Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

双水杨醛乙二胺中性载体的锰离子电极的研究

研究以双水杨醛乙二胺[BBG]为中性载体,制备了一种对锰离子(Mn2 )具有优良的电位响应特性的离子选择性电极,其选择性次序为:Mn2 >>Rb ＞Al3 ＞Ca2 ＞Bi3 ＞Cu2 ＞Co2 ＞Fe3 ＞Cd2 ＞Ba2 ＞Ce3 ＞Cr3 ＞La3 ＞Na .该电极在pH 3.0的NaOH-HNO3溶液体系中具有最佳的电位响应,在1.0×10-1mol/L～ 1.0×10-5 mol/L Mn2 浓度范围呈近能斯特响应,斜率为32.0 mV/p Mn2 (25 ℃),检测下限为8.0×10-6 mol/L.采用交流阻抗和紫外光谱分析技术研究了配合物本身的结构对电极电位响应行为的作用机理.将该电极用于实际样品的测定,获得满意的结果.     

Study of photoelectrochemical corrosion of lead oxide in alkaline solution by the rotating ring-disk electrode technique

Photoelectrochemical corrosion of n-type α-PbO electrodes in aqueous Fe(CN)₆ ^3−/4− and I⁻/I₃ ⁻ electrolytes using the rotating ring-disk electrode technique has been investigated. The α-PbO thin film is found to be more stable in I⁻/I₃ ⁻ (48%) than in Fe(CN)₆ ^3−/4− electrolyte (10%). Preferential adsorption of iodide ions decreases the photocorrosion reaction of holes with α-PbO. Addition of CsI (0.4 mM) to the I⁻/I₃ ⁻ electrolyte decreases the photocorrosion from 48% to less than 10%. Cs⁺ ions perhaps nullify the effect of negatively charged surface states of α-PbO, thus minimizing the trapping of holes at the surface of α-PbO and hence decrease the possibility of photocorrosion of lead oxide with holes. Received: 30 June 1998 / Accepted: 20 April 1999     

活化玻碳电极伏安法测定锰的研究

采用活化玻碳电极(GC)以伏安法对测定锰进行了研究。结果表明:沉积于电极表面的二氧化锰对锰(Ⅱ)的电化学氧化具有自催化作用,活化GC电极可极大地提高测定锰的灵敏度。在0.04mol LNH3 NH4Cl(pH9.0)底液中,锰浓度在6.0×10-8～1.0×10-5mol L范围内成线性关系,检出限为4.0×10-8mol L。用3×10-7mol L锰溶液重复测定9次,RSD为1.6%。     

Green oxidations. The use of potassium permanganate supported on manganese dioxide

Permanganate supported on active manganese dioxide can be used effectively for the oxidation of organic compounds under heterogeneous or solvent-free conditions. The residue that remains after extraction of the organic products, manganese dioxide, can be recycled, making the process infinitely sustainable, in theory. The use of this approach for the oxidation of arenes, alcohols and sulfides is described.     

Cathodic electrophoretic deposition of manganese dioxide films

Cathodic electrophoretic deposition (EPD) method has been developed for the deposition of manganese dioxide films. It was shown that phosphate ester (PE) is an effective charging additive, which provides stabilization of manganese dioxide nanoparticles in suspensions. The influence of PE concentration and deposition voltage on the deposition efficiency has been studied. EPD has been utilized for the fabrication of porous nanostructured films with thickness in the range of 0.5–20 μm for application in electrochemical supercapacitors (ES). Cyclic voltammetry and chronopotentiometry data for the films tested in the 0.1 M Na₂SO₄ solutions showed capacitive behavior in the voltage window of 1 V. The highest specific capacitance (SC) of 377 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness and increasing scan rate in the range of 2–100 mV s⁻¹. The deposition mechanism, kinetics of deposition and charge storage properties of the films are discussed.     

MnO_2电极上氧还原的电催化机理

研究了MnO2 催化氧还原的电催化性质 ,通过比较MnO2 的自还原和催化氧还原的相关性 ,结合极化曲线分析和中间产物检测 ,提出了氧在MnO2 上电催化机理 .根据这一机理 ,MnO2 首先还原为MnOOH ,随之氧的还原通过化学氧化MnOOH ,两者协同进行 .依此导出的极化曲线形式能够较好地解决实验中观测到的动力学特征     

Voltammetric and electrogravimetric study of manganese dioxide thin film electrodes. Part 1. Electrodeposited films

Voltammetry and electrochemical quartz crystal microbalance (EQCM) studies of MnO₂ films electrodeposited in acidic media at 85°C show the existence of matter exchange during repeated electrochemical reduction and oxidation in 1 M KOH solution. Usually, these reactions are written without mentioning the exchange of matter. The following are observed: a reversible exchange involving water between the crystal lattice and the solution within each successive sweep potential cycle; an irreversible mass loss caused by low dissolution and slow diffusion of Mn(III) and Mn(II) solubilized species; an irreversible large mass gain during the first cycle due to additional hydration of the material.     

Nafion effect on the lead dioxide electrodeposition kinetics

Electrodeposition of lead dioxide in the presence of Nafion in solution is described by a four-stage kinetic scheme. The limiting stage at low polarizations is that of the second-electron transfer, and at high polarizations, the stage of delivery of lead compounds to the electrode surface. Nafion adsorption at the oxide profoundly affects the process kinetics.     

Photoinduced redox reactions between colloidal manganese dioxide and some organic compounds of environmental importance

Numerous organic compounds of environmental importance, i.e., phenol, citric, tartaric, and oxalic acids, proved to promote or accelerate reductive dissolution of colloidal manganese dioxide upon irradiation. This is accounted for the formation of surface-located charge-transfer complexes between the MnO₂ particulates and the organic electron donors. From the dependences of the rate of the photoassisted and thermal dissolution on the concentration of the organic compounds, the equilibrium constants for the formation of these complexes have been determined in the case of phenol, resorcinol, citrate, and tartaric acid. The quantum yields for these photoinduced reactions (at λ _ir = 365 nm), however, do not show any correlation with the values of the corresponding equilibrium constants, although adsorption is prerequisite for the efficient reductive dissolution of MnO₂. The changes in pH markedly affect the rate of this process, indicating that protonation of both the electron donors and the surface of the MnO₂ particulates may play significant roles in these systems. The results of experiments carried out in manganese dioxide excess suggest that total mineralization of organic electron donors is strongly hindered by the disadvantageous adsorption properties of the primary redox products. Dedicated to Professor Janos H. Fendler on the occasion of his 70th birthday.     

Potentiometric determination of hydrogen peroxide at MnO2-doped carbon paste electrode

A novel hydrogen peroxide (H₂O₂) potentiometric sensor, made with a MnO₂-doped carbon paste electrode (CPE), is reported. Under optimum conditions, the electrode gives a Nernstian response for H₂O₂ in the concentration range 3.00×10⁻⁷–3.63×10⁻⁴ mol/l, with a slope of 21–19.4 mV/pH₂O₂ and a detection limit of 1.2×10⁻⁷mol/l H₂O₂. In addition, this sensor offers some analytical characteristics such as sensitivity, good reproducibility and a simple preparation procedure. The effects of both the components of the electrode and other conditions on the potential response of the sensor, as well as the possible response mechanism, are discussed.     

Peculiarities of metal electrodeposition inside a flow-through porous electrode with low initial conductivity in oxidant containing solution

The earlier developed dynamic model of a flow-through electrode is used for studying how the variations in initial conductivity of a porous matrix κ_s,ini and a metal deposit affect the rate of metal deposition from an oxidant-containing solution for the direct-flow operation mode of the porous electrode. It is found that in contrast to an oxidant-free solution in which the decrease of κ_s,ini improves the uniformity of deposit distribution inside the porous cathode and increases the deposit final mass m _f, the opposite situation is observed in the presence of an oxidant, namely, a decrease in κ_s,ini, under otherwise similar conditions reduces the deposit mass and leads to its specific spatial distribution. The final metal deposit is divided into two separate fragments (rear and front) with a region of low conductivity of the initial porous matrix in between. Dynamics of the current and metal redistribution within the porous electrode, the reasons for the formation and stabilization of the rear fragment of coating, the correlation between the metal deposition rate and changes in the anodic zone position and intensity are discussed. It is shown that with the appearance of a specific profile of deposit distribution, the dependence of m _f on the metal conductivity develops a limit that differs considerably from the deposit final mass for an equipotential porous electrode.     

Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

一种新型PbO2电极的研制

Pb O2 电极的制备一般有化学法和电解法 [1] .在 Pb O2 电极制作中基体的选择最为重要 ,石墨、金属、金属氧化物等均可作为基体 ,其中 Ti基体应用较多 ,但由于 Ti的膨胀率与 Pb O2 相差较大 ,而多用于 Sn O2 电极的制作 [2 ] .Pb O2 的沉积层有α和β型 2种 ,在碱性溶液中进行电沉积 ,一般只沉积α型结晶 ,它比β型沉积层牢固 ,但导电性、耐腐蚀性较差 .因此 ,在实际应用过程中可用 α- Pb O2 为中间层 ,用 β- Pb O2 为外层 .由于 α和 β型镀层内部都存在电积畸变 [3 ] ,若控制电沉积条件 ,使 α型不会产生电积畸变 ,作为中间层 ,…     

The rotating ring-disk electrochemistry of the copper(II) complex of thyrotropin-releasing hormone

Thyrotropin-releasing hormone (TRH) forms an electroactive Cu(II) complex in aqueous solution. Rotating ring-disk electrochemistry reveals oxidation at the disk electrode and reduction at the ring electrode. The plot of limiting current vs. square root of rotation frequency deviates from the Levich equation, indicating both preceding and following chemical reactions. The reaction following the oxidation is a multiple-electron ECE-type of process that has been seen before in Cu(II)–peptide electrochemistry. The preceding reaction is unusual. The deviation from diffusion-controlled behavior is more pronounced at higher initial concentration of Cu(II) and peptide. We propose that a non-electroactive dimer, Cu(II)₂–TRH₂, is in a slow equilibrium with the electroactive Cu(II)–TRH. Simulation of the RRDE behavior of the postulated Cu(II)–TRH system has succeeded in matching experimental data. Capillary electrophoresis indicates that there is a negative charge on the dimer. It is suggested that a hydroxo-bridge may link the two Cu(II) centers. Calculations verify that bi-nuclear Cu(II)₂–TRH₂ complexes are possible.     

A novel Mn PVC membrane electrode based on a recently synthesized Schiff base

A new PVC membrane electrode for manganese(II) ion based on a recently synthesized Schiff base of 5-[(4-nitrophenylazo)-N-hexylamine]salicylaldimine is reported. The electrode exhibits a Nernstian response for Mn²⁺ ions over a wide concentration range (4.0 × 10⁻⁷ to 1.8 × 10⁻² mol L⁻¹) with a slope of 30.1 (±1.0). The limit of detection is 1.0 × 10⁻⁷ mol L⁻¹. The electrode has a fast response time (∼10 s), a satisfactory reproducibility and relatively long life time. The proposed sensor revealed good selectivities over a wide variety of other cations include hard and soft metals. This electrode could be used in a pH range of 4.5-7.5. It was used as an indicator electrode in potentiometric titration of manganese(II) ions with EDTA solution.     

The processes involved in the Se electrodeposition and dissolution on Au electrode: the H<Subscript>2</Subscript>Se formation

The processes involved in the Se electrodeposition, mainly the one related to the formation of H₂Se species on Au electrode in perchloric acid solutions, have been investigated through cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), rotating ring-disc electrode (RRDE), and atomic force microscopy (AFM) techniques. In the experiments performed with the EQCM, with the potential sweep in the negative direction, the responses for the mass variation were divided in three well-defined potential regions: A (from 1.55 to 0.35 V), B (from 0.35 to −0.37 V), and C (from −0.37 to −0.49 V). It was verified that the following processes can occur, respectively: the species (AuO)₂H₂SeO₃ was desorbed during the AuO reduction, the reduction of Se(IV) to Se(0), and the formation of H₂Se. When the potential was swept in the positive direction, the responses for the mass variation were divided in four well-defined potential regions: D (from −0.49 to 0.66 V), E (from 0.66 to 0.99 V), F (from 0.99 to 1.26 V), and G (from 1.26 to 1.55 V), and the described processes in these regions were, respectively: the Se deposition and adsorption of water molecules and/or perchlorate ions, the Se dissolution, the Se incorporating mass in the form of HO–Se, and the Au oxidation (all potentials are referred to the Ag/AgCl electrode). Making use of the RRDE, using the collection technique, the formation of H₂Se species during the Se electrodeposition was investigated. Therefore, it was confirmed that this species is formed on the disc electrode between −0.3 and −0.55 V vs the Ag/AgCl potential range (collecting the oxidized compound onto the ring electrode). AFM images also indicated that the surface topography of the Se-massive deposit on Au is different from the images registered after the formation of H₂Se species, confirming the cathodic stripping of Se.     

Voltammetric determination of catechol using a sonogel carbon electrode modified with nanostructured titanium dioxide

In this study, we investigate highly efficient sonogel carbon electrode (SGC/TiO₂) modified with nanostructured titanium dioxide synthesized via sol-gel method employing surfactant template for tailor-designing the structural properties of TiO₂. The stable SGC/TiO₂ electrode detects catechol, a neurotransmitter, in the presence of ascorbic acid, a common interferent, using cyclic voltammetry. A possible rationale for the stable catechol detection of SGC/TiO₂ electrode is attributed to most likely the adsorption of catechol onto highly porous TiO₂ (surface area of 147 m² g⁻¹ and porosity of 46.2%), and the formation of C₆H₄(OTi)₂ bond between catechol and TiO₂. The catechol absorbed onto TiO₂ rapidly reaches the SGC surface, then is oxidized, involving two electrons (e⁻) and two protons (H⁺). As a result, the surface of TiO₂ acts as an electron-transfer accelerator between the SGC electrode and catechol. In addition to the quantitative and qualitative detection of catechol, the SGC/TiO₂ electrode developed here meets the profitable features of electrode including mechanical stability, physical rigidity, and enhanced catalytic properties.