/MM/PET was fabricated by bar coating, and it exhibited excellent opto-electrical properties with a transmittance of 90.3% and a sheet resistance of 0.745 Ω/sq. In addition, the fabricated AgNW/MM/PET showed more stable electrical performances than mono layer TCEs with AgNWs or metal mesh on PET under various environmental conditions, such as light, temperature, and humidity. The AgNW/MM/PET electrodes with excellent opto-electrical properties could be a possible replacement for indium tin oxide for large area flexible optoelectronic applications.