Kinetic Assessment and Numerical Modeling of Photocatalytic Water Splitting toward Efficient Solar Hydrogen Production

Hisatomi, Takashi; Minegishi, Tsutomu; Domen, Kazunari

doi:10.1246/bcsj.20120058

Cited by 70 publications

(76 citation statements)

References 38 publications

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“…Importantly, AQY generally depends on the light intensity. A number of previous studies have reported that AQY decreases with increasing light intensity because charge recombination is a second-order reaction with respect to light intensity in the high-intensity region [2]. If the dependence of AQY on photon irradiance is measured over a wide range of wavelengths using monochromatic light, the photocatalytic rates can be obtained for any light source power spectrum.…”

Section: Definition Of Photocatalytic Efficiencymentioning

confidence: 99%

“…Because the solar energy irradiating the surface of the Earth (1.3 9 10 5 TW) exceeds the current global human energy consumption (1.6 9 10 1 TW in 2010 [1]) by approximately four orders of magnitude, efficient photocatalytic solar energy conversion on a large scale should have a significant impact on energy and environmental issues as well as the economy, as described later. Figure 1 shows a simplified schematic of the reaction processes involved in overall water splitting using a single particulate photocatalyst [2]. Excited electrons and holes are generated in the bulk of the semiconductor photocatalyst particles upon band gap excitation.…”

Section: Introduction To Photocatalytic Water Splittingmentioning

confidence: 99%

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Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

2014

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Some particulate semiconductors loaded with nanoparticulate catalysts exhibit photocatalytic activity for the water-splitting reaction. The photocatalysis is distinct from the thermal catalysis because photocatalysis involves photophysical processes in particulate semiconductors. This review article presents a brief introduction to photocatalysis, followed by kinetic aspects of the photocatalytic water-splitting reaction.

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Section: Definition Of Photocatalytic Efficiencymentioning

confidence: 99%

Section: Introduction To Photocatalytic Water Splittingmentioning

confidence: 99%

Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

2014

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“…This is a general trend for powder systems due to the requirement for sites for both reduction and oxidation and potential competitive light absorption from Co species. 25,[48][49][50] To further elucidate the state of the catalyst after pretreatment, 2 wt% CoO x /Ta 3 N 5 treated at 700 °C under NH 3 was selected for further study unless otherwise noted. The XRD patterns of Ta 3 N 5 and CoO x /Ta 3 N 5 are compared in Figure 2.…”

Section: Photocatalytic Reactionmentioning

confidence: 99%

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst

et al. 2015

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ABSTRACT:In a photocatalytic suspension system with a powder semiconductor, the interface between the photocatalyst semiconductor and catalyst should be constructed to minimize resistance for charge transfer of excited carriers. This study demonstrates an in-depth understanding of pretreatment effects on the photocatalytic O 2 evolution reaction (OER) activity of visible-lightresponsive Ta 3 N 5 decorated with CoO x nanoparticles. The CoO x /Ta 3 N 5 sample was synthesized by impregnation followed by sequential heat treatments under NH 3 flow and air flow at various temperatures. Various characterization techniques, including X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS), were used to clarify the state and role of cobalt. No improvement in photocatalytic activity for OER over the bare Ta 3 N 5 was observed for the as-impregnated CoO x /Ta 3 N 5 , likely because of insufficient contact between CoO x and Ta 3 N 5 . When the sample was treated in NH 3 at high temperature, a substantial improvement in the photocatalytic activity was observed. After NH 3 treatment at 700 °C, the Co 0 -CoO x core-shell agglomerated cobalt structure was identified by XAS and STEM. No metallic cobalt species was evident after the photocatalytic OER, indicating that the metallic cobalt itself is not essential for the reaction. Accordingly, mild oxidation (200 °C) of the NH 3 -treated CoO x /Ta 3 N 5 sample enhanced photocatalytic OER activity. Oxidation at higher temperatures drastically eliminated the photocatalytic activity, most likely because of unfavorable Ta 3 N 5 oxidation. These results suggest that the intimate contact between cobalt species and Ta 3 N 5 facilitated at high temperature is beneficial to enhancing hole transport and that the cobalt oxide provides electrocatalytic sites for OER. IntroductionWater splitting using powder photocatalyst systems has attracted significant interest for the production of renewable hydrogen generation using abundant solar energy because of its simplicity, scalability, and low capital cost.1,2 To effectively convert solar energy, substantial utilization of photon energy in the visible-light range is essential. Using the AM 1.5G standard spectrum 3 , a photocatalyst with absorption from UV to 600 nm with a quantum efficiency of 30% accounts for ~5% solar to hydrogen efficiency, making the technology commercially feasible.1,4 Among the photocatalysts investigated to date, tantalum(V) nitride (Ta 3 N 5 ) has emerged as one of the most promising candidates and has been extensively investigated for more than a decade. [4][5][6][7][8][9][10][11][12][13][14][15] Ta 3 N 5 has a visible-light response (approximately 600 nm, ~2.1-eV band gap) and is capable of producing hydrogen or oxygen in the presence of appropriate sacrificial reagents and surface modifications under visible-light irradiation. 1,[5][6][7][8][9][10][11][12][13][14][15][16] Our recent work on Ta 3 N 5 thin films for the photo...

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“…20 Macroscopic design of photocatalyst particles was also proposed for efficient carrier separation. 21 …”

Section: Carrier Migration From Photocatalyst To Co-catalystmentioning

confidence: 99%

Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogen

Kubota

Domen

2013

Interface magazine

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W ater splitting using a photocatalyst for direct solar hydrogen production from sunlight and water, has been regarded as an important approach to artificial photosynthesis.1,2 Solar hydrogen, which is the simplest solar fuel, can then be converted to various energy carriers such as organic hydrides, methanol, methane, and ammonia for transportation and storage. Thus, energy systems based on solar hydrogen can lead to a stable, secure, and ecologically-friendly society. Although solar fuel production using electricity from photovoltaic cells and concentrated solar thermal power is an existing technology, direct synthesis of solar fuels by artificial photosynthesis has more scalability in terms of system cost.To split water into hydrogen and oxygen, 1.23 V of energy is required, corresponding to a 2 electron reaction. An energy of 1.23 V is equivalent to a photon energy of 1000 nm, so that the visible light (400-800 nm in wavelength) that represents half of the solar energy spectrum can be thermodynamically used for water splitting. The challenge is to obtain an efficient photocatalyst that has an absorption edge in longer wavelength and the ability to split water.Highly efficient oxide photocatalysts, such as La-doped NaTaO 3 , and Zn-doped Ga 2 O 3 , have been reported with quantum efficiencies of over 50%. [3][4][5] However, these oxides only absorb ultraviolet (UV) light with wavelengths shorter than 300 nm. In the solar spectrum at the earth's surface, such short UV light is not present, so that these oxides cannot operate efficiently under solar irradiation. Most oxides have band gaps wider than the UV energy because of the deeper O 2p potential of the valence band. The valence band of nitrides is composed of the shallower N 2p potential, and thus their band gaps are generally narrower than those of oxides. For photocatalytic water splitting, photoexcited electrons in the conduction band reduce water to evolve hydrogen, and photogenerated holes in the valence band oxidize water to evolve oxygen. Therefore, the potential of the conduction band should be shallower than the reversible hydrogen potential and the potential of the valence band should be deeper than the reversible oxygen potential. In this article, the properties of oxynitride and nitride photocatalysts for water splitting are described.Surface modification of semiconductor photocatalyst particles with hydrogenor oxygen-evolving cocatalysts is an indispensable technique in the study of photocatalytic water splitting. In fact, hydrogen-evolution cocatalysts are required Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogenby Jun Kubota and Kazunari Domen in most cases. A simple illustration of photocatalytic water splitting is shown in Fig. 1. Photoexcited electrons in the conduction band need to be smoothly transferred to the hydrogen-evolution cocatalyst particles without release of energy. The first requirement for the cocatalyst is a smaller barrier for migration of electrons from the...

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Kinetic Assessment and Numerical Modeling of Photocatalytic Water Splitting toward Efficient Solar Hydrogen Production

Cited by 70 publications

References 38 publications

Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst

Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogen

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Kinetic Assessment and Numerical Modeling of Photocatalytic Water Splitting toward Efficient Solar Hydrogen Production

Cited by 70 publications

References 38 publications

Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta3N5 Photocatalyst

Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogen

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Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst