Photoelectrochemical water splitting over ordered honeycomb hematite electrodes stabilized by alumina shielding

Jun, Hwichan; Im, Badro; Kim, Jae Young; Im, Yong-O; Jang, Ji‐Wook; Kim, Eun Sun; Kim, Jae Yul; Kang, Hyeon Joon; Hong, Suk Joon; Lee, Jae Sung

doi:10.1039/c1ee02526k

Cited by 92 publications

(54 citation statements)

References 56 publications

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“…9,12,25 The IPCE value at 350 nm for the wave-like nanotube arrays was ~3 times higher than that for the single layer nanotube arrays, and ~12 times higher than that for multilayer nanotube arrays. The differences in the IPCE values at low wavelengths were a result of differences in their nanostructures, with factors such as accessible electrochemical surface area and the presence of layer interfaces playing a central role.…”

Section: Materials Characterizationmentioning

confidence: 96%

Synthesis and Characterization of Hematite Nanotube Arrays for Photocatalysis

Mushove

Breault

Thompson

2015

Ind. Eng. Chem. Res.

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The synthesis and characterization of hematite nanotube arrays for use as photocatalysts are described in this paper. Novel morphologies, including multilayered and wave-like nanotube arrays, were synthesized via electrochemical anodization of iron foils in electrolytic solutions containing ammonium fluoride, ethylene glycol and water. The nanotube formation mechanism was investigated by tracking the current response data during anodization.The results indicate that there are four distinct stages associated with the evolution of the nanotube arrays: an ohmic response stage, an oxide film formation stage, a chemical dissolution/pitting stage, and a steady-state growth stage. Morphological, optical, and photoelectrochemical properties of the resulting materials were characterized using X-ray diffraction, scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy, linear sweep voltammetry, electrochemical impedance spectroscopy, and incident photon to current efficiency (IPCE). The IPCE for the wave-like nanotube arrays at 350 nm was ~3 times that for the single layer nanotube arrays and ~12 times that for the multilayer nanotube arrays. The IPCE also increased with electrochemical surface area and played a key role with regard to the photocatalytic performance.

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Section: Materials Characterizationmentioning

confidence: 96%

Synthesis and Characterization of Hematite Nanotube Arrays for Photocatalysis

Mushove

Breault

Thompson

2015

Ind. Eng. Chem. Res.

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“…Doping is commonly employed to improve the electrical conducting property of hematite by increasing donor density171819202122. Synthesis of nanostructures including one-dimensional (1-D) nanorods, nanowires, and nanotubes shortens the pathway that photoexcited electrons/holes have to travel2223242526. Other successful approaches include making hematite-based composite photoanode with a good conducting material27282930, forming a junction structure with another semiconducting material with a different band gap3132, or loading a co-catalyst on the semiconductor surface to facilitate oxygen evolution reaction (OER)33343536.…”

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confidence: 99%

Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting

Kim

Magesh

Youn

et al. 2013

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A hematite photoanode showing a stable, record-breaking performance of 4.32 mA/cm2 photoelectrochemical water oxidation current at 1.23 V vs. RHE under simulated 1-sun (100 mW/cm2) irradiation is reported. This photocurrent corresponds to ca. 34% of the maximum theoretical limit expected for hematite with a band gap of 2.1 V. The photoanode produced stoichiometric hydrogen and oxygen gases in amounts close to the expected values from the photocurrent. The hematitle has a unique single-crystalline “wormlike” morphology produced by in-situ two-step annealing at 550°C and 800°C of β-FeOOH nanorods grown directly on a transparent conducting oxide glass via an all-solution method. In addition, it is modified by platinum doping to improve the charge transfer characteristics of hematite and an oxygen-evolving co-catalyst on the surface.

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“…26 Moreover, in the 1-D structures, the hole diffusion pathway in the radial direction can be compatible with its short diffusion length so that the effect of hole diffusivity limitation can be minimized. 33 In consequence, one-dimensional nanostructure vertically grown onto a conducting substrate has been proposed as the idealized morphology for a hematite photoanode for water splitting. 26 However, based on the constraint of the thickness in the radial direction compatible with the diffusion length (∼ 4-10 nm), hematite nanowires with a very high aspect ratio are needed, which cannot stand individually, perpendicular to the substrate.…”

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confidence: 99%

“…26 However, based on the constraint of the thickness in the radial direction compatible with the diffusion length (∼ 4-10 nm), hematite nanowires with a very high aspect ratio are needed, which cannot stand individually, perpendicular to the substrate. 33 On the other hand, hematite nanotubes can give better mechanical stability compared to nanowires, 33 and nanotubular architecture gives an extra degree of freedom in its wall thickness that can be varied (in addition to diameter and length) for tuning the required properties. 31 Furthermore, nanotubes exhibit larger surface area than nanowires for a given diameter and length.…”

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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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Photoelectrochemical water splitting over ordered honeycomb hematite electrodes stabilized by alumina shielding

Cited by 92 publications

References 56 publications

Synthesis and Characterization of Hematite Nanotube Arrays for Photocatalysis

Synthesis and Characterization of Hematite Nanotube Arrays for Photocatalysis

Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting

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

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