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15 pages, 5183 KiB

Open AccessFeature PaperArticle

A Facile and Green Synthesis of a MoO₂-Reduced Graphene Oxide Aerogel for Energy Storage Devices

by Mara Serrapede, Marco Fontana, Arnaud Gigot, Marco Armandi, Glenda Biasotto, Elena Tresso and Paola Rivolo

Materials 2020, 13(3), 594; https://doi.org/10.3390/ma13030594 - 28 Jan 2020

Cited by 19 | Viewed by 3710

Abstract

A simple, low cost, and “green” method of hydrothermal synthesis, based on the addition of l-ascorbic acid (l-AA) as a reducing agent, is presented in order to obtain reduced graphene oxide (rGO) and hybrid rGO-MoO₂ aerogels for the fabrication [...] Read more.

A simple, low cost, and “green” method of hydrothermal synthesis, based on the addition of l-ascorbic acid (l-AA) as a reducing agent, is presented in order to obtain reduced graphene oxide (rGO) and hybrid rGO-MoO₂ aerogels for the fabrication of supercapacitors. The resulting high degree of chemical reduction of graphene oxide (GO), confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis, is shown to produce a better electrical double layer (EDL) capacitance, as shown by cyclic voltammetric (CV) measurements. Moreover, a good reduction yield of the carbonaceous 3D-scaffold seems to be achievable even when the precursor of molybdenum oxide is added to the pristine slurry in order to get the hybrid rGO-MoO₂ compound. The pseudocapacitance contribution from the resulting embedded MoO₂ microstructures, was then studied by means of CV and electrochemical impedance spectroscopy (EIS). The oxidation state of the molybdenum in the MoO₂ particles embedded in the rGO aerogel was deeply studied by means of XPS analysis and valuable information on the electrochemical behavior, according to the involved redox reactions, was obtained. Finally, the increased stability of the aerogels prepared with l-AA, after charge-discharge cycling, was demonstrated and confirmed by means of Field Emission Scanning Electron Microscopy (FESEM) characterization. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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13 pages, 5400 KiB

Open AccessFeature PaperArticle

Innovative Coatings Based on Peppermint Essential Oil on Titanium and Steel Substrates: Chemical and Mechanical Protection Ability

by Martina Cazzola, Sara Ferraris, Giuliana Banche, Giovanna Gautier Di Confiengo, Francesco Geobaldo, Chiara Novara and Silvia Spriano

Materials 2020, 13(3), 516; https://doi.org/10.3390/ma13030516 - 22 Jan 2020

Cited by 9 | Viewed by 2905

Abstract

A coating that was made of peppermint essential oil was obtained on different metal substrates: Ti6Al4V alloy (mechanically polished and chemically etched) and 316L stainless steel (mechanically polished and mechanically ground). The final aim is to get a multifunctional (chemical and mechanical) protection [...] Read more.

A coating that was made of peppermint essential oil was obtained on different metal substrates: Ti6Al4V alloy (mechanically polished and chemically etched) and 316L stainless steel (mechanically polished and mechanically ground). The final aim is to get a multifunctional (chemical and mechanical) protection of metal surfaces in contact with water media. The coatings were characterized by means of fluorescence microscopy, contact angle measurements, and Fourier Transformed Infrared spectroscopy (FTIR) spectroscopy. The chemical stability of the coatings was tested by means of soaking in water for different times (up to seven days) and washing with different alkaline or acidic solutions. The mechanical adhesion of the coating was tested by tape adhesion test (before and after soaking) and scratch tests to verify whether it has protection ability with respect to the metal substrate. All of the performed characterizations show that the coatings are chemically stable on all of the substrates and are nor dissolved or removed by water during soaking or by alkaline solutions during washing. The adhesion is high and classified as 4B or 5B (on the chemically etched or mechanically ground substrates) according to ASTM D3359-97, depending on the substrate roughness, both before and after soaking. In the case of scratch test (up to 10 N), the coating is not removed and it has a protection action that is able to avoid the surface damage, even if the substrate has a plastic deformation. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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15 pages, 3729 KiB

Open AccessArticle

Interface-Dominated Time-Dependent Behavior of Poled Poly(Vinylidene Fluoride–Trifluoroethylene)/Barium Titanate Composites

by Sara Dalle Vacche, Dragan Damjanovic, Véronique Michaud and Yves Leterrier

Materials 2020, 13(1), 225; https://doi.org/10.3390/ma13010225 - 4 Jan 2020

Cited by 8 | Viewed by 3025

Abstract

Composites in which particles of ferroelectric ceramic phase are randomly dispersed in a polymeric matrix are of interest because of flexibility, conformability, and ease of processing. However, their piezoelectric properties are rather low, unless very high volume fractions of ceramics are used. This [...] Read more.

Composites in which particles of ferroelectric ceramic phase are randomly dispersed in a polymeric matrix are of interest because of flexibility, conformability, and ease of processing. However, their piezoelectric properties are rather low, unless very high volume fractions of ceramics are used. This brings agglomeration and porosity issues due to the large mismatch between the surface energies of the ceramics and of the polymer. Particle surface modification is a common approach for better dispersion; however, it may bring other effects on the properties of the composites, which are usually concealed by the huge improvement in performance due to the more homogenous microstructure. In this work, we compared poly(vinylidene fluoride–trifluoroethylene)/barium titanate composites containing 15 vol.% and 60 vol.% of pristine ceramic particles or particles modified with an aminosilane or a fluorosilane. Similar morphology, with good particle dispersion and low porosity, was achieved for all composites, owing to an efficient dispersion method. The materials were poled with two different poling procedures, and the piezoelectric coefficient d₃₃, the relative permittivity, and the poling degree of barium titanate were followed in time. We highlighted that, although similar d₃₃ were obtained with all types of particles, the nature of the particles surface and the poling procedure were associated with different charge trapping and influenced the evolution of d₃₃ with time. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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11 pages, 3220 KiB

Open AccessArticle

Dielectric Properties of Graphene/Titania/Polyvinylidene Fluoride (G/TiO₂/PVDF) Nanocomposites

by Saira Ishaq, Farah Kanwal, Shahid Atiq, Mahmoud Moussa, Umar Azhar and Dusan Losic

Materials 2020, 13(1), 205; https://doi.org/10.3390/ma13010205 - 3 Jan 2020

Cited by 57 | Viewed by 5117

Abstract

Flexible electronics have gained eminent importance in recent years due to their high mechanical strength and resistance to environmental conditions, along with their effective energy storage and energy generating abilities. In this work, graphene/ceramic/polymer based flexible dielectric nanocomposites have been prepared and their [...] Read more.

Flexible electronics have gained eminent importance in recent years due to their high mechanical strength and resistance to environmental conditions, along with their effective energy storage and energy generating abilities. In this work, graphene/ceramic/polymer based flexible dielectric nanocomposites have been prepared and their dielectric properties were characterized. The composite was formulated by combining graphene with rutile and anatase titania, and polyvinylidene fluoride in different weight ratios to achieve optimized dielectric properties and flexibility. After preparation, composites were characterized for their morphologies, structures, functional groups, thermal stability and dielectric characterizations by using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and impedance spectroscopy. Dielectric results showed that prepared flexible composite exhibited dielectric constant of 70.4 with minor leakage current (tanδ) i.e., 0.39 at 100 Hz. These results were further confirmed by calculating alternating current (AC) conductivity and electric modulus which ensured that prepared material is efficient dielectric material which may be employed in electronic industry for development of next generation flexible energy storage devices. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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11 pages, 3730 KiB

Open AccessFeature PaperArticle

Li⁺ Insertion in Nanostructured TiO₂ for Energy Storage

by Mara Serrapede, Umberto Savino, Micaela Castellino, Julia Amici, Silvia Bodoardo, Elena Tresso and Angelica Chiodoni

Materials 2020, 13(1), 21; https://doi.org/10.3390/ma13010021 - 19 Dec 2019

Cited by 11 | Viewed by 2988

Abstract

Nanostructured materials possess unique physical-chemical characteristics and have attracted much attention, among others, in the field of energy conversion and storage devices, for the possibility to exploit both their bulk and surface properties, enabling enhanced electron and ion transport, fast diffusion of electrolytes, [...] Read more.

Nanostructured materials possess unique physical-chemical characteristics and have attracted much attention, among others, in the field of energy conversion and storage devices, for the possibility to exploit both their bulk and surface properties, enabling enhanced electron and ion transport, fast diffusion of electrolytes, and consequently high efficiency in the electrochemical processes. In particular, titanium dioxide received great attention, both in the form of amorphous or crystalline material for these applications, due to the large variety of nanostructures in which it can be obtained. In this paper, a comparison of the performance of titanium dioxide prepared through the oxidation of Ti foils in hydrogen peroxide is reported. In particular, two thermal treatments have been compared. One, at 150 °C in Ar, which serves to remove the residual hydrogen peroxide, and the second, at 450 °C in air. The material, after the treatment at 150 °C, results to be not stoichiometric and amorphous, while the treatment at 450 °C provide TiO₂ in the anatase form. It turns out that not-stoichiometric TiO₂ results to be a highly stable material, being a promising candidate for applications as high power Li-ion batteries, while the anatase TiO₂ shows lower cyclability, but it is still promising for energy-storage devices. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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13 pages, 6717 KiB

Open AccessArticle

Electrophysical Properties of PMN-PT-Ferrite Ceramic Composites

by Dariusz Bochenek, Przemysław Niemiec, Ryszard Skulski and Dagmara Brzezińska

Materials 2019, 12(20), 3281; https://doi.org/10.3390/ma12203281 - 9 Oct 2019

Cited by 3 | Viewed by 2600

Abstract

Ferroelectromagnetic composites based on (1−x)PMN-(x)PT (PMN-PT) powder and Ni-Zn ferrite powder were obtained and are described in this work. As a ferroelectric component, we used (1−x)PMN-(x)PT solid solution (with x = 0.25, 0.28, 0.31, 0.34, [...] Read more.

Ferroelectromagnetic composites based on (1−x)PMN-(x)PT (PMN-PT) powder and Ni-Zn ferrite powder were obtained and are described in this work. As a ferroelectric component, we used (1−x)PMN-(x)PT solid solution (with x = 0.25, 0.28, 0.31, 0.34, 0.37, 0.40), synthesized using the sol-gel method. As a magnetic component, we used nickel-zinc ferrite, obtained using classic ceramic technology. The six compositions of PMN-PT used have rhombohedral symmetry, tetragonal one and mixture of these phases (morphotropic phase area), depending on x. The final ceramic composite samples were obtained using the classic methods involving the calcination route and pressureless final sintering (densification). The properties of the obtained ceramic composite samples were investigated, including microstructure SEM (scanning electron microscope), dielectric properties, electromechanical properties, and DC (Direct Current) electrical conductivity. Results showed that the microstructures of the PP-F composite samples characterized by larger grains were better crystallized, compared with the microstructures of the PMN-PT ceramic samples. The magnetic properties do not depend on the ferroelectric component of the composite samples, while the insertion of ferrite into the PMN-PT compound reduces the values of remnant and spontaneous polarization, as well as the coercive field. The dielectric measurements also indicated that the magnetic subsystem influences the dielectric properties. The present results show that the PP-F ceramic composite has good dielectric, magnetic, and piezoelectric properties, which predisposes this type of material to specific applications in microelectronics and micromechatronics. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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6 pages, 1480 KiB

Open AccessArticle

Thermal Properties of Composite Polymer Electrolytes Poly(Ethylene Oxide)/Sodium Trifluoroacetate/Aluminum Oxide (PEO)₁₀CF₃COONa + x wt.% Al₂O₃

by Miguel I. Delgado Rosero, Nori M. Jurado Meneses and Ramiro Uribe Kaffure

Materials 2019, 12(9), 1464; https://doi.org/10.3390/ma12091464 - 7 May 2019

Cited by 19 | Viewed by 3075

Abstract

Polymeric membranes of poly(ethylene oxide) (PEO) and sodium trifluoroacetate (PEO:CF₃COONa) combined with different concentrations of aluminum oxide (Al₂O₃) particles were analyzed by impedance spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA). DSC results show changes in the [...] Read more.

Polymeric membranes of poly(ethylene oxide) (PEO) and sodium trifluoroacetate (PEO:CF₃COONa) combined with different concentrations of aluminum oxide (Al₂O₃) particles were analyzed by impedance spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA). DSC results show changes in the crystalline fraction of PEO when the concentration of Al₂O₃ is increased. TGA analysis showed thermal stability up to 430 K showing small changes with the addition of alumina particles. The decrease in crystalline fraction for membranes with low Al₂O₃ concentration is associated with the increase in conductivity of (PEO)₁₀CF₃COONa + x wt.% Al₂O₃ composites. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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Review

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35 pages, 3006 KiB

Open AccessFeature PaperReview

A Review of Non-Soil Biochar Applications

by Mattia Bartoli, Mauro Giorcelli, Pravin Jagdale, Massimo Rovere and Alberto Tagliaferro

Materials 2020, 13(2), 261; https://doi.org/10.3390/ma13020261 - 7 Jan 2020

Cited by 101 | Viewed by 11392

Abstract

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil [...] Read more.

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source. Full article

(This article belongs to the Special Issue Multifunctional Materials & Composites)

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