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)

Heterogeneous photocatalyst materials for water splitting

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

Semiconductor-based Photocatalytic Hydrogen Generation

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

Photochemical splitting of water into H2 and O2 using solar energy is a process of great economic and environmental interest. Since the discovery of the first water splitting system based on TiO2 and Pt in 1972 by Fujishima and Honda, over 130 inorganic materials have been discovered as catalysts for this reaction. This review discusses the known inorganic catalysts with a focus on structure–activity relationships.

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Inorganic Materials as Catalysts for Photochemical Splitting of Water

This communication presents our recent results that the activity of photocatalytic H2 production can be significantly enhanced when a small amount of MoS2 is loaded on CdS as cocatalyst. The MoS2/CdS catalysts show high rate of H2 evolution from photocatalytic re-forming of lactic acid under visible light irradiation. The rate of H2 evolution on CdS is increased by up to 36 times when loaded with only 0.2 wt % of MoS2, and the activity of MoS2/CdS is even higher than those of the CdS photocatalysts loaded with different noble metals, such as Pt, Ru, Rh, Pd, and Au. The junction formed between MoS2 and CdS and the excellent H2 activation property of MoS2 are supposed to be responsible for the enhanced photocatalytic activity of MoS2/CdS.

Enhancement of photocatalytic H2 evolution on CdS by loading MoS2 as Cocatalyst under visible light irradiation.

RuO2-dispersed Zn2GeO4 was found to become a stable photocatalyst for the overall splitting of water to produce H2 and O2. The photocatalytic properties were examined under various experimental conditions, and the band structure of Zn2GeO4 was revealed based on the DFT calculation. The photocatalytic activity depended on calcination temperatures of Zn2GeO4 and the amount of RuO2 loaded, and the combination of highly crystallized Zn2GeO4 with dispersed small RuO2 particles provided large photocatalytic activity. The GeO4 tertrahedron of Zn2GeO4 is so heavily distorted to generate a dipole moment inside, and the good photocatalytic performance of RuO2-dispersed Zn2GeO4 is in line with the view that the electron−hole separation upon photoexcitation is promoted by a local electric field due to dipole moment. The DFT calculation showed that the top of the valence band (HOMO) was composed of the O 2p orbital, whereas the bottom of conduction band (LUMO) was formed by the Ge 4p orbital with a small contribution ...

Photocatalytic Activity for Water Decomposition of RuO2-Dispersed Zn2GeO4 with d10 Configuration

The photocatalytic activity for water decomposition of RuO2-dispersed ZnGa2O4 with an octahedrally coordinated Ga3+ ion was studied in order to examine the photocatalytic properties of p-block metal oxides with d10 configuration. ZnGa2O4 was impregnated with Ru3(CO)12 or Ru(C5H7O2)3 in THF and oxidized to convert them to RuO2. For RuO2-loaded ZnGa2O4, hydrogen and oxygen were stably produced from the initial stage of reaction under Hg−Xe lamp light irradiation. The activity dependence on the calcination temperature of ZnGa2O4, the amount of RuO2 loaded, and the oxidation temperature of RuO2 showed that the dispersion of small RuO2 particles leads to high photocatalytic activity. The electronic structure of ZnGa2O4 was calculated by a plane-wave-based density function theory (DFT). The valence bands were mainly composed of the O 2p orbitals, whereas the conduction bands were formed by hybridzation of Ga 4s4p and Zn 4s4p orbitals. Large dispersion observed in the conduction band indicated the large mobility...

N. Saito

Papers

Photocatalytic Activity for Water Decomposition of RuO2-Dispersed Zn2GeO4 with d10 Configuration

Photocatalysis for Water Decomposition by RuO2-Dispersed ZnGa2O4 with d10 Configuration

Photocatalytic Activity for Water Decomposition of RuO2-Dispersed Zn2GeO4 with d10 Configuration.