Quantum Yield Of Hydrogen Research Articles

Hydrogen production from iron sulphate photolysis using mark-5 cycle

ABSTRACT Hydrogen production was carried out in a photochemical device in a Mark-5 cycle. The photolysis of iron sulphate solution was carried out in a close periodic system. The reaction mixture was 8.5 g iron sulphate compound (FeSO4•7 H2O), 2.5 g I2 and 1.0 g HI in 100 mL water. Fifty millilitres of this solution was filled into a quartz reactor and connected to cycle system. The optimisation of hydrogen production was achieved by temperature, flow rate and radiation irradiation. The maximum hydrogen generated was 50.0 × 1016 molecules per minute at 120 °C temperature, 0.08 mL/sec. Pump speed, pressure 0.30 MPas, and Hg-vapour λmax = 365 nm. Eact. = 14.92 kC/mol caused bimolecular reactions to occur at low temperatures by photochemical action. Quantum yield of hydrogen depended on the absorbed of 0.5 × 1015 kvant/s. The energy of the quantum above T ≥ 100°C temperatures was φ ≥ 1. The dependence of the hydrogen generation rate (W) increased from 0.001 to 0.0038 × 1016 molecules/sec at 10-90 minutes, respectively.

Salt‐melt synthesis of poly(heptazine imide) in binary alkali metal bromides for enhanced visible‐light photocatalytic hydrogen production

AbstractPoly(heptazine imide) (PHI), a semicrystalline version of carbon nitride photocatalyst based on heptazine units, has gained significant attention for solar H2 production benefiting from its advantages including molecular synthetic versatility, excellent physicochemical stability and suitable energy band structure to capture visible photons. Typically, PHI is obtained in salt‐melt synthesis in the presence of alkali metal chlorides. Herein, we examined the role of binary alkali metal bromides (LiBr/NaBr) with diverse compositions and melting points to rationally modulate the polymerization process, structure, and properties of PHI. Solid characterizations revealed that semicrystalline PHI with a condensed π‐conjugated system and rapid charge separation rates were obtained in the presence of LiBr/NaBr. Accordingly, the apparent quantum yield of hydrogen using the optimized PHI reaches up to 62.3% at 420 nm. The density functional theory calculation shows that the dehydrogenation of the ethylene glycol has a lower energy barrier than the dehydrogenation of the other alcohols from the thermodynamic point of view. This study holds great promise for rational modulation of the structure and properties of conjugated polymeric materials.

Charge Concentration Limits the Hydrogen Evolution Rate in Organic Nanoparticle Photocatalysts.

Time-resolved microwave conductivity is used to compare aqueous-soluble organic nanoparticle photocatalysts and bulk thin films composed of the same mixture of semiconducting polymer and non-fullerene acceptor molecule and the relationship between composition, interfacial surface area, charge-carrier dynamics, and photocatalytic activity is examined. The rate of hydrogen evolution reaction by nanoparticles composed of various donor:acceptor blend ratio compositions is quantitatively measured, and it is found that the most active blend ratio displays a hydrogen quantum yield of 0.83% per photon. Moreover, it is found that nanoparticle photocatalytic activity corresponds directly to charge generation, and that nanoparticles have 3× more long-lived accumulated charges relative to bulk samples of the same material composition. These results suggest that, under the current reaction conditions, with ≈3× solar flux, catalytic activity by the nanoparticles is limited by the concentration of electrons and holes in operando and not a finite number of active surface sites or the catalytic rate at the interface. This provides a clear design goal for the next generation of efficient photocatalytic nanoparticles.

Hole utilization in solar hydrogen production.

In photochemical production of hydrogen from water, the hole-mediated oxidation reaction is the rate-determining step. A poor solar-to-hydrogen efficiency is usually related to a mismatch between the internal quantum efficiency of photon-induced hole generation and the apparent quantum yield of hydrogen. This waste of photogenerated holes is unwanted yet unavoidable. Although great progress has been made, we are still far away from the required level of dexterity to deal with the associated challenges of wasted holes and its consequential chemical effects that have placed one of the greatest bottlenecks in attaining high solar-to-hydrogen efficiency. A critical assessment of the hole and its related phenomena in solar hydrogen production would, therefore, pave the way moving forward. In this regard, we focus on the contextual and conceptual understanding of the dynamics and kinetics of photogenerated holes and its critical role in driving redox reactions, with the objective of guiding future research. The main reasons behind and consequences of unused holes are examined and different approaches to improve overall efficiency are outlined. We also highlight yet unsolved research questions related to holes in solar fuel production.

Photocatalytic hydrogen evolution without an electron mediator using a porphyrin–pyrene conjugate functionalized Pt nanocomposite as a photocatalyst

A new system for photoinduced hydrogen production has been constructed using a porphyrin–pyrene conjugate functionalized Pt nanocomposite as a photocatalyst and ethylenediaminetetraacetic acid (EDTA) as a sacrificial reductant in the absence of an electron mediator. Detailed spectral, computational and photochemical studies reveal that a photoinduced energy transfer from the photoexcited state of pyrene to the porphyrin occurs, accompanied by an electron transfer from the excited porphyrin moiety to the platinum catalyst for the H 2 generation. Efficient photocatalytic hydrogen evolution from the system demonstrates the possibility of constructing a photocatalytic system that uses a Pt nanocomposite functionalized by self-assembled donor–acceptor conjugates as a photocatalyst. The turnover numbers (TON Pt and TON dye) and quantum yields of hydrogen ( Φ H 2 ) for the photoinduced hydrogen production system are 63, 6311, and 2.65%, respectively, and are calculated on the basis that the total amount of H 2 evolved after 12 h of irradiation.

Synthesis and photocatalytic hydrogen evolution of meso-tetrakis(p-sulfonatophenyl)porphyrin functionalized platinum nanocomposites

Meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS4) functionalized platinum nanocomposites were synthesized and characterized using ultraviolet-visible absorption spectroscopy (UV-vis), fluorescence spectroscopy (FL), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray diffraction (XRD) methods. The postulated configuration of TPPS4 functionalized platinum nanocomposite may be described as an antenna system containing a photoreceptive TPPS4 shell and a nanosize platinum core. Fluorescence and photoelectrochemistry studies of both TPPS4 and the platinum nanocomposites showed that efficient electron/energy transfer occurred from the TPPS4 donor to the metallic nanocore acceptor. TPPS4 functionalized platinum nanocomposites are photocatalytic active for water reduction to produce hydrogen. The turnover numbers (TONPt and TONTPPS4) and quantum yield of hydrogen (ϕH2) for the photocatalyst (nPt:nTPPS4= 250) were 44, 11056, and 1.8%, respectively, calculated on the basis of the total amount of H2 evolution for 12 h irradiation.

The synthesis, light-harvesting, and photocatalysis of naphthylporphyrin-functionalized platinum nanocomposites

A tetraphenylporphyrin bearing four naphthalene donor moieties (5,10,15,20-tetrakis(4-(naphthalen-1-ylmethoxy)phenyl)porphyrin were synthesized and characterized using 1H NMR, FTIR, UV–vis, FL, TEM, and XRD. Substituting the naphthalene groups onto the porphyrin ring led the molecule to absorb over a broader range (200–700 nm) and to undergo efficient intramolecular energy transfer from the naphthalene to the porphyrin ring. FTIR, XRD and TEM analyses indicated that within a functionalized platinum nanocomposite comprising the porphyrin, the photoreceptive dye forms a shell containing a nanosize Pt core (∼2.8 nm). The photocatalytic activity of the Pt nanocomposite towards water reduction to hydrogen was >twice that of a Pt-naphthalene-free porphyrin system. The turnover numbers (TON Pt and TON dye) and quantum yields of hydrogen ( Φ H 2 ) were 72, 7200 and 3.0%, respectively, calculated on the basis of the total amount of H 2 evolved after 12 h irradiation.

Visible Light Induced Catalytic Water Reduction without an Electron Relay

Protons from water are reduced by a catalytic system composed of a heteroleptic iridium(III) photosensitizer [Ir(ppy)2(bpy)]+, platinum catalyst, and sacrificial reductant. The hydrogen quantum yield reaches 0.26 in this study, which proceeds via reductive quenching of the excited photosensitizer by triethanolamine. This simplified approach allows the characterization of degradation products that are otherwise obscured in more complex systems. A novel 16-well setup for parallel kinetic analysis of H2 evolution enables high-throughput screening of reaction conditions and quantization of the decaying reaction rate. DFT calculations rationalize the differences between this and previous studies on tris-diimine ruthenium(II) photosensitizers.

Single-Layer Electroluminescent Devices and Photoinduced Hydrogen Production from an Ionic Iridium(III) Complex

We report the electronic structure and diverse applications of a highly luminescent ionic transition metal complex, [Ir(dF(CF3)ppy)2(dtbbpy)](PF6) (where dF(CF3)ppy = 2-(2,4-difluorophenyl)-5-trifluoromethylpyridine and dtbbpy = 4,4‘-di-tert-butyl-2,2‘-dipyridyl). The large HOMO−LUMO gap (ΔE = 3.06 V) enabled high-energy electroluminescence from the complex. Single-layer devices were fabricated and found to emit blue-green light (500 nm). The strong reducing strength of the excited state (E*ox = 1.21 V) enabled effective catalysis of the photoinduced reduction of H2O to H2. It was found that the relative quantum yield of hydrogen was over an order of magnitude improved from the standard photosensitizer Ru(dmphen)32+ (dmphen = 4,7-dimethyl-1,10-phenanthroline).

Enzyme‐assisted Reforming of Glucose to Hydrogen in a Photoelectrochemical Cell¶

ABSTRACTHydrogen gas has been produced by reforming glucose in a hybrid photoelectrochemical cell that couples a dye‐sensitized nanoparticulate wide band gap semiconductor photoanode to the enzyme‐based oxidation of glucose. A layer of porphyrin sensitizer is adsorbed to a TiO2 nanoparticulate aggregate sintered to a conducting glass substrate to form the photoanode. Excitation of the porphyrin results in electron injection into the TiO2, and migration to a microporous platinum cathode where hydrogen is produced by hydrogen ion reduction. The oxidized sensitizer dye is reduced by NADH, regenerating the dye and poising the NAD+/NADH redox couple oxidizing. The NAD+ is recycled to NADH by the enzyme glucose dehydrogenase, which obtains the necessary electrons from oxidation of glucose. The reforming of glucose produces gluconolactone, which hydrolyzes to gluconate; the electrochemical potential necessary to overcome thermodynamic and kinetic barriers to hydrogen production by NADH is provided by light. The quantum yield of hydrogen is ∼2.5%.

Enzyme-assisted Reforming of Glucose to Hydrogen in a Photoelectrochemical Cell¶

Hydrogen gas has been produced by reforming glucose in a hybrid photoelectrochemical cell that couples a dye-sensitized nanoparticulate wide band gap semiconductor photoanode to the enzyme-based oxidation of glucose. A layer of porphyrin sensitizer is adsorbed to a TiO2 nanoparticulate aggregate sintered to a conducting glass substrate to form the photoanode. Excitation of the porphyrin results in electron injection into the TiO2, and migration to a microporous platinum cathode where hydrogen is produced by hydrogen ion reduction. The oxidized sensitizer dye is reduced by NADH, regenerating the dye and poising the NAD /NADH redox couple oxidizing. The NAD is recycled to NADH by the enzyme glucose dehydrogenase, which obtains the necessary electrons from oxidation of glucose. The reforming of glucose produces gluconolactone, which hydrolyzes to gluconate; the electrochemical potential necessary to overcome thermodynamic and kinetic barriers to hydrogen production by NADH is provided by light. The quantum yield of hydrogen is ∼2.5%.

Enzyme Assisted Reforming of Glucose to Hydrogen in a Photoelectrochemical Cell

Hydrogen gas has been produced by reforming glucose in a hybrid photoelectrochemical cell that couples a dye-sensitized nanoparticulate wide band gap semiconductor photoanode to the enzyme-based oxidation of glucose. A layer of porphyrin sensitizer is adsorbed to a TiO2 nanoparticulate aggregate sintered to a conducting glass substrate to form the photoanode. Excitation of the porphyrin results in electron injection into the TiO2, and migration to a microporous platinum cathode where hydrogen is produced by hydrogen ion reduction. The oxidized sensitizer dye is reduced by NADH, regenerating the dye and poising the NAD+/NADH redox couple oxidizing. The NAD+ is recycled to NADH by the enzyme glucose dehydrogenase, which obtains the necessary electrons from oxidation of glucose. The reforming of glucose produces gluconolactone, which hydrolyzes to gluconate; the electrochemical potential necessary to overcome thermodynamic and kinetic barriers to hydrogen production by NADH is provided by light. The quantum yield of hydrogen is approximately 2.5%.

Polyimides with alicyclic diamines. II. Hydrogen abstraction and photocrosslinking reactions of benzophenone‐type polyimides

AbstractPhotosensitive polyimides with alicyclic diamines and benzophenone moiety were prepared by reactions of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) with diamines in aprotic solvents, followed by thermal or chemical imidizations. Among them the polyimide from BTDA and bis(4‐amino‐3‐methylcyclohexyl) methane (DMDHM) can be dissolved in several organic solvents such as dichloromethane, tetrachloroethane, and N‐methyl‐2‐pyrrolidone (NMP). In order to compare properties of the polyimides with alicyclic diamines with those of corresponding aromatic polyimides, the UV absorption spectra and fluorescence spectra of these polyimides and their model compounds were investigated. No occurrence of charge transfer at photoexcited states was ascertained for the polyimides with alicyclic diamines. The hydrogen abstraction and crosslinking during photoirradiation have been studied to learn the influence of the elimination of charge transfer process in these photosensitive polyimides. The quantum yield of hydrogen abstraction for the model compound of alicyclic polyimides is 0.56 in THF measured with HPLC. The quantum yield for the photocrosslinking reaction of the solvent‐soluble polyimide with alicyclic diamine, PI(BTDA/DMDHM), was determined to be 0.004 in air from gel permeation chromatography (GPC) measurement, which is four times higher than that for photosensitive polyimides with aromatic diamines. © 1994 John Wiley & Sons, Inc.

Laser induced decomposition of uranium tetrahydroborate

Electronic excitation of uranium tetrahydroborate, U(BH 4) 4, results in the decomposition of the molecule. Longer wavelength excitation seems to induce a molecular collapse and a larger quantum yield of hydrogen.

Efficient near ultraviolet light induced formation of hydrogen by ferrous hydroxide.

The formation of hydrogen on irradiating ferrous ion in aqueous solution or suspension was studied over a wide range of pH. In addition to the known reaction in acid solution which decreases in yield with increasing pH and required far UV light, there is an efficient reaction occurring between pH 6 and 9 which utilizes near UV light. The latter reaction is an approximately linear function of both the concentration of ferrous ion and the light intensity. The quantum yield of hydrogen from the suspension of Fe(OH)2 at pH 7.2 is very high: > or = 0.3. The quantum yield decreases by a factor of five at 1 mole percent of ferric ions. To explain these observations it is proposed that an intermediate formed on excitation of the Fe(OH)2 polymer is further reduced by a neighboring Fe(+2) to form H2. These results support the work of Braterman et al. (1983) which claimed that the near UV driven photooxidation of ferrous ions could be responsible for formation of the Banded Iron Formations on the early earth. The efficient photoreaction observed in the present work could also serve as a source of active reducing equivalents to reduce CO2 and thus provide a solution to a dilemma in the arguments on the role of reduced carbon in the origin of life.

Xenon-sensitized photolysis of hydrogen sulphide and ethane

Abstract The xenon-sensitized photolysis of hydrogen sulphide and ethane has been performed. The rate constant of the excitation transfer from the Xe(3P1) resonance state to hydrogen sulphide and ethane has been measured to be 3 × 10−10 and 4 × 10−10 cm3-molec−1 S−1. On the basis of the dependence of the hydrogen quantum yield on the xenon pressure at different hydrogen sulphide and ethane pressures the three-body decay of the Xe(3P1) state with xenon atoms and hydrogen sulphide or ethane taking a part in the process has been experimentally shown to have a rate constant of approximately 1 × 10−28 cm6 molec−2 S−1. Using Collins-Lee theory confirms the reliability of this high value.

Model systems for photocatalytic water reduction: role of pH and metal colloid catalysts

Model systems for the photocatalyzed water reaction which explains the role of a sacrifical organic electron donor to drive the series of reactions leading to hydrogen production have been proposed. Studies which clarify the role of pH, mediator potential and EDTA oxidation rate in such systems where metal colloid catalysts such as tin(bipyridyl) ruthenium (II) are used to catalyze the photoreduction of water are reported. An optimum pH of 6 to 7 was observed for the hydrogen quantum yield. A series of homologous electron-transfer quencher mediators listed in a table were synthesized and characterized for use in the H/sub 2/-generation system. All the mediators efficiently quenched the ruthenium excited state; and after the electron-transfer properties of the mediators had been characterized, the effect of the driving force on H/sub 2/ yield was studied. A clean linear yield relationship betwen quantum yield of hydrogen and driving forces for water reduction was observed. The same pH dependence of H/sub 2/ rate was seen in an electrochemical system in which neither amine nor ruthenium was present as with the ruthenium complex present. The rate of EDTA reduction decreased over 200 fold between pH7 and pH4. (BLM)

The photolysis of tetrahydrofuran and of some of its methyl derivatives at 185 nm

The uv photolysis of tetrahydrofuran, 1, 2-methyltetrahydrofuran, 2, cis-2,5-dimethyltetrahydrofuran, 3, trans-2,5-dimethyltetrahydrofuran, 4, and 2,2,5,5-tetramethyltetrahydrofuran, 5, has been investigated by product analysis in the liquid phase, and quantum yields have been determined. The photolysis of tetrahydrofuran itself was also studied in the gas phase at pressures ranging from 1 to 120 atm (pressurizing gas N2); and very little difference was found between the photolytic behaviour of the vapour at 120 atm and that of the liquid. The major products are in ail cases the cyclopropanes and the corresponding carbonyl compounds, as well as the olefinic alcohols and the carbonyl compounds that are isomeric with the starting material. These products are considered to be formed by the two major primary processes [i] and [ii].[Formula: see text]The cyclopropanes formed in reaction [i] retain some excess energy (apparently more than is needed to realize the trimethylene form), and in the photolysis of tetrahydrofuran vapour the hot cyclopropane rearranges to a considerable extent into propene. The propene to cyclopropane yield ratio falls strongly with increasing pressure, to a value of 0.065 at 120 atm. A similar value is observed in the liquid phase photolysis.The five-membered oxyl alkyl diradical from reaction [ii] is the likely intermediate in the cis-trans photoisomerization that is observable with the 2,5-dimethyltetrahydrofurans [Formula: see text]. The photolysis of these compounds also demonstrates that steric factors have a strong bearing on the course of the reaction, e.g. the quantum yield of methylcyclopropane from the cis compound is 0.22, vs. 0.08 from the trans compound.Molecular hydrogen is produced if the tetrahydrofurans carry hydrogen in α-position. Its production is enhanced if the α-position is shared with a methyl group (1 gives a hydrogen quantum yield of 0.07, 2 of 0.17, 3 of 0.27, 4 of 0.29, and 5 of zero).

Vacuum ultraviolet photolysis of hydrogen sulphide

A kinetic study of the vacuum ultraviolet photolysis of hydrogen sulphide at 147 nm is presented. The decomposition paths of hydrogen sulphide have been investigated using hydrogen atom scavengers (C2H4 and C4H6). The quantum yield of hydrogen has been measured to be 1.03 ± 0.03. Formation of radicals and hydrogen atoms is shown to be the major path of decomposition with a quantum yield of 0.99 ± 0.02 hv+ H2S → HS + H. (3)

Isotope effects in the photolysis of methanethiol

Quantum yields for the formation of hydrogen and methane in the photolysis of partially deuterated methanethiol (CH 3SD) have been measured at 185 and 254 nm. The sum of the quantum yields of these two products is unity, independent of thiol pressure, at both wavelengths. Adding n-butane or perfluorodimethylcyclobutane causes an increase in the hydrogen quantum yield, a decrease in the methane quantum yield, but no change in the sum of the two. These results are interpreted in terms of a hot atom mechanism involving cleavage of the CS and SD bonds in the parent molecule. Compared with earlier work using CH 3SH, replacing H by D causes a significant increase in the probability of CS cleavage suggesting that the photodissociation process is strongly influenced by the masses of the two species attached to the central sulfur atom.