Photoinduced Hydrogen Production Research Articles

A computational study photophysical properties of a series phenothiazine-linked-BODIPY as D-D-π-a photosensitizer unit for photo-induced hydrogen production from water

Phenothiazine-derivatives are designed as sensitizers which covalently-linked with BODIPY for application in a system of dye-sensitized photoelectrochemical cells (DSPECs). A series of phenothiazine-linked-BODIPY as D-D-π-A chromophore have been investigated by a computational approach for studying the capability of the photosensitizers for application in photoinduced water splitting hydrogen production in DSPECs. The geometries of sensitizers at the ground state and excited state were optimized by the CAM-B3LYP/6-31G (d,p) level method. The theoretical study has been done in order to investigate the photophysical properties such as absorption profile, HOMO-LUMO energy and surface plots of the photosensitizer. The result of calculation for HOMO-LUMO energy level of each dyes showed that the LUMO energy are ranging more than -2.8 - (-2.86) eV which is higher than -4.0 eV of conduction band of TiO2 as semiconductor in DSPEC, meaning that all these dyes could be used as photosensitizers in DSPECs. In addition, the oscillator strength data of each dyes showed the dyes have absorption profile in visible region, meaning the dyes could harvest higher intensity of sunlight to induce water splitting reaction to produce hydrogen.

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

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

Engineered MoxC/TiO2 interfaces for efficient noble metal-free photocatalytic hydrogen production

Photoinduced hydrogen production is a promising green strategy to store the power from the Sun as chemical energy. One major challenge is to obtain efficient photocatalytic systems without employing noble metals. In this contribution we combine different shape-controlled bipyramidal or nano-sheet anatase TiO2 nanoparticles, preferentially exposing {101} or {001} facets, and MoxC as co-catalyst to realize noble metal-free photocatalysts. The effect of TiO2 morphology on the functional properties and efficiency of the final composite materials in the photocatalytic H2 production is carefully assessed combining powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, photoluminescence, transient photocurrent and electrochemical impedance spectroscopy. Engineered MoxC/TiO2 interfaces, which exploit the superior reducing ability of the anatase (101) surface, result to be particularly active in the photocatalytic H2 production from ethanol aqueous solutions.

2.2]‐ and [3.3]Paracyclophane as Bridging Units in Organic Dyads for Visible‐Light‐Driven Dye‐Sensitized Hydrogen Production

Novel donor-acceptor dyads containing [2.2]- and [3.3]paracyclophane (PCP) as the bridging moiety were synthesized and used to effectively fabricate dye-sensitized hydrogen production systems. All the prepared compounds had a phenothiazine and a cyanoacrylic acid/pyridinyl acrylonitrile moiety acting as an electron donor and acceptor, respectively. Although cyclic voltammetry measurements showed similar electron-donating properties among all the synthesized dyads, the lowest absorption energy of the [2.2]PCP moiety was lower than that of the [3.3]PCP one; this was due to its shorter distance between benzene rings, which could effectively drive the charge transfer between the donor and acceptor chromophores. Under visible light (>395 nm), a dyad-loaded photocatalyst in a 0.5 M aqueous glycerol solution generated detectable hydrogen gases. The optimal turnover number and photocurrent order exhibited the same trend as the hydrogen production rate since the suggested number of excited photons played a critical role in hydrogen production.

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Photoinduced energy transfer in truxene-linked zinc porphyrin–fullerene-corrole tetrad and its application in triplet−triplet annihilation upconversion

Triplet photosensitizers (PSs) have attracted widespread interest due to their application in photocatalytic organic reactions, photodynamic therapy (PDT), photoinduced hydrogen production from water splitting, and triplet–triplet annihilation (TTA) upconversion. Herein, the triad T-P-Co and tetrad T-C60-P-Co were synthesized, characterized, and applied in triplet–triplet annihilation (TTA) upconversion. The photophysical processes were investigated with steady-state UV–visible absorption and fluorescence spectroscopies, nanosecond time-resolved transient absorption spectroscopy and electrochemical characterization. T-P-Co and T-C60-P-Co show efficient intramolecular singlet–singlet energy transfer from the porphyrin moiety to corrole/fullerene moiety. The energy transfer efficiency is nearly 100% for T-P-Co and 69.4% for T-C60-P-Co, respectively. Electrochemical investigation shows that the photo-induced intramolecular electron transfer of the excited triad T-P-Co and tetrad T-C60-P-Co is thermodynamically prohibited in toluene due to the positive ΔGCS for charge-separation. Nanosecond time-resolved transient difference absorption spectra indicate that the triplet excited states of T-P-Co and T-C60-P-Co are both distributed on the corrole moiety. The triplet lifetimes of T-P-Co and T-C60-P-Co are 86.9 μs and 73.3 μs, respectively. The triad T-P-Co and tetrad T-C60-P-Co were used as triplet photosensitizers for TTA upconversion, and upconversion quantum yields of 0.76% and 0.84% were observed, respectively.

Photocatalytic activity of the light-harvesting complex of photosystem II (LHCII) monomer

Light-harvesting complex of photosystem II (LHCII) is the most abundant membrane protein-chlorophyll complex in chloroplasts. Here, we evaluated the photocatalytic activity of the native trimer and the enzymatically treated monomer forms of LHCII. Upon white light irradiation using a solar simulator, photocatalytic reduction of methylviologen revealed that the activity of monomeric LHCII was higher than that of the trimer form. Fluorescence of the monomeric LHCII was more significantly quenched by methylviologen than that of the trimer form. In the presence of Pt nanoparticles in a catalytic solution system, photoinduced hydrogen production was observed for the LHCII monomer. The difference in photocatalytic activities of LHCII trimer and monomer are briefly discussed in terms of an interaction between LHCII and methylviologen.

Efficient Light-Driven Hydrogen Evolution Using a Thiosemicarbazone-Nickel (II) Complex.

In the following work, we carried out a systematic study investigating the behavior of a thiosemicarbazone-nickel (II) complex (NiTSC-OMe) as a molecular catalyst for photo-induced hydrogen production. A comprehensive comparison regarding the combination of three different chromophores with this catalyst has been performed, using [Ir(ppy)2(bpy)]PF6, [Ru(bpy)3]Cl2 and [ZnTMePy]PCl4 as photosensitizers. Thorough evaluation of the parameters affecting the hydrogen evolution experiments (i.e., concentration, pH, solvent nature, and ratio), has been performed in order to probe the most efficient photocatalytic system, which was comprised by NiTSC-OMe and [Ir(ppy)2(bpy)]PF6 as catalyst and chromophore, respectively. The electrochemical together with the photophysical investigation clarified the properties of this photocatalytic system and allowed us to propose a possible reaction mechanism for hydrogen production.

Revealing high hydrogen evolution activity in zinc porphyrin sensitized hierarchical porous TiO2 photocatalysts

In this work, a dye/TiO2 system for hydrogen generation via the reduction of water has been investigated. The use of simple and template free synthesis process for hierarchical porous architecture of TiO2 (HPT) with a panchromatic Zinc-porphyrin (LG5) sensitizer has been identified as the potential material in photoinduced hydrogen production. The effect of the dye absorbed by the Pt-HPT has been tested for the hydrogen production under visible light irradiation in presence of triethanolamine (TEOA) or Glycerol (Gly) as sacrificial electron donor (SED). The enhanced activity and effective charge transfer from the dye to the TiO2 molecule is significant in the PHPT-LG5 composite. The PHPT-LG5 catalyst exhibited higher photocatalytic activity of 4196 μmol g−1 h−1 with an impressive turnover numbers (TON) of 8392 and apparent quantum yield (AQY) of 7.43% of light irradiation using 450 W Xe lamp when compared to the corresponding simple semiconductor as well as the N719 dye loaded catalysts. The acrylic group present in the dye molecule helps in binding the semiconductor with the dye molecule and leads to superior photocatalytic activity. The diffuse reflectance spectroscopy (DRS), and computational studies of the dye molecule and the composite suggests the better photocatalytic performance of the composite. The Fourier Transform Infra-Red Spectroscopy (FTIR) studies reveals the strong attachment of the dye molecule with the semiconductor hierarchical porous TiO2 (HPT) results in the enhancement in hydrogen production, the stability tests of the photocatalyst shows higher reproducibility at neutral pH in TEOA. A systematic study of LG5 with sacrificial electron donors and pH were performed and are correlated with the photocatalytic activity of N719 dye. The presence of the cyanoacrylic group as an anchoring group in the LG5 leads to red shift in S and Q bands suggesting the efficient intramolecular charge transfer behavior (CT) and possess strategies for broadening the light harvesting properties. The present work opens up a new window toward solar energy conversion with extended light harvesting capacity and enhanced photocatalytic activity.

Exploration of CeO2-CuO Quantum Dots in Situ Grown on Graphene under Hypha Assistance for Highly Efficient Solar-Driven Hydrogen Production.

The development of an artificial model of photoinduced hydrogen production system requires efficient, long-term stability and cost-competitive photocatalysts to store solar energy in chemical bonds. However, the existing photocatalysts still suffer from the high cost, high recombination rate of photoexcited electron-hole pairs, and poor photostability. Herein, we demonstrate the synthesis of a p-type CuO/n-type CeO2 heterojunction in situ grown on graphene via a hypha assistance process. Amazingly, optical and photoelectrochemical measurements show the superiority of this hierarchically biomorphic structure. The observed H2 evolution rate of the CeO2-CuO quantum dots/graphene has reached 2481 μmol·h-1·g-1 and remains unchanged in four hydrogen production cycles. Considering the convenience of microbial culture, this heterostructure system has great potential as a photocatalyst for solar-fuel conversion.

Temperature dependence of photoinduced hydrogen production and simultaneous separation in TiO2 nanotubes/palladium bilayer membrane

Temperature dependence of photoinduced hydrogen production and simultaneous separation was examined in a bilayer membrane comprised by an anodized TiO2 nanotube array (TNA) and a palladium layer. This membrane was fabricated by transferring a TNA embedded in a titanium sheet onto an electroless-plated palladium film. Sacrificial water splitting with methanol was photocatalytically performed under ultraviolet (UV) irradiation and only generated hydrogen gas was concurrently separated with the Pd layer. The H2 production rate (rH2) with the membrane at various temperatures was evaluated by using a home-made characterization system. The measured rH2 showed larger values at higher temperature of the membrane and increased abruptly after several hours of UV irradiation. This inflection behavior appeared earlier at the higher temperature of the membrane, which can be related to the permeation and adsorption characteristics of hydrogen in the Pd layer.

Multiple exciton generation for photoelectrochemical hydrogen evolution reactions with quantum yields exceeding 100%

Multiple exciton generation (MEG) in quantum dots (QDs) has the potential to greatly increase the power conversion efficiency in solar cells and in solar-fuel production. During the MEG process, two electron–hole pairs (excitons) are created from the absorption of one high-energy photon, bypassing hot-carrier cooling via phonon emission. Here we demonstrate that extra carriers produced via MEG can be used to drive a chemical reaction with quantum efficiency above 100%. We developed a lead sulfide (PbS) QD photoelectrochemical cell that is able to drive hydrogen evolution from aqueous Na2S solution with a peak external quantum efficiency exceeding 100%. QD photoelectrodes that were measured all demonstrated MEG when the incident photon energy was larger than 2.7 times the bandgap energy. Our results demonstrate a new direction in exploring high-efficiency approaches to solar fuels. Multiple exciton generation has been shown to improve the performance of quantum-dot-based solar cells. Yan et al. now apply it to photoinduced hydrogen production and present a system using PbS quantum-dot photoelectrodes that yields an external quantum efficiency of over 100%.

Understanding the Structural and Electronic Effect of Zr4+-Doped KNb(Zr)O3 Perovskite for Enhanced Photoactivity: A Combined Experimental and Computational Study

Herein, for the first time we report the synthesis of a series of compositionally tunable Zr-doped novel KNb(Zr)O3 perovskites using green and facile methodology and their superior photocatalytic activities toward photoinduced hydrogen production and dye degradation. The substitutional doping of Zr(IV) in place of Nb(V) leads to a decrease in the electronic band gap by inclusion of a new acceptor level near the valence band. The results on the optimally doped perovskite for the photocatalytic hydrogen evolution reaction reveal that the 20 mol % Zr-doped KNb(Zr)O3 is 13 times more efficient as compared to the pristine KNbO3 in terms of rate of H2 evolution. The same nanocomposite is shown to exhibit 12-fold greater photocatalytic efficiency for degradation of Rhodamine B (RhB) (up to 83% after 210 min) than pure KNbO3. Density functional theory calculations are carried out to understand the Zr doping effect on the electronic structure as well as the surface hydrogen evolution reaction. Overall, an optimize...

A nickel phosphotungstate catalyst for efficient visible-light-driven H2 evolution from water splitting in a noble-metal-free system

A simply as-prepared nickel phosphotungstate complex was used as a carbon-free homogeneous catalyst for the H2 evolution from water splitting under visible light irradiation (λ ≥ 400 nm). Its catalytic activity, the rate of the H2 evolution about 237 μmol h−1, was much higher than those of the Ni2+ ions and cobalt phosphotungstate complex. Spectroscopic studies suggested that the Ni2+ ions could react with Na8HPW9O34 to form a complex with a unique double-sandwich structure in the as-prepared sample. And the electrochemical experimental results revealed that it possessed two satisfactory redox potentials, which were in favor of the electrons transfer in our photoinduced hydrogen production system. Furthermore, the electron-transfer steps for the H2 evolution from water splitting in the present system were investigated in detail. On the basis of the luminescence analysis results, it was found that the reductive quenching pathway was dominant for the photosensitizer in the present system.

Cobalt(III) tetraaza-macrocyclic complexes as efficient catalyst for photoinduced hydrogen production in water: Theoretical investigation of the electronic structure of the reduced species and mechanistic insight

We recently reported a very efficient homogeneous system for visible-light driven hydrogen production in water based on the cobalt(III) tetraaza-macrocyclic complex [Co(CR)Cl2]+ (1) (CR=2,12-dimethyl-3,7,11,17-tetra-azabicyclo(11.3.1)-heptadeca-1(17),2,11,13,15-pentaene) as a noble metal-free catalyst, with [RuII(bpy)3]2+ (Ru) as photosensitizer and ascorbate/ascorbic acid (HA−/H2A) as a sacrificial electron donor and buffer (PhysChemChemPhys 2013, 15, 17544). This catalyst presents the particularity to achieve very high turnover numbers (TONs) (up to 1000) at pH 4.0 at a relative high concentration (0.1mM) generating a large amount of hydrogen and having a long term stability. A similar activity was observed for the aquo derivative [CoIII(CR)(H2O)2]3+ (2) due to substitution of chloro ligands by water molecule in water. In this work, the geometry and electronic structures of 2 and its analog [ZnII(CR)Cl]+ (3) derivative containing the redox innocent Zn(II) metal ion have been investigated by DFT calculations under various oxidation states. We also further studied the photocatalytic activity of this system and evaluated the influence of varying the relative concentration of the different components on the H2-evolving activity. Turnover numbers versus catalyst (TONCat) were found to be dependent on the catalyst concentration with the highest value of 1130 obtained at 0.05mM. Interestingly, the analogous nickel derivative, [NiII(CR)Cl2] (4), when tested under the same experimental conditions was found to be fully inactive for H2 production. Nanosecond transient absorption spectroscopy measurements have revealed that the first electron-transfer steps of the photocatalytic H2-evolution mechanism with the Ru/cobalt tetraaza/HA−/H2A system involve a reductive quenching of the excited state of the photosensitizer by ascorbate (kq=2.5×107M−1s−1) followed by an electron transfer from the reduced photosensitizer to the catalyst (ket=1.4×109M−1s−1). The reduced catalyst can then enter into the cycle of hydrogen evolution.

Photoinduced hydrogen production with photosensitization of Zn chlorophyll analog dimer as a photosynthetic special pair model

Zinc chlorophyll a derivatives were synthesised for use as photosensitizers. Herein, we report a system for photoinduced hydrogen production with colloidal platinum via photoreduction of methylviologen (MV2+) using the photosensitization of a Zn pyropheophorbide a (ZnPyOH) dimer connected by lysine (ZnPy-K(ZnPy)OH) as a special pair model in the photosynthetic reaction centre in the presence of NADPH as an electron donor.

Protein secondary-shell interactions enhance the photoinduced hydrogen production of cobalt protoporphyrin IX.

Hydrogen is an attractive fuel with potential for production scalability, provided that inexpensive, efficient molecular catalysts utilizing base metals can be developed for hydrogen production. Here we show for the first time that cobalt myoglobin (CoMyo) catalyzes hydrogen production in mild aerobic conditions with turnover number of 520 over 8 hours. Compared to free Co-protoporphyrin IX, incorporation into the myoglobin scaffold results in a 4-fold increase in photoinduced hydrogen production activity. Engineered variants in which specific histidine resides in proximity of the active site were mutated to alanine result in modulation of the catalytic activity, with the H64A/H97A mutant displaying activity 2.5-fold higher than wild type. Our results demonstrate that protein scaffolds can augment and modulate the intrinsic catalytic activity of molecular hydrogen production catalysts.

Porphyrin-cobaloxime dyads for photoinduced hydrogen production: investigation of the primary photochemical process

Three porphyrin-cobaloxime dyads, suitable for application in photoinduced hydrogen generation with sacrificial donors, are characterized by ultrafast spectroscopy in order to clarify the primary photochemical events.

ChemInform Abstract: Triplet Photosensitizers: From Molecular Design to Applications

AbstractReview: 248 refs.

Observation of an Intermediate Band in Sn-doped Chalcopyrites with Wide-spectrum Solar Response

Nanostrcutured particles and polycrystalline thin films of Sn-doped chalcopyrite are synthesized by newly-developed methods. Surprisingly, Sn doping introduces a narrow partially filled intermediate band (IB) located ~1.7 eV (CuGaS2) and ~0.8 eV (CuInS2) above the valance band maximum in the forbidden band gap. Diffuse reflection spectra and photoluminescence spectra reveal extra absorption and emission spectra induced by the IBs, which are further supported by first-principle calculations. Wide spectrum solar response greatly enhances photocatalysis, photovoltaics, and photo-induced hydrogen production due to the intermediate band.