Research

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15 pages, 7415 KiB

Open AccessArticle

Growth of Anodic Layers on 304L Stainless Steel Using Fluoride Free Electrolytes and Their Electrochemical Behavior in Chloride Solution

by Laura Patricia Domínguez-Jaimes, María A. Arenas, Ana Conde, Beatriz Escobar-Morales, Anabel Álvarez-Méndez and Juan Manuel Hernández-López

Materials 2022, 15(5), 1892; https://doi.org/10.3390/ma15051892 - 03 Mar 2022

Cited by 2 | Viewed by 1973

Abstract

Anodic layers have been grown on 304L stainless steel (304L SS) using two kinds of fluoride-free organic electrolytes. The replacement of NH₄F for NaAlO₂ or Na₂SiO₃ in the glycerol solution and the influence of the H₂ [...] Read more.

Anodic layers have been grown on 304L stainless steel (304L SS) using two kinds of fluoride-free organic electrolytes. The replacement of NH₄F for NaAlO₂ or Na₂SiO₃ in the glycerol solution and the influence of the H₂O concentration have been examined. The obtained anodic layers were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and potentiodynamic polarization tests. Here, it was found that, although the anodic layers fabricated within the NaAlO₂-electrolyte and high H₂O concentrations presented limited adherence to the substrate, the anodizing in the Na₂SiO₃-electrolyte and low H₂O concentrations allowed the growth oxide layers, and even a type of ordered morphology was observed. Furthermore, the electrochemical tests in chloride solution determined low chemical stability and active behavior of oxide layers grown in NaAlO₂-electrolyte. In contrast, the corrosion resistance was improved approximately one order of magnitude compared to the non-anodized 304L SS substrate for the anodizing treatment in glycerol, 0.05 M Na₂SiO₃, and 1.7 vol% H₂O at 20 mA/cm² for 6 min. Thus, this anodizing condition offers insight into the sustainable growth of oxide layers with potential anti-corrosion properties. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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19 pages, 4407 KiB

Open AccessFeature PaperArticle

A Strategy towards Light-Absorbing Coatings Based on Optically Black Nanoporous Alumina with Tailored Disorder

by Mikhail Pashchanka and Gennady Cherkashinin

Materials 2021, 14(19), 5827; https://doi.org/10.3390/ma14195827 - 05 Oct 2021

Cited by 4 | Viewed by 1564

Abstract

This work provides a conceptually new way of thinking about the light-absorbing mechanism in additive-free black porous anodic alumina (black PAA, or b-PAA) layers obtained via “burning” anodizing regime. The new insight into the controllable photonic effects in PAA allows the implementation of [...] Read more.

This work provides a conceptually new way of thinking about the light-absorbing mechanism in additive-free black porous anodic alumina (black PAA, or b-PAA) layers obtained via “burning” anodizing regime. The new insight into the controllable photonic effects in PAA allows the implementation of the optical blackening method based on the deliberate randomization of the initially well-ordered nanopore arrangement. The proposed black coloration mechanism rests solely on the destructive interference of light after its multiple scattering. Similar effects have been earlier considered for some natural or artificially created biomimetic structures (e.g., the so-called “moth eye effect”, or the coloration mechanism in the Neurothemis tullia dragonfly wings). Comprehensive analysis confirmed that the chemical composition of b-PAA has only a minor influence on the color changes and the optical density increase, and that the light-absorbing properties most likely result from the structural effects. The new functional 2D materials exhibit strong adhesion to aluminum surface, are cost-effective and suitable for application under harsh thermal or UV-light conditions. They are potentially useful for manufacturing of optical devices or heat-resistant coatings in aerospace technologies, as well as solid supports for biological filtration and fluorescence imaging. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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13 pages, 4703 KiB

Open AccessArticle

Fabrication, Characterization and Photocatalytic Activity of Copper Oxide Nanowires Formed by Anodization of Copper Foams

by Alaa M. Abd-Elnaiem, Moustafa A. Abdel-Rahim, Atta Y. Abdel-Latief, Ahmed Abdel-Rahim Mohamed, Kristina Mojsilović and Wojciech Jerzy Stępniowski

Materials 2021, 14(17), 5030; https://doi.org/10.3390/ma14175030 - 02 Sep 2021

Cited by 16 | Viewed by 2645

Abstract

In recent paper anodization of copper foams in 0.1 M K₂CO₃ is reported. Anodization was performed in the voltage range of 5–25 V and in all the cases oxides with a developed surface area were obtained. However, anodizing only at [...] Read more.

In recent paper anodization of copper foams in 0.1 M K₂CO₃ is reported. Anodization was performed in the voltage range of 5–25 V and in all the cases oxides with a developed surface area were obtained. However, anodizing only at 20 and 25 V resulted in the formation of nanostruc-tures. In all the cases, the products of anodizing consisted of crystalline phases like cuprite (Cu₂O), tenorite (CuO), parameconite (Cu₄O₃) as well as spertiniite (Cu(OH)₂). Copper foams after ano-dizing were applied as catalysts in the photocatalytic decolorization of a model organic compound such as methylene blue. The highest photocatalytic activity was observed for samples anodized at 25 V and closely followed by samples anodized at 5 V. The anodized copper foams proved to be a useful material in enhancing the photocatalytic efficiency of organic dye decomposition. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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17 pages, 7376 KiB

Open AccessArticle

TiO₂ Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid

by Marcin Pisarek, Piotr Kędzierzawski, Mariusz Andrzejczuk, Marcin Hołdyński, Anna Mikołajczuk-Zychora, Andrzej Borodziński and Maria Janik-Czachor

Materials 2020, 13(5), 1195; https://doi.org/10.3390/ma13051195 - 06 Mar 2020

Cited by 17 | Viewed by 3568

Abstract

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO₂ nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO₂ nanotubes (TiO₂ NTs) with strictly defined [...] Read more.

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO₂ nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO₂ nanotubes (TiO₂ NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO₂ NTs, forming ‘rings’ and agglomerates. A part of metal nanoparticles decorated also TiO₂ NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO₂ NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO₂ NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst—Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO₂ NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO₂ NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO₂ catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy—XPS; Auger electron spectroscopy—AES). Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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12 pages, 4087 KiB

Open AccessFeature PaperArticle

A Superhydrophilic Aluminum Surface with Fast Water Evaporation Based on Anodic Alumina Bundle Structures via Anodizing in Pyrophosphoric Acid

by Daiki Nakajima, Tatsuya Kikuchi, Taiki Yoshioka, Hisayoshi Matsushima, Mikito Ueda, Ryosuke O. Suzuki and Shungo Natsui

Materials 2019, 12(21), 3497; https://doi.org/10.3390/ma12213497 - 25 Oct 2019

Cited by 27 | Viewed by 4547

Abstract

A superhydrophilic aluminum surface with fast water evaporation based on nanostructured aluminum oxide was fabricated via anodizing in pyrophosphoric acid. Anodizing aluminum in pyrophosphoric acid caused the successive formation of a barrier oxide film, a porous oxide film, pyramidal bundle structures with alumina [...] Read more.

A superhydrophilic aluminum surface with fast water evaporation based on nanostructured aluminum oxide was fabricated via anodizing in pyrophosphoric acid. Anodizing aluminum in pyrophosphoric acid caused the successive formation of a barrier oxide film, a porous oxide film, pyramidal bundle structures with alumina nanofibers, and completely bent nanofibers. During the water contact angle measurements at 1 s after the water droplet was placed on the anodized surface, the contact angle rapidly decreased to less than 10°, and superhydrophilic behavior with the lowest contact angle measuring 2.0° was exhibited on the surface covered with the pyramidal bundle structures. As the measurement time of the contact angle decreased to 200–33 ms after the water placement, although the contact angle slightly increased in the initial stage due to the formation of porous alumina, at 33 ms after the water placement, the contact angle was 9.8°, indicating that superhydrophilicity with fast water evaporation was successfully obtained on the surface covered with the pyramidal bundle structures. We found that the shape of the pyramidal bundle structures was maintained in water without separation by in situ high-speed atomic force microscopy measurements. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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18 pages, 8014 KiB

Open AccessArticle

Cubic Silver Nanoparticles Fixed on TiO₂ Nanotubes as Simple and Efficient Substrates for Surface Enhanced Raman Scattering

by Robert Ambroziak, Marcin Hołdyński, Tomasz Płociński, Marcin Pisarek and Andrzej Kudelski

Materials 2019, 12(20), 3373; https://doi.org/10.3390/ma12203373 - 16 Oct 2019

Cited by 27 | Viewed by 4218

Abstract

In this work we show that ordered freestanding titanium oxide nanotubes (TiO₂ NT) may be used as substrates for the simple and efficient immobilization of anisotropic plasmonic nanoparticles. This is important because anisotropic plasmonic nanostructures usually give greater spectral enhancement than spherical [...] Read more.

In this work we show that ordered freestanding titanium oxide nanotubes (TiO₂ NT) may be used as substrates for the simple and efficient immobilization of anisotropic plasmonic nanoparticles. This is important because anisotropic plasmonic nanostructures usually give greater spectral enhancement than spherical nanoparticles. The size of the pores in a layer of titanium oxide nanotubes can be easily fitted to the size of many silver plasmonic nanoparticles highly active in SERS (surface-enhanced Raman scattering) spectroscopy (for example, silver nanocubes with an edge length of ca. 45 nm), and hence, the plasmonic nanoparticles deposited can be strongly anchored in such a titanium oxide substrate. The tubular morphology of the TiO₂ substrate used allows a specific arrangement of the silver plasmonic nanoparticles that may create many so-called SERS hot spots. The SERS activity of a layer of cubic Ag nanoparticles (AgCNPs) deposited on a tubular TiO₂ substrate (AgCNPs@TiO₂ NT) is about eight times higher than that of the standard electrochemically nanostructured surface of a silver electrode (produced by oxidation reduction cycling). Furthermore, a super hydrophilic character of the TiO₂ nanotubes surface allows for a uniform distribution of AgCNPs, which are deposited from an aqueous suspension. The new AgCNPs@TiO₂ NT hybrid layer ensures a good reproducibility of SERS measurements and exhibits a higher temporal stability of the achievable total SERS enhancement factor—one that is far better than standard SERS silver substrates. To characterize the morphology and chemical composition of such evidently improved SERS platforms thus received, we applied microscopic techniques (SEM, and scanning transmission electron microscopy (STEM)) and surface analytical techniques (Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS)). Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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8 pages, 2057 KiB

Open AccessArticle

Formation of Nanoporous Mixed Aluminum-Iron Oxides by Self-Organized Anodizing of FeAl₃ Intermetallic Alloy

by Paulina Chilimoniuk, Marta Michalska-Domańska and Tomasz Czujko

Materials 2019, 12(14), 2299; https://doi.org/10.3390/ma12142299 - 18 Jul 2019

Cited by 6 | Viewed by 2436

Abstract

Nanostructured anodic oxide layers on an FeAl₃ intermetallic alloy were prepared by two-step anodization in 20 wt% H₂SO₄ at 0 °C. The voltage range was 10.0–22.5 V with a step of 2.5 V. The structural and morphological characterizations of [...] Read more.

Nanostructured anodic oxide layers on an FeAl₃ intermetallic alloy were prepared by two-step anodization in 20 wt% H₂SO₄ at 0 °C. The voltage range was 10.0–22.5 V with a step of 2.5 V. The structural and morphological characterizations of the received anodic oxide layers were performed by field emission scanning electron microscopy (FE-SEM). Therefore, the formed anodic oxide was found to be highly porous with a high surface area, as indicated by the FE-SEM studies. It has been shown that the morphology of fabricated nanoporous oxide layers is strongly affected by the anodization potential. The oxide growth rate first increased slowly (from 0.010 μm/s for 10 V to 0.02 μm/s for 15 V) and then very rapidly (from 0.04 μm/s for 17.5 V up to 0.13 μm/s for 22.5 V). The same trend was observed for the change in the oxide thickness. Moreover, for all investigated anodizing voltages, the structural features of the anodic oxide layers, such as the pore diameter and interpore distance, increased with increasing anodizing potential. The obtained anodic oxide layer was identified as a crystalline FeAl₂O₄, Fe₂O₃ and Al₂O₃ oxide mixture. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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Review

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38 pages, 5016 KiB

Open AccessReview

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

by Janaina Soares Santos, Patrícia dos Santos Araújo, Yasmin Bastos Pissolitto, Paula Prenholatto Lopes, Anna Paulla Simon, Mariana de Souza Sikora and Francisco Trivinho-Strixino

Materials 2021, 14(2), 383; https://doi.org/10.3390/ma14020383 - 14 Jan 2021

Cited by 16 | Viewed by 3729

Abstract

This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable [...] Read more.

This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable technologies operating via photo, photoelectrochemical, and electrochemical processes. The facile and scalable synthesis with strict control of the properties combined with the low-cost, high surface area, chemical stability, and unidirectional orientation of these nanostructures make the anodized oxides attractive for these applications. Assuming different functionalities, TiO₂-NT is the widely explored anodic oxide in dye-sensitized solar cells, PEC water-splitting systems, fuel cells, supercapacitors, and batteries. However, other nanostructured anodic films based on WO₃, Cu_xO, ZnO, NiO, SnO, Fe₂O₃, ZrO₂, Nb₂O₅, and Ta₂O₅ are also explored and act as the respective active layers in several devices. The use of AAO as a structural material to guide the synthesis is also reported. Although in the development stage, the proof-of-concept of these devices demonstrates the feasibility of using the anodic oxide as a component and opens up new perspectives for the industrial and commercial utilization of these technologies. Full article

(This article belongs to the Special Issue Nanostructured Anodic Oxides: Fabrication, Characterization and Application)

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