The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers.

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A metal-free polymeric photocatalyst for hydrogen production from water under visible light

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

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

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

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

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Enhancing catalytic performance holds promise for hydrogen production by water splitting in sunlight.

/pdf/photocatalyst-releasing-hydrogen-from-water-4wwvapcpjb.pdf

Photocatalyst releasing hydrogen from water

Noble‐Metal/Cr2O3 Core/Shell Nanoparticles as a Cocatalyst for Photocatalytic Overall Water Splitting

The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga1-xZnx)(N1-xOx), are investigated. Nitridation of a mixture of Ga2O3 and ZnO at 1123 K for 5−30 h under NH3 flow results in the formation of a (Ga1-xZnx)(N1-xOx) solid solution with x = 0.05−0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga1-xZnx)(N1-xOx) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga2O3 in the starting material, resulting in an increase in activity.

Overall Water Splitting on (Ga1-xZnx)(N1-xOx) Solid Solution Photocatalyst: Relationship between Physical Properties and Photocatalytic Activity

Photodeposited Rh/Cr2O3 (core/shell) nanoparticles on a (Ga1-xZnx)(N1-xOx) photocatalyst are studied as a cocatalyst for overall water splitting. Irradiation of Rh-loaded (Ga1-xZnx)(N1-xOx) with visible light (λ > 400 nm) in aqueous K2CrO4 solution results in the formation of core/shell-structured nanoparticles consisting of a Rh core and Cr2O3 shell through the site-selective photoreduction of CrO42- anions to Cr2O3 on Rh nanoparticles. The shell thickness increases with concentration of K2CrO4 in the reactant solution to a maximum of ca. 2 nm, at which a uniform Cr2O3 coating is obtained. The Cr2O3 shell suppresses water formation from H2 and O2 on Rh nanoparticles, allowing stoichiometric decomposition of pure water to be achieved. The core/shell structure also provides enhanced H2 evolution compared to that of bare Rh nanoparticles.

Roles of Rh/Cr2O3 (Core/Shell) Nanoparticles Photodeposited on Visible-Light-Responsive (Ga1-xZnx)(N1-xOx) Solid Solutions in Photocatalytic Overall Water Splitting

The photocatalytic activity of (Ga1-xZnx)(N1-xOx) loaded with Rh−Cr mixed-oxide (Rh2-yCryO3) nanoparticles for overall water splitting under visible-light irradiation (λ > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh2-yCryO3 as a cocatalyst on the (Ga1-xZnx)(N1-xOx) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.

Efficient Overall Water Splitting under Visible-Light Irradiation on (Ga1-xZnx)(N1-xOx) Dispersed with Rh−Cr Mixed-Oxide Nanoparticles: Effect of Reaction Conditions on Photocatalytic Activity

Yasunobu Inoue

Papers

Photocatalyst releasing hydrogen from water

Noble‐Metal/Cr2O3 Core/Shell Nanoparticles as a Cocatalyst for Photocatalytic Overall Water Splitting

Overall Water Splitting on (Ga1-xZnx)(N1-xOx) Solid Solution Photocatalyst: Relationship between Physical Properties and Photocatalytic Activity

Roles of Rh/Cr2O3 (Core/Shell) Nanoparticles Photodeposited on Visible-Light-Responsive (Ga1-xZnx)(N1-xOx) Solid Solutions in Photocatalytic Overall Water Splitting

Efficient Overall Water Splitting under Visible-Light Irradiation on (Ga1-xZnx)(N1-xOx) Dispersed with Rh−Cr Mixed-Oxide Nanoparticles: Effect of Reaction Conditions on Photocatalytic Activity