Anodic, cathodic and cyclic voltammetric deposition of ruthenium oxides from aqueous RuCl3 solutions

Anodic, cathodic and cyclic voltammetric (CV) deposition of ruthenium oxides from aqueous RuCl₃ solutions have been investigated using stationary and rotating disk electrodes (RDE) in this work. The CV deposition behavior was examined using a RDE to differentiate the contribution of current from the reactions of ruthenium ions in the electrolyte and ruthenium oxides already adsorbed on the electrode. The results indicate that the CV growth of ruthenium oxides within the potential range of aqueous electrolyte decomposition is attributed to the anodic oxidation of ruthenium ions in the electrolyte. Cathodic deposition occurs only at potential negative than −0.30 V versus saturated calomel electrode (SCE) when H₂ evolves on the electrodes. Anodic deposition of ruthenium oxides can be obtained effectively in the potential range of ca. 0.9-1.1 V versus SCE, depending on the pH value of the electrolyte. The optimum anodic and cathodic deposition potential for maximum deposition efficiency is 1.0 and −0.9 V versus SCE, respectively, in the electrolyte solution of pH 2.     

Polyaniline-deposited porous carbon electrode for supercapacitor

Electrodes for supercapacitors were fabricated by depositing polyaniline (PANI) on high surface area carbons. The chemical composition of the PANI-deposited carbon electrode was determined by X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of electrodes. An equivalent circuit was proposed to successfully fit the EIS data, and the significant contribution of pseudocapacitance from PANI was thus identified. A comparative analysis on the electrochemical properties of bare-carbon electrodes was also conducted under similar conditions. The performance of the capacitors equipped with the resulting electrodes in 1 M H₂SO₄ was evaluated by constant current charge-discharge cycling within a potential range from 0 to 0.6 V. The PANI-deposited electrode exhibits high specific capacitance of 180 F/g, in comparison with a value of 92 F/g for the bare-carbon electrode.     

Electrochemical fabrication of self assembled monolayer using ferrocene-functionalized gold nanoparticles on glassy carbon electrode

Electrochemical (EC) quantification of 11-Mercaptoundecylferrocene (thiolated-ferrocene substrate, Fc-SH) onto gold nanoparticles (AuNPs) was carried out through cyclic voltammetric (CV) investigations in different base electrolyte aqueous media on glassy carbon (GC) electrode. The electrochemical data including peak current, peak potential values revealed the Fc-SH–AuNPs redox system to be adsorption controlled in terms of self assembled monolayers (SAMs). The electrochemically generated SAMs were found quite stable as these maintained the redox activity upto 3 months after repeated CV scans at 298 K. The overall output of this research can be utilized in two ways: application of electroactivity and stability of these SAMs in detection of biologically important molecules and also towards the development of EC biosensors.     

Facile synthesis and electrochemical capacitance of composites of polypyrrole/multi-walled carbon nanotubes

Composites of polypyrrole (PPy) and multi-walled carbon nanotubes (MWCNTs) were synthesized by a facile method involving one-step electrochemical deposition from a thin-layer of ionic liquid solution attached on a glassy carbon electrode. The morphology of the composites was characterized by field emission scanning electron microscopy, and the capacitance properties were investigated by cyclic voltammetry (CV). The charge-discharge behavior of the composites prepared in this work was examined by chronopotentiometry at a constant current density for multi-cycle scans. The results show that the PPy/MWCNT composites have a porous 3D nanostructure, with high specific capacitance (SC) of 890 F/g (for the mass of the PPy in the composites) calculated from CV at 2 mV/s in 1.0 M KCl. The stability of the composites in 1.0 M KCl electrolyte was also examined by multi-cycle CV and only 9% decrease of SC value was observed for the 1000 cycles.     

Nickel foam and carbon felt applications for sodium polysulfide/bromine redox flow battery electrodes

The first use of nickel foam (NF) as electrocatalytic negative electrode in a polysulfide/bromine battery (PSB) is described. The performance of a PSB employing NF and polyacrylonitrile (PAN)-based carbon felt (CF) as negative and positive electrode materials, respectively, was evaluated by constant current charge-discharge tests in a single cell. Charge/discharge curves of the cell, positive and negative electrodes show that the rapid fall in cell voltage is due to the drop of positive potential caused by depletion of Br₂ dissolved in the catholyte at the end of discharge. Cell voltage efficiency was limited by the relatively high internal ohmic resistance drop (iR drop). Polarization curves indicated that both NF and CF have excellent catalytic activity for the positive and negative redox reactions of PSB. The average energy efficiency of the single cell designed in this work could be as high as 77.2% at 40 mA cm⁻² during 48 charge-discharge cycles.     

稻壳基活性炭电极材料制备及其电化学性能研究

以稻壳为原料,氢氧化钠为活化剂,制备活性炭.进一步将该活性炭作为电极材料,以氢氧化钾溶液为电解液,组装超级电容器.采用X射线衍射(XRD)、氮气吸附脱附(BET)、扫描电镜(SEM)等手段,分析了不同活化温度对活性炭的比表面积及孔结构的影响,并利用恒流充放电、循环伏安等方法研究了电容器的电化学性能.结果表明:800 ℃活化下活性炭的比表面积最佳,为2760 m2/g,孔结构发达.此条件下,在6 mol/L的KOH电解液中,活性炭电容器比电容达267.2 F/g,等效内阻仅2.2 Ω,倍率性能好.经过5000次循环后,其电容保持率仍有83.7%,表明该稻壳基活性炭电极具有优异的充放电可逆性和循环稳定性.     

The transient and stationary behaviour of first-order catalytic mechanisms at disc and hemisphere electrodes

The voltammetric response of a first-order catalytic mechanism at disc electrodes has been studied under transient and stationary conditions and compared with that obtained at spherical electrodes. From the analytical solutions here presented we demonstrate that the expression for the current is given by the product of a potential-dependent function and a function of time, the electrode size, shape, and the chemical kinetics. This fact is physically insightful since it shows that the dimensionless current–potential curve is independent of time, the geometry of the electrode and the chemical kinetics, being identical to that corresponding to a reversible E mechanism both under transient and stationary conditions. Analytical equations for a catalytic mechanism at disc electrodes were only available under limiting current conditions.The steady state cyclic voltammetric response is also analyzed, describing three different situations where a time-independent response is attained in function of the electrode size and the kinetics of the regeneration reaction. Necessary and sufficient mathematical conditions to obtain constant equivalence relationships in voltammetric techniques at electrodes of any geometry are given and applied to the time-independent voltammetric curves obtained for a first-order catalytic mechanism at disc and hemispherical electrodes of any size.     

Study of the formation of a solid electrolyte interphase (SEI) in ionically crosslinked polyampholytic gel electrolytes

An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate with acrylic acid. A novel ionically crosslinked polyampholytic gel electrolyte was prepared through the free radical copolymerization of the ionic complex and acrylamide in a solvent mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1:1:1, v/v) containing 1 mol/L of LiPF₆. The impedance analysis indicated that the ionic conductivity of the polyampholytic gel electrolyte was rather close to that of solution electrolytes in the absence of a polymer at the same temperature. The temperature dependence of the conductivity was found to be well in accord with the Arrhenius behavior. The formation processes of the solid electrolyte interphase (SEI) formed in both gel and solution electrolytes during the cycles of charge-discharge were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry curves show a strong peak at a potential of 0.68 V and an increase of the interfacial resistance from 17.2 Ω to 35.8 Ω after the first cycle of charge-discharge. The results indicate that the formation process of SEI formed in both gel and solution electrolytes was similar which could effectively prevent the organic electrolyte from further decomposition and inserting into the graphite electrode. The morphologies of SEI formed in both gel and solution electrolytes were analyzed by field emission scanning electron microscopy. The results indicate that the SEI formed in the gel electrolyte showed a rough surface consisting of smaller solid depositions. Moreover, the SEI formed in the gel electrolyte became more compact and thicker as the cycling increased.     

A rechargeable redox battery utilizing ruthenium complexes with non-aqueous organic electrolyte

A new-type redox battery has been developed. Some ruthenium complexes in organic electrolyte solution were utilized as the electrode active materials. A single cell consisting of [Ru(bpy)₃]²⁺ complex in acetonitrile solution had an open circuit voltage of 2.6 V and a discharge current of 5 mA cm^–2 (at a smooth carbon electrode). The characteristics of this type of cell were much influenced by such factors as the diaphragm material and the concentration of the complex. A cell with flowing electrolyte was also constructed and its charge-discharge performance was examined.     

An investigation of the interface between graphite and beta/beta″ alumina

The anodic degradation of beta/beta″ alumina of different compositions was investigated by voltammetric techniques in cells of the type Cu/Rodar alloy/carbon fibers/graphite layer/solid electrolyte/NaNO₃/Pt/Cu at 350°C. The possibility was evaluated if the voltammetric results are useful as a diagnostic tool for the prediction of the failure of beta/beta″ alumina electrolytes in sodium sulfur cells. Single voltage sweeps were applied into the anodic and also the cathodic direction at relatively low sweep rates (0.1-100mV s⁻¹), starting at the open circuirt voltage and extending to different voltages of reversal. The anodic current-voltage curves display a continuous rise of current with voltage up to 4.5 V, vs a Na reference electrode, followed by a gradual decrease afterwards. The anodic current is mainly attributed to the formation of sodium carbonate and carbon monoxide. The oxygen is supplied by the degradation of the solid electrolyte. The cathodic current-voltage curves reveal the intercalation of sodium into the graphite Structural studies of specimens from the solid electrolyte were carried out by electron microscopy before and after the electrochemical runs. They yielded information on how the anodic degradation proceeds with time.     

Electrochemical performances of nanostructured vanadium oxides

Vanadium oxide nanotubes (VOx-NTs) and nanourchin (4-phenylbutylamine/vanadium oxide) have been synthesized via one-step hydrothermal treatment. Compounds were analyzed through X-ray powder diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV curves illustrate reversible redox behavior with charge-discharge cycling corresponding to the reversible lithium intercalation/deintercalation. The EIS spectra were carried out in order to investigate the Li⁺ insertion mechanism at the electrode/electrolyte interface and evaluate the diffusion of Li⁺ within the bulk of cathode material.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

Electrospun PVdF-based fibrous polymer electrolytes for lithium ion polymer batteries

This paper discusses the preparation of microporous fibrous membranes from PVdF solutions with different polymer contents, using the electrospinning technique. Electrospun PVdF-based fibrous membranes with average fiber diameters (AFD's) of 0.45-1.38 μm have an apparent porosity and a mean pore size (MPS) of 80-89% and 1.1-4.3 μm, respectively. They exhibited a high uptake of the electrolyte solution (320-350%) and a high ionic conductivity of above 1 × 10⁻³ s/cm at room temperature. Their ionic conductivity increased with the decrease in the AFD of the fibrous membrane due to its high electrolyte uptake. The interaction between the electrolyte molecules and the PVdF with a high crystalline content may have had a minor effect on the lithium ion transfer in the fibrous polymer electrolyte, unlike in a nanoporous gel polymer electrolyte. The fibrous polymer electrolyte that contained a 1 M LiPF₆-EC/DMC/DEC (1/1/1 by weight) solution showed a high electrochemical stability of above 5.0 V, which increased with the decrease in the AFD The interfacial resistance (R_i) between the polymer electrolyte and the lithium electrode slightly increased with the storage time, compared with the higher increase in the interfacial resistance of other gel polymer electrolytes. The prototype cell (MCMB/PVdF-based fibrous electrolyte/LiCoO₂) showed a very stable charge-discharge behavior with a slight capacity loss under constant current and voltage conditions at the C/2-rate of 20 and 60 °C.     

Electrochemical supercapacitor material based on manganese oxide: preparation and characterization

A novel class of electrochemical supercapacitor electrode material has been electrochemically synthesized from a manganese halide complex in water-containing acetonitrile electrolyte at room temperature. This material has been physically and chemically characterized by scanning electron microscopy, X-ray photoelectron microscopy (XPS), FT-Raman microscopy and cyclic voltammetry. XPS and FT-Raman characterization suggest that this material is composed of manganese oxide with a chemical composition of Mn₃O₄ and containing a moderate amount of carbon. Cyclic voltammetric characterization indicates that this material has higher electronic conductivity than usually seen for manganese oxide and that it shows fast kinetics for the charge-discharge process in both aqueous and acetonitrile electrolytes. The material provides a large pseudocapacitance over a potential window of about 1 V in aqueous electrolyte and about 2 V in acetonitrile electrolyte. It is therefore a good candidate as a material for an electrochemical supercapacitor electrode.     

Interfacial synthesis of porous MnO2 and its application in electrochemical capacitor

In this paper, the porous manganese dioxide (MnO₂₎ was prepared by an interfacial reaction of potassium permanganate in water/ferrocene in chloroform. The surface area and pore distribution of MnO₂ can be controlled by simply adjusting the reaction time and the content of surfactant in the aqueous phase. The electrochemical performance of the prepared MnO₂ was evaluated as an electrode material for supercapacitors by the means of cyclic voltammetry and galvanostatic charge-discharge tests. Electrochemical tests results indicated that the pore size plays an important role at high charge-discharge rate, the sample with a large pore size shows a better rate capability, while the sample with a small pore size but large surface area delivers a large capacitance at low current rate.     

Calculation of ohmic resistance effects in rectangular electrodes of finite thickness

The current distribution in electrochemical cells consisting of parallel rectangular plates is determined. The calculations involve the evaluation of the appropriate analytical solution of Laplace's equation within the electrodes and electrolyte, with boundary conditions corresponding to potential continuity (primary current distribution) or linear electrode kinetics (secondary current distribution) at the electrode-electrolyte interface, and do not make the usual assumption that current flow in the resistive electrode is one-dimensional. The current distributions are given in the form of Fourier series that allow the effects of electrode resistance and electrical contact geometry to be determined.     

Modeling on lithium insertion of porous carbon electrodes

MCMBs with different crystal structure were tested for an anode of lithium ion batteries (LIB) and the model describing the behavior of porous anodes was simulated numerically by using orthogonal collocation method (OCM). Kinetic parameters such as diffusion coefficients, exchange current densities, and transfer coefficient, describing electrochemical intercalation system of lithium ions, were estimated by fitting the experimental cyclic voltametry (CV) results with the theoretical ones. It was investigated that the theoretical cyclic voltamograms obtained using above parameters fitted well with the experimental curves for the various scan rates from 1 mV s⁻¹ to 5 μV s⁻¹. The parameters were then evaluated on their extended application in various C-rate-charge/discharge cycling tests with showing good agreements between experiments and simulations. As the results show, it was found that numerical simulations based on both potentiometry and galvanometry experimental data resulted in more accurate parameters of electrochemical system. Simulations indicate there exist the optimum design conditions of electrode and separator to obtain the good performance of lithium ion batteries.     

Mechanism of potentiostatic deposition of MnO2 and electrochemical characteristics of the deposit in relation to carbohydrate oxidation

Cyclic voltammetric (CV) and chronoamperometric (CA) studies on potentiostatic deposition of MnO₂ on Pt from Mn(II) solution in very weakly alkaline media show the process to be controlled by a one-electron transfer step, which means that the deposition proceeds through the generation of Mn(III). The electrocatalytic activity of the deposited electrode towards carbohydrate oxidation is found to be maximum at an optimum amount of deposition. Chronopotentiometric (CP) and CV measurements show that the oxidation of carbohydrates on the deposited electrodes follows a catalytic EC (electrochemical-chemical) mechanism via electrolytic formation of Mn(V) and its subsequent consumption either by disproportionation or by chemical reaction in the presence of carbohydrates. The rate constants of the reaction of Mn(V) with dextrose and fructose have been obtained from CA results. The relative order of the oxidation currents for dextrose and fructose as well as their dependence on carbohydrate concentration has been discussed. Replacement of Pt by carbon as the electrode support material does not affect the electrocatalytic activity of the MnO₂ deposit. The observed linear variation of the steady state oxidation currents with carbohydrate concentration can be exploited for analytical application.     

Electrochemical properties of carbide-derived carbon electrodes in non-aqueous electrolytes based on different Li-salts

Electrochemical characteristics of carbide-derived micro/mesoporous carbon material C(TiC) (prepared from TiC) have been studied in 1 M LiClO₄, 0.5 M LiClO₄ + 0.5 M LiPF₆, and 1 M LiPF₆ electrolyte solutions in ethylene carbonate–dimethyl carbonate solvent mixture (1:1 by volume), by using cyclic voltammetry (CV), constant current charge/discharge and electrochemical impedance spectroscopy (EIS). Region of ideal polarizability, values of series capacitance and resistance, charge transfer resistance and capacitance, and other characteristics dependent on the electrolyte anion chemical composition have been established. The dependence of Li⁺ ion intercalation characteristics and solid electrolyte interface (SEI) formation on the salt anion composition have been established and discussed. It was found that the three electrolytes studied are comparatively weak candidates for long-lasting high energy and power density supercapacitors.     

Morphology- and magnetism-controlled electrodeposition of Ni nanostructures on TiO2 nanotubes for hybrid Ni/TiO2 functional applications

We investigate magnetic properties of nickel nanoparticles electrodeposited on TiO₂ nanotubes by different techniques including direct current (DC) and cyclic voltammetry (CV) deposition. TiO₂ nanotubes were fabricated by anodic oxidation from an organic electrolyte under constant voltage on Ti substrates. Using scanning and transmission electron microscopies, we observe that each technique provides different morphologies: DC electrodeposition makes large coalesced Ni nanoparticles mostly accumulated on top surface and mouths of the nanotubes, whereas CV deposition produces a homogenous dispersion of Ni nanoparticles across the nanotubes. The variation of coercivity and saturation magnetization values recorded is consistent with our scenario, though owing to large number of nanoparticles with size and shape varieties. The first order reversal curve (FORC) diagrams help to reveal the magnetic behavior of nanoparticle ensembles in relation to their morphology and crystal structure.