Two electrodeposition strategies for the morphology-controlled synthesis of cobalt nanostructures

In this contribution, two different strategies are discussed to synthesize cobalt nanostructures: direct cobalt electrodeposition on a planar aluminum electrode and cobalt electrodeposition into nanoporous alumina templates generated by aluminum anodization (template electrodeposition). In the direct electrodeposition of cobalt on aluminum, cobalt nanoparticles are formed during the early stage of electrodeposition, which causes the depletion of cobalt ions near the electrode. Water reduction then takes place catalyzed by electrodeposited cobalt nanoparticles, which increases the pH near the electrode and can induce cobalt hydroxide precipitation. By varying the electrode potential and the cobalt ion concentration, the interplay between electrochemical growth of cobalt and water reduction could be controlled to induce transition from cobalt hexagonal nano-platelets to nanostructured films composed of cobalt nanoparticles and cobalt hydroxide nano-flakes. Cobalt nanowires can be synthesized by electrodeposition into nanoporous alumina templates generated by aluminum anodization. This approach typically involves the application of alumina templates produced by a two-step anodization procedure: the alumina nanoporous layer generated by a first anodization is dissolved in a chromic acid solution while a very ordered alumina nanoporous layer is produced by a second anodization stage. In accordance with previous studies, this procedure is fundamental to achieve uniform filling of the nanopores in the subsequent electrodeposition stage. In the present study, uniform filling of the nanoporous alumina generated by one-step anodization could be achieved by the electrodeposition of cobalt nanowires. This result was made possible by the application of a novel pulsed electrodeposition strategy

Synthesis of cobalt nanoparticles by electrodeposition onto aluminium foils

In this contribution a study of electrochemical deposition of cobalt nanoparticles onto aluminium foils is presented. The study is aimed at deriving information required for design and control of cobalt nanoparticles electrodeposition onto aluminium foams employed as catalysts support in ethanol reforming. A thorough experimental analysis was in this perspective conducted to determine the influence of applied potential and amount of electric charge passing thorough the cell (amount of charge), on number density and size of the synthesized nanoparticles. Chronoamperometric tests were for this purpose performed in a three electrode cell to determine the current responses to variations in the selected operating parameters. Mathematical models accounting for charge transfer and diffusion limitations were implemented to attain fitting of the derived data, leading to an estimation of the number density of active sites. Scanning electron microscopy of cathode aluminium foils was performed to validate the predictions of the employed mathematical models and characterize the influence of the considered operating parameters on the size and number density of the electrodeposited nanoparticles

Ti/TiO2/Cu2O electrodes for photocatalytic applications: synthesis and characterization

Energy from renewables (solar, photovoltaic, geothermal), is a major challenge for researchers' efforts in reason of the intermittent nature of these energy sources. Systems like photoelectrochemical (PEC) cells are promising devices that allow the direct conversion of solar energy into electric power and/or chemical fuels. The direct conversion of solar energy in fuels can be achieved using photocatalysts, based on semiconductors like TiO2. In this work TiO2 nanotubes were achieved through “one-step” anodization of titanium, a low cost and accurate method which allowed to control dimensions and morphology of the nanostructured Ti/TiO2 electrodes. Central limit for TiO2 photoconversion efficiency is its wide bandgap (i.e. a3.2eV), which limits light absorption to the ultraviolet region (3-5% of the solar radiation). Composite Cu2O/TiO2 systems have attracted much attention: Cu2O is a promising semiconductor material (bandgap 2.0-2.6eV), suitable to absorb visible light. Traditionally, Cu2O deposition techniques include the impregnation of TiO2 with a copper salt and subsequent calcination, but offers little control on sizes, shape and deposit's composition. In this work we developed an electrodeposition method in order to control Cu2O morphology and sizes in the composed Ti/TiO2/Cu2O electrodes

Full recycling of spent lithium ion batteries with production of core-shell nanowires//exfoliated graphite asymmetric supercapacitor

A novel process is reported which produces an asymmetric supercapacitor through the complete recycling of end-of-life lithium ion batteries. The electrodic powder recovered by industrial scale mechanical treatment of spent batteries was leached and the dissolved metals were precipitated as mixed metals carbonates. Nanowires battery-type positive electrodes were produced by electrodeposition into nanoporous alumina templates from the electrolytic baths prepared by dissolution of the precipitated carbonates. The impact of the different metals contained in the electrodic powder was evaluated by benchmarking the electrochemical performances of the recovered nanowires-based electrodes against electrodes produced by using high-purity salts. Presence of inactive Cu in the nanowires lowered the final capacitance of the electrodes while Ni showed a synergistic effect with cobalt providing a higher capacitance with respect to synthetic Co electrodes. The carbonaceous solid recovered after leaching was in-depth characterized and tested as negative electrode. Both the chemical and electrochemical characterization indicate that the recovered graphite is characterized by the presence of oxygen functionalities introduced by the leaching treatment. This has led to the obtainment of a recovered graphite characterized by an XPS C/O ratio, Raman spectrum and morphology close to literature reports for reduced graphene oxide. The asymmetric supercapacitor assembled using the recovered nanowires-based positive electrodes and graphite as negative electrodes has shown a specific capacitance of 42 Fg-1, computed including the whole weight of the positive electrode and recovered graphite, providing a maximum energy density of ∼9 Whkg−1 and a power density of 416 Wkg−1 at 2.5 mA cm-

Magnetic force microscopy characterization of cobalt nanoparticles: a preliminary study

In order to characterize magnetic properties of cobalt-based nanoparticles synthesized through electrodeposition on metal substrates, methods must be employed which enable the imaging of sample surface, the selection of a specific nanoparticle, and the accurate evaluation of local magnetic parameters, such as magnetic moment or saturation magnetization. Due to the combination of imaging capability and quantitative probing of ultra-low magnetic field through the use of a nanometer sized tip with a magnetic coating, magnetic force microscopy (MFM) is a promising tool to characterize Co-based nanoparticles directly on substrates. In this work, the report the preliminary results of the use of MFM to analyze Co nanoparticles electrodeposited on an Al substrate. The aim wa to assess the effective capability of this technique to investigate this kind of nanomaterials, foresee offered possibilities, and highlight current limitations to overcome

Electrochemical pretreatments of carbon paper and their effect on the electrodeposition of metallic nanostructures

Gas diffusion electrodes (GDEs) represent a fundamental element for the development of gaseous electrochemical cells like water electrolysis reactors and fuel cells. Various technologies and materials are employed in order to obtain a conductive, stable and gas permeable structure. Among them, carbon-based structures such as carbon paper are widely used: their composition allows the diffusion of gaseous reagents and products and simultaneously does not permit the flooding of the gas-diffusion structure by aqueous electrolytes. However, the hydrophobicity of this material may represent a drawback to water-based electrode synthesis like galvanic deposition, and various chemical or thermal pretreatments were developed in the last decades. A new kind of pre-treatment based on electrical oxidation of the carbon paper surface is here described and evaluated. The electro-oxidative method allows a rapid and localized pre-treatment of the carbon paper, avoiding the use of highly reactive chemicals or long thermal treatments, reducing treatment wastes, time loss and electrical consumption. Surface wettability of the carbon paper before and after pretreatment was compared by contact angle analysis. Pre-treated and virgin carbon paper were subsequently electroplated from a copper deposition bath and deposition morphologies were compared, in order to establish the effect of the pre-treatment. Electroplated supports were analyzed by scanning electron microscopy (SEM) in order to analyze both micro and nanomorphology of the metallic structure

TiO2nanotubes in lithium-ion batteries

In this contribution we report on electrochemical approaches in TiO2 based electrodes synthesis. TiO2 nanotubes (NTs) were synthesized following a facile anodization of titanium sheets. Optimizing the experimental conditions two electrodes with NTs lengths of ∼10 μm (Long) and ∼2 μm (Short), were obtained. At the end of the anodization the amorphous TiO2 (a-TiO2) was thermally treated to promote the conversion in the anatase crystal phase (c-TiO2). Both the Long and Short NTs electrodes were tested for their applications as anodes in lithium-ion batteries (LIBs). A preliminary comparison was performed to evaluate the role of a-TiO2 and c-TiO2 phases. Here, Short a-TiO2 NTs exhibited a fast storage rate respect to Short c-TiO2. Comparing the NTs length, Long a-TiO2 electrodes exhibited the highest specific capacity, close to the theoretical value. Furthermore, all the electrodes tested showed an excellent capacity retention proceeding with Discharge/Charge cycles

Understanding the impact of Fe-doping on the structure and battery performance of a Co-free Li-rich layered cathodes

A series of Co-free Li-rich layered oxides, Li1.24Mn0.62-xNi0.14FexO2 (x=0, 0.01, 0.02 and 0.03) has been synthetized by a self-combustion reaction. Fe doping affects either lattice structure and bonding as shown by the changes in the size of unit cell calculated from diffraction patterns and in the vibrational frequencies observed in Raman spectra. The electrochemical performance has been evaluated in a lithium cell by galvanostatic cycling: Doped samples show better capacity retention and minor decreases in the specific capacity (i. e., Li1.24Mn0.60Ni0.14Fe0.02O2 can supply a specific capacity of 235 mAhg−1 with 94 % of capacity retention after 150 cycles). These positive effects originated by alterations in the point defectivity (Ni3+ concentration, anionic and cationic vacancies), changes in the transport properties, as showed by Cyclic Voltammetry; as well as an improved structural resilience compared to the un-doped material in postmortem analyses. © 2023 The Authors. ChemElectroChem published by Wiley-VCH GmbH

Production of nanostructured electrodes from spent Lithium ion batteries and their application in new energy storage devices

The present work is aimed at demonstrating the potentiality of lithium ion batteries recycling through the production of high added value nanostructured material. Nanostructured electrodic materials were synthesized starting from waste lithium ion batteries (LIBs). Firstly, the metals contained in the electrodic powder of exhausted LIBs were extracted by acid-reducing leaching. After filtration, metals rich solution was separated from graphite. Nanoparticles- based electrodes were produced by controlled precipitation and subsequent calcination of metals in order to obtain nanoparticles of LiNi1/3Co1/3Mn1/3O2, one of the most employed LIBs cathodic material. Cathodic materials synthesized starting from waste LIBs and from high grade synthetic reagents were compared after their characterization by SEM, EDX and XRD. The electrochemical performance of the electrodes was evaluated by galvanostatic cycling the electrodes in a lithium half-cell. Remarkably, the electrochemical performances obtained with the electrodes produced by the recovery of metals are close to those recorded using electrodes produced by synthetic reagents. © 2020 Author(s)

Electrochemical synthesis of nanowires electrodes and their application in energy storage devices

In this work, an electrochemical approach to synthesize Metal-MetalOxide/Hydroxide core-shell nanowires electrodes (NWE) is illustrated. NWE electrodes were obtained by electrodeposition of a targeted metal into the nanopores of nanoporous alumina templates generated by one-step anodization of aluminum. Following metal electrodeposition, the alumina template was selectively etched to obtain an array of free-standing metal nanowires. The imposed electrodeposition conditions allowed directly attaining a core-shell nanostructure, with a metal core covered by a thin metal oxide/hydroxide film. NWE electrodes produced by the proposed synthesis route were tested for the application as electrodes in lithium batteries and supercapacitors. To this purpose, an array of cobalt nanowires (CoNWs) supported by a nanostructured copper current collector was produced by sequential electrodeposition of cobalt and copper, and it was employed as anode in a lithium battery, while a NWE based on Ni-NiO/OH2 (NiNWs) was obtained by nickel electrodeposition and tested as electrode in a supercapacitor. A thorough analysis and characterization of the produced electrodes were performed. The experiments with the lithium cell evidenced the positive effect of metallic core on stability, while the electrochemical characterization of the supercapacitor showed the presence of both NiO and NiOH2 leading, when cycled, to a capacity close to the best literature value