Highly Efficient Water Splitting into H2 and O2 over Lanthanum-Doped NaTaO3 Photocatalysts with High Crystallinity and Surface Nanostructure
13 Feb 2003-Journal of the American Chemical Society (American Chemical Society)-Vol. 125, Iss: 10, pp 3082-3089
TL;DR: The small particle size and the ordered surface nanostep structure of the NiO/NaTaO(3):La photocatalyst powder contributed to the highly efficient water splitting into H(2) and O(2).
Abstract: NiO-loaded NaTaO3 doped with lanthanum showed a high photocatalytic activity for water splitting into H2 and O2 in a stoichiometric amount under UV irradiation. The photocatalytic activity of NiO-loaded NaTaO3 doped with lanthanum was 9 times higher than that of nondoped NiO-loaded NaTaO3. The maximum apparent quantum yield of the NiO/NaTaO3:La photocatalyst was 56% at 270 nm. The factors affecting the highly efficient photocatalytic water splitting were examined by using various characterization techniques. Electron microscope observations revealed that the particle sizes of NaTaO3:La crystals (0.1−0.7 μm) were smaller than that of the nondoped NaTaO3 crystal (2−3 μm) and that the ordered surface nanostructure with many characteristic steps was created by the lanthanum doping. The small particle size with a high crystallinity was advantageous to an increase in the probability of the reaction of photogenerated electrons and holes with water molecules toward the recombination. Transmission electron microsc...
Citations
More filters
TL;DR: This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent.
Abstract: This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)
8,850 citations
TL;DR: The biggest challenge is whether or not the goals need to be met to fully utilize solar energy for the global energy demand can be met in a costeffective way on the terawatt scale.
Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2
8,037 citations
TL;DR: Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting and its Applications d0 Metal Oxide Photocatalysts 6518 4.4.1.
Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519
6,332 citations
TL;DR: This introductory review covers the fundamental aspects of photocatalytic and photoelectrochemical water splitting and recent advances in the water splitting reaction under visible light will be presented with a focus on non-oxide semiconductor materials to give an overview of the various problems and solutions.
Abstract: Photocatalytic and photoelectrochemical water splitting under irradiation by sunlight has received much attention for production of renewable hydrogen from water on a large scale. Many challenges still remain in improving energy conversion efficiency, such as utilizing longer-wavelength photons for hydrogen production, enhancing the reaction efficiency at any given wavelength, and increasing the lifetime of the semiconductor materials. This introductory review covers the fundamental aspects of photocatalytic and photoelectrochemical water splitting. Controlling the semiconducting properties of photocatalysts and photoelectrode materials is the primary concern in developing materials for solar water splitting, because they determine how much photoexcitation occurs in a semiconductor under solar illumination and how many photoexcited carriers reach the surface where water splitting takes place. Given a specific semiconductor material, surface modifications are important not only to activate the semiconductor for water splitting but also to facilitate charge separation and to upgrade the stability of the material under photoexcitation. In addition, reducing resistance loss and forming p-n junction have a significant impact on the efficiency of photoelectrochemical water splitting. Correct evaluation of the photocatalytic and photoelectrochemical activity for water splitting is becoming more important in enabling an accurate comparison of a number of studies based on different systems. In the latter part, recent advances in the water splitting reaction under visible light will be presented with a focus on non-oxide semiconductor materials to give an overview of the various problems and solutions.
3,470 citations
TL;DR: This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials, and highlights crucial issues that should be addressed in future research activities.
Abstract: Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.
3,265 citations
References
More filters
TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
TL;DR: In this paper, a wide range of oxides were examined for use as anodes in photoelectrochemical cells for the conversion of solar energy into electrical power or hydrogen, and the Schottky barrier model of the semi-conductor-electrolyte interface was used throughout.
710 citations
TL;DR: In this article, the authors used NiO as a cocatalyst for water splitting into H2 and O2 in pure water without any additives under UV irradiation, and found that NiO increased the photocatalytic activity of the NiO(0.15 wt %)/Sr2Ta2O7 photocatalyst.
Abstract: Sr2Ta2O7 and Sr2Nb2O7 with similar layered perovskite structure showed activities for water splitting into H2 and O2 in pure water without any additives under UV irradiation. The band gaps of Sr2Ta2O7 and Sr2Nb2O7 were 4.6 and 3.9 eV, respectively. Sr2Ta2O7 gave H2 and O2 from pure water under UV irradiation even in the absence of a cocatalyst. The activity of Sr2Ta2O7 was much increased by loading NiO as a cocatalyst even without pretreatment. The quantum yield of the NiO(0.15 wt %)/Sr2Ta2O7 photocatalyst was 12% at 270 nm. On the other hand, native Sr2Nb2O7 did not possess the activity. The high activity was obtained for the Sr2Nb2O7 photocatalyst when NiO was loaded and pretreated. Factors affecting the photocatalytic activities were discussed by using the Sr2Ta2O7 and Sr2Nb2O7 powder with similar layered perovskite structure. A predominant factor affecting the photocatalytic behavior of Sr2Ta2O7 and Sr2Nb2O7 is the conduction band levels formed by Ta5d and Nb4d.
583 citations
TL;DR: In this article, it was shown that the photocatalytic decomposition of pure water over ZrO[sub 2] powder without any loaded metals under UV irradiation can be achieved without the use of any loaded metal.
Abstract: It was found for the first time that the photocatalytic decomposition of pure water proceeded over ZrO[sub 2] powder without any loaded metals under UV irradiation. The rate of H[sub 2] and O[sub 2] evolution increased upon addition of Na[sub 2]CO[sub 3] and NaHCO[sub 3]. Moreover, the evolution of CO (the photocatalytic reduction product of CO[sub 2]) was observed from NaHCO[sub 3] solutions. The special characteristics of ZrO[sub 2] semiconductor are believed to be associated with its highly negative flat-band potential and wide bandgap. In the case of Cu(1 wt %)-ZrO[sub 2] catalyst suspended in NaHCO[sub 3] aqueous solution, the rates of gas evolutions were 19.5 [mu]mol/h of H[sub 2], 10.8 [mu]mol/h of O[sub 2], and 2.5 [mu]mol/h of CO. These mass balances were indicative of a stoichiometric and catalytic reaction. 26 refs., 1 tab.
461 citations
TL;DR: In this paper, the mechanism of photocatalytic decomposition of H2O into H2 and O2 over NiO and SrTiO3 powder was studied on the basis of the structure of the catalyst.
369 citations