Light-induced Hydrogen Production Research Articles

Unraveling the solar and visible light-induced deactivation mechanism of Pt-decorated carbon/TiO2 nanocomposite in photocatalytic hydrogen production

Photocatalytic water splitting presents an attractive and environmentally friendly method for generation of "green" hydrogen. However, the most widely used photocatalyst for hydrogen production, Pt-doped TiO2, has low stability, thus limiting its application for long term performance. In this study, the deactivation mechanism of Pt-decorated carbon TiO2 nanocomposite photocatalysts during photocatalytic hydrogen production was thoroughly investigated under solar and visible light irradiation. Solar light irradiation promoted markedly higher H2 production activity, however with lower catalyst stability. Deactivation studies using fresh catalysts/deactivated solutions and deactivated catalysts/fresh solutions point out the effect of the light used on the catalyst stability through changes on the catalyst surface as well as by the kinetics of intermediate/products formation during the reaction course. The present study revealed the importance of charge transport direction between TiO2, carbon and Pt on catalyst activity and stability and highlights the difference in visible and solar light-induced hydrogen production.

Hollow rod-shaped Cu-In-Zn-S@ZnCo2O4@In2O3 tandem heterojunction for efficient visible light-induced photocatalytic hydrogen production

Photocatalytic hydrogen production technology is an efficient method to solve the environmental pollution problem and obtain renewable energy. To improve the hydrogen production efficiency, it is still a great challenge to develop novel photocatalysts with high activity and high stability. In this work, a hollow rod-shaped Cu-In-Zn-S@ZnCo2O4@In2O3 tandem heterojunction photocatalyst was designed and synthesized. Under visible light irradiation, the photocatalytic hydrogen production amount was up to 21404.54 μmol·g−1 in 5 h. The hollow tandem heterojunction would improve the light absorption, facilitate the electron transfer, inhibit the recombination of photogenerated electrons and holes, and provide more active sites for hydrogen production reaction. The design of Cu-In-Zn-S@ZnCo2O4@In2O3 photocatalyst provided an effective method to enhance the photocatalytic hydrogen production performance.

Z-scheme electron transfer mechanism of MoS2/CoP heterostructure for simulated solar light induced hydrogen production

Photocatalytic hydrogen production is a potential strategy to convert solar energy into chemical energy. Molybdenum disulfide (MoS2) semiconductor has been broadly used to synthesize high-efficient photocatalysts because of its superior light response and easy photoexcitation. However, its unstable microstructure and low-crystallinity generally lead to rapid recombination of photo-generated carriers, which severely restrict its performance. Herein, cobalt phosphide (CoP) was selected as cocatalyst to build MoS2/CoP heterostructure by a hydrothermal method. Research demonstrated the formation of Z-scheme electron transfer mechanism in the heterointerface, which effectively suppressed the recombination of photoinduced carriers due to the synergetic effect of internal electric field. Thereby, the optimum enhanced simulated solar light (SSL)-induced HER activity was achieved by the MoS2/CoP composite (76.45 μmol·g−1·h−1), which is ∼3.8 fold-greater of MoS2 (∼20.14 μmol·g−1·h−1) and ∼4.5 fold-greater of CoP NPs (∼16.92 μmol·g−1·h−1). Meanwhile, about 10.08% and 3.36% of apparent quantum yields were achieved at the wavelengths of 350 nm and 500 nm, which also reveals the high-efficiency of this catalyst for hydrogen production. This research provides a simple strategy to construct stable and high-efficient MoS2-based photocatalysts for hydrogen production.

S–scheme TiO2/ZnS heterojunction as dual-reaction sites: A high–efficiency and spontaneous photocatalyst for hydrogen production under light irradiation

Designing a compound heterojunction photocatalyst is a pragmatic approach for achieving effectively carriers separation and improving light-induced hydrogen production via water splitting. Nonadiabatic molecular dynamics (NAMD) and density functional theory (DFT) methods were used to thoroughly analyze the photo-induced carrier transfer and photocatalytic capabilities of TiO2/ZnS heterojunction. The calculations indicate that the heterojunction composed of TiO2 (101) slab and ZnS (110) slab featured suitable band gap and enhanced visible light absorption. According to the NAMD calculations, it is possible to classify the TiO2/ZnS heterojunction as an S-scheme photocatalyst with a potent redox capability. In TiO2/ZnS heterojunction, the inherent electric field and band bending cause carriers with weak (strong) redox abilities to recombine (separate) at the interface. Particularly, both the Ti and S active sites in the TiO2/ZnS heterojunction could spontaneously photo-catalyze hydrogen generation under different pH conditions. The theoretical solar-to-hydrogen conversion efficiency of the heterojunction can reach 23.46%. Consequently, our research not only identified an S–scheme photocatalyst for hydrogen production, but provided an approach for developing high-performance hydrogen evolution reaction photocatalysts.

CdS supported on ZIF-67-derived Co-N-C as efficient nano polyhedron photocatalysts for visible light induced hydrogen production

Hydrogen energy is vital important for solving pollution of environment and energy shortage. Hydrogen production via solar energy and semiconductor photo-splitting water is one of the most environmentally friendly strategies at present. In this work, Co-N-C, a non-noble metal-based ZIF-67 derivative, was employed as a co-catalyst to achieve an in situ growth of spherical CdS via simple one-step hydrothermal. Due to the large specific surface area of Co-N-C, the agglomeration of CdS is avoided and the photocorrosion phenomenon is weakened. Under irradiation of visible light, the hydrogen generation activity of Co-N-C/CdS was achieved 905 μmol g−1 h−1. It is 6 times that of pure CdS with excellent stability. At the contact interface of the Co-N-C and CdS, the transfer and the separation of photoinduced carriers had been enhanced by a great many of channels. DFT calculation further showed that Co nanoclusters, as the active sites of hydrogen production, significantly enhanced photocatalytic hydrogen evolution activity. Therefore, Co-N-C not only acts as electron acceptor, but also serves as support of highly dispersed CdS to promote the stability of system during photocatalytic hydrogen generation. This work demonstrates the advantages of CdS binding MOF derivatives to construct composite photocatalysts with enhanced dispersibility and hydrogen production activity.

Light-induced hydrogen production from water using nickel(II) catalysts and N-doped carbon-dot photosensitizers: catalytic efficiency enhancement by increase of catalyst nuclearity.

Solar energy conversion to chemical energy via light-induced H2O splitting to O2 and H2 is considered to be a promising solution to meet the growing global energy demands. To make this transformation economically viable, it is necessary to develop sustainable photocatalytic systems. Herein, we present an efficient photocatalytic H2 production system which relies on components comprised of low-cost and high-abundance elements. In particular, a series of mononuclear complexes [Ni(LNS)3]- and [Ni(N^N)(LNS)2] and a hexanuclear complex [Ni(LNS)2]6 (N^N = diimine and LNS- = heterocyclic thioamidate with different group-substituents) were synthesized and utilized as catalysts, in combination with N-doped carbon dots as photosensitizer, for efficient H2 evolution from aqueous protons. Differences in H2 production efficiency were observed among the studied Ni(II) catalysts, with complexes bearing ligands with stronger electron-donating ability exhibiting higher catalytic activity. A remarkable catalytic efficiency enhancement was observed for the hexanuclear complex, with catalyst loadings lower than those of the mononuclear Ni(II) complexes, affording TONs >1550 (among the highest values reported for photocatalytic systems of similar type operating in H2O). These data provide an indication of catalytic cooperativity between the metal centers of the hexanuclear complex, and demonstrate the crucial role of atomically precise polynuclear Ni(II) catalysts in light-induced H2 production, a result that can guide future catalyst design towards the development of highly efficient, low-cost and environmentally benign photocatalytic systems.

The influence of trinuclear complexes on light-induced hydrogen production

New trinuclear water reduction catalysts show turnover numbers for photochemical water splitting of up to 8899, a turnover frequency of 2737 h−1 and an incident photon conversion efficiency of 2.1%, thus outperforming mononuclear analogues.

NiPS3 ultrathin nanosheets as versatile platform advancing highly active photocatalytic H2 production

High-performance and low-cost photocatalysts play the key role in achieving the large-scale solar hydrogen production. In this work, we report a liquid-exfoliation approach to prepare NiPS3 ultrathin nanosheets as a versatile platform to greatly improve the light-induced hydrogen production on various photocatalysts, including TiO2, CdS, In2ZnS4 and C3N4. The superb visible-light-induced hydrogen production rate (13,600 μmol h−1 g−1) is achieved on NiPS3/CdS hetero-junction with the highest improvement factor (~1,667%) compared with that of pure CdS. This significantly better performance is attributed to the strongly correlated NiPS3/CdS interface assuring efficient electron-hole dissociation/transport, as well as abundant atomic-level edge P/S sites and activated basal S sites on NiPS3 ultrathin nanosheets advancing hydrogen evolution. These findings are revealed by the state-of-art characterizations and theoretical computations. Our work for the first time demonstrates the great potential of metal phosphorous chalcogenide as a general platform to tremendously raise the performance of different photocatalysts.

A stable metal-covalent-supramolecular organic framework hybrid: enrichment of catalysts for visible light-induced hydrogen production

Cubic metal-covalent-supramolecular organic framework (MCSOF-1) hybrid has been created from the reaction of two molecular components and subsequent co-assembly with cucurbit[8]uril (CB[8]) in water. In the presence of CB[8], [Ru(bpy)3]2+ -based acylhydrazine 1·2Cl reacted with aldehyde 2·Cl to quantitatively yield six-armed precursor 3·8Cl through the generation of MCSOF-1. MCSOF-1 combines the structural features of metal-, covalent- and supramolecular organic frameworks. Its periodicity in water and in the solid state was confirmed by synchrotron X-ray scattering and diffraction experiments. MCSOF-1 could enrich discrete anionic polyoxometalates (POMs), maintain periodicity in acidic medium, and remarkably facilitate visible light-induced electron transfer from its [Ru(bpy)3]2+ units to enriched POMs, leading to enhanced catalysis of the POMs for the reduction of proton to H2 in both aqueous (homogeneous) and organic (heterogeneous) media.

Hierarchical CdS/m-TiO2/G ternary photocatalyst for highly active visible light-induced hydrogen production from water splitting with high stability

Hierarchical semiconductors are the most important photocatalysts, especially for visible light-induced hydrogen production from water splitting. We demonstrate herein a hierarchical electrostatic assembly approach to hierarchical CdS/m-TiO2/G ternary photocatalyst, which exhibits high photoactivity and excellent photostability (more than twice the activity of pure CdS while 82% of initial photoactivity remained after 15 recycles during 80 h irradiation). The ternary nanojunction effect of the photocatalyst has been investigated from orbitals hybrid, bonding energy to atom-stress distortion and nano-interface fusion. And a coherent separation mechanism of charge carriers in the ternary system has been proposed at an atomic/nanoscale. This work offers a promising way to inhibit the photocorrosion of CdS and, more importantly, provide new insights for the design of ternary nanostructured photocatalysts with an ideal heterojunction.

Light-induced hydrogen production by photosystem I–Pt nanoparticle conjugates immobilized in porous glass plate nanopores

In recent years, a number of light-induced hydrogen production systems composed of photosystem I (PSI) and hydrogen production catalysts (e.g. hydrogenases and Pt nanoparticles) have been reported. However, the utility of these systems under aerobic conditions is limited due to their poor stability in the presence of oxygen. The development of light-induced hydrogen production systems that work under aerobic conditions is, therefore, of great importance to establish artificial photosynthetic devices. Ideally, these systems should utilise water as an electron source, via water splitting by photosystem II (PSII). We report the construction of a novel light-induced hydrogen production system composed of PSI-platinum nanoparticle conjugates and cytochrome c 6 (cyt c 6) immobilised in nanoporous glass plates (PGP50, 50-nm pore diameter). PSI trimer (PSIt) from Thermosynechococcus elongatus and Pt nanoparticles (PtNPs) were conjugated via electrostatic interactions (PSIt-PtNP). PSIt-PtNP and cyt c 6 were spontaneously absorbed in nanopores of PGP50 without denaturation. Upon irradiation in the presence of ascorbate as a sacrificial electron donor, catalytic H2 evolution was observed for PSIt-PtNP immobilised in the pores of PGP50 (PSIt-PtNP/PGP50) under both anaerobic and aerobic conditions, indicating that an effective photoinduced electron transfer system had been established. PSIt-PtNP/PGP50 was found to exhibit improved oxygen resistivity over the homogeneous solution system consisting of PSIt-PtNP, cyt c 6, and ascorbate, suggesting that the PSIt-PtNP/PGP50 system could be a potential candidate for artificial photosynthetic systems. The distribution of the components, PSIt-PtNP and cyt c 6, in PGP50 was characterised to discuss the efficiency of light-induced hydrogen production.

Light-energy conversion systems for hydrogen production and photocurrent generation using zinc chlorin derivatives

To develop efficient systems for light-energy conversion, monomeric and dimeric zinc chlorin derivatives were synthesized. These derivatives act as photosensitizers for light-induced hydrogen production with methylviologen as the electron mediator and Pt nanoparticles as the hydrogen-evolution catalyst. The monomeric derivative exhibited ~1.5-times higher activity than the dimeric derivative. The photocurrent-generating activity of the Zn chlorin derivatives assembled on a chemically modified indium tin oxide electrode was investigated; the dimeric derivative exhibited significant activity compared to the monomeric derivative. The photosensitizing activity of the derivatives in dye-sensitized solar cells was also investigated. The dimeric derivative exhibited two-fold higher performance than the monomeric derivative. The dimerization effect on the photosensitizing activities is briefly discussed in terms of stacking conformations based on the results of absorption and fluorescence spectroscopies.

Superior activity of the CuS–TiO2/Pt hybrid nanostructure towards visible light induced hydrogen production

A CuS–TiO2–Pt showed improved H2production (746 μmol h−1g−1) compared to CuS–TiO2(458 μmol h−1g−1) under the irradiation of UV-Vis light which is due to charge separation by the addition of Pt.

Efficient visible light-induced photoelectrocatalytic hydrogen production using CdS sensitized TiO2 nanorods on TiO2 nanotube arrays

CdS/TNRs/TNTs were synthesized by combining a hydrothermal method with a sequential-chemical bath deposition method and displayed enhanced visible light-induced photoelectrocatalytic hydrogen production activity compared with TNTs, TNRs/TNTs and CdS/TNTs.

Visible light induced hydrogen production over thiophenothiazine-based dye sensitized TiO2 photocatalyst in neutral water

Novel thiophenothiazine sensitized TiO2 photocatalysts show high photocatalytic hydrogen production from water splitting under visible light illumination.

Microporous organic nanorods with electronic push–pull skeletons for visible light-induced hydrogen evolution from water

This work shows that microporous organic network (MON) chemistry can be successfully applied for the development of a visible light-induced hydrogen production system. A visible light harvesting MON (VH-MON) was prepared by the Knoevenagel condensation of tri(4-formylphenyl)amine with [1,1′-biphenyl]-4,4′-diacetonitrile. Scanning electron microscopy (SEM) showed a 1D rod morphology of the VH-MON. Analysis of a N2 sorption isotherm showed a 474 m2 g−1 surface area and microporosity. Solid phase 13C nuclear magnetic resonance (NMR) and infrared (IR) absorption spectroscopy, and elemental analysis support the expected network structure. The VH-MON showed visible light absorption in 400–530 nm and vivid emission at 542 nm. The HOMO and LUMO energy levels of the VH-MON were simulated at −5.1 and −2.4 eV, respectively, by density functional theory (DFT) calculation. The VH-MON/TiO2–Pt composite exhibited promising activity and enhanced stability as a photocatalytic system for visible light-induced hydrogen production from water.

Photo-electrochemical characterization of polypyrrol: Application to visible light induced hydrogen production

The semi-conducting properties of polypyrrol (PPy) are investigated by the photo-electrochemical technique. The polymer is stable up to~190°C, above which a weight loss accounting for~60% is observed. An optical transition of 1.02eV is determined, directly allowed. Further indirect transition is determined at 0.37eV. The electrical conduction is characteristic of degenerate behavior with an activationless hopping and a hole mobility of 4.2×10−3cm2V−1s−1. The p-type conductivity is evidenced from the Mott–Schottky plots. In neutral solution, a flat band potential of 0.108VSCE and a holes density of 4.57×1021cm−3 are determined. The electrochemical impedance spectroscopy (EIS), measured over a wide frequency range (1mHz–105Hz), reveals the bulk contribution with a constant phase element (CPE). The straight line at 43° at low frequencies region is due to the Warburg diffusion. The energy diagram shows the feasibility of H2 photo-evolution with a low over-voltage. The best performance is achieved at pH∼7 in the presence of S2O32− as holes scavenger. A hydrogen liberation rate of 660μmolh−1 (g catalyst)−1 and a quantum efficiency of 0.21% under visible light (29mWcm−2) are determined. The system is valuable for the chemical storage through the uphill reaction: (S2O32−+3H2O→2SO32−+2H2+2H+, ΔGf°=24.3kJmol−1).

Dendrimer-Encapsulated Pt Nanoparticles: An Artificial Enzyme for Hydrogen Production

Two series of dendrimer encapsulated Pt nanoparticles (DENPt) were created by using sixth generation poly(amidoamine) (PAMAM) dendrimers terminated with different numbers of hydroxyl groups (s-G6-OH and t-G6-OH) to mimic hydrogenases. Pt nanoparticles act as the active site to generate H2 by reducing H+, and dendrimers provide cavities to maintain the integrity of small Pt nanoparticles and prevent agglomeration. The artificial hydrogenases (t-G6-OH/Ptx and s-G6-OH/Ptx) were successfully applied to a light-induced hydrogen production system with Pt-tppa+, ethyl viologen, and TEOA as photosensitizer, electron relay, and sacrificial reagent, respectively, exhibiting excellent stability and efficient catalytic activity. No passivation effect is caused by the periphery hydroxyl groups of dendrimers. The optimal size of the Pt clusters consists of 200 Pt atoms, and the most adapted pH value is 9 to gain the highest catalytic efficiency in the applied hydrogen production system. This study provides a new strate...

Efficient [FeFe] hydrogenase mimic dyads covalently linking to iridium photosensitizer for photocatalytic hydrogen evolution

Two [FeFe] hydrogenase mimics, [Fe(2)(μ-pdt)(CO)(5)L1] (L1 = PPh(2)SPhNH(2)) (Ph = phenyl) (2) and [Fe(2)(μ-pdt)(CO)(5)L2] (L2 = PPh(2)PhNH(2)) (3), and two molecular photocatalysts, [(CO)(5)(μ-pdt)Fe(2)PPh(2)SPhNHCO(bpy)(ppy)(2)Ir]PF(6) (bpy = bipyridine, ppy = 2-phenylpyridine) (2a) and [(CO)(5)(μ-pdt)Fe(2)PPh(2)PhNHCO(bpy)(ppy)(2)Ir](PF(6)) (3a), have been designed and synthesized, anchoring Ir(ppy)(2)(mbpy)PF(6) (mbpy = 4-methyl-4'-carbonyl-2,2'-bipyridine) (PS) to one of the iron centers of complexes 2 and 3 by forming amide bonds. Molecular dyads 2a, 3a and the intermolecular systems 2, 3 with PS have also been successfully constructed for photoinduced H(2) production using triethylamine (TEA) as a sacrificial electron donor by visible light (>400 nm) in CH(3)CN-H(2)O solution. The time-dependence of H(2) generation and spectroscopic studies suggest that the activity of H(2) evolution can be tuned by addition of a S atom to the phosphane ligand. The highest turnover numbers (TON) of hydrogen evolution obtained are 127, using 2a as a photocatalyst in a supramolecular system, and 138, based on catalyst 2 in a multi-component system. Density functional theory (DFT) computational studies demonstrate that the S atom in the second coordination sphere makes complex 2 accept an electron more easily than 3 and improves the activity in light-induced hydrogen production.

Visible light-induced hydrogen production from glycerol aqueous solution on hybrid Pt–CdS–TiO2 photocatalysts

Abstract Binary (Pt/hex-CdS) and ternary (Pt/CdS/TiO 2 and Pt/TiO 2 /hex-CdS) hybrid photocatalysts were evaluated in photoinduced reforming of glycerol under visible light irradiation ( λ > 418 nm). The resulting hybrid materials are photocatalytically efficient with respect to hydrogen gas production. The relative order of reactivity for the synthesized hybrid catalysts was found to be: Pt/hex-CdS > Pt/CdS/TiO 2 > Pt/TiO 2 /hex-CdS. The systems with CdS/aqueous solution interfacial contact showed higher activity, suggesting that the hydrogen production mechanism can be strongly influenced by hydrolytic surface reactions on CdS. The potential gradient created at the CdS/TiO 2 or TiO 2 /hex-CdS interface may also play an important role in the photoelectrochemical mechanism. Therefore, carbonyl compounds such as acrolein and propanone, identified in the liquid phase after 7 h of irradiation, lead us to propose the first steps of a photoelectrochemical mechanism in the photoinduced reforming of glycerol.