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.

In this work, an electrochemical sensor for uric acid determination is shown with a preliminary study for its validation in real samples (milk and urine). Uric acid can be electrochemically oxidized in aqueous solutions and thus it is possible to obtain electrochemical sensors for this chemical by means of this electrooxidation reaction. Indium tin oxide coated on flexible polyethylene terephthalate substrate, modified with reduced graphene oxide and gold nanoparticles by co-electrodeposition, was used. Electrodeposition was performed at -0.8V vs SCE for 200 s. All samples were characterized by electron scan microscopy and electron diffraction spectroscopy. A careful investigation on the effect of pH was performed to understand its influence on uric acid oxidation. The detection of uric acid was using the linear sweep voltammetry. Results show that the peak current increases linearly with uric acid concentration from 10 to 1000 µM with a limit of detection of about 7.1 µM. The sensor shows high selectivity towards different interferents that can be found in the milk and urine matrix, such as chloride, calcium, sodium and ammonium ions. To prove the applicability of the proposed sensor, uric acid was quantified in real milk and urine samples with excellent results comparable to those of conventional techniques.

Ni-Co alloy nanostructured electrodes with high surface area were investigated both as a cathode and anode for an alkaline electrolyzer. Electrodes were obtained by template electrosynthesis at room temperature. The electrolyte composition was tuned in order to obtain different NiCo alloys. The chemical and morphological features of nanostructured electrodes were evaluated by EDS, XRD and SEM analyses. Results show that electrodes with different composition of Ni and Co, made of nanowires well anchored to the substrate, were obtained. For both hydrogen and oxygen evolution reactions, electrochemical and electrocatalytic tests, performed in 30% w/w KOH aqueous solution, were carried out to establishing the best alloy composition. Mid-term tests conducted at a constant current density were also reported. Nanostructured electrodes with a Co atomic composition of 94.73% have the best performances for both hydrogen and oxygen evolution reactions. In particular, with this alloy, a potential of -0.43 V (RHE) and of 1.615 V (RHE) was measured for hydrogen and oxygen evolution reaction at -50 mA cm(-2) and at 50 mA cm(-2), respectively, after 6 h of electrolysis. The calculated Tafel's slopes for HER and OER were -0.105 and 0.088 V/dec, respectively. Furthermore, HER and OER eta(10) potential values were measured founding -0.231 V (RHE) and 1.494 V (RHE) respectively. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Indium tin oxide (ITO) coated on flexible polyethylene terephthalate (PET) substrate electrode was modified with reduced graphene oxide and gold nanoparticles by simple co-electrodeposition performed at -0.8 V vs SCE for 200 s. All samples were characterized by electron scan microscopy. The as prepared electrode was used as electrochemical sensor to selective detection of ascorbic acid using linear sweep voltammetry. Excellent results were obtained in a linear range from 20 to 150 μM of ascorbic acid with a limit of detection of about 3.1 μM (S/N=3.3). The sensors have a reproducibility of about 5.5% and also show high selectivity towards different interferents such as chlorine, calcium, magnesium, sulphate ions, sodium and glucose. Ascorbic acid was detected also in milk samples demonstrating the possibility quantify this analyte in real samples with a very cheap method.

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.

The fabrication and characterization of nickel-alloy electrodes for alkaline electrolysers is reported. Three different alloys (Ni–Co, Ni–Zn and Ni–W) at different composition were studied in order to determine the optimum condition. Nanostructured electrodes were obtained by template electrodeposition into a nanoporous membrane, starting from aqueous solution containing the two elements of the alloy at different concentrations. Composition of alloys can be tuned by electrolyte composition and also depends on the difference of the redox potential of elements and on the presence of complexing agents in deposition bath. Electrochemical and electrocatalytic tests, aimed at establishing the best alloy composition, were carried out for hydrogen evolution reaction. Then, test conducted at a constant current density in potassium hydroxide (30% w/w) aqueous solution were also performed. For all investigated alloys, very encouraging results were obtained and in particular Ni–Co alloys richer in Co showed the best performance.

In this work, a systematic investigation of the different parameters that control the electrodeposition processes was carried out at the aim to synthetizing AgGaSe₂ nanostructures. We found that pH is a key parameter to control both the morphology and composition of the nanostructures. Low pH favours mainly the formation of Ag2Se nanotubes with a scarce mechanical stability, while multi-phase nanowires well anchored to the substrate were obtained at higher pH. We also found that it was necessary to increase dramatically the concentration of the gallium precursor into the deposition bath in order to obtain AgGaSe₂ owing to lower redox potential of the Ga3+/Ga couple than Ag2+/Ag and Se4+/Se. Besides, the addition of specific complexing agents to deposition bath was necessary to better control the composition of the nanostructures. By increasing gallium precursor concentration and adding complexing agents, it was possible to obtain for the first time nanostructures of amorphous AgGaSe₂ with different amount of Ga via one-step electrodeposition.

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.

In this work, we present some results concerning the electrochemical behavior of nanostructured-based electrochemical sensors. In particular, the attention has been focused on Pd and Cu nanowires for detection of hydrogen peroxide and NiO thin film or Ni@NiO core-shell nanowires for detection of mercury ions. Ordered array of Pd and Cu nanowires was obtained through displacement deposition reaction in a commercial polycarbonate membrane acting as a template. The method leads to stable nanostructured electrodes of Pd and Cu with high surface area. For the detection of mercury ions, we have fabricated a Ni/NiO electrochemical sensor, obtained by mild thermal oxidation of Ni-foil. Some results on Ni@NiO core-shell nanowires were also reported. The effect of oxidation time and temperature was studied in order to compare performances of the Ni@NiO nanowire array with those of NiO thin film. All samples were characterized by XRD, SEM and EDS analysis. Electrochemical tests have been conducted in order to characterize specific electrode performance such as sensibility, selectivity, and accuracy. Highly satisfying results have been obtained.

In recent years, the storage of energy produced by renewable sources has become a topic of great interest. Lead-acid batteries are widely used in this field, in particular those based on VRLA (Valve-Regulated-Lead Acid) technology, in which the electrolyte is immobilized inside the battery. In this paper, the use of a hydrogel as an electrolyte was considered. Hydrogel can be described as a three-dimensional network of a hydrophilic polymer that can absorb large amounts of water (or aqueous solutions) without dissolving. Pb and PbO2 nanostructured electrodes were used in the battery that used hydrogel as an electrolyte. Two different types of hydrogels were synthesised, both based on PVA that is a biodegradable, biocompatible, non-toxic, and non-carcinogenic polymer. The first one was obtained through physical gelling, the second one was obtained using borax (sodium tetraborate decahydrate) as a cross-linking agent. Preliminary tests of nanostructured lead-acid batteries using both types of hydrogels as an electrolyte were conducted for 100 cycles at 1C. The physically gelled hydrogel gave the best results in terms of efficiency, likely, owing to its greater absorption capacity. It was also verified that the recombination of the gases evolved during the charge phase (hydrogen and oxygen) takes place inside the battery itself. This is the major advantage of the gelled electrolyte in comparison with the liquid one.

Owing to the progressive abandoning of the fossil fuels and the increase of atmospheric CO2 concentration, the use of renewable energies is strongly encouraged. The hydrogen economy provides a very interesting scenario. In fact, hydrogen is a valuable energy carrier and can act as a storage medium as well to balance the discontinuity of the renewable sources. In order to exploit the potential of hydrogen it must be made available in adequate quantities and at an affordable price. Both goals can be potentially achieved through the electrochemical water splitting, which is an environmentally friendly process as well as the electrons and water are the only reagents. However, these devices still require a lot of research to reduce costs and increase efficiency. An approach to improve their performance is based on nanostructured electrodes characterized by high electrocatalytic activity. In this work, we show that by using template electrosynthesis it is possible to fabricate Ni nanowires featuring a very high surface area. In particular, we found that water-alkaline electrolyzers with Ni nanowires electrodes covered by different electrocatalyst have good and stable performance at room temperature as well. Besides, the results concern nickel-cobalt nanowires electrodes for both hydrogen and oxygen evolution reaction will be presented and discussed. Finally, preliminary tests concerning the use of Ni foam differently functionalized will be shown. For each electrode, electrochemical and electrocatalytic tests aimed to establishing the performance of the electrolyzers were carried out. Long term amperostatic test carried out in aqueous solution of KOH will be reported as well.

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.

Template electrosynthesis is a facile and cheap approach for obtaining nanostructures with very high surface area. This fabrication method has been used to produce electrodes for different applications, among which the electrolysis. In previous works, Ni and IrO2 nanostructured electrodes were tested for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution, respectively, without and with addition of Pd nanoparticles. In this work, Ni-Co alloy electrodes were fabricated by the same method, starting from a bath containing a mixture of Ni and Co. After fabrication of the nanostructures and template dissolution, electrodes were characterized by EDS and SEM. The results show that i) alloy deposition is possible by this method, and ii) alloy is richer in Co compared to the composition of the bath employed for deposition. In order to evaluate the electrocatalytic properties of Ni-Co electrode, electrochemical tests were performed and the results were compared with pure Ni and Co electrodes. The tests were conducted through either cyclic or linear sweep voltammetry in 30% w/w KOH aqueous solution at room temperature. For the HER, pure Ni electrode was found to be more performing. Whereas, with regard to the OER, performance of the nanostructured Ni-Co electrodes show an improvement more than 20% in terms of electrocatalysis, in comparison with pure Ni and Co electrodes.

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.

Currently, lead acid battery is extensively investigated owing to its prevalent use as a startinglighting and ignition device. An essential role for electrochemical reactions is played by the surface area available for conversion reactions and a possible approach is the use of nanostructured electrodes. In this work, lead dioxide nanostructured electrodes were tested in order to investigate the dependence of the charge and discharge behaviour on some parameters such as electrolyte concentration, and a new type of thin separator. In this last case, it is possible to reduce the size of the cell by using a very thin separator comparable to the nanostructured electrode thickness. Besides, a low concentration of electrolyte was also tested for studying its influence on the performance of a nanostructured electrode. Lead dioxide electrodes were cycled at 1C-rate and discharged to a cutoff voltage of 1.2 V up to 90% of the gravimetric capacity. Electrodes were assembled in a zero gap configuration using a commercial negative plate as counter-electrode with a large excess of active mass in comparison to the nanostructured one. Tests were conducted in very stressful conditions, in order to compare the behaviour of this new type of battery with that of the commercial one.

The worldwide growing of electrical and electronic equipment makes increasingly urgent to find environmentally friendly treatments for e-waste. In this paper, the attention has been focused on i) the eco-friendly dismantling of the electronic components from Waste Printed Circuit Boards and ii) recovering of pure metallic copper, which is the most abundant metal and one of the most valuable in Printed Circuit Boards. After an experimental optimization study, we found that a solution containing 0.5 M H2SO4, 0.4 M CuSO4, and 4 M NaCl can be successfully used to disassemble the electronic components from the boards by leaching of all exposed metals. Air was blown into the leaching solution in order to regenerate Cu2+ ions, which acts as the predominant oxidant specie. The key role in dismantling/leaching process is played by Cl- ion that stabilizes Cu+ through the chloro-complexes formation. The results show that, in this manner, the electronic components can be easier disassembled in undamaged state, allowing the efficient recycling and valorization of the base materials. The feasibility to recover electrochemically the copper from the solution resulting from dismantling/leaching tests was verified through a preliminary cyclic voltammetry study aimed to investigate the copper electrodeposition in sulphate-chloride solutions in the presence of other metal ions such as Ni2+, Fe2+, Zn2+, Pb2+, Sn2+. A two-compartment electrochemical cell operating in either galvanostatic or potentiostatic mode was employed to investigate simultaneous copper recovery and leaching solution regeneration. The results indicate that, in both modes, pure copper can be obtained after the removal of all surface impurities by dipping in acidic concentrated sodium chloride solution. The galvanostatic mode leads to deposit of higher quality, meanwhile the potentiostatic one determines a faster deposition and leaching solution regeneration. (C) 2019 Elsevier Ltd. All rights reserved.