Liberation Of Hydrogen Research Articles

Electrospun CoCr7C3-supported C nanofibers: Effective, durable, and chemically stable catalyst for H2 gas generation from ammonia borane

Cobalt-chromium carbide-embedded carbon nanofibers (nanocomposite) were prepared via electrospinning of a solution containing cobalt acetate tetrahydrate (CoAc), chromium (II) acetate dimer monohydrate (CrAc), and polyvinylpyrrolidone (PVP) followed by carbonization. Carbonization was achieved at a low temperature (850°C, Ar gas, 6h) as the nanocomposite contained metal carbide. The synthesized nanocomposite was analyzed using advanced analytical techniques. The catalytic activity of the nanocomposite in hydrogen liberation through the hydrolysis of aqueous ammonia borane (AB) solution was evaluated and compared to those of cobalt/carbon nanofibers (Co/CNFs) and cobalt nanoparticles (Co NPs). The synthesized nanocomposite showed the highest catalytic activity at 0.2475mol/min compared to Co/CNFs, 0.174molmin−1, and Co NPs, 0.09molmin−1. The synthesized nanocomposite also showed high stability; it was reused six times without makeup, reactivation, or regeneration. Kinetic studies showed that the rate of AB hydrolysis is dependent on the catalyst concentration and temperature; the value of turn over frequency (TOF) and the activation energy for the prepared nanocomposite were found to be 25.78 molH2 min−1(molmetal−1) and ∼24.2kJmol−1, respectively.

Release of hydrogen from nanoconfined hydrides by application of microwaves

The release of hydrogen from solid hydrides by thermolysis can be improved by nanoconfinement of the hydride in a suitable micro/mesoporous support, but the slow heat transfer by conduction through the support can be a limitation. In this work, a C/SiO2 mesoporous material has been synthesized and employed as matrix for nanoconfinement of hydrides. The matrix showed high surface area and pore volume (386 m2/g and 1.41 cm3/g), which enabled the confinement of high concentrations of hydride. Furthermore, by modification of the proportion between C and SiO2, the dielectric properties of the complex could be modified, making it susceptible to microwave heating. As with this heating method the entire sample is heated simultaneously, the heat transfer resistances associated to conduction were eliminated. To demonstrate this possibility, ethane 1,2-diaminoborane (EDAB) was embedded on the C/SiO2 matrix at concentrations ranging from 11 to 31%wt using a wet impregnation method, and a device appropriate for hydrogen release from this material by application of microwaves was designed with the aid of a numerical simulation. Hydrogen liberation tests by conventional heating and microwaves were compared, showing that by microwave heating hydrogen release can be initiated and stopped in shorter times.

All-solid-state magnesium oxide supported Group VIII and IB metal catalysts for selective catalytic reforming of aqueous aldehydes into hydrogen

Molecular hydrogen is of critical importance in the chemical industry and might play vital role in future for benign and secure energy technologies. However, its generation from renewable sources, such as water and biomass without the addition of external energy (heat, light and electricity) remains difficult. Herein, we report that Group VIII and Group IB transition metal nanoparticles supported on magnesium oxide are active all-solid-state catalyst systems for external energy-free liberation of molecular hydrogen by aldehyde reforming in liquid water at ambient conditions. Based on experimental observation and DFT calculation, it is suggested that molecular oxygen as well as water can be readily reduced on Group IB metals via two-electron process to form peroxy radicals, while most of Group VIII metals such as Pt end up with sites creating oxo species but instead form hydroxyl radicals via four-electron processes. Therefore, by altering supporting metals, we are able to control the reaction pathways (reduction of aldehydes into H2 or oxidation of aldehydes into CO2) due to the difference of oxygen reduction products.

Hydrogen gas of organic origin in shales and metapelites

The changes in inorganic and organic gases retained in shales and metapelites with increasing heating temperature are not fully understood. The compositional and isotopic changes of residual gases such as H2, CH4, and CO2 in marine shales and metapelites during burial diagenesis and metamorphism were investigated in the present study. Shale rocks and metapelites which experienced paleo-temperatures in the range of 100–600°C were collected from the borehole cores in Niigata sedimentary basin and outcrops exposed in Kochi district, Japan. Gases released from shale or metapelite fragments during pulverization in the laboratory were analyzed as the residual gas.The major residual gas in shales and metapelites changes from CO2, CH4, to H2 in this order with increasing temperature. Drastic decrease of CO2 derived from decarboxylation of sedimentary organic matter is due to the expulsion of pore fluids with dissolved CO2. The CH4 concentration in residual gas subsequently increases with organic maturation and reaches the maximum at paleo-temperature of ca. 250°C. The CH4 concentration decreases during late metagenesis to metamorphism probably due to the formation of H2 gas and graphite. The H2 starts to increase at paleo-temperature of ca. 200°C. The H2 gas is the most abundant gas in residual gas of metapelite. The δ2Η value of H2 in shales and metapelites is quite low to be in the range of ca. –850 to −650‰. The change of major residual gas from CH4 to H2 with increasing paleo-temperature and the significantly low δ2H values of H2 suggest that H2 gas in shales and metapelites is largely derived from liberation of hydrogen in organic matter.

Insight into visible light spectrum changes with increasing reflectance in bituminite and inertinite macerals

White Light Reflectance Spectrometry (WLRS) allows the wavelength dispersion of reflectance (Ro) values to be measured and recorded. Previous studies have extensively evaluated the wavelength dispersion of macerals in various coal ranks and types. This study examines the wavelength dispersion of recycled vitrinite and inertinite macerals as well as bituminite macerals in an immature oil shale with the objective of studying the variation in wavelength dispersion associated with changes in Ro due to bacterial degradation of bituminite macerals and recycling of vitrinite macerals.Four samples were measured from the thermally immature zone of the Upper Cretaceous Second White Specks Formation in Central Alberta. These samples were analyzed geochemically (using Rock-Eval) and petrographically for reflectance and using WLRS. Red/green wavelength reflectance ratios in bituminite macerals demonstrate a drop off in variation due to bacterial degradation at Ro of approximately 0.55%, which is close to the onset of maturity. This dropoff suggests that the transformation of the organic matter (OM) leading to the liberation of hydrogen and oxygen rich molecules not only increases Ro but also results in a shift in the R/G ratio of the measured maceral. Wavelength dispersion trends in recycled vitrinite/inertinite macerals follows similar trends to those observed previously in coals, with a gradual decrease in reflectance toward lower wavelengths.Results indicate that the wavelength dispersion trends of recycled vitrinite/inertinite macerals in an organic rich mud rock closely follow the trends previously observed in coals. Determination of unaltered macerals is a difficult but important step in characterizing the organic matter of the oil shale and in calculating its source rock potential. This study demonstrates that the WLRS method can be used in conjunction with Ro by observing the R/G variability dropoff in order to distinguish the best preserved primary OM population from OM that has been bacterially or thermally degraded or altered.

Gas-Phase Ion-Molecule Reactions of Copper Hydride Anions [CuH2]- and [Cu2H3

Gas-phase reactivity of the copper hydride anions [CuH2]- and [Cu2H3]- toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH2]- is more reactive than [Cu2H3]-, consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH2]- was found to react with CS2 via hydride transfer to give thioformate (HCS2-) in competition with the formation of the organometallic [CuCS2]- ion via liberation of hydrogen; CO2 via insertion to produce [HCuO2CH]-; methyl iodide and allyl iodide to give I- and [CuHI]-; and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCH2CF3)]- and [CuH(SBu)]-. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS2 and CO2 are due to the lower lying π* orbital of the former, which allows it to accept electron density from the Cu center to form the initial three-membered ring complex intermediate, [H2Cu(η2-CS2)]-. In contrast, CO2 undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on SN2 mechanisms for reactions of [CuH2]- with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH2]- by methanol, 2,2,2-trifluoroethanol, and 1-butanethiol correlate with their gas-phase acidities, suggesting that reactivity is mainly controlled by the acidity of the substrate.

A Ni-Mg-Al layered triple hydroxide-supported Pd catalyst for heterogeneous acceptorless dehydrogenative aromatization.

In the presence of a Ni-Mg-Al layered triple hydroxide-supported Pd catalyst, the acceptorless dehydrogenative aromatization of a wide range of cyclohexanols/cyclohexanones and cyclohexylamines efficiently proceeded to give the corresponding phenols and anilines, respectively, in moderate to high yields with the liberation of molecular hydrogen.

Enhanced Visible-Light-Sensitive Two-Step Overall Water-Splitting Based on Band Structure Controls of Titanium Dioxide and Strontium Titanate

Visible light-induced two-step overall water-splitting was achieved by combining two types of photocatalysts, which were prepared by introducing foreign elements into rutile titanium dioxide (TiO2) and strontium titanate (SrTiO3) with a controlled electronic band structure. Rutile TiO2 and SrTiO3 were doped with chromium and tantalum (Cr,Ta-TiO2) and with rhodium (Rh-SrTiO3), respectively, to introduce visible-light sensitivity. Under irradiation with only visible light from a 420-nm LED lamp, the simultaneous liberation of hydrogen and oxygen with a molar ratio of ~2:1 was achieved with these two types of photocatalysts in the presence of iodate ion/iodide ion as a redox mediator.

Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles.

An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X-ray crystal analysis, and by quantum-mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate-determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.

Nonstationary processes that occur on nonpolarizable lead surface in sulfuric acid

The dynamics of variations in the currentless potential of a lead electrode in 2 M solution of sulfuric acid after cathode treatment by liberating hydrogen is studied. It is shown that, in the course of cathodic polarization, the liberation of hydrogen is accompanied by the formation of a film of lead sulfates due to corrosion that occurs on the metal surface. The major component of the measured potential is the voltage drop in the sulfate film. Two explanations for the simultaneous occurrence of the processes of hydrogen liberation and lead corrosion, which is impossible from the viewpoint of thermodynamics, are proposed. The first explanation is based on the electrical nonuniformity of the surface, which results from current localization at single active points (microzones), and on the absence of a protective cathodic potential at a distance from these points. The second explanation involves the voltage drop in the sulfate film, which is the component of the potential measured at the film–electrolyte interface. At the metal–film interface, the anodic polarization of the metal surface can occur, while nominally cathodic polarization takes place. Upon current interruption, the intricate processes of the growth and recrystallization of the sulfate film accompanied by the stepwise passivation of lead continue to occur. The limiting process for the corrosion system is the anodic reaction of the dissolution of lead.

Hydrogen evolution under visible light over the solid solution NiFe2−xMnxO4 prepared by sol gel

The continuous solid solution NiFe2−xMnxO4 (0 ≤ x ≤ 2) prepared by sol–gel is successfully tested for the hydrogen production under visible light. All spinels crystallize in a cubic structure with a particle size ranging from 30 to 63 nm. They exhibit p-type conductivity with an average thermopower of ∼135 μV K−1, a hole mobility of ∼9 × 10−5 cm2 V−1 s−1 and an activation energies in the range (0.12–0.33 eV). The optical transition of the most active photocatalyst NiFe1.6Mn0.4O4 (1.53 eV) is well matched to the solar spectrum. The chemical and physical properties are correlated to assess the feasibility of the spinels for the hydrogen liberation. The conduction band (−1.54 VSCE) is located below the H2O/H2 potential (∼−0.8 VSCE), allowing H2-evolution under visible light. The spinel dose, pH and S2O32− concentration are optimized. Under the ideal conditions, the volume of H2 liberation reaches 124 μmol at saturation after 20 min of irradiation.

PdAu-MnOx nanoparticles supported on amine-functionalized SiO2 for the room temperature dehydrogenation of formic acid in the absence of additives

Formic acid (HCOOH) has recently been suggested as a promising hydrogen carrier for fuel cell applications. However efficient hydrogen production through the decomposition of formic acid in the absence of additives under mild thermodynamic conditions constitutes a major challenge because of the ease poisoning of active metals with CO formed as intermediate during formic acid decomposition. Recently, we have reported (App. Catal. B: Env. 164 (2015) 324) our discovery that the separately nucleated MnOx nanoparticles act as CO-sponge around catalytically active Pd nanoparticles exist on the same support and enhances both the activity and CO-resistivity of Pd nanoparticles. Using this important finding, herein, we present a new catalyst system consists of the physical mixture of PdAu alloy and MnOx nanoparticles supported on amine-grafted silica (PdAu-MnOx/N-SiO2) for the room temperature dehydrogenation of formic acid in the absence of any additives. PdAu-MnOx/N-SiO2 catalyst was simply prepared by deposition–reduction technique in water at room temperature with high reproducibility and characterized by the combination of various spectroscopic tools including ICP-OES, P-XRD, DR/UV–vis, XPS, BFTEM, STEM-EDX, STEM-line analysis and CO-stripping voltammetry techniques. The sum of their results shows that the formation of physical mixture of PdAu alloy and MnOx (dmean=2.2nm) nanoparticles on the surface of support material. This new catalytic material facilitates the hydrogen liberation through the additive-free formic acid dehydrogenation at room temperature with previously unprecedented activity (TOF=785molH2molcatalyst−1h−1), converging to that of the existing state of the art homogenous catalysts. This new superior catalytic system enables facile catalyst recovery and very high stability against agglomeration, leaching and CO poisoning, which make it highly reusable catalyst (retains >92% activity and 85% conversion at the 5th catalytic reuse) in the additive-free formic acid dehydrogenation at room temperature.

Enhanced photocatalytic activity by bulk trapping and spatial separation of charge carriers: A case study of defect and facet mediated TiO2

Revealing the interplay between composition and structure of a given photocatalyst allows in-depth understanding of the photocatalytic mechanism and also presents as an effective way to optimise the photocatalytic activity. In this work, by studying the property and performance of defect and facet mediated rutile TiO2 synthesized via a facile oxidation reaction, we demonstrated that the abundant self-doped defects can not only render visiblie responce to the reduced TiO2 but also supress the prompt recombination of the charge carriers through bulk trapping, while the {111}–{110} facet couples can induce the spatial separation of the e–h pairs. A synergistic effect between the defects and the facets was observed in the co-mediated TiO2, and its performance of hydrogen liberation was enhanced by a factor of 18 under simulated solar light compared with referenced commercial rutile, consequently. The present work sheds new light on how the composition and structure of a material can be finely tuned and work synergistically to achieve a much boosted performance.

Visible-light-sensitive two-step overall water-splitting based on band structure control of titanium dioxide

Visible light-induced two-step overall water splitting was achieved by combining two types of photocatalysts, which were prepared by introducing foreign elements into titanium dioxide (TiO2) with a controlled electronic band structure. Rutile and anatase TiO2 were doped with chromium and tantalum to introduce visible-light sensitivity. Under irradiation with only visible light from a 420-nm LED lamp, the simultaneous liberation of hydrogen and oxygen with a molar ratio of ∼2:1 was achieved with these two types of TiO2-based photocatalysts in the presence of iodate ion/iodide ion as a redox mediator.

Experimental and theoretical mechanistic investigation of the iridium-catalyzed dehydrogenative decarbonylation of primary alcohols.

The mechanism for the iridium-BINAP catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of molecular hydrogen and carbon monoxide was studied experimentally and computationally. The reaction takes place by tandem catalysis through two catalytic cycles involving dehydrogenation of the alcohol and decarbonylation of the resulting aldehyde. The square planar complex IrCl(CO)(rac-BINAP) was isolated from the reaction between [Ir(cod)Cl]2, rac-BINAP, and benzyl alcohol. The complex was catalytically active and applied in the study of the individual steps in the catalytic cycles. One carbon monoxide ligand was shown to remain coordinated to iridium throughout the reaction, and release of carbon monoxide was suggested to occur from a dicarbonyl complex. IrH2Cl(CO)(rac-BINAP) was also synthesized and detected in the dehydrogenation of benzyl alcohol. In the same experiment, IrHCl2(CO)(rac-BINAP) was detected from the release of HCl in the dehydrogenation and subsequent reaction with IrCl(CO)(rac-BINAP). This indicated a substitution of chloride with the alcohol to form a square planar iridium alkoxo complex that could undergo a β-hydride elimination. A KIE of 1.0 was determined for the decarbonylation and 1.42 for the overall reaction. Electron rich benzyl alcohols were converted faster than electron poor alcohols, but no electronic effect was found when comparing aldehydes of different electronic character. The lack of electronic and kinetic isotope effects implies a rate-determining phosphine dissociation for the decarbonylation of aldehydes.

Hydrogen Generation through Cuprous Chloride-Hydrochloric Acid Electrolysis

Due to fast industrialization the consumption as well as the cost of fossil fuels like petrol, diesel etc in the world is rising enormously leading to the generation of greenhouse gases like carbon monoxide, carbon dioxide etc besides decreasing the availability of the above fuels. The emission of these greenhouse gases rises the globe’s temperature leading the earth to face many dangerous complications. In order to save the earth from effect of rise of temperature and also to have an eco-friendly alternate energy fuel especially for the transport sector, attention is being focused on the generation of hydrogen gas which meets the above situations. During the combustion of hydrogen gas it emits only the beneficial water vapour to the atmosphere. In this research paper investigation has been carried out through CuCl-HCl electrolysis with 1M CuCl anolyte and 6M HCl catholyte for the generation of hydrogen gas at 70oC at normal atmospheric pressure employing a double compartment electrolytic cell having a nafion cation exchange membrane-324. Anode was graphite and cathode was 0.30 mg cm-2 platinum coated graphite. At a current density of 250 A m-2 the current efficiency for the oxidation of CuCl to CuCl2 and the formation of hydrogen gas was nearly 100% and the rate of hydrogen liberation was found to be 2 l h-1. Voltage efficiency and energy consumption values are calculated and are found to be more encouraging since they are more economical with less energy operation. The formed CuCl2 was reduced back to CuCl anolyte by chemical reduction with copper powder in 6M HCl at 70oC and the regenerated CuCl anolyte was again used in the CuCl-HCl electrolysis.

Sintering effect on crystallite size, hydrogen bond structure and morphology of the silane-derived silicon powders

The effect of sintering treatment on the amorphous silicon powders from monosilane pyrolysis was investigated to enhance polysilicon yield in the FBR-CVD process. The crystallite size, hydrogen bond structure and morphology of the powders were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Diffuse Reflection Fourier Transform Infrared Spectroscopy (DR-FT-IR) and Zeta Potential Analyzer (ZPA). The results showed that the higher sintering temperature and lower pressure were more favorable to the growth of silicon crystallites and the liberation of hydrogen from silicon hydrides. The crystallite size increased significantly with a critical low FWHM when the sintering temperature was at 750°C, and the hydrogen releasing from polysilanes and OSiH took place remarkably with a relative flat IR spectrum when the vacuum condition was implemented. Moreover, the particle aggregation was strengthened with broad particle size distribution as long sintering duration or high temperature applied, and the fusion occurred as the temperature was high enough but still with good crystallinity.

Liberation of molecular hydrogen (H2) and methane (CH4) during non-isothermal pyrolysis of shales and coals: Systematics and quantification

Open system non-isothermal (programmed) pyrolysis experiments have been conducted to investigate the pyrolytic liberation of molecular hydrogen (H2) and methane (CH4) from carbonaceous shales and coals of different rank and organo- and lithofacies types. The aim was to explore the origin and generation pathways of H2 and their relation to methane generation mechanisms. The experiments were performed at two heating rates (0.5 and 1°C/min) up to a final temperature of 1200°C. CH4 and H2 generation usually did not proceed simultaneously but with a distinct temperature offset. Molar yields of H2 under open system pyrolysis conditions were always considerably higher than the corresponding CH4 yields. While coaly material showed one single, broad H2 generation peak, H2 evolution from shales revealed complex release patterns.The pyrograms (gas generation rate as a function of temperature) were classified according to the number and shape of peaks and the maximum temperatures of the main phases' gas liberation. H2 pyrograms were tentatively subdivided into five groups (A–E) according to peak patterns, reflecting different thermal stabilities of precursor moieties.Based on previous research on H2 generation mechanisms, different evolution pathways are proposed to explain the observed H2 release patterns. For shales, the dominant mechanism shifts from cracking of hetero-bonds and demethylation in Group A towards aromatization and condensation in Groups B and C. In coals, aromatization and condensation are considered to be the predominant H2 evolution mechanisms. The molar yields of H2 correlate like the CH4 yields with the TOC and Rock-Eval S2 values of the samples, indicating a purely organic origin. The results have implications for hydrogen balance considerations during thermal maturation of coals and gas/oil shales.

Photocatalytic hydrogen evolution on the hetero-system polypyrrol/TiO2 under visible light

The semiconducting properties of the hetero-system polypyrrol (PPy)/TiO2 are investigated for the first time to assess its photo catalytic hydrogen evolution under visible light. The hetero-system PPy/TiO2 is stable up to ∼345 K, with a weight loss accounting for ∼1.2%. The X-ray diffraction shows mixed phases with the rutile TiO2 variety. Optical transitions at 0.42 and 3.01 eV, directly allowed, are determined for PPy and TiO2 respectively. The p-type conductivity of PPy is evidenced from the Mott–Schottky plot; In neutral solution, a flat band potential of 0.11 VSCE and a holes density of 4.57 × 1021 cm-3 are obtained. The electrochemical impedance spectroscopy, measured over a wide frequency range (1 mHz–105 Hz), reveals the contribution of the bulk and grain boundaries with a constant phase element (CPE). The energetic diagram predicts the electron injection from PPy into TiO2 and the best photoactivity is achieved at pH ∼7. A hydrogen liberation rate of 1.15 mmol h−1 (g catalyst)−1 and a quantum efficiency of 0.17% under full light (29 mW cm−2) are determined in presence S2O32−. The photoactivity is completely restored during the second cycle, indicating a zero deactivation effect.

Effect of current mode on PEO treatment of magnesium in Ca- and P-containing electrolyte and resulting coatings

Plasma electrolytic oxidation (PEO) coatings were produced on commercially pure magnesium in a biologically friendly electrolyte composed of 2gL−1 Ca(OH)2 and 12gL−1 Na3PO4·12H2O using pulsed unipolar and bipolar current regimes with negative biasing varying from 0 to 20mAcm−2. Analysis of voltage transients was performed to characterise the PEO processes. The coating morphology and phase composition were studied by scanning electron microscopy and X-ray diffraction technique, respectively. In vitro corrosion performance of the coatings was evaluated in a simulated body fluid at 37±1°C, using electrochemical techniques including open circuit potential monitoring, electrochemical impedance spectroscopy and potentiodynamic polarisation scans. The influence of the negative biasing on the PEO process and resulting coating characteristics is discussed. Unlike generally recognised beneficial effects of the negative biasing in PEO treatments of some other metal-electrolyte systems, it was found that detrimental effects are induced to the coatings on cp-Mg produced in the studied electrolyte when the negative current amplitude increases, which may be attributed to hydrogen liberation at the coating/substrate interface during the negative biasing cycles. As a result, a deterioration of vitro corrosion performance was observed for the pulsed bipolar PEO coatings compared to those produced using the pulsed unipolar regime which provides better quality coatings.