Ali Eftekhari

Abstract: A homotopy perturbation method (HPM) is proposed to solve non-linear systems of second-order boundary value problems. HPM yields solutions in convergent series forms with easily computable terms, and in some cases, yields exact solutions in one iteration. Moreover, this technique does not require any discretization, linearization or small perturbations and therefore reduces the numerical computations a lot. Some numerical results are also given to demonstrate the validity and applicability of the presented technique. The results reveal that the method is very effective, straightforward and simple. © 2008 Elsevier Ltd. All rights reserved.

Abstract: In order to study the effects of seedling age and planting spaces on yield and yield components of rice (Neda Variety) a field experiment was carried out in field of Ghaemshahr Azad University. Experimental design was arranged in split plot in basis of Randomized Completely Block design with four replication. Some agronomical traits such as total tiller number, fertile tiller number, panicle number per m2, total spikelet per panicle, total strile spikelet per panicle, 1000 grains weight and grain yield were measured. Results showed that the effect of seedling age on total tiller number and panicle number per m2 was significant at 0.01 probability level. Also seedling age had a significant effect on fertile tiller number at 0.05 probability levels. Planting spaces had a significant effect on total tiller, fertile tiller, panicle per m2, total spikelet per panicle and grain yield, when the age of seedling is less than optimum, the tender seedlings may die in greater number due to high temperature and ultimately the plant population is reduced. For this variety transplanting in seedling age at 25 day and 15x15 cm planting space for the best performance of yield attributes were recommended. © 2007 Asian Network for Scientific Information.

Abstract: The influence of phase transformation-induced plastic deformation in Pd|H system on the electrode surface was investigated. Since the Pd surface is subject of severe plastic deformation during this process, the structure and roughness of the electrode surface significantly change. Quantitative analysis of the electrode surfaces for comparative study of such changes is a valuable tool to inspect the plastic deformation induced. Fractal dimension can be used as a quantitative measure for this purpose. Since inappropriate methods may lead to significant errors, an appropriate approach was proposed for the determination of fractal dimensions in such systems. It was demonstrated that the surface roughness generated is mainly due to the plastic deformation induced, not the other side processes, as the electrodes were coated with a uniform layer of gold with thickness smaller than 10 nm. Since plastic deformation is due to hydrogen insertion/extraction and occurs in atomic-scale, it is necessary to divide structural changes appeared in nano- and micro-scale. © 2006 Elsevier B.V. All rights reserved.

Abstract: Simultaneous chemical and electrochemical polymerization of aniline was investigated to explore the competition between two polymerization routes. It was found that initial chemical polymerization may significantly affect the electrochemical polymerization; thus, it is possible to control the polymer morphology. By performing the electropolymerization with slow scans, the initial chemical polymerization results in the formation of a nanostructured backbone, which will also affect subsequent electropolymerization (even in the absence of chemical polymerization). By this trick, it is possible to prepare highly porous and uniform nanostructured polyaniline film adherently attached to the substrate surface. In fact, chemically synthesized polyaniline nano-particles acts as growth sites for electrochemical polymerization, and in appropriate condition, numerous sites are formed instead of their continuous growth. © 2006 The Society of Polymer Science.

Abstract: Surface morphologies of thin films of polypyrrole doped with two similar anions (with different ionic radii) viz. chloride and bromide were compared by means of fractal geometry. Scanning electron micrographs of the polymer surfaces showed a significant difference between the surface structures of two anion-doped polypyrrole films in microscale and particularly in nanoscale. Surprisingly, the bromide-doped polypyrrole had nanostructure; whereas, the chloride-doped polypyrrole surface was smooth in nanoscale. An electrochemical method based on gold-masking approach was employed to reveal the fractality of these polymer surfaces in microscale. Fractal geometry successfully discovered the effect of anion doping on microstructure of the conductive polymer by suggesting different fractal dimensions. In addition, SAXS analysis indicated significant difference in fractality of the polymer in nanoscale. © 2006 The Society of Polymer Science.

Abstract: Electrochemical polymerization of aniline on the surface of a plastically deformed Pd electrode was investigated. Initially, the Pd electrode was subject of plastic deformation as a result of hydrogen insertion/extraction. Plastically deformed structure of the substrate has a significant influence on the electropolymerization process. In this case, an adherent film with smooth surface is formed. Although the plastically deformed surface is rougher than the conventional Pd surface, the polyaniline film electropolymerized is smoother in both micro- and nano-scale. This is of particular interest for applied purposes, as it guarantees higher stability of the conductive polymer. In addition, these results indicate the importance of surface structure of substrate electrode on electropolymerization process. On the other hand, it suggests Pd as a suitable substrate for the preparation of thin films of conductive polymers.

Abstract: The electrochemical synthesis of common conductive polymers such as polyaniline in phosphoric acid is a little different from that in other acidic media such as sulfuric acid. Electropolymerization in phosphoric acid is difficult, and this electrolyte medium is not applicable for this purpose. However, it is possible to overcome this problem by the addition of a small amount of sulfuric acid. In this case, the electropolymerization process can be successfully performed when the phosphate ion is doped. For instance, polyaniline films electrodeposited from an electrolyte solution of phosphoric acid have good stabilities and useful morphologies. Interestingly, phosphate doping results in the formation of nanostructures, whereas the polymer surface is macroscopically smooth. In an appropriate ratio, a mixed electrolyte of H3PO4 and H2SO4 can be used for the electropolymerization of aniline; thus, H2SO4 acts as a required agent for successful polymer growth, and H3PO4 acts as a doping agent. In this case, a small amount of sulfate is incorporated into the polymer matrix, which does not participate in the electrochemical insertion/extraction process. © 2006 Wiley Periodicals, Inc.

Abstract: Carbon nanotubes were prepared by catalytic chemical vapor deposition using washable catalyst support of barium and calcium chlorides. It was found that under this experimental condition, carbon nanotubes with cone-like heads are formed. This special shape guarantees easier diffusion and transfer inside the carbon nanotubes due to larger orifices. Copyright © 2006 The Chemical Society of Japan.

Abstract: A new bunching of nanomaterials is reported, as nanofibers (ca. 10-50 nm in diameter) which form huge skeins of ca. 20-50 μm. LiMn2O4, as a promising candidate for lithium batteries which needs improvement of solid-state diffusion, was synthesized with this nanostructure. The process was simply a hydrothermal synthesis of LiMn2O4 while a small amount of vanadium is incorporated into the spinel lattice. This work reports a novel bunching phenomenon in the realm of solid-state physics and nanotechnology. © 2006 Elsevier Ltd. All rights reserved.

Abstract: The enhancement of the conventional synthesis of carbon nanotubes by means of catalytic chemical vapor deposition (CCVD), was investigated. This synthesis route is more efficient than conventional and commercial ones employing metal oxide catalyst supports. Electron microscopy investigations were made using a Philips XL30 scanning electron microscope and a Philips transmission electron microscope. The results show that NaCl catalysts support has an inhibiting effect on the growth of carbon nanotubes.

Abstract: A novel structure of conductive polymer films was synthesized by electropolymerization on aluminum substrate under potentiostatic condition at a relatively high applied potential. A thick film of polypyrrole was electrodeposited onto aluminum substrate from an aqueous electrolyte solution of NaNO3 with pH 12 by applying a constant potential of 2.0 V versus SCE. This polypyrrole film has a good stability with strong adhesion to the substrate surface. However, the morphological structure of the film is different from those previously observed for conductive polymers. Large tubes (ca. 100-200 μm in diameter) are formed, which are spiraled around the cylindrical substrate electrode. Although, the internal channels of these polypyrrole macro-tubes are very wide, the polypyrrole synthesized is sufficiently dense, guaranteeing excellent mechanical stability for this novel morphological structure. On the other hand, such large walls of the macro-tubes have nano-structures. © 2005 Elsevier B.V. All rights reserved.

Abstract: Based on solid arguments, it was demonstrated that: (i) the fractality scale detected during electrochemical measurements depends only on the yardstick length, i.e., the diffusion layer width, and not on the size of the diffusing electroactive species; (ii) Fractal analysis cannot be performed by electrochemical methods at scales smaller than 100 nm, since the thickness of Helmholtz double layer is comparable with the diffusion layer width, and the diffusion layer width cannot be assumed to act as yardstick length. Indeed, it should be taken into account that the yardstick length is equal to "diffusion layer width + Helmholtz double layer." On the other hand, thin diffusion layers on rough surfaces lead to 3D diffusion; thus, the fundamental electrochemistry is no longer valid. In general, fractal analyses by electrochemical methods has severe limitations, which should be taken into account before applying it for different cases. In other words, surface analysis by this approach just senses microscale roughness, and ignores nanostructure. © World Scientific Publishing Company.

Abstract: Synthesis of larger particles of conductive polymers is usually favorable due to higher conductivity (as a result of lesser interfacial resistance). On the other hand, advantages of nanostructured materials are well known. Thus, it is desirable to fabricate large particles that have nanostructure, to gain double advantage. A simple method based on chemical polymerization under centrifugal forces is proposed to achieve this goal. It was typically employed for a well-known conductive polymer, namely, polyaniline to fabricate large particles (e.g., 400 μm) with internal nanostructure of ∼100 nm. This also significantly increases the electrical conductivity of the polymer. This is indeed a simple approach, which can be easily performed using a conventional centrifuge system. © 2006 Wiley Periodicals, Inc.

Abstract: Metal substation as an efficient approach for improvement of battery performance of LiMn2O4 was performed by an actinide dopant. Uranium as the last natural element and most common actinide was employed for this purpose. Cyclic voltammetric studies revealed that incorporation of uranium into LiMn2O4 spinel significantly improves electrochemical performance. It also strengthens the spinel stability to exhibit better cycleability. Surprisingly, the capacity increases upon cycling of LiU0.01Mn1.99O4 cathode. This inverse behavior is attributed to uniform distribution of dopant during insertion/extraction process. In other words, this is an electrochemical refinement of the nanostructure which is not detectable in microscale morphology, as rearrangement of dopant in nanoscale occurs and this is an unexceptional nanostructural ordering. In addition, uranium doping strengthens the Li diffusion, particularly at redox potentials. © 2005 Elsevier B.V. All rights reserved.

Abstract: Electropolymerization of pyrrole on lead substrate electrode was studied. Due to electrochemical activity of Pb in acidic media, this process is only possible at basic pHs. For this purpose, electropolymerization process was performed in an aqueous solution of Na2SO4 with pH 12. Potentiodynamic cycling shows the Pb oxidation at the first cycles. In subsequent cycles, polypyrrole film grows on the oxidized lead substrate. Of course, as the passive film is highly porous, a composite of polypyrrole/PbSO4 is formed in the first layers. However, subsequent cycling leads to the formation of pure polypyrrole film. According to this structure and strong connection of the polymer film to the substrate surface via this composite layer, the polypyrrole film deposited on the lead surface has enhanced mechanical stability. AFM measurements showed peculiar smoothness of both composite and lateral polypyrrole films. This synthesis approach is of particular interest for the preparation of highly stable polymer films and fabrication of supercapacitors with a polymer/PbSO4 conductive structure. © 2006.

Abstract: Usefulness of W substitution for improvement of battery performance of LiMn2O4 cathode was investigated. Small amounts of tungsten were incorporated into LiMn2O4 spinel instead of available Mn. For this purpose, two sources of tungsten (metallic W or WO3) were examined. W concentration and source have significant influence on both morphology and electrochemical behavior of W-substituted LiMn2O4 spinels. W substitution of LiMn2O4 spinel can lead to the formation of uniform spinel particles and improved battery performance. Cyclic voltammetric behaviors of the samples were examined in an aqueous solution, and Li diffusion process was investigated for different cases. The best case was the LiW0.01Mn1.99O4 spinel prepared from metallic W powder, as exhibits excellent rate capability, but better cycleability was observed for the LiW0.01Mn1.99O4 spinel prepared from WO3. This means that because of significant influence of the dopant source, this parameter should be chosen in respect with the desire improvement. © 2006 Elsevier Ltd. All rights reserved.

Abstract: In a hydrothermal route developed for synthesis of ZnO nanostructures, morphology can be controlled by experimental condition to form hollow nanospheres or nanostructured nanoparticles. In an intermediate condition, a novel nanostructure, namely flower-like bundle of ZnO nanosheets was found, which is different from known ZnO nanostructures. © 2006 Elsevier B.V. All rights reserved.

Abstract: It has been demonstrated that there is a geometrical order in text structures. Fractal geometry, as a modern mathematical approach and a new geometrical standpoint on natural objects including both processes and structures, is here employed for textual analysis. For this first study, the works of William Shakespeare were chosen as the most important items in Western literature. By counting the number of letters in a text, it is possible to study the whole text statistically. A novel method based on basic assumption of fractal geometry is proposed for the calculation of fractal dimensions of texts. The results are compared with Zipf's law. Zipf's law is successfully used for letters instead of words. Two new concepts - namely Zipf's dimension and Zipf's order - are also introduced. It can be seen that changes of both fractal dimension and Zipf's dimension are similar, and dependent on the text length. Interestingly, directly plotting the data obtained in semi-logarithmic and logarithmic forms also leads to a power-law. © Taylor & Francis.

Abstract: Surface defects on the substrate electrode have significant effects on electropolymerization processes. Influence of surface defects mechanically formed on a Pt electrode on electrochemical polymerization of aniline was investigated. Interestingly, it was found that existence of such surface defects leads to more favorable electropolymerization. In this case, surface defects acts as nucleation centers for subsequent growth of the conductive polymer. This is accompanied by the formation of denser polymer film with smoother surface. This smoothness also exists in nanoscale. These are interesting advantages for application purposes. © World Scientific Publishing Company.

Abstract: Manganese oxide nanowires were prepared from MnO2 with Na ions inserted within the raw MnO2 by a simple solid-state process.

Abstract: To clarify the vague points appeared in the literature, it was discussed that fractal analysis of electrode surfaces based on the concept of 'diffusion toward electrode surfaces' is only able to monitor surface roughness in scales larger than 10 nm. When inspecting fractality in atomic scale (and even up to 10 nm), electrochemical measurements are not reliable due to the presence of surface defects, which affect the electrochemical reaction. In other words, for fractal analysis of electrode surfaces, the diffusion layer width which acts as yardstick length, should be sufficiently large, incomparable to the scale of atomic inhomogeneities. To this aim, the experiment time should be sufficiently long or the diffusion coefficient should be sufficiently large. © 2004 Elsevier B.V. All rights reserved.

Abstract: Small-angle X-ray scattering (SAXS) was employed as a powerful technique for quantitative surface analysis of Pd electrodes subjected to severe plastic deformation. The experimental data obtained from SAXS measurements were analyzed by means of fractal geometry, as so-called fractal dimensions can be used as a quantitative measure of surface roughness. The influence of the strength of plastic deformation induced to the Pd/H system (due to phase transformation) on the degree of surface roughness was inspected. The powerfulness of this approach is ability for inspecting surface roughness in nanoscale. The surface fractality at nanoscale is significantly different from that at microscale. © 2004 Published by Elsevier B.V.

Abstract: A simple method based on a conventional solid-state process is proposed for synthesis of manganese oxide nanowires. This method provides an opportunity for bunching the nanowires synthesized, since the nanowires form in one direction. Thus, aligned bunches (e.g. > 100 μm long and about 50 μm in diameter) consisting of individual nanowires (diameters ranging between 50 and 200 nm) can be prepared simply. The phenomenon of simultaneous alignment of the nanowires in one direction to form ordered bunches is indeed an interesting development in the realm of nanotechnology. It can be considered as an alternative to conventional template-based methods.

Abstract: Deiss [Electrochim. Acta 47 (2002) 4027] claimed that the diffusion coefficient of electrochemical systems is potential-independent and apparent dependency is just related to the experimental errors. In this commentary paper, based on solid arguments, it was demonstrated that it is not a correct conclusion. The diffusion coefficient is strongly potential-dependent as can be understood from statistico-mechanical standpoint. This is well known from more than a century with convincing theoretical formulations. Of course, the possible experimental errors mentioned by Deiss are true, but not responsible for potential dependency of the diffusion coefficient. © 2004 Elsevier Ltd. All rights reserved.

Abstract: Diffusion of sodium through MnO2 lattice in a high-temperature solid-state reaction can affect the original structure of manganese oxide. This effect is significantly concentration-dependent. For x < 0.5 in Na xMnO2, the chemical structure of sodium manganese oxide is accompanied by the formation of manganese oxide nanowires. The amount of such nanowires increases by increasing the concentration. For x > 0.5, it tends to form conventional layered structure (with microscale particles). In the case of MnO2, this phenomenon is only for Na diffusion, when a chemical structure corresponding to Na0.44MnO2 (JCPDS: 27-0750) is formed. © 2005 Elsevier Ltd. All rights reserved.

Abstract: A new form of 1D nanomaterials is reported. Solid-state synthesis of manganese oxide nanowires is accompanied by bunching of individual nanowires. It was found that a peculiar structure of individual nanowires is formed in the course of this synthesis. In this case, nanowires have rectangular shape instead of conventional cylindrical shape. In fact, each individual nanowire consists of smaller ingredients, which are sheet-like nanoribbons. Of course, these nanoribbons are closely packed and can only be distinguished on broken heads of nanowires. Both SEM and TEM results confirm this novel structure. High resolution AFM with scanning area of about one individual nanowire was also employed to visualize rectangular structure of these nanowires with high resolution. © 2005 Elsevier B.V. All rights reserved.

Abstract: A system was designed based on a sensing process for continuous release of Fe(CN)64-. A polymer-modified electrode was prepared by electropolymerization of aniline onto a platinum electrode from a solution containing the monomer and Fe(CN)64- to form a layer of polyaniline/Fe(CN)64- (PA/FCN). The FCN incorporated into the polymer film can be released by applying a sufficient potential. An FCN-selective electrode was used as the counter electrode of the system. As the sensor exhibits potentiometric response to the FCN ions, the generated potential causes the release of Fe(CN)64- from the polymer film electrode. The system was examined as a continuous releaser of Fe(CN)64- for study of a chemical oscillator as a typical application. Copyright © Taylor & Francis Inc.

Abstract: A simple electrochemical procedure is proposed for surface modification of cathode materials. A metal oxide-retaining layer deposited electrochemically on the electroactive material avoids its direct contact with the electrolyte. For 5 V cathodes, which are extremely oxidant at charged state, this action significantly enhances the cyclability. In addition, the own stability of the metal oxide-retaining layer deposited on the cathode surface has a significant effect on the cyclability, which can be enhanced by inducing a mechanical force during the electrodeposition process.

Abstract: A 5 V lithium secondary cell was fabricated using LiFe0.5Mn 1.5O4 cathode material with all-solid-state design. As an additional approach to improve the battery performance of the all-solid-state secondary cell, a metal oxide-retaining layer was placed between the cathode material and solid electrolyte. The cathode material has an excellent cyclability in this cell design, since it just loses 5 and 18% of its initial capacity after 100 and 500 charge-discharge cycles, respectively. © 2004 Elsevier B.V. All rights reserved.

Abstract: An LiMn2O4 electrode was prepared based on mixed-metals (gold-titanium) codeposition method. By this method, titanium oxide is also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO2 can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn2O4 spinel can be improved by the surface modification with TiO2. This action improves cyclability for lithium battery performance and reduces capacity fades of LiMn2O 4 at elevated temperatures. © 2004 Elsevier B.V. All rights reserved.

Abstract: All-solid-state thin-film secondary cells were prepared using transition metal hexacyanometallates as anode and cathode materials. Two different approaches were employed to prepare highly stable films of the electroactive materials viz. using aluminum substrate as current collector and deposition under centrifugal forces. At the first stage, the cell design was examined for a well-known case, Prussian blue (PB) secondary cell. The experimental results were indicative of the fact that the cell properties such as its charge/discharge behavior, specific capacity, cyclability, and coulombic efficiency are significantly improved. At the second state, the cell design proposed was successfully used to fabricate a high-voltage secondary cell based on chromium hexacyanochromate (CrHCC) anode and Prussian blue (PB) cathode. Then, eight unit cells were connected in series to prepare a rechargeable battery with an operating voltage of ca. 20V. Thus, the results are of interest for the preparation of microbatteries with specified properties. © 2004 Elsevier B.V. All rights reserved.

Abstract: Electrochemical polymerization/deposition of conductive polymers under centrifugal fields was introduced as an efficient method to enhance physical properties of the conductive polymers synthesized. The approach was typically employed for the preparation of thin films of polypyrrole. The results obtained from the experimental measurements obviously showed that the electroactive films formed in the presence of stronger centrifugal forces have significantly higher stability and electronic conductivity. © 2003 Elsevier B.V. All rights reserved.

Abstract: A potassium secondary cell was designed employing a potassium anode and a Prussian blue (PB)-based cathode. The electrolyte solution for the nonaqueous battery was 1M KBF4 in 3:7 EC/EMC. The potassium battery designed had some valuable advantages in comparison with similar lithium batteries. The cell design is simple, and both the material used and the procedure needed for the cell fabrication are cheaper. In addition, the cell has an excellent cyclability for more than 500 reversible cycles. There is only a negligible capacity fade for the battery performance at elevated temperatures. Moreover, the chemical diffusion coefficient of K+ in the cell is higher than that of Li+ in lithium batteries, which is due to a smaller Stoke's radius of K+ in electrolyte solution (solvated ions). The results obtained from the experimental measurements and the prospective of this rechargeable cell suggest it as a promising alternative to lithium secondary cells. © 2003 Elsevier B.V. All rights reserved.

Abstract: Aluminum oxide was used with three different applications to improve battery performance of LiMn2O4 cathode. Indeed, Al 2O3 was placed beneath, within and upon the electroactive film. In the first application, aluminum oxide was deposited onto the current collector to strengthen connection of the electroactive material with the substrate surface. In the second one, Al2O3 particles were dispersed within the electroactive film to improve Li intercalation/ deintercalation process. And in the last one, Al2O3 was used as a surface-coating agent to cover the spinel surface to avoid Mn dissolution. The influence of these three approaches on the battery performance of LiMn2O4 cathode was examined separately and in combination. The results were indicative of the fact that Al2O 3 could be used as a multi-function agent to improve various problems of LiMn2O4 to achieve an acceptable behavior for battery performance. Indeed, it was demonstrated how combination of different methods using a single agent can lead to superiority improvement of the battery performance. The LiMn2O4 cathode prepared based on these three approaches exhibits 1000 charge/discharge cycles at room temperature and 400 cycles at an elevated temperature (55 °C), retaining 90% of its initial specific capacity. As Al2O3 is a simple and low-cost agent, the results are of interest for the practical performance. © 2004 Published by Elsevier B.V.

Abstract: Fractal dimension of a thin-film of Au deposited on the liquid|liquid interface generated between 4-methyl-2-pentanone and aqueous solution was determined. The Au film was electrochemically deposited on the interface using an interfacial deposition method. In the specified experimental conditions employed, the electrodeposition provides an Au film with uniform surface structure, and the fractal dimension of the Au film can be considered as a factor of the interface structure. Thus, an electrochemical method, based on the time-dependency of the diffusion-limited current after a potential step, was applied for determination of the fractal dimension of the Au film deposited on the liquid|liquid interface. The validity of the results were examined by determining the fractal dimension of the Au film deposited on the liquid|liquid interface using another technique viz. cyclic voltammetry. There was a good agreement between the results obtained from different methods. Similar approaches were also employed for fractal study of an Au film deposited on a liquid|gas interface, i.e. between an aqueous solution and air. © 2003 Elsevier B.V. All rights reserved.

Abstract: Lanthanum hexacyanoferrate (LaHCF) was immobilized onto a substrate surface as an electroactive material by Au-codeposition method. The LaHCF particles were attached to the electrode surface as the result of occlusion within the gold film deposited. This deposition method was first introduced for the preparation of hexacyanoferrate-based modified electrodes. It was demonstrated that this deposition method provides a higher stability of the electroactive film in comparison with available methods for the mechanical attachment of electroactive films. On the other hand, electrochemical properties of the LaHCF film modified electrode were studied for the first time. The results showed that LaHCF film has excellent electrochemical activity as well as other analogues of Prussian blue. The modified electrode was successfully used as an electrocatalyst for the oxidation of ascorbic acid.

Abstract: Electrochemistry of gallium hexacyanoferrate (GaHCF) as an analogue of prussian blue having a high-potential redox system was studied. A thin film of GaHCF was directly generated on a Ga substrate surface to fabricate a modified electrode. Electrochemical behavior of the modified electrode was studied at a typical cool environment of ca. 5°C. Although electrochemical activity of the electroactive film for ion insertion/extraction at this temperature is weaker than that at ambient temperature, the GaHCF film, however, showed excellent electrochemical activities. The redox potential of GaHCF was found to be higher than other transition metal hexacyanoferrates. The electroactive film formed on the electrode surface had an acceptable stability during both potential cycling and long-term usage. The results were indicative of the fact that GaHCF is a suitable modifier for the modification of electrode surfaces. On the other hand, the present work reports electrochemistry of an electroactive solid film with high-potential redox, and also well-defined electrochemical behavior of such systems, in a cool environment. © 2004 The Electrochemical Society. All rights reserved.

Abstract: Non-steady state nature of impedance spectroscopy for the investigation of electrochemical systems displaying oscillatory behavior was shown. To this aim, an electrochemical oscillator involving metal dissolution was chosen as a typical example. It was demonstrated that the impedance spectra recorded for the Fe/H3PO4 system are strongly time-dependent, which is attributed to the growth of passive layer on the electrode surface. Indeed, resistance of the passive film formed on the electrode surface increases gradually, which has a significant effect on the system dynamic. Interestingly, impedance measurements recorded suggest instability of the system (and consequently appearance of oscillatory behavior) for certain values of film resistance and indeed at a certain time range of the experiments. Generally, as a typical example, it was demonstrated that how time-dependency of complex systems with complicated dynamics such as oscillators could be a source of errors in their analyzing. © 2004 Published by Elsevier B.V.

Abstract: A new technique, pulsed electrodeposition under a centrifugal force, is introduced for the preparation of soft magnetic CoNiFe films. The films have enhanced properties such as a high BS (magnetic saturation) and a low Hc (coercivity), which are desirable for soft magnetic materials. They are also smoother than films deposited under non-pulsed conditions. It is suggested that the technique could be used to prepare various other materials with desirable properties.

Abstract: The electrochemical performance of LiCoPO4 as a 5 V cathode material for lithium batteries was investigated in LiBF4 electrolyte. It was demonstrated that using this electrolyte salt significantly improves the electrochemical behavior of LiCoPO4, as it is accompanied by a faster diffusion process. In addition, another approach, viz., surface/chemical modification of the cathode with a metal oxide, was employed to reduce capacity fades appearing at elevated temperatures. To this aim, a thin layer of Al 2O3 was deposited on the cathode surface by a sputtering method. The results obtained from experimental investigations are indicative of the fact that both approaches significantly improve cyclability of the cathode. Such improvements provide a satisfactory cyclability for LiCoPO4 to be used as a 5 V cathode material. © 2004 The Electrochemical Society. All rights reserved.

Abstract: LiFePO4 was deposited onto substrate surface during Au electrodeposition. Formation of this LiFePO4 /Au mixed film leads to better electrochemical performance of the LiFePO4, because Au modifies its low conductivity. This simple electrochemical method also provides an opportunity for the incorporation of modifying materials such as metal oxides during a mixed-metal codeposition process. Interestingly, it is possible to use a similar method to coat the electroactive material surface with modifier. After the deposition of the electroactive film, a thin layer of metal oxide was additionally coated on the film surface. The results obtained from the experimental investigations show that the LiFePO4 cathode prepared by the simple electrochemical method proposed has an excellent battery performance, including higher specific capacity, less capacity fading, and faster diffusion process. The LiFePO4 cathode prepared shows only a 10% capacity fading after 1000 cycles at 80°C, while approaching its theoretical capacity at this condition. © 2004 The Electrochemical Society. All rights reserved.

Abstract: The reaction dimension of electrochemical processes was introduced as a quantitative factor for reactivity of catalysts. It is representative of the effective (reactive) surface area of the electrode for a catalytic reaction. Such a dimension can be estimated from the reaction efficiency at different particles sizes of the catalyst. The approach was proposed theoretically and was examined based on experimental results. For this purpose, three known electrochemical processes viz. electrochemical oxidation of methanol and of CO and electroreduction of O2 at Pt particles were chosen as typical examples. The results obtained from experimental measurements showed the validity of the theory proposed. It was demonstrated that the approach proposed is not restricted to fractal surfaces and all catalysts with noninteger dimensions (due to the universal aspect of fractal geometry) can be considered. © 2004 The Electrochemical Society. All rights reserved.

Abstract: The electrodeposition of polyaniline film on an iron substrate electrode was studied for the preparation of an enzyme-modified electrode. The electrochemical polymerization of aniline was carried out using a passivated Fe substrate. The existence of a passive layer on the substrate surface has a significant effect on the formation of the electroactive film. Chronopotentiometric measurements were employed to investigate the influence of the passivated substrate on the electropolymerization process. The enzyme-modified electrodes were fabricated by incorporating glucose oxidase into the depositing polyaniline. Two different enzyme-electrodes using a conventional Fe electrode and a passivated Fe electrodes were prepared and compared. Experimental results illustrated that the polyaniline film formed on the passivated Fe electrode is highly stable and the approach proposed (using a passivated substrate) can be used to enhance stability of conductive polymer films. © 2004 Elsevier B.V. All rights reserved.

Abstract:

Abstract: An erratum to the article "Potassium secondary cell based on Prussian blue cathode" [J. Power Sources 126 (2004) page 221-228] is presented. The following note was omitted from the Experimental Section (Section 2) of the paper: For investigating the cyclability of the PB cathode at elevated temperatures, i.e., the results reported in Fig. 5, a carbon-based anode was employed instead of conventional metallic potassium.

Abstract: Mixed-metals codeposition was introduced as an efficient method for the deposition of cathode materials onto substrate surfaces. The approach proposed was typically used for the deposition of LiMn2O4 with codeposition of mixed gold-cobalt. The results obtained for the system under investigation showed that the method employed is applicable for lithium secondary battery performance. In addition to the efficient deposition of the cathode material which is of interest for battery applications, the approach was used to incorporate cobalt oxide into the cathode material. It was demonstrated that the metal oxide deposited with the cathode material significantly reduces the capacity fade of LiMn2O4 in both room and elevated temperatures.

Abstract: A film of LiMn2O4 with 3D macroporous structure was deposited on a substrate surface during gold codeposition. Fractal analysis of the LiMn2O4 suggested a 3D structure for the film deposited with a fractal dimension approaching 3. Battery performance of a lithium secondary cell employing the 3D LiMn2O4 cathode was investigated and compared with that of using a conventional LiMn 2O4 cathode. The results indicated that the 3D cathode fabricated has higher capacity in comparison with the conventional cathode. It is due to the existence of higher surface area for lithium intercalation/deintercalation processes. Indeed, 3D structure of the electrode provides chance for the Li deintercalation in three directions. © 2003 Elsevier B.V. All rights reserved.

Abstract: Electrodeposition of a thin film of copper onto a silicon surface was investigated under centrifugal fields. The results are indicative of the fact that Cu metallization of silicon based on the approach proposed has better properties for practical applications. In this case, more metal is deposited onto the Si substrate suggesting the requirement of a shorter deposition time, which is useful to avoid passivation processes occurring during the deposition process. In addition, denser films with higher electrical conductivity are deposited under stronger centrifugal fields. Moreover, the surfaces of copper films deposited under stronger centrifugal fields are smoother, which is a desirable advantage for the practical performances. © 2003 Elsevier B.V. All rights reserved.

Abstract: Diffusion towards solid film in an electrochemical system was studied from nonequilibrium thermodynamic point of view. To this aim, electrochemical redox of Prussian blue in the presence of different supporting electrolyte cations was chosen as a well-known system. The variation of the phenomenological coefficient was investigated. The theory derived from theoretical hypothesis was supported by experimental results obtained from chronoamperimetric and cyclic voltammetric measurements. The fulfillment of reciprocity Onsager relation was also presented. Interestingly, it was demonstrated that the phenomenological coefficient for a diffusing electrochemical system is strongly time-dependent, and can be considered as a dynamic representative of the flux. © 2003 Elsevier Science B.V. All rights reserved.

Abstract: A solid-state secondary cell was fabricated using two different transition metal hexacyanometallates as anode and cathode materials. To reach a high-voltage cell, a hexacyanometallate with less negative redox potential, chromium hexacyanochromate (CrHCC), was employed as the active material of the anode and a hexacyanometallate with high positive redox potential, chromium hexacyanoferrate (CrHCF) was employed as the active material of the cathode. Consequently, a secondary cell with relatively high voltage of about 1.5V was obtained, which is relatively high for this type of batteries. The preliminary studies of the battery performance were carried out based on a simply designed cell. The results indicate that the idea for the fabrication of this type of secondary cells is of interest and further investigations (improving the battery properties) can lead to reach an acceptable situation for the practical performances. © 2003 Elsevier Science B.V. All rights reserved.

Abstract: Two modified electrodes were fabricated by deposition of thin films of α-PbO2 and β-PbO2 on aluminum substrate electrodes. Both electrodes exhibit potentiometric response to the hydrogen ion concentration and, consequently, can be used as pH sensors. The potentiometric responses of the modified electrodes were close to the theoretical slope of Nerustian response and comparable with glass electrodes. The electrochemical properties and stability of the constructed electrode were investigated. The possibility of the pH sensor for using in flow injection analysis (FIA) was also studied, and the optimum conditions were obtained. © 2002 Published by Elsevier Sciece B.V.

Abstract: A chemically modified electrode (CME) was fabricated by direct modification of a silver electrode with a thin film of silver hexacyanoferrate. The modified electrode was used as a potentiometric sensor for the determination of potassium ion. The sensor exhibits a response to potassium ion in a wide concentration range from 8.0 × 10-5 to 1.0 M with a low detection limit of 4.0 × 10-5 M. The potassium-selective electrode has a relatively short response time. It has a good sensitivity with a near-Nernstian slope of 53-57 mV/decade and good selectivity in the presence of possible interferences. The electrode response is highly sensitive to some controllable parameters mainly the thickness of electroactive film which is controlled by the charge passed in the cell during the deposition of the film. Stability of the directly modified electrode and its potentiometric response were also investigated during long-term usage, which were indicative of the possibility of the potassium-selective electrode for using in a long period.

Abstract: The electrocatalytic activity of an aluminum microelectrode modified with cobalt hexacyano-ferrate film is described. A simple method was used for the preparation of the modified microelectrode. The modified microelectrode exhibits good electrocatalytic properties for electrochemical reduction of hydrogen peroxide. The effect of solution pH and applied potential on the electrocatalytic properties of the modified microelectrode is investigated. The results show that the best potential for the detection of hydrogen peroxide is 0.0 vs. SCE for better response and decrease of interferences. Due to the microelectrode scale, it can be used for the determination of small amounts of H2O2. The calibration plot is linear up to 1.7 mM (r = 0.988) with a response time of 5.1 s. The detection limit of the microelectrode as H2O2 sensor is 2 × 10-7 M. The sensivity of the H2O2 sensor is 225.6 nA mmol-1 and RSD of this sensor is less than 2.3%. In addition, effects of possible interferences and possibility of the sensor for real samples is investigated. The present work shows the potential of the proposed method for the fabrication of modified electrodes, as it can be used to employ for different purposes in micro scale.

Abstract: Physical and magnetic properties of soft magnetic CoNiFe films electrodeposited under centrifugal forces were investigated. It was demonstrated that employing an external centrifugal force during the deposition process provides stronger magnetic properties of the soft magnet electrodeposited. Based on the approach proposed, preparation of soft magnetic CoNiFe film with Bs higher than 2.1 T and Hc lower than 1.1 Ωe is possible. For a conventional CoNiFe film with Bs of 1.96 T (electrodeposited under Earth's gravity), the saturation induction can be increased to 2.14 T by applying a 290g centrifugal force during the electrodeposition process, while the Hc approximately remained the same. It is thought that this enhancement provided by an applied centrifugal force is due to the increase of bcc/fcc ratio, where this increase is not associated with a significant crystallite growth in this case.

Abstract: Fractal dimension of a LiMn2O4 electrode prepared by sol-gel method was determined using electrochemical techniques based on the phenomenon of "diffusion towards electrode surface". A simple discussion was made on the methodology to understand what is really estimated as the fractal dimension. It was demonstrated that the value of fractal dimension determined based on electrochemical methods is strongly dependent on the electrochemical system situation. This is generally true for all real electrodes involving insertion/extraction processes. This comes from the fact that surface morphology of the electrode is subject of significant changes during the electrochemical experiment. © 2003 Elsevier Ltd. All rights reserved.

Abstract: Magnetic field was employed as a useful tool to improve stability of electroactive films deposited on substrate surfaces. To this aim, electrochemical preparation/deposition of Prussian blue (PB) was carried out in the presence of an external magnetic field to form a thin film onto a Pt substrate electrode. The results were compared with a conventional PB modified electrode throughout the research. For the electrode prepared in the presence of the magnetic field, a stronger voltammetric behavior with higher peak current was observed. It was accompanied by higher chemical and electrochemical stabilities of the deposited electroactive film. Spectroscopic measurements were also performed to investigate the influence of the applied magnetic film on the properties of the electroactive film deposited. The results were indicative of the fact that deposition under magnetic filed is accompanied by stronger chemical bonds and different elemental composition of the electroactive material formed on the electrode surface. Based on the experimental results, it was concluded that both Lorentz and magnetic forces are responsible for the behavior observed.

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Abstract: Phenomenological coefficient was used as a quantitative factor to examine cyclability of an electrochemical redox system. The insertion/extraction of potassium ions into/from solid film of Prussian blue (PB) was chosen as a typical example with a known electron-ion hopping mechanism. The phenomenological coefficient for the flux of counter ion (or equivalently electron) at various cycles were estimated based on an approach using different techniques, viz. cyclic voltammetry and simple conductivity measurement. The advantage of phenomenological coefficient in comparison with peak current for the investigation of cyclability of an electrochemical system was described. © 2003 Elsevier B.V. All rights reserved.

Abstract: Fractal dimension of a carious tooth surface was determined using an electrochemical method. The method was based on time-dependent diffusion towards electrode surfaces, which is one of the most useful and reliable methods for the determination of fractal dimension of electrode surfaces. For this purpose, the tooth was covered with a gold layer, which acted as an electrode in electrochemical experiments. It is suggested that the fractal dimension can be used as a quantitative measure of the state of dental surfaces. The method presented demonstrates the power of electrochemical techniques for the determination of fractal dimension of surface of non-conducting objects. © 2003 Elsevier B.V. All rights reserved.

Abstract: Different Ni-based alloys with various compositions were prepared by varying the amounts of beryllium. Effect of the amount of beryllium added to the alloy on its corrosion in an electrolyte solution of artificial saliva was investigated. Fractal dimension was used as a quantitative factor for surface analysis of the alloys before and after storage in the artificial salvia. The fractal dimensions of the electrode surfaces were determined by means of the most reliable method in this context viz. time dependency of the diffusion-limited current for a system involving "diffusion towards electrode surface". The results showed that increase of the beryllium amount in the alloy composition significantly increases the alloy corrosion. It is accompanied by increase of the fractal dimension and roughness of the electrode surface, whereas a smooth and shiny surface is required for dentures. From the methodology point of view, the approach utilized for fractal analysis of the alloy surfaces (Au-masking of metallic surfaces) is a novel and efficient method for study of denture surfaces. Generally, this approach is of interest for corrosion studies of different metals and alloys, particularly where changes in surface structure have a significant importance. © 2003 Published by Elsevier B.V.

Abstract: An equation was mathematically derived using the theory of irreversible thermodynamics for the diffusion of electrolytes in solution in the presence of an external gravitational force. It was demonstrated that diffusion coefficients of electrolyte species are dependent on the difference of radii and densities of anion and cation ionized from the electrolyte in solution. For a special case that radii and densities of the anion and cation are the same, the diffusion coefficient is independent of the external gravitational force. Entropy production was also estimated for the system under consideration. It was found that the rate of entropy production is proportional to the sum of the gravitational forces induced to all electrolyte species. © 2003 Elsevier B.V. All rights reserved.

Abstract: Electrochemical behavior of a thin film of LiFe0.5Mn 1.5O4 spinel deposited on a Pt substrate electrode in nonaqueous medium of LiBF4 in ethylene carbonate/dimethyl carbonate (EC/DMC) solution was investigated using cyclic voltammetric technique. In addition, the chemical diffusion coefficients of Li+ at different states of charge (different electrode potentials) in the system under investigation were estimated using chronoamperometric technique. The charge/discharge characterization of the lithium secondary cell employing this 5 V cathode material shows an acceptable electrochemical performance with high-voltage and specific capacity. The disadvantage of the material was related to significant capacity fades at elevated temperature. It was demonstrated that the capacity fading in this electrolyte solution is significantly lesser than common electrolyte solutions, e.g. LiPF6. In addition, an approach viz. surface modification of the spinel with aluminum oxide was utilized to reduce the capacity fade at elevated temperatures. The sources for the appearance of such capacity fades appearing at both 4 and 5 V performance of the cathode material were discussed. © 2003 Elsevier B.V. All rights reserved.

Abstract: Iron hexacyanochromate (Fe-HCC) can be used as an excellent anode material to fabricate high-voltage secondary cells, due to its negative redox potential. In addition, good cycleability and other advantages of hexacyanometallates such as low cost and nontoxicity make FeHCC a promising candidate for anode materials. In contrast to cyanide compounds, hexacyanoferrates are not hazardous compounds for human health and they even have medical applications.

Abstract: The possibility of using silicon as the substrate electrode for the deposition of electroactive films of transition metal hexacyanoferrates was investigated. The silicon surface was successfully modified by the electroactive films based on a simple method. The studies of the electrochemical behavior and electrocatalytic properties of a palladium hexacyanoferrate (PdHCF) film-modified silicon electrode showed that the electrode fabricated had excellent properties and electrochemical activity. The possibility of the use of silicon substrate was also examined for the deposition of NiHCF and CoHCF films. The modification was carried out by electrodeposition of metals onto the substrate surface and chemical transformation of the metallic films deposited into their hexacyanoferrate salts. The results obtained from electrochemical studies indicate clearly that the electroactive films have excellent electrochemical activities compared with conventional hexacyanoferrate-based modified electrodes. In addition, deposition of electroactive films onto silicon surface provides an enhanced stability of the electroactive films during potential cycling and long-term storage. © 2003 Elsevier B.V. All rights reserved.

Abstract: Surfaces with lower fractal dimensions were generated during gold deposition under stronger centrifugal fields.

Abstract: Electrochemical polymerization of aniline onto an aluminum substrate electrode was studied. The obtained results were compared to those obtained with Pt substrate electrode. It indicates the possibility of aluminum for using as substrate electrode for electropolymerization. Moreover, the electrochemical polymerization of aniline on a passivated Al electrode was studied. The stability of the three different electrodes were studied and compared during potential cycling. Incorporation of glucose oxidase as a typical enzyme into the polymer films was investigated to prepare an enzyme-modified electrode. The activity of the enzyme incorporated into the polyaniline films formed on different substrate electrodes was also discussed. © 2001 Elsevier Science B.V. All rights reserved.

Abstract: Highly stable modified electrodes were fabricated by the deposition of electroactive films onto substrate electrode surfaces under centrifugal fields.

Abstract: Fractal structure of a LiMn2O4 film electrode has been investigated and its fractal dimensions was determined using different electrochemical techniques, viz. cyclic voltammetry and chronoamperometry. The results obtained from both these methods are in good agreement indicating the reliability of the estimated Df. The fractal study of the LiMn2O4 film electrode suggests a complex surface with high fractal dimension. In addition, length scales of the electrode surface were also calculated. © 2002 Published by Elsevier Science Ltd.

Abstract: A thin film of zinc hexacyanoferrate (ZnHCF) was formed directly on a Zn electrode to prepare a chemically modified electrode. The electroactive film was strongly attached to the electrode surface and was stable against gradual dissolution during potential cycling and long-term usage. The voltammetric characteristics of the directly modified ZnHCF film electrode were also investigated in the presence of different alkali metal cations. In view of the fact that, unlike the other transition metal hexacyanoferrates, ZnHCF film can be generated only at a certain ratio of modifier species, the modification process has an essential role in the nature and properties of the generated electroactive film. Due to the mechanism of the direct modification process, concentrations of the modifier species including Zn2+ and Fe(CN)63- have no effect on the nature of the generated electroactive film. Thus, by using direct modification, the film formation is not affected by the ratio of Zn2+/Fe(CN)63-, as this ratio is kept at 1:1 for any possible case. This results from the fact that, by involving a mole of Fe(CN)63- in the surface reaction (the reaction which occurs at the electrode surface and causes the formation of the ZnHCF film), only a mole of Zn2+ dissolves from the electrode surface to share in the surface reaction (plus a mole of K+ from the supporting electrolyte). The electrocatalytic properties of the modified electrode for oxidation of thiosulfate were also investigated. © 2002 Published by Elsevier Science B.V.

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Abstract: A chemically modified electrode was fabricated based on manganese hexacyanoferrate (MnHCF) film. The MnHCF was used as a modifier immobilized onto an aluminum electrode. Stability of the electroactive film formed on the Al electrode surface indicated that MnHCF is a suitable material for the preparation of modified electrodes. The analytical applicability of the modified electrode for the determination of hydrogen peroxide was examined. A linear response in concentration range of 6.0 × 10-7 -7.4 × 10-3 M (r = 0.9997) was obtained with detection limit of 2.0 × 10-7 M for the determination of hydrogen peroxide. The modified electrode exhibited a good selectivity for H2O2 in real samples. The mentioned electrode has advantages of being highly stable, sensitive, inexpensive, ease of construction and use. © 2001 Elsevier Science B.V. All rights reserved.

Abstract: Enzyme-modified electrodes were fabricated by the immobilization of glycerol dehyrogenase into the polyaniline film and were used as glycerol biosensors. Two different electrodes were prepared by forming monolayer and bilayer electroactive films on the electrode surface and were compared. Potassium ferrocyanide was used as mediator of the biosensing reaction. The biosensors exhibit amperometric response to the glycerol in the range 5 × 10-6 to 2 × 10-3M with detection limit of 1 × 10-6M. The Michaelis-Menten constants, K′m, of the electrodes were calculated, their values indicates that the enzyme has not chemically modified with the electrode materials and has its original enzymatic activity. The electrode has a good stability and selectivity due to the enhanced stability of the deposited polyaniline film on Al substrate. © 2001 Elsevier Science B.V. All rights reserved.

Abstract: The electrochemical properties of a thin-film LiMn2O4 electrode were studied in an aqueous medium. The studies were done in a saturated aqueous medium to increase similarity of the electrolyte solution with a non-aqueous medium. The apparent diffusion coefficient was calculated and discussed for different potentials at the aqueous electrolyte. In addition, stability of the thin solid film was investigated during potential cycling, which indicates that the electrode is highly stable in aqueous medium as well as in non-aqueous media. The obtained results from electrochemical measurements indicate that the properties of the thin-film LiMn2O4 electrode in aqueous medium are similar to those that have been found in non-aqueous media. © 2001 Elsevier Science Ltd. All rights reserved.

Abstract: A new bunching of nanomaterials is reported, as nanofibers (ca. 10-50 nm in diameter) form huge skeins of ca. 20-50 μm. LiMn2O4, which is a promising candidate for lithium batteries and needs improvement of solid-state diffusion, was synthesized with this nanostructure. The process was simply a hydrothermal synthesis of LiMn2O4 while vanadium as a dopant is incorporated into the spinel lattice. This work reports a novel bunching phenomenon in the realms of solid-state physics and nanotechnology.

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