Maximum Hydrogen Evolution Rate Research Articles

Nano Anatase TiO2 Quasi-Core-Shell Homophase Junction Induced by a Ti3+ Concentration Difference for Highly Efficient Hydrogen Evolution.

The fabrication of heterojunctions or homojunctions between semiconductors is a controllable strategy to facilitate charge separation in photocatalysis. The homophase junctions exhibit atomic-level contact for the fast-speed charge transfer via inducing the built-in electric fields. Herein, a new concept of TiO2 quasi-core-shell homophase junction induced by a Ti3+ concentration difference for remarkably enhancing photocatalytic activity is proposed. Nano anatase TiO2 quasi-core-shell homophase junctions are constructed between the interior with high Ti3+ concentration (quasi-core) and the surface with no detected Ti3+ (quasi-shell). Diverse Ti3+ concentration differences are obtained via regulating the mass ratio of the Ti source. The nano anatase TiO2 quasi-core-shell homophase junctions exhibit improved photocatalytic hydrogen evolution compared with commercial anatase nanoparticles. To be specific, the maximum hydrogen evolution rate of 50.02 mmol/h/g is 25.4 times superior to that of commercial anatase nanoparticles under solar illumination. Besides, the photocatalytic activity remains stable (H2 evolution rate of 49.21 mmol/h/g, activity loss of <2%) after five cycles of catalytic test. The promoted photocatalytic activities are ascribed to the constitution of a built-in electrical field between the quasi-shell and quasi-core induced by the band bending, which accelerates the spatial charge separation and suppresses the recombination of carriers. Moreover, the atomic-level contact at the homophase junction interface provides smooth channels for carrier transfer, resulting in more effective separation and transfer of photogenerated electrons and holes. The synthesis of nano anatase TiO2 quasi-core-shell homophase junctions provides new insights into the efficient separation and transfer of photogenerated carriers for photocatalytic applications.

One-step fabrication of highly self-hydroxylated TiO2 mesocrystals and photocatalytic behavior towards water splitting

TiO2 mesocrystals have been considered as an efficient photocatalyst due to the effective charge transport. Introducing hydroxyls in TiO2 is respected to reduce the energy barrier of hydrogen formation. Herein, a simple one-step fabrication of highly self-hydroxylated TiO2 mesocrystals (MCs) for enhancing photocatalytic hydrogen evolution is proposed. TiO2 single crystals (SCs), polycrystals (PCs) and MCs are obtained via regulating the pH of the precursor during hydrothermal treatment. Results indicate that the moderate alkaline condition is favorable for the synthesis of highly self-hydroxylated TiO2 MCs. Compared with SCs, PCs and commercial P25 TiO2 nanoparticles, MCs exhibit the best photocatalytic activity in H2 evolution. Specifically, the maximum hydrogen evolution rate under solar light illumination (22.8 mmol/h/g) is 10.5 times higher than that of P25. Moreover, the MCs exhibit excellent catalytic stability and the hydrogen evolution rate can be maintained at 20.8 mmol/h/g under solar illumination after five cycles of reactions. The highly self-hydroxylated TiO2 MCs are constructed from crystallographically oriented nanocrystals with abundant hydroxyls. The unique superstructure and large surface area of MCs enable the effective charge separation and transport. Moreover, the high density of hydroxyls can reduce the recombination rate of photo-generated free charges and energy barrier for hydrogen formation while facilitate light absorption. The synthesis of highly self-hydroxylated TiO2 MCs and the underlying mechanism offer interesting insights for modifying the structure and properties of TiO2 towards high-performance hydrogen evolution.

Rational regulation of transition metals in polyoxometalate hybrids without noble metal assistance for efficient light-driven H2 production.

Four new rationally designed polyoxometalate (POM)-based hybrids are reported with a maximum photocatalytic hydrogen evolution rate of 12245.59 μmol g-1 h-1, which outperform all known POM-based metal-organic photocatalysts.

High‐Efficiency Photocatalysis of Self‐Hydroxylated TiO2 Nanocrystals for Water Splitting

AbstractHerein, a facile and controllable strategy to synthesize self‐hydroxylated TiO2 nanocrystals with promoted photocatalytic activity in hydrogen evolution is demonstrated. Various colors (yellow, light yellow, blueish gray and gray) in appearance are induced by controlling the molar ratio of titanium source to oxidant during the hydrothermal treatment. Compared with commercial P25 TiO2 nanoparticles, the as‐obtained self‐hydroxylated TiO2 nanocrystals exhibit better photocatalytic performance in H2 evolution. Specifically, the maximum hydrogen evolution rate under solar light illumination (10.0 mmol/h/g) is 4.6 times superior to that of P25. The characterization results confirm the presence of abundant hydroxyls resulting from the hydrothermal treatment, which decreases the recombination rate of carriers and the energy barrier of hydrogen formation while facilitates light absorption for promoting photocatalytic performance.

Pyrene-alt-dibenzothiophene-S,S-dioxide copolymers for highly efficient photocatalytic hydrogen production: The role of linking pattern

Two analogous positional polymers P16PySO and P27PySO have been synthesized via the copolymerization from dibenzothiophene-S,S-dioxide and pyrene building blocks. The effect of the linking pattern on the molecular packing, photophysical and photocatalytic properties of the two isomers was investigated. It was interestingly found that a minor change at the substitution position of pyrene unit was demonstrated to largely influence the photocatalytic properties of the two isomers. P16PySO exhibited an encouraging average hydrogen evolution rate (HER) of 619.5 μmol h−1 and the maximum HER of 774 μmol h−1, much higher than that of 2,7-counterpart with a moderate rate of 282 μmol h−1. The increased photocatalytic activity of P16PySO is mainly ascribed to its more ordered molecular packing, broader absorption region, better wettability, and higher photo-generated charge mobilities. Moreover, the optimum HER was increased from 774 to 1013 μmol h−1 when the amount of the photocatalyst P16PySO was increased from 50 to 100 mg, which is among the top solar-to‑hydrogen conversion efficiencies reported so far for the polymeric photocatalysts.

Photocatalytic H2 evolution on graphdiyne/g-C3N4 hybrid nanocomposites

Hydrogen is considered an ideal alternative energy source to replace fossil energy. Herein, a novel graphdiyne (GD)/graphitic carbon nitride (g-C3N4) nanocomposite was successfully synthesized via a facile calcination approach, and display excellent H2-generation performance under visible light. When the mass ratio of GD reaches 0.5 wt% in GD/g-C3N4 nanocomposite, it shows a maximum hydrogen evolution rate, exceeding that of g-C3N4 by 6.7-fold. After systematic characterization, a new CN bond is confirmed to form between GD and g-C3N4 following heat treatment, and this bond serves as a charge carrier channel that facilitates the migration of photogenerated electrons from g-C3N4 to GD. Positive effects, such as a prolonged photogenerated charge carrier lifetime, intensified electron density, decreased reaction overpotential and improved charge carrier mobility, also contribute to the enhanced photocatalytic performance of the nanocomposites. The proposed technique provides a promising approach for modifying photocatalysts in future applications.

Bimetallic metal–organic frameworks-derived mesoporous CdxZn1−xS polyhedrons for enhanced photocatalytic hydrogen evolution

Abstract

In-situ construction of coral-like porous P-doped g-C3N4 tubes with hybrid 1D/2D architecture and high efficient photocatalytic hydrogen evolution

Developing novel methods to prepare hollow one-dimensional (1D) carbon nitride (g-C3N4) nanostructure is highly attractive in photocatalytic water splitting for hydrogen production. Herein, a simple, self-assembly synthesis of coral-like 3D porous P-doped g-C3N4 tubes (PCNT) by the combination of pyrolysis and freeze-drying method was reported. Attributed to the integrated merits of 1D tubular structure, 2D nanosheets and phosphorus doping, the as-prepared hollow PCNT exhibits superior photocatalytic activity under visible light irradiation. Owing to their higher specific surface area, enhanced light absorption, and better charge carrier separation and transfer, the maximum apparent photocatalytic hydrogen evolution rate of PCNT is 2020 μmol g−1 h−1, which is about 4.7 folds and 22.4 folds than that of g-C3N4 tubes and pristine bulk g-C3N4, respectively. Moreover, a possible photocatalytic mechanism and nanostructure formation process based on the experimental results are proposed. The novel growth strategy developed here may offer a new avenue for the rational design and synthesis of potentially efficient photocatalyst with 1D/2D integrated nanoarchitecture.

Halloysite nanotube-based cobalt mesocatalysts for hydrogen production from sodium borohydride

We report the novel hybrid metal-clay mesocatalysts with halloysite nanotubes as carriers and cobalt as catalytic metal for hydrogen production from sodium borohydride. The ligand assisted metal adsorption on the surface of halloysite and intercalation into nanotubes was achieved using azines or silane. The catalyst with pre-formed cobalt oxide nanoparticles adsorption on the pristine halloysite surface showed low catalytic efficiency. The most active cobalt-containing system was formed using ketazine as the ligand. The chelating agent selection strongly affected the hydrogen evolution process and was optimized. The best halloysite based core-shell mesocatalyst contained 16 wt% of cobalt with maximum hydrogen evolution rate of 3 L/min×g(cat).

Improved performance of tri-doped photocatalyst SrTiO3:Rh/Ta/F for H2 evolution under visible light irradiation

A photocatalyst for visible light irradiation was prepared by simultaneously doping SrTiO3 with F− anion and Rh3+ and Ta5+ cations for the first time through a spray pyrolysis process. The ternary doping of F− contributed to the reduction of Ti4+ and Rh4+ to Ti3+ and Rh3+, respectively, by generating extra electron in the lattice. The partially substituted structure of the photocatalyst could be expressed as Sr(Ti4+1−2x−zTi3+zRh3+x−yRh4+yTa5+x)(O2−3−wF−w). The doping of F− into SrTiO3:Rh/Ta increased the photocatalytic hydrogen evolution rate to 4123.7 μmol g−1 h−1 (quantum efficiency: 6.60%) under visible light irradiation, which was 1.93 times higher than that of SrTiO3:Rh/Ta. The optimum composition of dopants for maximum hydrogen evolution rate was Rh (0.15 mol%), Ta (0.15 mol%), and F (6.0 mol%).

Overexpressing F0/F1 operon of ATPase in Rhodobacter sphaeroides enhanced its photo-fermentative hydrogen production

The effect of atp genes overexpression in Rhodobacter sphaeroides HY01 on the amount of ATP, nitrogenase activity and hydrogen production were studied. The ATP content of ZTHF0 (F0 operon+), ZTHF1 (F1 operon+) and ZTHFF (F0 operon+, F1 operon+) was 6.5 ± 0.2 nmol/mL, 7.6 ± 0.2 nmol/mL and 8.3 ± 0.3 nmol/mL, respectively, which enhanced by 20.3%, 40.7%, and 53.7% compared with that of the control strain ZTH (pRK415+), respectively. However, the nitrogenase activities of ZTHF0, ZTHF1 and ZTHFF were 35.8 ± 0.5 nmol acetylene/(min·mg-dcw), 40.1 ± 0.7 nmol acetylene/(min·mg-dcw) and 29.3 ± 0.7 nmol acetylene/(min·mg-dcw), respectively, which increased by 18.2%, 32.3% and 0% compared with that of ZTH, respectively. The expression level of atp genes by real-time PCR showed that ZTHF0 or ZTHF1 only enhanced the expression of F0 operon or F1 operon, respectively, and ZTHFF enhanced the expression of both F0 and F1 operons. At the 5000 ± 200 lux with 10 mL culture, the hydrogen yields of ZTHF0 and ZTHF1 were 7636 ± 59 mL/L-culture and 8458 ± 76 mL/L, which increased by 10.5% and 27.8% compared with that of the control strain, respectively. Moreover, the maximum hydrogen evolution rate of ZTHF0 and ZTHF1 were 94.5 ± 4.1 mL/(Lh) and 103.1 ± 5.0 mL/(Lh), which enhanced by 15.4% and 20.6% compared with that of the control strain, respectively. The results suggested that overexpressing F0 operon or F1 operon could improve ATP content and hydrogen production performance in R. sphaeroides.

Sonochemical synthesis of Cd1−xZnxS solid solutions for application in photocatalytic reforming of glycerol to produce hydrogen

A simple sonochemical method for the preparation of Cd1−xZnxS solid solutions was successfully applied. The sonochemical method has shown to be fast, with low energy demand and allowed to obtain nano-sized particles. The obtained materials were characterized by XRD, EDX, SEM and DRS UV/vis. The Pt-loaded photocatalysts were evaluated in photoinduced reforming of glycerol under visible light irradiation (λ > 418 nm). Pure CdS and solid solutions obtained by sonochemical method have shown photocatalytic activity with respect to hydrogen gas production. The maximum hydrogen evolution rate achieved was 239 μmol g−1 h−1, when the solid solution Cd0.6Zn0.4S contaminated with γ-Zn(OH)2 was irradiated with visible light.

Preparation and Characteristics of Novel Cobalt Oxide Catalysts for Hydrogen Generation from Metal Borohydride Solution

AbstractFor the first time, a high performance cobalt oxide catalyst for hydrogen generation has been developed in a cost-effective way. The novel cobalt oxide catalyst was prepared by microwave-assisted thermal oxidation of cobalt metal. Microwave heating produced cobalt oxide from cobalt metal powder within 10 min through oxidation and consolidation simultaneously. An as-synthesized cobalt oxide catalyst (a centimeter-sized chip) has revealed high activity for the catalytic hydrolysis of sodium borohydride (NaBH4) showing a maximum hydrogen evolution rate of 6,000 mL/min-g from an aqueous solution containing 20 wt% of NaBH4+5 wt% of sodium hydroxide (NaOH) under room temperature. Furthermore, a powder sample of cobalt oxide showed a maximum hydrogen evolution rate of 13,412 mL/min-g under the same conditions as above. The hydrogen evolution rates were affected by temperature and concentrations of NaBH4 and NaOH as well as the amount of the cobalt oxide catalyst. Based on X-ray photoelectron spectrosc...

Hydrogen extraction characteristics of high-temperature proton conductor ceramics for hydrogen isotopes purification and recovery

To develop high-efficiency and economical hydrogen isotope purification and recovery processes for a tritium extraction system in a fusion reactor, hydrogen extraction characteristics of an electrochemical hydrogen pump using high-temperature proton conductors were studied. The driving forces of hydrogen transportation in the proton conductors are electric potential difference, which can extract hydrogen isotopes selectively from a solid breeder blanket purge gas with low-pressure hydrogen isotope gas. In the experiments, a one-end closed tube made of proton-conducting ceramic CaZr0.9In0.1O3−α (effective electrode area: 160cm2) was developed because of its high chemical stability, mechanical strength, and durability in a series of perovskite-type proton conductors. The hydrogen pumping characteristics were evaluated over the temperature range from 923K to 1073K by extraction of 664–1200ppm H2 balanced with He, H2 was selectively extracted from and the mixture of He and H2 at the rate of Faraday's Law under an applied voltage of 3.5V DC. In the case of He with 0.12% H2 at 1023K and at 1.15V DC, the maximum hydrogen evolution rate was 0.12ml/min, the hydrogen recovery efficiency was more than 99%, suggesting the extraction of hydrogen could be operated with a current efficiency close to unity. The possible application of hydrogen pumps for the TES of CIPITISE at CIAE has been estimated.

Effects of F for enhancement of H2 evolution on visible-light-driven photocatalyst of SrTiO3:Cr/Ta/F prepared by spray pyrolysis

Both anion (F−) and cation (Cr3+/Ta5+) doping were conducted simultaneously to prepare tri-doped photocatalyst, SrTiO3:Cr/Ta/F, by spray pyrolysis from aqueous precursor solutions. The ternary doping of F− ion into SrTiO3:Cr/Ta increased the hydrogen evolution rate up to 3887.9 μmol g−1 h−1 (quantum efficiency: 6.22%) under visible light irradiation, which was 1.84 times higher than that over SrTiO3:Cr/Ta. The optimum contents of dopants for the maximum hydrogen evolution rate were Cr (0.1 mol%), Ta (0.1 mol%) and F (6.0 mol%), respectively. The ternary doping of F− ion contributed to the reduction of Ti4+ and Cr6+ ions to Ti3+ and Cr3+ ions, respectively, by the generation of extra electrons in the lattice. The partially substituted structure of the photocatalyst could be expressed as Sr(Ti4+1−2x−zTi3+zCr3+x−yCr6+yTa5+x)(O2−3−wF−w).

Photocatalytic H2 evolution on a novel CaIn2S4 photocatalyst under visible light irradiation

A novel visible-light-driven photocatalyst CaIn2S4 was synthesized using a facile hydrothermal method followed by a post-calcination process. The influence of the calcination temperature and time on the activities of the photocatalyst was investigated. CaIn2S4 exhibits optical absorption predominantly in visible region with an optical band gap of 1.76 eV. Considerable activity for hydrogen evolution from pure water was observed without any sacrificial agents or cocatalysts under visible light irradiation. The maximum hydrogen evolution rate achieved was 30.92 μmol g−1 h−1 without obvious deactivation of the photocatalytic activity for four consecutive runs of 32 h.

Effects of charge balance with Na+ on SrTiO3:Mo6+ prepared by spray pyrolysis for H2 evolution under visible light irradiation

Photocatalyst powders of SrTi1−xMoxO3 and Sr1−2xNa2xTi1−xMoxO3 were prepared by spray pyrolysis for hydrogen evolution for the first time from aqueous methanol solution under visible light irradiation. The co-doping of Mo6+/Na+ ions resulted in increase of BET surface area and pore volume, and formation of unique morphology with wrinkled, furrowed and porous surface, without significant distortion of lattice structure of host material. The hydrogen evolution rate of Sr1−2xNa2xTi1−xMoxO3 photocatalyst was enhanced up to 1115.8 μmol g−1 h−1 with an induction period of 1 h under visible light irradiation, which was 1.5 times higher than that of SrTi1−xMoxO3. The co-dopant Na+ ion contributed to the charge balance in the host material by compromising the excess positive charge of Mo6+, which was effective for enhancing the hydrogen evolution rate. The optimum composition of photocatalyst corresponding to the maximum hydrogen evolution rate was Sr1−2xNa2xTi1−xMoxO3 (x = 0.004).

Synergetic catalysis of CuO and graphene additives on TiO2 for photocatalytic water splitting

A highly efficient and visible-light-responsive CuO/TiO2-GR photocatalyst had been synthesized by a two-step process. The as-prepared CuO/TiO2-GR composites were characterized by X-ray diffraction, N2-physisorption, transmission electron microscope, X-ray photoelectron spectroscopy, Raman spectra, UV–vis diffuse reflectance spectra and Photoluminescence spectra. The results indicated that a chemical bond formed between GR and TiO2 in CuO/TiO2-GR composites. CuO/TiO2-GR composites had a higher photocatalytic activity for hydrogen production due to a synergistic effect between CuO and GR. The synergistic effect could efficiently suppress charge recombination, improve interfacial charge transfer, enhance visible-light adsorption and provide plentiful phtotocatalytic reaction active sites. The maximum hydrogen evolution rate of CuO/TiO2-GR-0.5 was 2905.60 μmol/(h·g), which was 20.20 times larger than pure P25.

Hydrogen production by the newly isolated Clostridium beijerinckii RZF-1108

A fermentative hydrogen-producing strain, RZF-1108, was isolated from a biohydrogen reactor, and identified as Clostridium beijerinckii on the basis of the 16S rRNA gene analysis and physiobiochemical characteristics . The effects of culture conditions on hydrogen production by C. beijerinckii RZF-1108 were investigated in batch cultures. The hydrogen production and growth of strain RZF-1108 were highly dependent on temperature, initial pH and substrate concentration. Yeast extract was a favorable nitrogen source for hydrogen production and growth of RZF-1108. Hydrogen production corresponded to cell biomass yield in different culture conditions. The maximum hydrogen evolution, yield and production rate of 2209 ml H 2/l medium, 1.97 mol H 2/mol glucose and 104.20 ml H 2/g CDW h −1 were obtained at 9 g/l of glucose, initial pH of 7.0, inoculum volume of 8% and temperature of 35 °C, respectively. These results demonstrate that C. beijerinckii can efficiently produce H 2, and is another model microorganism for biohydrogen investigations.

Optimization of bio‐hydrogen production from biodiesel wastes by Klebsiella pneumoniae

Biodiesel wastes containing glycerol were utilized by Klebsiella pneumoniae DSM 2026 to produce hydrogen. The optimization of medium components was performed using both Plackett-Burman and uniform design methods. Using the Plackett-Burman design, glycerol, yeast extract, NH(4)Cl, KCl and CaCl2 were found to be the most important components, which were further investigated by uniform design and second-order polynomial stepwise regression analysis. The optimized medium containing 20.4 g.L(-1) glycerol, 5.7 g.L(-1) KCl, 13.8 g.L(-1) NH(4)Cl, 1.5 g.L(-1) CaCl(2) and 3.0 g.L(-1) yeast extract resulted in 5.0-fold increased level of hydrogen (57.6 mL/50 mL medium) production compared to initial level (11.6 mL/50 mL medium) after 24 h of fermentation The optimization of fermentation condition (pH, temperature and inoculum) was also conducted. When the strain grew in the optimized medium under optimal fermentation condition in a 5-L stirred tank bioreactor for batch production, hydrogen yield and production reached 0.53 mol/mol and 117.8 mmol/L, respectively. The maximum hydrogen evolution rate was 17.8 mmol/(L.h). Furthermore, 1,3-propanediol (6.7 g.L(-1)) was also obtained from the liquid medium as a by-product.