Photo‐Induced Electron Transfer Between Photosystem 2 via Cross‐linked Redox Hydrogels

Photosystem 2 (PS2) that catalyses light driven water splitting in photosynthesis was ‘wired’ to electrode surfaces via osmium‐containing redox polymers based on poly(vinyl)imidazol. The redox polymer hydrogel worked as both immobilization matrix and electron acceptor for the enzyme. Upon illumination, the enzymatic reaction could be switched on and a catalytic current was observed at the electrode. The catalytic current is directly dependent on the intensity of light used for the excitation of PS2. A typical current density of 45 μA cm^?2 at a light intensity of 2.65 mW cm^?2 could be demonstrated with a significantly improved operational stability.     

Molecular Engineering of Conjugated Acetylenic Polymers for Efficient Cocatalyst‐free Photoelectrochemical Water Reduction

Conjugated polymers featuring tunable band gaps/positions and tailored active centers, are attractive photoelectrode materials for water splitting. However, their exploration falls far behind their inorganic counterparts. Herein, we demonstrate a molecular engineering strategy for the tailoring aromatic units of conjugated acetylenic polymers from benzene‐ to thiophene‐based. The polarized thiophene‐based monomers of conjugated acetylenic polymers can largely extend the light absorption and promote charge separation/transport. The C≡C bonds are activated for catalyzing water reduction. Using on‐surface Glaser polycondensation, as‐fabricated poly(2,5‐diethynylthieno[3,2‐b]thiophene) on commercial Cu foam exhibits a record H₂‐evolution photocurrent density of 370 μA cm^?2 at 0.3 V vs. reversible hydrogen electrode among current cocatalyst‐free organic photocathodes (1–100 μA cm^?2). This approach to modulate the optical, charge transfer, and catalytic properties of conjugated polymers paves a critical way toward high‐activity organic photoelectrodes.     

Electropolymerization of Metallophthalocyanines Carrying Redox Active Metal Centers and their Electrochemical Pesticide Sensing Application

In this study, modified electrodes were constructed with the electropolymerization of metallophthalocyanines (MPcs) carrying redox active metal cations and electropolymerizable substituents. Then these electrodes were tested as selective and sensitive electrochemical pesticide sensors. Incorporation of the redox active Co(II) (CoPc(MOR‐NAF)), Cl–Mn(III) (MnPc(MOR‐NAF)), and Ti(IV)O (TiOPc(MOR‐NAF)) metal cations into Pc cavity increased the redox activity of Pc ring. Moreover, redox active and electropolymerizable 5‐{[(1E)‐(4‐morpholin‐4‐ylphenyl)methylene]amino}‐1‐naphthoxy substituents (MOR‐NAF) on the Pc ring triggered coating of the complexes on the electrode surface with the electropolymerization reactions. Therefore, modified electrodes GCE/MPc(MOR‐NAF) were constructed with the electropolymerizations of MPcs. These electrodes illustrated reasonable redox activity and conductivity for the potential applications in different fields of the electrochemical technologies. Pesticide sensing measurements indicated that changing the metal center of the complexes significantly altered their sensing activities. Among the complexes, GCE/CoPc(MOR‐NAF) electrode behaved as the most sensitive and selective electrode and it sensed the parathion with good selectivity and sensitivity. GCE/CoPc(MOR‐NAF) electrode showed a wider linear range (0.075‐5.75 μmoldm⁻³) and smaller LOD (0.025 μmoldm⁻³) and higher sensitivity (3.46 Acm⁻²M⁻¹) for the parathion sensing. Although GCE/TiOPc(MOR‐NAF) electrode also sensed the parathion with a high sensitivity, its selectivity was poor and the linear range of this sensing was very narrow. Differently GCE/Cl–MnPc(MOR‐NAF) electrode only sensed eserine with reasonably sensitivity.     

Visualisation of the local bio-electrocatalytic activity in biofuel cell cathodes by means of redox competition scanning electrochemical microscopy (RC-SECM)

Optimisation of biocatalytic systems for the electroreduction of molecular O₂ in biofuel cell cathodes implies screening of the catalytic activity of enzyme/redoxpolymer assemblies. Os-complex modified electrodeposition polymers are suggested for linking bilirubin oxidase catalysed O₂ reduction via an electron hopping sequence along the redox polymer to the electrode. They can be non-manually precipitated on electrode surfaces by electrochemically induced pH modulation. Cyclic voltammetry provides a good estimation of the electrocatalytic activity of a redox polymer/enzyme modified electrode surface. In addition, scanning electrochemical microscopy operating in redox competition mode (RC-SECM) supplies images of the spatial distribution of the biocatalytic activity.     

Direct Electrochemistry of Catalase at a Gold Electrode Modified with Single‐Wall Carbon Nanotubes

The direct electrochemistry of catalase (Ct) was accomplished at a gold electrode modified with single‐wall carbon nanotubes (SWNTs). A pair of well‐defined redox peaks was obtained for Ct with the reduction peak potential at ?0.414 V and a peak potential separation of 32 mV at pH 5.9. Both reflectance FT‐IR spectra and the dependence of the reduction peak current on the scan rate revealed that Ct adsorbed onto the SWNT surfaces. The redox wave corresponds to the Fe(III)/Fe(II) redox center of the heme group of the Ct adsorbate. Compared to other types of carbonaceous electrode materials (e.g., graphite and carbon soot), the electron transfer rate of Ct redox reaction was greatly enhanced at the SWNT‐modified electrode. The peak current was found to increase linearly with the Ct concentration in the range of 8×10^?6–8×10^?5 M used for the electrode preparation and the peak potential was shown to be pH dependent. The catalytic activity of Ct adsorbates at the SWNTs appears to be retained, as the addition of H₂O₂ produced a characteristic catalytic redox wave. This work demonstrates that direct electrochemistry of redox‐active biomacromolecules such as metalloenzymes can be improved through the use of carbon nanotubes.     

Electrochemical properties of lanthanum nickel oxide

Electrochemical properties of lanthanum nickel oxide, LaNiO₂₈₄, were studied in alkaline solutions. It was concluded that redox reactions of Ni⁴⁺/Ni³⁺ and Ni³⁺/Ni²⁺ in a solid surface layer took place at 0.4 V and ?0.4 V (vs. Hg/HgO), respectively. As the conductivity of the oxide is a function of the oxygen concentration due to σ^* bond formation, the resistivity of the electrode was changed depending on polarization potentials. The catalytic activity for oxygen reduction of a preoxidized electrode seemed to be higher than that of an electrode not intentionally oxidized, and the activity depended on the concentration of the alkaline solution. It was presumed that Ni³⁺ cations which form the σ^* bond with oxygen have an important role in the electrocatalysis of oxygen reduction on lanthanum nickel oxide.     

Three‐dimensional Nitrogen‐Doped Reduced Graphene Oxide/Carbon Nanotube Composite Catalysts for Vanadium Flow Batteries

The development of vanadium redox flow battery is limited by the sluggish kinetics of the reaction, especially the cathodic VO₂⁺/VO²⁺ redox couples. Therefore, it is vital to develop new electrocatalysts with enhanced activity to improve the battery performance. Herein, we synthesized the hydrogel precursor by a facile hydrothermal method. After the following carbonization, nitrogen‐doped reduced graphene oxide/carbon nanotube composite was obtained. By virtue of the large surface area and good conductivity, which are ensured by the unique hybrid structure, as well as the proper nitrogen doping, the as‐prepared composite presents enhanced catalytic performance toward the VO₂⁺/VO²⁺ redox reaction. We also demonstrated the composite with carbon nanotube loading of 2 mg/mL exhibits the highest activity and remarkable stability in aqueous solution due to the strong synergy between reduced graphene oxide and carbon nanotubes, indicating that this composite might show promising applications in vanadium redox flow battery.     

Thin polymer films on semiconductors: From their protection to the realization of molecular electronic devices

When homogeneously grafted as thin films on small band-gap inorganic semiconductors (n-GaAs, n-CdS), organic conjugated polymers such as poly-methylthiophene afford interesting new structures. In their doped conducting state, these polymer films bring a long-term protection of these semiconductors against their photocorrosion in aqueous medium, and the subsequent inclusion of metallic aggregates in these films allows increased catalytic activity for achieving photoelectrochemical reactions. In their undoped semiconducting state, they lead to the realization of “organic-on-inorganic” p-n junctions which show very low leakage current and high allowed current density. As photovoltaic cell, an energy conversion efficiency of 17.5% has been obtained under 100 mW.cm⁻² irradiation with a p-PMeT/n-GaAs cell. The larger number of work already devoted to organic conjugated polymers such as polyacetylene, polypyrrole, polythiophene, has shown that these compounds can be switched between a doped oxidized state, with a nearly metallic conductivity, σ ∼ 10²-10³S.cm⁻¹, and an undoped neutral state which presents semiconducting properties, σ ∼ 10⁻⁷ -10⁻⁹ S. cm⁻¹. Either as free standing film or grafted on an electrode, these polymers exhibit interesting organic electrode properties which have been widely characterized. On the other hand much less is known on their behavior when deposited on inorganic semiconductors. In the following, this area will be discussed on two examples, the protection of narrow band-gap semiconductors against their photo-degradation in aqueous solution, and the new junction properties presented by “organic-on-inorganic” electronic devices.     

Signal‐Enhanced Amperometric Immunosensor Based on Ferrocene‐Branched Poly(allylamine)/Multiwalled Carbon Nanotubes Redox‐Active Composite

A signal‐enhanced immunosensor has been developed by self‐assembling Au NPs onto a ferrocene‐branched poly(allylamine)/multiwalled carbon nanotubes (PAA‐Fc/MWNTs) modified electrode for the sensitive determination of hepatitis B surface antigen (HBsAg) as a model protein. The formation of PAA‐Fc/MWNTs composite not only effectively avoided the leakage of Fc and retained its electrochemical activity, but also enhanced the conductivity and charge‐transport properties of the composite. Further adsorption of Au NPs into the PAA matrix provided both the interactive sites for the immobilization of hepatitis B surface antibody (HBsAb) and a favorable microenvironment to maintain its activity. Tests performed with this immunosensor showed a specific response to HBsAg in the range of 0.1–350.0 ng mL^?1 with a detection limit of 0.03 ng mL^?1.     

Growth of aligned polypyrrole acicular nanorods and their application as Pt‐free semitransparent counter electrode in dye‐sensitized solar cell

Polypyrrole films on fluorine doped tin oxide (FTO)‐coated glass substrate were prepared in situ by placing FTO/glass substrates where pyrrole was polymerized by methyl orange‐ferric chloride complex. The atomic force microscopy image indicated growth of acicular nanorods of polypyrrole. These films exhibited catalytic activity towards I₃⁻/I⁻ redox couple and have been investigated for counter electrode application in dye‐sensitized solar cell (DSSC). The fabricated DSSC with N719 dye/TiO₂ as photoanode, and PPy/FTO as counter electrode shows ~1.7% efficiency.     

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

Room temperature polymerization of poly(3,4‐ethylenedioxythiophene) as transparent counter electrodes for dye‐sensitized solar cells

Poly(3,4‐ethylenedioxythiophene) (PEDOT) counter electrode is prepared with in situ polymerization of 3,4‐ethylenedioxythiophene on a fluorine‐doped tin oxide over‐layer glass at room temperature. The cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization are measured to evaluate the catalytic activity of PEDOT counter electrode for I₃^?/I^? redox couple. Comparing the data with that of traditional thermal decomposed Pt counter electrode, it is found that PEDOT has higher catalytic activity than that of Pt counterpart. Power conversion efficiency of the dye‐sensitized solar cell (DSC) with PEDOT counter electrode can attain to 7.713%, a little higher than that of the cell with Pt counter electrode (7.300%). Taking the advantage of high transparency of PEDOT counter electrode, an Ag mirror is put on the back side of PEDOT counter electrode of the DSC to reflect light back for power conversion. Power conversion efficiency of the DSC with this special structure can be further enhanced to 8.359%, which mainly stems from the improved short‐circuit current density by the increased irradiated light intensity. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication of Glucose Biosensor Based on Encapsulation of Glucose‐Oxidase on Sol‐Gel Composite at the Surface of Glassy Carbon Electrode Modified with Carbon Nanotubes and Celestine Blue

A simple procedure was developed to prepare a glassy carbon electrode modified with multi walled carbon nanotubes (MWCNTs) and Celestin blue. Cyclic voltammograms of the modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range (2–12). The formal potential of redox couple (E′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of Celestine blue immobilized on CNTs glassy carbon electrode was approximately 1.95×10^?10 mol cm^?2. The charge transfer coefficient (α) and heterogeneous electron transfer rate constants (k_s) for GC/MWCNTs/Celestine blue were 0.43 and 1.26 s^?1, respectively. The modified electrode show strong catalytic effect for reduction of hydrogen peroxide and oxygen at reduced overpotential. The glucose biosensor was fabricated by covering a thin film of sol‐gel composite containing glucose oxides (GOx) on the surface of Celestine blue /MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 0.3 μM, 18.3 μA/mM and 10 μM–6.0 mM, respectively. The accuracy of the biosensor for glucose detection was evaluated by detection of glucose in a serum sample, using standard addition protocol. In addition biosensor can reach 90% of steady currents in about 3.0 sec and interference effect of the electroactive existing species (ascorbic acid–uric acid and acetaminophen) was eliminated. Furthermore, the apparent Michaelis–Menten constant 2.4 mM, of GOx on the nano composite exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of glucose biosensor.     

A non‐gassing electroosmotic pump with sandwich of poly(2‐ethyl aniline)‐Prussian blue nanocomposite and PVDF membrane

Low voltage, non‐gassing electroosmotic pump (EOP) was assembled with poly(2‐ethyl aniline) (EPANI)‐Prussian blue nanocomposite electrode and commercially available hydrophilic PVDF membranes. The nanocomposite material combines excellent oxidation/reduction capacity of EPANI with exceptional stability by shuttling of proton between Prussian blue nanoparticles and EPANI redox matrix. The flow rate was highly dependent on the electrode composition but it was linear with applied voltage. The flow rate at 5 V for different nanocomposite, EPANI, EPANI‐A, EPANI‐B, and EPANI‐C were 127.29, 187.41, 148.51, and 95.47 µL/min cm², respectively, which increases substantially with increase in the Prussian blue content. The obtained best electro osmotic flux was 43 µL/min/V/cm² for EPANI‐A. It was higher than most of the EOP assembled using polyquinone and polyanthraquinone redox polymers. The assembled EOP remained exceptionally stable until the electrode charge capacity was fully utilized. The best EOP produces a maximum stall pressure of 1.2 kPa at 2 V. These characteristics make it suitable for a variety of microfluidic/device applications.     

Modified multiwalled carbon nanotubes as an electrode reaction catalyst for an all vanadium redox flow battery

Different modified multiwalled carbon nanotubes (MWCNTs) are prepared by heat treatments in the air and in the H₂SO₄?+?HNO₃ (1:1) mixed acids which are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Brunaur–Emmett–Teller, and cyclic voltammetry measurements. The results show the physicochemical properties of MWCNTs change significantly after these different modification processes, especially the electrochemical catalytic activity towards the VO₂ ⁺/VO²⁺ and V³⁺/V²⁺ redox pairs. The MWCNTs treated in the air at 600 °C for 30 min shows better electrochemical performances for the VO₂ ⁺/VO²⁺ redox reactions (58.8 and ?32.4 μA for the oxidation and reduction peaks at 10 mV?s^?1, respectively) than any other samples. Compared with the V³⁺/V²⁺ redox couple, the VO₂ ^+/VO²⁺ redox reactions are more easily affected by the physicochemical property changes of the MWCNTs. The enhanced electrochemical catalytic activity of the modified MWCNTs is not only related to the surface oxygen content, but also to the specific surface area, conductivity and the unique structure variations of the MWCNTs. The investigation demonstrated that the modified MWCNTs have a promising future application in the vanadium redox flow battery.     

Polybenzimidazoles tethered with N‐phenyl 1,2,4‐triazole units as polymer electrolytes for fuel cells

Polybenzimidazole (PBI) polymers tethered with N‐phenyl 1,2,4‐triazole (NPT) groups were prepared from a newly synthesized aromatic diacid, 3′‐(4‐phenyl‐4H‐1,2,4‐triazole‐3,5‐diyl) dibenzoic acid (PTDBA). The obtained polymers show superior thermal and chemical stability and good solubility in many aprotic solvents. The inherent viscosities of all polymers were around 1 dL/g. They exhibit high thermal stability with initial decomposition temperature ranging from 515 to 530 °C, high glass transition temperature ranging from 375 to 410 °C, and good mechanical properties with tensile stress in the range of 66–98 MPa and modulus 1897–2600 MPa. XRD analysis indicates that these polymers are amorphous in nature. Physicochemical properties such as water and phosphoric acid‐uptake, oxidative stability, and proton conductivity of membranes of these polymers have also been determined. The proton conductivity ranged from 4.7 × 10^?3 to 1.8 × 10^?2 S cm^?1 at 175 °C in dry conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2289–2303, 2009     

Sonochemical synthetic methods to produce functionalized conducting copolymers

Polyaniline (PANI) is one of the most investigated intrinsically conducting polymers. Copolymerization of aniline with aniline derivatives was considered one of the most effective and promising ways of improving the properties of PANI. In this work, firstly ethyl 3‐aminobenzoate and butyl 3‐aminobenzoate were synthesized from 3‐aminobenzoic acid by direct esterification. Then the copolymerization of 3‐amino benzoic acid, ethyl 3‐aminobenzoate, and butyl 3‐aminobenzoate with aniline was carried out by sonochemical polymerization in aqueous hydrochloric acid using ammonium persulfate (APS) as an initiator. The effects of variation in the molar ratio of the two monomers on chain structure, conductivity, and the redox properties of the copolymer are discussed. The prepared polymers are characterized by ¹H NMR spectroscopy, X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR). Thermal behavior of the prepared copolymers was studied by differential scanning calorimetry. The copolymers were doped with HCl and their conductivity was measured. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of Imidacloprid in Tomato Grown in Greenhouse Based on Copper(II) Phthalocyanine Modified Carbon Ceramic Electrode by Differential Pulse Voltammetry

A new sol‐gel derived electrocatalytic carbon ceramic electrode was prepared by incorporating copper(II) phthalocyanine (CuPc) in a carbon ceramic network. This electrode was used as a sensitive electrochemical sensor for determination of the insecticide Imidacloprid (1‐(6‐chloro‐3‐pyridylmethyl)‐N‐nitro‐imidazolidin‐2‐ylideneamine) by differential pulse voltammetry (DPV). The resulting modified electrode exhibits a cathodic peak potential shifted positively and an increasing in cathodic peak current in comparison with unmodified electrode. The redox properties of this modified electrode at various pH values and CuPc percentage were investigated. The catalytic current obtained from differential pulse voltammetry is linearly dependent on Imidacloprid concentration over the two linear ranges of 0.67‐17 μM and 17‐93 μM with correlation coefficient of R² = 0.9999 and R² = 0.990, respectively. The detection limit for Imidacloprid was found to be 0.28 μM according to lower linear range. Possible interferences from several common pesticides were also evaluated. The inherent stability, high sensitivity, low detection limit and low cost for each preparation are advantages of this sensor. Determination of Imidacloprid in commercial formulation and residual Imidacloprid in tomato grown in greenhouse (protected cultivation) was also conducted. The results obtained from commercial formulation were completely consistent with those obtained through the standard high‐performance liquid chromatography (HPLC) method.     

Picomolar Detection of Hydrogen Peroxide at Glassy Carbon Electrode Modified with NAD+ and Single Walled Carbon Nanotubes

Potential cycling was used for oxidation of NAD⁺ and producing an electroactive redox couple which strongly adsorbed on the electrode surface modified with single walled carbon nanotubes (SWCNTs). Modified electrode shows a pair of well defined and nearly reversible redox peaks at pH range 1–13 and the response showed a surface‐controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (k_s) of adsorbed redox couple onto CNTs films were about 6.32×10^?10 mol cm^?2 and 2.0 (±0.20) s^?1, respectively, indicating the high loading ability of CNTs toward the oxidation product of NAD⁺ (2,8‐dihydroxy adenine dinucleotide) and great facilitation of the electron transfer between redox couple and CNTs immobilized onto electrode surface. The modified electrode exhibited excellent electrocatalytic activity for H₂O₂ reduction at reduced overpotential. The catalytic rate constant for H₂O₂ reduction was found to be 2.22(±0.20)×10⁴ M^?1 s^?1. The catalytic reduction current allows the amperometric detection of H₂O₂ at an applied potential of ?0.25 V vs. Ag/AgCl with a detection limit of 10 pM and linear response up to 100 nM and resulting analytical sensitivity 747.6 nA/pM. The remarkably low detection limit (10 pM) is the lowest value ever reported for direct H₂O₂ determination on the electrodes at pH 7. The modified electrode can be used for monitoring H₂O₂ without the need for an enzyme or enzyme mimic. The proposed method for rapid amperometric detection of H₂O₂ is low cost and high throughput. Furthermore, the sensor can be used to any detection scheme that uses enzymatically generated H₂O₂ as a reactive product in biological systems.     

Effect of Poly(amine)s on the Redox Properties of Carboxymethylcellulose and Ferrocene‐modified Poly(amine) Layer‐by‐Layer Films

Multilayer films consisting of carboxymethylcellulose (CMC) and ferrocene‐modified poly(ethyleneimine) (Fc‐PEI) or poly(allylamine hydrochloride) (Fc‐PAH) were successfully prepared on a gold electrode to examine their redox properties. The redox current of (Fc‐PEI/CMC)_n film‐coated electrodes increased with the number of layers, while the (Fc‐PAH/CMC)_n film‐coated electrodes exhibited increased response only for the first eight bilayers. The (Fc‐PEI/CMC)_n and (Fc‐PAH/CMC)_n films deposited on the surface of Fc‐free multilayer film‐coated electrodes also showed a redox response. The (PEI/CMC)₅ film‐coated electrode showed redox responses in Fc‐PEI and Fc‐PAH solutions, confirming the uptake of the Fc‐polymers in the inner film. In contrast, the uptake of the Fc‐polymers in the (PAH/CMC)₅ film was severely suppressed, suggesting that different permeability of (PEI/CMC)₅ and (PAH/CMC)₅ films.