High H2 Production Activity Research Articles

Heterostructure CdS/ZnS nanoparticles as a visible light-driven photocatalyst for hydrogen generation from water

ABSTRACT(CdS)x/(ZnS)1–x nanoparticles were synthesized as a visible light-driven photocatalyst using the stepped microemulsion technique with a series of the ratio factors (x). The photocatalytic test results showed that (CdS)x/(ZnS)1-x with x = 0.8 had the highest photo-reactivity for H2 production from water under visible light. The composite (CdS)0.8/(ZnS)0.2 catalyst had a heterogeneous structure that exhibited a much greater photocatalytic hydrogen production activity than either pure CdS or the homogeneous Cd0.8Zn0.2S solid solution. ZnS deposition also was shown to largely improve the stability of CdS in the heterostructured CdS/ZnS catalyst. Thermal treatment of the catalyst, i.e., annealing (CdS)0.8/(ZnS)0.2 at 723 K, improved the crystallinity of the catalyst and increased its photocatalytic H2 production rate by more than 36 times. Deposition of Ru on the surface of the catalyst particles by in situ photo-deposition further increased the photo-H2 generation rate by 3 times. The photocatalyst of 0.5%Ru/CdS/ZnS achieved the highest H2 production activity, at a rate of 12650 μmol/g-h and with a light to hydrogen energy conversion efficiency of 6.5%.

Visible/Near-Infrared-Light-Induced H2 Production over g-C3N4 Co-sensitized by Organic Dye and Zinc Phthalocyanine Derivative

A new route is carried out to achieve broad spectral responsive photocatalytic H2 production over g-C3N4 co-sensitized by an indole-based D-π-A organic dye (LI-4) and an asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) with complementary absorption spectra. Experimental results indicate that both LI-4 and Zn-tri-PcNc are efficient photosensitizers of g-C3N4 for H2 production, and their co-sensitized g-C3N4 (LI-4/g-C3N4/Zn-tri-PcNc) exhibits an extremely high H2 production activity (371.4 μmol h–1) under visible/near-infrared (NIR) light (λ ≥ 420 nm) irradiation, which approximates the summation of the H2 production activity of LI-4/g-C3N4 (233.8 μmol h–1) and Zn-tri-PcNc/g-C3N4 (132.3 μmol h–1), although LI-4 and Zn-tri-PcNc can just absorb the light in the range of 400–600 and 600–750 nm, respectively. Moreover, the co-sensitized catalyst shows a broad visible/NIR light responsive range (400–800 nm) with impressively high apparent quantum yields (AQY) of 16.3, 7.7, and 1.75% at 420, 500, and 700 nm monochromatic light irradiation, respectively. The present work gives a new advance toward panchromatic light responsive photocatalytic application by combining the photosensitization of two different dyes with complementary absorption spectra on one kind of semiconductor.

Graphene Acting as Surface Phase Junction in Anatase–Graphene–Rutile Heterojunction Photocatalysts for H2 Production from Water Splitting

The construction of heterojunction photocatalysts has received much attention in the field of photocatalytic H2 production from water splitting. The surface phase junction of semiconductors is very important to the activity of heterojunction photocatalysts. In this study, an effective anatase–graphene–rutile heterojunction structure was designed and fabricated by using graphene as the surface phase junction between anatase and rutile particles. Results show that both the anatase/rutile ratio (A/R ratio) and graphene amount represent important influence on H2 production activities of anatase–graphene–rutile heterojunction photocatalysts. Under our experimental condition, the optimum A/R ratio is 7/3 and graphene addition amount is 2 wt %, the corresponding AR7/3–2%G sample has the highest H2 production rate of 1.714 mmol/h. By further experimental study, we think the high H2 production activity of anatase–graphene–rutile heterojunction photocatalyst is from the enhanced charge separation rather than other ...

Synergetic effect of dual cocatalysts in photocatalytic H₂ production on Pd-IrOx/TiO₂: a new insight into dual cocatalyst location.

Introducing appropriate dual cocatalysts is one of the most efficient strategies to improve the photocatalytic activity. Herein, we investigated the promotion effect of dual cocatalysts on TiO2 for hydrogen production. Compared with the Pd/TiO2 and Ir/TiO2 with the individual cocatalyst, TiO2 coloaded with Pd and Ir species exhibited an obviously enhanced H2 production activity and reduced CO/H2 ratio. XPS and IR spectra of CO adsorption analysis indicated that the dual cocatalysts on TiO2 were actually composed of Pd(0) and partially oxidized IrOx, which acted as the reduction and oxidation cocatalysts, respectively. Interestingly, EDX elemental mappings of Pd and Ir indicated that the two elements on TiO2 were inclined to depositing together. The synergetic effect of reduction and oxidation cocatalysts with their intimate contact is proposed to contribute to the high H2 production activity, which is different from the common view that the reduction and oxidation sites should be spatially separated to avoid the charge recombination.

Improvement of carbon monoxide-dependent hydrogen production activity in Citrobacter amalonaticus Y19 by over-expressing the CO-sensing transcriptional activator, CooA

Citrobacter amalonaticus Y19 (Y19) can produce hydrogen (H2) from oxidation of carbon monoxide (CO) via the water-gas shift reaction. The reaction is catalyzed by two enzymes, carbon monoxide dehydrogenase (CODH) and carbon monoxide-dependent hydrogenase (CO-Hyd). The contig genome sequencing of Y19 exhibited the presence of unique CO oxidizing gene clusters encoding CODH (cooFS), CO-Hyd (cooMKLXUH) and a putative CO-responsive transcriptional activator (cooA). To improve CO-dependent H2 production activity, we developed recombinant Y19 by homologously over-expressing cooA. The over-expression of cooA improved the whole-cell CO-dependent H2 production activity (3.4-fold), and enzyme activities of CODH (5.3-fold) and CO-Hyd (1.2-fold). Furthermore, quantitative PCR analysis revealed a significant increase in the transcription of the genes located in CODH and CO-Hyd operons of recombinant Y19. The high CO-dependent H2 production activity of the recombinant C. amalonaticus was stably maintained during repeated exposure to CO.

Hierarchical composites of TiO2 nanowire arrays on reduced graphene oxide nanosheets with enhanced photocatalytic hydrogen evolution performance

Reduced graphene oxide (RGO)–TiO2 nanowire array hierarchical composites were prepared via an in situ controlled growth process and subsequent calcination, and showed much higher H2 production activity than that of pure TiO2 and RGO–TiO2 generated by mechanical mixing.

Single crystal CdS nanowires with high visible-light photocatalytic H2-production performance

Single crystalline hexagonal CdS nanowires were prepared by a solvothermal method using ethylenediamine as a solvent. Pt/CdS nanocomposites were produced by different reduction methods and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, UV-visible spectroscopy, nitrogen absorption, pulse H2 chemisorption and X-ray photoelectron spectroscopy. The photocatalytic performance of the as-synthesized Pt/CdS nanocomposites was evaluated towards H2 generation from a lactic acid aqueous solution under visible light (λ ≥ 420 nm). The sample prepared by the NaBH4 reduction method showed a higher photocatalytic H2-production activity than the sample prepared by the photo-reduction deposition method. A remarkable H2-production rate of 1.49 mmol h−1 with a quantum efficiency (QE) of 61.7% was first achieved on the former with a small amount of Pt (0.3 wt%) as a co-catalyst. The photocatalytic activity difference of the samples is because reduction methods influence the size and dispersion of Pt nanoparticles (NPs), which further influence the photocatalytic H2-production activity. The sample from the NaBH4 reduction method contains smaller Pt NPs (ca. 1–2 nm) and has higher Pt dispersion (72%), thus resulting in the higher H2-production activity. Further experiments showed that the one-dimensional nanostructure markedly enhanced the photocatalytic H2-production activity of CdS. After ball milling of the nanowires, which leads to destruction of their structure, the photocatalytic H2-production activity of CdS decreases by more than 30%. The underlying mechanism for the observed photocatalytic H2-production performance of Pt/CdS nanocomposites was discussed.

Biohydrogen production from carbon monoxide and water byRhodopseudomonas palustris P4

A reactor-scale hydrogen (H2) productionvia the water-gas shift reaction of carbon monoxide (CO) and water was studied using the purple nonsulfur bacterium,Rhodopseudomonas palustris P4. The experiment was conducted in a two-step process: an aerobic/chemoheterotrophic cell growth step and a subsequent anaerobic H2 production step. Important parameters investigated included the agitation speed, inlet CO concentration and gas retention time. P4 showed a stable H2 production capability with a maximum activity of 41 mmol H2 g cell−1h−1 during the continuous reactor operation of 400 h. The maximal volumetric H2 production rate was estimated to be 41 mmol H2 L1h−1, which was about nine-fold and fifteen-fold higher than the rates reported for the photosynthetic bacteriaRhodospirillum rubrum andRubrivivax gelatinosus, respectively. This is mainly attributed to the ability of P4 to grow to a high cell density with a high specific H2 production activity. This study indicates that P4 has an outstanding potential for a continuous H2 productionvia the water-gas shift reaction once a proper bioreactor system that provides a high rate of gas-liquid mass transfer is developed.

Redox properties of the iron-sulfur clusters in activated Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough).

The periplasmic Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough) contains three iron-sulfur prosthetic groups: two putative electron transferring [4Fe-4S] ferredoxin-like cubanes (two F-clusters), and one putative Fe/S supercluster redox catalyst (one H-cluster). Combined elemental analysis by proton-induced X-ray emission, inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, atomic absorption spectroscopy and colorimetry establishes that elements with Z > 21 (except for 12-15 Fe) are present in 0.001-0.1 mol/mol quantities, not correlating with activity. Isoelectric focussing reveals the existence of multiple charge conformers with pI in the range 5.7-6.4. Repeated re-chromatography results in small amounts of enzyme of very high H2-production activity determined under standardized conditions (approximately 7000 U/mg). The enzyme exists in two different catalytic forms: as isolated the protein is 'resting' and O2-insensitive; upon reduction the protein becomes active and O2-sensitive. EPR-monitored redox titrations have been carried out of both the resting and the activated enzyme. In the course of a reductive titration, the resting protein becomes activated and begins to produce molecular hydrogen at the expense of reduced titrant. Therefore, equilibrium potentials are undefined, and previously reported apparent Em and n values [Patil, D. S., Moura, J. J. G., He, S. H., Teixeira, M, Prickril, B. C., DerVartanian, D. V., Peck, H. D. Jr, LeGall, J. & Huynh, B.-H. (1988) J. Biol. Chem. 263, 18,732-18,738] are not thermodynamic quantities. In the activated enzyme an S = 1/2 signal (g = 2.11, 2.05, 2.00; 0.4 spin/protein molecule), attributed to the oxidized H cluster, exhibits a single reduction potential, Em,7 = -307 mV, just above the onset potential of H2 production. The midpoint potential of the two F clusters (2.0 spins/protein molecule) has been determined either by titrating active enzyme with the H2/H+ couple (E,m = -330 mV) or by dithionite-titrating a recombinant protein that lacks the H-cluster active site (Em,7.5 = -340 mV). There is no significant redox interaction between the two F clusters (n approximately 1).