Conducting polymer enzyme alloys : electromaterials exhibiting direct electron transfer

Glucose oxidase (GOx) is an important enzyme with great potential application for enzymatic sensing of glucose, in implantable biofuel cells for powering of medical devices in vivo and for large-scale biofuel cells for distributed energy generation. For these applications, immobilisation of GOx and direct transfer of electrons from the enzyme to an electrode material is required. This paper describes synthesis of conducting polymer (CP) structures in which GOx has been entrained such that direct electron transfer is possible between GOx and the CP. CP/enzyme composites prepared by other means show no evidence of such “wiring”. These materials therefore show promise for mediator-less electronic connection of GOx into easily produced electrodes for biosensing or biofuel cell applications.

Controllable graphene oxide mediated efficient electron transfer pathways across self-assembly monolayers: a new class of graphene based electrodes

In this paper, the influence of chemically reduced graphene oxide sheets (CRGOs) on the electrochemical performance through methyl or carboxylic acid terminated self-assembled monolayers (SAMs) is reported. The gold electrode was initially modified with methyl or carboxylic acid terminated alkanethiols with various carbon chain lengths (n = 4, 6, 8 and 11) and subsequently immobilization of the CRGOs on a SAM surface was achieved via a hydrophobic and electrostatic interaction. By using the potassium ferricyanide as a redox probe, it was observed that CRGOs could effectively enhance the heterogeneous electron transfer (ET) of the SAM due to a tunneling effect. The assemblies based on thiol end groups with methyl head groups were observed to afford more hydrophobic interaction binding with CRGOs with a higher reduction time than the assemblies developed with thiol end groups and a -COOH group which were shown to bind more electrostatically with CRGOs, a lowering reduction time. The Nyquist plots developed show a gradual decrease of the charge transfer resistance (Rct) of [Fe(CN)6]3-/4- redox couple at the CRGOs-SAMs electrode with the controllable adsorption of different CRGO's onto the SAM. Depending on the chain length and terminal functional group the electron transfer rate kinetics were observed to differ considerably.

Unusual spectroscopic properties of PPE/TiO2 composite and its sensor response to TNT

A composite from a broad bandgap polymer, poly(phenylene ethylene) (PPE), and nano-sized TiO₂ particles was found to be able to sense 2,4,6-trinitrotoluene (TNT) for TNT sensor. Fluorescence quenching induced by charge transfer from PPE to nano-sized TiO₂ was observed in toluene solution. At high TiO₂ composition, a strong exciplex band occurred at 550 nm. Under prolonged light irradiation at 400 nm, unusual fluorescence gains took place at 460 nm, companied with a very small change in the UV–vis absorbance. After 30 min light irradiation, the fluorescence at 460 nm reached a maximum, but the peak at 550 nm disappeared. This composite showed amplified sensor response to TNT compared to the pristine PPE film, which can be potentially used as sensing material for detecting TNT based explosives.

Composite cell components for elevated temperature all-solid-state Li-ion batteries

Application of Li-ion batteries with liquid electrolytes at elevated temperatures (above 60°C) is limited due to the decomposition of the electrolyte. Stable solid state electrolytes can solve this problem, but the conductivity of these electrolytes are relatively low, the interfacial contacts with the electrodes are poor, and the charge transfer kinetics in the electrodes are limited. Solutions for these problems by using composite electrodes and electrolytes have been investigated and the results are described. A new concept for making all-solid-state Li-ion batteries that can be applied in the temperature range between room temperature and about 150°C will be presented.

In situ photopolymerization of a gel ionic liquid electrolyte in the presence of iodine and its use in dye sensitized solar cells

We report for the first time an in situ photopolymerization of model co-monomers, 2-hydroxyethyl methacrylate (HEMA) and tetra (ethylene glycol) diacrylate (TEGDA), in an IL electrolyte containing I₂ for DSSCs. TiO₂ nanoparticles were used as the photo-initiator and co-gelator in a charge transfer polymerization reaction. The gel-IL polymer obtained was characterized in terms of the diffusion properties of the electrolyte. Preliminary results from DSSCs assembled using the gel-IL electrolyte showed energy conversion efficiency of 3.9% at 1 sun (AM1.5) and 5.0% at 0.39 sun illumination.

Surface-Enhanced Infrared Spectra of Manganese (III) Tetraphenylporphine Chloride Physisorbed on Gold Island Films

Surface-enhanced infrared absorption (SEIRA) spectra of manganese (III) tetraphenylporphine chloride (Mn(TPP)Cl) on metal island films were measured in transmission mode. Dependences of the enhancement factor of SEIRA on both the sample quantity and the type of evaporated metal were investigated by subsequently increasing the amount of Mn(TPP)Cl on gold and silver substrates. The enhancement increases nonlinearly with the amount of sample and varies slightly with the thickness of metal islands. In particular, the SEIRA transmission method presents an anomalous spectral enhancement by a factor of 579, with substantial spectral shifts, observed only for the physisorbed Mn(TPP)Cl that remained on a 3-nm-thick gold film after immersion of the substrates into acetone. A charge-transfer (CT) interaction between the porphyrinic Mn and gold islands is therefore proposed as an additional factor in the SEIRA mechanism of the porphyrin system. The number of remaining porphyrin molecules was estimated by calibration-based fluorescence spectroscopy to be 2.36×1013 molecules (i.e., ~2.910-11 mol/cm2) for a 3-nm-thick gold film, suggesting that the physisorbed molecules distributed very loosely on the metal island surface as a result of the weak van der Waals interactions. Fluorescence microscopy revealed the formation of microcrystalline porphyrin aggregates during the consecutive increase in sample solution. However, the immersion likely redistributed the porphyrin to be directly attached on the gold surface, as evidenced by an absence of porphyrinic microcrystals and the observed SEIRA enhancement. The distinctive red shift in the UV-visible spectra and the SEIRA-enhanced peaks indicate the presence of a preferred orientation in the form of the porphyrin ring inclined with respect to the gold surface.

Electrochemiluminescent monomers for solid support syntheses of Ru(II)-PNA bioconjugates : multimodal biosensing tools with enhanced duplex stability

The feasibility of devising a solid support mediated approach to multimodal Ru(II)-peptide nucleic acid (PNA) oligomers is explored. Three Ru(II)-PNA-like monomers, [Ru(bpy)2(Cpp-L-PNA-OH)]2+ (M1), [Ru(phen)2(Cpp-L-PNA-OH)]2+ (M2), and [Ru(dppz)2(Cpp-L-PNA-OH)]2+ (M3) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2′,3′-c]phenazine, Cpp-L-PNA-OH = [2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycine), have been synthesized as building blocks for Ru(II)-PNA oligomers and characterized by IR and 1H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. As a proof of principle, M1 was incorporated on the solid phase within the PNA sequences H-g-c-a-a-t-a-a-a-a-Lys-NH2 (PNA1) and H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-lys-NH2 (PNA4) to give PNA2 (H-g-c-a-a-t-a-a-a-a-M1-lys-NH2) and PNA3 (H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-M1-lys-NH2), respectively. The two Ru(II)-PNA oligomers, PNA2 and PNA3, displayed a metal to ligand charge transfer (MLCT) transition band centered around 445 nm and an emission maximum at about 680 nm following 450 nm excitation in aqueous solutions (10 mM PBS, pH 7.4). The absorption and emission response of the duplexes formed with the cDNA strand (DNA: 5′-T-T-T-T-T-T-T-A-T-T-G-C-T-T-T-3′) showed no major variations, suggesting that the electronic properties of the Ru(II) complexes are largely unaffected by hybridization. The thermal stability of the PNA·DNA duplexes, as evaluated from UV melting experiments, is enhanced compared to the corresponding nonmetalated duplexes. The melting temperature (Tm) was almost 8 °C higher for PNA2·DNA duplex, and 4 °C for PNA3·DNA duplex, with the stabilization attributed to the electrostatic interaction between the cationic residues (Ru(II) unit and positively charged lysine/arginine) and the polyanionic DNA backbone. In presence of tripropylamine (TPA) as co-reactant, PNA2, PNA3, PNA2·DNA and PNA3·DNA displayed strong electrochemiluminescence (ECL) signals even at submicromolar concentrations. Importantly, the combination of spectrochemical, thermal and ECL properties possessed by the Ru(II)-PNA sequences offer an elegant approach for the design of highly sensitive multimodal biosensing tools.

Photoreactive azido-containing silica nanoparticle/polycation multilayers : durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C–H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.

Use of electrochemical impedance spectroscopy for study of CO2 corrosion prevention by batch treatment inhibitor films

Electrochemical impedance spectroscopy (EIS) was used to study and evaluate commercial batch treatment inhibitors which are used for protecting oil wells, gas wells, and pipelines from CO2 corrosion, focusing on the evaluation of inhibitor film persistency. It was found that theformation and deterioration of batch treatment inhibitor films were accompanied by typical impedance spectral changes. During the formation of inhibitor films, electrode impedance showed a rapid increase and the Bode phase angle plots also showed a sudden change. Thus, the formation of inhibitor film was a very fast process. During the deterioration of inhibitor films, electrode impedance showed a gradual decrease and the Bode phase angle plots showed changes which characterised the three stages of the inhibitor film deterioration process. The relationships between EIS and corrosion rate are discussed, including comparisons with weight loss measurements. Based on the experimental findings in the present work, a method is suggested for estimating the persistency of inhibitor films by monitoring the characteristic changes in the Bode phase angle plots and by measuring electrochemical charge transfer resistance at the second and third stages of the inhibitor film deterioration process.

Effect of Ag addition on the corrosion properties of Sn-based solder alloys

Corrosion properties of three different Sn-Ag lead free solder alloys have been investigated in 0.3 wt% Na₂SO₄ solution as corrosive environment. As cast solder alloy was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Volume fractions of the Ag₃Sn in the solders were determined by image analysis technique. Pitting potential and corrosion potential for the alloys were determined by potentiodynamic tests. Electrochemical impedance spectroscopy (EIS) was carried out to measure the film and charge transfer resistance. Alloys with lower Ag content have been found as better corrosion resistance material.

Effect of aluminum on the corrosion resistance of low-alloy steel in 10wt% sulfuric acid solution

The aqueous corrosion behavior of low-alloy steel with aluminum contents was examined in a 10 wt% H₂SO₄ (pH 0.13) solution using electrochemical techniques and surface analyses. The corrosion resistance of the new alloy steel was evaluated in terms of electrochemical parameters, such as passive current density, film, and charge transfer resistances. The results showed that a high Al content in the steel imparted better passivation behavior resulting in a lower corrosion rate. It related to the enrichment of iron carbonate and hydrocarbon by the dissolution of the carbide phase.

Electrochemical behavior of CrN coating for polymer electrolyte membrane fuel cell

CrN films on a bipolar plate in polymer electrolyte membrane fuel cells have several advantages owing to their excellent corrosion resistance and mechanical properties. Three CrN samples deposited at various radio frequency (RF) powers by RF magnetron sputtering were evaluated under potentiodynamic, potentiostatic and electrochemical impedance spectroscopy conditions. The electrochemical impedance spectroscopy data were monitored for 168 h in a corrosive environment at 70 °C to determine the coating performance at +600 mV_SCE under simulated cathodic conditions in a polymer electrolyte membrane fuel cell. The electrochemical behavior of the coatings increased with decreasing RF power. CrN films on the AISI 316 stainless steel substrate showed high protective efficiency and charge transfer resistance, i.e. increasing corrosion resistance with decreasing RF power. X-ray diffraction confirmed the formation of a CrN(200) preferred orientation at low RF power.

Effect of gold on the corrosion behavior of an electroless nickel/immersion gold surface finish

The performance of surface finishes as a function of the pH of the utilized plating solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. In addition, the surface finishes were examined by x-ray diffraction (XRD), and the contact angle of the liquid/solid interface was recorded. NiP films on copper substrates with gold coatings exhibited their highest coating performance at pH 5. This was attributed to the films having the highest protective efficiency and charge transfer resistance, lowest porosity value, and highest contact angle among those examined as a result of the strongly preferred Au(111) orientation and the improved surface wettability.

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38–99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (−0.12 to −0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 × 10⁻⁶ to 7 × 10⁻⁸ S cm⁻¹.

Facile synthesis of NiCo2O4 nanorod arrays on Cu conductive substrates as superior anode materials for high-rate Li-ion batteries

In this work, we report a mild and cost-effective solution method to directly grow Ni-substituted Co3O4 (ternary NiCo2O4) nanorod arrays on Cu substrates. Electrochemical impedance spectroscopy (EIS) measurements show that the values of the electrolyte resistance Re and charge-transfer resistance Rct of NiCo2O4 are 6.8 and 63.5 Ω, respectively, which are significantly lower than those of binary Co3O4 (10.4 and 122.4 Ω). This EIS characterization strongly confirms that the ternary NiCo2O4 anode has much higher electrical conductivity than that of the binary Co3O4 electrode materials, which should greatly enhance the lithium storage performances. Due to the well-aligned 1D nanorod microstructure and a higher electrical conductivity, these ternary NiCo2O4 nanorod arrays manifest high specific capacity, excellent cycling stability (a high reversible capacity of about 830 mA h g−1 was achieved after 30 cycles at 0.5 C) and high rate capability (787, 695, 512, 254, 127 mA h g−1 at 1 C, 2 C, 6 C 50 C and 110 C, respectively).