In the last decade, nanostructuration is a demanding research topic due to the observation of interesting properties and, in consequence, applications on these nanostructures. This review collects ...the synthesis and possible applications of ZnO nanowires grown by electrodeposition and electroless methods. Respect to the synthesis of ZnO nanowires, growth mechanism and parameters are analysed depending on the technique used, electrodeposition or electroless. The mechanism growth of the nanowires using templateless and hard-templates is analysed resulting in different architecture of the ZnO nanowires. Moreover, ZnO nanowires and hybrid materials based on ZnO are also considered. Depending on the architecture of ZnO nanowires, the properties and applications are different. This review also studies the properties and applications in which ZnO nanowires can be used and how these applications are different depending on the architecture of the nanostructure. This review gives a complete perspective referent to the synthesis, properties and application of ZnO nanowires grown by electrosynthesis techniques.
Titanium dioxide (TiO2) nanoparticles were synthesized by nonaqueous sol–gel route using titanium tetrachloride and benzyl alcohol as the solvent. The obtained 4 nm-sized anatase nanocrystals were ...readily dispersible in various polar solvents allowing for simple preparation of colloidal dispersions in water, isopropyl alcohol, dimethyl sulfoxide, and ethanol. Results showed that dispersed nanoparticles have acidic properties and exhibit positive zeta-potential which is suitable for their deposition by cathodic electrophoresis. Aluminum substrates were anodized in phosphoric acid in order to produce porous anodic oxide layers with pores ranging from 160 to 320 nm. The resulting nanopores were then filled with TiO2 nanoparticles by electrophoretic deposition. The influence of the solvent, the electric field, and the morphological characteristics of the alumina layer (i.e., barrier layer and porosity) were studied.
Ordered anodic aluminum oxide (AAO) templates with pores <15 nm in diameter and an aspect ratio (length-to-diameter ratio) above 3 × 103 have been fabricated using a nonlithographic approach; ...specifically, by anodizing aluminum in an ethylene-glycol-containing sulfuric acid electrolyte. The pores are the smallest in diameter reported for a self-ordered AAO without pore aspect-ratio limitations and good ordering, which opens up the possibility of obtaining nanowire arrays in the quantum confinement regime that is of interest for efficient thermoelectric generators. The effect of the ethylene glycol addition on both the pore diameter and the ordering is evaluated and discussed. Moreover, 15-nm-diameter Bi2Te3 and poly(3-hexyl thiophene) (P3HT) nanowires have been prepared using these AAO templates. As known, Bi2Te3 is currently the most efficient thermoelectric bulk material for room-temperature operations and, according with theory, its Seebeck coefficient should be increased when it is confined to nanowires with diameters close to 10 nm. On the other hand, P3HT is one of the main candidates for integrating organic photovoltaic and thermoelectric devices, and its properties are also proposed to increase when it is confined to nanoscale structures, mainly due to molecular orientation effects.
We show here for the first time the use of a cold sintering process (CSP) to sinter CoSb3-based thermoelectric materials. CSP at 150 °C for 90 min under a uniaxial pressure of 750 MPa yields pieces ...with a relative density of 86 %, which is increased to around 92 % after a post-annealing at temperatures ≥ 500 °C in Ar atmosphere. The reported CSP produces Te doped-CoSb3 nanocomposites with similar morphological and structural characteristics to the starting nanopowders obtained by ball milling in air atmosphere. The post-thermal treatment induces grain coalescence and grain growth, crystallite size growth as well as compositional changes in the nanocomposite, decreasing the amount of the main phase, CoSb3, and increasing the weight of secondary phase, CoSb2, up to a 30 wt% at 600 °C. Remarkably, the average valence for the Co, Sb and Te absorbing atoms is neither transformed by the sintering process nor by the subsequent heat treatment. The functional response of the sintered thermoelectric nanocomposites exhibits a maximum figure of merit of 0.12(3) at room temperature for the nanocomposites sintered by CSP with a subsequent post-annealing at 500 °C. This is mainly due to its low thermal conductivity in comparison with similar powders sintered by other approaches, and it is explained by the morphological and structural properties. These findings represent an attractive alternative for obtaining efficient thermoelectric skutterudites by a scalable and cost-effective route.
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•First dense CoSb3-based skutterudite nanocomposites prepared by cold sintering process.•New methodology for the cost-effective fabrication of nanostructured thermoelectrics.•Control of the characteristics of the thermoelectric materials during the manufacturing route.•The highest zT values for the nanocomposites sintered close to the operating temperature
Electrodeposition of stainless steel-like materials such as FeCrNi alloy into micro- and nanotemplates provides a sustainable framework for creating biomedical-oriented micro- and nanocomponents with ...outstanding characteristics. While Cr(III)-based electrodeposition represents a ‘green’ alternative to toxic Cr(VI), its use is limited by Cr(III) aqueous chemistry which leads to the incorporation of impurities and the hydrogen evolution reaction (HER). These factors are responsible for low deposition efficiencies, brittleness and porosity. The current work sought to investigate the use of ‘green’ Cr(III)-glycine electrolyte to improve FeCrNi electrodeposition from Cr(III) precursors. Mixed-solvent electrolyte containing ethylene glycol (EG) was employed to reduce HER aftereffects. FeCrNi mixed EG electrolytes were compared to their aqueous counterparts to observe differences in Cr(III)-glycine complexation, coatings' composition and current efficiency. The feasibility of this method for creating nanostructures was verified by template-assisted electrodeposition using anodic aluminium oxide (AAO) templates. This study established that mixed-solvent electrolytes are an effective strategy to improve Cr(III)-based plating of alloys into miniaturised moulds. For the first time, electrodeposited FeCrNi nanowires (NWs) and nanotubes (NTs) were achieved via the framework developed in this work. The possible mechanisms controlling the morphological variations in FeCrNi nanostructures were discussed in relation to the kinetic and growth models in single metal electroplating into nanotemplates.
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•Cr(III)-glycine complexation similar for aqueous and mixed solvent electrolytes•Hydrogen evolution (HER) inhibited using mixed ethylene glycol (EG) electrolyte.•Impurities incorporation in films decreases when using mixed solvent electrolyte.•Electrodeposition of nanostructures is achieved only with EG mixed solution.•FeCrNi nanotubes and nanowires formation depends on current density and HER.
Research into the artificial reproduction of vibrant colours in natural creatures and the reproduction of their structural colours has generated considerable interest. One inorganic material that has ...been studied for the generation of these artificial colours is anodic aluminium oxide (AAO). For example, 3D anodic aluminium oxide (3D-AAO) metamaterials act as distributed Bragg reflectors. This study examines the effect of the application of various waves (square, sinusoidal, and sawtooth) during the generation of 3D-AAO on the optical and morphological properties of these 3D metamaterials. The effect of the waveform in the colours and hues has been explained by a theoretical model. Furthermore, the work analyses how colour can be improved by depositing a thin metal layer on top, obtaining, from a simplistic point of view, a combination of two effects: a Bragg reflector (3D-AAO) and an optical reflector (metal mirror). For that, different metals like Au, Pt, and Cr have been studied. The thickness of the metal layer has been theoretically modelled. This study paves the way for a new approach to developing structural colours for their use in for example RGB display technologies.
In the last few years, the use of inexpensive and scalable materials in industry for thermoelectric applications has received great interest, such as CuNi alloys. In this work, nanocrystalline CuNi ...alloys with different compositions were grown by pulsed electrodeposition. The incorporation of saccharine in the electrolyte allowed reduction of the crystallite size of CuNi down to 30-40 nm. The thermoelectric properties, such as the electrical conductivity, Seebeck coefficient, and thermal conductivity of these nanocrystalline alloys, were studied. The maximum figure of merit obtained at room temperature was (6.1 ± 1.4) × 10
−2
for nanocrystalline Cu
0.55
Ni
0.45
. The thermal conductivity of CuNi alloys was reduced by the nanostructuration to a value of 9.0 ± 0.9 W m
−1
K
−1
, making these nanocrystalline CuNi alloys more competitive than other more classical thermoelectric materials. This work opens a new field to be investigated, that can be described as the use of commercial alloys such as CuNi for thermoelectric applications and shows the use of a new approach to enhance the thermoelectric properties of inexpensive and/or fewer pollutant materials.
The thermal conductivity of CuNi alloys grown by pulsed electrodeposition is reduced by the nanostructuration to a value of 9.0 ± 0.9 W m
−1
K
−1
due to the incorporation of saccharine in the electrolyte which allowed reduction of the crystallite size.
ZnO has been widely studied in the last decades as an n-type semiconductor due to its wide application range, for example, in optoelectronics, solar cells, light-emitting diodes, thermoelectrics, ...amongst others. The material efficiency for certain applications is highly dependent on the presenting film morphology. Electrodeposition is well-known as a technique with precise control over the structural and morphological properties of the obtained materials. When the structural and morphological properties are tuned, it is possible to find a wide variety of defects in the ZnO structure. In this study, ZnO films were grown using pulsed electrodeposition with variation of the reduction potential. The crystal order, structural defects and optical emissions of the films have been analyzed by X-Ray Diffraction (XRD), X-ray Absorption Near-Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Photoluminescence (PL). ZnO film grown at less negative reduction potential presents a stronger texture along 0001 by XRD, higher crystalline order, and more zinc vacancies by XANES and EXAFS. The films obtained at less negative potential present less OH− trapped in the ZnO structure and a relatively higher level of defects Oi0, OZn0, Oi−/2− and OZn0/− than those grown at higher reduction potentials by PL. This will be related to the fact that at less negative potentials there is less concentration of OH− at the film surface than at more negative potentials. The combination of X-ray absorption spectroscopy and photoluminescence reveals the complicated nature of the atomic defect in electrodeposited ZnO films. Allowing to evidence the preferential presence of atomic defect as a function of the reduction potential. In this work, we have also compared those defects with reference compounds such as a Zn foil and ZnO polycrystalline powder.
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Nanostructuration is an intensive field of research due to the appearance of interesting properties at the nanoscale. For instance, in thermoelectricity the most outstanding improvements obtained ...lately are related to phenomena that appear as a result of nano-engineering different materials. The thermoelectric effect is the direct conversion from temperature gradients into electricity and
. When going to low dimensions, for example in the particular case of thermoelectric nanowires, the transport properties of phonons are modified with respect to those found in bulk leading to a higher thermoelectric figure of merit
. In more detail, this review tries to compile some of the landmarks in the electrodeposition of Bi
Te
-based nanowires. We will focus on the achievements using different templates, electrolytes and deposition modes. We will also summarize the measurements performed in those nanowires and the main conclusions that can be extracted from the published works. Finally, an update of nanowire-based thermoelectric generators is also included.
Highly oriented 1 1 0 Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), ...both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10(-2) and (10.4 ± 2.6)·10(-2), respectively.
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