Hydrogen Generation Reaction Research Articles

Hydrogen production by Chlamydomonas reinhardtii under light driven sulfur deprived condition

This article explores the possibility of demonstrating sustainable photohydrogen production using Chlamydomonas reinhardtii when grown in sulfur deprived photoautotrophic condition. The hydrogen evolving capability of the algal species was monitored based on alternating light and dark period. Investigation was carried out during the day time in order to exploit the solar energy for meeting the demand of the light period. The results showed that when the reactor was operated at varying photoperiod namely 2, 3 and 4 h of alternating light and dark period, the gas generation was found to be 32 ± 4, 63 ± 7 and 52 ± 5 mL/h, while the corresponding hydrogen content was 47, 86 and 87% respectively. Functional components of hydrogen generation reaction centers were also analyzed, which showed that the PS(I) reaction centers were involved in hydrogen production pathway, as the light absorption by PS(I) was prerequisite for hydrogen generation under sulfur deprived photoautotrophic condition. The findings showed a higher gas yield and hydrogen content under dark period, whereas under light period the gas content was below detectable level for hydrogen due to the reversible hydrogenase reaction.

A novel method for generating hydrogen by hydrolysis of highly activated aluminum nanoparticles in pure water

A simple method with 100% efficiency for generating pure hydrogen in large scale by hydrolysis of highly activated aluminum in water was established. In this activation method, Aluminum is milled using salt particles (as nano-miller) with different salt to aluminum mole ratios. Due to their brittle nature, salt particles are fractured during milling and their sharp edges chop aluminum particles into pieces. This leads to an increment in hydrolysis kinetics. Meantime, salt particles are driven into newly created surfaces of aluminum particles, producing salt gates that will be removed in water environment, causing hydrogen generation reaction to proceed. The other product of reaction is aluminum oxide hydroxide (AlOOH) which is nature-friendly and can be easily separated from water. The highest average rate of hydrogen generation was 75 ml/min per 1 g of aluminum.

Improvement of Photoelectrochemical Reaction for Hydrogen Generation from Water using N-face GaN

AbstractPhotoelectrochemical properties of Ga- and N-face GaN grown by hydride vapor phase epitaxy (HVPE) were investigated. The properties were also compared with Ga-face GaN grown by metal-organic vapor phase epitaxy (MOVPE). The flatband potentials were in order of Ga-face GaN grown by MOVPE < N-face GaN < Ga-face GaN. The highest photocurrent density at zero bias was obtained from the N-face GaN. The photocurrent density was over 3 times larger than that of Ga-face GaN.

Kinetics of sodium borohydride hydrolysis reaction for hydrogen generation

In this work, a ruthenium catalyst was prepared for hydrogen generation from the hydrolysis reaction of an alkaline sodium borohydride solution. The reactions were carried out in a batch reactor at temperatures of 10, 30, 40 and 60 °C for at least 70% conversion or 500 min, whichever came first. The experimental data was fitted to the following three kinetic models: zero-order, first-order, and Langmuir–Hinshelwood. The results indicate that the Langmuir–Hinshelwood model gives a reasonable description of the hydrogen generation rate over the entire temperature range studied as well as the time spans of the experiments. The zero-order model gives good behavior description only at relatively low temperature, i.e. 10 °C. The first-order model works fairly well for a temperature range up to 30 °C.

Formation of Nickel Nanoparticles by Electroless Deposition Using NiO and Ni ( OH ) 2 Suspensions

Nickel particles in diameter were fabricated by electroless deposition using hydrazine as a reducing agent in nickel hydroxide/ethylene glycol suspension at without any dispersing agent. The formation mechanism of nickel nanoparticles is discussed from the viewpoint of thermodynamics with in situ monitoring of nickel deposition and mixed potential. Specifically, in situ monitoring of mixed potential in combination with thermodynamic calculation is useful in discriminating whether or not nickel will be deposited in a reaction. The mixed potential drastically changed at the end point of the nickel deposition reaction, indicating that the cathodic reaction, which determined the mixed potential, switched from the nickel deposition reaction to hydrogen generation reaction.

Controlled synthesis of pentagonal gold nanotubes at room temperature

Large quantities of pentagonal gold nanotubes have been synthesized by reducing chloroauricacid with silver nanowires in an aqueous solution of hexadecyltrimethylammonium bromide(CTAB) at room temperature. These gold nanotubes possess perfect structures, smoothsurfaces, highly crystalline walls, and similar cross-sections to that of the silver template. Inthis process, the CTAB participation was found to be crucial for shape-controlled synthesisof pentagonal gold nanotubes. In the absence of CTAB, loose and hollow gold structureswere routinely generated, while bundled gold nanotubes with rough surfaces wereobtained by replacing the CTAB with poly(vinyl pyrrolidone) (PVP). The possibleformation mechanism of pentagonal gold nanotubes has also been discussed onthe basis of various growth stages studied by field-emission scanning electronmicroscopy (FE-SEM) images. In addition, the catalytic properties of these hollownanostructures for hydrogen generation reaction from HCHO solution have also beeninvestigated. They showed higher activity than that of spherical gold nanoparticles.

Exergetic assessment of transmission concentrated solar energy systems via optical fibres for building applications

Solar lighting with fibre optic bundles can be considered as a very promising option from the viewpoint of energy efficient green buildings. This study dealt with the exergetic analysis and the performance assessment of the system based on the idea of transmission concentrated solar energy via optical fibres (TCSEvOF). Although the main objective of the present study includes the solar lighting to non-daylit areas, it could be possible to transform by additional components and some modifications for other applications, such as solar power generation, solar surgery, photobioreactors, hydrogen generation and photochemical reactions and solar pumped lasers. In the analysis, the experimental data obtained from the system composed of low cost dual sun tracking offset paraboloidal dish and fibre optic bundle and installed in Ege University Solar Energy Institute, Turkey were used. Monthly average hourly exergy efficiencies of the TCSEvOF system were calculated by applying the exergetic model. Exergy efficiencies varied between 1% and 28% in daytime depending on the solar radiation values along the whole year. The seasonal average exergy efficiencies were found to be 16%, 20%, 18%, and 7% for the spring, summer, autumn and winter seasons, respectively. Average annual exergy efficiency of the system for the whole year was obtained to be 15%. Parameters affecting the performance were discussed, while some suggestions towards increasing energy and exergy efficiencies of the system for further researches were made. It is expected that the model presented here would be beneficial to everyone involved in the design and performance evaluation of solar lighting with fibre optic bundles in building applications.

Simple and fast fabrication of polymer template-Ru composite as a catalyst for hydrogen generation from alkaline NaBH 4 solution

Polymer template-Ru composite (Ru/IR-120) catalyst was prepared using a simple and fast method for generating hydrogen from an aqueous alkaline NaBH 4 solution. The hydrogen generation rate was determined as a function of solution temperature, NaBH 4 concentration, and NaOH (a base-stabilizer) concentration. The maximum hydrogen generation rate reached 132 ml min −1 g −1 catalyst at 298 K, using a Ru/IR-120 catalyst that contained only 1 wt.% Ru. The catalyst exhibits a quick response and good durability during the hydrolysis of alkaline NaBH 4 solution. The activation energy for the hydrogen generation reaction was determined to be 49.72 kJ mol −1.

Kinetics of Ru-promoted sulphated zirconia catalysed hydrogen generation by hydrolysis of sodium tetrahydroborate

Pure hydrogen can be catalytically generated by hydrolysis of sodium tetrahydroborate NaBH 4. The present paper reports the kinetics of hydrolysis of aqueous alkaline solution of NaBH 4. The investigated catalyst was 1 wt% Ru-promoted sulphated zirconia. The reaction orders for both NaBH 4 and NaOH, the reaction order for Ru and the apparent activation energy were determined. The hydrogen generation rate can be written following a power law: r = k[NaBH 4] 0.23[NaOH] −0.35[Ru] 1.27. The activation energy for the hydrogen generation reaction is of 76 kJ mol −1. Otherwise, the present paper shortly reviews the kinetic data that are available in the open literature and notices the discrepancies that exist for these data. The kinetic data of the present study also contribute to these discrepancies.

Preparation and characterization of lithium niobate as a novel photocatalyst in hydrogen generation

Several chemical compounds based lithium niobate have been tested in the reaction for the photocatalytic hydrogen generation. The photocatalysts have been prepared by impregnation of Nb 2O 5 in the aqueous solution of lithium hydroxide and then the calcination at the temperature range of 400–650 °C. In this report, we present the interesting study showing that the most active catalyst for the photocatalytic generation of hydrogen is the one containing two lithium niobate phases such as LiNbO 3 and LiNb 3O 8. It means that the lithium niobates based catalyst without any further modification or doping can be applied as a novel material for this process.

Improved hydrogen generation from alkaline [formula omitted] solution using carbon-supported [formula omitted] as catalysts

Carbon-supported Co–B catalysts with various loading contents were prepared by impregnation–chemical reduction method. The XRD, ICP, SEM and TEM analyses revealed that the as-prepared Co–B catalysts were in amorphous form with the composition of Co 2.0 – 3.3 B and the carbon-supported Co–B catalysts had a good dispersion and coating condition. The hydrogen generation measurement showed that the average hydrogen generation rate at 25 ∘ C was 1127.2 mL min - 1 g - 1 for unsupported Co–B catalyst, while it was 1268.1, 1482.1 and 2073.1 mL min - 1 g - 1 for the carbon-supported catalysts with the Co–B loading of 30.0, 15.6 and 7.44 wt%, respectively. The activation energy of the 30.0 wt% Co–B loading catalyst for the hydrogen generation reaction was measured to be 57.8 kJ mol - 1 . Compared with the unsupported Co–B catalyst, the as-prepared carbon-supported catalysts presented higher activity for hydrolysis of NaBH 4 aqueous solution, indicating their potential application in mobile hydrogen production for fuel cells.

Room temperature hydrogen generation from aqueous ammonia-borane using noble metal nano-clusters as highly active catalysts

Nano-clusters of noble metals Ru, Rh, Pd, Pt and Au have been supported on γ-Al 2O 3, C and SiO 2, of which the catalytic activities have been investigated for hydrolysis of NH 3BH 3. Among these catalysts, the Ru, Rh and Pt catalysts exhibit high activities to generate stoichiometric amount of hydrogen with fast kinetics, whereas the Pd and Au catalysts are less active. Support effect has been studied by testing the hydrogen generation reaction in the presence of Pt supported on γ-Al 2O 3, VULCAN ® carbon and SiO 2, and it is found that Pt on γ-Al 2O 3, which has the smallest particle size, is the most active. Concentration dependence of the hydrogen generation from aqueous NH 3BH 3 solutions has been investigated in the presence of Pt/γ-Al 2O 3 by keeping the amount of Pt/γ-Al 2O 3 catalyst unchanged, which exhibits that the hydrogen release versus time (ml H 2 min −1) does not significantly change with increasing the NH 3BH 3 concentration, indicating that the hydrogen release rate is not dependent on the NH 3BH 3 concentration and the high activity of the Pt catalyst can be kept at high NH 3BH 3 concentrations. Activation energies have been measured to be 23, 21 and 21 kJ mol −1 for Ru/γ-Al 2O 3, Rh/γ-Al 2O 3 and Pt/γ-Al 2O 3 catalysts, respectively, which may correspond to the step of B–N bond breaking on the metal surfaces. The particle sizes, surface morphology and surface areas of the catalysts have been obtained by TEM and BET experiments.

Kinetics of Catalytic Hydrolysis of Stabilized Sodium Borohydride Solutions

The kinetics of catalytic hydrolysis of stabilized sodium borohydride solutions has been studied for a Ni-metal supported catalyst over a temperature range from 273 to 303 K and a NaBH4 concentration range from 1.34 to 5.44 M. The rate may be represented by the expression: −(dNNaBH4/w·dt) = k·[NaBH4]-0.41[NaOH]0.13[H2O]0.68 k = 11579.1·exp(−6269.9/T) The activation energy for the hydrogen generation reaction was determined to be 52 kJ/mol. The factors affecting energy storage density of sodium borohydride based systems and the performance of hydrogen generation reactors are discussed.

Catalytic activities of non-noble metals for hydrogen generation from aqueous ammonia–borane at room temperature

We have studied catalytic performance of supported non-noble metals for hydrogen generation from aqueous NH 3BH 3 at room temperature. Among the tested non-noble metals, supported Co, Ni and Cu are the most catalytically active, with which hydrogen is released with an almost stoichiometric amount from aqueous NH 3BH 3, whereas supported Fe is catalytically inactive for this reaction. Support effects on the catalytic activity have been investigated by testing the hydrogen generation reaction in the presence of Co supported on γ-Al 2O 3, SiO 2 and C and it is found that the Co/C catalyst has higher activity. Activation energy for hydrogen generation from aqueous NH 3BH 3 in the presence of Co/γ-Al 2O 3 was measured to be 62 kJ mol −1; this may correspond to the step of B N bond breaking. Particle size, surface morphology and surface area of the supported metal catalysts were examined by X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) and BET experiments. It is found that with decreasing the particle size the activity of the supported catalyst is increased. The low-cost and high-performance supported non-noble metal catalysts may have high potential to find its application to the hydrogen generation for portable fuel cells.

Nafion Quantity Variation on Electrodes used in SPE Electrolyzer

The production of hydrogen using renewable sources by for example electrolysis and photoelectrolysis, avoids the emission of pollutants to the environment, especially if the electrical power for the electrolyzer is supplied by renewable energy. At the moment two types of commercial hydrogen generators exist by means of an electrolysis process: the alkaline electrolyzer (EA) and the solid polymer electrolyte electrolyzer, called SPE. SPE electrolyzer technology has brought the possibility of having a cleaner hydrogen generator. Essential part of an SPE electrolyzer, is the membrane- electrode assembly (MEA), where hydrogen generation (cathode electrode) and oxygen evolution (anode electrode) reactions take place. In the present work IrO2 and Pt/Vu were used as anode and cathode respectively for an ESP electrolyzer. Electrochemical measurements were realized using 5 different MEÁs, prepared by a hot-spray technique, where electrocatalytic inks were prepared and airbrushdeposited onto the membrane at 20 cm. After several deposited layers the obtained dried catalytic surfaces were rather homogeneous. After deposition, a thermomechanical process was used. All assemblies were prepared using Nafion® 117 and loads of 2 mg-cm-2 of IrO2 (Electrochem)as anode and 1 mg-cm-2 of 20% Pt/Vu (Electrochem) as cathode, nafion solution, ethylic alcohol to the catalyzer and then ultrasound stirred. The Nafion solution quantity was varied for the cathode and anode. Data were collected obtaining the polarization, power density and EIS (Electrochemical Impedance Spectroscopy)curves at 25{degree sign}C using a hardware manufactured in the laboratory, containing titanium mesh as current collector

Carbon-supported platinum catalysts for on-site hydrogen generation from NaBH 4 solution

A flexible hydrogen generation (HG) method based on catalytic hydrolysis of NaBH 4 solution is developed. Carbon-supported platinum (Pt/C) samples served as the catalysts, and the catalytic strategies for hydrolysis of NaBH 4 solution are analyzed via the studies on apparent morphology, catalytic activity, BET surface, and sustaining H 2 supply test. Pt/C catalysts are proved to be excellent accelerators, and Pt-loading plays an important role in the hydrogen generation reactions. For a reactor loaded with 100 mg 13.1% Pt/C catalyst, when 10% NaBH 4–5% NaOH solution is pumped into the reactor with a speed of 10 ml/min, it can achieve a maximum HG rate of 29.6 (l/min/g catalyst), and give sustaining H 2 supply for a proton exchange membrane fuel cell (PEMFC) with an average HG rate of 23.0 (l/min/g catalyst).

Nickel- and cobalt-based catalysts for hydrogen generation by hydrolysis of borohydride

Borohydrides, a group of compounds with large hydrogen contents, can generate hydrogen readily by their hydrolysis reaction. In this study catalysts based on nickel and cobalt were developed to accelerate the hydrolysis reaction for hydrogen generation. Catalysts in four forms were tested for each metal: fine metal powder, metal salt, metal boride and Raney metal. It was found that the hydrolysis reaction was primary a zero-order reaction under the catalysis of these catalysts. Although cobalt showed higher catalytic activity than nickel in most cases, Raney Ni exhibited almost the same activity as the Raney Co. Among four chemical forms for nickel, Raney Ni demonstrated the best performance. Moreover, Raney catalysts made from alloys of nickel and cobalt showed even higher activity. The reaction on Raney metals was also characterized by a slowdown in hydrogen generation rate at low borohydride concentrations because of a mass transfer limitation.

Hydrogen generation from catalytic hydrolysis of sodium borohydride for proton exchange membrane fuel cells

A novel hydrogen generation (HG) method for proton exchange membrane fuel cell (PEMFC) is developed. Carbon-supported platinum catalysts were synthesized by an impregnation method, and adopted to catalysis hydrolysis of NaBH 4 solution. These catalysts exhibit excellent hydrogen generation rates and approximate 100% efficiencies. A HG system with 100 mg 20% Pt/C catalyst has the ability to supply a 299 W PEMFC. Specific surface of the support is not a crucial factor affecting the HG performances of the catalysts, while Pt loading, Pt particle size and size distribution, and micropore structure play important roles in hydrogen generation reactions.

Solar hydrogen generation with H 2O/ZnO/MnFe 2O 4 system

The hydrogen generation reaction in the H 2O/ZnO/MnFe 2O 4 system was studied to clarify the possibility of whether this reaction system can be used for the two-step water splitting to convert concentrated solar heat to chemical energy of H 2. At 1273 K, the mixture of ZnO and MnFe 2O 4 reacted with water to generate H 2 gas in 60% yield. X-ray diffractometry and chemical analysis showed that 48 mol% of Mn II (divalent manganese ion) in the A-site of MnFe 2O 4 was substituted with Zn II (divalent zinc ion) and that chemical formula of the solid product was estimated to be Zn 0.58Mn II 0.42Mn III 0.39Fe 1.61O 4 (Mn III: trivalent manganese ion). Its lattice constant was smaller than that of the MnFe 2O 4 (one of the two starting materials). From the chemical composition, the reaction mechanism of the H 2 generation with this system was discussed. Since the Mn ions in the product solid after the H 2 generation reaction are oxidized to Mn 3+, which can readily release the O 2− ions as O 2 gas around 1300 K, the two-step of H 2 generation and O 2 releasing seem to be cyclic.

Solid–solid palladium-catalysed water reduction with zinc: mechanisms of hydrogen generation and direct hydrogen transfer reactions

Facile generation of hydrogen gas from water takes place under moderate conditions in the presence of zinc powder and catalytic palladium on carbon; 82% conversion of zinc is obtained. An unusually large kinetic isotope effect is observed using D2O (kH/kD=14), which may reflect the cleavage of both O–H bonds in the rate-determining step. Experiments using D2O–H2O mixtures evidence that water molecules adsorbed on the catalyst surface undergo H–D exchange reactions (with molecules from the solvent bulk) that are approximately 100 times faster than the hydrogen generation reaction. The primary factors in this system appear to be palladium–hydrogen and zinc–oxygen interactions. Conversely, in the presence of an organic hydrogen acceptor, such as benzaldehyde, a different course is realised, consisting of direct hydrogen transfer from ‘‘zinc-activated ’’ water to the substrate, without the participation of Pd–H intermediates. Quantitative hydrogenation of benzaldehyde to benzyl alcohol, and of aromatic nitro compounds to the corresponding amines, is obtained. Another application of the above system is the specific deutero-dehalogenation of aromatic halides. Possible mechanisms and the implications of a chemical reaction involving two macroscopic solid particles are discussed.