High Hydrogen Production Activity Research Articles

Facile synthesis of porous microspheres composed of TiO2 nanorods with high photocatalytic activity for hydrogen production

A facile, high-yield and reproducible hydrothermal route was developed to synthesize novel well-knit (i.e., solid and compacted) and porous anatase TiO2 microspheres, consisting of morphologically controlled and uniform TiO2 nanorods. Field emission scanning electron microscopy (FE–SEM) and transmission electron microscopy (TEM) revealed that the resulting TiO2 microspheres exhibited a nanoporous structure that was formed by the self-assembled accumulation of uniform nanorods, which is reported here for the first time. The effect of the surfactant type, surfactant amount and other additives such as urea and water on the formation of the microspheres was investigated. X-ray diffraction and N2 adsorption–desorption characterization showed that the synthesized TiO2 microspheres exhibited a high degree of crystallinity with a high surface area (∼103.9m2/g), which was twice larger than that of commercial P25. The synthesized TiO2 microsphere photocatalysts also exhibited superior photocurrent density with a 4.8-fold improvement in photocurrent over the commercial P25. Additionally, these TiO2 microspheres showed good performance in the generation of hydrogen.

Amine-Functionalized MIL-125 with Imbedded Palladium Nanoparticles as an Efficient Catalyst for Dehydrogenation of Formic Acid at Ambient Temperature

Palladium nanoparticles were immobilized within the pores of metal organic frameworks MIL-125 and amine-functionalized NH2-MIL-125 using photoassisted and ion exchange deposition methods. The resulting materials showed a very high activity for hydrogen production at ambient temperature in comparison to other titanium-based porous materials. The amine groups in NH2-MIL-125 greatly increased the H2-generating activity and acted as a stabilizer of Pd NPs. The photoassisted deposition method was a more efficient method for producing highly dispersed small NPs in the MOF materials.

Fabrication of noble-metal-free Cd0.5Zn0.5S/NiS hybrid photocatalyst for efficient solar hydrogen evolution

Up to now, most of the semiconductor photocatalysts can only achieve their high photocatalytic activity for hydrogen production with the loading of noble metals, such as Pt or Ru, as cocatalysts, which drastically increases the total cost of the designed photocatalyst. Herein, we report the design and fabrication of a highly efficient Cd0.5Zn0.5S photocatalyst decorated with nanosized NiS surface heterojunctions. The hydrogen evolution rate over this photocatalyst reached 1.4 mmol/h, with a remarkable quantum yield of 33.9%. This efficiency is even much higher than many noble metal loaded photocatalysts. In this hybrid photocatalyst, the nanosized NiS on the surface can serve as electron trapping sites, by which, photogenerated electrons were extracted from Cd0.5Zn0.5S substrate, leading to spatially separated photoreduction and oxidation reactions. More interestingly, it was found that NiS played a similar role as noble metal, providing active sites for proton reduction, and hence efficiently enhancing the overall hydrogen production rate. Our work demonstrates the possibility of substitution of noble metal cocatalyst by a properly engineered surface hetero-junction to achieve efficient and low cost photocatalytic hydrogen production.

Redox state-dependent changes in the crystal structure of [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough

Hydrogenases are enzymes that can potentially be used in bioelectrical devices or for biological hydrogen production, the most studied of which are the [NiFe] type. Most [NiFe] hydrogenases are inactivated by oxygen and the few known O2-tolerant enzymes are hydrogen-uptake enzymes, unsuitable for hydrogen production, due to strong product inhibition. In contrast, the [NiFeSe] hydrogenases, where a selenocysteine is bound to the nickel, are very attractive alternatives because of their high hydrogen production activity and fast reactivation after O2 exposure. Here we report five high-resolution crystallographic 3D structures of the soluble form of the [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough in three different redox states (oxidized as-isolated, H2-reduced and air re-oxidized), which revealed the structural changes that take place at the active site during enzyme reduction and re-oxidation. The results provide new insights into the pathways of O2 inactivation in [NiFe], and in particular [NiFeSe], hydrogenases. In addition, they suggest that different enzymes may display different oxidized states upon exposure to O2, which are probably determined by the protein structure.

Disordered Co1.28Mn1.71O4 as a Visible‐Light‐Responsive Photocatalyst for Hydrogen Evolution

Catching the sunlight: The disordered Co1.28Mn1.71O4 was synthesized by a facile reduction method in the presence of amorphous MnO2 precursors and Co(2+). It exhibits relatively high hydrogen-production activity under visible-light irradiation (see figure). The larger number of active sites in the bulk catalyst endow nanoparticles with improved water-reduction activity. This is the first demonstration of disordered ternary oxides for visible-light-driven hydrogen evolution in the absence of a cocatalyst.

Iron vs. cobalt clathrochelate electrocatalysts of HER: the first example on a cage iron complex

New macrobicyclic 2-thiopheneboron-capped iron and cobalt(II) tris-dioximates showed high electrocatalytic activity for hydrogen production from H(+) ions. This is the first example of the hydrogen evolution reaction electrocatalyzed by a clathrochelate iron complex, which catalyzes the hydrogen production at low overpotential.

A Ni@ZrO2nanocomposite for ethanol steam reforming: enhanced stability via strong metal–oxide interaction

This communication describes the synthesis of a nanocomposite Ni@ZrO2 catalyst with enhanced metal-support interaction by introducing metal nanoparticles into the framework of the oxide support. The catalyst shows high catalytic activity and stability for hydrogen production via steam reforming of ethanol.

Non-equilibrium partial oxidation of TiN surface for efficient visible-light-driven hydrogen production

The non-equilibrium quick oxidation of titanium nitride (TiN) particles is found to be capable of kinetically controlling the partial oxidation on the surface and constructing a TiOxNy@TiN core–shell structure, in which the TiOxNy shell exhibits different components (x = 0.0–2.0). The TiOxNy@TiN structure can absorb visible light and display a high photocatalytic activity for hydrogen production, without any help from noble metal co-catalysts. A hydrogen generation rate of 506 μmol g−1 h−1 can be reached. The strong catalytic ability of TiOxNy@TiN can be attributed to the formation of heterojunction among the hybrid TiOxNy, which can facilitate the separation of light-induced electron–hole pairs. Furthermore, the non-equilibrium quick oxidation leads to the partial survival of electro-conductive TiN tiny crystals on the surface, which can act as co-catalysts to further improve the electron–hole separation and to catalyze hydrogen ion reduction.

Glycerol as an efficient mesopore-controlling agent for synthesis of mesoporous-assembled TiO 2 nanocrystals and their remarkable photocatalytic H 2 production activity

In this work, the mesoporous-assembled TiO 2 nanocrystals were successfully synthesized by a modified sol–gel process under mild conditions with the aid of glycerol, which is a main by-product from biodiesel production via the transesterification of vegetable oils. The synthesized TiO 2 nanocrystals were characterized by various techniques, i.e. N 2 adsorption–desorption, SEM, high resolution TEM, and XRD. The characterization results clearly showed that the glycerol could behave as an efficient mesopore-controlling agent, which induced the mesoporous-assembled characteristic of the synthesized TiO 2 nanocrystals with very narrow pore size distribution. The synthesized mesoporous-assembled TiO 2 nanocrystals were applied for hydrogen production from the photocatalytic water splitting. The photocatalytic activity results revealed that the synthesized mesoporous-assembled TiO 2 nanocrystals possessed much higher hydrogen production activity than the commercially available P-25 TiO 2 and ST-01 TiO 2 powders.

Initial Study of a Photocatalytic Process for Flue Gas Desulfurization

A photocatalytic process combined with ammonia-water method was developed for flue gas desulfurization. With the photocatalytic technology we can not only achieve the purpose of solving the problem of SO2 emissions but also realize the desire of hydrogen production from water splitting. CdS loaded with Pt were selected for the photocatalytic gas desulfurization. It was found that Pt/CdS showed a high activity for hydrogen production from ammonia sulfite solution, which is the prime product of ammonia-water method for flue gas desulfurization.

Comparative study of NiLaZr and CoLaZr catalysts for hydrogen production by ethanol steam reforming: Effect of CO 2 injection to the gas reactants. Evidence of Rh role as a promoter

The catalytic performance of trimetallic oxides MeLaZr (Me: Ni, Co) was evaluated in the steam reforming of ethanol for hydrogen production. Rh doped and non doped catalysts were prepared by the pseudo sol–gel like method, characterized by X-ray diffraction (XRD), thermo-programmed reduction (TPR), micro-homogeneity analysis (TEM-EDXS), specific surface areas (BET). A phase-segregation process takes place during the calcination for both trimetallic systems leading to the formation of La 2Zr 2O 7 pyrochlore-type compound in coexistence with the Me-oxide. NiLaZr and CoLaZr catalysts show high activity and high selectivity for hydrogen production. Addition of Rh promotes reducibility at lower temperatures for both trimetallic catalysts and remarkably improves the activity and selectivity for H 2. The H 2 selectivity is lowered by CO 2 injection because of the increase of the rate of the reverse WGSR and/or methanation reaction. The CH 4 selectivity is lowered by the dry reforming reaction. The key-role played by oxycarbonate species formed during the reforming tests leads to a highly efficient gasification of carbon deposits by the Boudouard reaction.

Production of biohydrogen by heterologous expression of oxygen-tolerant Hydrogenovibrio marinus [NiFe]-hydrogenase in Escherichia coli

Oxygen sensitivity of hydrogenase is a critical issue in efficient biological hydrogen production. In the present study, oxygen-tolerant [NiFe]-hydrogenase from the marine bacterium, Hydrogenovibrio marinus, was heterologously expressed in Escherichia coli, for the first time. Recombinant E. coli BL21 expressing H. marinus [NiFe]-hydrogenase actively produced hydrogen, but the parent strain did not. Recombinant H. marinus hydrogenase required both nickel and iron for biological activity. Compared to the recombinant E. coli [NiFe]-hydrogenase 1 described in our previous report, recombinant H. marinus [NiFe]-hydrogenase displayed 1.6- to 1.7-fold higher hydrogen production activity in vitro. Importantly, H. marinus [NiFe]-hydrogenase exhibited relatively good oxygen tolerance in analyses involving changes of surface aeration and oxygen proportion within a gas mixture. Specifically, recombinant H. marinus [NiFe]-hydrogenase produced ∼7- to 9-fold more hydrogen than did E. coli [NiFe]-hydrogenase 1 in a gaseous environment containing 5-10% (v/v) oxygen. In addition, purified H. marinus [NiFe]-hydrogenase displayed a hydrogen evolution activity of ∼28.8 nmol H₂/(minmg protein) under normal aerobic purification conditions. Based on these results, we suggest that oxygen-tolerant H. marinus [NiFe]-hydrogenase can be employed for in vivo and in vitro biohydrogen production without requirement for strictly anaerobic facilities.

Effects of anions on the photocatalytic H 2 production performance of hydrothermally synthesized Ni-doped Cd 0.1Zn 0.9S photocatalysts

A series of Ni 2+ doped Cd 0.1Zn 0.9S photocatalysts were prepared with different salt by hydrothermal method. The prepared photocatalysts were characterized by XRD, UV–Vis, BET and SEM. The effects of SO 4 2−, CH 3COO −, Cl − and NO 3 − anions on the photocatalytic hydrogen production performance of these photocatalysts were examined. Experimental results showed that the photocatalysts prepared with acetates and chlorides have the highest hydrogen production activity, and their initial hydrogen production rate reaches to 76.52 μmol/h and 80.75 μmol/h under visible-light irradiation with the apparent quantum yield of 12.30% and 14.36% at 420 nm without any noble metal loading, respectively. The absence of noble metal is propitious to reduce the cost of photocatalyst preparation.

Bio-hydrogen production from cellulose by sequential co-culture of cellulosic hydrogen bacteria of Enterococcus gallinarum G1 and Ethanoigenens harbinense B49

Microbial conversion of lignocellulose to hydrogen is a fascinating way to provide a renewable energy source. A mesophilic bacterium strain G1 that had high cellulose degradation and hydrogen production activity (2.38 mmol H(2) g(-1) cellulose) was isolated from rumen fluid and identified as the Enterococcus gallinarum. Hydrogen production from cellulose by using sequential co-cultures of a cellulosic-hydrolysis bacterium G1 and Ethanoigenens harbinense B49 was investigated. With an initial Avicel concentration of 5 g l(-l), the sequential co-culture with G1 and strain Ethanoigenens harbinense B49 produced H(2) yield approximately 2.97 mmol H(2) g(-1) cellulose for the co-culture system.

Reinvestigation of the Steady-State Kinetics and Physiological Function of the Soluble NiFe-Hydrogenase I of Pyrococcus furiosus

Pyrococcus furiosus has two types of NiFe-hydrogenases: a heterotetrameric soluble hydrogenase and a multimeric transmembrane hydrogenase. Originally, the soluble hydrogenase was proposed to be a new type of H2 evolution hydrogenase, because, in contrast to all of the then known NiFe-hydrogenases, the hydrogen production activity at 80 degrees C was found to be higher than the hydrogen consumption activity and CO inhibition appeared to be absent. NADPH was proposed to be the electron donor. Later, it was found that the membrane-bound hydrogenase exhibits very high hydrogen production activity sufficient to explain cellular H2 production levels, and this seems to eliminate the need for a soluble hydrogen production activity and therefore leave the soluble hydrogenase without a physiological function. Therefore, the steady-state kinetics of the soluble hydrogenase were reinvestigated. In contrast to previous reports, a low Km for H2 (approximately 20 microM) was found, which suggests a relatively high affinity for hydrogen. Also, the hydrogen consumption activity was 1 order of magnitude higher than the hydrogen production activity, and CO inhibition was significant (50% inhibition with 20 microM dissolved CO). Since the Km for NADP+ is approximately 37 microM, we concluded that the soluble hydrogenase from P. furiosus is likely to function in the regeneration of NADPH and thus reuses the hydrogen produced by the membrane-bound hydrogenase in proton respiration.

Visible light-induced splitting of water using CdS nanocrystallites immobilized over water-repellant polymeric surface

The paper reports on a well dispersed cadmium sulfide (CdS) catalyst that exhibits high activity for visible light-driven hydrogen production from photocatalytic splitting of water, and at the same time maintains a significantly long active life because of its hydrophobic nature. The catalyst comprises of uniform CdS crystallites of 2–5 nm size, coated at loadings of 5–17 wt% over a polymeric support (polystyrene) having a rough and porous texture. The samples are characterized using the techniques of powder X-ray diffraction, UV–Visible spectroscopy, scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of this supported CdS catalyst, as well as that of an aqueous suspension of CdS powder, is monitored for the visible light-induced evolution of H 2 from water in the presence of hole scavengers S 2 - and SO 3 2 - . While the rate of hydrogen evolution was found to increase with loading, a reverse trend was observed for the amount of H 2 produced per unit mass of CdS. Furthermore, much smaller quantities of hydrogen were evolved under the identical test conditions when an equivalent amount of bulk CdS powder was directly suspended in water. These results clearly demonstrate the vital role played by the particle size and dispersion in the photocatalytic splitting of water for hydrogen generation. In the experiments conducted over the period of several days, with random breaks in photo-irradiation but no in-between catalyst activation, the evolution of hydrogen was found to stop at the stage when sacrificial agents S 2 - / SO 3 2 - were completely oxidized. The reaction was revived again when the aqueous solution was replaced by a fresh lot, though the progressively lower amounts of H 2 were produced in these repeated cycle experiments. It can therefore be concluded that the slow activity loss of CdS/polyester is related to the formation of S 2 O 6 2 - and/or SO 4 2 - species produced on photo-oxidation of the sacrificial agents, rather than to the degradation of the photocatalyst.

Evaluation of alternative methods of preparing hydrogen producing seeds from digested wastewater sludge

Six digested sludges, pre-treated by different methods (heat-shock, aeration, acid and base treatments, 2-bromoethanesulfonic acid (BESA) inhibition and iodopropane inhibition) as well as an untreated sample were compared for their suitability in the preparation of hydrogen producing seeds by cultivations in a sucrose medium. The heat-shock and acid treatment methods completely repressed methanogenic activity; however, they also partially repressed hydrogen production. The base treatment option did not completely repress methanogenic activity and also significantly impacted hydrogen production. The aeration method was unsuccessful at completely repressing methanogenic activity; however, it did not significantly affect the hydrogen production activity. The BESA and iodopropane pre-treatment methods specifically inhibited the methanogens, and there were no significant effects found on hydrogen production. Similar to the aeration pre-treated digested sludge sample, the untreated sludge showed high hydrogen production activity and a small amount of methanogenic activity (lower than the activity detected in the base treatment sample). In the subsequent second-step batch cultivations with the same sucrose medium and the diluted media, methanogenic activity was not detected in any of the test bottles. The microbial seed prepared from base treatment exhibited the highest hydrogen production activity, whereas those prepared from acid treatment did not exhibit any activity. Again, the microbial seed prepared from untreated sludge also exhibited relatively high hydrogen producing activity. A lower pH was detected at the end of the cultivation in all the test bottles. Interestingly, the variations in pH in the different tests bottles indicate that pH is an important parameter in the control of methanogenic activity.

Production of the hydrogen by methane steam reforming over nickel catalysts prepared from hydrotalcite precursors

Catalysts were prepared from hydrotalcite precursors, characterized and tested in the reaction of methane steam reforming to produce hydrogen. The precursors were synthesized by: the traditional technique, with co-precipitation of Ni, Mg and Al nitrates with carbonate; co-precipitation of Mg and Al nitrates with pre-synthesized nickel chelate and anion-exchange of NO 3− of hydrotalcite with nickel chelate. The oxides were analyzed using atomic absorption spectrophotometry, specific surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR) with H 2, catalytic tests and elemental analysis. The catalytic tests demonstrated high methane conversion, high activity for hydrogen production and high stability during the time of reaction for a molar ratio in the feed H 2O:CH 4 = 2:1.