Anodic Electron Transfer Research Articles

A novel carboxymethylcellulose–gelatin–titanium dioxide–superoxide dismutase biosensor; electrochemical properties of carboxymethylcellulose–gelatin–titanium dioxide–superoxide dismutase

A novel highly sensitive electrochemical carboxymethylcellulose–gelatin–TiO2–superoxide dismutase biosensor for the determination of O2•− was developed. The biosensor exhibits high analytical performance with a wide linear range (1.5nM to 2mM), low detection limit (1.5nM), high sensitivity and low response time (1.8s). The electron transfer of superoxide dismutase was first accomplished at the carboxymethylcellulose–gelatin–Pt and carboxymethylcellulose–gelatin–TiO2–Pt surface. The electron transfer between superoxide dismutase and the carboxymethylcellulose–gelatin–Pt wihout Fe(CN)64−/3− and carboxymethylcellulose–gelatin–Pt, carboxymethylcellulose–gelatin–TiO2–Pt with Fe(CN)64−/3− is quasireversible with a formal potential of 200mV, 207mV, and 200mV vs Ag|AgCl respectively. The anodic (ksa) and cathodic (ksc) electron transfer rate constants and the anodic (αa) and cathodic (αc) transfer coefficients were evaluated: ksa=6.15s−1, αa=0.79, and ksc=1.48s−1αc=0.19 for carboxymethylcellulose–superoxide dismutase without Fe(CN)64−/3−, ksa=6.77s−1, αa=0.87, and ksc=1s−1αc=0.13 for carboxymethylcellulose–superoxide dismutase with Fe(CN)64−/3−, ksa=6.85s−1, αa=0.88, and ksc=0.76s−1αc=0.1 carboxymethylcellulose–gelatin–TiO2–superoxide dismutase. The electron transfer rate between superoxide dismutase and the Pt electrode is remarkably enhanced due to immobilizing superoxide dismutase in carboxymethylcellulose–gelatin and TiO2 nanoparticles tend to act like nanoscale electrodes.

Electrocatalysis of Ni-promoted Cd coated graphite toward methanol oxidation in alkaline medium

The nickel–cadmium (Ni-promoted Cd) catalyst for using direct methanol fuel cell (DMFC) applications is electrochemically deposited on a graphite substrate. The activity of methanol oxidation is assessed by recording cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. The surface morphologies and chemical compositions of catalysts are determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray florescence spectroscopy (XRF). Mean roughness of catalysts is measured by atomic force microscopy (AFM). Kinetic parameters of oxidation such as the anodic electron transfer coefficient (αa), cathodic electron transfer coefficient (αc) and charge transfer rate constant (ks) are calculated. The effect of methanol concentration and temperature on methanol oxidation is also investigated. The electrochemical measurements show that the addition of Cd to single coating enhances the electrocatalytic properties for methanol oxidation and Ni-promoted Cd/C has the best catalytic activity and stability.

Electrochemical treatment of aqueous solutions containing one or many organic pollutants at boron doped diamond anodes. Theoretical modeling and experimental data

The electrochemical oxidation of organics in water at boron doped diamonds (BDD) was experimentally investigated with the aim to discuss the correlations among the conversion of the pollutants and the instantaneous current efficiency ICE with the operative conditions. A simple theoretical model previously developed for the oxidation of oxalic acid accounting for the cases of mass transfer control, oxidation reaction control and mixed kinetic regimes was adopted and extended to challenge its predictive capability in the case of organics of different nature and in systems with more pollutants. A quite good agreement, between theoretical predictions and experimental data pertaining to the electrochemical oxidation of numerous organics, including some carboxylic acids and aliphatic chlorides, was observed, both for experiments performed in the presence of one or more organics. Results clearly indicate that such a simple model can be used to describe properly the “direct oxidation” (including oxidation by anodic electron transfer or by means of hydroxyl radicals) of organics at BDD. The comparison between the theoretical model and the experimental data strongly sustained the hypothesis that oxalic acid is oxidized by anodic electron transfer exchange while formic and maleic acids by reaction with hydroxyl radicals.

Solar Energy Powered Microbial Fuel Cell with a Reversible Bioelectrode

The solar energy powered microbial fuel cell is an emerging technology for electricity generation via electrochemically active microorganisms fueled by solar energy via in situ photosynthesized metabolites from algae, cyanobacteria, or living higher plants. A general problem with microbial fuel cells is the pH membrane gradient which reduces cell voltage and power output. This problem is caused by acid production at the anode, alkaline production at the cathode, and the nonspecific proton exchange through the membrane. Here we report a solution for a new kind of solar energy powered microbial fuel cell via development of a reversible bioelectrode responsible for both biocatalyzed anodic and cathodic electron transfer. Anodic produced protons were used for the cathodic reduction reaction which held the formation of a pH membrane gradient. The microbial fuel cell continuously generated electricity and repeatedly reversed polarity dependent on aeration or solar energy exposure. Identified organisms within biocatalyzing biofilm of the reversible bioelectrode were algae, (cyano)bacteria and protozoa. These results encourage application of solar energy powered microbial fuel cells.

Flavins contained in yeast extract are exploited for anodic electron transfer by Lactococcus lactis

Cyclic voltammograms of yeast extract-containing medium exhibit a clear redox peak around − 0.4 V vs. Ag|AgCl. Fermentative bacterium Lactococcus lactis was hereby shown to exploit this redox compound for extracellular electron transfer towards a graphite anode using glucose as an electron donor. High performance liquid chromatography revealed that this may be a flavin-type compound. The ability of L. lactis to exploit exogenous flavins for anodic glucose oxidation was confirmed by tests where flavin-type compounds were supplied to the bacterium in well defined media. Based on its mid-point potential, riboflavin can be regarded as a near-optimal mediator for microbially catalyzed anodic electron transfer. Riboflavin derivative flavin mononucleotide (FMN) was also exploited by L. lactis as a redox shuttle, unlike flavin adenine dinucleotide (FAD), possibly due to the absence of a specific transporter for the latter. The use of yeast extract in microbial fuel cell media is herein discouraged based on the related unwanted artificial addition of redox mediators which may distort experimental results.

Lactococcus lactis catalyses electricity generation at microbial fuel cell anodes via excretion of a soluble quinone

Lactococcus lactis is a gram-positive, normally homolactic fermenter that is known to produce several kinds of membrane associated quinones, which are able to mediate electron transfer to extracellular electron acceptors such as Fe 3+, Cu 2+ and hexacyanoferrate. Here we show that this bacterium is also capable of performing extracellular electron transfer to anodes by utilizing at least two soluble redox mediators, as suggested by the two-step catalytic current developed. One of these two mediators was herein suggested to be 2-amino-3-dicarboxy-1,4-naphthoquinone (ACNQ), via evaluation of standard redox potential, ability of the bacterium to exploit the quinone when exogenously provided, as well as by high performance liquid chromatography coupled with UV spectrum analysis. During electricity generation, L. lactis slightly deviated from its normal homolactic metabolism by excreting acetate and pyruvate in stoichiometric amounts with respect to the electrical current. In this metabolism, the anode takes on the role of electron sink for acetogenic fermentation. The finding that L. lactis self-catalyses anodic electron transfer by excretion of redox mediators is remarkable as the mechanisms of extracellular electron transfer by pure cultures of gram-positive bacteria had previously never been elucidated.

Use of Pseudomonas species producing phenazine-based metabolites in the anodes of microbial fuel cells to improve electricity generation

The rate of anodic electron transfer is one of the factors limiting the performance of microbial fuel cells (MFCs). It is known that phenazine-based metabolites produced by Pseudomonas species can function as electron shuttles for Pseudomonas themselves and also, in a syntrophic association, for Gram-positive bacteria. In this study, we have investigated whether phenazine-based metabolites and their producers could be used to improve the electricity generation of a MFC operated with a mixed culture. Both anodic supernatants obtained from MFCs operated with a Pseudomonas strain (P-PCA) producing phenazine-1-carboxylic acid (PCA) and those from MFCs operated with a strain (P-PCN) producing phenazine-1-carboxamide (PCN) exerted similarly positive effects on the electricity generation of a mixed culture. Replacing supernatants of MFCs operated with a mixed culture with supernatants of MFCs operated with P-PCN could double the currents generated. Purified PCA and purified PCN had similar effects. If the supernatant of an engineered strain overproducing PCN was used, the effect could be maintained over longer time courses, resulting in a 1.5-fold increase in the production of charge. Bioaugmentation of the mixed culture MFCs using slow release tubes containing P-PCN not only doubled the currents but also maintained the effect over longer periods. The results demonstrated the electron-shuttling effect of phenazine-based compounds produced by Pseudomonas species and their capacity to improve the performance of MFCs operated with mixed cultures.

On the use of cyclic voltammetry for the study of anodic electron transfer in microbial fuel cells

In this communication we discuss, by means of the metal reducing bacterium Geobacter sulfurreducens, a strategy to use cyclic voltammetry for the study of anodic bioelectrocatalytic electron transfer in microbial fuel cells.

Metabolites produced by Pseudomonas sp. enable a Gram-positive bacterium to achieve extracellular electron transfer

Previous studies revealed the abundance of Pseudomonas sp. in the microbial community of a microbial fuel cell (MFC). These bacteria can transfer electrons to the electrode via self-produced phenazine-based mediators. A MFC fed with acetate where several Pseudomonas sp. were present was found to be rich in a Gram-positive bacterium, identified as Brevibacillus sp. PTH1. Remarkably, MFCs operated with only the Brevibacillus strain in their anodes had poor electricity generation. Upon replacement of the anodic aqueous part of Brevibacillus containing MFCs with the cell-free anodic supernatants of MFCs operated with Pseudomonas sp. CMR12a, a strain producing considerable amounts of phenazine-1-carboxamide (PCN) and biosurfactants, the electricity generation was improved significantly. Supernatants of Pseudomonas sp. CMR12a_Reg, a regulatory mutant lacking the ability to produce PCN, had no similar improvement effect. Purified PCN, together with rhamnolipids as biosurfactants (1 mg L(-1)), could clearly improve electricity generation by Brevibacillus sp. PTH1, as well as enable this bacterium to oxidize acetate with concomitant reduction of ferric iron, supplied as goethite (FeOOH). When added alone, PCN had no observable effects on Brevibacillus' electron transfer. This work demonstrates that metabolites produced by Pseudomonas sp. enable Gram-positive bacteria to achieve extracellular electron transfer. Possibly, this bacterial interaction is a key process in the anodic electron transfer of a MFC, enabling Brevibacillus sp. PTH1 to achieve its dominance.

Anodic electron transfer mechanisms in microbial fuel cells and their energy efficiency

The performance of a microbial fuel cell (MFC) depends on a complex system of parameters. Apart from technical variables like the anode or fuel cell design, it is mainly the paths and mechanisms of the bioelectrochemical energy conversion that decisively determine the MFC power and energy output. Here, the electron transfer from the microbial cell to the fuel cell anode, as a process that links microbiology and electrochemistry, represents a key factor that defines the theoretical limits of the energy conversion. The determination of the energy efficiency of the electron transfer reactions, based on the biological standard potentials of the involved redox species in combination with the known paths (and stoichiometry) of the underlying microbial metabolism, is an important instrument for this discussion. Against the sometimes confusing classifications of MFCs in literature it is demonstrated that the anodic electron transfer is always based on one and the same background: the exploitation of the necessity of every living cell to dispose the electrons liberated during oxidative substrate degradation.

Microbial Fuel Cells in Relation to Conventional Anaerobic Digestion Technology

AbstractConventional anaerobic digestion based bioconversion processes produce biogas and have as such been widely applied for the production of renewable energy so far. An innovative technology, based on the use of microbial fuel cells, is considered as a new pathway for bioconversion processes towards electricity. In comparison with conventional anaerobic digestion, the microbial fuel cell technology holds some specific advantages, such as its applicability for the treatment of low concentration substrates at temperatures below 20 °C, where anaerobic digestion generally fails to function. This provides some specific application niches of the microbial fuel cell technology where it does not compete with but complements the anaerobic digestion technology. However, microbial fuel cells still face important limitations in terms of large‐scale application. The limitations involve the investment costs, upscale technical issues and the factors limiting the performance, both in terms of anodic and cathodic electron transfer. Research to render the microbial fuel cell technology more economically feasible and applicable should focus on reactor configuration, power density and the material costs.

Bond and Structure Activation by Anodic Electron Transfer: Metal—Hydrogen Bond Cleavage and cis/trans Isomerization in Coordination Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

A perfluorinated micellar reaction system in lithium perchlorate/acetonitrile; enhanced efficiency in anodic electron-transfer and intermolecular cycloaddition

A micellar electrolytic reaction system composed of lithium perfluorooctanesulfonate (LiFOS), highly concentrated lithium perchlorate in acetonitrile, effectively dispersed slightly soluble compounds to promote anodic electron transfers, and it further accelerated the formation of desired cycloadducts between electrogenerated quinones and dienes.

What anodic and chemical stability for 2-thienyl carbinol ethers? Polymerization and/or cleavage?

The electrochemical and chemical properties of the title compounds 1 have been investigated. It was shown that either anodic electron transfer or lithium cation electrophilic assistance may induce elimination and therefore yield relevant vinylic compounds. Under such conditions, when conducted in the presence of a lithium salt, the anodic polymerization may occur either on 1 (and yield afterward to elimination at the oligomer state) or on the vinylic products. Similar conclusions may appear from 1 radical cations which can afford elimination reactions.

PH-Modulated Vectorial Electron Transfer Reactions at a Self-Assembled Monolayer on a Gold Electrode

Abstract A self-assembled monolayer of 1-dodecanethiol (C12SH) on a gold electrode was prepared by dipping a polished bare electrode into an ethanolic solution of C12SH (1.0 mmol dm−3) for 10 min. The obtained modified electrode blocked the direct electron-transfer reaction of [Fe(CN)6]3− and [Fe(CN)6]4− with the underlying electrode. However, a pH-dependent redox compound, 4,4′-biphenyldiol (1) in solution, was permeable into the monolayer and gave well-defined cyclic voltammograms at both higher and lower pHs. Using this chemical-recognition ability of the modified electrode together with the formal potential shift of 1 according to the Nernst equation, pH–modulated vectorial electron transfer reactions were examined. At pH 3, cyclic voltammograms at the modified electrode in a 1 + [Fe(CN)6]4− aqueous solution revealed that one-way electron flow from [Fe(CN)]4− to the electrode via1 (oxidized form) occurred. On the contrary, at higher pHs (pH 9—11), the vectorial electron flow at the electrode in 1 + [Fe(CN)6]3− solution was reversed. A triggered change (‘switching’) between the anodic and cathodic vectorial electron transfer reactions by changing the pH was also possible at the C12SH-modified electrode in the presence of 1, [Fe(CN)6]4− and [Fe(CN)6]3− in solution. This finding may offer possibilities for the construction of functional molecular devices based on the tuning of rectified electron transfer reactions.

Electrochemical characteristics of the Al 2Cu, Al 3Ta and Al 3Zr intermetallic phases and their relevancy to the localized corrosion of Al alloys

The electrochemical behaviors of θ-Al 2Cu phase, β-Al 3Ta and, to a lesser extent, Al 3Zr were compared to high purity Al in ambient temperature inert buffer solutions and, in certain cases, dilute halide solutions. The aim of this work is to develop a better understanding of electrochemical characteristics of these intermetallic phases. In particular, information was sought concerning (a) their galvanic couple relationship with respect to Al and (b) the relationship between the passive film formed on each phase and its ability to support both cathodic and anodic electron transfer reactions (ETR). The open circuit potentials (OCPs) of all three intermetallic phases were more positive than that of Al in inert solutions ranging from pH 2 to 12. The Al 2Cu phase supports the reduction of water reaction at enhanced rates relative to pure Al due to the presence of metallic Cu o in an Al 2O 3 rich oxide but supports oxygen evolution due to a combination of this effect as well as formation of more electrically conductive copper oxides. A similar effect is observed for Al 3Ta and is attributed mainly to the formation of a more conductive mixed oxide containing Ta 2O 5.

Kinetics of electron transfer in a mono-linked isoalloxazine-gold electrode

A cyclic voltammetric investigation of the stability and redox properties of a mono-linked isoalloxazine-gold electrode in aqueous solution has been performed using repetitive cycles of potential. The effects of pH and the composition of the electrolyte solution on the kinetics of the anodic and cathodic electron transfer processes have been determined. A linear relationship between the formal potential and pH exists over the range pH 4.4–8.0 and the value of electron transfer rate constants for both of the anodic and cathodic processes are markedly pH dependent. The maximum values for these rate constants occur at about pH 6.0 where k anode = 1420 s −1 and where k cathode = 2240 s −1 although the cathodic rate is slower than the anodic process outside of the pH range 5.0–7.0. The electronic absorption spectra of the precursor N 3-( N-phenylthioureaylethyl)- N 10-phenethylisoalloxazine show pH-dependent changes in the extinction coefficient (ε) at 348 nm although simpler isoalloxazines, including riboflavin, do not. The maximum value of ε 348 also occurs at pH 6.0. The results indicate that the conformation of the substituted isoalloxazine changes with pH and that similar geometric changes in the molecule occur in the gold electrode system and alter its electrochemical properties.

ChemInform Abstract: Electroreductive “Barbier Type” Allylation of Imines with a Combination of a Pb(0)/Pb(II) Redox Mediator and Sacrificial Anode (Al).

Abstract An electroreductive “ Barbier Type ” allylation of imines with allyl bromide has been performed in a PbBr 2 /Bu 4 NBr/THF-(Al anode)-(Pt cathode) system. A combination of Pb(0)/Pb(II) redox and a sacrificial aluminum anode works as a mediator for both cathodic and anodic electron transfer processes, respectively.

Electroreductive “Barbier Type” allylation of imines with a combination of a Pb(0)/Pb(II) redox mediator and sacrificial anode (Al)

An electroreductive “ Barbier Type” allylation of imines with allyl bromide has been performed in a PbBr 2/Bu 4NBr/THF-(Al anode)-(Pt cathode) system. A combination of Pb(0)/Pb(II) redox and a sacrificial aluminum anode works as a mediator for both cathodic and anodic electron transfer processes, respectively.

Electrochemical studies of TiO 2 films with various palladium implantation profiles

To investigate the radiation damage as well as the doping effect of ion implantation, oxide-covered titanium electrodes were implanted with various concentration profiles of palladium ions (Pd +). The comparison of the electrochemical data allows separation of the influences of doping and Frenkel defects. Measurements of repassivation, capacity and photocurrent show a dominant influence of defect production increasing in the following order of the profiles: out < in < tot < through. For repassivation up to 2 V, defects with a high mobility migrate out of the film and form new oxide of up to 0.2 nm thickness. In capacity measurements, donor production of up to 4 × 10 19 cm −3 can be detected, but less than 40% of the donors can be eliminated during repassivation. The photocurrent spectrum shows amorphization of the oxide, a decrease in the mobility gap and the production of localized electronic states in the mobility gap. The rate of electron transfer reactions increases in the order out < in ≈ through < tot by several orders of magnitude. This shows that the production of defects enhances electron transfer reactions but that doping with palladium ions is most effective. For the out profiles, the unchanged inner layer represents an additional barrier for anodic electron transfer. When the data for the various profiles are compared and summarized, various defects with different concentrations, energies and mobilities can be distinguished, and the potential distributions can be estimated for the various profiles.