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Dye-sensitizedH(2) evolution photocatalysts have attractedconsiderable attention as promising systems for the photochemicalgeneration of H-2 from water. In this study, to mimic thereaction field of natural photosynthesis artificially, we synthesizeda hydrophobic Ru-(II) dye-sensitized Pt-TiO2 nanoparticlephotocatalyst, RuC ( 9 )@Pt-TiO2 (RuC ( 9 ) = [Ru-(dC(9)bpy)(2)(H(4)dmpbpy)](2+); dC(9)bpy = 4,4 '-dinonyl-2,2 '-bipyridine, H(4)dmpbpy= 4,4 '-dimethyl phosphonic acid-2,2 '-bipyridine), andintegrated it into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC) lipid bilayer vesicle membranes. The photocatalytic H-2 production activity in 0.5 M l-ascorbic acid aqueous solutionenhanced by more than three times in the presence of DPPC vesicles(apparent quantum yield = 2.11%), whereas such a significant enhancementwas hardly observed when the vesicle formation was omitted. Theseresults indicate that the highly dispersed state of the hydrophobic RuC ( 9 )@Pt-TiO2 nanoparticlesin the DPPC bilayer vesicles is a key factor in achieving enhancedphotocatalytic H-2 production activity in aqueous solution.

The influence of the structural differences in titanium dioxide (TiO2- Degussa P25 and Mesh 325) as supporting materials for cobalt (Co) nanoparticles, has been revealed in aqueous and alkaline sodium borohydride (NaBH4) hydrolysis. The very little amount of Co nanoparticles, which was 2.2 and 1.5 wt%, has been successfully embedded on TiO2 (P25) and TiO2 (Mesh 325), respectively, via facile impregnation and magnetic separation method. The activation energies for TiO2 (Mesh 325)/Co and TiO2 (P25)/Co catalysts in the aqueous solution of NaBH4 were 64.3 kJ.mol(-1) and 56.76 kJ.mol(-1), respectively. On the other hand, the activation energy values of the hydrolysis process in alkaline NaBH4 solutions using TiO2 (Mesh 325)/Co and TiO2 (P25)/Co catalysts have been calculated as 55 kJ.mol(-1) and 45.2 kJ.mol(-1), respectively. Consequently, the hydrogen generation rate (HGR) for TiO2(Mesh 325)/Co and TiO2(P25)/Co in an aqueous-alkaline solution are 360 and 660 mL.min.gcat(-1), respectively which are twice higher in that of aqueous NaBH4 hydrolysis reaction. The maximum HGR of 9000 mL.min(-1).gcat(-1) for TiO2(P25) loaded with 2.2 wt% Co in an aqueous-alkaline solution at 60 degrees C, indicates this catalysis is very promising as the cost-effective catalytic hydrolysis of NaBH4. [GRAPHICS] ., Belarusian Republican Foundation for Basic Research [T19TYuB-004]; Council for Scientific and Technological Research of Turkey (TUBITAK) [119M030], This work was supported by the Belarusian Republican Foundation for Basic Research (Project No. T19TYuB-004) and the Council for Scientific and Technological Research of Turkey (TUBITAK) (Project No. 119M030).

The influence of the structural differences in titanium dioxide (TiO2- Degussa P25 and Mesh 325) as supporting materials for cobalt (Co) nanoparticles, has been revealed in aqueous and alkaline sodium borohydride (NaBH4) hydrolysis. The very little amount of Co nanoparticles, which was 2.2 and 1.5 wt%, has been successfully embedded on TiO2 (P25) and TiO2 (Mesh 325), respectively, via facile impregnation and magnetic separation method. The activation energies for TiO2 (Mesh 325)/Co and TiO2 (P25)/Co catalysts in the aqueous solution of NaBH4 were 64.3 kJ.mol(-1) and 56.76 kJ.mol(-1), respectively. On the other hand, the activation energy values of the hydrolysis process in alkaline NaBH4 solutions using TiO2 (Mesh 325)/Co and TiO2 (P25)/Co catalysts have been calculated as 55 kJ.mol(-1) and 45.2 kJ.mol(-1), respectively. Consequently, the hydrogen generation rate (HGR) for TiO2(Mesh 325)/Co and TiO2(P25)/Co in an aqueous-alkaline solution are 360 and 660 mL.min.gcat(-1), respectively which are twice higher in that of aqueous NaBH4 hydrolysis reaction. The maximum HGR of 9000 mL.min(-1).gcat(-1) for TiO2(P25) loaded with 2.2 wt% Co in an aqueous-alkaline solution at 60 degrees C, indicates this catalysis is very promising as the cost-effective catalytic hydrolysis of NaBH4. [GRAPHICS] ., Belarusian Republican Foundation for Basic Research [T19TYuB-004]; Council for Scientific and Technological Research of Turkey (TUBITAK) [119M030], This work was supported by the Belarusian Republican Foundation for Basic Research (Project No. T19TYuB-004) and the Council for Scientific and Technological Research of Turkey (TUBITAK) (Project No. 119M030).

Hydrogen is an important aspirant for the substitution of fossil fuels in future because of its net zero emissions of carbon dioxide. Escalating the green hydrogen will be vital for assisting worldwide economies with accomplishing net zero emissions by 2050 and limiting the global temperature ascends to 1.5 °C. Hydrogen fuel may provide reliable long-term solution for clean energy transition. Semiconductor materials have great potential in harvesting solar energy and improved charge separation ability. In recent years, efforts have been put by the researchers to develop niobium-based photocatalyst for H2 production through water splitting. An enormous assortment of niobium complexes shows an appropriate electronic properties and morphological structure for enhanced photocatalytic performance. It is therefore important to explore suitable light harvesting properties having appropriate structures of photocatalyst. In this review, recent progress in niobium-based photocatalyst, novel structures and factors influencing the photocatalytic efficiencies for hydrogen production are extensively studied. The mechanism and principles of catalyst are discussed and the main group of niobium-based photocatalyst namely perovskite niobates, niobium pentoxide complexes, aurivillius niobates, dye doped niobates are introduced. Attention has been paid to photocatalyst design with more detail on synthesis procedures which can provide the scientific community for better design of photocatalyst towards hydrogen production. Finally, emergent research trends and perspectives for photocatalytic water splitting are also suggested. The technological advancement of niobium-complexes for hydrogen generation through water splitting is believed to significantly promote the clean and affordable energy production in practice.

To develop H-2 photoproduction by using the N-2-fixing cyanobacterium Fischerella muscicola TISTR 8215, a novel strain isolated from soil in Thailand, the factors affecting H-2 production were investigated in this study. Enhanced H-2 production in suspension culture was obtained when adapting the cells under N-2-fixing condition (modified AA medium) with continuous illumination of 250 mu mol photons m(-2) s(-1) under aerobic condition for 24 h, followed by further incubation under anaerobic condition for 9 h for production phase. The maximum H-2 production rate was 38.5 mu mol mg(-1) chl a h(-1). Low concentration of Fe2+ and Mo6+, essential elements for nitrogenase, enhanced H-2 production. The enhanced H-2 production was accompanied by the upregulation of nifD. On the other hand, an increased hupL transcript level was observed when there was a decrease of H-2 production. In cells immobilization, 1.5% (w/v) agar-immobilized cells had a 23-fold increase in maximum H-2 yield compared with that using free cell suspension at the same cell concentration, i.e., 7.48 mmol H-2 L-1 by immobilized cells and 0.32 mmol H-2 L-1 by suspended cells. Moreover, cell immobilization in agar could prolong H-2 production up to 108 h. This study underlines the strategies toward enhanced and sustained H-2 production from cyanobacteria. Furthermore, it will pave the way for large-scale production of biohydrogen to be used as an eco-friendly energy resource.

Several Ni catalysts of supported (on La2O3-alpha Al2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts' regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 degrees C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 degrees C. The spent catalysts have been characterized by N-2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H-2 selectivity-stability corresponds to Ni/La2O3-alpha Al2O3, due to its smaller Ni-0 particle size. Additionally, it is more selective to H-2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 degrees C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.

Several Ni catalysts of supported (on La2O3-alpha Al2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts' regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 degrees C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 degrees C. The spent catalysts have been characterized by N-2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H-2 selectivity-stability corresponds to Ni/La2O3-alpha Al2O3, due to its smaller Ni-0 particle size. Additionally, it is more selective to H-2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 degrees C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.

Several Ni catalysts of supported (on La2O3-alpha Al2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts' regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 degrees C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 degrees C. The spent catalysts have been characterized by N-2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H-2 selectivity-stability corresponds to Ni/La2O3-alpha Al2O3, due to its smaller Ni-0 particle size. Additionally, it is more selective to H-2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 degrees C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.

Redox properties of the acceptor side of Photosystem II were studied during H-2 gas production in cells of Chlamydomonas reinhardtii. Flash-induced variable fluorescence changes and thermoluminescence measurements were performed in wild type and Stm6 mutant cells during different stages of sulfur (S)-deprivation. Analysis of the fluorescence decay kinetics indicated that the forward electron transfer on the acceptor side of Photosystem II was dramatically slowed down during the O-2 evolution and O-2 consumption stages and was completely blocked in the anaerobic stage of S-deprivation, thus, indicating a complete reduction of the PQ-pool. During the H-2 formation stage, the forward electron transfer kinetics in the mu sec and msec time scale re-appeared indicating partially restored electron flow from Q(A)(-) to Q(B) and the PQ-pool. Thermoluminescese measurements fully confirmed the fluorescence kinetic analysis. Activation of hydrogenase in the H-2 formation stage is responsible for re-oxidation of the PQ pool and reactivation of the electron flow which was found to be faster and more efficient on the Stm6 mutant due to the higher amount of functionally preserved Photosystem II.

A silicone microreactor with 500 mu m-width microchannels coated with a Au/TiO2 photocatalyst was manufactured and tested for the photocatalytic generation of hydrogen from gaseous water-ethanol mixtures under dynamic conditions. The manufacture of the microreactor included the fabrication of a polylactic acid (PLA) mold with a 3D printer and casting with polydimethylsiloxane (PDMS) prepolymer. After curing, the silicone microreactor was peeled off and the microchannels were coated with a Au/TiO2 photocatalyst prepared by impregnation of preformed Au nanoparticles over TiO2, and sealed with a thin silicone cover. The microreactor was tested at room temperature and atmospheric pressure under different operational conditions (photon irradiance, residence time, photocatalyst loading, and water ethanol ratio). Hydrogen production rates of 5.4 NmL W-1 h(-1) were measured at a residence time of 0.35 s using a H2O:C2H5OH molar ratio of 9:1, a photocatalyst load of 1.2 mg cm(-2) and a UV irradiance (365 nm) of 1.5 mW cm(-2) achieving an apparent quantum efficiency of 9.2%. The photogeneration of hydrogen with commercial bioethanol was also tested. A long-term photocatalytic test of two days revealed a stable hydrogen photoproduction rate. The use of silicone microreactors represents an attractive and customizable solution for conducting photochemical reactions for producing hydrogen at low cost. (C) 2016 Elsevier B.V. All rights reserved., Postprint (published version)

We present a DFT study of the reaction mechanism on electrocatalytic oxidation of formate by a family of [Ni((P2N2R')-N-R)(2)](2+) complexes ((P2N2R')-N-R = 1,5-diR'-3,7-diR derivative of 1,5-diaza-3,7-diphosphacyclooctane, where R and R' are aryl or alkyl groups). [Ni((P2N2Me)-N-Ph)(2)](2+) complex 1 was used as a model complex to mimic a family of [Ni((P2N2R')-N-R)(2)](2+) complexes. Our calculated results show that the decarboxylation step (corresponding to TS3) is the rate-determining step for the electrocatalytic oxidation of formate and that a NiII-H intermediate is involved in the reaction mechanism. The pendant amine plays an important role in the deprotonation of the nickel hydride complex generated in the decarboxylation step. In addition, our study indicates that the choice of external bases is important for removing the proton (H+) from the nitrogen-protonated nickel(0) complexes. For the electrocatalytic oxidation of formate using the catalytically inactive [Ni(depe)(2)](2+) (depe = 1,2-bis(diethylphosphino)ethane) complex, calculations on 1-depe have also been carried out for comparison., QC 20140611

A series of nickel complexes containing N-5-pentadentate ligands with different amine-to-pyridine ratios were studied for electrochemical H-2 production in neutral water and the one with a diamine-tripyridine ligand displays a TON of up to 308000 over 60 h electrolysis at -1.25 V vs. SHE, with a Faradaic efficiency of similar to 91%., QC 20141208

Electrocatalytic reduction of water to molecular hydrogen via the hydrogen evolution reaction may provide a sustainable energy supply for the future, but its commercial application is hampered by the use of precious platinum catalysts. All alternatives to platinum thus far are based on nonprecious metals, and, to our knowledge, there is no report about a catalyst for electrocatalytic hydrogen evolution beyond metals. Here we couple graphitic-carbon nitride with nitrogen-doped graphene to produce a metal-free hybrid catalyst, which shows an unexpected hydrogen evolution reaction activity with comparable overpotential and Tafel slope to some of well-developed metallic catalysts. Experimental observations in combination with density functional theory calculations reveal that its unusual electrocatalytic properties originate from an intrinsic chemical and electronic coupling that synergistically promotes the proton adsorption and reduction kinetics.

Efficient and cost-effective conversion of solar energy to useful chemicals and fuels could lead to a significant reduction in fossil hydrocarbon use. Artificial systems that use solar energy to produce chemicals have been reported for more than a century. However the most efficient devices demonstrated, based on traditionally fabricated compound semiconductors, have extremely short working lifetimes due to photocorrosion by the electrolyte. Here we report a stable, scalable design and molecular level fabrication strategy to create photoelectrochemically active heterostructure (PAH) units consisting of an efficient semiconductor light absorber in contact with oxidation and reduction electrocatalysts and otherwise protected by alumina. The functional heterostructures are fabricated by layer-by-layer, template-directed, electrochemical synthesis in porous anodic aluminum oxide membranes to produce high density arrays of electronically autonomous, nanostructured, corrosion resistant, photoactive units (~10(9)-10(10) PAHs per cm(2)). Each PAH unit is isolated from its neighbor by the transparent electrically insulating oxide cellular enclosure that makes the overall assembly fault tolerant. When illuminated with visible light, the free floating devices have been demonstrated to produce hydrogen at a stable rate for over 24 h in corrosive hydroiodic acid electrolyte with light as the only input. The quantum efficiency (averaged over the solar spectrum) for absorbed photons-to-hydrogen conversion was 7.4% and solar-to-hydrogen energy efficiency of incident light was 0.9%. The fabrication approach is scalable for commercial manufacturing and readily adaptable to a variety of earth abundant semiconductors which might otherwise be unstable as photoelectrocatalysts.

Efficient and cost-effective conversion of solar energy to useful chemicals and fuels could lead to a significant reduction in fossil hydrocarbon use. Artificial systems that use solar energy to produce chemicals have been reported for more than a century. However the most efficient devices demonstrated, based on traditionally fabricated compound semiconductors, have extremely short working lifetimes due to photocorrosion by the electrolyte. Here we report a stable, scalable design and molecular level fabrication strategy to create photoelectrochemically active heterostructure (PAH) units consisting of an efficient semiconductor light absorber in contact with oxidation and reduction electrocatalysts and otherwise protected by alumina. The functional heterostructures are fabricated by layer-by-layer, template-directed, electrochemical synthesis in porous anodic aluminum oxide membranes to produce high density arrays of electronically autonomous, nanostructured, corrosion resistant, photoactive units (~10(9)-10(10) PAHs per cm(2)). Each PAH unit is isolated from its neighbor by the transparent electrically insulating oxide cellular enclosure that makes the overall assembly fault tolerant. When illuminated with visible light, the free floating devices have been demonstrated to produce hydrogen at a stable rate for over 24 h in corrosive hydroiodic acid electrolyte with light as the only input. The quantum efficiency (averaged over the solar spectrum) for absorbed photons-to-hydrogen conversion was 7.4% and solar-to-hydrogen energy efficiency of incident light was 0.9%. The fabrication approach is scalable for commercial manufacturing and readily adaptable to a variety of earth abundant semiconductors which might otherwise be unstable as photoelectrocatalysts.

The inhibition of competitive metabolic pathways by various inhibitors in order to redirect electron flow towards nitrogenase and bidirectional Hox-hydrogenase was investigated in Anabaena siamensis TISTR 8012. Cells grown in BG11(0) supplemented with KCN, rotenone, DCMU, and DL-glyceraldehyde under light condition for 24 h showed enhanced H-2 production. Cells grown in BG11 medium showed only marginal H-2 production and its production was hardly increased by the inhibitors tested. H-2 production with either 20 mM KCN or 50 mu M DCMU in BG11(0) medium was 22 mu mol H-2 mg chl a(-1) h(-1), threefold higher than the control. The increased H-2 production caused by inhibitors was consistent with the increase in the respective Hox-hydrogenase activities and nifD transcript levels, as well as the decrease in hupL transcript levels. The results suggested that interruption of metabolic pathways essential for growth could redirect electrons flow towards nitrogenase and bidirectional Hox-hydrogenase resulting in increased H-2 production. (C) 2012 Elsevier Ltd. All rights reserved.

The diiron hydride [(mu-H)Fe-2(pdt)-(CO)(4)(dppv)](+) ([H-2](+), dppv = cis-1,2-C2H2(PPh2)(2)) is shown to be an effective photocatalyst for the H-2 evolution reaction (HER). These experiments establish the role of hydrides in photocatalysis by biomimetic diiron complexes. Trends in redox potentials suggests that other unsymmetrically substituted diiron hydrides are promising catalysts. Unlike previous catalysts for photo-HER, [H-2](+) functions without sensitizers: irradiation of [H-2] in the presence of triflic acid (HOTf) efficiently affords H-2. Instead of sacrificial electron donors, ferrocenes can be used as recyclable electron donors for the photocatalyzed HER, resulting in 4 turnovers.

The effects of external factors on both H-2 production and bidirectional Hox-hydrogenase activity were examined in the non-N-2-fixing cyanobacterium Synechocystis PCC 6803. Exogenous glucose and increased osmolality both enhanced H-2 production with optimal production observed at 0.4% and 20 mosmol kg(-1), respectively. Anaerobic condition for 24 h induced significant higher H(2)ase activity with cells in BC11(0) showing highest activities. Increasing the pH resulted in an increased Hox-hydrogenase activity with an optimum at pH 7.5. The Hox-hydrogenase activity gradually increased with increasing temperature from 30 degrees C to 60 degrees C with the highest activity observed at 70 degrees C. A low concentration at 100 mu M of either DTT or beta-mercaptoethanol resulted in a minor stimulation of H-2 production. beta-Mercaptoethanol added to nitrogen- and sulfur-deprived cells stimulated H-2 production significantly. The highest Hox-hydrogenase activity was observed in cells in BG11(0)-S-deprived condition and 750 mu M beta-mercaptoethanol measured at a temperature of 70 degrees C; 14.32 mu mol H-2 mg chl alpha(-1) min(-1).