bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Current Understanding and Future Aspects of Direct Electron Transfer Mechanism of Fad Dependent Glucose Dehydrogenase Complex
Authors: Sode Koji 
Published: February 2020

Direct electron transfer (DET) between enzyme molecule and electrode provides the ideal principle for the enzyme based sensing system. In DET principle the electrons are transferred from enzyme active site to electrode directly in the absence of any additional electron acceptors, or mediators. This intriguing reaction is useful for various biodevices such as biosensors and biofuel-cells, especially by focusing anodic reactions, such as the oxidation of glucose, fructose, and ethanol. The absence of redox mediators in the system enables the operation of the sensor in redox potential closer to the co-factor in the enzyme, reducing the effect of interfering reactions by electroactive compounds in the sample. However, only a limited number of redox enzymes are capable of DET-reaction with electrodes. Among these, several dehydrogenases harboring a redox center in the catalytic subunit/domain and haem which is not involved in catalysis but act as a built-in mediator for electron transfer between enzyme and electrode are reported. One of the representative groups of DET enzymes is the oligomeric dehydrogenases composed of catalytic subunit harboring FAD as a co-factor, and an electron transfer subunit with haem c, the FAD dependent dehydrogenase complexes. Our research group have been engaged in the isolation, characterization, application and engineering of one of the representative FAD-dependent dehydrogenase complexes. FAD glucose dehydrogenase complex (FADGDH). FADGDH is comprised the three distinct subunits: the catalytic subunit (α subunit) that has an FAD cofactor in its redox center, shows catalytic activity, and oxidizes the first hydroxyl group of glucose; the small subunit (γ subunit), a hitch-hiker protein of the bacterial TAT secretion system, which is necessary for the proper folding and secretion of the α subunit; and the three heme-cytochrome c subunit (β subunit) that is in responsible for the transfer of electrons between the active-site cofactor and external electron acceptors. Thanks to the presence of β subunit, FADGDH is capable to transfer electrons directly to an electrode, making FADGDH as the ideal molecule for the 3rd Gen glucose sensors.
This paper focuses on biomolecular aspects on DET mechanism of FAD dependent dehydrogenase complexes, considering current increasing number of applicational researches, and recent remarkable progress in understanding their DET mechanism, especially about the recent progress in understanding inter- and intra-molecular electron transfer of FADGDH are introduced. These studies included protein engineering approaches of these molecules, thereby led to construct engineered GDH. Finally, the future prospect of the FAD dependent dehydrogenase complexes will be addressed.
Operando Observation of Cobalt Catalysts for Water Splitting By X-Ray and Infrared Absorption Spectroscopy
Authors: Yamada Kanta , Sakata Yoshihisa , Yoshida Masaaki 
Published: February 2020

Recently, electrochemical hydrogen production by water splitting has been receiving attention with regard to achieving a sustainable society. For commercial applications, improving overall water splitting efficiency has been required for the development of highly active oxygen evolution electrocatalysts. In this situation, Nocera and colleagues reported that a cobalt oxide electrodeposited from a dilute Co2+ solution in a potassium phosphate buffered electrolyte (Co-KPi) is efficient electrocatalyst for oxygen evolution reaction (OER) [1]. The local structure of Co species in the Co-KPi catalyst was investigated by Co K-edge X-ray absorption fine structure (XAFS) spectroscopy and X-ray pair distribution function (PDF) analysis, and it was revealed that the Co-KPi is composed of nano-sized clusters with an edge-sharing CoO6 octahedral structure [2]. However, the detailed information about oxygen species in this electrocatalyst under working condition is not yet obtained enough.
In this situation, we have developed many operando observation techniques for XAFS and infrared absorption spectroscopy using attenuated total reflection mode (ATR-IR) to observe the oxygen evolution electrocatalysts. For example, hard X-ray XAFS can observe the electronic states and local structures of metal species in the catalysts. On the other hand, tender and soft X-ray XAFS and ATR-IR can reveal the chemical states of light elements in the catalysts. Therefore, we investigated the reaction mechanism of Co-KPi and similar catalysts for water splitting using various kinds of operando XAS and ATR-IR spectroscopy (Figure 1).
At first, we prepared for Co-KPi and some similar cobalt catalysts in a potassium acetate (Co-KOAc) or a potassium chloride (Co-KCl) aqueous solution by electrodeposition method. It was confirmed that these cobalt catalysts are composed of the edge-sharing CoO6 octahedral structure (CoOOH) by Co K-edge XAFS using hard X-ray. Next, operando O K-edge XAFS spectra for cobalt catalysts were taken using soft X-ray under electrochemical control. When the electrode potential was changed from 0.0 to 1.1 V, a new absorption peak assigned to oxygen species of CoO2 was observed around 529 eV, indicating that the part of CoOOH cluster was oxidized to CoO2 with the high-valent cobalt species (Co4+). The CoO2 peak was obviously observed for Co-KPi of highly active OER electrocatalyst, compared with Co-KOAc and Co-KCl. Finally, operando P K-edge XAFS and ATR-IR revealed the phosphate ion is bounded on the cobalt clusters to stabilize the CoO2 structure. Therefore, we revealed that Co-KPi can function as highly active OER electrocatalyst due to the presence of CoO2 strucutre stabilized by phosphate ion.
[1] D. G. Nocera et al, J. Am. Chem. Soc. 131, 2615 (2009).
[2] (a) D. G. Nocera et al, J. Am. Chem. Soc. 132, 13692 (2010). (b) J. Am. Chem. Soc. 135, 6403 (2013).

Figure 1
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
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.
(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.
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.