Electrocatalysis of Water Oxidation by H2O‐Capped Iridium‐Oxide Nanoparticles Electrodeposited on Spectroscopic Graphite

Electrocatalysis of water oxidation by 1.54 nm IrO_x nanoparticles (NPs) immobilized on spectroscopic graphite electrodes was demonstrated to proceed with a higher efficiency than on all other, hitherto reported, electrode supports. IrO_x NPs were electrodeposited on the graphite surface, and their electrocatalytic activity for water oxidation was correlated with the surface concentrations of different redox states of IrO_x as a function of the deposition time and potential. Under optimal conditions, the overpotential of the reaction was reduced to 0.21 V and the electrocatalytic current density was 43 mA cm^?2 at 1 V versus Ag/AgCl (3 M KCl) and pH 7. These results beneficially compete with previously reported electrocatalytic oxidations of water by IrO_x NPs electrodeposited onto glassy carbon and indium tin oxide electrodes and provide the basis for the further development of efficient IrO_x NP‐based electrocatalysts immobilized on high‐surface‐area carbon electrode materials.     

High Performance Oxide Functionalized Nitrogen‐Doped Mesocellular Carbon Foam for Biosensor Construction

Nitrogen‐doped mesocellular carbon foam (denoted as MCF? CN_x) with high surface area and large pore volume was prepared and characterized in detail. The MCF? CN_x was further functionalized by oxidation with HNO₃ (denoted as MCF? CN_x‐O) in order to effectively improve its hydrophilicity and biocompatibility. Both MCF? CN_x and MCF? CN_x‐O were used for immobilization of Hb and design of electrochemical biosensors. The activity of Hb immobilized on MCF? CN_x‐O is two times higher than that of Hb immobilized on MCF? CN_x. The Hb‐MCF? CN_x‐O‐Nafion modified electrode displays fast response, high sensitivity and low detection limit to the detection of hydrogen peroxide. The sensitivity of Hb‐MCF? CN_x‐O‐Nafion modified electrode (477 μA mM^?1 cm^?2) is twice that of Hb‐MCF? CN_x‐Nafion modified electrode.     

CC Coupling of N‐Heterocycles at the fac‐Re(CO)3 Fragment: Synthesis of Pyridylimidazole and Bipyridine Ligands

A new family of cationic rhenium tricarbonyl complexes with either two N‐alkylimidazole (N‐RIm) and one pyridine (Py) ligand, or two pyridine and one N‐RIm ligand, [Re(CO)₃(N‐RIm)_(3?x)(Py)_x]⁺, has been prepared. The reaction of these complexes with a strong base, followed by an oxidant, selectively afforded 2,2’‐pyridylimidazole complexes as the result of intramolecular dehydrogenative C?C coupling reactions. For tris(pyridine) complexes [Re(CO)₃(Py)₃]⁺ the reaction pattern upon a deprotonation/oxidation sequence is maintained, which allows the generation of complexes with 2,2’‐bipyridine ligands. In the particular combination of two different types of pyridine ligand in the cationic fac‐Re(CO)₃ complexes only the cross‐coupling products with asymmetric 2,2’‐bipyridine ligands were obtained; the homocoupling products were not observed.     

Fabrication of Covalently Attached Multilayer Film Electrode Containing Iron Porphyrin and Its Electrocatalysis Toward Sulfite

Construction of a highly stable covalently attached multilayer film electrode containing iron porphyrin was achieved by UV irradiation of ionic self‐assembled multilayer films of diazo‐resins (DAR) and anionic Fe(III)tetrakis(p‐sulfonatophenyl)porphyrin (FeTSPP). The multilayer films had been characterized by UV, IR spectra and cyclic valtammetry. The electrocatalytic transformation of sulfite to SO₄^2? by the multilayer film electrode containing FeTSPP was investigated. In 0.1 M NH₄OH? NH₄Cl buffer solution (pH 8.74) and 0.1 M borate buffer solution (pH 9.18) the electrocatalytic oxidation of sulfite through the multilayer film electrode can be performed. However, in acetate buffer solution (pH 4.0) the electrocatalytic reduction of sulfite by the multilayer film electrode had also good activity. The modified electrode also exhibited a fast response and good stability.     

Robust SnO2−x Nanoparticle‐Impregnated Carbon Nanofibers with Outstanding Electrochemical Performance for Advanced Sodium‐Ion Batteries

The sluggish sodium reaction kinetics, unstable Sn/Na₂O interface, and large volume expansion are major obstacles that impede practical applications of SnO₂‐based electrodes for sodium‐ion batteries (SIBs). Herein, we report the crafting of homogeneously confined oxygen‐vacancy‐containing SnO_2?x nanoparticles with well‐defined void space in porous carbon nanofibers (denoted SnO_2?x/C composites) that address the issues noted above for advanced SIBs. Notably, SnO_2?x/C composites can be readily exploited as the working electrode, without need for binders and conductive additives. In contrast to past work, SnO_2?x/C composites‐based SIBs show remarkable electrochemical performance, offering high reversible capacity, ultralong cyclic stability, and excellent rate capability. A discharge capacity of 565 mAh g^?1 at 1 A g^?1 is retained after 2000 cycles.     

Ultrathin,Porous and Oxygen Vacancies‐Enriched Ag/WO3−x Heterostructures for Electrocatalytic Hydrogen Evolution

Exploring advanced electrocatalysts for electrocatalytic hydrogen evolution is highly desired but remains a challenge due to the lack of an efficient preparation method and reasonable structural design. Herein, we deliberately designed novel Ag/WO_3?x heterostructures through a supercritical CO₂‐assisted exfoliation‐oxidation route and the subsequent loading of Ag nanoparticles. The ultrathin and oxygen vacancies‐enriched WO_3?x nanosheets are ideal substrates for loading Ag nanoparticles, which can largely increase the active site density and improve electron transport. Besides, the resultant WO_3?x nanosheets with porous structure can form during the electrochemical cycling process induced by an electric field. As a result, the exquisite Ag/WO_3?x heterostructures show an enhanced hydrogen evolution reaction (HER) activity with a low onset overpotential of ≈30 mV, a small Tafel slope of ≈40 mV dec^?1 at 10 mA cm^?2, and as well as long‐term durability. This work sheds light on material design and preparation, and even opens up an avenue for the development of high‐efficiency electrocatalysts.     

A cobalt(II) phthalocyanine with indole substituents: formation,characterization and electrocatalytic studies

Herein, we report the formation of a new cobalt(II) phthalocyanine (CoPc) containing peripheral tetra-substituted indole (CoPc-ind, 2) moieties. The derivatized phthalonitrile, 4-(indole-4-oxy)phthalonitrile (1) as well its corresponding metal complex was characterized by NMR (for 1), IR– and UV–Vis spectroscopy as well as TOF mass spectrometry and elemental analysis (for 2). The electrochemical properties of the N₄-macrocyclic metal complex were investigated using cyclic- and square-wave voltammetry as well as corroborated by UV–Vis spectroelectrochemistry. The CoPc was electrodeposited onto the surface of a Pt working electrode followed by the immobilization of multiwalled carbon nanotubes (MWCNTs) onto the modified working electrode surface. The electrocatalytic activity of the resultant modified electrode toward dopamine revealed a lower ΔE value of 80?mV versus Ag|AgCl for the modified (2-MWCNTs) Pt electrode compared to the bare Pt electrode (ΔE?=?280?mV vs. Ag|AgCl). The diffusion- and convection-controlled electron-transfer kinetics of the chemically modified electrode were evaluated by chronoamperometry and rotating disk electrode techniques. Electrochemical impedance spectroscopic studies revealed that the 2-MWCNTs Pt electrode had a lower charge-transfer resistance and a higher apparent electron-transfer rate constant.     

Preparation and Characterization of Mixed‐Valent Osmium Hexacyanoferrate/Silicomolybdate Hybrid Films and Their Electrocatalytic Properties

A polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film electrode has been prepared using repetitive cyclic voltammetry. The cyclic voltammograms have been recorded for the deposition of a mixed‐valent osmium hexacyanoferrate/silicomolybdate hybrid film directly from the mixture of Os³⁺, Fe(CN₆)^3?, and SiMo₁₂O₄₀^4? ions from the acidic aqueous solutions. The polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film exhibited four redox couples. The electrocatalytic properties of the osmium hexacyanoferrate/silicomolybdate film electrode have been studied. The modified electrode has shown good electrocatalytic properties towards the oxidation of dopamine, ascorbic acid, epinephrine, norepinephrine, and reduction of IO₃^?, Fe³⁺.     

Electrodeposition of Cobalt Oxide Nanostructure on the Glassy Carbon Electrode for Electrocatalytic Determination of para‐Nitrophenol

Cobalt oxide nanostructure (CoO_xNS) deposited on the glassy carbon (GC) electrode surface is proposed as a novel electrocatalytic system for the reduction of para‐Nitrophenol. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscopy were used for characterization of deposited CoO_xNS. CoO_xNS deposited by cycling at positive potentials (0 to +1.3 V) show less charge‐transfer resistance (Rct) and more catalytic activity for the electroreduction of p‐nitrophenol compared to those CoO_xNS obtained by scanning the applied potential throughout a negative V range. The GC/CoO_xNS electrode showed good electrocatalytic activity toward the reduction of p‐nitrophenol at different pH values.     

Synthesis of Iridium Oxide Nanotubes by Electrodeposition into Polycarbonate Template: Fabrication of Chromium(III) and Arsenic(III) Electrochemical Sensor

For the first time iridium oxide (IrO₂) nanotubes are synthesized by electrodeposition in a polycarbonate (PC) template. Potential cycling (90 cycles) between 0.0 and 0.9 V is used for the preparation of IrO_x nanotubes onto the PC template with a pore diameter of 100 nm. Field‐emission scanning electron microscopy (FESEM) images show, that IrO₂ nanotubes with uniform diameters of 110±10 nm and an estimated length of 1–3 µm are formed. The electrochemical properties and the electrocatalytic activity of a glassy carbon‐IrO_x nanotube modified electrode toward Cr³⁺ and As³⁺ oxidation are investigated. Finally, the modified electrode is used for micromolar detection of the proposed analytes using differential pulse voltammetry.     

Electrocatalytic Oxidation of Some Carbohydrates by Nickel/Poly(o‐Aminophenol) Modified Carbon Paste Electrode

This study investigates the electrocatalytic oxidation of glucose and some other carbohydrates on nickel/poly(o‐aminophenol) modified carbon paste electrode as an enzyme free electrode in alkaline solution. Poly(o‐aminophenol) was prepared by electropolymerization using a carbon paste electrode bulk modified with o‐aminophenol and continuous cyclic voltammetry in HClO₄ solution. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the capability of this modified electrode for catalytic oxidation of glucose and other carbohydrates was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for each carbohydrate were calculated. Also, the electrocatalytic oxidation peak currents of all tested carbohydrates exhibit a good linear dependence on concentration and their quantification can be done easily.     

Electroanalysis of Dopamine at RuO2 Modified Vertically Aligned Carbon Nanotube Electrode

Electrochemical behavior of dopamine at the RuO₂‐modified vertically aligned carbon nanotubes electrode was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The RuO₂‐modified carbon nanotube electrode showed higher electrocatalytic activity towards the oxidation of dopamine than the MWNTs electrode in 0.10 M phosphate buffer solution. At an applied potential of +0.4 V, the RuO₂/MWNTs electrode exhibited a wide detection range up to 3.6×10^?3 M with detection limit of 6.0×10^?8 M (signal/noise=3) for dopamine determination. Meanwhile, the optimized sensor for dopamine displayed a sensitivity of 83.8 μA mM^?1 and response time of 5 s with addition of 0.20 mM dopamine. In addition, DPV experiment revealed that interfering species such as ascorbic acid and uric acid could be effectively avoided. The RuO₂/MWNTs electrode presents stable, highly sensitive, favorable selectivity and fast amperometric response of dopamine.     

Electrochemical Properties of Th(IV)‐Hexacyanoferrate Sol‐Gel Carbon Composite Electrode: Electrocatalytic Oxidation of Dopamine and Ascorbic Acid

A new sol‐gel carbon composite electrode using hexacyanoferrate (HCF)‐Th(IV) ion pair as a suitable modifier is fabricated in the present study. The Th(IV)‐HCF‐sol‐gel carbon composite electrode (THCF‐CCE) has been prepared by mixing methyl trimethoxysilan (MTMOS) sol‐gel precursor and carbon powder with ion pair and then to fix in a plastic tube. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical and electrocatalytic properties of proposed electrode. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between ion‐pair and sol‐gel CPE were calculated as 3.10 ± 0.10 s^?1 and 0.52, respectively. The THCF‐CCE showed a significant electrocatalytic activity towards oxidation of ascorbic acid (AA) and dopamine (DA) in 0.1 M acidic phosphate buffer solutions (pH 3) containing KCl as a supporting electrolyte. The mean value of the diffusion coefficients for ascorbic acid and dopamine were found 4.12 × 10^?5 and 4.43 × 10^?5 (cm²s^?1), respectively. High stability, good reproducibility, rapid response, easy surface regeneration and fabrication are the important characteristics of the proposed sensor. The resulting peaks from the electrocatalytic oxidation of AA and DA were well resolved with good sensitivity. A linear response was observed for AA and DA in the concentration range of 1 × 10^?5 to 3 × 10^?3 M and 4 × 10^?6 to 2.2 × 10^?4 M, respectively.     

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L^?1 Ag(NH₃)₂⁺ solution, to synthesize the den‐Ag/Ti electrode. Binary Ag_xCo_y/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and Ag_xCo_y/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐Ag_xCo_y/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag₃₁Co₆₉/Ti>Ag₃₁Co₆₉/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag₃₁Co₆₉/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm^?2 at ?0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.     

Development of a Carbon Paste Electrode Modified with Reduced Graphene Oxide and an Imidazole Derivative for Simultaneous Determination of Biological Species of N‐acetyl‐L‐cysteine,Uric Acid and Dopamine

In this work, the modified carbon paste electrode (CPE) with an imidazole derivative 2‐(2,3 dihydroxy phenyl) 4‐methyl benzimidazole (DHPMB) and reduced graphene oxide (RGO) was used as an electrochemical sensor for electrocatalytic oxidation of N‐acetyl‐L‐cysteine (NAC). The electrocatalytic oxidation of N‐acetyl‐L‐cysteine on the modified electrode surface was then investigated, indicating a reduction in oxidative over voltage and an intensive increase in the current of analyte. The scan rate potential, the percentages of DHPMB and RGO, and the pH solution were optimized. Under the optimum conditions, some parameters such as the electron transfer coefficient (α) between electrode and modifier, and the electron transfer rate constant) k_s) in a 0.1 M phosphate buffer solution (pH=7.0) were obtained by cyclic voltammetry method. The diffusion coefficient of species (D) 3.96×10^?5 cm² s^?1 was calculated by chronoamperometeric technique and the Tafel plot was used to calculate α (0.46) for N‐ acetyl‐L‐cysteine. Also, by using differential pulse voltammetric (DPV) technique, two linear dynamic ranges of 2–18 µM and 18–1000 µM with the detection limit of 61.0 nM for N‐acetyl‐L‐cysteine (NAC) were achieved. In the co‐existence system of N‐acetyl‐L‐cysteine (NAC), uric acid (UA) and dopamine (DA), the linear response ranges for NAC, UA, and DA are 6.0–400.0 µM, 5.0–50.0 µM and 2.0–20.0 µM, respectively and the detection limits based on (C=3s_b/m) are 0.067 µM, 0.246 µM and 0.136 µM, respectively. The obtained results indicated that DHPMB/RGO/CPE is applicable to separate NAC, uric acid (UA) and dopamine (DA) oxidative peaks, simultaneously. For analytic performance, the mentioned modified electrode was used for determination of NAC in the drug samples with acceptable results, and the simultaneous determination of NAC, UA and DA oxidative peaks was investigated in the serum solutions, too.     

Preparation,Characterization and Electrocatalytic Studies on Copper Complex Dye Film Modified Electrodes

Copper complex dye (C.I. Direct Blue 200) film modified electrodes have been prepared by multiple scan cyclic voltammetry. The effect of solution pH and nature of electrode material on film formation was investigated. The optimum pH for copper complex film formation on glassy carbon was found to be 1.5. The mechanism of film formation on ITO seems to be similar to that on GC surface but completely different mechanism followed with gold electrode. Cyclic voltammetric features of our modified electrodes are in consistent with a surface‐confined redox process. The voltammetric response of modified electrode was found to be depending on pH of the contacting solution. UV‐visible spectra show that the nature of copper complex dye is identical in both solution phase and after forming film on electrode. The electrocatalytic behavior of copper complex dye film modified electrode towards oxidation of dopamine, ascorbic acid and reduction of SO₅^2? was investigated. The oxidation of dopamine and ascorbic acid occurred at less positive potential on film electrode compared to bare glassy carbon electrode. Feasibility of utilizing our modified electrode in analytical estimation of dopamine, ascorbic acid was also demonstrated.     

Temperature‐dependent fluorescence from pyrenyl‐modified polyethylene films. A comparison of attachment methods and morphology changes by irradiation with eV‐range photons and bombardment with MeV‐range positive ions

1‐Pyrenyl groups were attached covalently to three polyethylene ( Py–PE ) films with different crystallinities by irradiating (eV‐range photons–UV‐photons) or by bombarding (MeV‐range ions–protons and alpha particles) pyrene‐doped PE films ( Py/PE ). Onset temperatures of relaxation processes (T_x) of the Py–PE were approximated from (1) Arrhenius‐type plots of the normalized integrated intensities of the films and (2) the temperature dependence of the full‐width half‐maximum (FWHM) films and the position of the 0–0 fluorescence band. DSC thermograms of the native and irradiated or bombarded films were also compared to independently assess the morphological changes. The onset temperatures T_x in lower crystallinity Py–PE films were more difficult to locate when prepared by bombardment with high doses than with low doses of photons or ions or by irradiation. The ease of locating the T_x in higher crystallinity Py–PE films was independent of dose, suggesting little change in the mobility in the vicinity of pyrenyl probes. Fluorescence from Py–PE bombarded with alpha particles indicated the presence of both singly‐ and doubly‐attached pyrenyl groups. The singly‐attached pyrenyl groups were less sensitive than the doubly attached to the T_x. Py–PE films were more sensitive luminescence reporters of T_γ segmental motions than were 9‐anthryl groups covalently attached to the same polymers. We also discuss possible reasons why the values of the activation energies for the relaxation processes, as calculated from the Arrhenius plots, were much smaller than those based on the dynamic mechanical methods. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2957–2970, 2004     

Facile in situ Electrosynthesis and High Electrocatalytic Performance of Interconnected Layered Double Hydroxides/Graphene Hybrids for Dopamine Oxidation: A Comparative Study

We are reporting a facile in situ electrodeposition approach to prepare a rational design of M?Al (M: Ni, Co) layered double hydroxide (LDH)/reduced graphene oxide (G) hybrids and its superior electrocatalytic activity towards the electrooxidation of dopamine. Comparatively, the worm like interconnected nano‐chain networks of as‐prepared NiAl‐LDH/G hybrid modified electrode exhibits better performance than the CoAl‐LDH/G hybrid modified electrode. The enhanced electrocatalytic activity is because of its morphological evolution, which is due to its enhanced reduction rate, attachment pathway and incorporation or heterogeneous combination of Al³⁺ in the bimetallic LDHs/G hybrid. The satisfactory results are obtained for modified electrodes for the real‐time quantitative detection of dopamine in the real injectable medicine as well as human blood serum samples and it has also shown good reproducibility, stability and anti‐interference. This cost‐effective and facile in situ electrodeposition approach will give insights to design high performing hybrid materials and its application to non‐invasive electrochemical sensing which will be useful for daily diagnosis of neurological disorder.     

Synthesis,Crystal Structures,and Magnetic Properties of Two Copper(II) Radical Heterospin Complexes

Two heterospin complexes [Cu(NIT3Py)(cda)H₂O] · H₂O ( 1 ) and [Cu(NIT2Py)(cda)H₂O] · H₂O · CH₃OH ( 2 ) with Cu^II ions and pyridyl‐substituted nitronyl nitroxide radicals (NITxPy = 2‐(x′‐pyridyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide, x = 3, 2; H₂cda = 4‐hydroxy‐pyridine‐2,6‐dicarboxylic acid) were synthesized and characterized structurally and magnetically. The single crystal structures show that the two complexes are both two‐spin complexes, in which the different radicals make the two complexes have different hydrogen bonding interactions to form 2D and 1D supramolecular network for complexes 1 and 2 , respectively. The magnetic measurements indicate that complexes 1 and 2 both exhibit antiferromagnetic interactions between Cu^II and radicals.     

Highly Sensitive and Selective Determination of Dopamine in the Presence of Ascorbic Acid Using Gold Nanoparticles‐Decorated MoS2 Nanosheets Modified Electrode

Herein, a novel nanocomposite has been synthesized by molybdenum disulfide (MoS₂) nanosheets and gold nanoparticles (AuNPs) via a microwave‐assisted hydrothermal method, which possesses the specific features of both MoS₂ and AuNPs. The AuNPs@MoS₂ nanocomposite modified electrode exhibits excellent electrocatalytic activity toward dopamine (DA). Its oxidation peak current shows a linear dependence over the DA concentration in the range from 0.1 to 200 µM, with a detection limit of 80 nM (S/N=3). More importantly, the AuNPs@MoS₂‐based sensor can detect DA in the presence of a large excess of ascorbic acid. The AuNPs@MoS₂‐based sensor shows good sensitivity, reproducibility and selectivity, suggesting that the AuNPs@MoS₂ nanocomposite is a promising candidate in electrochemical sensing and other electrocatalytic applications.