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Close proximity between different catalytic sites is crucial for accelerating or even enabling many important catalytic reactions. Photooxidation and photoreduction in photocatalysis are generally separated from each other, which arises from the hole-electron separation on photocatalyst surface. Here, we show with widely studied photocatalyst Pt/TiO2 as a model, that concentrating abundant oxygen vacancies only at the metal-oxide interface can locate hole-driven oxidation sites in proximity to electron-driven reduction sites for triggering unusual reactions. Solar hydrogen production from aqueous-phase alcohols, whose hydrogen yield per photon is theoretically limited below 0.5 through conventional reactions, achieves an ultrahigh hydrogen yield per photon of 1.28 through the unusual reactions. We demonstrated that such defect engineering enables hole-driven CO oxidation at the Pt- TiO2 interface to occur, which opens up room-temperature alcohol decomposition on Pt nanoparticles to H2 and adsorbed CO, accompanying with electron-driven proton reduction on Pt to H2. [ABSTRACT FROM AUTHOR]

A core-shell structural Rh-CrO x loaded on Al3+ doped strontium titanate was used for photocatalytic water splitting. A specially designed twin photoreactor, which integrates the water splitting and the degradation of isopropanol, can simultaneously carry out the degradation of isopropanol and hydrogen production. A flux method was conducted to prepare Rh@CrO 3 cocatalyst on Al3+ doped high-crystallinity strontium titanate for the photocatalyst of hydrogen evolution. Nearly 1200 μmole/g of hydrogen was evolved in photocatalytic whole water splitting in five hours under simulated AM 1.5 G sunlight. Pt-loaded WO 3 was utilized to degrade 100 ppm isopropanol solution. The above photocatalysts were used in the twin reactor with electron-mediator I-/IO 3 - and a Neosepta anion-exchanged membrane. Hydrogen evolution of 1102 μmole/g and isopropanol removal of 10.1% were achieved in five hours, indicating the rate-limiting H 2 rate was overcome. The quantum efficiencies on the hydrogen-evolution and degradation sides were estimated to be 0.102% and 0.123%, respectively. [Display omitted] • A core-shell structure of Al3+ doped strontium titanate with Rh-CrO x was synthesized by the flux molten salt. • The twin photoreactor achieved simultaneously water splitting for hydrogen production and isopropanol degradation. • A pure hydrogen evolution rate of 1102 μmole/g in 5 h was achieved on the hydrogen side in the twin photoreactor. [ABSTRACT FROM AUTHOR]

Abstract: A non-isothermal unsteady-state model was established to simulate methanol steam reforming using a double-jacketed Pd membrane reactor. At steady state, a self-sustained membrane reactor was achieved by the oxidation of residual methanol and hydrogen from reformer for endothermic steam reforming. The molar fractions of species and reformer temperature were analyzed under co-current operation between oxidation and reformer sides. The start-up of reformer was simulated under two conditions: (1) The catalyst temperature was lower than the influent temperature and (2) The catalyst temperature was higher than influent temperature. Condition 1 yielded higher methanol conversion and reformer temperature than condition 2 at steady state. Moreover, the instability of species can be minimized on condition 1 during start-up. The fluctuation of membrane reactor at steady state was also studied. Two strategies were compared to analyze the reformer response when temporary extra hydrogen was required. The results showed that increasing inlet methanol outperformed increasing reformer temperature. [Copyright &y& Elsevier]

A unique magnesium salt of titanium phosphite (MgTiP) was synthesized by the hydrothermal method and applied for the photocatalytic hydrogen evolution using seawater. The spent MgTiP was analyzed by XPS after photocatalytic reaction indicating that Ti3+ in MgTiP structure was oxidized to Ti4+ by photo-induced holes in a pure water environment, i.e., photo-corrosion. A sacrificial agent, 2 mM FeCl 2 in the photocatalytic system, could enhance hydrogen evolution and prevent photo-corrosion of MgTiP. Thus this research conducted the reaction of photocatalytic hydrogen evolution using seawater. Two seawater sources were taken from the estuary of the Tamsui River and the east coast of Taiwan. The ions in seawater could act as a sacrificial agent. The result showed that the ions of seawater could enhance photocatalytic hydrogen evolution and also prevent MgTiP from photo-corrosion. The unique 12-membered ring (12 R) channels structure of MgTiP with tunable hexa-hydrated magnesium ions showed excellent photo-stability. The concentration of proton (pH) and chloride ions as hole scavenger were favorable factors. Its H 2 production rate could reach up to 629.3 µmol·g cat −1·h−1 under simulated sunlight. Furthermore, the hydrogen evolution from photocatalytic seawater splitting showed better stability than pure water in a long-term test. ga1 • We synthesized unique visible-light titanium phosphite MgTiP photocatalyst. • Photocatalytic seawater splitting can prevent the photo-corrosion of MgTiP. • Hydrogen evolution from natural seawater showed long-term stability. [ABSTRACT FROM AUTHOR]

Recently, an increasing interest has been devoted to produce chemical energy – hydrogen (H 2) by converting sustainable sunlight energy via water splitting and reforming of renewable biomass-derived organic substances. These photocatalytic processes are very promising, sustainable, economic, and environment-friendly. Herein, this article gives a concise overview of photocatalysis to produce H 2 as solar fuel via two approaches: water splitting and reforming of biomass-derived organic substances. For the first approach – photocatalytic water splitting, there are two reaction types have been used, including photoelectrochemical (PEC) and photochemical (PC) cell reactions. For the second approach, biomass-derived oxygenated substrates could undergo selective photocatalytic reforming under renewable solar irradiation. Significant efforts to date have been made for photocatalysts design at the molecular level that can efficiently utilize solar energy and optimize the reaction conditions, including light irradiation, type of sacrificial reagents. Critical challenges, prospects, and the requirement to give more attention to photocatalysis for producing H 2 are also highlighted. • Photocatalytic processes open opportunities for the development of renewable energy. • Hydrogen from photocatalytic water splitting and reforming of biomass are reviewed. • Critical challenges, prospects and attentions of photocatalysis for producing H 2 are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Visible-light absorbing TiO2 and WO3 photocatalytic thin films were prepared by radio-frequency (RF) magnetron sputtering. The effects of sputtering condition on the structural, optical, as well as photocatalytic properties of the prepared thin films were explored. In addition, a novel dual-layer photocatalytic thin film that combines both visible-light TiO2 and WO3 was prepared by the same deposition technique to further enhance the photocatalytic performance. Instrumental analyses such as XRD, SEM-EDX, and UV–visible absorption spectrometry were performed to reveal the crystallinity, surface morphology, chemical composition, and light absorption of the prepared photocatalytic thin films. The activities of the prepared photocatalytic thin films under both UV and visible-light irradiations were evaluated by conducting photovoltammetry and water-splitting reaction in an H-type reactor. The enhanced photocurrent of dual-layer photocatalytic thin film was proved to be resulted from the improved charge separation of the dual-layer structure. The H2 and O2 yields obtained from the water-splitting reactions were consistent with the photocurrent results, showing dual-layer photocatalyst with higher photoactivity than mono-layer photocatalyst. [Copyright &y& Elsevier]

Abstract: Photocatalytic TiO2 thin films were prepared via an electron beam-induced deposition (EBID) method. The effects of post-calcination treatment on the properties of the prepared TiO2 thin films were studied. X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectrometry (SEM-EDS), and UV–V is absorption spectrometry were performed to reveal the crystallinity, surface morphology, chemical composition, and light absorbance of the prepared TiO2 thin films. The photoelectrochemical characteristics of the TiO2 thin films were investigated with a potentiostat. Under UV irradiation, a photocurrent of ˜2.1 mA was observed for the TiO2 thin film with post-calcination at 500 °C. A water-splitting reaction was conducted over the TiO2 thin film with the best photoelectrochemical performance. The yields of hydrogen and oxygen were 59.8 and 30.6 μmole, respectively, after 8 h of reaction under UV irradiation. [ABSTRACT FROM AUTHOR]

Abstract: InTaO4 is a photocatalyst with visible-light response that is used to split water and produce hydrogen. InTaO4 is traditionally prepared by solid-state fusion of In2O3 and Ta2O5 at ≥1100°C. A sol–gel procedure was developed to synthesize InTaO4 from In(NO3)3 and Ta(OC4H9)5 precursors. A uniform crystalline InTaO4 phase was easily obtained on calcination at 1100°C because the sol–gel method allows homogeneous liquid-phase mixing. The method yields small InTaO4 particles with a high specific surface area. InTaO4 catalysts with different Ni loading were prepared by incipient wetness impregnation. Ni loading greatly enhanced the initial rate of H2 production during photocatalytic splitting of water. Ni metal within Ni–NiO core/shell nanoparticles can efficiently transfer photoelectrons on the InTaO4 surface and thus reduce H+ to hydrogen. NiO x /InTaO4 was deactivated due to the formation of Ni(OH)2. Overall, NiO x /InTaO4 prepared by the sol–gel method had higher activity than catalysts prepared by solid-state fusion. Among all the photocatalysts, 3.0wt.% NiO x /InTaO4 exhibited the highest photoactivity, with an initial rate of H2 production of 2.10μmol/gh. [Copyright &y& Elsevier]

Graphical abstract Highlights • A novel dual-function photocatalytic twin-reactor is designed. • H 2 production rate increased 2.7 times when using a twin-reactor, compared to that in a single reactor. • The oxidation of phenol simultaneously enhances the production of H 2. • Pt was photo-deposited on SrTiO 3 which was prepared by the solid-state fusion reaction. Abstract Coupling photocatalytic H 2 evolution and phenol degradation have drawn much attention on H 2 as clean energy and phenol as an organic pollutant to the environment. Such dual-function reaction can utilize the chemical potential of phenol oxidation to make up the chemical potential required for hydrogen evolution from water splitting. The production of H 2 thus was enhanced via the phenol oxidation. However, H 2 is still needed to be purified from the reaction products by traditional methods. In this study, we demonstrated the simultaneous separation of H 2 using a photo twin-reactor under artificial sunlight, in which the photocatalytic efficiency was substantially increased due to the inhibition of backward reaction by separating H 2 from the products directly. Three Rh-doped SrTiO 3 (STO) photocatalysts calcined at 900, 1100, 1200 °C (named as STO:Rh900, STO:Rh1100, and STO:Rh1200, respectively) were prepared by solid-state fusion reaction, then photo-deposition method was applied to synthesize Pt loading STO:Rh. All photocatalysts were fully characterized by XRD, XPS, UV–vis, SEM, TEM, and DLS. A single reactor and a twin-reactor (Z-scheme system) were systematically designed by using Pt/STO:Rh for H 2 evolution photocatalyst and WO 3 for phenol oxidation photocatalyst, where Fe3+/Fe2+ pairs were served as electron transfer mediators to conduct the dual-function reaction. In the single reactor, the stoichiometric of the dual-function reaction was proposed and with high consistency to the experimental data. By using the twin-reactor, H 2 production rate increased 2.7 times, reaching 1.90 μmol g−1 h−1, compared to that in the single reactor. Moreover, the H 2 concentration of the gas-phase products increased from 70% (in the single reactor) to 94% owing to the separation function of the twin-reactor, which would significantly reduce the cost for further purification. The effect of phenol concentration on H 2 production in the twin-reactor was also thoroughly investigated. The results showed that increased phenol initial concentration would enhance the production of H 2. With 200 μmol L−1 phenol, the H 2 yield (11.37 μmol g−1 in 6-h reaction) was increased by 20% compared to that of pure water splitting. [ABSTRACT FROM AUTHOR]

CO 2 photocatalytic reduction over TiO 2 -based catalyst has attracted wide attention. In this work, a novel reaction model was used to proceed CO 2 photocatalytic reduction and compared with two conventional reaction modes. The results indicate that reaction mode has great influence on the photocatalytic performance of the catalyst. The solid-liquid reaction mode prefers to reduce water, while the solid-gas reaction mode tends to reduce CO 2 . The novel reaction model can enhance CO 2 reduction by using H 2 produced from solid-liquid reaction to reduce CO 2 through solid-gas interface reaction, which may not only guarantee the contact between CO 2 and catalyst but also provide strong reductant for CO 2 reduction. [ABSTRACT FROM AUTHOR]

Abstract: Multi-junction solar cell (MJSC) was integrated into an H-type reactor system to carry out water-splitting reaction without external circuit and bias. In the H-type reactor, hydrogen and oxygen could be evolved separately. Different kinds of materials were deposited on the bottom cell to prevent corrosion. These materials include silver, platinum, and iron oxide layers which were prepared via an electron beam-induced deposition (EBID) method. Under visible-light irradiation, hydrogen production was achieved by using the MJSC; however, only a small amount of oxygen was evolved. The photogenerated holes may oxidize the photoelectrode instead of water, meaning that Ge subcell or the deposited thin film was oxidized during the photoreaction. The thin films ranked from highest hydrogen evolution to lowest are: Pt> bare Ge> Fe3O4> Ag. The photoelectrode deposited with metal thin film showed better activity due to its higher conductivity, except Ag. The poor performance of photoelectrode with silver thin film was due to the formation of silver oxide during photoreaction which may trap electrons, lowering the amount of electrons available to carry out water reduction. The chemical bias for H-type reactor system was eliminated by using sodium sulfate as the electrolyte. The ratio of evolved hydrogen to oxygen was near 2:1, suggesting that real water-splitting reaction can be achieved by using the MJSC incorporated H-type reactor system without chemical bias. [Copyright &y& Elsevier]

Abstract: Photocatalytic water splitting with separate H2 and O2 evolution is crucial because it eliminates the explosion potential and hydrogen-purification cost. A novel twin reactor was designed to separate the evolution of hydrogen and oxygen in photocatalytic water splitting under visible light. A modified Nafion membrane was employed to segregate the two photocatalysts in the twin reactor so that hydrogen and oxygen can be evolved separately. Conventional Z-scheme catalysts, Pt/SrTiO3:Rh and WO3, were used as hydrogen-photocatalyst and oxygen-photocatalyst, respectively. Fe2+ and Fe3+ were added in the reaction solution as electron-transfer mediator. The ratio of evolved H2 and O2 was in agreement with the stoichiometric ratio (2:1) of hydrogen and oxygen of water. An average hydrogen generation rate of 1.59μmol/g-h was achieved in the twin-reactor system, which was twice as much as that in the conventional Z-scheme system. The improved H2 yield was due to the prevention of the water-splitting backward reaction in the twin reactor. [Copyright &y& Elsevier]