bluuebunny/crossref_metadata_2025 huggingface dataset:
NO Electrochemical Reduction on Pt Electrocatalysts: A DFT Approach
Authors: Chun Hee-Joon , Clayborne Andre , Rankin Rees , Greeley Jeff
Published: February 2020

Electrochemical denitrification is a promising technology for the removal of toxic nitrate and nitrite species from groundwater due to the process’s environmental compatibility, energy efficiency, safety, and product selectivity. The adsorbed NO is generally considered to be a selectivity-determining species during this electrochemical potential dependent reaction. Atomic-scale studies using density functional theory (DFT), in turn, can provide powerful molecular-level information about the elementary mechanisms of reductive NO electrocatalysis. These basic building blocks can further serve as a starting point for future trends-based analysis on different transition metal surfaces.  

In this work, we employ periodic, self-consistent DFT calculations to clarify the adsorption structures and thermochemistry of NO and its related reaction intermediate species on different Pt single crystal surfaces ((111) and (100)). Kinetics are further determined by calculating the activation barriers for N-O dissociation, protonation, and N-N bond formation. We begin by describing results for the reaction at low NO coverage (ca. 0.11 ML). After describing the thermodynamics (the adsorption) and kinetics (N-O bond breaking and protonation barrier) for the dentirification reaction scheme, a plausible mechanistic reaction pathway is proposed. Water-assisted protonation barriers are generally shown to be lower than barriers for non-electrochemical reactions, such as surface hydrogenation or N-O bond breaking. Consistent with available experimental evidence, from the most probable reaction pathway, we conclude that ammonium ion would be the most favorable product that would evolve. There is no evidence for the formation of hydroxylamine (H2NOH) at low coverage. At higher NO coverages (ca. 0.45 ML), the relative energy states of the intermediates show a similar trend for the energetics when it is compared with the study with lower NO coverage.

Finally, N2O formation is examined. We find that trans NO dimer species could be a precursor state for the N­2O formation due to its lower kinetic barrier than barriers that are found for cis-type NO dimers. The simulation demonstrates that N2O could be formed at higher potentials through two protonations of trans NO species, and the reaction is thermodynamically more favorable at higher NO coverage.  This barrier could be surmountable at room temperature, and these mechanistic conclusions hold on both the (111) and (100) surfaces.    

Based on our study, we find that reduction of NO proceeds through the water-assisted protonations which will finally lead to ammonia. The primary pathway for N2O formation occurs through trans-type NO dimer species. The proposed pathways occur with different applied electrochemical potentials and NO coverages.
Ab Initio Thermodynamic Modeling of Electrified Metal-Oxide Interfaces: Consistent Treatment of Electronic and Ionic Chemical Potentials
Authors: Zeng Zhenhua , Hansen Martin Hangaard , Greeley Jeff , Rossmeisl Jan , Björketun Mårten E
Published: February 2020

Solid oxide fuel cells are attractive devices in a sustainable energy context because of their fuel flexibility and potentially highly efficient conversion of chemical to electrical energy. The performance of the device is to a large extent determined by the atomic structure of the electrode-electrolyte interface. Lack of atomic-level information about the interface has limited the fundamental understanding, which further limits the opportunity for optimization. The atomic structure of the interface is affected by electrode potential, chemical potential of oxygen ions, temperature and gas pressures. Here we present a scheme to determine the metal-oxide interface structure at a given set of these environmental parameters based on quantum chemical calculations. As an illustration we determine the structure of a Ni-YSZ anode as a function of electrode potential at 0 and 1000 K. We further describe how the structural information can be used as a starting point for accurate calculations of the kinetics of fuel oxidation reactions, in particular the hydrogen oxidation reaction. More generally, we anticipate that the scheme will be a valuable theoretical tool to describe solid-solid interfaces.

Figure 1
Electrocatalytic Oxidation of Ethanol and Formic Acid on Bimetallic Nanoalloys and Core-Shell Nanoparticles
Authors: Lewera Adam , Gorzkowski Maciej T. , Piwowar Justyna , Jablonski Andrzej , Gralec Barbara , Jurczakowski Rafal Robert
Published: February 2020

Mechanism of ethanol electrooxidation on numerous materials has been widely investigated in the past. It is well known that in acidic conditions the electrooxidation of ethanol on platinum surface leads to strongly adsorbed surface groups (i.e. CO), poisoning the surface of catalyst and inhibiting further reactions. Presence of metals other than platinum will make it possible to oxidize adsorbed CO by surface OH groups, present on the other metal (so called “bi-functional mechanism”). Such bi-metallic surface is more resistant to poisoning and as a result more catalytically active. Hovewer it is still not well understood, how the presence of the other metal influences the surface’s electronic properties, which in turn alter adsorption properties, and reaction mechanism.

Electronic properties of the catalyst can be modified by the following methods: they can be related directly to charge transfer from other component of the system, such as another component of the alloy, from substrate, or they can be induced by geometric factors, such as change in lattice parameter. Change in lattice parameter influences the degree of overlapping of valence orbitals forming the conduction band. When lattice is contracted, the conduction band becomes broader. When the conduction band is filled in more than half the broadening of the conduction band leads to shift of the d-band center towards Fermi edge. The lattice parameter can be (to some degree) modified, and as a result, the degree of orbital overlapping can be changed, for instance by alloying.  It is known that in alloys the atom-atom distance changes linearly as a function of composition, in the range determined by inter-atomic distances of the pure elements (Vegard’s law). Similarly, when thin layers are formed, the layer forming metal will exhibit the lattice parameter of the substrate (so called “pseudomorphic monolayer”). Consequently experimental investigation of materials, where lattice parameter has been intentionally modified, allows for experimental determination of the relation between reaction mechanism and electronic properties of the material used.
Study of the Supported Catalysts Core-Shell Type of Gold and Palladium: Analysis of the Reaction Products and Mechanism for the Electrooxidation of Ethanol in Alkaline Medium
Authors: Ruiz Montoya José Gabriel , Chávarri Marín Violeta Herminia , Ocón Esteban Pilar , Morales Gomero Juan Carlos
Published: February 2020

One of the main disadvantages to the development of fuel cells direct ethanol (DEFCs) is the synthesis of catalysts which are able to break the C-C bond in the molecule of ethanol. In this context, Xu et al.,[1] compares the activity of palladium and platinum for ethanol oxidation reaction (EOR) in alkaline medium, showing that the onset of ethanol oxidation on palladium occurs to potential more negative compared to platinum, and the oxidation current density is higher for the palladium.

One way to study the reaction and propose a reaction mechanism for an electrochemical process is using in situ FTIR spectroscopy. For example Tremiliosi-Filho et al., [2] propose an accepted mechanism of ethanol oxidation on gold by FTIR in situ, while Zhou et al., [3] studied the adsorption and oxidation of ethanol on polycrystalline Pd. Since, palladium is more electroactive for ethanol electrooxidation than gold, in this work, the effect of a supported catalyst core-shell Au-Pd, in different proportions were studied.

In this work, the preparation of core-shell catalysts supported Au-Pd/C, in different ratios detailed. The characterization of the catalysts was performed using X-ray diffraction, Energy Dispersive Spectrometer (EDS), transmission electron microscopy (TEM), and electrochemical tests, to calculate the real electroactive area. Cyclic voltammetry tests showed that for the case of Au-Pd catalysts, the parameters like onset and density current oxidation of ethanol were better in relation to gold and palladium alone. This is due largely to the gold produces a stable nucleus where Pd nanoparticles can be dispersed better. On the other hand, the in situ FTIR studies showed an identical oxidation of Au and Pd in an alkaline medium with acetate ion with main product, but variations are also observed in the symmetry and intensity of the collected peaks, this has to see strongly with different intensities bond between ethanol and Pd onset of oxidation.

In conclusion, in this study it was found that the Au-Pd catalysts show better electrocatalytic properties that gold and palladium catalysts. This leads to a more efficient oxidation of ethanol, and use less amount of Pd in the anode catalysts.

References:

[1] Xu, Changwei, et al. "Methanol and ethanol electrooxidation on Pt and Pd supported on carbon microspheres in alkaline media." Electrochemistry Communications 9.5 (2007): 997-1001.

[2] Tremiliosi-Filho, G., et al. "Electro-oxidation of ethanol on gold: analysis of the reaction products and mechanism." Journal of Electroanalytical Chemistry444.1 (1998): 31-39.

[3] Zhou, Zhi-You, et al. "In situ FTIR spectroscopic studies of electrooxidation of ethanol on Pd electrode in alkaline media." Electrochimica Acta 55.27 (2010): 7995-7999.

Figure 1
Improving Activity and Stability of ORR Electrocatalysts with Pt-Rich Hollow Nanostructures
Authors: Dubau Laetitia , Asset Tristan , Chattot Raphaël , Maillard Frederic
Published: February 2020

The ever-growing energy demand worldwide and the announced end of the so-called “fossil fuel era” are currently boosting the development of electrochemical energy technologies, such as fuel cells, batteries and supercapacitors. In proton-exchange membrane fuel cells (PEMFC), special effort has been paid to improve the catalytic activity for the oxygen reduction reaction (ORR) of the cathodic material, its stability and to decrease its precious metal content.  

This study describes the advantages of hollow nanostructures composed of a Pt-rich outer-layer surrounding a central void. Pt-rich hollow nanoparticles with different Pt-shell thicknesses were synthesized via a method involving the galvanic replacement of Ni atoms by Pt atoms, and the nanoscale Kirkendall effect [1]. Increasing the Pt:Ni stoichiometry from 1:1 to 1:5 in the initial metal precursor solution resulted into a thinner Pt-rich shell and an increased Pt lattice contraction. The specific activity and the mass activity for the ORR at E = 0.95 V vs. RHE of the most active hollow electrocatalyst were 9-fold and 3.6-fold that of a reference solid carbon-supported Pt nanocrystallites with a comparable crystallite size (Figure 1). Their structural stability was investigated at different temperatures ranging from T= 293 to 353 K by identical-location and conventional transmission electron microscopy.

Acknowledgements

This work was performed within the framework of the Centre of Excellence of Multifunctional Architectured Materials "CEMAM" n° AN-10-LABX-44-01 funded by the "Investments for the Future" program. The authors acknowledge financial support from University of Grenoble-Alpes through the AGIR program (grant # LL1492017G), and from the French national Research Agency through the HOLLOW project (grant # ANR-14-CE05-0003-01).

References

[1] L. Dubau, M. Lopez-Haro, J. Durst, L. Guétaz, P. Bayle-Guillemaud, M. Chatenet, F. Maillard, “Beyond conventional electrocatalysts: Hollow nanoparticles for improved and sustainable oxygen reduction reaction activity”, J. Mater. Chem. A. 2 (2014) 18497-18507.

Figure 1
(Invited) Electrocatalysis on Tailored Electrochemical Interfaces
Authors: Kang Yijin , Li Dongguo , Strmcnik Dusan , Markovic Nenad M , Stamenkovic Vojislav R
Published: February 2020

The primary barrier to broad applications of electrocatalyst for electrolyzers, fuel cells and metal-air batteries is lack of fundamental understanding of processes that are taking place at solid-liquid interfaces. Moreover, the cost, performance and durability of the current state of the art electrocatalysts are still not at level that would warrant commercialization of these technologies.

 This presentation will bring the most recent progress in the development of advanced interfaces for electrochemical energy conversion and storage.  The structure-function relationships in electrocatalysis that led to establishment of principles for the design of advanced electrocatalysts will be particularly discussed.  It will be also demonstrated that fine tuning of the properties of solid and liquid components at the interfaces can led towards unprecedented improvements in functionality of practical materials for energy conversion and storage applications.
(Invited) Epitaxial Oxide Surfaces: New Insights in Oxygen Electrocatalysis
Authors: Stoerzinger Kelsey A. , Shao-Horn Yang
Published: February 2020

Fundamental understanding of transition metal oxides for oxygen electrocatalysis is often hampered by heterogeneity of oxide powder surfaces and the composite nature of electrodes used for electrochemical measurements. Surfaces of epitaxial thin films, with well-defined crystallographic orientations and strains offer an excellent opportunity to develop insights into what parameters can govern catalytic activity and deduce active sites for oxygen electrocatalysis. In addition, these surfaces allow spectroscopic study of the chemical speciation and electronic structure in an aqueous reaction environment, using ambient pressure X-ray photoelectron and absorption spectroscopy coupled with mass spectrometry to analyze the reaction productions. Here, control of the surface homogeneity is critical for quantifying the adsorption of intermediates and comparing the reactivity between surfaces. The insights obtained from study of these epitaxial surfaces build fundamental understanding of the mechanisms of oxygen electrocatalysis, as well as guide the rational design of high surface area oxide catalysts for technical application.
Metal Organic Frameworks: A Platform for Electrocatalytic Fuel Generation
Authors: Hod Idan , Farha Omar K. , Hupp Joseph T.
Published: February 2020

Over the last two decades, metal-organic frameworks (MOFs) have attracted a great deal of scientific interest due to their extremely high porosity and surface areas. The vast number of combinations of node and ligand-based properties makes MOFs exciting candidates for a wide variety of applications, including gas storage, chemical separation and catalysis, where bulk crystalline powders or solution dispersions of MOFs have been utilized. However, only a few attempts have been made to explore the incorporation of MOFs into thin films to be used in electrocatalysis.

In this work we demonstrate that MOFs could be beneficial when utilized in an electrocatalytic system. An electrode-supported MOF scaffold was used as a platform for NiS electrodeposition to create a hybrid HER electrocatalyst. In aqueous pH 1 solution, the MOF-NiS hybrid exhibit significantly improved catalytic performance compared to a flat NiS-only based system, reducing the required overpotential at current density of 10 mA/cm2 by more than 200 mV down to 238 mV. It was found that the aquo- and hydroxo-rich nodes of the MOF appear to modify the immediate environment of the NiS electrocatalyst, rendering it more favorable for local proton delivery and/or transport.

Figure 1
Electrochemical and UV-Visible Spectroscopic Studies of Self-Organized Gold Nanoparticle~Cytochrome C Superstructures
Authors: Harper-Leatherman Amanda S. , Pacer Elizabeth R. , Abunar Bayan H. , Spiridigliozzi Julia K. , Graffam Molly E. , Garvey Elizabeth M. , Buzard Kaitlyn L.
Published: February 2020

The addition of the protein, cytochrome c (cyt. c), to gold nanoparticles in solution results in self-organization of cyt. c into multilayered protein superstructures (abbreviated as Au~cyt. c superstructures) and stabilizes the thousands of organized cyt. c proteins to unfolding both when encapsulated in porous solids and when remaining in solution.  Our research has shown that the electrochemical characteristics of superstructure-assembled cyt. c are enhanced compared to cyt. c alone and vary as the ratio of cyt. c to Au varies.  In order to determine whether the enhanced electrochemical properties are directly related to the multiple protein layers of the superstructures staying intact at the electrode surface, the protein superstructures were stripped from the electrode surface and measured with UV-visible spectroscopy.   The UV-visible absorbance of the cyt. c Soret peak, and subsequent calculated cyt. c electrode surface coverage, varied as the ratio of gold to protein varied.  These results support the idea that at an optimal ratio of gold to protein when forming superstructures, the cyt. c electrochemical properties are enhanced and are related to multiple proteins remaining active within superstructures at the electrode surface.  These results may prove useful to those developing bioanalytical devices when a good understanding of the interaction between protein and material surface is needed.
(Invited) High Performance Nano-Carbon/Silicon Solar Cells Via Strategic Doping Processes
Authors: Taylor André D.
Published: February 2020

Hybrid approaches that combine silicon (Si) and nano-carbon (nano-C) materials-based thin films (i.e., single walled carbon nanotube (SWNT) films or graphene) have recently led to novel and promising photovoltaic devices. The main advantage is that the intrinsically high photovoltaic efficiency of Si can be realized in a cost-effective manner owing to the low-temperature solution processibility inherent to the fabrication of nano-C/Si junctions. Indeed, efficiencies up to 15% have recently been reported, which surpasses the best efficiency of any polymer/Si hybrid solar cells developed with a similar motivation towards reduced fabrication cost. This superiority is mainly due to the excellent electrical properties of the nano-C materials in comparison to conventional conjugated polymers. In this talk, we demonstrate that easy to handle metallocenes and related complexes can be used to both p-type and n-type dope SWNT thin films, using a simple spin coating process [1]. We report n-SWNT/p-Si photovoltaic devices that are >450 times more efficient than the best solar cells of this type currently reported and show that the performance of both our n-SWNT/p-Si and p-SWNT/n-Si devices is related to the doping level of the SWNT. Furthermore, we establish that the electronic structure of the metallocene or related molecule can be correlated to the doping level of the SWNT, which may provide the foundation for controlled doping of SWNT thin films in the future [1]. In a separate approach we will show how HF treatment of SWNTs followed by current stimulation is a very effective method for oxygen removal with broad applications for carbon electronics [2]. Finally, we will describe how direct solution casting of silver nanowires (AgNWs) onto the SWNT/Si junctions leads to a significant improvement of photovoltaic properties owing to enhanced carrier transport in the bilayer AgNW/SWNT composites [3]. This improvement becomes particularly more pronounced with increasing junction area, which results in a significantly high efficiency of ~11 % in SWNT/Si solar cells with the largest junction area (49 mm2) developed so far [3].

[1] X. Li, L.M. Guard, J. Jiang, K. Sakimoto, J.-S. Huang, J. Wu, J. Li, L. Yu, R. Pokhrel, G.W. Brudvig, S. Ismail-Beigi, N. Hazari and A.D. Taylor (2014) Controlled doping of carbon nanotubes with metallocenes for application in hybrid carbon nanotube/Si solar cells, Nano Letters, 14 (6), 3388–3394. DOI: 10.1021/nl500894h

[2] X. Li, J-S. Huang, S. Nejeti, L. McMillon, S. Huang, C.O. Osuji, N. Hazari, A.D. Taylor (2014), The Role of HF in Oxygen Removal from Carbon Nanotubes: Implications for High Performance Carbon Electronics, Nano Letters, 14 (11), 6179-6184. DOI: 10.1021/nl502401c

[3] X. Li, Y. Jung, J-S. Huang, T. Goh , and A.D. Taylor (2014), Device Area Scale-Up and Improvement of SWNT/Si Solar Cells Using Silver Nanowires, Advanced Energy Materials, 4 (12), 1400186. DOI: 10.1002/aenm.201400186
Li@SWCNT and Cup-Stacked Carbon Nanotubes for Dye-Sensitezed Solar Cells
Authors: Matsubara Elaine Yoshiko , Rosolen Jose Mauricio , Bregadiolli Bruna Andressa , Congiu Mirko , Graeff Carlos Frederico de Oliveira
Published: February 2020

Carbon Nanotubes (CNTs) are extensively studied for energy applications, mainly as additives in composite electrodes to promote electric and thermal conductivity, reinforce the mechanical strength, and enhance the flexibility and performance. Also, introduction of this nanomaterial into the semiconductors electrodes can reduce the resistance of the active materials and produce a composite nanomaterial, due to the electronic interactions between carbon nanostructures and other nanomaterials or substrates.

The studies developed by our group are concentrating on the synthesis of doped carbon nanotubes having different pristine properties produced by CVD or arc-reactor methods for energy devices applications.

The synthesis of Li@SWCNT by arc-reactor method produced selectively metallic tubes, with wettability in water and polar solvents [1]. For Cup-stacked carbon nanotubes (CSCNT) synthetized by CVD method, the tubes present semiconductor properties, high defective structure and wettability too. Herein, we realized studies in photoanode and counter electrode for dye-sensitized solar cells (DSSC) about the use of these two CNTs due to their special properties.

The photovoltaic properties were characterized by photocurrent-voltage (J-V) curves under illumination and impedance spectroscopy in order to study the incorporation of CNTs effects in the photoanode (CSCNT) and counter electrode (Li@SWCNT).

The CSCNT presented better performance for photoanode in DSSC due to the semiconductor and defective structure that promotes better interaction between CSCNT and TiO2 paste used to prepare the electrode. The addition of CSCNT in the concentration range 0.3 to 0.1 wt% (TiO2 electrode doping with CSCNT) has positive effects on the efficiency of DSSC, like the increase of the photocurrent and the efficiency, further on the photoanode remains transparent. The best result was obtained for 0.26% wt% of CSCNT.

On the other hand, Li@SWCNT showed best results when used as counter electrode. This material showed the same behavior as platinum in impedance spectroscopy and was incorporated by spray method in the FTO glass substrate.

[1] Matsubara, E.Y.; Luengo, C.A. and J.M. Rosolen. Lithium-doped endohedral single-walled carbon nanotubes can arise during tube growth. Chemical Physics Letters 590, 175–179 (2013).
Effect of Gate Electrode in Electrochemical Cells
Authors: Chowdhury Tazima , Grebel Haim
Published: February 2020

Electrochemical cells consist of two half-cells containing each an anode and a cathode.  There is an ionic contact between the two half-cells to maintain the flow of ionic charge.  In order to maintain the charge flow in a voltaic cell, a salt bridge is placed between the two half-cells.  We replaced the salt-bridge by a third electrode - a conductive and permeable gate electrode.  A bias potential was then applied to this gate electrode.  In that way, we were able to control the external current of the cell.  This would be the first step towards the realization of ion transistors.  

In preliminary studies, several gate electrodes were considered: layers of functionalized carbon nanotubes (CNT) and metal plate capacitors.  Cyclic voltammetry and electrochemical impedance spectroscopy revealed the effect of the gate bias on the effective capacitance and impedance of the cell.  

Current-Voltage measurements (I-V curves) were made on layered structures, which were made of p-type and n-type CNT.  These data clearly exhibited the formation of barrier(s) between the two layers.  Cyclic voltammetry (CV) measurements were carried out using an electrochemical workstation (CHI760C, Electrochemical Instrument) at room temperature and using 0.01 M solution of NaCl as electrolyte.  Various scan rates of 0.01, 0.05, 0.1 and 0.5 Vs-1 were assessed.  Two graphite rods, one serving as a working and the other as a counter electrode, were used.  Ag/AgCl (3M KCl filled) electrode served as the reference.  The gate electrode was placed in the middle of the cell, between the working and counter electrodes.  The corresponding specific capacitances were calculated from the CV data.

Electrochemical impedance spectroscopy (EIS) was performed for each of the gate electrodes, as well.  The data were taken at a dc bias of 0.24 V with sinusoidal signal of small magnitude over sub to kilo Hertz frequency range. The capacitive behavior was more pronounced at low frequencies. Membranes composed of p-i-n structures, a p-type layer of CNT, followed by an insulating layer of MMA and finished by an n-type CNT all deposited on a 10-micron Teflon filter substrate exhibited the larger capacitive behavior compared to p-n layered membranes or metallic capacitor. 

Chrono-potentiometry method was performed for gate electrodes. The curve within a potential window indicated from the time constant better capacitive behavior in p-i-n than other two gate electrodes. The value indicated in milli farad magnitude which is similar to the range of values found in cyclic voltammetry and electrochemical impedance spectroscopy techniques.     

References:

[1] Y. Zhang, H. Grebel, “Controlling Ionic Currents with Transistor-like Structure”, ECS Transactions 2 (18). 2007

[2] S. Sreevatsa, H. Grebel, “Carbon Nanotube Structures as Ionic Barriers: A New Corrosion Prevention Concept”, ECS Transactions 19 (29) 91-100. 2009
(Invited) Roll-to-Roll Synthesis of Vertically Aligned Carbon Nanotubes with Embedded Redox Polymers
Authors: Roberts Mark E. , Arcila-Velez Margarita Rosa , Zhu Jingyi , Podila Ramakrishna , Karakaya Mehmet , Rao Apparao M.
Published: February 2020

Electrochemical double layer capacitors (EDLCs), often referred to as supercapacitors, have been the focus of considerable research to develop ultra-high surface area materials with high power and energy density. Activated carbon represents the state-of-the-art EDLC electrode material due to its high porosity, high surface area, and chemical stability. More recently, vertically aligned carbon nanotubes (VACNTs) have emerged as an alternative material due to their high conductivity, stability, facile synthesis and the ability to control the ion-accessible area by varying nanotube density.

VACNT electrodes have been used to achieve high power EDLCs; however, scalable manufacturing methods remain elusive, and the ability to grow VACNTs directly on current collectors will help overcome many hurdles facing commercial application. While the chemical vapor deposition (CVD) method is relatively versatile in terms of controlling CNT characteristics (e.g., tube diameter, number of walls, and dopant ratio), three primary factors limit continuous manufacturing of nanomaterials: i) substrate size determined by reactor geometry, ii) requirements of complex catalytic substrate preparation, and iii) high operating temperatures that are incompatible with traditional current collectors (e.g., Al foil).

In this work, we present a continuous, roll-to-roll process for synthesizing VACNT forests directly on inexpensive Al foil using the ferrocene-xylene liquid injection floating catalyst technique. The Al foil is continuously drawn through a chemical vapor deposition reactor operating at ambient pressure and a relatively low temperature (600 °C). EDLC electrodes comprising VACNT forests synthesized in continuous and stationary CVD processes were directly assembled into supercapacitor cells, which yielded high power densities (1270 W/kg) and energy densities (11.5 Wh/kg). These devices exhibited very low internal series resistance due to their intimate contact with the current collector and excellent cycle stability with no loss in performance over multiple thousands of cycles.

The energy density of VACNT electrodes is increased by integrating high charge capacity redox polymers within the VACNT eelctrodes. In the continuous process, electroactive conducting polymers and redox polymers are embedded into VACNTs using electrochemical methods and physical adsorption processes. Current progress on the performance and limitations of incorporating redox polymers with carbon nanomaterials will be discussed along with the advantages and challenges in future material development.
Graphene for Energy: Which Promising Applications and How?
Authors: Quesnel Etienne
Published: February 2020

With thousands of publications per year, graphene has raised a particularly great attention these last years. It is true that with an extraordinary combination of physical and technical properties including high flexibility, lightness, electronic mobility and ability to easily change its chemical properties by surface chemistry, graphene appears as an outstanding material which characteristics can interest many fields of application. Among them, energy conversion, production or storage are of such interest that the European's biggest research initiative, the “Graphene Flagship[1]” dedicated a specific work package only to that topic.

The present talk aims at reviewing some of these energy applications where graphene and graphene related materials are thought to provide disruptive performances. Actually, fulfil of these promises will depend on the control of the full value chain going from graphene production to integration into the energy devices. Moreover, to fully benefit from graphene properties, the integration strategies have to address the interfacing issue of graphene with hosting material. Further graphene functionalization steps are thus often necessary to adapt the surface graphene properties. It leads to the development of various graphene functionalization technologies without which a successful transfer of graphene into energy applications would be impossible. Various examples dealing with graphene doping, nano-structuring or nano-decorating will be discussed to illustrate the key role of these enabling technologies.

[1] http://graphene-flagship.eu/
Enhancement of Platinum Mass Activity at Polymer-Wrapped Carbon Nanotube-Based Fuel Cell Electrocatalysts
Authors: Nakashima Naotoshi , Hafez Inas , Berber Mohamed Reda , Fujigaya Tsuyohiko
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are one of the most promising power sources for cars and houses due to their high-energy conversion efficiency [1-7].

    Cost reduction and improved durability are the two major targets for accelerating the commercialization of PEFCs. To achieve these goals, the development of a novel method to fabricate platinum (Pt)-based electrocatalysts with a high mass activity, deposited on durable conductive support materials, is necessary.

    In this study, we report a facile approach to grow homogeneously dispersed Pt nanoparticles (Pt) with a narrow diameter distribution in a highly controllable fashion on polymer-wrapped carbon nanotubes (CNTs)[8]. A PEFC cell employing a composite with the smallest Pt nanoparticle size (2.3 nm diameter) exhibited a ~8 times higher mass activity compared to a cell containing Pt with a 3.7 nm diameter. This is the first example of the diameter control of Pt on polymer-wrapped carbon supporting materials. using a minimal amount of Pt.

  References

[1] M. R. Berber, T. Fujigaya, N. Nakashima, M. R. Berber, T. Fujigaya, N. Nakashima, J. Mater. Chem. A, 2014, 2, 19053.

[2] M. R. Berber, T. Fujigaya, N. Nakashima, ChemCatChem, 2014, 6, 567.

[3] M. R. Berber, T. Fujigaya, K. Sasaki, N. Nakashima, Scientific Reports, 2013, 3, art. no. 1764.

[4] T. Fujigaya, M. Okamoto, N. Nakashima, ChemCatChem, 2013, 5, 1701.

[5] T. Fujigaya, N. Nakashima, Adv. Mater., 2013, 25, 1666-1681.

[6] T. Fujigaya, C.R. Kim, K. Matsumoto, N. Nakashima, Poly. J. 2013, 45, 326-330.

[7] T. Fujigaya, T. Uchinoumi, and K. Kaneko, N. Nakashima, Chem. Commun. 2011, 47, 6843.

[8] I. H. Hafez, M. R. Berber, T. Fujigaya, N. Nakashima, Scientific Reports, 2014, 4, art no.6295.
Integrated Micro-Heater Solid State Based NO2 Gas Sensors with Enhanced Response
Authors: Sharma Anjali , Singh Avneet , Gupta Reema , Rana Lokesh , Tomar Monika , Gupta Vinay
Published: February 2020

Microelectromechanical systems (MEMS) based integrated gas sensors offer many potential advantages for sensing applications including low power consumption, low fabrication cost, high quality, and reliability. A conductance type gas sensor system can be implemented in a cost effective manner using MEMS technology. In the present work an effort has been made to develop highly sensitive gas sensors for trace level detection of NO2 gas. SnO2 thin film was deposited by RF sputtering technique under 30% O2 and 70% Ar in the reactive gas mixture using a metallic tin (Sn) target at an optimized deposition pressure of 16 mTorr. Bare SnO2 thin film based gas sensor showed a very high sensitivity of ~1.4x104 towards 10 ppm of NO2 gas at a low operating temperature of 100 oC, but with very slow response and recovery times of ~4 min. and ~33min. respectively. Platinum micro-heater has been fabricated using micromachining technique on silicon dioxide membrane of about 1.8 mm thickness which provided improved thermal isolation of the active area. This mircrohotplate has been integrated with the SnO2 based gas sensor for the fast detection of 1 ppm NO2 gas. The temperature of mircrohotplate could be controlled by varying the applied dc voltage. The microhoheater has obtained a maximum temperature of ~800 oC at a dc voltage of 3 V. The SnO2 sensor based on MEMS structure exhibits the maximum sensing response of about 56 towards 1 ppm of NO2 gas at an operating temperature of 70 oC. Thus to attain an operating temperature of 70 oC, the power consumption of MEMS sensor was found to be about 1.2 mW. The studies indicate that the fabricated NO2 gas sensor having integrated micro-heater and SiO2 membrane can be utilized efficiently for the fabrication of a commercial gas sensor with low power consumption.
Detection of Salmonella on Bird Feces Contaminated Leafy Green Vegetables Using Phage-Based Magnetoelastic Biosensors
Authors: Dai Jing , Chai Yating , Hu JiaJia , Horikawa Shin , Chin Bryan A
Published: February 2020

The outbreak of foodborne diseases caused by bacteria, such as O157:H7 E. coli and Salmonella has become a great concern in food safety[1]. The consumption of foodborne bacteria contaminated vegetables is one of the causes of foodborne disease. Vegetables can be contaminated by animal manure, for example, bird feces. Bird feces contain Salmonella which is a pathogen that lives in the intestines of the infected birds and is shed through feces. Bird could fly over or land on leafy green vegetables, such as spinach, iceberg lettuce and cabbage, leading to the potential bird feces contamination. Recently, USFDA found that the outbreak of Salmonella in peanut butter may be linked to the exposure of bird feces to the raw, unshelled peanuts that were stored outdoors where birds were observed flying over and landing on the in-shell peanuts[2]. Even though water washing can remove feces and reduce bacterial contamination, it is still difficult to eliminate bacteria at all. Therefore, rapid detection Salmonella in bird feces contaminated leafy green vegetables is required. The phage-based magnetoelastic biosensor has been developed to detect Salmonella on food surface [3, 4]. In the present work, we optimized the current detection procedures to detect Salmonella on bird feces contaminated vegetables using phage-based magenoelastic biosensors. Several parameters influencing the effectiveness of detection were optimized, such as, blocking agent concentration and incubation time. A protocol was developed to visualize Salmonella on biosensor surface to correlate the resonance frequency measurement of biosensors. Our detection protocol could contribute to screening the leafy green vegetables after harvesting to reduce effort and cost. 

Reference:

1. WHO: Food safety and foodborne illness. In Fact sheet no 237; 2007.

2. FDA: Inspectional Observations. Denver, CO; 2012.

3. Chai, Y, Horikawa, S, Wikle, HC, Wang, Z, Chin, BA, Surface-scanning coil detectors for magnetoelastic biosensors: A comparison of planar-spiral and solenoid coils. Applied Physics Letters. 2013. 103:p.173510.

4. Lakshmanan, RS, Guntupalli, R, Hu, J, Kim, D-J, Petrenko, VA, Barbaree, JM, Chin, BA, Phage immobilized magnetoelastic sensor for the detection of Salmonella typhimurium. Journal of Microbiological Methods. 2007. 71:p.55-60.
Carbon Nanofibers As Transducer Layers in Potentiometric Sensors
Authors: Jaworska Ewa , Madejak Joanna , Kisiel Anna , Maksymiuk Krzysztof , Michalska Agata
Published: February 2020

Many reports on application of nanostructured materials for potentiometric sensing purposes point out advantages of carbon nanostructures [1,2].  In this case, for the first time, carbon nanofibers (CNFs) were used as ion-electron transducers. Stable suspensions of CNFs in water or organic solvent (inks) were prepared. Potassium selective electrodes with CNFs solid contact and plasticized poly(vinyl chloride) or polyacrylate based membranes  were prepared based on different carbon nanofibers ink. The effect of CNFs dispersion stabilizing agent used on the performance of resulting all-solid state potassium selective electrodes was evaluated. Analytical parameters of sensors, prepared using carbon nanofibers  (as an effective transducer layer in ion-selective electrodes) are similar to those of all-solid-state sensors based on conducting polymers.

REFERENCES

1. G. A. Crespo, S. Macho, F. X Rius, Anal. Chem. 2008, 80. 1316-1322.

2. F. X. Rius - Ruiz, G. A. Crespo, D. Bejarano - Nosas, P. Blondeau, J. Riu, F. X. Rius, Anal. Chem. 2011, 83, 8810-8815.
A Novel Graphene/Chitosan/ZrO2 Nanocomposite Sensor for Electrochemical Investigation of a Non-Steroidal Anti-Inflammatory Drug Tolfenamic Acid
Authors: Srivastava Ratnanjali , Satsangee Soami Piara
Published: February 2020

A highly sensitive and selective sensor based on graphene/chitosan/zirconium oxide nanocomposite modified GCE (GRP/CHIT/ZrO2/GCE) has been fabricated for a convenient study of anodic behavior of tolfenamic acid (TA) using cyclic voltammetry (CV) and square wave voltammetry (SWV). Scanning electron microscopy (SEM) was used to investigate the assemble process of the nanocomposite modifier (GRP/CHIT/ZrO2). Electrochemical characterization of the modified electrode has been characterized by CV and electrochemical impedance spectroscopy. GRP/CHIT/ZrO2/GCE exhibited higher electrocatalytic behavior towards the electro-oxidation of TA as compared to GRP/CHIT/GCE and bare GCE which can be described on the basis of mass transport regime within the porous layer of the nanocomposite modifier. TA exhibited an irreversible diffusion controlled process and a linear dynamic range from 5-40 ng/mL at GRP/CHIT/ZrO2/GCE. The proposed method has been further scrutinized by the successful determination of TA in pharmaceutical formulation.
Sensitive and Selective Determination of Dopamine at a Nanocomposite Modified Sensor
Authors: Devnani Harsha , Ansari Sana , Satsangee Soami Piara
Published: February 2020

A sensitive electrochemical sensor for determination of dopamine has been developed by modiﬁcation of carbon paste electrode (CPE) with graphene (GRP), chitosan (CHIT) and zirconium oxide (ZrO2) nanoparticles. The morphological characteristics of nanocomposite (GRP-CHIT-ZrO2) were studied by scanning electron microscope and atomic force microscopy. Electrochemical characterization of the modified sensor was done using cyclic voltammetry and electrochemical impedance spectroscopy. Enhancement in electron transfer process and reduction in charge transfer resistance was observed. Electrochemical behavior of dopamine at nanocomposite modified CPE (GRP-CHIT-ZrO2/CPE) was investigated in pH 7.4 phosphate buffer solution using cyclic voltammetry and square wave voltammetry. The modified sensor showed enhancement in current response as compared to bare CPE. The modified sensor showed a linear response for dopamine in the range 1000 to 5000 nM. The limit of detection and limit of quantification were found to be 20 and 67 nM respectively which is lower than many other sensors reported for dopamine in literature. The modified sensor showed high sensitivity (2.23 nA/nM) and selectivity for determination of dopamine. The method was also successfully employed for determination of dopamine in human blood serum samples.
Direct Electron Transfer and Oxygen Reduction Reaction on Hemoglobin with Indium Tin Oxide Synthesized with Different Metal Compositions
Authors: Ayato Yusuke , Sugimoto Wataru
Published: February 2020

Biofuel cells (BFCs) are nature-inspired electrochemical systems. Natural bio-materials (e.g. glucose as the fuel and enzymes as the electrocatalysts) are used under mild conditions at around body temperature at near-neutral pH. We have developed BFCs with hemoglobin (Hb), [1, 2] making it possible for use as body implantable power supplies applied to medical devices such as pacemakers for cardiac resynchronization therapy and deep brain stimulation. In this study, indium tin oxide (ITO) thin films were synthesized on glass plates with different metal molar ratio by dip-coating methods and used as bio-electrodes for Hb. Electrochemical evaluation was conducted under a three-electrode system consisting of the synthesized ITO working, a platinum wire counter, and an Ag|AgCl|KCl(satd.) reference electrode. Cyclic voltammograms (CVs) in a Hb containing solution with pH 7.4 revealed a pair of well-defined redox peaks at around -0.15 V vs. Ag|AgCl|KCl(satd.) on the ITO electrode with In:Sn=19:1. The quantity of electrochemically active Hb molecules was estimated from the oxidation current of the CV curve. The estimated value of 9.1 pmol in this study corresponds well with the theoretical monolayer deposition of 8.3 pmol, assuming one Hb molecule occupies 20 nm2 [3]. On the other hand, it was found that remarkably large redox current was observed for the ITO electrode with In:Sn=1:1, 222.3 pmol of Hb was estimated to be electrochemically active. It indicates that the electrochemically active species were not only Hb molecules in monolayer deposition on the ITO electrode but also included adsorbed multilayer Hb molecules, suggesting the charge transfer through several Hb molecules in multilayer deposition. Hb molecules exhibited oxygen reduction reaction (ORR) activity on all ITO electrodes with different metal molar ratio. The ITO with In:Sn=1:1 showed the highest ORR activity. These results prove that the Hb-ITO system can be used as the BFC cathode. These findings are great advantages for practical use of the Hb-ITO system, in particular for body implantable power supplies, as the BFC ITO cathode may be inserted into blood vessels.

References

[1] Y. Ayato, K. Sakurai, S. Fukunaga, T. Suganuma, K. Yamagiwa, H. Shiroishi, J. Kuwano, Biosens Bioelectron, 55 (2014) 14.

[2] Y. Ayato, N. Matsuda, Energies, 7(1) (2014) 1.

[3] M. Revenga-Parra, E. Lorenzo, F. Pariente, Sens. Actuat. B, 107 (2005) 678.
Selective Electrochemical Sensing of Human Albumin By Semi-Covalent Imprinting
Authors: Cieplak Maciej , Szwabinska Katarzyna , KC Chandra , Borowicz Pawel , Noworyta Krzysztof R. , D'Souza Francis , Kutner Wlodzimierz
Published: February 2020

We devised and fabricated a conducting molecularly imprinted polymer (MIP) for human albumin (HA) determination using semi-covalent imprinting (Scheme 1).  The bis(2,2’-bithien-5-yl)methane units constituted the MIP backbone.  This MIP was deposited as a thin film on an Au disk electrode by oxidative potentiodynamic electropolymerization.  The HA template imprinting, and then its releasing from the MIP was confirmed by the XPS and PM-IRRAS measurements as well as by AFM imaging.  The DPV and EIS response to the HA presence in a test solution of the MIP film coated electrode was linear in the range of 0.8 to 20 and 4 to 80 µg/mL HA, respectively, with the limit of detection of 16.6 ng/mL and 0.8 µg/mL HA, respectively.  The semi-covalent imprinting provided a very well defined location of recognition functionalities in the MIP molecular cavities.  Those were placed only on surface of the imprinted molecular cavities and the polymer surface.  The MIP selectivity against low-molecular interferences, common for body fluids, such as blood and urea, was very high.  It showed no response to their presence at concentrations encountered in natural samples. Moreover, selectivity of the MIP film coated electrode with respect to macromolecular interferences, such as myoglobin and cytochrome c, was excellent while to lysozyme was slightly lower but still high.

Figure 1
Nanomaterial-Based Sensitive Detection for Live Cell Dynamics of Compartmentalized Metabolic Processes
Authors: Horoszko Christopher Peter , Budhathoki-Uprety Januka , Heller Daniel A
Published: February 2020

Single-walled carbon nanotubes are promising as biomedical research tools due to their uniquely photostable near-infrared photoluminescence. Complex changes that occur in biological microenvironments should be suitable for interrogation based upon nanotube emission changes. Such changes may be resolved through the use of pharmacological and cell biological techniques to isolate relevant nanotube responses associated with particular biological phenomena. We have designed new chemical functionality into nanomaterials to impart sensitivity towards metabolic flux. Environmentally-controlled in vitro photoluminescence was used to test nanomaterials in conditions that closely mimic conditions found in the cell. We found that these tests were able to afford accurate prediction of the nanomaterial photoluminescence in live cells. In vitro control experiments were closely followed by in-cell measurement during pharmacologic assessment. When the latter method was performed iteratively, we were able to de-convolute the natural background response of nanomaterials in complex cellular systems from biologically relevant and detectable changes. We found that this experimental paradigm was useful to evolve the design of nanomaterials into consistently better detection platforms. With the ability to modulate various characteristics of the nanomaterials, environment-specific responses and location are controllable. These experimental findings are important for future work that aims to measure discreet and temporally distinct biological processes during normal and abnormal cell physiology. The sensors will be used to elucidate mechanisms of drug efficacy and cellular homeostasis.