Noble Metal Electrodes Research Articles

Dithiocarbamate Self-Assembled Monolayers as Efficient Surface Modifiers for Low Work Function Noble Metals.

Tuning the work function of the electrode is one of the crucial steps to improve charge extraction in organic electronic devices. Here, we show that N,N-dialkyl dithiocarbamates (DTC) can be effectively employed to produce low work function noble metal electrodes. Work functions between 3.1 and 3.5 eV are observed for all metals investigated (Cu, Ag, and Au). Ultraviolet photoemission spectroscopy (UPS) reveals a maximum decrease in work function by 2.1 eV as compared to the bare metal surface. Electronic structure calculations elucidate how the complex interplay between intrinsic dipoles and dipoles induced by bond formation generates such large work function shifts. Subsequently, we quantify the improvement in contact resistance of organic thin film transistor devices with DTC coated source and drain electrodes. These findings demonstrate that DTC molecules can be employed as universal surface modifiers to produce stable electrodes for electron injection in high performance hybrid organic optoelectronics.

Nanoscale Electrochemistry of sp2 Carbon Materials: From Graphite and Graphene to Carbon Nanotubes

Carbon materials have a long history of use as electrodes in electrochemistry, from (bio)electroanalysis to applications in energy technologies, such as batteries and fuel cells. With the advent of new forms of nanocarbon, particularly, carbon nanotubes and graphene, carbon electrode materials have taken on even greater significance for electrochemical studies, both in their own right and as components and supports in an array of functional composites. With the increasing prominence of carbon nanomaterials in electrochemistry comes a need to critically evaluate the experimental framework from which a microscopic understanding of electrochemical processes is best developed. This Account advocates the use of emerging electrochemical imaging techniques and confined electrochemical cell formats that have considerable potential to reveal major new perspectives on the intrinsic electrochemical activity of carbon materials, with unprecedented detail and spatial resolution. These techniques allow particular features on a surface to be targeted and models of structure-activity to be developed and tested on a wide range of length scales and time scales. When high resolution electrochemical imaging data are combined with information from other microscopy and spectroscopy techniques applied to the same area of an electrode surface, in a correlative-electrochemical microscopy approach, highly resolved and unambiguous pictures of electrode activity are revealed that provide new views of the electrochemical properties of carbon materials. With a focus on major sp(2) carbon materials, graphite, graphene, and single walled carbon nanotubes (SWNTs), this Account summarizes recent advances that have changed understanding of interfacial electrochemistry at carbon electrodes including: (i) Unequivocal evidence for the high activity of the basal surface of highly oriented pyrolytic graphite (HOPG), which is at least as active as noble metal electrodes (e.g., platinum) for outer-sphere redox processes. (ii) Demonstration of the high activity of basal plane HOPG toward other reactions, with no requirement for catalysis by step edges or defects, as exemplified by studies of proton-coupled electron transfer, redox transformations of adsorbed molecules, surface functionalization via diazonium electrochemistry, and metal electrodeposition. (iii) Rationalization of the complex interplay of different factors that determine electrochemistry at graphene, including the source (mechanical exfoliation from graphite vs chemical vapor deposition), number of graphene layers, edges, electronic structure, redox couple, and electrode history effects. (iv) New methodologies that allow nanoscale electrochemistry of 1D materials (SWNTs) to be related to their electronic characteristics (metallic vs semiconductor SWNTs), size, and quality, with high resolution imaging revealing the high activity of SWNT sidewalls and the importance of defects for some electrocatalytic reactions (e.g., the oxygen reduction reaction). The experimental approaches highlighted for carbon electrodes are generally applicable to other electrode materials and set a new framework and course for the study of electrochemical and interfacial processes.

Monolayer borophene electrode for effective elimination of both the Schottky barrier and strong electric field effect

The formation of Schottky barriers between 2D semiconductors and traditional metallic electrodes has greatly limited the application of 2D semiconductors in nanoelectronic and optoelectronic devices. In this study, metallic borophene was used as a substitute for the traditional noble metal electrode to contact with the 2D semiconductor. Theoretical calculations demonstrated that no Schottky barrier exists in the borophene/2D semiconductor heterostructure. The contact remains ohmic even with a strong electric field applied. This finding provides a way to construct 2D electronic devices and sensors with greatly enhanced performance.

Continuous On-Chip Cell Separation Based on Conductivity-Induced Dielectrophoresis with 3D Self-Assembled Ionic Liquid Electrodes.

Dielectrophoresis (DEP) has been widely explored to separate cells for various applications. However, existing DEP devices are limited by the high cost associated with the use of noble metal electrodes, the need of high-voltage electric field, and/or discontinuous separation (particularly for devices without metal electrodes). We developed a DEP device with liquid electrodes, which can be used to continuously separate different types of cells or particles based on positive DEP. The device is made of polydimethylsiloxane (PDMS), and ionic liquid is used to form the liquid electrodes, which has the advantages of low cost and easy fabrication. Moreover, the conductivity gradient is utilized to achieve the DEP-based on-chip cell separation. The device was used to separate polystyrene microbeads and PC-3 human prostate cancer cells with 94.7 and 1.2% of the cells and microbeads being deflected, respectively. This device is also capable of separating live and dead PC-3 cancer cells with 89.8 and 13.2% of the live and dead cells being deflected, respectively. Moreover, MDA-MB-231 human breast cancer cells could be separated from human adipose-derived stem cells (ADSCs) using this device with high purity (81.8 and 82.5% for the ADSCs and MDA-MB-231 cells, respectively). Our data suggest the great potential of cell separation based on conductivity-induced DEP using affordable microfluidic devices with easy operation.

Long-term deconditioning of gas-filled surge arresters

ABSTRACTThe aim of this paper is to identify parameters that influence the long-term deconditioning effect of gas-filled surge arrester (GFSA) and to provide practical recommendations for mitigating this effect. Namely, after some period of time, on order of hours or days, during which there is no activation due to overvoltage, the deconditioning of GFSA occurs. This effect was observed experimentally within the paper. The observed parameters that could influence the long-term deconditioning effect were the following: shape of voltage load, gas type, gas pressure, interelectrode distance, electrode material, electrode surface topography as well as GFSA design such as two- or three-electrode configuration. According to the results obtained, it has been shown that the occurrence of long-term deconditioning in an insulating system, insulated by a noble gas at a subpressure and with small interelectrode distances, is a phenomenon that always occurs when the insulating system is at rest for about an hour. It has been found that the type of noble gas does not influence the long-term deconditioning. Analysis of such insulating systems' parameters, with a prospect of being used as GFSAs, has demonstrated that this phenomenon is less pronounced at higher pressures (for the same value of the pressure (p) and interelectrode distance (d) product) and for electrodes with microscopically embossed surfaces. According to the results that were obtained by noble gases and their mixtures, as well as the results that were obtained by mixtures of SF6 gas with noble gasses, it can be claimed with confidence that the effect of the long-term deconditioning is an electrode effect. It has also been established that the deconditioning effect does not depend on the electrode material except in the case of electrodes made out of noble metals, which reduce the effect. Based on these results, it can be recommended that the working point of GFSAs be set (according to the DC breakdown voltage value) at a pressure that is as high as possible (with pd = const), and that the electrode active surface should have a marked microscopic topography. In addition to this, an essential conclusion for GFSA manufacturers is that long-term system deconditioning is caused by impurities and adsorbed gases that appear at electrode during the state of rest. Out of these two causes, the influence of impurities is probably the dominant one, which is proved by considerably reduced long-term deconditioning in the case of noble metal electrodes, not susceptible to corrosion. This has also been confirmed by a less distinct effect of long-term deconditioning in the case of sandblasted electrodes that have a stronger tendency towards gas adsorption and a weaker tendency towards corrosion. However, it has been shown that adding of the third electrode (that is concentric to the main electrode system) on a free floating potential along with usage of sandblasted electrodes and with smaller interelectrode distance significantly reduces the effects of the long-term deconditioning.

Manganese-titanium-oxide-hydroxide-supported palladium nanostructures – A facile electrocatalysts for the methanol, ethylene glycol and xylitol electrooxidation

The formation of organic poisoning intermediate species during fuel (alcohol) oxidation over a noble-metal catalyst electrode retards the electrooxidation reaction. To address this problem, we report the synthesis of a manganese-titanium-oxide-hydroxide-supported palladium nanocatalyst (Pd@MTOH), whereby a hydrothermal reaction is followed by an in situ reduction process. The physical characterizations confirm the formation of Pd NPs and a mixed-valance MTOH. The voltammetric-study results for the Pd@MTOH show a high level of electrochemical activity toward alcohol (methanol, ethylene glycol, and xylitol), and oxidation toward the Pd@MnOOH and Pd@C electrodes. At the Pd@MTOH electrode, the poisonous intermediate species that were formed during alcohol electrooxidation were successfully removed at a higher forward potential; the excellent catalytic activity, better intermediate tolerance, and sound long-term stability of the Pd@MTOH electrode can be credited to the uniform dispersion of the Pd NPs and the support (MTOH). This work outlines a facile method for the fabrication of a catalyst with a high electrochemical performance and great potential in alcohol fuel-cell applications.

Observing Oxygen Vacancy Driven Electroforming in Pt-TiO2-Pt Device via Strong Metal Support Interaction.

Oxygen vacancy formation, migration, and subsequent agglomeration into conductive filaments in transition metal oxides under applied electric field is widely believed to be responsible for electroforming in resistive memory devices, although direct evidence of such a pathway is lacking. Here, by utilizing strong metal-support interaction (SMSI) between Pt and TiO2, we observe via transmission electron microscopy the electroforming event in lateral Pt/TiO2/Pt devices where the atomic Pt from the electrode itself acts as a tracer for the propagating oxygen vacancy front. SMSI, which originates from the d-orbital overlap between Pt atom and the reduced cation of the insulating oxide in the vicinity of oxygen vacancies, was optimized by fabricating nanoscale devices causing Pt atom migration tracking the moving oxygen vacancy front from the anode to cathode during electroforming. Experiments performed in different oxidizing and reducing conditions, which tune SMSI in the Pt-TiO2 system, further confirmed the role of oxygen vacancies during electroforming. These observations also demonstrate that the noble metal electrode may not be as inert as previously assumed.

Revisiting the oxidation peak in the cathodic scan of the cyclic voltammogram of alcohol oxidation on noble metal electrodes

The origin of the oxidation peak in the cathodic scan of alcohol oxidation is elucidated with suggestion of new performance indicators.

Durable electromechanical actuator based on graphene oxide with in situ reduced graphene oxide electrodes

Conventional ionic polymer–metal composite actuator had two major drawbacks: (i) complicated and time-consuming fabrication of noble metal electrode and (ii) degradation of electromechanical property in open air. In this study, we proposed a facile method to fabricate graphene oxide (GO)-based electromechanical actuators with surface-reduced graphene oxide (rGO) as its electrodes. Such GO actuators were fabricated by evaporating the aqueous dispersion of exfoliated GO nanosheets, followed with in situ reduction of the surface of the GO nanosheets by hydrogen iodide (HI). When subjected to a 3 V electrical field, the GO actuator performed electromechanical bending action with a tip displacement of 5 mm and exhibited a blocking force of 10 gf g−1 for 10 s. In addition, the GO actuator showed an almost identical actuating behavior in cyclic measurements. The durable actuation could be attributed to both the unique lamellar structure of the GO film which blocked the diffusion of cationic clusters and the surface rGO electrodes which protected the interlamellar water from evaporation.

Conduction barrier offset engineering for DRAM capacitor scaling

DRAM capacitors are reaching the scaling limit and new approaches are necessary to enable further reduction of the physical thickness of the capacitor dielectric. The conduction band offset (CBO) of a platinum noble metal electrode on atomic layer deposited ZrO2/Al2O3/ZrO2 is evaluated and compared to a titanium nitride electrode. Internal Photo Emission Spectroscopy and Photoconductivity measurement are used to estimate the barrier height and band gap, respectively. The barrier height difference between the two electrodes is evaluated in comparison with a previously reported model. Finally, the impact of an increased barrier height on dielectric scaling will be discussed based on a leakage current simulation of a ZrO2 capacitor.

IrxRu1-XO2 Electrocatalysts for PEM Water Electrolysis

A potential method for storing energy from renewable energy sources into hydrogen is water electrolysis [1]. Direct electrochemical splitting of water is a non-polluting way to produce pure hydrogen and oxygen. Proton Exchange Membrane Electrolysis Systems have attracted great interest as a hydrogen production method. The combination of water electrolysers and fuel cells in coupled with renewable sources could provide an ideal green and efficient mode for future energy utilization systems. PEM water electrolysers offer various advantages [2] but the major disadvantage is the relatively high anodic overpotential for the oxygen evolution reaction (OER). Oxygen evolution occurs on noble metal electrodes but metal oxides like IrO2, RuO2, etc. are generally more active for oxygen evolution than metal electrodes [3]. However, issues like electrocatalyst stability and reduction of the catalyst loading are of great and continuous research interest. In this work, unsupported IrxRu1-xO2electrocatalysts, synthesized by the modified Adams fusion method, were evaluated as potential electrodes for water splitting. Complete physicochemical characterisation of the synthesised materials was performed regarding their structure, morphology, specific surface area as well as surface composition using X-ray Diffraction (XRD), BET analysis, High Resolution Transmission Electron Microscopy (HTTEM) and X-ray Photoelectron Spectroscopy (XPS). The electrochemical performance and stability of the prepared electrocatalysts, casted on glassy carbon (GC), were evaluated with repetitive cyclic voltammetry in a typical three-cell electrode configuration using 0.5 M H2SO4solution. Furthermore, the mixed oxides have been used as anodes in Nafion® based MEAs and evaluated in a PEM electrolysis cell. The results have shown that the synthesis method leads to the formation of rutile structure oxides with high surface area (90-127 m2/g) and nano-level particle size (5-7 nm). The stability of the mixed oxides during potentiostatic cycling has been proven remarkable, while the best performing MEA with an anode of Ir0.4Ru0.6O2 reached a current density of 320 mA/cm2at 1.7 V. The work is supported by the European Space Agency (ESA).

Real Time Monitoring of Electrostatic Potentials in the Vicinity of Electrodes Delivering Current Pulses Used in Neural Stimulation

Neural stimulation by metal electrodes such as Pt and its alloys and W has been used previously to evoke electrical activity in neurons1. This process involves passing short extracellular current pulses (ca. 100 µs) aimed at modifying the extracellular potential (Vext) and thereby altering the cell membrane potential. However, direct experimental measurements of Vext during such stimuli have been lacking. Theory suggests that Vext depends on both space and time. We have developed a method (ohmic microscopy) to measure Vext quantitatively with both spatial and temporal resolution, while passing current across noble metal electrodes during voltammetric scans.2-4 The present work extends application of this technique to current stimulus protocols commonly used in neural stimulation, including functional neural stimulation in clinical settings. EXPERIMENTAL Thin wall glass capillaries were pulled to a diameter of ca. 10 µm for each barrel, and filled with an aqueous 0.1 M H2SO4 solution. Microreference (μ-ref) Ag/AgCl electrodes were made by inserting Ag wires coated with a layer of AgCl (0.125 mm in diameter) formed by dipping the wire in a saturated KCl aqueous solution for at least 12 h. The μ-ref Ag/AgCl electrodes were mounted on individual holders connected in turn to individual micromanipulators. Pt disk (diameter 1.6mm) as working electrode, Pt wire as counter electrode, and Ag/AgCl(saturated) as reference electrode, 0.1M H2SO4 with their tips aligned along the normal to the center of the Pt disk (see Fig 1) at prescribed heights. A current pulse of a few mA was then applied to the Pt disk using a function generator (Agilent 33220A) coupled to a potentiostat (Autolab, PGSTAT302N, Nova 1.10, Metrohm). The time response of the potential difference between the two μ-ref electrodes, denoted as, Δφsol, amplified 10 times (Ina141, Texas instrument), was recorded on an oscilloscope (Agilent DSO-X 2014A). A schematic diagram of the instrument setup is shown is Fig. 1. RESULTS AND DISCUSSION For these experiments a current pulse of 5 mA, 100 μs in duration was applied across the Pt disk electrode (see red curve in Fig. 2), while recording the potential difference, Dϕ, across the two μ-ref Ag/AgCl electrodes placed at 1 mm, and 2mm normal to the disk along its center line (see blue curve, Fig. 2). As indicate therein, during the passage of current Dϕ was found to be ca. 62.5 mV. This value compares very well, i.e. slightly over 2%, with that predicted by Newman5, i.e. 61.2 mV. Excellent agreement was also found for other current values, duty cycles, and placement of the μ-ref Ag/AgCl electrodes. Efforts are underway to measure the response of dissociated neurons as a function of the placement of the electrodes and the stimulation parameters. ACKNOWLEDGEMENTS This work was supported by a Grant from NSF. REFERENCE D. R. Merrill, M. Bikson, J. G. R. Jefferys, J . Neurosci. Methods, 141 (2005), 171C. A. Cartier, D. Kumsa, Z. Feng, H. Zhu, D. A. Scherson, Anal. Chem. 84 (2012), 7080Y. Chen , A. Belianinov, D. A. Scherson, J. phy. Chem. C, 112 (2008), 8754M. Ignatowitz, E. Oesterschulze, App. Phy. Lett., 101 (2012), 251601J. Newman, J. Electrochem. Soc., 113 (1966), 501. Figure 1

Selective Patterning on Pyrocarbon Interdigitated Electrodes for Bienzymatic Sensing of Glutamate

Electrochemical detection of electroactive molecules is a quantitative and sensitive methodology to characterize neurotransmitter release. Enzymatic immobilization onto an electrode surface offers a route to indirectly detect non-electroactive neurotransmitters, such as glutamate. However, diffusion away from the electrode surface and biological reuptake of analytes can render electrochemical biosensing of neurotransmitters challenging. Furthermore, detection as close as possible to the transducer element is desirable. Many bienzymatic systems rely on multilayers of enzymes and polymers, which may hinder analyte diffusion and result in slow sensor response times. Rand et al. previously constructed an electrochemical glutamate sensor based on the immobilization of two different enzyme systems to amplify glutamate in solution.1 Here, we describe a bienzymatic system for amplification and in situ electrochemical detection of glutamate within pyrolyzed carbon gapped electrodes spaced in closer proximity than has previously been reported for bienzymatic glutamate sensing. Carbon electrodes offer a wider potential operating window, less susceptibility to biofouling, and more stability in ionic solutions, as compared to noble metal electrodes fabricated from platinum or gold.2 Electrodes were fabricated from pyrolyzed photoresist (PPF), an amorphous pyrocarbon material that enables photolithographic patterning of electrode devices and sensors.3 An interdigitated electrode array (IDEA) geometry, in which two sets of individually-addressable electrode bands 1-3 μm wide and spaced approximately 1-3 μm apart, was adopted (Figure 1). Thus, redox-active species can be electrochemically generated at one band (the generator) and detected at the other band (the collector). Due to the small spacing between adjacent electrode bands, a redox species can be electrolyzed at the collector and diffuse back to the generator several times (redox cycling), which has been shown to amplify the current at both the collector and generator when the electrode is operated in a generator-collector or dual mode.4 , 5 Although redox cycling in typical IDEAs is achieved with oxidation/reduction when operated in dual mode, we chose to devise an analyte cycling strategy based on the re-generation of glutamate via a dual enzyme system that did not rely on electrochemically-driven oxidation/reduction (Figure 2). Firstly, glutamate oxidase (GLUT), which converts L-glutamate into 2-oxoglutarate and hydrogen peroxide, is immobilized onto one of two individually-addressable electrode bands within the PPF IDEA. A second enzyme, glutamate-pyruvate transaminase, which converts 2-oxoglutarate and L-alanine back into glutamate, is immobilized on the other electrode. Due to the small spacing between each type of electrode, cycling of enzymatic products (e.g., glutamate and 2-oxoglutarate) will occur resulting in an enhancement of electrochemically-detectable hydrogen peroxide under a negative bias. One challenge of this sensor design is the patterning and stable attachment of enzymes. Oxidase enzymes are often immobilized onto carbon electrode surfaces via cross-linking in a matrix of glutaraldehyde and bovine serum albumin;6 however, these chemistries do not offer an inherent route to selective patterning of enzymes. Microcontact printing of enzymes attached to polymer stamps can be utilized to achieve selective spatial distribution in a bienzymatic system, but is difficult to implement in an IDEA geometry with small spacing.1 Madou and co-workers have previously reported a method of glucose oxidase and 2,5-dihydroxybenzaldehyde (redox mediator) attachment to 2D millimeter-sized electrodes via electrochemical oxidation of amine linkers.7 We chose to adopt a related approach, by attaching 4-aminobenzoic acid (ABA) via electro-oxidation to the PPF surface and coupling the free carboxylic acid groups of ABA with several amine groups in lysine residues of GLUT with carbodiimide chemistry. In this presentation, we will discuss experimental variables such as electrode width, spacing and height, as these variables been previously shown to play an essential role in PPF IDEA electrode response in terms of collection efficiency and current signal amplification when operated in generator-collector mode. Furthermore, microscopy, surface and electrochemical characterization of ABA-functionalized electrodes will be introduced to illustrate the challenges and merits of this approach to selective bienzymatic patterning.

Combining Noble Metals and Enzymes for Relay Cascade Electrocatalysis of Nitrate Reduction to Ammonia at Neutral pH

AbstractElectrocatalytic reduction of nitrate at noble metals is particularly sluggish at neutral pH, while nitrate reductase enzymes are highly active for selective reduction of nitrate to nitrite under these conditions. However, noble metal electrodes can effectively reduce nitrite, even at millimolar concentrations in neutral media. In this study, we demonstrate tandem electrochemical reduction of nitrate to ammonia by combining Escherichia (E.) coli nitrate reductase (NarGHI) on an electrode with Pt or Rh nanoparticles. Under potential control, the enzyme first reduces nitrate to nitrite, which is further reduced by the metal at a slightly more negative potential. This creates a novel electrocatalytic relay cascade where the enzyme overcomes an inherent limitation of the metal. This proof‐of‐concept study, using biological and metal catalysts supported on commercial carbon beads, demonstrates a simple approach to the assembly of ‘hybrid’ electrocatalysts.

Structure and Dynamics at Ionic Liquid/Electrode Interfaces

Ionic liquids (ILs) are potentially ‘game changing’ electrolytes for energy conversion applications such as capacitors [i] ,[ii] , batteries [iii] ,[iv] , fuel cells [v] ,[vi] , and solar cells. [vii] ,[viii] Significant progress has been made towards utilizing these remarkably adaptable materials for specific applications however, much work remains to generate technologically and economically relevant devices and processes.[ix] Characterizations of interfaces between IL-based electrolyte/electrode systems are crucial to continued development for these enterprises. In specific, detailed descriptions and understanding of structure and dynamics at electrolyte/electrode interfaces are necessary to realize engineered progress because device efficiencies are often largely determined by processes that occur at the interface. [x] ,[xi] Our presentation will focus on initial efforts to employ spectroscopic techniques that characterize interfacial structure and dynamics between ionic liquid media and electrode surfaces during simultaneous electrochemical perturbation. In specific, we will present surface enhanced infrared absorption (SEIRA) spectroscopy data for ILs composed of imidazolium-based cations with bis(trifluoromethylsulfonyl)imide anions at nanostructured noble metal electrodes (i.e, Au). [i]. T. Sato, G. Masuda, K. Takagi, Electrochim. Acta, 2004, 49, 3603-3611. [ii]. A. Orita, K. Kamijima, M. Yoshida, J. Power Sources, 2010, 195, 7471-7479. [iii]. A. S. Best, A. I. Bhatt, A. F. Hollenkamp, J. Electrochem. Soc., 2010, 157, A903-A911. [iv]. J.-K. Kima, A. Matica, J.-H. Ahnb, P. Jacobsson, J. Power Sources, 2010, 195, 7639-7643. [v]. S.-Y. Lee, A. Ogawa, M. Kanno, H. Nakamoto, T. Yasuda, M. Watanabe, J. Am. Chem. Soc., 2010, 132, 9764-9773. [vi]. M. Guo, J. Fang, H. Xu, W. Li, X. Lu, C. Lan, K. Li, J. Membr. Sci., 2010, 362, 97-104. [vii]. P. K. Singh, N. A. Jadhav, S. K. Mishra, U. P. Singh, B. Bhattacharya, Ionics, 2010, 16, 645-648. [viii]. C.-P. Lee, P.-Y. Chen, R. Vittal, K.-C. Ho, J. Mater. Chem., 2010, 20, 2356-2361. [ix]. M. Armand, F. Endres, D. R. MacFarlane, H. Ohno, B. Scrosati, Nature Materials, 2009, 8, 621-629. [x]. A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., 2002, John Wiley & Sons, Inc., New York, NY. [xi]. M. Yoshida, A. Yamakata, K. Takanabe, J. Kubota, M. Osawa, K. Domen, J. Am. Chem. Soc., 2009, 131, 13218-13219.

Multi-frequency bioimpedance in human muscle assessment.

Bioimpedance analysis (BIA) is a well-known and tested method for body mass and muscular health assessment. Multi-frequency BIA (mfBIA) equipment now makes it possible to assess a particular muscle as a whole, as well as looking at a muscle at the fiber level. The aim of this study was to test the hypothesis that mfBIA can be used to assess the anatomical, physiological, and metabolic state of skeletal muscles. mfBIA measurements focusing on impedance, resistance, reactance, phase angle, center frequency, membrane capacitance, and both extracellular and intracellular resistance were carried out. Eight healthy human control subjects and three selected cases were examined to demonstrate the extent to which this method may be used clinically, and in relation to training in sport. The electrode setup is shown to affect the mfBIA parameters recorded. Our recommendation is the use of noble metal electrodes in connection with a conductance paste to accommodate the typical BIA frequencies, and to facilitate accurate impedance and resistance measurements. The use of mfBIA parameters, often in conjunction with each other, can be used to reveal indications of contralateral muscle loss, extracellular fluid differences, contracted state, and cell transport/metabolic activity, which relate to muscle performance. Our findings indicate that mfBIA provides a noninvasive, easily measurable and very precise momentary assessment of skeletal muscles.

In situ synthesis of a NiS/Ni3S2 nanorod composite array on Ni foil as a FTO-free counter electrode for dye-sensitized solar cells.

A NiS/Ni3S2 nanorod composite array that directly grows on Ni foil has been used as a counter electrode for dye-sensitized solar cells; these nickel sulfide nanorods exhibit excellent photo-electrical conversion efficiency when compared with conventional noble-metal Pt electrodes.

Organic dipole layers for ultralow work function electrodes.

The alignment of the electrode Fermi level with the valence or conduction bands of organic semiconductors is a key parameter controlling the efficiency of organic light-emitting diodes, solar cells, and printed circuits. Here, we introduce a class of organic molecules that form highly robust dipole layers, capable of shifting the work function of noble metals (Au and Ag) down to 3.1 eV, that is, ∼1 eV lower than previously reported self-assembled monolayers. The physics behind the considerable interface dipole is elucidated by means of photoemission spectroscopy and density functional theory calculations, and a polymer diode exclusively based on the surface modification of a single electrode in a symmetric, two-terminal Au/poly(3-hexylthiophene)/Au junction is presented. The diode exhibits the remarkable rectification ratio of ∼2·10(3), showing high reproducibility, durability (>3 years), and excellent electrical stability. With this evidence, noble metal electrodes with work function values comparable to that of standard cathode materials used in optoelectronic applications are demonstrated.

Microstructure at the Ionic Liquid/Electrode Interface

In the past decade, ionic liquids (ILs) have been investigated as electrolytes for energy conversion applications such as capacitors [i] ,[ii] , batteries [iii] ,[iv] , fuel cells [v] ,[vi] , and solar cells. [vii] ,[viii] While significant progress has been made towards utilizing these remarkably adaptable materials for specific applications, much work remains to generate technologically and economically relevant devices and processes. Fundamental characterizations of IL-based electrolyte/electrode systems are crucial to continued development for these enterprises. [ix] In specific, detailed descriptions and understanding of electrolyte/electrode interfaces are prerequisites to engineered progress because adsorbed species and their associated interfacial dynamics play critical roles in determining device efficiencies. [x] ,[xi] Our initial studies focus on spectroscopic techniques such as surface enhanced infrared absorption (SEIRA) spectroscopy to characterize interfacial structure and dynamics between ionic liquid media and electrode surfaces during electrochemical perturbation. More specifically, we will discuss characterizations of ILs composed of imidazolium-based cations with alkylsulfate, tetrafluoroborate, thiocyanate, dicyanamide, and bis(trifluoromethylsulfonyl)imide anions at noble metal electrodes (i.e, Au). [i]. T. Sato, G. Masuda, K. Takagi, Electrochim. Acta, 2004, 49, 3603-3611.[ii]. A. Orita, K. Kamijima, M. Yoshida, J. Power Sources, 2010, 195, 7471-7479.[iii]. A. S. Best, A. I. Bhatt, A. F. Hollenkamp, J. Electrochem. Soc., 2010, 157, A903-A911.[iv]. J.-K. Kima, A. Matica, J.-H. Ahnb, P. Jacobsson, J. Power Sources, 2010, 195, 7639-7643.[v]. S.-Y. Lee, A. Ogawa, M. Kanno, H. Nakamoto, T. Yasuda, M. Watanabe, J. Am. Chem. Soc., 2010, 132, 9764-9773.[vi]. M. Guo, J. Fang, H. Xu, W. Li, X. Lu, C. Lan, K. Li, J. Membr. Sci., 2010, 362, 97-104.[vii]. P. K. Singh, N. A. Jadhav, S. K. Mishra, U. P. Singh, B. Bhattacharya, Ionics, 2010, 16, 645-648.[viii]. C.-P. Lee, P.-Y. Chen, R. Vittal, K.-C. Ho, J. Mater. Chem., 2010, 20, 2356-2361.[ix]. C. Aliaga, C. S. Santos, S. Baldelli, Phys. Chem. Chem. Phys., 2007, 9, 3683-3700.[x]. A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., 2002, John Wiley & Sons, Inc., New York, NY.[xi]. M. Yoshida, A. Yamakata, K. Takanabe, J. Kubota, M. Osawa, K. Domen, J. Am. Chem. Soc., 2009, 131, 13218-13219.

Mechanics and electrochemistry of ionic polymer metal composites

Ionic polymer metal composites (IPMCs) are electroactive materials composed of a hydrated ionomeric membrane that is sandwiched between noble metal electrodes. Here, we propose a modeling framework to study quasi-static large deformations and electrochemistry of IPMCs. Specifically, IPMC kinematics is described in terms of its mechanical deformation, the concentration of mobile counterions neutralizing the ionomer, and the electric potential. The chemoelectromechanical constitutive behavior is obtained from a Helmholtz free energy density, which accounts for mechanical stretching, ion mixing, and electric polarization. The three-dimensional framework is specialized to plane bending of thin IPMCs. Hence, we propose a structural model, where the moment and the charge stored along the IPMC are computed from the solution of a modified Poisson–Nernst–Planck system, in terms of the through-the-thickness coordinate. For small static deformations, we present a semianalytical solution based on the method of matched asymptotic expansions, which is ultimately used to study IPMC sensing and actuation. We demonstrate that the linearity of IPMC actuation in a broad voltage range could be attributed to the interplay of two competing nonlinear phenomena, associated with Maxwell stress and osmotic pressure. In agreement with experimental observations, our model confirms the possibility of tailoring IPMC actuation by varying the counterion size and the concentration of fixed ions. Finally, the model is successful in predicting the significantly different voltage levels displayed by IPMC sensors and actuators, which are associated with remarkable variations in the ion mixing and polarization energies.