Mechanism Of Hydrogen Production Research Articles

Synthesis of Ti3 + and P5 + co-doped TiO2 nanocrystal with enhanced visible light photocatalytic activity

The surface Ti3+ and P5+ co-doped {001} and {101} faceted TiO2 nanocrystal was successfully prepared by a shape-control regent-free method. The as-synthesized TiO2 nanocrystal showed amazing visible-light absorption and ultra-high visible-light-driven photocatalytic hydrogen evolution activity (724μmolg−1h−1), which was 24 times than that of P25 TiO2 catalyst, and the visible light photocatalytic mechanism for hydrogen production was proposed.

Resourceful treatment of alcohol distillery wastewater by pulsed discharge

Resourceful treatment of alcohol distillery wastewater by pulsed discharge in liquid (PDL) was first studied in this work. The biodegradability of alcohol wastewater can be effectively improved and chemical oxygen demand (COD) removal attained over 40% within 15min PDL treatment. Hydrogen produced from the treating processes was emphatically analyzed. The flow rate, and yield of hydrogen achieved were 80mL/min, 146mL/g COD removed within 30min respectively, which were much better than existing technologies. Meanwhile, the mechanism of hydrogen production from alcohol distillery wastewater by PDL was presented in this work indicating that different region in reactor has different mechanism. In discharge channel, high-energy electrons and resultant free radicals played a leading role. Far away from discharge channel, the neutral particles with strong oxidizing were more important. This work can be a good guidance for both treatment of refractory wastewater and mechanism of hydrogen production by plasma reforming.

Coupling g-C3N4 nanobelts and Cu(OH)2 nanoparticles with TiO2 for visible-light photocatalytic H2 production

Herein, a robust graphitic carbon nitride (denoted as Lg-CN) with narrow bandgap and nanobelt structure was prepared and firstly used as solid sensitizer of TiO2 prepared by in situ hydrothermal method. Simultaneously, cocatalyst Cu(OH)2 was loaded onto Lg-CN-TiO2 surface via a facile precipitation process. The obtained three-component composite showed good stability and the H2 evolution rate of 6wt% Lg-CN-TiO2/1.5wt% Cu(OH)2 reached 37.8μmolh−1 under visible light irradiation, much higher than that of pure Lg-CN or g-CN-TiO2/Cu(OH)2 (g-CN=graphitic carbon nitride prepared by urea pyrolysis). The enhanced H2-evolving performance was attributed to the better visible-light response of Lg-CN and the intimate contact between Lg-CN and TiO2. In addition, the mechanism of hydrogen production was tentatively proposed according to photoluminescense quenching results and electrochemical properties. We think that these valuable results would provide a guidance for the use of Lg-CN in other photocatalytic systems in the future.

Study of ethanol dehydrogenation reaction mechanism for hydrogen production on combustion synthesized cobalt catalyst

Cobalt nanoparticles synthesized via solution combustion synthesis were used to study the decomposition mechanism of ethanol for hydrogen production. Thermodynamic studies were conducted on the synthesis of cobalt nanoparticles using cobalt nitrate as a metal precursor in presence of different reducing agents; hydrazine, glycine, urea and citric acid. Thermodynamic results along with experimental characterizations show that the type and amount of fuel influence the adiabatic combustion temperature and the gases released during synthesis process affecting nanoparticle size, porosity and microstructure. The synthesized nanoparticles were activated by passing H2 at 300 °C inside the reaction chamber before being used for studying the reaction pathway of catalytic dehydrogenation of ethanol. These studies indicate that cobalt catalyst is selective for aldehyde and acetate species along with the formation of H2, H2O and CO2. Production of methane was also observed on cobalt surface at 400 °C. The spent catalyst nanoparticles were characterized after the reaction using XRD, SEM and TEM to analyze the particle size and its morphology. Results indicate a growth in particle size due to sintering, and carbon formation on the catalyst surface due to coking during ethanol dehydrogenation reaction.

Enhanced hydrogen production from ammonia borane using controlled plasmonic performance of Au nanoparticles deposited on TiO2

Mechanisms for hydrogen production from ammonia borane using plasmonic performance of Au nanoparticles deposited on TiO2have been investigated systematically.

Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC) Study of the Reaction Mechanism of Hydrogen Production from Methanol on ZnCu(111)

Cu/ZnO-based catalysts have been widely used for methanol decomposition (MD), partial oxidation of methanol (POM), steam reforming of methanol (SRM), and oxidative steam reforming of methanol (OSRM). In this work, we systematically studied all possible reaction paths involved in MD, POM, SRM, and OSRM on ZnCu alloys (111) using density functional theory (DFT). On the basis of these results, Kinetic Monte Carlo (KMC) simulations show that the rate-limiting step of the four reactions is CH2O formation from CH3O dehydrogenation. The reaction pathway of MD occurs via the direct decomposition of CH3OH, and the main reaction pathways of POM and SRM occur via CH2OO and CH2OOH, respectively. There are two main reaction pathways of OSRM as follows: one occurs via CH2OO, whereas the other occurs via CH2OOH. Finally, according to the results of sensitivity analysis, some possible modifications to improve the CO2 selectivity and turnover frequency (TOF) of H2 for OSRM on Cu/ZnO-based catalysts are also presented. The...

A detailed reaction mechanism for hydrogen production via hydrogen sulphide (H2S) thermolysis and oxidation

Hydrogen production from the thermolysis of undesirable hydrogen sulphide (H2S) represents a viable means of extracting energy from it while enhancing the efficiency of Claus process, which is a widely used technology for sulphur recovery from H2S laden streams of oil and gas industries. This paper examines the thermolysis of H2S for direct hydrogen and sulphur production. A detailed reaction mechanism is proposed that captures the chemistry involved in its high temperature decomposition. The simulation results obtained using the proposed mechanism is compared with a wide range of experimental data from plug flow and stirred reactors, premixed laminar flames, and shock tubes, and a satisfactory agreement between them is found. Significant improvements in model predictions are obtained with the proposed mechanism when compared to previously published mechanism. After its validation, the mechanism is then used to investigate the major reactions involved in hydrogen production. It is shown through simulations under adiabatic conditions that the addition of small amount of oxygen in the inlet H2S gas stream exhibits a synergistic effect in H2 yield, and can significantly enhance the production of hydrogen. The results reported herein provide design guidelines and viable means of seeking cost effective methods of hydrogen production from industrial waste streams containing H2S.

Surface synergism of Pd/H2Ti3O7 composite nanowires for catalytic and photocatalytic hydrogen production from ammonia borane

Pd-incorporated H2Ti3O7 nanowires are synthesized using a facile one-step procedure. H2Ti3O7 nanowires are prepared using a modified alkaline hydrothermal method and Pd is incorporated into the H2Ti3O7 nanowires using a photodeposition technique. The prepared Pd-incorporated H2Ti3O7 nanowires are characterized using XRD, TEM, XPS, ultraviolet–visible spectroscopy, and photoluminescence spectroscopy. The results show that Pd-incorporated H2Ti3O7 nanowires are formed and that the photocatalytic properties of the H2Ti3O7 nanowires are improved by the doping and deposition processes. Furthermore, 1 wt% Pd/H2Ti3O7 composite nanowires show a high hydrogen production rate (up to 0.31 mol min−1) under visible light illumination at 20 °C, and the efficiency of 0.25 wt% Pd/H2Ti3O7 composite nanowires is enhanced by 20% under visible light illumination. The detailed mechanism of hydrogen production through hydrolysis of ammonia borane by using Pd/H2Ti3O7 composite nanowires is discussed.

Dimerization assembly mechanism involving proton coupled electron transfer for hydrogen evolution from water by molybdenum-oxo catalyst

In this work, the mechanism for hydrogen generation of a recently reported Mo-oxo catalyst is investigated by theoretical method. A novel dimerization assembly mechanism has been elaborated. Structural details of the Mo-oxo complex which are essential to the catalytic activity are provided. The dimerization mechanism of hydrogen production is demonstrated to be more feasible than the monomer mechanism proposed in the previous work. Furthermore, proton-coupled electron transfer (PCET) reaction in the hydrogen bond network after dimerization assembly plays a very significant role on the hydrogen evolution from water by molybdenum-oxo catalyst. This study can be useful in understanding of many catalytic processes for hydrogen generation and designing new catalysis with high efficiency.

Efficient hydrogen production by water-splitting over Pt-deposited C–HS–TiO2 hollow spheres under visible light

A Pt-deposited C–HS–TiO2 hollow sphere prepared through a simple template approach as well as their implementation as a photocatalyst for water splitting. The obtained Pt-deposited C–HS–TiO2 hollow spheres are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–vis absorption spectrum (UV–vis), and transmission electron microscope (TEM). The results show that hollow spherical morphology was successfully synthesized. Compared with commercial P-25 TiO2 and C–TiO2 hollow sphere, Pt-deposited C–HS–TiO2 hollow spheres exhibit significant improvement in photoactivity under the visible light irradiation. It can be attributed to the enhanced visible light absorption by the deposited Pt. Furthermore, 1.0 wt% Pt/C–HS–TiO2 presents an ultra-high photocatalytic water splitting activity. The maximum production rate of hydrogen at a reaction temperature of 25 °C is measured as 2857 µmol/h. In addition, 1.0 wt% Pt/C–HS–TiO2 exhibits excellent long-term stability and durability of photocatalytic activity. The rate of visible light water splitting has no significant change. After 22 days of operation, an 8% loss of the initial activity occurs. Finally, the probable mechanism of hydrogen production by water splitting under visible light irradiation is proposed in this study.

On the role of metal particle size and surface coverage for photo-catalytic hydrogen production: A case study of the Au/CdS system

Photo-catalytic hydrogen production has been studied on Au supported CdS catalysts under visible light irradiation in order to understand the effect of Au particle size as well as the reaction medium properties. Au nanoparticles of size about 2–5nm were deposited over hexagonal CdS particles using a new simple method involving reduction of Au3+ ions with iodide ions. Within the investigated range of Au (between 1 and 5wt.%) fresh particles with mean size of 4nm and XPS Au4f/Cd3d surface ratio of 0.07 showed the highest performance (ca. 1 molecule of H2/Auatoms−1) under visible light irradiation (>420nm and a flux of 35mW/cm2). The highest hydrogen production rate was obtained from water (92%)-ethanol (8%) in an electrolyte medium (Na2S–Na2SO3). TEM studies of fresh and used catalysts showed that Au particle size increases (almost 5 fold) with increasing photo-irradiation time due to photo-agglomeration effect yet no sign of deactivation was observed. A mechanism for hydrogen production from ethanol–water electrolyte mixture is presented and discussed.

Transcriptional Profiling of Hydrogen Production Metabolism of Rhodobacter capsulatus under Temperature Stress by Microarray Analysis.

Biohydrogen is a clean and renewable form of hydrogen, which can be produced by photosynthetic bacteria in outdoor large-scale photobioreactors using sunlight. In this study, the transcriptional response of Rhodobacter capsulatus to cold (4 °C) and heat (42 °C) stress was studied using microarrays. Bacteria were grown in 30/2 acetate/glutamate medium at 30 °C for 48 h under continuous illumination. Then, cold and heat stresses were applied for two and six hours. Growth and hydrogen production were impaired under both stress conditions. Microarray chips for R. capsulatus were custom designed by Affymetrix (GeneChip®. TR_RCH2a520699F). The numbers of significantly changed genes were 328 and 293 out of 3685 genes under cold and heat stress, respectively. Our results indicate that temperature stress greatly affects the hydrogen production metabolisms of R. capsulatus. Specifically, the expression of genes that participate in nitrogen metabolism, photosynthesis and the electron transport system were induced by cold stress, while decreased by heat stress. Heat stress also resulted in down regulation of genes related to cell envelope, transporter and binding proteins. Transcriptome analysis and physiological results were consistent with each other. The results presented here may aid clarification of the genetic mechanisms for hydrogen production in purple non-sulfur (PNS) bacteria under temperature stress.

Analysis of the Promoted Activity and Molecular Mechanism of Hydrogen Production over Fine Au–Pt Alloyed TiO2 Photocatalysts

Fine metal nanoparticles (2–3 nm; Au, Pt, and alloyed Au–Pt) with a narrow size distribution were deposited on active TiO2 through a facile chemical reduction method. Compared to the bare TiO2, a remarkable enhancement of up to 10-fold for photocatalytic hydrogen evolution was achieved on the alloyed nanocomposites. By using core level and valence band XPS analysis, two electronic properties are shown to contribute to the promoted photocatalytic activity: stronger metal–support interaction between the alloyed structures and TiO2 and higher electron population on the Au–Pt/TiO2 photocatalysts in comparison with the bare TiO2. Moreover, an improved charge separation over TiO2 using Au–Pt nanoparticles was clearly evidenced by the significant increase of photocurrent responses obtained from the photoelectrochemical measurements. For the first time, in situ 13C and 1H NMR spectroscopy was applied to monitor the gas–liquid–solid photocatalytic reactions under real working conditions. Via a two-electron oxidati...

Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in the Molten Carbonate Electrolysis Cell (MCEC)

There is a growing interest in electrolysis cell technology for producing hydrogen that is today considered as an important fuel in the future systems. Electrolysis in molten carbonate salts at high temperature is a promising method for hydrogen- and/or syngas (H2+CO2) production. Due to the favorable thermodynamic and kinetic conditions, high-temperature electrolysis will gain higher overall efficiency and require lower applied voltage when compared to low-temperature electrolysis. Electrolysis in molten carbonates has been investigated by some authors mainly by converting CO2into CO [1-3]. In our previous study, the feasibility of running the molten carbonate fuel cell reversibly with conventional state-of-the-art cell components is evidenced [4]. However, the Ni hydrogen electrode shows slightly higher polarization losses in water electrolysis than in hydrogen oxidation. For the development of molten carbonate electrolysis cells it is important to figure out the activity of the Ni electrode for water electrolysis in molten carbonates. In the present study the kinetics and reaction mechanism of hydrogen production in the Ni porous electrode in a molten carbonate electrolysis cell is investigated. For this purpose the electrochemical reaction orders of hydrogen, carbon dioxide and water were determined on basis of the steady-state polarization data. Within the temperature range of 600-650 °C the electrochemical reaction order of hydrogen is not constant; the value was found to be 0.49-0.44 at lower H2 concentration, while increasing to 0.79-0.94 when containing 25-50% H2, i.e. not strongly depending on the temperature. On the other hand the partial pressure dependence of CO2 exhibits a larger influence by temperature increasing from 0.62 to 0.86 when the temperature rose from 600 to 650 °C. The reversed water-gas shift reaction has little or almost no impact on the electrochemical reaction order of hydrogen and carbon dioxide. The electrochemical reaction order of water shows two cases as does hydrogen. At lower water concentration, 10-30%, the reaction order is in the range of 0.47-0.67 while it increases to 0.83-1.07 with 30-50% water at 600-650 °C. When taking the shift equilibrium into account, the reaction order of water is constant and the value is approaching to that of higher water content. The activation energy of the Ni porous electrode for hydrogen production is in the range of 55-100 kJ·mol-1, which indicates that the Ni electrode is under mixed-control. Reference [1] W.H.A. Peelen, K. Hemmes, and J. H. W. De Wit, Electrochim. Acta, 43, 763 (1997). [2] V. Kaplan, E. Wachtel, K. Gartsman, Y. Feldman, and I. Lubomirsky, J. Electrochem. Soc., 157, B552 (2010). [3] D. Chery, V. Albin, V. Lair, and M. Cassir, Int. J. Hydrogen Energy, 39, 12330 (2014). [4] L. Hu, I. Rexed, G. Lindbergh, and C. Lagergen, Int. J. Hydrogen Energy, 39, 12323 (2014).

Palladium versus platinum: the metal in the catalytic center of a molecular photocatalyst determines the mechanism of the hydrogen production with visible light.

To develop highly efficient molecular photocatalysts for visible light-driven hydrogen production, a thorough understanding of the photophysical and chemical processes in the photocatalyst is of vital importance. In this context, in situ X-ray absorption spectroscopic (XAS) investigations show that the nature of the catalytically active metal center in a (N^N)MCl2 (M=Pd or Pt) coordination sphere has a significant impact on the mechanism of the hydrogen formation. Pd as the catalytic center showed a substantially altered chemical environment and a formation of metal colloids during catalysis, whereas no changes of the coordination sphere were observed for Pt as catalytic center. The high stability of the Pt center was confirmed by chloride addition and mercury poisoning experiments. Thus, for Pt a fundamentally different catalytic mechanism without the involvement of colloids is confirmed.

Production and Application of a Soluble Hydrogenase from Pyrococcus furiosus.

Hydrogen gas is a potential renewable alternative energy carrier that could be used in the future to help supplement humanity's growing energy needs. Unfortunately, current industrial methods for hydrogen production are expensive or environmentally unfriendly. In recent years research has focused on biological mechanisms for hydrogen production and specifically on hydrogenases, the enzyme responsible for catalyzing the reduction of protons to generate hydrogen. In particular, a better understanding of this enzyme might allow us to generate hydrogen that does not use expensive metals, such as platinum, as catalysts. The soluble hydrogenase I (SHI) from the hyperthermophile Pyrococcus furiosus, a member of the euryarchaeota, has been studied extensively and used in various biotechnological applications. This review summarizes the strategies used in engineering and characterizing three different forms of SHI and the properties of the recombinant enzymes. SHI has also been used in in vitro systems for hydrogen production and NADPH generation and these systems are also discussed.

A unique approach to the vapour phase of the HIx feed of the sulfur iodine thermochemical cycle: A Raman spectroscopy study

The Sulfur Iodine cycle has great potential for large scale hydrogen production from water. The HIx processing stage (Section III) of the cycle exhibits the major challenges. Among them, experimental vapour liquid equilibrium data is scarce, mainly due to inherent hurdles to monitor the system under operating conditions of this section, i.e. temperature, acidity, and corrosion. Until now, UV–Visible and FTIR spectroscopies are the online monitoring techniques of choice, however due their selection rules, there is no experimental spectroscopic evidence of H2 during direct decomposition of HIx. Bearing this in mind, here we demonstrate the feasibility of exploiting two different Raman spectroscopic techniques as in situ monitoring tools, to gain substantial knowledge on the mechanisms of hydrogen production in Section III. Whereas resonance Raman spectra revealed the occurrence of HI·(H2O)3 in the vapour phase; coherent anti-Stokes Raman spectra of H2 allowed us to estimate kinetic data such as the activation energy for HI decomposition of a given hyper-azeotropic ternary mixture (i.e. xHI: 0.144; xI2:0.308; xH2O:0.548) is 149.15 kJ/mol.

Mechanism of hydrogen production via water splitting on 3C-SiC’s different surfaces: A first-principles study

The reaction mechanism of producing hydrogen via water splitting on the different surfaces of cubic silicon carbide (3C-SiC), the adsorption energy and the activation energy have been studied here by using density functional theory. The results indicated that the adsorption behavior of water molecule could take place on 3C-SiC’s different surfaces and it leads to the surface reconstruction. Besides, the water splitting reaction is found to be a thermally activated process, and the first hydrogen atom is easier decomposing from the adsorbed water molecule than the second one for most of the 3C-SiC surfaces. Furthermore, the water molecule that splitting on 3C-SiC (111) surface requires relatively small activation energy by contrast with other surfaces. Photon excitation is considered to be essential for the overall water splitting reaction to proceed further.

Genome Sequence of a Promising Hydrogen-Producing Facultative Anaerobic Bacterium, Brevundimonas naejangsanensis Strain B1.

Brevundimonas naejangsanensis strain B1 is a newly isolated, facultative anaerobic bacterium capable of producing hydrogen with high efficiency. Here, we present a 2.94-Mb assembly of the genome sequence of strain B1, which may provide further insights into the molecular mechanism of hydrogen production from bioresource.

Genome Sequence of Bacillus cereus Strain A1, an Efficient Starch-Utilizing Producer of Hydrogen.

Bacillus cereus strain A1 is a newly isolated hydrogen producer capable of utilizing bioresources and biowaste, such as starch and starch wastewater. Here, we present a 5.67-Mb assembly of the genome sequence of strain A1, which may provide insights into the molecular mechanism of hydrogen production from bioresources and biowaste.