Photochemical Hydrogen Production Research Articles

Molecular charge transfer and quantum efficiency analyses of a photochemical reactor for hydrogen production

This paper examines a lab-scale, batch-type photochemical reactor design for hydrogen generation from water. The reactor comprises a transparent cylindrical reaction vessel of 100 ml volume, which is illuminated with monochromatic LED arrays from 4 sides. The reaction is kept at constant pressure by a mechanism which enlarges the volume above the liquid in correspondence to the rate of hydrogen production. The measurement of volume, pressure and temperature is used to determine the number of moles of gas generated. The vessel is filled with a non-aqueous solution containing 0.62 M water and a supramolecular device (SMD), namely {[Ru(bpy)2dpp]2Rh(OH)2}5+ (with bpy = 2,2′–bipyridine and dpp = 2,3–bis(2–pyridil)pyrazine)), which reduces water photochemically under the presence of DMA as sacrificial electron donors (DMA = n,n-dimethylaniline), according to the following reaction: 2H2O(l)+2DMA→2hνH2(g)+2OH−+2DMA+. The equations for modelling of the photo-catalytic process are identified and used for simulations and analyses to improve the apparatus design and find the best operating conditions. The molecular simulations with Discovery Studio software are used for 3D representation of the SMD to identify its fundamental properties in the relevant energetic states, i.e., ground, metal to ligand charge transfer (MLCT), metal to metal charge transfer (MMCT) and the photo-activated catalyst states. The quantum efficiency of each sub-process is determined based on specified assumptions and subsequent analysis. It shows that the quantum efficiency is 0.01, which is consistent with experimental results from past studies. Two routes of the catalysis were identified: one short (300 ns), where the catalyst is activated from the 3MLCT state, and one long (400 ns) where the catalyst is activated via a 3MMCT state. The turnover frequency is mostly influenced by the rate of incident photons. A mathematical model of five differential equations predicts the molar concentration of the relevant species in the batch reactor. The model is used to determine the variation of concentration, hydrogen production and quantum efficiency in time. It is found that the process has an initial phase, when the concentration of hydrogen dissolved in the solution increases up to saturation; thereafter it remains constant. This result is also consistent with past literature experimental results. Because of other species production (e.g., hydroxyl, DMA+), water and DMA consumption, the quantum efficiency of the process decreases in time. Also the pressure in the head space influences the process. If the reactor operates with a full head space (50 ml), the pressure increases by ∼20 kPa in 12 h. The study provides useful input to the design of the experiment and also its application to the modelling of photochemical hydrogen production.

Photochemical hydrogen production with molecular devices comprising a zinc porphyrin and a cobaloxime catalyst

Two new noble-metal-free molecular devices, [{Co(dmgH)2Cl}{Zn(PyTPP)}] (1, dmgH = dimethyloxime, PyTPP = 5-(4-pyridyl)-10,15,20-triphenylporphyrin) and [{Co(dmgH)2Cl}{Zn(apPyTPP)}] (2, apPyTPP = 5-[4-(isonicotinamidyl)phenyl]-10,15,20-triphenylporphyrin), for light-driven hydrogen generation were prepared and spectroscopically characterized. The zinc porphyrin photosensitizer and the CoIII-based catalyst unit are linked by axial coordination of a pyridyl group in the periphery of zinc-porphyrin to the cobalt centre of catalyst with different lengths of bridges. The apparent fluorescence quenching and lifetime decays of 1 and 2 were observed in comparison with their reference chromophores, Zn(PyTPP) (3) and Zn(apPyTPP) (4), suggesting a possibility for an intramolecular electron transfer from the singlet excited state of zinc porphyrin unit to the cobalt centre in the molecular devices. Photochemical H2-evolving studies show that complexes 1 and 2 are efficient molecular photocatalysts for visible light-driven H2 generation from water with triethylamine as a sacrificial electron donor in THF/H2O, with turnover numbers up to 46 and 35 for 1 and 2, respectively. In contrast to these molecular devices, the multicomponent catalyst of zinc porphyrin and [Co(dmgH)2PyCl] did not show any fluorescence quenching and as a consequence, no H2 gas was detected by GC analysis in the presence of triethylamine with irradiation of visible light. The plausible mechanism for the photochemical H2 generation with these molecular devices is discussed.

Unsensitized Photochemical Hydrogen Production Catalyzed by Diiron Hydrides

The diiron hydride [(μ-H)Fe(2)(pdt)(CO)(4)(dppv)](+) ([H2](+), dppv = cis-1,2-C(2)H(2)(PPh(2))(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, [H2](+) functions without sensitizers: irradiation of [H2](+) 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.

Heterostructured Ceramic Powders for Photocatalytic Hydrogen Production: Nanostructured TiO2 Shells Surrounding Microcrystalline (Ba,Sr)TiO3 Cores

Heterostructured photocatalysts were prepared to have nanostructured (ns) TiO2 shells surrounding microcrystalline (mc) cores of (Ba,Sr)TiO3. The as‐prepared heterostructures were annealed between 400°C and 600°C to improve crystallinity and core‐shell interfacial bonding. X‐ray diffraction, electron microscopy, and gas adsorption measurements demonstrated that 50 nm thick shells composed of nanocrystalline and nanoporous TiO2 surrounded mc‐cores such that the heterostructured particles had surface areas of 50–100 m2/g. The mc‐(Ba,Sr)TiO3/ns‐TiO2 core‐shell photocatalysts annealed at 600°C had slightly reduced surface areas, but had the highest rates of photochemical hydrogen production from water/methanol solutions, rates much greater than those for ns‐TiO2 or mc‐(Ba,Sr)TiO3 alone. Such heterostructured powders represent a new strategy for the design of efficient photocatalysts and the use of nanostructured catalytic coatings.

Photochemical Production of Hydrogen from Water Using Microporous Porphyrin Coordination Lattices

In this study, we investigated the photochemical production of hydrogen from water using bio-inspired heterogeneous microporous porphyrin coordination lattices (PCLs), [Ru2(MTCPP)BF4] (M = H2 (PCL-1), Zn (PCL-2); TCPP = Tetrakis(4-carboxyphenyl)porphyrin), under visible (380 nm <) and UV (320 nm <) light irradiations. In the presence of Na2EDTA (as a sacrificial donor) and MV2+ (methyl-vilologen; as a electron relay), PCLs exhibits photocatalytic activity for hydrogen evolution; the maximum amounts of turnover numbers (TONs) of PCL-1 and PCL-2 at 24 h irradiation were 20.8 and 29.9, respectively. In the catalytic reactions, the relation between PCLs and MV2+ was similar to the relation between a [cytochrome c3 hydrogenase] pair and lysine residues in enzymatic reactions. By using the hydrogen production rate and the MV+ (methyl-vilologen radical-cation) concentration, kinetic parameters such as affinities between MV+ and PCLs, maximum reaction rate, and total efficiency of the reaction are introduced using the Michaelis-Menten equation. These parameters indicated that PCLs are good artificial enzyme model catalysts. The stability of the PCLs after the catalytic reactions was confirmed by X-ray photoelectron spectroscopy and Fourier transform-infrared spectra. These results indicated that the frameworks of PCLs are stable for this catalytic reaction.

Modification of MOF catalysts by manipulation of counter-ions: experimental and theoretical studies of photochemical hydrogen production from water over microporous diruthenium (II, III) coordination polymers

In this study we investigated the photochemical production of hydrogen from water using three heterogeneous microporous ruthenium coordination polymers [Ru2(p-BDC)2X] n (p-BDC = 1,4-benzenedicarboxylate, X = Cl, Br and BF4) in the presence of multi-component systems. The order of catalytic performances is [Ru2(p-BDC)2Br] n >[Ru2(p-BDC)2BF4] n >[Ru2(p-BDC)2Cl] n . The most active catalyst, [Ru2(p-BDC)2Br] n , caused the evolution of 46.7 μmol hydrogen molecules with a turn-over number of 18.7 based on [Ru2(p-BDC)2Br] n under visible light irradiation for 4 h. We ascertained that the differences in catalytic activities originated from (1) the efficiency of the quenching of methyl-viologen radicals by [Ru2(p-BDC)2X] n and (2) the durability of the structure in the reaction. In order to examine the catalytic reaction mechanism, we performed theoretical calculations for neutral model structures [Ru2(HCOO)4X(H2O)] (X = Cl, Br), one-electron reduction model complexes [Ru2(HCOO)4X(H2O)]− and deduced intermediate model structures [H–Ru2(HCOO)4X] using broken-symmetry hybrid density functional theory methods.

Photoelectrochemical Production of Hydrogen in Aqueous Suspensions Nanoparticles Composites of CdS/ZnS

Aqueous solutions of mixed CdS/ZnS semiconductor (SC) nanoparticle suspensions in phosphate buffers containing 10 mM [Fe(CN)6]4– were used for photochemical production of hydrogen via hydrated electron intermediates. CdS was doped with varying percentages of ZnS to expand the absorption range of the composite to the UV region. Results show that maximum generation of hydrated electrons by [Fe(CN)6]4– occurs at pH 6. Furthermore, native CdS amorphous nanoparticles give the greatest photocurrent. Studies also show that, in phosphate buffer, the steady state photocurrent was directly proportional to the CdS content in the mixture of CdS/ZnS. The aqueous nano-systems sustained their stability as indicated by the reproducibility of their photocatalytic activities. Solar radiated assemblies of CdS/ZnS/ [Fe(CN)6]4– sustained cyclic systems for continuous hydrogen production.

Synthesis and characterization of heterooligonuclear ruthenium complexes with tri(phenanthrolino)hexaazatriphenylene ligands

A homologous series of homo- and heterooligonuclear ruthenium/palladium complexes of 9,10,19,20,29,30-hexaazahexapyrido[3,2-a:2′,3′-c:3′′,2′′-k:2′′′,3′′′-m:-3′′′′,2′′′′-u:2′′′′′,3′′′′′-w]-trinaphthylene (PHAT) with the formula [{Ru(tbbpy)2} n (μ-phat)]2n+ (n = 1, 2, 3) and [{Ru(tbbpy)2} m (μ-phat){PdCl2}3- m ]2m+ (m = 1, 2) was prepared and characterized, where TBBPY = 4,4′-di-tert-butyl-2,2′-bipyridine. Toward this aim, a new synthetic route was developed for which a microwave-assisted successive complexation reaction of the multitopic ligand was used. In accordance to the only known complex of this kind, [{Ru(phen)2}3(μ-phat)]6+, only the outer 1,10-phenanthroline (PHEN) like coordination spheres of the ligand could be substituted with octahedral ruthenium and square planar palladium fragments. This allows the construction of new supramolecular structures with at least three metal centers that are potentially capable of intramolecular multielectron transfer and photocatalytic redox activity. Electrochemical investigations show that the metal centers in the homonuclear ruthenium complex do not interact and that the ligand-based redox steps are reversible. Preliminary investigations also show that PHAT may be photochemically reduced as seen by UV-Vis spectroscopy; however, no catalytic activity for photochemical hydrogen production could be observed.

Artificial Inorganic Leafs for Efficient Photochemical Hydrogen Production Inspired by Natural Photosynthesis

Artificial Inorganic Leafs for Efficient Photochemical Hydrogen Production Inspired by Natural Photosynthesis

Light Harvesting: Artificial Inorganic Leafs for Efficient Photochemical Hydrogen Production Inspired by Natural Photosynthesis (Adv. Mater. 9/2010)

A natural leaf is a synergy of elaborated structures and functional components, producing a highly complex machinery for photosynthesis in which light harvesting, photoinduced charge separation, and catalysis modules combine to capture solar energy and split water into oxygen and “hydrogen” efficiently. On p. 951, Tongxiang Fan, Di Zhang, and co-workers report on the development of artificial inorganic leaves with enhanced light-harvesting and photocatalytic water splitting abilities, which stem from reproduction of natural leaves' complex structures and self-doping with nitrogen during synthesis.

Tin-porphyrin sensitized TiO2 for the production of H2 under visible light

Hydrogen was successfully produced under visible light irradiation in a tin porphyrin (SnP)-sensitized TiO2 system in the wide pH range (pH 3–11) although SnP hardly adsorbs on TiO2. The number of H2 produced in the SnP/TiO2 system after 9 h irradiation corresponds to the turnover number of 410. The apparent photonic efficiency for H2 evolution was estimated to be 35% with the monochromatic radiation of 550 ± 10 nm. The photochemical production of hydrogen is mediated through the formation of the π-radical anion (SnP˙−) that subsequently transfers electron to TiO2. The photogenerated SnP˙− was monitored by transient absorption spectroscopy and its lifetime is long enough to survive the slow diffusion from the solution bulk to the TiO2 surface, which makes the adsorption of SnP on TiO2 not required for hydrogen production. This is clearly contrasted with the common ruthenium complex-sensitized TiO2 system where the adsorption of the sensitizer complex is essentially required and the hydrogen production is limited to the acidic condition where the adsorption of the sensitizers on TiO2 is allowed. The photocatalytic activity of SnP was mainly attributed to the Q-band (500–650 nm), not to the Soret band (420–430 nm) of which absorption intensity is much higher.

Photochemical and thermal hydrogen production from water catalyzed by carboxylate-bridged dirhodium(ii) complexes

A series of dinuclear Rh(II) complexes, [Rh(2)(μ-OAc)(4)(H(2)O)(2)] (HOAc = acetic acid) (1), [Rh(2)(μ-gly)(4)(H(2)O)(2)] (Hgly = glycolic acid) (2), [Rh(2)(μ-CF(3)CO(2))(4)(acetone)(2)] (3), and [Rh(2)(bpy)(2)(μ-OAc)(2)(OAc)(2)] (4), were found to serve as H(2)-evolving catalysts in a three-component system consisting of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)), methylviologen (MV(2+)), and ethylenediaminetetraacetic acid disodium salt (EDTA). It was also confirmed that thermal reduction of water into H(2) by MV(+)˙, in situ generated by the bulk electrolysis of MV(2+), is effectively promoted by 1 as a H(2)-evolving catalyst. The absorption spectra of the photolysis solution during the photocatalysis were monitored up to 6 h to reveal that the formation of photochemical or thermal byproducts of MV(+)˙ is dramatically retarded in the presence of the Rh(II)(2) catalysts, for the H(2) formation rather than the decomposition of MV(+)˙ becomes predominant in the presence of the Rh(II)(2) catalysts. The stability of the Rh(II)(2) dimers was confirmed by absorption spectroscopy, (1)H NMR, and ESI-TOF mass spectroscopy. The results indicated that neither elimination nor replacement of the equatorial ligands take place during the photolysis, revealing that one of the axial sites of the Rh(2) core is responsible for the hydrogenic activation. The quenching of Ru*(bpy)(3)(2+) by 1 was also investigated by luminescence spectroscopy. The rate of H(2) evolution was found to decrease upon increasing the concentration of 1, indicating that the quenching of Ru*(bpy)(3)(2+) by the Rh(ii)(2) species rather than by MV(2+) becomes predominant at the higher concentrations of 1. The DFT calculations were carried out for several possible reaction paths proposed (e.g., [Rh(II)(2)(μ-OAc)(4)(H(2)O)] + H(+) and [Rh(II)(2)(μ-OAc)(4)(H(2)O)] + H(+) + e(-)). It is suggested that the initial step is a proton-coupled electron transfer (PCET) to the Rh(II)(2) dimer leading to the formation of a Rh(II)Rh(III)-H intermediate. The H(2) evolution step is suggested to proceed either via the transfer of another set of H(+) and e(-) to the Rh(II)Rh(III)-H intermediate or via the homolytic radical coupling through the interaction of two Rh(II)Rh(III)-H intermediates.

Recent advances in nanoelectrode architecture for photochemical hydrogen production

We review recent advances in nanoelectrode architecture for photochemical hydrogen production by water splitting. Today, solar energy is recognized as one of the most important renewable energy sources that humanity must harness in addressing the future energy sustainability issues. Of the different strategies for solar energy conversion, solar fuel or solar hydrogen conversion is attractive in that one can store the harvested energy in chemical bonds. Recent work in this field has focused on the use of nanoarchitecture designs that aim to increase photocatalytic activity, enable visible light harvesting, and ensure chemical stability and cost-effectiveness. In this perspective review, we focus on selected work in the following areas: (1) oxide semiconductor nanoelectrodes; (2) sensitization of semiconductor nanowire/nanotube arrays; (3) bioinorganic conjugate architectures; and (4) hybrid nanoarchitectures.

High‐Turnover Photochemical Hydrogen Production Catalyzed by a Model Complex of the [FeFe]‐Hydrogenase Active Site

Lifting the diiron curtain: 200 equivalents of H2 per catalyst at a maximum turnover rate of 3.7 H2 per minute can be obtained in a light-driven proton reduction process in near-neutral H2O/DMF (pH 5.5) by using an [FeFe]-hydrogenase active-site model complex as the catalyst (see scheme).

Photochemical hydrogen production catalyzed by polypyridyl ruthenium–cobaloxime heterobinuclear complexes with different bridges

Two heterobinuclear complexes [(bpy) 2Ru(bpy-4-CH 3,4′-CONH(4-py)Co(dmgBF 2) 2(OH 2)](PF 6) 2 ( 1, dmgBF 2 = (difluoroboryl)dimethylglyoximato) and [(bpy) 2Ru(bpy-4-CH 3,4′-CONHCH 2(4-py)Co(dmgBF 2) 2(OH 2)](PF 6) 2 ( 2) were prepared, in which the polypyridyl ruthenium photosensitizer and the cobaloxime catalyst are connected either by a conjugated bridge ( 1) or by an unconjugated one ( 2). Complexes 1 and 2 were used as photocatalysts for hydrogen generation. Under optimal conditions, the turnover numbers (ton) for hydrogen evolution were 38 for 1 and 48 for 2 in the presence of 300 equiv of both Et 3N and [Et 3NH][BF 4] in the acetone solution during an 8-h irradiation of visible light ( λ > ca. 400 nm). The complex 2 with an unconjugated bridge proved to be more efficient for photochemical hydrogen generation than the complex 1 with a conjugated bridge under the same reaction condition.

Design Considerations for a System for Photocatalytic Hydrogen Production from Water Employing Mixed-Metal Photochemical Molecular Devices for Photoinitiated Electron Collection

Supramolecular complexes coupling Ru(II) or Os(II) polyazine light absorbers through bridging ligands to Rh(III) or Ir(III) allow the study of factors impacting photoinitiated electron collection and multielectron water reduction to produce hydrogen. The [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) system represents the first photoinitiated electron collector in a molecular system (bpy = 2,2'-bipyridine, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline). The [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) system represents the first photoinitiated electron collector that affords photochemical hydrogen production from water in the presence of an electron donor, N,N-dimethylaniline (dpp = 2,3-bis(2-pyridyl)pyrazine). The complexes [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Ru(dpp)}(2)RhBr(2)](PF(6))(5), [{(phen)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Os(dpp)}(2)RhCl(2)](PF(6))(5), [{(tpy)RuCl(dpp)}(2)RhCl(2)](PF(6))(3), [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), and [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) are herein evaluated with respect to their functioning as hydrogen photocatalysts (tpy = 2,2':6',2''-terpyridine, phen = 1,10-phenanthroline). With the exceptions of [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) and [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), all other complexes demonstrate photocatalytic activity. The functioning systems possess a rhodium localized lowest unoccupied molecular orbital that serves as the site of electron collection and a metal-to-ligand charge-transfer ((3)MLCT) and/or metal-to-metal charge-transfer ((3)MMCT) excited-state with sufficient driving force for excited-state reduction by the electron donor. The lack of photocatalytic activity by [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5), although photoinitiated electron collection occurs, establishes the significance of the rhodium center in the photocatalytic system. The lack of photocatalytic activity of [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3) is attributed to the lower-energy (3)MLCT state that does not possess sufficient driving force for excited-state reduction by the electron donor. The variation of electron donor showed the photocatalysis efficiency to decrease in the order N,N-dimethylaniline > triethylamine > triethanolamine. The general design considerations for development of supramolecular assemblies that function as water reduction photocatalysts are discussed.

Synthesis, crystal structure, solution and spectroscopic properties, and hydrogen-evolving activity of [K(18-crown-6)][Pt(ii)(2-phenylpyridinato)Cl2

A water-soluble ortho-metalated platinum(II) complex [K(18-crown-6)][Pt(ppy)Cl2]·0.5H2O (1) (ppy = phenylpyridinate, 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) was prepared from a 1 : 1 reaction of [K(18-crown-6)]2[PtCl4] and 2-phenylpyridine in methanol. The compound crystallizes in the triclinic system, space groupP (No. 2). A solvolysis product of 1, Pt(ppy)Cl(DMF) (DMF = N,N-dimethylformamide) (10), was also isolated and structurally characterized by X-ray diffraction (monoclinic system, space groupP21/n (No. 14)), revealing the lability of the coordination bond trans to the C(ppy) donor. Ligand substitution reactions of 1 in water were investigated by means of UV-visible absorption spectroscopy and time-dependent DFT calculations. The initial hydrolysis product in aqueous media was suggested to be Pt(ppy)Cl(OH2), in which the chloride ion trans to the C(ppy) donor in [Pt(ppy)Cl2]− is replaced with an aqua ligand due to the stronger trans effect originated by the C(ppy) donor. It was found that the ligand substitution reactions of [Pt(ppy)Cl2]− is extremely complicated. Leaving the complex in solution for a prolonged time resulted in deposition of a yellowish green chloride-bridged dimer Pt2(ppy)2(μ-Cl)2. Moreover, an unidentified blue species, ascribable to a Pt(II)/Pt(III) mixed-valence species, started to form while the initial hydrolysis reactions proceeded. Photochemical hydrogen production from water catalyzed by [Pt(ppy)Cl2]− was examined using a photosystem made up of Ru(bpy)32+ (bpy = 2,2′-bipyridine), methylviologen, and a sacrificial electron donor (EDTA) in an acetate buffer (pH 5). It is shown that the H2-evolving activity of [Pt(ppy)Cl2]− is higher that those of the hydrolysis products of [Pt(ppy)Cl2]−, but are comparable to those of other common Pt(II) complexes having a cis-Pt(II)Cl2 unit, such as cis-PtCl2(NH3)2, PtCl2(4,4′-dicarboxy-bpy), and PtCl2(2,2′-bipyrimidine).

Photoactive component-loaded Nafion film as a platform of hydrogen generation: Alternative utilization of a classical sensitizing system

The photochemical hydrogen production was achieved by integrating photoactive components in a polymer membrane film under visible-light irradiation. The classical homogeneous photochemical system employing ruthenium bipyridyl complex (Ru(bpy) 3 2+) as a sensitizer, methyl viologen (MV 2+) as an electron shuttle, Pt as a hydrogen-evolving catalyst was heterogenized by immobilizing the active components within Nafion film. The integrated Nafion film provides a unique environment in which the immobilization of the components, light absorption, charge separation/transfer, and hydrogen production concur. The hydrogen evolution from the loaded Nafion film under visible light ( λ > 420 nm) was successfully demonstrated. The loaded Pt particles were mainly located at the external surface of the film while the sensitizer was bound at the cation-exchange sites in the nanoporous channel. The electron-relaying action of MV 2+ was effective only above 1 mM because most MV 2+ ions below this concentration were bound at the ion-exchange site with restricted mobility. The effects of various components on the hydrogen production in this heterogenized system were investigated and discussed. The present Nafion film system may serve as a prototype of solar hydrogen generating films and can be further modified and optimized for practical applications.

Photochemical production of molecular hydrogen in lake water and coastal seawater

Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L − 1 h − 1 ) and lower in seawater (range: 19–45 pmol L − 1 h − 1 ). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H 2 production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.

04/00714 Highly efficient photochemical hydrogen production system using zinc porphyrin and hydrogenase in CTAB micellar system: Yutaka, A. et al. Solar Energy Materials and Solar Cells, 2003, 79, (1), 103–111

04/00714 Highly efficient photochemical hydrogen production system using zinc porphyrin and hydrogenase in CTAB micellar system: Yutaka, A. et al. Solar Energy Materials and Solar Cells, 2003, 79, (1), 103–111