The application of photoelectrochemical techniques to the in situ characterisation of passive layers on metals and alloys is reviewed. Complications arise when dealing with thin films having strongly disordered structure. Some selected examples are presented concerning model systems, which form stable surface layers with constant composition in large ranges of electrode potential and film thickness, as well as corrosion product layers on metals and alloys of commercial interest.

The great success of anodic alumina membranes is due to their morphological features coupled to both thermal and chemical stability. The electrochemical fabrication allows accurate control of the porous structure: in fact, the membrane morphological characteristics (pore length, pore diameter and cell density) can be controlled by adjusting the anodizing parameters (bath, temperature, voltage and time). This article deals with both the fabrication and use of anodic alumina membranes. In particular, we will show the specific role of the addition of aluminum ions to phosphoric acid-based anodizing solution in modifying the morphology of anodic alumina membranes. Anodic alumina membranes were obtained at −1 °C in aqueous solutions of 0.4 M H3PO4 added with different amounts of Al(OH)3. For sake of completeness, the formation of PAA in pure 0.4 M H3PO4 in otherwise identical conditions was also investigated. We found that the presence of Al(OH)3 in solution highly affects the morphology of the porous layer. In particular, at high Al(OH)3 concentration (close to saturation) more compact porous layers were formed with narrow pores separated by thick oxide. The increase in the electric charge from 20 to 160 C cm−2 also contributes to modifying the morphology of porous oxide. The obtained anodic alumina membranes were used as a template to fabricate a regular array of PdCo alloy nanowires that is a valid alternative to Pt for hydrogen evolution reaction. The PdCo alloy was obtained by electrodeposition and we found that the composition of the nanowires depends on the concentration of two metals in the deposition solution.

Organometallic perovskites are one of the most investigated materials for high-efficiency thin-film devices to convert solar energy and supply energy. In particular, methylammonium lead iodide has been used to realize thin-film perovskite solar cells, achieving an efficiency higher than 20%. Different fabrication procedures based on the spin-coating technique have been proposed, which do not ensure homogenous morphologies. In this work, we present a scalable process to fabricate methylammonium lead iodide thin films directly on conductive substrates, consisting of electrodeposition and two subsequent chemical conversions. A thorough investigation of the morphological, structural and compositional properties of the layer is performed after each fabrication step. It is demonstrated that this method allows fine control of the thickness of the layer by tuning the cell parameters during the electrodeposition step. X-ray diffraction patterns and energy-dispersive X-ray analysis indicate the achievement of high-purity methylammonium lead iodide layers. Micro-Raman analyses were used to demonstrate the formation of methylammonium lead iodide. Finally, ultraviolet-visible absorption spectra were acquired to determine the optical band edge of the layer (is an element of 1.56 eV) and the absorbance of methylammonium lead iodide as a function of the film thickness. As expected, the material exploits excellent optical properties, achieving an absorption >= 99.9% in the entire visible range for a layer thickness of 1.3 mu m. The results presented here pave the way for the application of cost-friendly solution-based processes to fabricate high-quality perovskite solar cells.

In this work, the galvanic deposition method is used to deposit coatings of brushite/hydroxyapatite/polyvinyl acetate on 304 stainless steel. Coatings are obtained at different temperatures and with different sacrificial anodes, consisting of a mixture of brushite and hydroxyapatite. Samples are aged in a simulated body fluid (SBF), where a complete conversion of brushite into hydroxyapatite with a simultaneous change in morphology and wettability occurred. The corrosion tests show that, compared with bare 304, the coating shifts Ecorr to anodic values and reduces icorr Ecorr, and icorr has different values at different aging times due to chemical interactions at the solid/liquid interface. The best performing deposits are those obtained by using Al as the sacrificial anode. The metal ion release, measured after 21 days of aging, is very low and is attributable to the presence of a coating that slows the steel corrosion. Coating cytotoxicity is investigated through cell viability assays with MC3T3-E1 osteoblastic cells. The results reveal a high cytocompatibility comparable to that of a pure cell culture medium.

It is well known that physical and surface properties of nanomaterials are promising to enhance efficiency of nanostructured devices for sensing and for sustainable energy production, conversion, and storage. However, the practical use of nanomaterials is often complicated by the lack of scalable and cost-efficient synthesis procedures and the challenge of integrating into devices 1D nanomaterials saving their structural features. In this field, one of the most severe challenges is to find suitable methods for fabricating nanomaterials. Over the years, numerous preparation methods were proposed in the literature, but not all of them are easily scalable and economically advantageous for industrial application. In this context, electrochemical deposition in template is a facile method for fabricating either two- or one-dimensional nanostructured materials because it allows to easily adjusting the fundamental parameters controlling their final features. Electrochemical processes are, usually, cheap and environmental friendly, and they can be easily scaled-up from lab to industrial level. In this chapter, we will describe different electrochemical methods, electrodeposition, galvanic deposition electroless deposition and electrogeneration of base, that permit to obtain different type of nanomaterials such as metals, oxide, and semiconductors. In addition, also the performances of different nanostructured materials are presented.

It is well known that physical and surface properties of nanomaterials are promising to enhance efficiency of nanostructured devices for sensing, and for sustainable energy production, conversion, and storage. However, the practical use of nanomaterials is often complicated by the lack of scalable and cost-efficient synthesis procedures and the challenge of integrating into devices 1D nanomaterials saving their structural features. In this field, one of the most severe challenges is to find suitable methods for fabricating nanomaterials. Over the years, numerous preparation methods were proposed in the literature, but not all of them are easily scalable and economically advantageous for industrial application. In this context, electrochemical deposition in template is a facile method for fabricating either two- or one-dimensional nanostructured materials because it allows to easily adjusting the fundamental parameters controlling their final features. Electrochemical processes are, usually, cheap and environmental friendly, and they can be easily scaled-up from lab to industrial level. In this chapter we will describe different electrochemical methods, electrodeposition, galvanic deposition, electroless deposition, and electrogeneration of base, that permit to obtain different types of nanomaterials such as metals, oxide, and semiconductors. In addition, also the performances of different nanostructured materials are presented.

During the last decades, biomaterials have been deeply studied to perform and improve coatings for biomedical devices. Metallic materials, especially in the orthopedic field, represent the most common material used for different type of devices thanks to their good mechanical properties. Nevertheless, low/medium resistance to corrosion and low osteointegration ability characterizes these materials. To overcome these problems, the use of biocoatings on metals substrate is largely diffused. In fact, biocoatings have a key role to confer biocompatibility properties, to inhibit corrosion and thus improve the lifetime of implanted devices. In this work, the attention was focused on Hydroxyapatite-Chitosan (HA/CS) and Hydroxyapatite-Polyvinylacetate (HA/PVAc) composites, that have been studied as biocoatings for 304 SS based devices. Hydroxyapatite was selected for its osteoconductivity thanks to its chemical structure similar to bones. Furthermore, Chitosan and Polyvinylacetate are largely used yet in medical field (e.g. antibacterial agent or drug deliver) and in this work were used to create a synergic interaction with hydroxyapatite to increase the strength and bioactivity of coating. Biocotings were obtained by galvanic deposition process that does not require an external power supply. It is a spontaneous electrochemical deposition in which materials with different standard electrochemical potential were short-circuited and immersed in an electrolytic solution. Electrons supply for the cathodic reaction in the noblest material comes from oxidation of the less noble material. SEM, EDS, XRD and RAMAN were performed for chemical-physics characterization of biocoatings. Polarization and impedance measurements have been carried out to evaluate corrosion behavior. Besides, in-vitro cytotoxicity assays have been done for the biological features.

A galvanic method to deposit chitosan coatings on stainless steel substrate is reported. Deposition of suitable coatings is desired to improve biocompatibility and corrosion resistance of metallic medical devices to be implanted in human body. In the present work, a thin hydrogel layer of chitosan was deposited on 304SS by a galvanic displacement reaction, which is advantageous first as it does not require external power supply. 304SS was immersed into an aqueous solution of chitosan/lactic acid and electrochemically coupled with magnesium acting as a sacrificial anode. SEM images showed the formation of a uniform layer of chitosan with a thickness controlled by deposition time. Corrosion tests in simulating body fluid showed that chitosan coatings shift the corrosion potential of 304 substrates toward nobler values. Finally, the cytotoxicity of the coating was investigated through cell viability assays with osteoblastic cell MC3T3-E1. The results revealed highly satisfying biocompatibility of the coating.

In this paper, we report a detailed study on the synthesis of composite nanowires of Pb-PbOHCl via galvanic deposition into the pores of a membrane acting as a template. PbOHCl deposition quantitatively occurs as the solution pH exceeds the value of about 4.12. Simultaneously, owing to the galvanic coupling, electro-deposition of lead occurs, so composite nanowires were formed. The role of different parameters controlling the kinetic evolution of the process, such as oxygen bubbling, solution pH, surface area and type of sacrificial anode were investigated one at a time. The results suggest that every modification accelerating the alkalization of the solution inside the template pores favors growth of composite nanowires richer in PbOHCl. Alumina and polycarbonate membranes were investigated as template, and the best results were obtained for polycarbonate membrane, which can be easily removed by dissolution in CHCl₃ avoiding the collapse and successive loss of the nanowires.

Corrosion behavior and cytotoxicity was reported for mixed brushite (BS)/hydroxyapatite (HA) coatings deposited on 316LSS substrate through a displacement reaction. Corrosion tests, carried out in a simulated body fluid, showed that in comparison with bare 316L, coating shifts E-corr to anodic values and reduces i(corr) even if oscillations were observed, which were explained in terms of the chemical interactions at the solid/liquid interface. Cell biocompatibility of the coating was investigated through osteoblastic cell line MC3T3-E1, evidencing the absence of any cytotoxicity Taken together, the results show that galvanic deposition is a simple and cost-effective method for producing bioactive coatings which enhance corrosion resistance and biocompatibility of the substrate. (C) 2018 The Electrochemical Society.

NiO thin film thermally grown on Ni was investigated for the first time as an electrochemical sensor of mercury ions in water. The film was obtained by thermal oxidation in air of a commercial Ni foil. The influence of oxidation temperature, and time have been investigated by XRD, SEM, and EDS analysis. Square wave anodic stripping voltammetry was used for detecting Hg2+ ions in aqueous solution with different ion concentrations. In order to improve the response signal, all the operational parameters related to the sensing process such as pH, deposition time, potential, and square wave frequency, have been optimized. We obtained a detection limit of 4.4 ppb with a sensitivity of 1.1 µA ppb-1 cm-2.

AgSe based nanostructures (nanowires or nanotubes) were obtained by electrodeposition. A systematic investigation was carried out, varying concentration of the precursors, pH of the electrolytic solution, ligands, and deposition mode, to study the effect of all these parameters on the growth of nanostructures. Nanostructure morphology depends also on the type of metal that was used as support, due to the secondary reaction of hydrogen evolution. On Ni support, the H-2 evolution reaction led to formation of only nanotubes, while on copper substrate also nanowires were obtained. Composition of nanostructures depends strongly on solution pH. X-ray diffraction and Raman spectroscopy showed that in thiocyanate-free bath nanostructures consist in orthorhombic Ag2Se and metallic Ag. At higher pH values, the metallic Ag phase increased and the co-deposition of Se also occurred. We also found that the use of a thiocyanate bath with a specific composition permits to obtain nanostructures of pure orthorhombic Ag2Se. (C) 2016 Elsevier Ltd. All rights reserved.

This paper presents an innovative lead acid battery, based on nanostructured active materials. Both charging time and specific energy are greatly enhanced in comparison with commercial lead acid battery. Starting from the extremely valuable performances of the nanostructured battery, also a circuital model, for application in electric vehicle traction, has been specifically developed. The circuital model has demonstrated that an enhanced nanostructured battery allows an increase of traveled distance by electric vehicles.

A nanostructured electrochemical sensor of hydrogen peroxide was fabricated growing self-standing Pd nanowires (Pd NWs) into polycarbonate (PC) membranes through a simple metal galvanic deposition. Conditions of deposition were adjusted in order to attain 2-5 mu m long Pd wires. Characterization of Pd NWs was performed by scanning electrode microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Properties of the nanostructured sensor were studied by cyclic voltammetry and chronoamperometry in phosphate buffer ethanol solution. Addition of pure ethanol to the test solution was essential in order to increase wettability of the nanostructures. Sensing features were compared with those of both compact and nanoparticle film. Results show stable behavior and sensitive response of Pd NWs towards H2O2 with a wide linear dependence over H2O2 concentration for the electrodes consisting of long Pd nanowires/nanotubes, which display an increase of sensitivity and lower limit of detection (LOD) in comparison with the other sensors. Also the linear-response interval widens with electrode specific surface area. Accuracy and selectivity (towards different electroactive species) is excellent. (C) 2017 Elsevier B.V. All rights reserved.

This study was carried out to recover copper from printed circuit boards of waste computers through an electrochemical process. To simplify the overall recovery process, large pieces of printed circuit boards were used instead of pulverized samples. In particular, these large pieces were directly used as an anode for copper electrorefining. For this purpose, electronic components and solder mask were initially removed from the boards. The electronic components can be treated separately to recover precious metals using various methods. The removal of solder mask was necessary to expose copper layers to the electrolytic solution and it was removed by a chemical treatment with sodium hydroxide. Electrolytic solution was a mixture of copper sulphate and sulphuric acid, and was maintained at 60°C during the process. The recovery of copper was conducted in an electrochemical cell where the anode was supplied by a constant current of 900 mA. The deposited copper was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Results show a uniform cathodic deposit of pure copper having a thickness of about 32.35 µm. The copper current efficiency was of 84% with a removal degree of copper from printed circuit board of about 46%.

In the field of water-alkaline electrolyzer, the development of nanoporous low cost nickel electrodes is one of the potential approaches to increase electrocatalytic activity. Template electrodeposition is a facile and cheap technique for obtaining Ni nanowires (NWs) with high surface area. These nanostructures were fabricated by a two-step procedure. In the first step, a Ni compact layer was deposited on one side of the template where a gold film was previously sputtered, while, in the second-step, an ordered array of Ni-NWs was obtained by electrodeposition inside the template channels. The NWs were firmly connected to the underlying Ni layer, acting as a current collector. In order to enhance the catalytic activity, Pd nanoparticles were deposited onto the NW surface by metal displacement. All electrodes were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The comparison between the two types of electrodes revealed that the composite electrode (Ni+Pd) shows better electro-catalytic features, which quickly decay under operation, so that after 5 min. of polarization at a constant current in 30% w/w aqueous solution of potassium hydroxide, the other electrode performs better.

Lead-acid batteries are widely used for energy storage, due to a well-established and reliable technology. Over the years, various studies for improving the performance of this battery have been performed. The main goal is to replace conventional plates with innovative electrodes having good stability, high capacity and high surface area. In particular, it is necessary to improve the kinetics of electrochemical conversion reactions at the electrode-solution interface, and to guarantee good electrical continuity during repeated charge/discharge cycles. To achieve these goals, the attention was focused on nanostructured electrodes. Up-to-date, two principal approaches have been followed. In the first approach, 3D nanostructured current collector, such as carbon foam or 3D porous titanium, was used in place of conventional lead grid. The second method is based on the fabrication of nanostructured active material, such as nanoparticles. Our idea follows the last approach, making nanostructured active material through the synthesis of nanowires. In particular, we have obtained Pb nanostructured electrodes by template electrosynthesis in nanoporous polycarbonate membrane. These electrodes have high surface area, and allow high utilization of the active material leading to high specific energy. Here, we show that battery with nanostructured Pb electrode works at 1C charge and discharge with very good stability for over 1200 cycles, and discharge efficiency around 90%. It is important to highlight that the C- rate here tested is far higher than that of commercial batteries, whose highest operative rate is C/5 while at 1C typically provide a capacity of 30 mAh g-1 for only 20-30 cycles.

In this work, the electrodeposition of Cu2ZnSnS4 thin films on molybdenum thin foil was reported. In order to guarantee co-deposition of elements with different standard electrochemical potential, an aqueous electrolyte added with ligand agents was used. I addition, deposition parameters were carefully chosen, in order to ensure good quality and suitable composition of the films. The deposited films were sulfurized in controlled atmosphere at 580 degrees C, scrutinizing the influence of the annealing conditions on the features of the films. Structure, morphology and composition were investigated by XRD SEM, EDS and Raman spectroscopy. Results reveal the growth of good quality films, with a uniform morphology and chemical composition suitable for solar cell application. (C) 2016 The Electrochemical Society. All rights reserved.

In this work, brushite and brushite/hydroxyapatite (BS, CaHPO4·H2O; HA, Ca10(PO4)6(OH)2) coatings were deposited on 316L stainless steel (316LSS) from a solution containing Ca(NO3)2·4H2O and NH4H2PO4 by a displacement reaction based on a galvanic contact, where zinc acts as sacrificial anode. Driving force for the cementation reaction arises from the difference in the electrochemical standard potentials of two different metallic materials (316LSS and Zn) immersed in an electrolyte, so forming a galvanic contact leading to the deposition of BS/HA on nobler metal. We found that temperature and deposition time affect coating features (morphology, structure, and composition). Deposits were characterized by means of several techniques. The morphology was investigated by scanning electron microscopy, the elemental composition was obtained by X-ray energy dispersive spectroscopy, whilst the structure was identified by Raman spectroscopy and X-ray diffraction. BS was deposited at all investigated temperatures covering the 316LSS surface. At low and moderate temperature, BS coatings were compact, uniform and with good crystalline degree. On BS layers, HA crystals were obtained at 50°C for all deposition times, while at 25°C, its presence was revealed only after long deposition time. Electrochemical studies show remarkable improvement in corrosion resistance.