Electrochemical Deposition Technique Research Articles

Synthesis of zinc oxide nanotwins using electrochemical deposition technique at different current densities

Synthesis of zinc oxide nanotwins using electrochemical deposition technique at different current densities

Influence of precursor pH on the optical and electrical properties of electrochemically deposited cobalt-doped ZnSe thin films for photovoltaic application

Thin films of zinc selenide (ZnSe) were doped with cobalt during the synthesis using various doping concentrations with the aid of electrochemical deposition techniques. These films were synthesized at pH of 8–10 and characterized for optical, elemental, structural, morphological, and electrical properties to ascertain their usability in photovoltaic applications with the aid of UV-Vis, EDX, XRD, and SEM. The samples showed absorption within the visible region of the electromagnetic spectrum while the energy bandgap obtained ranged from 2.0 to 2.3 ​eV. The SEM micrograph showed round-like shaped grains of the deposited samples while the XRD revealed a crystalline structure with JCPDS card number 01-088-3500 with a face-cantered cubic structure. The EDX demonstrated peaks of the deposited elements such as Zn, Se, and Co. The overall results revealed positive shifts in the properties of the materials when they are doped with cobalt and these materials have been observed to have great potential for photovoltaic applications.

Morphology and I-V Characteristics of Electrochemically Deposited Zinc Oxide on Silicon

This paper reported on the electrochemical deposition of zinc oxide (ZnO) on p-silicon (p-Si) (100) substrate in the mixture of 0.1 M of zinc chloride (ZnCl2) and potassium chloride (KCl) electrolyte at a volume ratio of 1:1, 3:1 and 5:1 namely Sample A, B and C. The deposition process was done in room temperature with a current density of 10 mA/cm2 for 30 minutes. Prior to the experiment, all samples were treated by RCA cleaning steps. All samples were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results show that all samples have the same morphology of a flake-like structure with different Zn:O ratio that were 2.81, 2.35 and 2.49 for samples A, B and C. The current-voltage (I-V) characteristic graph was obtained by dark current measurement using Keithley SMU 2400 and the threshold voltage (Vth) values were determined at 2.21 V, 0.85 V and 1.22 V for sample A, B and C respectively which correspond with the Zn:O ratio where the highest value of Zn:O ratio can be found in sample A and the lowest in sample B. Based on these results, it shows that electrochemical deposition technique is capable of being used to deposit the flake-like structure ZnO on semiconductor material to form the p-n junction which behaves like a diode. The value of Vth seems to be depended on the ratio between Zn and O. Higher ratio of Zn and O will cause the higher value of intrinsic carrier concentration and built in potential which will increase the Vth value.

A sensitive electrochemical sensor based on metal cobalt wrapped conducting polymer polypyrrole nanocone arrays for the assay of nitrite.

The conducting polymer polypyrrole nanocones wrapped by metal cobalt (Co/PPy) are a promising platform for the detection of sodium nitrite, which can be obtained by an electrochemical deposition technique under a mild condition. Co/PPy nanocone arrays combined the high conductivity and large specific surface area of PPy nanocones with the redox properties of metal cobalt, and their 3D structure can provide more active sites for nitrite detection. Owing to the microstructure and excellent electrical properties of the nanocomposite, Co/PPy nanocone arrays were convenient to construct a high-performance nitrite sensor. The microscopic morphology and composition of Co/PPy nanocone arrays were characterized by SEM, FT-IR, XPS, and XRD, and their electrochemical performances were also investigated. The experimental results showed that Co/PPy nanocones exhibited excellent performance for nitrite determination. Thesensors were used for the determination of nitrite in pickled Chinese cabbage and water samples, and the results were consistent with thoseof spectrophotometry. Hence, the synthesized Co/PPy nanocone arrays have a broad application prospect in food safety, environmental protection, and industrial manufacturing.

Electrochemical deposition of Indium(III) hydroxide nanostructures for novel battery-like capacitive materials

In the last decades, the metal hydroxide-based battery-like supercapacitors have more attracted researchers interest due to their superior power density, unique reversibility, and low-cost. Herein, we synthesized Indium(III) hydroxide (In(OH)3) nanostructures by a one-step electrochemical deposition technique and reported the supercapacitor properties for the first time in the literature to propose an alternative active material for the metal hydroxide-based battery-like supercapacitors. The X-ray powder diffraction spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller method were used to realize the analytical and morphological characterizations. The reported supercapacitor and electrochemical properties of In(OH)3 nanostructures were obtained through cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy in an aqueous 3 M KOH electrolyte. The electrodeposited In(OH)3 nanostructures exhibit a good specific capacitance of 271.4, 226.4, 192.6, 167.3, 149.2 F g−1 at 1, 2, 4, 8, 20 A g−1, respectively and acceptable cycling stability with capacitance loss of 27.7% after 10,000 cycles at 4 A g−1. Moreover, the designed symmetric supercapacitor based on fluorine doped tin oxide (FTO)-In(OH)3 electrodes offers a good capacitive performance (167.6 F g−1 at a low current density of 1 A g−1 and 67.36 F g−1 at a higher current density of 8 A g−1), cycling stability (80.2% retention after 2000 cycles at 4 A g−1), and a maximum energy density of 23.3 Wh kg−1 at a power density of 499.9 W kg−1. The results compared with previously reported other metal hydroxides are promising a novel battery-like capacitive material for energy storage devices as metal hydroxide-based battery-like supercapacitors.

Direct Electrosynthesis of Selective Transition-Metal Chalcogenides as Functional Catalysts with a Tunable Activity for Efficient Water Electrolysis

Transition-metal chalcogenides (TMCs) are cheap and abundant and have recently been demonstrated as promising electrocatalysts for sustainable and efficient water electrolysis. The existing TMC synthesizing methods are limited by difficulties in precise composition control and complexities in synthetic parameters, highlighting the need for a facile and viable strategy for direct synthesis of TMCs on conducting substrates. Here, we report a generalized approach for direct synthesis of a variety of high-efficient, robust TMCs and stoichiometric composition-controlled TMC catalysts on conducting three-dimensional porous substrates via an anion-assisted electrochemical deposition technique. Using this strategy, 10 different types of TMC electrocatalysts were designed and synthesized using representative transition-metal elements (Co, Fe, Mo, Ni, and W) and chalcogen elements (S and Se). In particular, NiS and FeSe exhibited excellent activity with overpotentials of 83 and 171 mV to reach a current density of 10 mA cm–2 in HER and OER, respectively. In addition, control over the stoichiometric composition was also demonstrated by adjusting the ratio of binary chalcogen anions, in turn allowing for the modification of catalytic properties. Furthermore, a water electrolysis cell with the NiS cathode and FeSe anode showed remarkable overall water splitting performance with a cell voltage of 1.52 V at 10 mA cm–2 and superior long-term stability for 100 h even at a high current density (100 mA cm–2), which was a significantly higher performance in comparison with the other reported TMC-based cells and the benchmark noble Pt/C∥IrO2 cell.

Template-Free Nanodeposition Via Surface-Specific Electrochemical Deposition for Microfluidic Applications

Many current nanodeposition techniques either require a sacrificial template or depend on brief pulsed techniques that thermodynamically prefer only specific growth orientations. Herein, an electrochemical deposition technique that permits selective growth direction without the need for a sacrificial template is presented. Using a modified surface limited redox replacement (SLRR) approach, dendritic features can be grown directly on a conductive substrate in order to prepare high surface area Au electrodes. The generally undesired defect growth in monolayer electrodeposition is exploited to promote three-dimensional metal growth at selected crystal orientations, as evidenced by scanning electron microscopy. In the present study, gold with feature sizes on the order of 100 nm has been prepared using a sacrificial lead cation. In situ demonstration of mass growth on the surface is illustrated using a quartz crystalline microbalance. Subsequent characterization with underpotential deposition emphasizes the change in surface area. Scanning electron microscopy coupled with energy dispersive x-ray analysis confirms the desired feature sizes and composition.This work is primarily motivated by the current trends towards miniaturization of analytical platforms, in particular translation of electrochemical sensors to microfluidic devices. As such, this work has been adapted towards direct electrodeposition on fluorine-doped tin oxide (FTO). Devices composed of polydimethylsiloxane (PDMS) are first activated with standard oxygen plasma treatment followed by bonding to the FTO substrate. The precursor electrodeposition solution is passed through a microfluidic channel and electrodeposition occurs within the device. Future work includes x-ray diffraction to further verify preferred growth orientations as well as biofouling studies to determine anti-fouling resiliency.

Development of Bimetallic Film with Electrocatalytic Activity in Non-Enzymatic Glucose Oxidation

Fast and reliable detection of glucose is of great scientific and technological importance both in clinical diagnostics and analytical practices industrial applications. Besides the necessity of glucose detection and quantization as an application in environmental pollution monitoring, biotechnology, and food industry, it is essential for the detection and regular monitoring of diabetes mellitus in clinical diagnostics. This metabolic disorder results from the deficiency of insulin and hyperglycemia and results in the fluctuation of blood glucose level with a value falling outside the normal range of 4.4 – 6.6 mM. In detail, blood sugar concentration for healthy people range between 4.0 and 5.4 mM in fasting and up to 7.8 mM in postprandial glucose. A prolonged increase in the blood glucose concentration, will cause severe damage to essential human body organs. Thus affordable, efficient and regular monitoring of blood glucose level is necessary to avoid major health complications.Presently, enzyme-based glucose sensors are the most widely distributed and commercially produced devices for monitoring glucose level at home and clinics. Despite the prompt sensitivity and selectivity, enzymatic glucose sensors suffer from drawbacks due to denaturization of enzymes, higher cost, lesser reproducibility, and lack of stability from temperature fluctuations, pH variation, and humidity. These drawbacks were overcome by the non-enzyme sensors, particularly, the metal based amperometric sensors with direct detection of glucose, owing to its good stability, simplicity, and reproducibility. However, detection of glucose using non-enzymatic metal-based sensors via direct oxidation have their own set of challenges. Precious metal-based sensors, besides being expensive, have recorded narrow linear current response ranges, limited sensitivity and selectivity, and surface poisoning from the adsorbed intermediates and interferences from chloride ions.In this work fabrication of non-enzymatic transition metal-based glucose sensors with good stability, linear range of response covering the normal glucose levels of human, lower detection limit, faster response, workable sensitivity and low cost, were studied. Here, we have researched thin film electrodes of single transition metal as well as bimetallic nanostructures to enhance the surface area, catalytic active sites and electrochemical properties via synergic effects. A two-stage electrochemical deposition technique was used to fabricate bimetallic thin films. A uniform film of nickel (Ni) crystals were formed on the titanium (Ti) cathode. Post the deposition of Ni coating, another two set of samples were prepared with a second-stage electrochemical reduction of silver (Ag) and copper (Cu) nanoparticles on the surface on Ni-coated Ti plate. Scanning electron microscopy images revealed a uniform film of transition-metal nanocrystals with varying diameter depending on the deposition conditions.The electrochemical behavior and the electrocatalytic properties of the as-prepared bimetallic films towards glucose oxidation were studied using cyclic voltammetry and amperometric techniques. The three metallic films investigated, namely, Ni, NiAg, and NiCu showed a fast response towards non-enzymatic glucose oxidation and detected amperometric signals that were linearly proportional in the 0.2-1.8 mM, 0.2-6.4 mM, and 0.2-12.2 mM ranges, respectively and with sensitivity values of 110 μm mM-1 cm-2, 320 μm mM-1 cm-2, and 420 μm mM-1 cm-2, respectively. The sensitivity of the bimetallic films was recorded higher than the monolayer of Ni nanocrystals due to higher surface area and low detection limits were recorded for all the samples. Besides that, for all the three samples, both the cathodic reduction peak current (Ipc) and anodic oxidation peak current (Ipa) increased linearly with the square root of the scan rate between 10 mV/s and 100 mV/s signifying that the electrocatalytic reaction is limited by the diffusion of the glucose molecules into the electrode/electrolyte interface. The as-fabricated bimetallic films are thus promising candidates for electrocatalytic glucose oxidation reaction with wide linear detection range covering the physiological levels of glucose.

Facile Fabrication of MnO2/Graphene/Ni Foam Composites for High-Performance Supercapacitors.

A novel MnO2/graphene/Ni foam electrode was fabricated via the impregnation and electrochemical deposition technique with Ni foams serving as substrates and graphene serving as a buffer layer for the enhanced conductivity of MnO2. The samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Compared with other methods, our strategy avoids using surfactants and high-temperature treatments. The electrodes exhibited excellent electrochemical performance, high capabilities, and a long cycle life. Various electrochemical properties were systematically studied using cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that the specific capacitance of the MnO2/graphene/Ni composite prepared at 1 mA cm−2 of electrodeposition could achieve a scan rate of 10 mV s−1 at 292.8 F g−1, which confirmed that the graphene layer could remarkably improve electron transfer at the electrolyte–electrode interface. The capacitance retention was about 90% after 5000 cycles. Additionally, a MnO2/graphene//graphene asymmetric supercapacitor was assembled and it exhibited a high-energy density of 91 Wh kg−1 as well as had an excellent power density of 400 W kg−1 at 1 A g−1. It is speculated that the strong adhesion between the graphene and MnO2 can provide a compact structure to enhance the mechanical stability, which can be applied as a new method for energy storage devices.

Electrochemical growth of two-dimensional MoS2 nanosheets for development of femtomolar Hg(II) ion label-free biosensor

2D-Molybdenum disulfide (MoS2) is a transition metal dichalcogenide with unique conducting and optoelectronic properties. This paper proposes a novel facile method to grow 2D (MoS2) thin films by carboxylation of (MoS2) nanoflakes using electrochemical deposition technique. The growth of the films was confirmed by atomic force microscopy. Further, an electrochemical Hg(II) ion biosensor was developed using as-grown (MoS2) nanosheets functionalized with single-stranded deoxyribonucleic acid (ssDNA). The label-free electrochemical biosensor offered an excellent detection limit in the range of 10 fM to 10 nM of mercury concentrations. The selectivity measurements and environmental sample studies further revealed their superior applicability in environmental monitoring purposes.

Electrochemical synthesis of PdNPs@MnO2-PPy nanocomposite and its electrocatalytic application towards glycerol oxidation

Direct alcohol fuel cell (DAFC) exhibits several unique features, such as the high tendency to energy conversion, low cost, abundance of fuel, less hazardous to the environment, and simple handling, and has diverse applications in microelectronics. In this context, the present study describes a facile and straightforward method to fabricate the PdNPs@MnO2-PPy catalyst as an anode electrode for the oxidation of glycerol in an alkaline medium. Herein, the PdNPs@MnO2-PPy catalyst was developed through a two-step electrochemical deposition technique. The as-prepared catalyst was characterized by physicochemical and electrochemical techniques. Electrochemical measurements revealed that the PdNPs@MnO2-PPy catalyst exhibits excellent catalytic properties, anti-poisoning resistance to intermediates, and durability than that of already reported catalysts and Pd/C. These unique advantages of the proposed catalyst have been achieved due to PdNPs, strong synergistic effects, and MnO2-PPy support providing superior electron transfer. The proposed electrocatalyst exhibits high current density (240.2mA/cm2), large electrochemically active surface area (302.1 m2g−1), and good long-term stability (450 cycles). Further, the electrocatalysis mechanism of glycerol oxidation was studied. The design, synthesis, and excellent catalytic response of PdNPs@MnO2-PPy offer a conception and promising potential to be used as an anode electrode in direct alcohol fuel cells.

Investigation on the Electrochemical Deposition of Nanocrystalline Zinc with Cationic Polyacrylamide (CPAM)-ZnSO4 Electrolyte.

The electrochemical deposition of nanocrystalline zinc has high potential to deposit zinc coatings, which have improved wear and corrosion properties compared to conventional coating methods. Conventionally, two or more additives are used in the electrolyte for the formation nanocrystalline zinc; these electrolyte components are complex, and their maintenance is inconvenient, making it unstable and not suitable for industrial scale production. This paper proposes an electrochemical deposition technique for nanocrystalline zinc using a ZnSO4 solution with cationic polyacrylamide (CPAM) as the unique additive. The results reveal that the cationic degree of CPAM has a significant influence on the deposition process and that the cationic degree of 20% enhances the electrolyte conductivity and improves the density of the deposited coating. The concentration of CPAM affects the electrolyte viscosity and conductivity. CPAM with a concentration of 20 g/L could simultaneously improve the electrolyte conductivity and maintain the viscosity at a low value, which promotes the formation of a bright deposited coating with a grain size of 87 nm. Additionally, the current density affects the grain structure of the deposited coating. With a current density of 0.5 A/dm2, a dense coating with lamellar grains and a grain size of 54.5 nm was obtained, which has, and the surface roughness was reduced to 0.162 μm. Moreover, the corrosion resistant property of the deposited coating was also improved.

Studying structural, magnetic and morphological features of electrochemically fabricated thin films of Co–Ni–Fe with different Fe compositions

In this work, a detailed study on the influence of the Fe composition on the crystallite size, lattice parameter, crystallographic texture, coercive field (Hc), magnetic squareness ratio (SQR), domain structure, surface roughness and grain size in electroplated Co–Ni–Fe deposits was carried out. For this aim, Co–Ni67, Co–Ni61–Fe6 and Co–Ni54–Fe13 thin films with different Fe compositions were fabricated using electrochemical deposition technique. The results showed that the composition of Fe in the deposit depends on the concentration of Fe ions in the electroplating solution. An increase in the Fe composition caused a noticeable reduction in the size of crystallites and induced a considerable enhancement in the strength of the preferred orientation being in the [111] direction. It was also observed that an increase in the Fe composition makes the lattice parameter larger. Compared to other deposits, the Co–Ni54–Fe13 with the highest Fe composition exhibited a lower surface roughness and a more compact nodular surface topography consisting of relatively finer grains. All deposits displayed a stripe domain (SD) structure, an in–plane magnetic hysteresis loop with a vertical magnetization component and a semi–hard magnetic property. However, the Hc value, SQR parameter and SD width varied in accordance with the Fe composition.

Enzyme-Free Molecularly Imprinted and Graphene-Functionalized Photoelectrochemical Sensor Platform for Pollutants.

In this work, a label-free nonenzymatic photoelectrochemical (PEC) sensor is successfully developed for the detection of a typical pollutant, microcystin-LR (MC-LR), based on a visible-light-responsive alloy oxide, with highly ordered and vertically aligned Ti-Fe-O nanotubes (NTs) as substrates. Ti-Fe-O NTs consisting mainly of TiO2 and atomically doped Fe2O3 are in situ prepared on a Ti-Fe alloy by electrochemical anodic oxidation. Using a simple electrochemical deposition technique, reduced graphene oxide (RGO) could be grown onto Ti-Fe-O NTs, exhibiting significant bifunctions. It not only provides an ideal microenvironment for functionalization of molecularly imprinted polymers (MIPs) on the surface but also serves as the PEC signal amplification element because of its outstanding conductivity for photons and electrons. The designed MIP/RGO/Ti-Fe-O NT PEC sensor exhibits high sensitivity toward MC-LR with a limit of detection as low as 10 pM. High selectivity toward MC-LR is also proven for the sensor. A promising detection platform not only for MC-LR but also for other pollutants has therefore been provided.

The effect of boric acid content on the properties of electrochemically prepared Ni–Fe/ITO thin films

This paper reports the role of the boric acid (H3BO3) content in a sulphate based aqueous electrolyte (AE) on the magnetic characteristics, deposit composition, domain structure, surface morphologies and structural properties of the Ni–Fe/ITO thin film samples grown by electrochemical deposition (ED) technique. The results show that the amount of the H3BO3 must be controlled to obtain the proper Ni–Fe/ITO thin film samples without brittle properties. The influence of the H3BO3 content in the AE on the deposit composition, structural parameters and magnetic characteristics is found to be negligible. However, the roughness parameters and the size of the nodular particles are noticeably influenced by the H3BO3 content. All samples have nanosized crystallites in the range of 19.6–20.5 nm. The films possess almost the same magnetic squareness ratio (%11 ± 2) and coercivity values (49 ± 1 Oe). In all deposits, regardless of the H3BO3 content, quite large magnetic stripe domains with a width of 1.6 ± 0.2 μm are also detected. The films exhibit a uniform surface structure consisting of nodular particles. However, increasing H3BO3 content in the AE leads to a dramatic reduction in the width of the surface particles. Furthermore, the surface roughness of the samples considerably decreases as the H3BO3 content in the AE is increased.

Impact of precursor concentrations and substrate type on properties of electrodeposited CdO nanorod thin films for optoelectronic applications

We present here the fabrication of CdO nanorod thin films employing electrochemical deposition technique as low temperature and economical method. Effect of cadmium ions precursor and substrate type were deeply studied to examine structural, morphology, and optical properties of deposited thin films utilizing XRD, SEM, UV–Vis, and PL spectroscopy techniques, respectively. The results designate the formation of a pure phase of face-centered cubic for CdO thin films for different ion concentrations and both substrates. Grown samples have surface morphology of nanorods that changed to nanosheets with increasing Cd+2 ions concentration on ITO substrates while for FTO substrates, it has the same shape with a small decrease in grain sizes. Band gap energy was estimated from the Tauc equation that has average values from 2.5 to 2.2 eV and from 2.5 to 2.3 eV for ITO and FTO, respectively with increasing of molarity from 0.2 to 0.8 M. The growth rate and the conductivity of substrates are the main factors for obtaining different structure, morphology, and different optical band gaps for the fabricated CdO samples as confirmed by current-time curves of electrodeposition process. Photoresponse of the fabricated CdO thin films was evaluated under dark and light conditions. Therefore, our results indicate that the electrodeposited CdO nanorods and nanosheets shapes with different bandgap energy is a promising candidate for the fabrication of optoelectronic devices.

Novel nano-engineered environmental sensor based on polymelamine/graphitic-carbon nitride nanohybrid material for sensitive and simultaneous monitoring of toxic heavy metals

Heavy metal ions (HMIs) pollution is always a serious issue worldwide. Therefore, monitoring HMIs in environmental water is an important and challenging step to ensure environmental health and human safety. In this study, we spotlight an effortless, single-step in-situ electrochemical polymerization deposition technique to fabricate a novel, low-cost, efficient, nano-engineered poly(melamine)/graphitic-carbon nitride nanonetwork (PM/g-C3N4) modified screen-printed carbon electrode (SPE) for sensitive, selective, and simultaneous electrochemical monitoring of toxic HMIs in environmental waters. g-C3N4 nanomaterial was prepared using melamine as a precursor via pyrolysis technique. As-prepared g-C3N4 and melamine monomer were electrochemically in-situ polymerized/deposited over pre-anodized SPE (ASPE) using cyclic voltammetry technique. XRD, XPS, and SEM were engaged to characterize the developed electrode. The fabricated PM/g-C3N4/ASPE was applied as an environmental sensor to selective and simultaneous electrochemical detection of Pb2+ and Cd2+ ions using differential pulse voltammetry technique. The developed sensor displayed excellent selectivity and sensitivity towards Pb2+ and Cd2+ with limit of detections of 0.008 µM and 0.02 µM, respectively. The fabricated PM/g-C3N4/ASPE sensor exhibits superior stability, repeatability, good anti-interference, and applicability for recognition of Pb2+ and Cd2+ ions in real water samples. These results proved that developed environmental sensor is low-cost, efficient, practical platform for rapid, selective, simultaneous monitoring of HMIs in the environment.

Synthesis of Nanostructured Metallic Foams By Plasma Electrolysis Deposition

Within the framework of fundamental physics studies at CEA, laser target experiments are conducted to investigate laser-matter interactions. Some of these experiments require metallic foams samples in a milimetric scale with an apparent volumetric mass within few hundreds milligrams per cube centimeters. Metallic foams materials are developed and studied since few years for their unique properties offered by their aerated structure. For example, due to a high specific surface, metallic foams could find applications in batteries, supercapacitors, as well as chemical sensors. However, all the metallic foams obtained by the processes referenced in the literature do not meet the specifications needed for laser experiments. This is why, the CEA has developed a new and innovative technique to synthetize metallic foams by plasma electrolysis deposition [1].This process consists in applying a voltage within the 20-100V range at a cathode immerged in a solution containing metallic ions. Under these specific conditions, a uniform gaseous sheath is created around the cathode which is then isolated from the liquid. Due to the high electrical field applied at the electrode surface, several electrical plasma discharges are formed between the cathode and the gas/liquid interface. When the electrical discharges meet the solution, metallic cations are reduced to form metallic strands about 100 nm in diameter. The formed strands are all interconnected together to form metallic foam with micrometric porosities [2]. A few millimeters wide foam with a volumetric mass up to 100mg/cc is obtained in about 10 seconds which is very fast compared to classical electrochemical deposition techniques. The foams synthetized can be made up of pure metals (Cu, Au, Pt ...) or alloys (AuCu ...) in accordance to the metallic ions diluted in the solution.In order to control the shape and homogeneity of the synthetized foams, a better understanding of the mechanisms involved in the foams’ growth is required. By direct camera observation, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), we can show that the growth behavior and the structure of the foams vary with the applied voltage. We observe three main growth patterns which seem to correspond to the different propagation modes of streamer type electrical discharges reported in the literature on plasma discharges in dielectric liquids [3,4]. The first one obtained at “low” voltage is composed of very thin strands (Ø < 100 nm) growing linearly with few ramifications. The second one is formed by highly branched strands about 100 to 600 nm in diameter. TEM observations of first and second mode strands show that their structure is monocrystalline and field oriented. A third mode obtained at the highest voltages is made up of strands above 1 µm thick with a shape very similar to the aggregates obtained in diffusion limited conditions [5]. Voltammetry studies conducted on the electrolytes show that the reduction of metallic species are indeed diffusion limited. Moreover a lower limit current corresponds to a more predominant germination phenomenon on strands. The mass transportation plays a major role alongside the applied voltage in defining the growth mode of the metallic foams and the microstructure of the strands. The structure of the metallic strands and it’s evolution with the synthesis parameters seems in accordance to the electrodeposition theory [6]. However if our results indicate that the reduction and crystallization of the strands may result from an electrochemical process, the field oriented crystalline structure obtained is unlikely to be possible inside an aqueous electrolyte with the speed of growth observed. We conclude this work by proposing an original mechanism for the growth of the foam involving electrochemistry within a plasma medium.

Coelectrodeposition of crystalline copper-manganese oxide containing CuMn2O4 spinel for high energy supercapacitor application

In this study, copper manganese oxide films with various compositions were synthesized using electrochemical deposition technique. In order to achieve different chemical compositions, the influence of sodium citrate as a complex agent was investigated. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Brunauer-Emmet-Teller adsorption (BET) were used to study the morphology, chemical composition, crystal structure and surface area of deposited layers, respectively. We observed that by optimizing the citrate concentration in the electrodeposition electrolyte, improved capacitance of 744 F/g at 10 mV/s with retention capacitance of 91% over 10,000 cycles can be achieved. The obtained stability of copper-manganese oxide is 3 times and about 2 times higher than pristine copper oxide and manganese oxide, respectively. The enhanced stability of the achieved crystalline copper-manganese oxide ascribe to formation of CuMn2O4 spinel, improved ultrafine structure and a better chemical stability.

Insight towards Nucleation Mechanism and Change in Morphology for Nanostructured Platinum Thin Film Directly Grown on Carbon Substrate via Electrochemical Deposition.

Nanocrystalline platinum with different morphologies is synthesized via electrochemical deposition technique. The nucleation mechanism and its structural effect over the electrodeposited Pt on carbon electrodes have been systematically studied. Powder X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy are employed to study nucleation, oxidation states, and Pt structure growth on a carbon electrode. This study reports significant development of Pt metal nanoparticles with different morphologies such as a sphere, flower, core-flower, and rod-like structure directly fabricated on carbon electrode while tuning the deposition parameters such as current density, time, temperature, pH during the deposition process. The proposed electrochemical route represents a superior fabrication procedure for large-scale electrode fabrication compared to a conventional method for preparing membrane electrode assemblies for fuel cell stacks.