Thermal air oxidation of Fe: rapid hematite nanowire growth and photoelectrochemical water splitting performance

Grigorescu, Sabina; Lee, Chong; Lee, Ki-Young; Albu, Sergiu P.; Paramasivam, Indhumati; Demetrescu, Ioana; Schmuki, Patrik

doi:10.1016/j.elecom.2012.06.038

Cited by 57 publications

(49 citation statements)

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“…However, it is well established that various precursor iron oxides are formed by anodizing and thus a suitable annealing procedure is needed to obtain α‐Fe 2 O 3 . Annealing conditions such as temperature and atmosphere affect the PEC performance of α‐Fe 2 O 3 layers . Ling et al .…”

Section: Introductionsupporting

confidence: 50%

“…Therefore, the compact inner layer due to thermal annealing is considered to be detrimental to the PEC performance. Furthermore, literature generally describes that a thermal oxidative annealing leads to oxide layers that consist of a gradient of wustite (FeO), magnetite (Fe 3 O 4 ), and α‐Fe 2 O 3 . Since FeO and Fe 3 O 4 are either metal‐like or behave like a narrow band gap (<1 eV) semiconductor, they are not desired for photolysis .…”

Section: Resultsmentioning

confidence: 99%

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Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Makimizu

Nguyen

Tuček

et al. 2020

Chemistry A European J

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Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α‐Fe2O3) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α‐Fe2O3 is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O2 in Ar). It was found that low oxygen annealing can activate a significant PEC response of α‐Fe2O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α‐Fe2O3 annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm−2, being 20 times higher than that of annealing in air. The obtained results show that the α‐Fe2O3 annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α‐Fe2O3. Additionally, we demonstrate the photocurrent of α‐Fe2O3 annealed in low oxygen ambient can be further enhanced by Zn‐Co LDH, which is a co‐catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α‐Fe2O3 photoanodes.

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Section: Introductionsupporting

confidence: 50%

Section: Resultsmentioning

confidence: 99%

Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Makimizu

Nguyen

Tuček

et al. 2020

Chemistry A European J

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“…However, the practical use of this material is limited because of its low electron mobility (10 -2 to 10 -1 cm 2 V -1 s -1 ) and short hole diffusion length (2-4 nm), as well as the short life time of its charge carriers (about 10 pico second) that lead in practice to very low solar light to current conversion efficiencies and large overpotential for O 2 evolution [15]. Various strategies have been employed to address these issues, for example, doping of the material to adjust the carrier mobility, incorporation of co-catalysts which reduce the over-potential, surface passivation to minimize losses by carrier recombination at the semiconductor-electrolyte interface and so on [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Solar water splitting for hydrogen production with Fe2O3 nanotubes prepared by anodizing method: effect of anodizing time on performance of Fe2O3 nanotube arrays

Momeni

Ghayeb

Mohammadi

2014

J Mater Sci: Mater Electron

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Self-organized iron oxide nanotubes were successfully prepared on the iron foils by a simple electrochemical anodization method in NH 4 F organic electrolyte. The Fe 2 O 3 nanotubes were characterized by field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, UV-vis absorbance spectra, and X-ray diffraction spectroscopy. Scanning electron microscopy images show that dependent upon the anodizing time, the pore diameters range from 30 to 45 nm. Crystallization and structural retention of the synthesized structure are achieved upon annealing the initial amorphous sample in oxygen atmosphere at 450°C for 1 h. The crystallized nanoporous film, having a 2.04 eV bandgap, exhibited a maximum photocurrent density of 0.68 mA cm -2 in 1 M NaOH at 0.5 V versus Ag/AgCl. The current potential characteristics showed that the water-splitting photocurrent strongly depends on the anodizing time and its increases with anodization time.

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“…[13][14][15][16][17] For anodically prepared nanoporous/nanotubular materials, the composition and structure, that is, the formation of FeO, Fe 3 O 4 , and a-Fe 2 O 3 , can be adjusted depending on the annealing temperature and environment. [20][21][22] In practice, a-Fe 2 O 3 is the desired photoactive phase for photoelectrochemical water splitting applications. [2,5,21] Overall, for such anodic nanotubular or nanoporous layers, a considerable range of photoelectrochemical results has been published, evaluating various influences such as anodization and annealing conditions on the resulting water-splitting performance.…”

mentioning

confidence: 99%

“…[20][21][22] In practice, a-Fe 2 O 3 is the desired photoactive phase for photoelectrochemical water splitting applications. [2,5,21] Overall, for such anodic nanotubular or nanoporous layers, a considerable range of photoelectrochemical results has been published, evaluating various influences such as anodization and annealing conditions on the resulting water-splitting performance. However, an important factor that has been overAnodization of iron substrates is one of the most simple and effective ways to fabricate nanotubular (and porous) structures that could be directly used as a photoanode for solar water splitting.…”

mentioning

confidence: 99%

Anodic Nanotubular/porous Hematite Photoanode for Solar Water Splitting: Substantial Effect of Iron Substrate Purity

et al. 2014

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Anodization of iron substrates is one of the most simple and effective ways to fabricate nanotubular (and porous) structures that could be directly used as a photoanode for solar water splitting. Up to now, all studies in this field focused on achieving a better geometry of the hematite nanostructures for a higher efficiency. The present study, however, highlights that the purity of the iron substrate used for any anodic-hematite-formation approach is extremely important in view of the water-splitting performance. Herein, anodic self-organized oxide morphologies (nanotubular and nanoporous) are grown on different iron substrates under a range of anodization conditions, including elevated temperatures and anodization supported by ultrasonication. Substrate purity has not only a significant effect on oxide-layer growth rate and tube morphology, but also gives rise to a ninefold increase in the photoelectrochemical water-splitting performance (0.250 vs. 0.028 mA cm−2 at 1.40 V vs. reversible hydrogen electrode under AM 1.5 100 mW cm−2 illumination) for 99.99 % versus 99.5 % purity iron substrates of similar oxide geometry. Elemental analysis and model alloys show that particularly manganese impurities have a strong detrimental effect on the water-splitting performance.

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Thermal air oxidation of Fe: rapid hematite nanowire growth and photoelectrochemical water splitting performance

Cited by 57 publications

References 20 publications

Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Solar water splitting for hydrogen production with Fe2O3 nanotubes prepared by anodizing method: effect of anodizing time on performance of Fe2O3 nanotube arrays

Anodic Nanotubular/porous Hematite Photoanode for Solar Water Splitting: Substantial Effect of Iron Substrate Purity

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Thermal air oxidation of Fe: rapid hematite nanowire growth and photoelectrochemical water splitting performance

Cited by 57 publications

References 20 publications

Activation of α‐Fe2O3 for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Activation of α‐Fe2O3 for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Solar water splitting for hydrogen production with Fe2O3 nanotubes prepared by anodizing method: effect of anodizing time on performance of Fe2O3 nanotube arrays

Anodic Nanotubular/porous Hematite Photoanode for Solar Water Splitting: Substantial Effect of Iron Substrate Purity

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Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Activation of α‐Fe₂O₃ for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient