Compositional and structural characterization of nanoporous films produced by iron anodizing in ethylene glycol solution

Jagminas, Arūnas; Mažeika, Kęstutis; Bernotas, Nerijus; Klimas, Vaclovas; Selskis, A.; Baltrūnas, D.

doi:10.1016/j.apsusc.2010.11.113

Cited by 32 publications

(20 citation statements)

References 27 publications

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“…: no significant crystalline oxide structure was found), in agreement with previously published works for quite similar ethylene glycol anodic iron films. 35,36 Thus, to improve their crystallinity they were subjected to thermal treatment. Figure 3 shows a typical X-ray diffraction pattern of an annealed nanostructured iron oxide sample electrochemically grown onto an iron substrate pretreated at −1.0 V (HN(−1.0 V)).…”

Section: Resultsmentioning

confidence: 99%

Electrochemically Grown Self-Organized Hematite Nanotube Arrays for Photoelectrochemical Water Splitting

Schrebler

Ballesteros

Gómez

et al. 2014

J. Electrochem. Soc.

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Hematite nanostructures were electrochemically grown by ultrasound-assisted anodization of iron substrates in an ethylene glycol based medium. These hematite nano-architectures can be tuned from a 1-D nanoporous layer to a self-organized nanotube one if the grown is done onto a bare iron foil substrate or onto an electrochemical pretreated one, respectively. Depending upon the pre-treatment conditioning, the self-organized nanotube layer consists of nanotube arrays with a single tube inner diameter of approximately 40-50 nm and wall thickness of 20-30 nm. Their morphological, structural and optoelectronic properties are studied. The photoelectrochemical properties of the resulting hematite nanostructures are studied from the point of view of their application as photoanodes in splitting of water. Through the photocurrent transients for the three nanostructured hematite type electrodes under study, the rate constants k tr and k rec corresponding to the rate constant of charge transfer and recombination processes have been determined. In all cases, the potential value where k tr > k rec was attained at more negative values than the reversible potential of water oxidation, indicating a photocatalytic effect. All samples show a maximum IPCE value between 350 and 375 nm, being the samples pretreated at −1.0 V which shows the highest IPCE value: 45% at 375 nm. In the last years, hydrogen energy has found increased attention as a renewable and clean energy source.1-5 Among many methods, solar hydrogen generation by photoelectrochemical (PEC) water splitting is a particularly attractive one because of the environmental friendless and the abundance of water and solar energy without emission of pollutants. [1][2][3][4][5] Since 1972, when the pioneering work on PEC water splitting was reported by Fujishima and Honda, 6 a wide range of materials has been investigated. In fact, semiconductor materials such as TiO 2 , SrTiO 3 , WO 3 , ZnO, BiVO 4 and Cu(In,Ga)Se 2,3,4,[7][8][9][10] have been used for the development of photoanodes in PEC cells.Compared to these materials, α-Fe 2 O 3 (hematite), has a narrower band-gap (1.9-2.2 eV), which allows to harvest up to 40% of the incident solar radiation. Furthermore, α-Fe 2 O 3 is a promising semiconducting material for photoelectrochemical and photocatalysis applications due to its stability, abundance and environmental compatibility, as well as convenient position of the valence band. 3,[11][12][13][14][15][16][17][18][19][20][21][22][23] In spite of the good properties presented by the α-Fe 2 O 3 , several problems must be solved in order to convert this material in an optimal one for certain applications. For instance, two of these problems correspond to: i) the very short hole diffusion length (20 nm, 24 2-4 nm) 25 compared to the light penetration depth (α −1 = 118 nm at λ = 550 nm), which results in the rapid non-radiative electron-hole recombination inside the semiconductor, and ii) poor electrical conductivity. [26][27][28] Two approaches have been taken to tackle the shor...

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Section: Resultsmentioning

confidence: 99%

Electrochemically Grown Self-Organized Hematite Nanotube Arrays for Photoelectrochemical Water Splitting

Schrebler

Ballesteros

Gómez

et al. 2014

J. Electrochem. Soc.

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“…4 Nanoporous a-Fe 2 O 3 film can be prepared by a polymer precursor method 5 and more recently by anodic oxidation of iron (Fe). [6][7][8][9][10] The latter is more effective for preparing nanoporous a-Fe 2 O 3 film with aligned and perpendicular pores; uniformly sized, rather thin pores wall and equally spaced. In anodic process for nanoporous anodic film formation, electrolyte is the most important parameter: its composition as well as its temperature.…”

Section: Introductionmentioning

confidence: 98%

Annealing temperature-dependent crystallinity and photocurrent response of anodic nanoporous iron oxide film

et al. 2016

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The effects of annealing temperatures on the structure and photocurrent response of nanoporous iron oxide film prepared by anodization of iron foil in an ethylene glycol, NH 4 F, and H 2 O electrolyte were studied. The as-anodized anodic film was found to be rather amorphous and crystallized to predominantly a-Fe 2 O 3 upon annealing in nitrogen. Nitrogen was used as to reduce the thickening of the barrier layer which affects the photocurrent response of the oxide. However, annealing must be done above 300°C to produce crystalline oxide but must be kept lower than 500°C since high temperature promotes grain growth, destroying the nanoporous structure and also thickens the barrier layer, which significantly reduce the photocurrent of the film. Sample annealed at 450°C in nitrogen has the highest photocurrent of 1.04 mA/cm 2 (0.5 V versus Ag/AgCl in 1 M NaOH) compared to 0.13 mA/cm 2 at 0.5 V for air-annealed sample.

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“…Recently, self-ordered nanostructured oxide films have been developed on iron using organic electrolytes containing fluoride and trace amounts of water. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] Depending upon the anodizing conditions, either nanoporous or nanotubular anodic films are formed on iron. 14,18,24,27 The as-formed anodic films are often amorphous and contain a relatively high concentration of fluoride species; however, such films are not chemically stable.…”

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confidence: 99%

Formation of Porous Anodic Films on Carbon Steels and Their Application to Corrosion Protection Composite Coatings Formed with Polypyrrole

Konno

Farag

Tsuji

et al. 2016

J. Electrochem. Soc.

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The growth behavior of nanoporous anodic films on carbon steel containing 0.213 mass% carbon has been examined. The films were grown by anodizing in an ethylene glycol (EG) electrolyte containing 0.1 mol dm −3 NH 4 F and 0.5 mol dm −3 H 2 O. The steel contains carbide precipitates with sizes in the range 50-800 nm. The anodic film formed on the carbide phase grew more slowly and was more chemically soluble during anodizing, resulting in submicrometer pits on the anodic film. The nanoporous morphology of the anodic films formed on an α-Fe matrix resembled those formed on iron. Heat treatment of the anodized specimens caused transformation of the chemically soluble fluoride-containing amorphous or poorly crystalline anodic films to crystalline oxide films containing α-Fe 2 O 3 and Fe 3 O 4 . Polypyrrole (PPy) was electropolymerized on the transformed surfaces to form a corrosion-protective composite coating. The resultant specimens coated with the composite coating showed improved durability compared to passivated steel with a PPy coating. Porous oxide films formed on aluminum and magnesium alloys by anodizing have been extensively studied for their ability to protect alloys from corrosion and wear; in addition, an anodizing process is of fundamental interest for the growth of self-ordered porous films. 1-3Recently, attention has been drawn to the formation of highly ordered nanoporous structures on aluminum, which are formed by the anodizing process, and their use in nanoscience and nanotechnology. 4 Furthermore, the formation of self-ordered nanoporous oxide films on a range of metals, including titanium, 5 zirconium, 6-8 niobium, 9 tantalum, 10 tungsten is also of interest. 11,12Iron is the most widely used metal. Recently, self-ordered nanostructured oxide films have been developed on iron using organic electrolytes containing fluoride and trace amounts of water. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] Depending upon the anodizing conditions, either nanoporous or nanotubular anodic films are formed on iron. 14,18,24,27 The as-formed anodic films are often amorphous and contain a relatively high concentration of fluoride species; however, such films are not chemically stable. Heat treatment of the anodized iron samples causes crystallization of the amorphous anodic film, forming mainly α-Fe 2 O 3 .16,17,21 α-Fe 2 O 3 is a promising material for solar-driven water splitting due to its low bandgap, low cost, abundance, and high chemical stability; consequently, nanostructured porous α-Fe 2 O 3 films formed by anodizing and subsequent heat-treatment have recently attracted much attention. 17,18 In addition to photocatalytic applications, porous anodic films on iron can be used to protect iron and steel from corrosion. Iron and steel alloys are often coated with paints to protect them from environmental corrosion. In addition, interest in the use of conducting polymer coatings has increased because they provide anodic protection due to their oxidizing ability; in addition, they act as a physical ba...

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Compositional and structural characterization of nanoporous films produced by iron anodizing in ethylene glycol solution

Cited by 32 publications

References 27 publications

Electrochemically Grown Self-Organized Hematite Nanotube Arrays for Photoelectrochemical Water Splitting

Electrochemically Grown Self-Organized Hematite Nanotube Arrays for Photoelectrochemical Water Splitting

Annealing temperature-dependent crystallinity and photocurrent response of anodic nanoporous iron oxide film

Formation of Porous Anodic Films on Carbon Steels and Their Application to Corrosion Protection Composite Coatings Formed with Polypyrrole

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