Investigation of mediated oxidation of ascorbic acid by ferrocenemethanol using large-amplitude fourier transformed ac voltammetry under quasi-reversible electron-transfer conditions at an indium tin oxide electrode

The ability of the technique of large-amplitude Fourier transformed (FT) ac voltammetry to facilitate the quantitative evaluation of electrode processes involving electron transfer and catalytically coupled chemical reactions has been evaluated. Predictions derived on the basis of detailed simulations imply that the rate of electron transfer is crucial, as confirmed by studies on the ferrocenemethanol (FcMeOH)-mediated electrocatalytic oxidation of ascorbic acid. Thus, at glassy carbon, gold, and boron-doped diamond electrodes, the introduction of the coupled electrocatalytic reaction, while producing significantly enhanced dc currents, does not affect the ac harmonics. This outcome is as expected if the FcMeOH (0/+) process remains fully reversible in the presence of ascorbic acid. In contrast, the ac harmonic components available from FT-ac voltammetry are predicted to be highly sensitive to the homogeneous kinetics when an electrocatalytic reaction is coupled to a quasi-reversible electron-transfer process. The required quasi-reversible scenario is available at an indium tin oxide electrode. Consequently, reversible potential, heterogeneous charge-transfer rate constant, and charge-transfer coefficient values of 0.19 V vs Ag/AgCl, 0.006 cm s (-1) and 0.55, respectively, along with a second-order homogeneous chemical rate constant of 2500 M (-1) s (-1) for the rate-determining step in the catalytic reaction were determined by comparison of simulated responses and experimental voltammograms derived from the dc and first to fourth ac harmonic components generated at an indium tin oxide electrode. The theoretical concepts derived for large-amplitude FT ac voltammetry are believed to be applicable to a wide range of important solution-based mediated electrocatalytic reactions.

The active site behaviour of electrochemically synthesised gold nanomaterials

Even though gold is the noblest of metals, a weak chemisorber and is regarded as being quite inert, it demonstrates significant electrocatalytic activity in its nanostructured form. It is demonstrated here that nanostructured and even evaporated thin films of gold are covered with active sites which are responsible for such activity. The identification of these sites is demonstrated with conventional electrochemical techniques such as cyclic voltammetry as well as a large amplitude Fourier transformed alternating current (FT-ac) method under acidic and alkaline conditions. The latter technique is beneficial in determining if an electrode process is either Faradaic or capacitive in nature. The observed behaviour is analogous to that observed for activated gold electrodes whose surfaces have been severely disrupted by cathodic polarisation in the hydrogen evolution region. It is shown that significant electrochemical oxidation responses occur at discrete potential values well below that for the formation of the compact monolayer oxide of bulk gold and are attributed to the facile oxidation of surface active sites. Several electrocatalytic reactions are explored in which the onset potential is determined by the presence of such sites on the surface. Significantly, the facile oxidation of active sites is used to drive the electroless deposition of metals such as platinum, palladium and silver from their aqueous salts on the surface of gold nanostructures. The resultant surface decoration of gold with secondary metal nanoparticles not only indicates regions on the surface which are rich in active sites but also provides a method to form interesting bimetallic surfaces.

Large amplitude Fourier transformed AC voltammetric investigation of the active state electrochemistry of a copper/aqueous base interface and implications for electrocatalysis

The higher harmonic components available from large-amplitude Fourier-transformed alternating current (FT-ac) voltammetry enable the surface active state of a copper electrode in basic media to be probed in much more detail than possible with previously used dc methods. In particular, the absence of capacitance background current allows low-level Faradaic current contributions of fast electron-transfer processes to be detected; these are usually completely undetectable under conditions of dc cyclic voltammetry. Under high harmonic FT-ac voltammetric conditions, copper electrodes exhibit well-defined and reversible premonolayer oxidation responses at potentials within the double layer region in basic 1.0 M NaOH media. This process is attributed to oxidation of copper adatoms (Cu*) of low bulk metal lattice coordination numbers to surface-bonded, reactive hydrated oxide species. Of further interest is the observation that cathodic polarization in 1.0 M NaOH significantly enhances the current detected in each of the fundamental to sixth FT-ac harmonic components in the Cu*/Cu hydrous oxide electron-transfer process which enables the underlying electron transfer processes in the higher harmonics to be studied under conditions where the dc capacitance response is suppressed; the results support the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. The underlying quasi-reversible interfacial Cu*/Cu hydrous oxide process present under these conditions is shown to mediate the reduction of nitrate at a copper electrode, while the mediator for the hydrazine oxidation reaction appears to involve a different mediator or active state redox couple. Use of FT-ac voltammetry offers prospects for new insights into the nature of active sites and electrocatalysis at the electrode/solution interface of Group 11 metals in aqueous media.

Liquid metal marbles

Liquid metal marbles that are droplets of liquid metal encapsulated by micro- or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO3, TiO2, MoO3, In2O3 and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics.

Study of the initial stage of solid electrolyte interphase formation upon chemical reaction of lithium metal and N-Methyl-N-Propyl-Pyrrolidinium-Bis (Fluorosulfonyl) Imide

Chemical reaction studies of N-methyl-N-propyl-pyrrolidinium-bis(fluorosulfonyl)imide-based ionic liquid with the lithium metal surface were performed using ab initio molecular dynamics (aMD) simulations and X-ray Photoelectron Spectroscopy (XPS). The molecular dynamics simulations showed rapid and spontaneous decomposition of the ionic liquid anion, with subsequent formation of long-lived species such as lithium fluoride. The simulations also revealed the cation to retain its structure by generally moving away from the lithium surface. The XPS experiments showed evidence of decomposition of the anion, consistent with the aMD simulations and also of cation decomposition and it is envisaged that this is due to the longer time scale for the XPS experiment compared to the time scale of the aMD simulation. Overall experimental results confirm the majority of species suggested by the simulation. The rapid chemical decomposition of the ionic liquid was shown to form a solid electrolyte interphase composed of the breakdown products of the ionic liquid components in the absence of an applied voltage.

Extensive charge-discharge cycling of lithium metal electrodes achieved using ionic liquid electrolytes

The effect of extended cycling on lithium metal electrodes has been investigated in an ionic liquid electrolyte. Cycling studies were conducted on lithium metal electrodes in a symmetrical Li|electrolyte|Li coin cell configuration for 5000 charge–discharge cycles at a current density of 0.1 mA cm− 2. The voltage–time plots show evidence of some unstable behavior which is attributed to surface reorganization. No evidence for lithium dendrite induced short circuiting was observed. SEM imaging showed morphology changes had occurred but no evidence of needle-like dendrite based growth was found after 5000 charge–discharge cycles. This study suggests that ionic liquid electrolytes can enable next generation battery technologies such as rechargeable lithium-air, in which a safe, reversible lithium electrode is a crucial component.

Aqueous phase synthesis of copper nanoparticles : a link between heavy metal resistance and nanoparticle synthesis ability in bacterial systems

We demonstrate aqueous phase biosynthesis of phase-pure metallic copper nanoparticles (CuNPs) using a silver resistant bacterium Morganella morganii. This is particularly important considering that there has been no report that demonstrates biosynthesis and stabilization of pure copper nanoparticles in the aqueous phase. Electrochemical analysis of bacterial cells exposed to Cu2+ ions provides new insights into the mechanistic aspect of Cu2+ ion reduction within the bacterial cell and indicates a strong link between the silver and copper resistance machinery of bacteria in the context of metal ion reduction. The outcomes of this study take us a step closer towards designing rational strategies for biosynthesis of different metal nanoparticles using microorganisms.

Effect of Imidazolium-based Ionic Liquids on the nanoscale morphology of CuTCNQ (TCNQ= 7, 7, 8, 8-tetracyanoquinodimethane) metal-organic semiconductors

We demonstrate for the first time the ionic-liquid-mediated synthesis of nanostructured CuTCNQ by the simple immersion of copper in a solution of TCNQ where the viscosity of the medium significantly impacts the corrosion–crystallization process and the final morphology of the material.

Reusable surface confined semi-conducting metal-TCNQ and metal-TCNQF4 catalysts for electron transfer reactions

The synthesis of organic semiconducting materials based on silver and copper-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) and their fluorinated analogues has received a significant amount of attention due to their potential use in organic electronic applications. However, there is a scarcity in the identification of different applications for which these interesting materials may be suitable candidates. In this work, we address this by investigating the catalytic properties of such materials for the electron transfer reaction between ferricyanide and thiosulphate ions in aqueous solution, which to date has been almost solely limited to metallic nanomaterials. Significantly it was found that all the materials investigated, namely CuTCNQ, AgTCNQ, CuTCNQF4 and AgTCNQF4, were catalytically active and, interestingly, the fluorinated analogues were superior. AgTCNQF4 demonstrated the highest activity and was tested for its stability and re-usability for up to 50 cycles without degradation in performance. The catalytic reaction was monitored via UV-vis spectroscopy and open circuit potential versus time measurements, as well as an investigation of the transport properties of the films via electrochemical impedance spectroscopy. It is suggested that morphology and bulk conductivity are not the limiting factors, but rather the balance between the accumulated surface charge from electron injection via thiosulphate ions on the catalyst surface and transfer to the ferricyanide ions which controls the reaction rate. The facile fabrication of re-usable surface confined organic materials that are catalytically active may have important uses for many more electron transfer reactions.

Electrochemically induced actuation of liquid metal marbles

Controlled actuation of soft objects with functional surfaces in aqueous environments presents opportunities for liquid phase electronics, novel assembled super-structures and unusual mechanical properties. We show the extraordinary electrochemically induced actuation of liquid metal droplets coated with nanoparticles, so-called “liquid metal marbles”. We demonstrate that nanoparticle coatings of these marbles offer an extra dimension for affecting the bipolar electrochemically induced actuation. The nanoparticles can readily migrate along the surface of liquid metals, upon the application of electric fields, altering the capacitive behaviour and surface tension in a highly asymmetric fashion. Surprising actuation behaviours are observed illustrating that nanoparticle coatings can have a strong effect on the movement of these marbles. This significant novel phenomenon, combined with unique properties of liquid metal marbles, represents an exciting platform for enabling diverse applications that cannot be achieved using rigid metal beads.

Probing the effect of charge transfer enhancement in off resonance mode SERS via conjugation of the probe dye between silver nanoparticles and metal substrates

The charge transfer-mediated surface enhanced Raman scattering (SERS) of crystal violet (CV) molecules that were chemically conjugated between partially polarized silver nanoparticles and optically smooth gold and silver substrates has been studied under off-resonant conditions. Tyrosine molecules were used as a reducing agent to convert silver ions into silver nanoparticles where oxidised tyrosine caps the silver nanoparticle surface with its semiquinone group. This binding through the quinone group facilitates charge transfer and results in partially oxidised silver. This establishes a chemical link between the silver nanoparticles and the CV molecules, where the positively charged central carbon of CV molecules can bind to the terminal carboxylate anion of the oxidised tyrosine molecules. After drop casting Ag nanoparticles bound with CV molecules it was found that the free terminal amine groups tend to bind with the underlying substrates. Significantly, only those CV molecules that were chemically conjugated between the partially polarised silver nanoparticles and the underlying gold or silver substrates were found to show SERS under off-resonant conditions. The importance of partial charge transfer at the nanoparticle/capping agent interface and the resultant conjugation of CV molecules to off resonant SERS effects was confirmed by using gold nanoparticles prepared in a similar manner. In this case the capping agent binds to the nanoparticle through the amine group which does not facilitate charge transfer from the gold nanoparticle and under these conditions SERS enhancement in the sandwich configuration was not observed.

Fabrication of metal-nanoparticle-modified semiconducting copper--and silver--TCNQ materials as substrates for the reduction of chromium (VI) using thiosulfate ions at ambient temperature

The formation of readily recoverable and reusable organic semiconducting Cu- and AgTCNQ (TCNQ=7,7,8,8-tetracyanoquinodimethane) microstructures decorated with Pt and Pd metallic nanoparticles is described for the effective reduction of CrVI ions in aqueous solution at room temperature using both formic acid and an environmentally friendly thiosulfate reductant. The M-TCNQ (M=metal) materials were formed by electrocrystallisation onto a glassy carbon surface followed by galvanic replacement in the presence of H2PtCl6 or PdCl2 to form the composite material. It was found that loading of the surface with nanoparticles could easily be controlled by changing the metal salt concentration. Significantly, the M-TCNQ substrates facilitated the formation of well-isolated metal nanoparticles on their surfaces under appropriate galvanic replacement conditions. The semiconductor–metal nanoparticle combination was also found to be critical to the catalyst performance, wherein the best-performing material was CuTCNQ modified by well-isolated Pt nanoparticles with both formic acid and thiosulfate ions as the reductant.

Improved adhesion of active electrode materials to metal electrode substrates

A battery electrode for a lithium ion battery comprising an elec. conductive substrate having an electrode layer applied thereto, characterized in that the electrode layer includes an org. material having high alky., or an org. material which can be dissolved in org. solvents, or an org. material having an imide group(s) and aminoacetal group(s), or an org. material that chelates with or bonds with a metal substrate or that chelates with or bonds with an active material in the electrode layer. The org. material may be guanidine carbonate. [on SciFinder(R)]

Removing organic impurities from bayer process liquors

A process for treating a Bayer liquor by wet oxidn. to oxidize org. contaminants in the Bayer liquor in which the wet oxidn. process is conducted in the presence of a mixed Ce/Mn oxide. The catalyst may have nano-sized grains, and be supported on a mesoporous oxide support. The catalyst may also contain a platinum group metal. [on SciFinder(R)]

Production of fine-grained particles

A method of producing particles having nano-sized grains comprises the steps of: (a) prepg. a soln. contg. one or more metal cations; (b) mixing the soln. from step (a) with one or more surfactants to form a surfactant/liq. mixt. and (c) heating the mixt. from step (b) above to form the particles. [on SciFinder(R)]