Hydrogen generation from splitting water with Al–Bi(OH)3 composite promoted by NaCl

In this paper, a novel Al–Bi(OH)₃ system hydrogen-generating material is investigated. Hydrolysis experiments show that the hydrolysis properties of the Al–10 wt% Bi(OH)₃ composite are significantly improved by doping with sodium chloride, and the Al–10 wt% Bi(OH)₃–5 wt% NaCl composite has a low activation energy (10.4 kJ mol⁻¹). With the further optimization of milling time, the hydrogen yield of Al–10 wt% Bi(OH)₃–5 wt% NaCl composite reaches 1000 mL g⁻¹ in 1 min. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy and thermogravimetric analysis are applied to characterize the composite and explore the hydrolysis mechanism. The characterization results show that the activation of aluminum mainly comes from three factors: (1) The formation of alumina during ball milling plays an important role in preventing the agglomeration between Al–Bi, Al–Al and Bi–Bi; (2) Bismuth generated during ball milling can form micro-galvanic cell with aluminum to promote the corrosion of aluminum; (3) Sodium chloride as a grinding aid contributes to crush aluminum powder, and chloride ions facilitate the corrosion of aluminum in the hydrolysis process. In addition, the drying method and initial water temperature have a great influence on by-products. The composite is expected to be used in mobile emergency fuel cell due to its rapid hydrogen production capacity.     

Hydrogen generation by aluminum corrosion in seawater promoted by suspensions of aluminum hydroxide

Nowadays, new processes of H₂ generation from water via Al corrosion are mainly limited by Al passivation. Here we report on the systematic assessment of H₂ production by corrosion of Al in seawater suspensions prepared with NaAlO₂. The reported results are encouraging, since it was observed that seawater suspensions tested can prevent Al passivation during H₂ evolution, reaching 100% yields at ca. 700 cm³ H₂ min⁻¹. XRD analysis revealed the formation of solid Al(OH)₃ (bayerite) in initial seawater suspensions. So, model suspensions were prepared using NaAlO₂ + Al(OH)₃ in distilled water, which even improved the results obtained in seawater. Suspended particles of Al(OH)₃ act as nuclei in a mechanism of seeded crystallization, which prevents Al surface passivation. Moreover, a synergistic effect of Al(OH)₃ suspensions in combination with NaAlO₂ solutions was key in promoting Al corrosion. The effect of NaCl in aqueous suspensions was also studied, but it was insignificant compared to this synergistic effect. The composition of suspensions was optimized and a 0.01 M NaAlO₂ solution with 20 g dm⁻³ Al(OH)₃ was selected as candidate to generate H₂ at pH ca. 12 with high efficiency. Consecutive runs of the selected composition were performed obtaining ca. 90% yields in all of them.     

Al–Li3AlH6: A novel composite with high activity for hydrogen generation

A novel material for hydrogen generation with high capacity of H₂ generation has been successfully prepared by ball milling the mixture of Al and home-made fresh Li₃AlH₆ powder. Its theoretical capacity of hydrogen released is higher than that of pure Al. Results obtained have shown conversion efficiency of Al–Li₃AlH₆ composite can be close to 100% by increasing the content of Li₃AlH₆. When the content of Li₃AlH₆ is 20 wt%, the maximum hydrogen generation rate and hydrogen yield are 2737.6 mL g⁻¹ min⁻¹ and 1513.1 mL g⁻¹, respectively, at room temperature. By XRD, SEM analyses and reaction heat measurements, it demonstrates that the additive Li₃AlH₆ can provide an additional source of H₂ and an alkaline environment (LiOH) as well as additional heat to promote the Al/H₂O reaction. Therefore, the Al–Li₃AlH₆ composite has a very high activity and high capacity of hydrogen released.     

Hydrogen generation by aluminum‐water reaction in acidic and alkaline media and its reaction dynamics

The additives AlCl₃, CoCl₂, Al(OH)₃, Ca(OH)₂, and NaAlO₂ are added to water to regulate its pH value (pH = 2‐13) in this study. The effects of media on the aluminum‐water reaction are investigated. Up to an increase in temperature, the hydrogen generation rate in different media increases. H⁺, OH^?, Cl^?, or Co produced from the additive favors the initial removal of the oxide film and aluminum corrosion. Therefore, the initial hydrogen generation rate increases in acidic and alkaline media. The synergistic effect of the formed fresh Co and Cl^? catalyzes aluminum‐water reactions. However, the amount of hydrogen decreases with increasing mass of CoCl₂ because of agglomeration of the catalyst Co. The higher concentration of OH^? ions aids hydrogen generation. However, the reaction rate became slow after the rapid consumption of OH^?, when the concentration of OH^? was relatively small. Hydrogen is quickly generated and Al is completely reacted upon following additions of Al due to the cooperation between H⁺, Cl^?, OH^? ions, and the formed Al(OH)₃.     

Examination of the catalytic effect of Ni,NiCr, and NiV catalysts prepared as thin films by magnetron sputtering process in the hydrolysis of sodium borohydride

In this study, nickel, nickel-chromium alloy, and nickel-vanadium alloy were coated to form a thin film on the slides prepared by magnetron sputtering process, which were used as a catalyst for the hydrolysis of alkaline sodium borohydride. Factors, such as the temperature of the solution, amount of the catalyst, initial pH of the solution and the performance of these catalysts on hydrogen generation rate were investigated using response surface methodology. Moreover, the catalysts were characterized using XRD and FE-SEM/EDS analyses. Utilizing the obtained optimum conditions of the response surface methodology estimation, the maximum hydrogen generation rate was 35,071 mL min⁻¹ g_NiV⁻¹ from NiV catalyst at 60 °C, pH 6, and 1.75 g catalyst conditions. Under the same experiment conditions, the maximum hydrogen generation rates of Ni and NiCr catalyst systems are 28,362 mL min⁻¹ g_Ni⁻¹, and 30,608 mL min⁻¹ gNiCr⁻¹, respectively.     

Room temperature hydrogen generation from hydrolysis of ammonia–borane over an efficient NiAgPd/C catalyst

NiAgPd nanoparticles are successfully synthesized by in-situ reduction of Ni, Ag and Pd salts on the surface of carbon. Their catalytic activity was examined in ammonia borane (NH₃BH₃) hydrolysis to generate hydrogen gas. This nanomaterial exhibits a higher catalytic activity than those of monometallic and bimetallic counterparts and a stoichiometric amount of hydrogen was produced at a high generation rate. Hydrogen production rates were investigated in different concentrations of NH₃BH₃ solutions, including in the borates saturated solution, showing little influence of the concentrations on the reaction rates. The hydrogen production rate can reach 3.6–3.8 mol H₂ mol_cat⁻¹ min⁻¹ at room temperature (21 °C). The activation energy and TOF value are 38.36 kJ/mol and 93.8 mol H₂ mol_cat⁻¹ min⁻¹, respectively, comparable to those of Pt based catalysts. This nanomaterial catalyst also exhibits excellent chemical stability, and no significant morphology change was observed from TEM after the reaction. Using this catalyst for continuously hydrogen generation, the hydrogen production rate can be kept after generating 6.2 L hydrogen with over 10,000 turnovers and a TOF value of 90.3 mol H₂ mol_cat⁻¹ min⁻¹.     

Hydrogen generation by splitting water with Al–Li alloys

In order to prevent the inert alumina film from forming on the surface of Al metal particles, Li is added into Al to form Al–Li alloy. It can improve the reactivity of Al with water. The prepared Al–Li alloy can rapidly split water to produce hydrogen. With increasing Li content of alloy, the hydrogen generation rate is promoted. The ultimate hydrogen yields of samples can reach 100%. The effect of initial water temperature on the hydrogen generation has been investigated. Even in the water at 0 °C, hydrogen can also be produced rapidly. Composition of solution has some effect on the hydrogen generation. Especially, Mg²⁺ or NO₃^? has negative influence on the hydrogen generation and can reduce the ultimate hydrogen yield of alloy. Longer air exposure time will also decrease the ultimate hydrogen yield. After reaction, Al and Li enter into the residue in the form of LiAl₂(OH)₇·2H₂O and LiAl₂(OH)₇·xH₂O or Al(OH)₃. After calcinations, these reaction by‐products can be easily recycled by existing metallurgical process. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrogen evolution under visible light illumination on the solid solution CdxZn1-xS prepared by ultrasound-assisted route

The complete solid solution Cd_xZn_1-xS (0 ≤ x ≤ 1) prepared by ultrasound-assisted route is used for the H₂ formation upon visible light illumination. The correlation of chemical and physical characterizations permits to assess the feasibility of the system for the photocatalytic hydrogen evolution. The compounds crystallize in a cubic structure (x < 0.5) and convert to hexagonal variety above 0.5 with a crystallite size (8–17 nm). All materials exhibit n-type conduction with an activation energy (0.22–0.05 eV). The optical transitions are directly allowed (3.10–2.30 eV) and appropriately matched to the sun spectrum while the conduction band, deriving from (Zn, Cd) ns orbital (∼-1 V_SCE), is positioned above the H₂O/H₂ potential (∼-0.68 V_SCE), allowing H₂-liberation under visible illumination. The photocatalyst dose, pH and SO₃²⁻ concentration are optimized. Under the favorable conditions, the H₂ liberation rate reaches 12 × 10⁻⁴ mL mg⁻¹ min⁻¹ with a quantum yield η(H₂) of 1.40%.     

Single-step synthesized dual-layer hollow fiber membrane reactor for on-site hydrogen production through ammonia decomposition

On-site hydrogen production via catalytic ammonia decomposition presents an attractive pathway to realize H₂ economy and to mitigate the risk associated with storing large amounts of H₂. This work reports the synthesis and characterization of a dual-layer hollow fiber catalytic membrane reactor for simultaneous NH₃ decomposition and H₂ permeation application. Such hollow fiber was synthesized via single-step co-extrusion and co-sintering method and constitutes of 26 μm-thick mixed protonic-electronic conducting Nd_5.5Mo_0.5W_0.5O_11.25-δ (NMW) dense H₂ separation layer and Nd_5.5Mo_0.5W_0.5O_11.25-δ-Ni (NMW-Ni) porous catalytic support. This dual-layer NMW/NMW-Ni hollow fiber exhibited H₂ permeation flux of 0.26 mL cm⁻² min⁻¹ at 900 °C when 50 mL min⁻¹ of 50 vol% H₂ in He was used as feed gas and 50 mL min⁻¹ N₂ was used as sweep gas. Membrane reactor based on dual-layer NMW/NMW-Ni hollow fiber achieved NH₃ conversion of 99% at 750 °C, which was 24% higher relative to the packed-bed reactor with the same reactor volume. Such higher conversion was enabled by concurrent H₂ extraction out of the membrane reactor during the reaction. This membrane reactor also maintained stable NH₃ conversion and H₂ permeation flux as well as structure integrity over 75 h of reaction at 750 °C.     

Fe–Ni/MMT nanocomposites as efficient H2 generation catalyst: Tandem approach towards one-pot synthesis of secondary amines

A non-noble metal-based bifunctional Fe–Ni/MMT nanocomposites exhibit excellent H₂ generation capability from the methanolysis of NaBH₄ at a rate of 16,200 mL min⁻¹ g⁻¹_Fe–_Ni with 10%Fe–Ni loading on MMT support. Moreover, the evolved H₂ from this catalytic process is efficiently utilized for the one-pot step-wise synthesis of secondary amines from nitrobenzene and aldehydes using NaBH₄ as a source of hydrogen at room temperature. Circumventing the reduction of aldehyde and triggering the formation of imine intermediate through sequential addition of reactants in a time dependent manner has resulted in the excellent yields for aliphatic, aromatic and heterocyclic amines (91–98%). The catalytic activity of Fe–Ni/MMT nanocomposite is ascribed to synergic association of Fe–Ni NPs, Lewis and Brønsted acidity as well as adsorptive nature of MMT. Thus, a simple, facile and greener route is developed for the synthesis of secondary amines with an efficient H₂ generation non-noble metal catalyst and easily accessible H-donor at room temperature.     

Enhanced hydrogen generation from graphite-mixed aluminum hydroxides catalyzed Al/water reaction

The high catalytic effect of a graphite-mixed Al(OH)₃ nanoparticles (NPs) for the hydrogen generation from the reaction of Al and water is reported. These graphite-mixed Al(OH)₃ NPs were synthesized through a simple solvothermal procedure. Characterization using powder X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) were carried out. The results show that small amounts of graphite added into Al(OH)₃ NPs could significantly enhance the hydrolysis reaction of Al and H₂O reaction, releasing 1360 mL g^-1 hydrogen in 20 min at room temperature. This reaction accomplishes 100% yield of hydrogen using 1 g modified Al(OH)₃ in 1 g Al and 200 g water. The synthesized graphite-mixed Al(OH)₃ exhibits good activity-stability, which can be used for multiple Al/water reactions. This work demonstrates a novel and possible way to generate hydrogen for portable devices.     

A novel AlBiOCl composite for hydrogen generation from water

In this paper, a novel AlBiOCl material has been prepared by milling Al powder and BiOCl firstly. Experimental results show that BiOCl-doped can prevent an inert alumina film forming on the surface of Al particles and induce the rapid hydrogen generation as well as high conversion rate. SEM, XRD, EDS, TEM, XPS and calorimetric techniques are used for the mechanism analysis of the samples. The results demonstrate the fresh surface of Al, AlCl₃, Bi and Bi₂O₃ are produced in situ under ball milling Al and BiOCl, which play an important role in hydrolysis reaction of Al. The hydrogen yield of Al-15 wt% BiOCl rises to 1058.1 mL g⁻¹ in about 5 min, corresponding to the high conversion yield of 91.6% at room temperature. After doping additives (such as LiH, Bi or AlCl₃), hydrogen generation performances of AlBiOCl-additive are further improved. For example, the conversion yield and maximum hydrogen generation rate (MHGR) of AlBiOClLiH can increase to 94.9% and 3178.5 mL g⁻¹ min⁻¹, respectively. Therefore, the proposed materials in this paper are expected to serve as a hydrogen generation material for the fuel cells.     

Kinetics and mechanism of MgH2 hydrolysis in MgCl2 solutions

In the present work we systematically studied the hydrolysis of magnesium hydride in MgCl₂ aqueous solutions, which was used as a process promotor. The initial hydrolysis rate, the pH of the reaction mixture, and the overall reaction yield are all found to be linearly dependent of the logarithm of MgCl₂ concentration. The phase-structural and elemental compositions of the formed precipitates showed that they do not contain chlorine ions and solely consist of Mg(OH)₂. The size of the Mg(OH)₂ crystallites increased with increasing content of MgCl₂ in the aqueous solution.The best agreement between the observed and modelled hydrolysis kinetics was achieved by applying a pseudo-homogeneous model that describes the process rate as increasing with H⁺ ions concentration. The deposition of Mg(OH)₂ which is impermeable to water and blocks the surface of the remaining MgH₂ however simultaneously and partially suspends this reaction. We therefore propose a mechanism of MgH₂ hydrolysis in the presence of MgCl₂ that is based on the comparison of the kinetic dependencies, variations of solutions pH and the structural and elemental analysis data for the solid deposits formed during the interaction. We furthermore define the kinetic model of the process, and the equation that describes the variation in pH of solutions containing chloride salts. Hydrolysis efficiency increased with increased relative MgCl₂ amount; the best performance being achieved for the stoichiometric ratio MgH₂+0.7MgCl₂ (MgCl₂/MgH₂ weight ratio of 12.75/100). This provided a hydrogen yield of 1025 mL (H₂)/g MgH₂. Maximum hydrogen yield peaked at 89% of the theoretical H₂ generation capacity, and was achieved within 150 min of hydrolysis start, 35% of hydrogen being released in the first 10 min after start, the hydrogen generation rate being as high as 800 mL min⁻¹·g⁻¹ MgH₂.     

Preparation and characterization of high temperature Sr(Ce0.6Zr0.4)0.9Y0.1O3-δ/YBaCo2O5+δ mixed proton-electron composite membrane

In this study, the various Sr(Ce_0.6Zr_0.4)_0.9Y_0.1O_3-δ/YBaCo₂O_5+δ (SCZY/YBCO) composite ceramic membranes were prepared by sintering at different temperatures and used as proton membranes for hydrogen permeation. SCZY and YBCO powders were prepared by the citrate-ethylenediaminetetraacetic acid sol-gel process and solid-state reaction method, respectively. The chemical reaction, structure, morphology, thermal expansion, and electrical conductivity of SCZY/YBCO were investigated through X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermal mechanical analyzer (TMA) and direct current four-probe method. The relative sintered density of SCZY/YBCO membrane sintered at 1250 °C was as high as 99.5%. The conductivity of the SCZY/YBCO increased with the sintering temperature. The SCZY/YBCO sample sintered at 1250 °C exhibited the highest conductivity of 13.44 S/cm at 800 °C. The H₂ permeability of the SCZY/YBCO membrane was 3.83 mL min⁻¹ cm⁻², much higher than that of SCZY at 800 °C (1.37 mL min⁻¹ cm⁻²).     

Using a food and paper-cardboard waste blend as a novel feedstock for hydrogen production: Influence of key process parameters on microbial diversity

In this study, fermentation of a thermally treated simulated organic solid waste into hydrogen (H₂) was examined using a pretreated anaerobic mixed culture. The culture was fed a steam exploded food waste plus paper-cardboard waste blend liquor with and without linoleic acid (LA). The individual and interaction effects of the initial pH, LA concentration and the initial chemical oxygen demand (COD) concentration on H₂ and methane (CH₄) production was assessed using a Box–Behnken design (BBD). The BBD model predicted a maximum H₂ yield of 87 mL g⁻¹ COD or 98 mL H₂ g⁻¹ VS with 1.6 g L⁻¹ LA, an initial pH of 5.93 and an initial COD of 9.34 g COD L⁻¹. The major microbial populations detected in cultures at pH 5.5 with and without LA included Clostridium sp., Enterococcus asini, Enterococcus faecalis, and Lactobacillus gallinarum. The dendrogram for the 16S rRNA gene T-RFs profiles showed four major groups with a similarity index of 72–75% for Clade III. The major H₂-producing populations were grouped in Clade I with a similarity index range of 55–75%.     

Hydrogen generation from alkaline NaBH4 solution using nanostructured Co–Ni–P catalysts

In the present study, nanostructured Co–Ni–P catalysts have been successfully prepared on Cu sheet by electroless plating method. The morphologies of Co–Ni–P catalysts are composed of football-like, granular, mockstrawberry-like and shuttle-like shapes by tuning the depositional pH value. The as-deposited mockstrawberry-like Co–Ni–P catalyst exhibits an enhanced catalytic activity in the hydrolysis of NaBH₄ solution. The hydrogen generation rate and activation energy are 2172.4 mL min⁻¹ g⁻¹ and 53.5 kJ mol⁻¹, respectively. It can be inferred that the activity of catalysts is the result of the synergistic effects of the surface roughness, the particle size and microscopic architectures. Furthermore, the stability of mockstrawberry-like Co–Ni–P catalyst has been discussed, and the hydrogen generation rate remains about 81.4% of the initial value after 5 cycles.     

PDMA cryogel beads as a catalyst for hydrogen generation from NaBH4 alcoholysis

Poly[2-(dimethylamino)ethyl methacrylate] cryogel beads were prepared under cryogenic conditions via free radical polymerization and used as a catalyst in the production hydrogen (H₂) from NaBH₄ by alcoholysis. The efficiency of the catalyst was investigated in the range of 0–40 °C by both methanolysis and ethylene glycolysis reactions, and its reuse was tested. Accordingly, it was observed that the methanolysis reaction was faster than the ethylene glycolysis reaction. When the hydrogen generation rate (HGR) values between 0 and 40 °C were compared, it was concluded that the methanolysis reaction rate increased from 1550 to 4800 mL.min⁻¹g⁻¹ and the ethylene glycolysis reaction rate increased from 923 to 3551 mL.min⁻¹g⁻¹. In the alcoholysis reaction catalyzed by PDMA cryogel beads, the activation energy was calculated as 19.34 and 22.77 kJ.mol⁻¹ for the methanolysis and ethylene glycolysis reactions, respectively. After six repetitions, the catalyst activity was calculated over 50% for NaBH₄ methanolysis and ethylene glycolysis.     

Investigation on different valence B-site ions doped Pr0.6Sr0.4FeO3-δ ceramic membrane for hydrogen production from water splitting

This study investigates the different valence B-site ions doped on perovskite-type oxygen transport membrane for hydrogen production by water splitting. Perovskite-type Pr_0.6Sr_0.4Fe_0.9M_0.1O_3-δ (PSFM, M = Fe, Al, Zr, and W) are fabricated successfully by the sol-gel method and form dense membranes with orthorhombic structure. The microstructure, chemical stability, and hydrogen production performance of membranes are studied systematically. The doping of Al³⁺, Zr⁴⁺, and W⁶⁺ ions can enhance membranes chemical stability and long-term stability significantly, which is due to the increase of average binding energy and decrease of the valence of B-site ions. Because of higher oxygen vacancy content and lower oxygen vacancy formation energy, the PSFA membrane shows the highest hydrogen production rate of 1.07 mL min⁻¹·cm⁻² at 900 °C and stabilizes at about 1.0 mL min⁻¹·cm⁻² on long-term test. The performance degradation of PSFM membranes is attributed to the much valence variation of B-site Fe^3+/4+ ions and the oxygen vacancy-related phase transition.     

Asymmetric dual-phase MIEC membrane reactor for energy-efficient coproduction of two kinds of synthesis gases

An asymmetric 75 wt% Sm_0.15Ce_0.85O_1.925-25 wt% Sm_0.6Sr_0.4Al_0.3Fe_0.7O_3-δ (SDC-SSAF) dual-phase mixed ionic-electronic conducting (MIEC) oxygen-permeable membrane reactor was applied to coproduce ammonia synthesis gas (ASG, H₂/N₂ = 3) and liquid fuels synthesis gas (LFSG, H₂/CO = 2). The effects of CH₄ concentration, CH₄ flow rate, steam flow rate and temperature on the performance of the membrane reactor were studied. The SDC-SSAF membrane reactor showed an excellent performance for the coproduction of ASG and LFSG. An ASG production rate of 20.7 mL cm⁻² min⁻¹, a LFSG production rate of 51.0 mL cm⁻² min⁻¹ and an oxygen permeation rate of 9.1 mL cm⁻² min⁻¹ were achieved at 925 °C. Compared with traditional industrial processes, the energy saving of this membrane reactor process is expected as high as 66.5%. The post-mortem of the membrane reactor using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) characterization revealed that the membrane has an excellent structural stability under operation condition.     

Very efficient dehydrogenation of methanolysis reaction with nitrogen doped Chlorella Vulgaris microalgae carbon as metal-free catalysts

In this study, nitrogen (N) doped metal-free catalysts were obtained as a result of nitric acid (HNO₃) activation of carbon sample (C–KOH–N), which was obtained based on Chlorella Vulgaris microalgae by KOH activation (C–KOH). These catalysts have been effectively used to produce hydrogen (H₂) from the sodium borohydride (NaBH₄) methanolysis reaction. Compared to the C–KOH catalyst, the catalytic activity for C–KOH–N showed a seven-fold improvement. Hydrogen generation rate (HGR) values obtained for the NaBH₄ methanolysis reaction for C–KOH and C–KOH–N metal-free catalysts were 3250 and 20,100 mL min^?1 g^?1. The catalysts were characterized using various analytical techniques such as XPS, XRD, SEM, FTIR, BET, and elemental analysis. This work can provide a new alternative strategy to produce specific heteroatom-doped metal-free carbon catalysts for environmentally friendly conversion to produce H₂ efficiently.