The problem of nonuniformity of pore filling in the template synthesis of nanowires is considered. The effect of the applied gradient of temperature on the instability of pore filling is analyzed. The model proposed takes into account the presence of outer thermal boundary layer and outer diffusion layer. The metal electrodeposition in porous template under the quasi-steady-state conditions is considered. The role of the temperature dependences of the exchange current density and the diffusion coefficient of metal cation is revealed. The deposition modes at which the initial dispersion of nanowire lengths can be reduced are determined.
The mass transfer during the nanowire formation by the metal electrodeposition into the pores with a high aspect ratio from a binary electrolyte is studied theoretically. The application of quasi-steady-state approximation is justified. The equations for the ion concentration and electric potential at the bottom and in the mouth of the pores, the reaction overpotential, and the variation of the current density with time are obtained. The problem of time dependence of unfilled pore part length is solved numerically. The distinctions between the results obtained under the potentiostatic and galvanostatic conditions are demonstrated.
Charge-discharge processes of supercapacitor with carbon black KJEC 600/Li in non-aqueous electrolyte: 1 M LiPF6 in a mixture of ethylene carbonate (1/3), diethyl carbonate (1/3), dimethyl carbonate (1/3) are investigated. Galvanostatic cycling was carried out in the range from 1 to 4 V with currents from 100 to 5000 mA/g of carbon black. The maximum discharge capacity of 196 F/g has been reached. The porous structure and hydrophilic-hydrophobic properties of carbon black KJEC 600 were investigated by the standard contact porosimetry method (MSCP). The following values were obtained: total specific surface area of 2500 m2/g, total porosity of 7.8 cm3/g, hydrophilic porosity of 4.9 cm3/g, hydrophobic porosity of 2.9 cm3/g. The obtained experimental dependence of the energy efficiency has a maximum (80%) at a current of 250 mA/g. Mathematical modeling of charge-discharge processes of the supercapacitor is developed with taking into account the charging of the double electric layer (EDL) and adsorption of lithium ions according to the Butler-Volmer equation and the Frumkin isotherm for the carbon electrode are taken into account. From the comparison of the calculated and measured charge-discharge curves it follows that these curves are satisfactorily consistent with each other, which indicates the correctness of the model. The density of the exchange current and the specific capacitance of the EDL refereed to the true surface found by the fitting are equal to i0,ad = 2.8 × 10−29A/сm2 and Cdl = 3.5 μF/сm2 respectively.
On the basis of the developed model for different specific currents the energy efficiency dependences on the exchange current density of the adsorption reaction were calculated. Interestingly, these dependencies have a minimum. Based on the model, the profiles of the potential the surface coverage of lithium ions were also calculated.
In this work we analyze the applicability limits of the rotating ring-disk electrode (RRDE) technique for
quantifying the amount of oxygen produced during the oxygen evolution reaction (OER). We utilize a
state-of-the art IrO2 oxide as a carbon-free OER catalyst and La1xSrxMn0.5Co0.5O3d, x . 0.25 and 0.5
perovskites, which are studied in the presence of carbon. RRDE experiments are performed at different
IrO2 loadings under both potentiodynamic and potentiostatic modes. The experimental data allow us to
formulate the requirements to the experimental conditions necessary to avoid underestimation of the
A simple model of electrochemical growth of nanowires in the pores of anodic aluminum oxide (AAO) template is developed. The metal deposition is considered at various overpotentials. The model takes into consideration the ionic transfer both in the varying diffusion layer in the pores and in the diffusion layer above the template, which is determined by the external hydrodynamic conditions. The model takes into account the kinetics of electrochemical reaction by means of the Tafel equation and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. The analytical solution of the problem with several simplifications yields the equations for calculating the time dependence of current, the pore filling time, and other parameters of the process. An example of the application of the model for the analysis of nanowire growth in the template pores is compared with the experimental data showing good agreement.
A model of inhomogeneous pores filling during electrodeposition of ordered metal nanowire arrays isdeveloped. The model takes into consideration the ionic transfer both in the varying diffusion layer in thepores and in the diffusion layer above the template, which is determined by the external hydrodynamicconditions. The model takes into account the kinetics of electrochemical reaction (the Tafel equation)and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. In the quasi-steady-state approximation, two problems were considered. The problem for the case that the initiallength of one pore differs from that of all other pores is solved analytically. The problem for the case thatthe initial lengths of all pores are different is solved numerically. The time dependences of unfilled porelength are obtained for various overpotentials and various initial distributions of pore length. It is foundthat the pores filling inhomogeneity increases with increasing overpotential.
The six new bis(4-cyano-1-pyridino)alkanes derivatives with different alkyl chain length (n = 2-6) and cyanometallate anions ([Fe(CN)(6)](3) , [Co(CN)(6)](3) , [Fe(CN)(4)(CNH)(2)](2) and [Fe(CN)(6)](4) ) have been synthesized and characterized by 1H-NMR, single-crystal X-ray analysis and UV-vis spectroscopy. The electroreduction of the obtained compounds under potentiostatic conditions (E-1 = -0.75 V) and further electrode stabilization at E-2 = 0V resulted in the deposition of polyviologen films. The current efficiency of electropolymerization was found to increase with varying the counter anion in the row: [Fe(CN)(6)](3) < Br < [Co(CN)(6)](3) similar to [Fe(CN)(6)](4) . Analysis of cyclic voltammograms and EDX data demonstrated the simultaneous incorporation of [Fe(CN)(6)](4) and K+ ions into poly(pentyl-viologen) film during electropolymerization, and further expulsion of K+ ions during the film stabilization at E-2 = 0V. The electropolymerization efficiency was found to increase with increasing the alkyl chain length, resulting in the formation of polyviologen film with higher content of dimer form of viologen cation radical.
Non-turnover voltammetry is a sensitive tool to characterize the electrochemical properties of redox proteins. However, the catalytically competent oxidation states of most peroxidases do not display the required electrochemical reversibility. In this report, we circumvent this limitation and exploit the voltammetric response associated with the Fe(III)/Fe(II) redox couple of tobacco peroxidase to probe the energetics and electronic connectivity of the heme pocket. We have applied this approach to rationalize the previously reported influence of the immobilization protocol on the electrocatalytic activity of tobacco peroxidase. To decouple proton and electron transfer steps, measurements have been carried out over the 3 ≤ pH ≤ 9 range and a 1e − /2H + ladder scheme has been adopted for their analysis. At each pH, thermodynamic and kinetic parameters associated with the Fe(III)/Fe(II) redox conversion were determined as a function of temperature in the 0-30 °C range. Reduction entropies and reorganization energies displayed different values for covalently immobilized and physisorbed enzymes, pointing to a larger involvement of the solvent in the last case. These findings, together with a larger electronic coupling between the prosthetic group and the electrode, are indicative of a partial denaturation of the physisorbed enzymes as the origin of their lower electrocatalytic activity.
We propose and develop a classical density functional theory for the description of a minor amount of water dissolved in ionic liquid in the vicinity of an electrode. In addition to the electrostatic energy and lattice-gas mixing entropy terms, the utilised grand canonical potential contains several phenomenological terms/parameters that describe short-range interactions between ions of ionic liquid, water molecules and the electrode. Some of these have been earlier introduced in the theory of electrical double layer in pure ionic liquids. Based on this, we investigate the role of the remaining ’specific interaction’ parameters e those that characterize possible (i) specific interaction of ions and molecules with the electrode, which are responsible for their specific adsorption; and (ii) hydrophilicity/hydrophobicity of ions. As a result we obtain water electrosorption isotherms as a function of the potential drop across the electrical double layer, investigate its asymmetry with respect to the sign of electrode potential, and establish the relationship between the sign of this asymmetry and hydrophobicity/hydrophilicity of cations and anions. We also calculate the effect of water electrosorption on the double layer differential capacitance which brings clear new features to its voltage dependence, some of which have been already experimentally observed.