Solar Photocatalytic Hydrogen Production Research Articles

Photodeposited-metal/CdS/ZnO heterostructures for solar photocatalytic hydrogen production under different conditions

In this study, photocatalytic hydrogen production over metal-incorporated CdS and ZnO (M/CdS/ZnO) nanocomposites under simulated solar light illumination was investigated. M/CdS/ZnO samples were synthesized by photodepositing a metal into CdS/ZnO powders. All photocatalysts showed increased hydrogen production with an increase in the light exposure time. The M/CdS/ZnO samples exhibited better hydrogen production yields than the CdS/ZnO nanocomposites, which in turn showed higher hydrogen production yields than pure ZnO did. The hydrogen production yields of the CdS/ZnO samples increased as the CdS/ZnO weight ratio increased from 0.01 to 0.10. However, they decreased with further increases in CdS loading, although the light absorption edges of the CdS/ZnO samples were further extended to the visible region. Pt/CdS/ZnO and Pd/CdS/ZnO exhibited similar hydrogen production yields, which were higher than the Ni/CdS/ZnO yield. The hydrogen production yield of Pt (0.5%)/CdS/ZnO was higher than that of Pt (0.1%)/CdS/ZnO. Notably, the hydrogen production yield of CdS/Pt/ZnO was lower than that of Pt/CdS/ZnO. Among three different electron donors (Na2S + Na2SO3, methanol, and lactic acid solutions), the Na2S + Na2SO3 solution led to the highest hydrogen production yield. A tentative mechanism for photocatalytic hydrogen production over M/CdS/ZnO nanocomposites under solar light irradiation, using a Na2S + Na2SO3 solution as an electron donor, was proposed. In summary, M/CdS/ZnO photocatalysts can be utilized efficiently for photocatalytic hydrogen production with solar light exposure through proper control of operating parameters.

Cu2O-sensitized TiO2 nanorods with nanocavities for highly efficient photocatalytic hydrogen production under solar irradiation

Hydrogen trititanate (H2Ti3O7) nanorods were synthesized by using a hydrothermal method. The transformation of the crystal structure from H2Ti3O7 to TiO2 occurred into either single crystalline TiO2 (B) [calcined at 400 or 450°C] or bicrystalline TiO2 (B) with anatase phases [calcined at 500 or 550°C] during a calcination process. Calcination temperature from 450 to 550°C induced both phase transformation and formation of large size nanocavities, and the changes in the nanorods morphology were confirmed using HRTEM/TEM images. Nanocomposites of Cu2O/TiO2 nanorods with different copper loading (CuxTNR) were prepared by using the wet impregnation method with TiO2 nanorods [calcined at 500°C] and copper nitrate as copper source. The structural, optical, surface elemental and morphological properties of the synthesized catalysts were extensively characterized. Solar photocatalytic hydrogen (H2) production experiment was carried out with aqueous-glycerol solution for 4h. The photocatalytic activity of TiO2 nanorods that are calcined at 500°C exhibited very high rate of H2 production, is ascribed to the improved separation of electron/hole pairs and catalytic activity at bicrystalline TiO2 surface. For the first-time, we have achieved the higher rate of H2 (50,339µmolh−1g−1cat) production under the set of the optimized conditions using Cu1.5TNR nanorods containing nanocavities as catalyst under solar irradiation. This enhancement in the activity can be attributed to the desirable absorption of UV–visible light in natural solar spectrum and minimization of the recombination of electron–hole pairs, multiple internal reflection of light within nanocavities, which improved the surface–interface reactions. The present study clearly demonstrated that Cu loaded on titania nanorods containing nanocavities were found to be more efficient and promising photocatalyst for H2 production under solar light irradiation.

Enhanced optical absorption of the plasmonic nanoshell suspension based on the solar photocatalytic hydrogen production system

The absorption properties of the random Al/CdS nanoshell systems are simulated using the finite difference time domain (FDTD) method. The interactions between the nanoshells have been taken into account in the simulation. By comparing the optical absorption of dispersion system with that of single nanoshell, it reveals that the inter-particle coupling cannot be neglected in the simulation of dispersion system. The absorption enhancement is affected by both the inter-particle coupling and the localized surface plasmon resonance (LSPR) effect. The dispersed nanoparticles induce longer optical path inside the dispersion system and enhance light trapping as well as absorption. It can be considered to increase the nanoshell concentration and reduce the particle size to obtain an enhanced absorption.

Oxygen tolerance of an in silico -designed bioinspired hydrogen-evolving catalyst in water

Certain bacterial enzymes, the diiron hydrogenases, have turnover numbers for hydrogen production from water as large as 10(4)/s. Their much smaller common active site, composed of earth-abundant materials, has a structure that is an attractive starting point for the design of a practical catalyst for electrocatalytic or solar photocatalytic hydrogen production from water. In earlier work, our group has reported the computational design of [FeFe](P)/FeS(2), a hydrogenase-inspired catalyst/electrode complex, which is efficient and stable throughout the production cycle. However, the diiron hydrogenases are highly sensitive to ambient oxygen by a mechanism not yet understood in detail. An issue critical for practical use of [FeFe](P)/FeS(2) is whether this catalyst/electrode complex is tolerant to the ambient oxygen. We report demonstration by ab initio simulations that the complex is indeed tolerant to dissolved oxygen over timescales long enough for practical application, reducing it efficiently. This promising hydrogen-producing catalyst, composed of earth-abundant materials and with a diffusion-limited rate in acidified water, is efficient as well as oxygen tolerant.

Structure and Properties of Water on the Anatase TiO2(101) Surface: From Single-Molecule Adsorption to Interface Formation

The interaction of water with titanium dioxide surfaces has a vital role in many energy- and environment-related applications, such as dye-sensitized solar cell, photocatalytic or photoelectrochemical hydrogen production, and environmental purification. Structure and properties of water on the anatase TiO2(101) surface have been studied by using a combination of density functional theory and force field molecular dynamics. Owing to the amphotericity of this surface and the competition between water–water and water–substrate interactions, the structure and properties of water on the anatase TiO2(101) surface exhibited some peculiar and complicated features. The overall evolutionary process of interface formation has been obtained by investigating the coverage-dependent adsorption configuration and energy of water. The competition between water–water and water–substrate interaction results in the existence of a stable bilayer of water (Θ ≥ 2 ML) and an ice-like structure of water at higher coverage (Θ ≥ 3 M...

Study on the Radiation Distribution in A Fluidized Tubular Reactor for Heterogeneous Photocatalytic Hydrogen Production

Abstract Radiation distribution study is of importance for the design and the optimization of fluidized photocatalytic tubular reactor which has been developed for photocatalytic hydrogen production under direct solar light. In the present study, the radiation distribution in such reactor was successfully simulated by adopting Monte Carlo method and the six-flux radiation absorption-scattering models. Both the incident angles of light around the reactor and the concentration distribution of photocatalyst were taken into account. Our analysis indicates that the angles and the intensity of the incident rays significantly affect the radiation distribution. Moreover, it was also found that the equilibrium radiation distribution has a close relationship with the density distribution of the photocatalysts. The simulated results are expected to be helpful for obtaining the optimal operating parameters for solar photocatalytic hydrogen production.

Tailored TiO2−SrTiO3 Heterostructure Nanotube Arrays for Improved Photoelectrochemical Performance

TiO(2) nanotube arrays formed on Ti substrate by electrochemical anodization have been converted into TiO(2)-SrTiO(3) heterostructures by controlled substitution of Sr under hydrothermal conditions. The growth of SrTiO(3) crystallites on the nanotube array electrode was probed by electron microscopy and X-ray diffraction. As the degree of Sr substitution increases with the duration of hydrothermal treatment, an increase in the size of SrTiO(3) crystallites was observed. Consequently, with increasing SrTiO(3) fraction in the TiO(2)-SrTiO(3) nanotube arrays, we observed a shift in the flat band potential to more negative potentials, thus confirming the influence of SrTiO(3) in the modification of the photoelectrochemical properties. The TiO(2)-SrTiO(3) composite heterostructures obtained with 1 h or less hydrothermal treatment exhibit the best photoelectrochemical performance with nearly 100% increase in external quantum efficiency at 360 nm. The results presented here provide a convenient way to tailor the photoelectrochemical properties of TiO(2)-SrTiO(3) nanotube array electrodes and employ them for dye- or quantum-dot-sensitized solar cells and/or photocatalytic hydrogen production.

Solar light photocatalytic hydrogen production from water over Pt and Au/TiO 2(anatase/rutile) photocatalysts: Influence of noble metal and porogen promotion

Hydrogen production from water under artificial solar light irradiation was performed over a series of Pt and Au/TiO 2(anatase/rutile) photocatalysts. Different TiO 2 supports with varying anatase/rutile contents were compared, based on either sol–gel synthesis or commercial TiO 2. The influence of template promotion on sol–gel TiO 2 synthesis has been studied using different porogens or templates. Among various factors influencing the hydrogen evolution efficiency, it was pointed out that the following parameters were crucial to enhance H 2 evolution: (i) the nature and content of the metallic co-catalyst, (ii) the surface, crystallographic, and porosity properties of the TiO 2 anatase/rutile support, (iii) the anatase/rutile ratio, (iv) the metal–support interactions, and (v) the relative amount of methanol added as a sacrificial reagent. The influence of these different factors was studied in detail. In optimized conditions, important H 2 production efficiency (120 μmol/min) was obtained over days without deactivation and with very low amounts of methanol.

Photocatalytic hydrogen production under direct solar light in a CPC based solar reactor: Reactor design and preliminary results

In despite of so many types of solar reactors designed for solar detoxification purposes, few attempts have been made for photocatalytic hydrogen production, which in our option, is one of the most promising approaches for solar to chemical energy conversion. Addressing both the similarity and dissimilarity for these two processes and by fully considering the special requirements for the latter reaction, a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar reactor has been designed for the first time. The design and optimization of this CPC based solar reactor has been discussed in detail. Preliminary results demonstrated that efficient photocatalytic hydrogen production under direct solar light can be accomplished by coupling tubular reactors with CPC concentrators. It is anticipated that this first demonstration of concentrator-based solar photocatalytic hydrogen production would draw attention for further studies in this promising direction.