Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests

Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests.     

Underpotential deposition of copper on electrodes modified with colloidal gold

This communication is concerned with the electrochemical addressability of gold colloidal particles deposited on a conducting substrate. Cyclic voltammetry of electrodes modified with gold colloid layers indicates that an underpotential deposition of copper onto the gold surface takes place. Analysis of the charge associated with the underpotential deposition permits the electroactive gold area to be calculated. The total gold area may be determined from transmission electron microscopy (TEM) images. Comparison of the geometric and electroactive areas obtained indicates that electrochemically all the gold particles are addressable and the entire colloid surface is accessible.     

Graphene as a spacer to layer-by-layer assemble electrochemically functionalized nanostructures for molecular bioelectronic devices

This study demonstrates the capability of graphene as a spacer to form electrochemically functionalized multilayered nanostructures onto electrodes in a controllable manner through layer-by-layer (LBL) chemistry. Methylene green (MG) and positively charged methylimidazolium-functionalized multiwalled carbon nanotubes (MWNTs) were used as examples of electroactive species and electrochemically useful components for the assembly, respectively. By using graphene as the spacer, the multilayered nanostructures of graphene/MG and graphene/MWNT could be readily formed onto electrodes with the LBL method on the basis of the electrostatic and/or π-π interaction(s) between graphene and the electrochemically useful components. Scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), and cyclic voltammetry (CV) were used to characterize the assembly processes, and the results revealed that nanostructure assembly was uniform and effective with graphene as the spacer. Electrochemical studies demonstrate that the assembled nanostructures possess excellent electrochemical properties and electrocatalytic activity toward the oxidation of NADH and could thus be used as electronic transducers for bioelectronic devices. This potential was further demonstrated by using an alcohol dehydrogenase-based electrochemical biosensor and glucose dehydrogenase-based glucose/O(2) biofuel cell as typical examples. This study offers a simple route to the controllable formation of graphene-based electrochemically functionalized nanostructures that can be used for the development of molecular bioelectronic devices such as biosensors and biofuel cells.     

Characterization of Pt nanoparticles deposited onto carbon nanotubes grown on carbon paper and evaluation of this electrode for the reduction of oxygen

Multiwalled carbon nanotubes (MWCNTs) were grown on the fibers of a commercial porous carbon paper used as carbon-collecting electrodes in fuel cells. The tubes were then covered with Pt nanoparticles in order to test these gas diffusion electrodes (GDEs) for oxygen reduction in H2SO4 solution and in H2/O2 fuel cells. The Pt nanoparticles were characterized by cyclic voltammetry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The majority of the Pt particles are 3 nm in size with a mean size of 4.1 nm. They have an electrochemically active surface area of 60 m2/g Pt for Pt loadings of 0.1-0.45 mg Pt/cm2. Although the electroactive Pt surface area is larger for commercial electrodes of similar loadings, Pt/MWCNT electrodes largely outperform the commercial electrode for the oxygen reduction reaction in GDE experiments using H2SO4 at pH 1. On the other hand, when the same electrodes are used as the cathode in a H2/O2 fuel cell, they perform only slightly better than the commercial electrodes in the potential range going from approximately 0.9 to approximately 0.7 V and have a lower performance at lower voltages.     

硫醇分子链长对氧化还原自组装多层膜电化学行为影响的初步研究(英文)

以烷基硫醇和二茂铁衍生物构建的氧化-还原自组装多层膜为模型体系,研究烷基硫醇分子链长对多层膜电化学行为的影响.实验表明,二茂铁基团和电极之间的电子传递反应速率随两者距离的增加呈现指数级下降的趋势;烷基硫醇分子链长对自组装膜电化学行为的影响于不同情况下表现不同.本实验条件下,当多层膜上的电活性基团与电极比较接近时,长链分子自组装膜呈现较强的电化学响应.而当电极与电活性基团之间的距离较远时,短链烷基硫醇分子自组装膜呈现较强的电化学响应.     

Unfolding Tin–Cobalt Interactions in Oxide‐Based Composite Electrodes for Li‐Ion Batteries by Mössbauer Spectroscopy

With a view to the development of new composite electrodes for lithium-ion batteries with electroactive tin and cobalt, Co-doped tin dioxide samples are studied. The role played by oxygen and cobalt atoms in the electrochemical behavior of tin-based electrodes for Li-ion batteries is examined by the powerful and selective (119)Sn M?ssbauer spectroscopy. For the discharged electrodes, the oxygen atoms in the lithia matrix tend to destabilize the Sn(0) atoms. In contrast, the presence of cobalt atoms helps to form a matrix that stabilizes the reduced tin atoms. Cobalt-tin interactions in electrochemical reduced Co(x)Sn(1-x)O(2) electrodes are deduced from the electrochemical and M?ssbauer results.     

电位调控制备还原氧化石墨烯的电催化性能研究

本文通过控制电位还原氧化石墨烯,可控制备不同含氧官能团的石墨烯纳米材料。以多巴胺、[Fe(CN)_6]~(3-)、NADH为电活性探针,研究了石墨烯表面含氧官能团、缺陷、表面荷电性质以及导电性等对石墨烯电催化性能的影响。研究发现,低还原程度的氧化石墨烯表面含有大量缺陷和丰富的官能团,能够促进多巴胺自催化反应,也有利于K_3[Fe(CN)_6]在电极表面的电子转移;随着氧化石墨烯还原程度提高,其导电性逐渐得到改善,且其表面官能团和缺陷位点数量逐渐减少,对NAD~+的吸附变弱,因而能促进NADH发生电催化氧化。     

An electrochemical immunosensor using p-aminophenol redox cycling by NADH on a self-assembled monolayer and ferrocene-modified Au electrodes

Redox cycling of enzymatically amplified electroactive species has been widely employed for high signal amplification in electrochemical biosensors. However, gold (Au) electrodes are not generally suitable for redox cycling using a reducing (or oxidizing) agent because of the high background current caused by the redox reaction of the agent at highly electrocatalytic Au electrodes. Here we report a new redox cycling scheme, using nicotinamide adenine dinucleotide (NADH), which can be applied to Au electrodes. Importantly, p-aminophenol (AP) redox cycling by NADH is achieved in the absence of diaphorase enzyme. The Au electrodes are modified with a mixed self-assembled monolayer of mercaptododecanoic acid and mercaptoundecanol, and a partially ferrocenyl-tethered dendrimer layer. The self-assembled monolayer of long thiol molecules significantly decreases the background current of the modified Au electrodes, and the ferrocene modification facilitates easy oxidation of AP. The low amount of ferrocene on the Au electrodes minimizes ferrocene-mediated oxidation of NADH. In sandwich-type electrochemical immunosensors for mouse immunoglobulin G (IgG), an alkaline phosphatase label converts p-aminophenylphosphate (APP) into electroactive AP. The amplified AP is oxidized to p-quinoneimine (QI) by electrochemically generated ferrocenium ion. NADH reduces QI back to AP, which can be re-oxidized. This redox cycling enables a low detection limit for mouse IgG (1 pg mL(-1)) to be obtained.     

Ring‐disc Microelectrodes towards Glutathione Electrochemical Detection

An alternative approach for space‐resolved glutathione (GSH) detection using a ring‐disc microelectrode and an appropriate electroactive probe (acetaminophen) is reported. Acetaminophen is electrochemically oxidized at one of the electrodes and a fraction of the reaction product (N‐acetyl‐p‐quinoneimine) diffuses to the other, where it is detected. The collection efficiency value is dependent on the concentration of glutathione in solution, which consumes N‐acetyl‐p‐quinoneimine during its transit from the disc to the ring. Collection efficiency values close to 100 % were obtained by confining the electroactive species in a gap (<2 μm) that resembles a thin layer cell in a SECM configuration. The proposed indirect method was used to image the transport of GSH across an impermeable membrane in a SECM experiment. The method proved to be useful as a proof of concept for space‐resolved GSH electrochemical detection and a topography independent electrochemical image was acquired.     

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 μM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.     

The use of auger electron spectroscopy for the characterisation of the surfaces of spherical gold electrodes

Gold spheres (1.5 mm diameter) were obtained from wires of different purities by melting under various conditions (nature and pressure of the atmosphere used, sputtering and transfer conditions to the Auger spectroscope). Their surfaces were analysed by Auger electron spectroscopy (AES) as regards conditions of preparation. The main impurities detected were sulphur, carbon and oxygen, the latter appeared to be bonded to oxidizable elements such as silicon, calcium or even iron for the less pure samples. The origin of the surface contaminants has been investigated (bulk metal impurities, air pollutants, emission from the inner surface of pyrex tube used for melting, annealing and sputtering). Spheres of known surface condition were used as electrodes. The shape of differential capacity-potential curves obtained just after the electrode was dipped into the electrolyte was in good agreement with expectation based on previous AES analysis. Other gold electrodes were analysed by AES after various electrochemical treatments. Oxygen appeared to be stable under AES vacuum conditions on the surface of an electrochemically oxidized electrode. Such oxidized gold surfaces did not adsorb carbon compounds and sulphur unlike those which were reduced. Metallic impurities were not detected by AES on electrochemically reduced gold electrodes which did not retain oxygen from previous electro-oxidizing treatments. In this case oxygen traces observed by AES which amounted to random values according to the electrochemical treatment, seemed to be assignable to cumulative contribution of oxidized impurities not detected individually by AES.     

锇-聚乙烯吡啶复合物与辣根过氧化物酶分子多层膜的制备及电化学性质研究

基于分子间静电相互作用力,将锇-聚乙烯吡啶复合物(PVP-Os)与辣根过氧化物酶(HRP)交替沉积于固体基质表面,制得了包含生物成分的分子多层膜.膜层间的聚合物分子起到了粘接与导电的双重作用.用紫外-可见光谱法跟踪了石英基片上的组装过程,研究了多层膜电极对过氧化氢的电催化还原性能,并描述了多层膜电化学行为.     

Nucleosides and ODN electrochemical detection onto boron doped diamond electrodes

Boron doped diamond (BDD) is a promising material for electroanalytical chemistry due mainly to its chemical stability, its high electrical conductivity and to the large amplitude of its electroactive window in aqueous media. The latter feature allowed us to study the direct oxidation of the two electroactive nucleosides, guanosine and adenosine. The BDD electrode was first activated by applying high oxidizing potentials, allowing to increase anodically its working potential window through the oxidation of CH surface groups into hydroxyl and carbonyl terminations. Guanosine (1.2 V vs. Ag/AgCl) and adenosine (1.5 V vs. Ag/AgCl) could then be detected electrochemically with an acceptable signal to noise ratio. The electrochemical signature of each oxidizable base was assessed using differential pulse voltammetry (DPV), in solutions containing one or both nucleosides. These experiments pointed out the existence of adsorption phenomena of the oxidized products onto the diamond surface. Scanning electrochemical microscopy (SECM) was used to investigate these adsorption effects at the microscopic scale. The usefulness of BDD electrodes for the direct electrochemical detection of synthetic oligonucleotides is also evidenced.     

Simulation of nonstationary processes in solid electrolyte electrochemical cells for the pulsed mode of gas composition variations

Studying processes that occur in solid electrolyte electrochemical cells when the working electrode is subjected to an impact of the reactive gas medium are of interest for both their practical application and the understanding of mechanisms of these processes. There are grounds to assume that the methods of studying the processes on electrodes by subjecting the latter to chemical pulses provide more information as compared with the conventional methods based on electric perturbations. A computer simulation of nonstationary processes in a solid electrolyte electrochemical cell of the flow-through kind is carried out. The model of these processes takes into account the transport of electrochemically active components in the gas phase, the kinetics and statics of adsorption of these substances on the gas/electrode interface, and the kinetics of electrode reactions including chemical and charge-transfer stages. Time dependences of concentration fields are calculated as well as the integral characteristics of flows, namely, the oxygen flow from the gas phase to the electrode, the oxygen flow from the electrode to the solid electrolyte, and the flow of the electrochemically active component at the cell outlet.     

Use of electrolysis under pressure for destructive oxidation of phenol and azo dyes

Trends in the development of electrochemical methods for solving environmental problems were considered. Modern tendencies in research on the electrochemical destruction of toxic organic substances resistant to oxidation were analyzed. The use of three-dimensional (3D) electrodes and combined methods (electro-Fenton process combined with ultrasound, UV irradiation, etc.) increases the efficiency of destruction. Special attention was paid to studies at increased pressures. Increased pressure initially created with an inert gas did not substantially affect the kinetics of the anodic process. Increased pressure initially created with an electrochemically active gas (oxygen) accelerated the anodic oxidation of organic compounds (phenol and azo dyes (direct black 2S and stable disperse yellow 4K). The organic substances under study inhibit the cathodic reduction of oxygen, and the positive role of increased pressure is proven.     

A New Infrared Spectroelectrochemical Cell for the Detection of Species Generated by Platinum and Screen‐Printed Carbon Electrodes

In this paper, we describe a simple and effective infrared (IR) spectroelectrochemical cell for detecting species generated from an electrochemical system featuring low‐IR‐reflectivity electrodes. The IR detection mode of attenuated total reflection (ATR) was employed to construct the spectroelectrochemical cell. Two kinds of electrodes, platinum (Pt) and screen‐printed carbon (SPC), were used to examine the performance of this new cell in detection of electroactive species generated by cyclic voltammetry. Because data generated from highly reflective electrodes are available in the literature, Pt electrode was used to characterize the performances of the developed spectroelectrochemical cell. Results indicated that species generated electrochemically can be observed readily and their responses were comparable to those described in the literature. The cell volume could be lower than 300 μL, which suggests that this approach may be very useful to obtain chemical information during electrochemistry for biological fluids with limited sample volumes. By examining the electrochemical behavior of several amino acids using both Pt and SPC electrodes, the redox behaviors can be readily observed indicating a new spectroelectrochemical cell was successfully developed for the purpose of using of SPC electrode.     

Introducing hydrophilic carbon nanoparticles into hydrophilic sol-gel film electrodes

A hydrophilic carbon nanoparticle–sol-gel electrode with good electrical conductivity within the sol-gel matrix is prepared. Sulfonated carbon nanoparticles with high hydrophilicity and of 10–20 nm diameter (Emperor 2000) are co-deposited onto tin-doped indium oxide substrates employing a sol-gel technique. The resulting carbon nanoparticle-sol-gel composite electrodes are characterized as a function of composition and salt (KCl) additive. Scanning electron microscopy and voltammetry in the absence and in the presence of a solution redox system suggest that the composite electrode films can be made electrically conducting and highly porous to promote electron transport and transfer. The effect of the presence of hydrophilic carbon nanoparticles is explored for the following processes: (1) double layer charging, (2) diffusion and adsorption of the electrochemically reversible solution redox system 1,1′-ferrocenedimethanol, (3) electron transfer to the electrochemically irreversible redox system hydrogen peroxide, and (4) electron transfer to the redox liquid tert-butylferrocene deposited into the porous composite electrode film. The extended electrochemically active hydrophilic surface area is beneficial in particular for surface sensitive processes (1) and (3), and it provides an extended solid|organic liquid|aqueous solution boundary for reaction (4). The carbon nanoparticle–sol-gel composite electrodes are optimized to provide good electrical conductivity and to remain stable during electrochemical investigation.     

Highly Active Bidirectional Electron Transfer by a Self‐Assembled Electroactive Reduced‐Graphene‐Oxide‐Hybridized Biofilm

Low extracellular electron transfer performance is often a bottleneck in developing high‐performance bioelectrochemical systems. Herein, we show that the self‐assembly of graphene oxide and Shewanella oneidensis MR‐1 formed an electroactive, reduced‐graphene‐oxide‐hybridized, three‐dimensional macroporous biofilm, which enabled highly efficient bidirectional electron transfers between Shewanella and electrodes owing to high biomass incorporation and enhanced direct contact‐based extracellular electron transfer. This 3D electroactive biofilm delivered a 25‐fold increase in the outward current (oxidation current, electron flux from bacteria to electrodes) and 74‐fold increase in the inward current (reduction current, electron flux from electrodes to bacteria) over that of the naturally occurring biofilms.     

Photochromism and electrochemistry of a dithienylcyclopentene electroactive polymer

A bifunctional substituted dithienylcyclopentene photochromic switch bearing electropolymerisable methoxystyryl units, which enable immobilization of the photochromic unit on conducting substrates, is reported. The spectroscopic, electrochemical, and photochemical properties of a monomer in solution are compared with those of the polymer formed through oxidative electropolymerization. The electroactive polymer films prepared on gold, platinum, glassy carbon, and indium titanium oxide (ITO) electrodes were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The thickness of the films formed is found to be limited to several monolayer equivalents. The photochromic properties and stability of the polymer films have been investigated by UV/vis spectroscopy, electrochemistry, and XPS. Although the films are electrochemically and photochemically stable, their mechanical stability with respect to adhesion to the electrode was found to be sensitive to both the solvent and the electrode material employed, with more apolar solvents, glassy carbon, and ITO electrodes providing good adhesion of the polymer film. The polymer film is formed consistently as a thin film and can be switched both optically and electrochemically between the open and closed state of the photochromic dithienylethene moiety.     

Light‐Triggered Release of Trapped Charges in Molecular Assemblies

We demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo‐ and electrochemically‐active components is essential for the function of the thin films. Layers of well‐defined ruthenium complexes on indium‐tin‐oxide electrodes provide electron‐transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal‐oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron‐transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.