Liberation Of Hydrogen Research Articles

Neutron diffraction studies for realtime leaching of catalytic Ni.

The leaching of Al from intermetallic samples of Nickel Aluminium alloys to form Raney-type nickel catalysts is widely used in the hydrogenation industry, however, little is known of the leaching process itself. In this study, the leaching of Al was measured in realtime, in situ, using the high-flux powder neutron diffractometer, D20, at the Institut Laue-Langevin. Despite the liberation of hydrogen and effervescent nature of the reaction the transformation of the dry powder phases into Raney-type Ni was determined. Samples produced by gas-atomisation were found to leach faster than those produced using the cast and crushed technique. Regardless of processing route of the precursor powder, the formation of spongy-Ni occurs almost immediately, while Ni2Al3 and NiAl3 continue to transform over longer periods of time. Small-angle scattering and broadening of the diffraction peaks is an evidence for the formation of the smaller Ni particles. Understanding the kinetics of the leaching process will allow industry to refine production of catalysts for optimum manufacturing time while knowledge of leaching dynamics of powders produced by different manufacturing techniques will allow further tailoring of catalytic materials.

Defect self-doped TiO₂ for visible light activity and direct noble metal anchoring.

A facile approach was developed for preparing defective, self-doped TiO2, which shows remarkable visible light activity in the photocatalytic degradation of RhB and hydrogen liberation from water. Moreover, noble metal was directly deposited onto the TiO2 surface via an in situ redox reaction between surficial Ti(3+) and metal salt. The lack of involvement of foreign reducing agents or stabilizers permits intimate contact between metal nanoparticles and the TiO2 substrate, which ensures the facilitated interfacial charge transfer. The strategy presented in this work may be applied to design other defect and noble metal mediated visible-light-active photocatalysts.

Enhanced photocatalytic hydrogen production under visible light over a material based on magnesium ferrite derived from layered double hydroxides (LDHs)

The magnesium ferrite derived from layered double hydroxides (molar ratio Mg/Fe = 2), synthesized by coprecipitation method is found to be an active photocatalyst for hydrogen production from water under visible light. The structural, morphological, and optical properties of the material are characterized by powder X-ray diffraction, scanning electron microscopy, and Fourier transform infrared and UV-Vis diffuse reflectance spectroscopy. The results indicated that the material has small particles with a diameter of ~1.8 nm and a specific surface area above 60m g . The optical properties revealed semiconducting properties with band gap energy of 1.74 eV, showing an efficient visible light absorption. The cyclic voltammetry indicated that the photoelectrochemical response of the material is characterized by type p conductivity. Furthermore, the solid exhibited a high photoactivity toward the reduction of water, which is attributed to the efficient separation and transportation of the photogenerated charge carriers. Under visible light, the best performance is achieved at pH 10 with a hydrogen liberation amount and quantum efficiency of 223mol and 0.5%, respectively, after 1 h of irradiation. Copyright © 2014 John Wiley & Sons, Ltd.

Thermal Decomposition of Thin Methanol Films on Deoxygenated Vanadium

A polycrystalline V sheet was deoxygenated via high-temperature annealing. Then, interactions with methanol films deposited on it were investigated at T < 200 K using temperature-programmed desorption and time-of-flight secondary ion mass spectrometry. The methanol decomposes at the interface when the film is deposited at 70 K, as inferred from modifications of sputtered ion intensities. By heating multilayer films at T > 120 K, hydrogen liberation occurs along with a strong depression of methanol desorption because methanol is decomposed sequentially at the interface. No release of reacted species including oxygen and carbon was identified, except for a trace of water and methane. The hydrogen is abstracted not only from the O–H bond but also from the C–H bond, as evidenced by isotope scrambling of liberated hydrogen. The results differ significantly from those of previous studies that examined single-crystal V substrates. The reduction of oxygen content in the bulk of the V substrate is necessary for multilayer methanol decomposition because reacted species including oxygen must be incorporated in the subsurface layers.

Photocatalytic hydrogen evolution over the hetero-junction CoAl2O4/ZnO

The photoevolution of hydrogen is demonstrated on the new hetero-junction CoAl2O4/ZnO. The nano sized spinel obtained from hydrotalcite calcination exhibits a high specific surface area (130 m2 g−1) and good photocatalytic activity. The optical transition of the spinel CoAl2O4 (1.56 eV), directly allowed, is due to Co2+: d–d transition. The capacitance measurements indicate a negative slope, characteristic of p type conduction with a flat band potential of −0.11 V SCE. The photoactivity is thermodynamically predicted from the energy band diagram. The potential of the conduction band (−1.51 V SCE) is more negative than the hydrogen level, leading to spontaneous hydrogen liberation. The spinel is activated by visible light and the electrons are transferred to water via ZnO. A reducing agent is required to prevent the photocorrosion, SO3 2− being particularly favorable and CoAl2O4 approaches 100 % stability. The hetero-junction consists of a mixture of powders (x%CoAl2O4/125 mg ZnO) exhibits self-sensitization for the hydrogen production in basic medium (pH~12.5) with an evolution rate of 2.04 × 10−2 cm3 h−1 (g catalyst)−1 under optimal conditions.

Fabrication, Characterization, and Photoelectrochemical Properties of Cu‐Doped PbTiO3 and Its Hydrogen Production Activity

AbstractWe report herein the fabrication of visible‐light responsive n‐type PbTiO3 by a combustion method and p‐type Cu‐doped PbTiO3 by an impregnation method to improve hydrogen production activity. Copper was doped into the PbTiO3 lattice up to 1 wt %; any further increase in the loading resulted in the formation of CuO on the surface of the sample. Photoluminescence confirmed that 1 wt % Cu‐doped PbTiO3 effectively suppressed the defects in PbTiO3, which helped to reduce the recombination rate of the photoinduced charge carriers. The prepared PbTiO3 photocatalyst behaves as an n‐type semiconductor, whereas 1 wt % Cu‐doped PbTiO3 behaves as a p‐type semiconductor. The photocatalytic hydrogen production activity of PbTiO3 increased with increasing Cu content up to 1 wt % and thereafter decreased upon further loading. The 1 wt % Cu‐doped PbTiO3 sample showed higher activity for hydrogen liberation than pristine PbTiO3 (2.5 times) and all of the other CuO‐loaded samples. The energy conversion efficiency of 1 wt % Cu‐doped PbTiO3 was 5.95 % for hydrogen production under visible‐light irradiation. The enhanced hydrogen production activity of Cu‐doped PbTiO3 was discussed on the basis of optimum copper doping, photoluminescence intensity, and their band‐edge positions. However, the higher activity of CuO‐loaded (&gt;1 wt %) PbTiO3 relative to that of neat PbTiO3 is perhaps a result of the extensive light absorption properties of the CuO nanoparticles, which help to generate more electron–hole pairs on the surface.

Improved dehydrogenation properties of the combined Mg(BH4)2·6NH3–nNH3BH3 system

A combined strategy via mixing Mg(BH4)2·6NH3 with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH4)2·6NH3. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH4)2·6NH3–6AB is achieved with the assistance of ZnCl2, which plays a crucial role in stabilizing the NH3 groups and promoting the recombination of NHδ+⋯HBδ−. Specifically, the Mg(BH4)2·6NH3–6AB/ZnCl2 (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.

Hydrogen Generation by Water Reduction with [Cp*2Ti(OTf)]: Identifying Elemental Mechanistic Steps by Combined In Situ FTIR and In Situ EPR Spectroscopy Supported by DFT Calculations

A detailed mechanism of hydrogen production by reduction of water with decamethyltitanocene triflate [Cp*2 Ti(III) (OTf)] has been derived for the first time, based on a comprehensive in situ spectroscopic study including EPR and ATR-FTIR spectroscopy supported by DFT calculations. It is demonstrated that two H2 O molecules coordinate to [Cp*2 Ti(III) (OTf)] subsequently forming [Cp2 *Ti(III) (H2 O)(OTf)] and [Cp*Ti(III) (H2 O)2 (OTf)]. Triflate stabilizes the water ligands by hydrogen bonding. Liberation of hydrogen proceeds only from the diaqua complex [Cp*Ti(III) (H2 O)2 (OTf)] and involves, most probably, abstraction and recombination of two H atoms from two molecules of [Cp*Ti(III) (H2 O)2 (OTf)] in close vicinity, which is driven by the formation of a strong covalent TiOH bond in the resulting final product [Cp*2 Ti(IV) (OTf)(OH)].

Imperfections in plaster surfaces caused by the release of hydrogen gas of polyvinylsiloxane impression materials

Purpose: The purpose of this study was to evaluate the number of bubbles of hydrogen liberation from different polyvinylsiloxane impression materials. Material and Methods: A metallic stainless steel jig containing six receptacles, like trays, was constructed to accommodate the impression materials. The molds were poured immediately, and at 1 hour, 12 hours and 24 hours in order to evaluate the number of bubbles present in each sample. Each sample was made of improved stone (type IV), totaling 48 samples for each polyvinylsiloxane impression material. After setting, the surface of each sample was inspected under a light microscope at 40x magnification and the number of bubbles was recorded. Results were submitted to statistical analysis by ANOVA and Tukey Test (p=.05). Results: ANOVA test showed statistically significant differences among the polyvinylsiloxane impression materials, as determined by the number of bubbles (p&lt;.05). The Tukey test showed statistically significant differences among the three groups (p&lt;.05). Conclusions: Statistical differences were found between addition silicone with regard to the ideal time to wait for the plaster cast, showing that Aquasil results in fewer bubbles in plaster, followed by the President and Simply Perfect samples.

ChemInform Abstract: Mechanisms of Metal‐Catalyzed Dehydrocoupling Reactions

AbstractReview: 59 refs.

Self-similar approximation for the process of formation of microporosity in alloys of light metals

A physical and mathematical model is proposed for description of the formation of microporosity in an alloy within the framework of the two-phase zone approximation with account for the real state diagram of the alloy. The formation of microporosity in an Al–Si melt in the process of its solidification as a result of the liberation of hydrogen from it was investigated in the self-similar approximation. The influence of the parameters of solidification of this alloy on the formation of a gas microporosity in it was analyzed.

Efficient Hydrogen Liberation from Formic Acid Catalyzed by a Well‐Defined Iron Pincer Complex under Mild Conditions

Hydrogen liberation: An attractive approach to reversible hydrogen storage applications is based on the decomposition of formic acid. The efficient and selective hydrogen liberation from formic acid is catalyzed by an iron pincer complex in the presence of trialkylamine. Turnover frequencies up to 836 h⁻¹ and turnover numbers up to 100,000 were achieved at 40 °C. A mechanism including well-defined intermediates is suggested on the basis of experimental and computational data.

Photo-electrochemical characterization of polypyrrol: Application to visible light induced hydrogen production

The semi-conducting properties of polypyrrol (PPy) are investigated by the photo-electrochemical technique. The polymer is stable up to~190°C, above which a weight loss accounting for~60% is observed. An optical transition of 1.02eV is determined, directly allowed. Further indirect transition is determined at 0.37eV. The electrical conduction is characteristic of degenerate behavior with an activationless hopping and a hole mobility of 4.2×10−3cm2V−1s−1. The p-type conductivity is evidenced from the Mott–Schottky plots. In neutral solution, a flat band potential of 0.108VSCE and a holes density of 4.57×1021cm−3 are determined. The electrochemical impedance spectroscopy (EIS), measured over a wide frequency range (1mHz–105Hz), reveals the bulk contribution with a constant phase element (CPE). The straight line at 43° at low frequencies region is due to the Warburg diffusion. The energy diagram shows the feasibility of H2 photo-evolution with a low over-voltage. The best performance is achieved at pH∼7 in the presence of S2O32− as holes scavenger. A hydrogen liberation rate of 660μmolh−1 (g catalyst)−1 and a quantum efficiency of 0.21% under visible light (29mWcm−2) are determined. The system is valuable for the chemical storage through the uphill reaction: (S2O32−+3H2O→2SO32−+2H2+2H+, ΔGf°=24.3kJmol−1).

The postmodern human

A combined strategy via mixing Mg(BH4)2·6NH3 with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH4)2·6NH3. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH4)2·6NH3–6AB is achieved with the assistance of ZnCl2, which plays a crucial role in stabilizing the NH3 groups and promoting the recombination of NHδ+⋯HBδ−. Specifically, the Mg(BH4)2·6NH3–6AB/ZnCl2 (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.

Enhancing the Electrocatalytic Activity of Pt–Pd Catalysts by Introducing Porous Architectures

AbstractImproving the electrocatalytic activity of Pt‐based catalysts is of great importance for the development of heterogeneous catalysis, fuel cells, and analytical sensors. Herein, we achieve significant enhancement of the catalytic activity of Pt–Pd bimetallic materials towards glucose electrooxidation by introducing porous architectures with three‐dimensional dendritic microstructures, which were fabricated in situ on desired substrates through electrochemically reducing precursors along with periodic bubbling caused by the intermittent liberation of hydrogen. The synthesized Pt–Pd materials were characterized by SEM, nitrogen adsorption/desorption, energy dispersive spectroscopy, XRD, inductively coupled plasma optical emission spectrometry, and electrochemical techniques. Encouragingly, an extra‐large active surface area of up to 80.8 m2 g−1 was obtained for the porous Pt–Pd nanostructures, almost 3.8 times that of the Pt–Pd alloys prepared by standard electrodeposition techniques. As a result, the synthesized Pt–Pd with porous frameworks exhibited remarkably improved electrocatalytic properties for glucose oxidation in neutral media, with 1.5 times the mass activity compared to the conventional Pt–Pd structure. In addition, the porous Pt–Pd catalysts could be reused at least 100 times in the presence of chloride ions, with negligible loss of activity.

Mechanisms of metal-catalyzed dehydrocoupling reactions

This review summarizes selected mechanistic insight garnered from reactions that form bonds between main group elements with liberation of hydrogen, dehydrocoupling or dehydropolymerization reactions. Focus has been made where mechanistic study has been done or provides unique insight as compared to previous work. Thus, a limited number of catalysts and substrates will be discussed, but a broad range of mechanistic features will be noted. A comparative approach considering dehydrocoupling reactions that appear to proceed by certain mechanistic steps is taken here, beginning with steps that are well established and general then moving to those that are newer, at least to this application.

Ruthenium Pincer‐Catalyzed Cross‐Dehydrogenative Coupling of Primary Alcohols with Secondary Alcohols under Neutral Conditions

AbstractCross‐dehydrogenative coupling of primary alcohols with secondary alcohols to obtain mixed esters with the liberation of molecular hydrogen is achieved in high yield and good selectivity under neutral conditions, using a bipyridyl‐based PNN ruthenium(II) pincer catalyst.

Hydrogen and Oxygen Evolution Photocatalysts Synthesized from Strontium Titanate by Controlled Doping and Their Performance in Two-Step Overall Water Splitting under Visible Light

A visible-light-induced two-step overall water splitting was achieved by combining two types of photocatalysts prepared by introducing foreign elements into the identical mother structure with a controlled electronic band structure. Strontium titanate (SrTiO3) was selected as the mother structure and was doped with either vanadium (and sodium) or rhodium to introduce visible light sensitivity. By utilizing these two types of SrTiO3-based photocatalysts, simultaneous liberation of hydrogen (H2) and oxygen (O2) with a molar ratio of ∼2:1 was achieved in the presence of iodate ion (IO3–)/iodide ion (I–) as a redox mediator under irradiation with only visible light (>420 nm).

Selective Acceptorless Conversion of Primary Alcohols to Acetals and Dihydrogen Catalyzed by the Ruthenium(II) Complex Ru(PPh3)2(NCCH3)2(SO4)

AbstractThe complex bis(acetonitrile)bis(triphenylphosphine)ruthenium(II) sulfate [Ru(PPh3)2(NCCH3)2(SO4)], fully characterized spectroscopically and by a single crystal X‐ray study, catalyzes at 110 °C the direct transformation of primary alcohols to the corresponding acetals with liberation of molecular hydrogen. The formation of acetals proceeds via direct substitution of the hydroxy group of the hemiacetal intermediate by an alcohol molecule. The closely related bis(triphenylphosphine)ruthenium(II) acetate [Ru(PPh3)2(OAc)2] catalyzes the conversion of primary alcohols to the corresponding esters rather than acetals.

The Application Study of Surfactant in Preparation of Battery Materials

With the decline in the amount of global energy and degradation of the environment, the development of environmentally friendly new energy is paid widely attention. New energy material plays a great guiding and supporting role. Battery material, mainly related to cathode, anode, electrolyte and diaphragm, is an important part of energy storage and power supply. Surfactants can change metal oxide crystal formation, inhibit liberation of hydrogen; grow and corrosion of fern-leaf crystal; delay passivation electrode. Therefore, latex made of surfactants can serve as a "micro-reaction tank" and prevent nano-particles agglomeration. This paper provides an overview of surfactant in preparation of battery materials and research progress of waste battery recycling.