CeO2 supported multimetallic nano materials as an efficient catalyst for hydrogen generation from the hydrolysis of NaBH4

Nowadays, there is still no suitable method to store large amounts of energy. Hydrogen can be stored physically in carbon nanotubes or chemically in the form of hydride. In this study, sodium borohydride (NaBH₄) was used as the source of hydrogen. However, an inexpensive and useful catalyst (Co–Cr–B/CeO₂) was synthesized using the NaBH₄ reduction method and its property was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), x-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) measurements. The optimized Co–Cr–B/CeO₂ catalyst exhibited an excellent hydrogen generation rate (9182 mLg_metal⁻¹min⁻¹) and low activation energy (35.52 kJ mol⁻¹). The strong catalytic performance of the Co–Cr–B/CeO₂ catalyst is thought to be based on the synergistic effect between multimetallic nanoparticles and the effective charge transfer interactions between the metal and the support material.     

Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO₂ capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several A_xCe_1-xO_2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe₂O₃ for hydrogen production at 750 °C. It was shown that Fe₂O₃/Gd_0.3Ce_0.7O_2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe₂O₃/Gd_0.3Ce_0.7O_2-δ > Fe₂O₃/La_0.1Ce_0.9O_2-δ > Fe₂O₃/Gd_0.1Ce_0.9O_2-δ > Fe₂O₃/La_0.3Ce_0.7O_2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO₂ contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.     

Tungsten(VI) oxide supported rhodium nanoparticles: Highly active catalysts in hydrogen generation from ammonia borane

Herein, we report the use of tungsten(VI) oxide (WO₃) as support for Rh⁰ nanoparticles. The resulting Rh⁰/WO₃ nanoparticles are highly active and stable catalysts in H₂ generation from the hydrolysis of ammonia borane (AB). We present the results of our investigation on the particle size distribution, catalytic activity and stability of Rh⁰/WO₃ catalysts with 0.5%, 1.0%, 2.0% wt. Rh loadings in the hydrolysis reaction. The results reveal that Rh⁰/WO₃ (0.5% wt. Rh) is very promising catalyst providing a turnover frequency of 749 min^?1 in releasing 3.0 equivalent H₂ per mole of AB from the hydrolysis at 25.0 °C. The high catalytic activity of Rh⁰/WO₃ catalyst is attributed to the reducible nature of support. The report covers the results of kinetics study as well as comparative investigation of activity, recyclability, and reusability of colloidal(0) nanoparticles and Rh⁰/WO₃ (0.5 % wt. Rh) catalyst in the hydrolysis reaction.     

A highly active Co-B catalyst for hydrogen generation from sodium borohydride hydrolysis

Co-B catalysts were prepared by the chemical reduction of CoCl₂ with NaBH₄ for hydrogen generation from borohydride hydrolysis. The catalytic properties of the Co-B catalysts were found to be sensitive to the preparation conditions including pH of the NaBH₄ solution and mixing manner of the precursors. A Co-B catalyst with a very high catalytic activity was obtained through the formation of a colloidal Co(OH)₂ intermediate. The ultra-fine particle size of 10 nm accounted for its super activity for hydrogen generation with a maximum rate of 26 L min⁻¹ g⁻¹ at 30 °C. The catalyst also changed the hydrolysis kinetics from zero-order to first-order.     

Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane

Ruthenium(0) nanoparticles supported on the surface of titania nanospheres (Ru(0)/TiO₂) were in situ generated from the reduction of ruthenium(III) ions impregnated on nanotitania during the hydrolysis of ammonia borane. They were isolated from the reaction solution by centrifugation and characterized by a combination of advanced analytical techniques. The results reveal that highly dispersed ruthenium(0) nanoparticles of size in the range 1.5–3.3 nm were formed on the surface of titania nanospheres. Ru(0)/TiO₂ show high catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value up to 241 min⁻¹ at 25.0 ± 0.1 °C. They provide unprecedented catalytic lifetime measured by total turnover number (TTO = 71,500) in hydrogen generation from the hydrolysis of ammonia borane at 25.0 ± 0.1 °C. The report also includes the results of kinetic study on the catalytic hydrolysis of ammonia borane depending on the temperature to determine the activation energy of the reaction (E_a = 70 ± 2 kJ/mol) and the catalyst concentration to establish the rate law of the reaction.     

Gd,La co-doped CeO2 as an active support for Fe2O3 to enhance hydrogen generation via chemical looping water gas shift

Support materials are indispensable to promote the durability of iron oxides for chemical looping applications. However, the dilution effect of supports on the active phase would lead to decreased bulk oxygen conduction, thus leading to compromised activity. Here, we propose several Gd³⁺, La³⁺ and Nd³⁺ doped CeO₂ as active supports for iron oxides and investigate the support effect to improve hydrogen generation via chemical looping water gas shift. The characterizations show that the dopants improve the oxygen vacancy concentration in the CeO₂ lattice and Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ exhibits the most oxygen vacancy concentration among all the oxygen carriers. Pulse reactions of oxygen carriers show that an abundance of oxygen vacancy concentration can promote the lattice oxygen transfer in bulk, thus contributing to improved redox reactions. The high oxygen conductivity mitigates the dilution effect on the active phase. Therefore, Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ shows the highest hydrogen yield (～9.49 mmol^?1.g^?1) and hydrogen generation rate (～0.632 mmol.g^?1.min^?1) with only a slight decrease at 650 °C over 100 cycles. Overall, this work highlights the influence of support properties on the redox reactivity of iron oxides for chemical looping applications.     

Boron nitride supported NiCoP nanoparticles as noble metal-free catalyst for highly efficient hydrogen generation from ammonia borane

Herein, ternary metal phosphides NiCoP nanoparticles supported on porous hexagonal boron nitride (h-BN) was fabricated via hydrothermal-phosphorization strategy. The as-prepared Ni_0.8Co_1.2P@h-BN exhibited excellent catalytic performance for the hydrogen generation from ammonia borane (AB) hydrolysis, with an initial turnover frequency of 86.5 mol(H₂) mol(Ni_0.8Co_1.2P) ⁻¹ min⁻¹ at 298 K. The experimental outcome can be attributed to the synergistic effect between Ni, Co and P, as well as the strong metal-support interaction between NiCoP and h-BN. This study presents a new paradigm for supporting transition metal phosphides, and provides a new avenue to develop high performance and low cost non noble metal catalysts for hydrolysis of AB.     

Highly active heteropolyanions supported Co catalysts for fast hydrogen generation in NaBH4 hydrolysis

This paper reports on the use of Co supported catalyst for the hydrolysis of NaBH₄. Various materials with different acid/base surface properties have been chosen as supports (hydrotalcites, KF/Al₂O₃, heteropolyanions). The supports and the Co-containing catalysts were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, nitrogen adsorption. The NaBH₄ hydrolysis reaction was studied in a liquid phase calorimeter coupled with a gas counter in order to follow at the same time the kinetics and the heat of reaction. Co supported on heteropolyanions showed great results in terms of reaction rate. Cobalt dispersed on heteropolyanions is a real promising catalytic system for the development of hydrogen generation in PEM fuel cells for portable devices.     

Al2O3 based Co-Schiff Base complex catalyst in hydrogen generation

This work presents the study of the catalytic activity of aluminum oxide supported Co-Schiff Base complex derived from 4,4′-Methylenebis(2,6-diethylaniline)-3,5-ditertbutylsalicylaldimine-Co-Schiff Base complex in sodium borohydride hydrolysis. This catalyst is characterized with XRD, FT-IR, SEM, TEM, and BET. The respective reaction kinetics have been calculated. With the catalyst condition, maximum reaction (initial) rate is 106540 and 147193,3 mL H₂/g_cat.^.min. at 30 °C and 50 °C. For this reaction apparent activation energy is 44,7792 kJ^.mol⁻¹ with 20–50 °C. The reaction order value (n) for this catalytic system is 0,31. Additionally when Al₂O₃ supported Co-Schiff Base complex compared with pure Co-Schiff Base complex, the experimental results show that the aluminum oxide support exhibits enhancing effect with 106540 and 64147 mL H₂/g_cat. min respectively in sodium borohydride hydrolysis to Hydrogen production.     

Polymer-immobilized palladium supported on TiO2 (Pd-PVB-TiO2) as highly active and reusable catalyst for hydrogen generation from the hydrolysis of unstirred ammonia-borane solution

Herein we report the preparation, characterization and the catalytic use of the polymer-immobilized palladium catalyst supported on TiO₂ (Pd-PVB-TiO₂) in the hydrolysis of unstirred ammonia-borane solution. The polymer-immobilized palladium catalyst is stable enough to be isolated as solid materials and characterized by XRD, SEM, and EDX. The immobilized palladium catalyst supported on TiO₂ is found highly active, isolable, and reusable in the hydrolysis of unstirred ammonia-borane even at low concentrations and temperature. The work reported here also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 55.9 kJ/mol) and the effects of catalyst and substrate concentration on the rate for the hydrolysis of unstirred ammonia-borane solution. Maximum H₂ generation rate of ∼642 mL H₂ min⁻¹ (g Pd)⁻¹ and ∼4367 mL H₂ min⁻¹ (g Pd)⁻¹ was measured by the hydrolysis of AB at 25 °C and 55 ± 0.5 °C, respectively.     

Hydrogen generation utilizing alkaline sodium borohydride solution and supported cobalt catalyst

Supported Co catalysts with different supports were prepared for hydrogen generation (HG) from catalytic hydrolysis of alkaline sodium borohydride solution. As a result, we found that a γ-Al₂O₃ supported Co catalyst was very effective because of its special structure. A maximum HG rate of 220 mL min⁻¹ g⁻¹ catalyst and approximately 100% efficiency at 303 K were achieved using a Co/γ-Al₂O₃ catalyst containing 9 wt.% Co. The catalyst has quick response and good durability to the hydrolysis of alkaline NaBH₄ solution. It is feasible to use this catalyst in hydrogen generators with stabilized NaBH₄ solutions to provide on-site hydrogen with desired rate for mobile applications, such as proton exchange membrane fuel cell (PEMFC) systems.     

Highly stable CdS-modified short TiO2 nanotube array electrode for efficient visible-light hydrogen generation

A highly stable photoelectrocatalytic electrode made of CdS-modified short, robust, and highly-ordered TiO₂ nanotube array for efficient visible-light hydrogen generation was prepared via sonoelectrochemical anodization and sonoelectrochemical deposition method. The short nanotube electrode possesses excellent charge separation and transfer properties, while the sonoelectrochemical deposition method improves the combination between CdS and TiO₂ nanotubes, as well as the dispersion of CdS nanoparticles. Different characterization techniques were used to study the nanocomposite electrode. UV-vis absorption and photoelectrochemical measurements proved that the CdS coating extends the visible spectrum absorption and the solar spectrum-induced photocurrent response. Comparing the photoactivity of the CdS/TiO₂ electrode obtained using sonoelectrochemical deposition method with others that synthesized using plain electrochemical deposition, the current density of the former electrode is ∼1.2 times higher that of the latter when biased at 0.5 V. A ∼7-fold enhancement in photocurrent response is obtained using the sonoelectrochemically fabricated CdS/TiO₂ electrode in comparison with the pure TiO₂ nanotube electrode. Under AM1.5 illumination the composite photoelectrode generate hydrogen at a rate of 30.3 μmol h⁻¹ cm⁻², nearly 13 times higher than that of pure titania nanotube electrode. Recycle experiments demonstrated the excellent stability and reliability of CdS/TiO₂ electrode prepared by sonoelectrochemical deposition. This composite electrode, with its strong mechanical stability and excellent combination of CdS and TiO₂ nanotubes, offers promising applications in visible-light-driven renewable energy generation.     

Hydrogen generation via cross-linked glucomannan supported cobalt nano catalyst

Hydrogen generation through hydrolysis of sodium borohydride was examined over a series of supported cobalt nano particles as novel catalysts. For the first time extracted Glucomannan from Orchis Mascula used as a suitable matrix for preparation and stabilization of cobalt catalysts. Insoluble glucomannan obtained by polymerization reaction in the presence of MBA cross-linker and MAA monomer. Size, morphology and hydrogen generation activity of Co-glucomannan powders are studied by varying MAA/MBA ratios. XRD, XPS, FE-SEM and TEM techniques were used to characterization of obtained catalysts. All nano catalysts are formed in amorphous phase. Electron microscopic images confirmed that almost all particles are less than 10 nm. It is shown, cobalt particles are dispersed on the surface of glucomannan polymer without agglomeration. Catalytic activity of obtained Co-glucomannan are tested on hydrogen generation over hydrolysis of sodium borohydride reaction. Kinetic studies were applied to determine partial order respect to catalyst dosage and initial concentration of sodium borohydride. Finally, Arrhenius equation was used to find activation energy of hydrolysis sodium borohydride reaction over Co-glucomannan nano catalyst.     

Co-P nanoparticles supported on dandelion-like CNTs-Ni foam composite carrier as a novel catalyst for hydrogen generation from NaBH4 methanolysis

We used the chemical vapor deposition method to prepare dandelion-like CNTs-Ni foam composite carrier, and then the electroless plating method was used to deposit Co-P nanoparticles on the CNTs of the CNTs-Ni foam. The CNTs-Ni foam and Co-P/CNTs-Ni foam were characterized by BET, SEM, XRD, XPS, and EDS. The results showed that CNTs were uniformly and densely grown in situ on the surface of Ni foam and were further successfully coated with Co-P nanoparticles. The Co-P/CNTs-Ni foam catalysts still maintained the dandelion-like structure and reached a maximum hydrogen production rate of 2430 mL min⁻¹ g⁻¹ at 25 °C. Furthermore, the Co-P/CNTs-Ni foam catalysts also exhibit a remarkable cycling performance and low activation energy (49.94 kJ mol⁻¹) for the methanolysis of sodium borohydride.     

An effective low Pd-loading catalyst for hydrogen generation from formic acid

As an interesting hydrogen carrier, formic acid is bio-renewable, non-toxic and available in the liquid state at room temperature. The development of active and low-cost catalyst is of significance for hydrogen generation from formic acid. In this study, both a relatively cheap metal (Ag) and a functional support (nitrogen modified reduced graphene oxide, N-rGO) were applied to prepare Pd catalyst. It was found that the Ag atoms facilitated the formation of Pd-rich surface in the preparation strategy, in which the reductive N-rGO and a two-step feeding process of metal precursors played important roles. In addition, Ag additive was found to benefit catalyst stability. Most interestingly, the obtained low Pd-loading Pd₁Ag₆/N-rGO catalyst showed a specific Pd loading turnover frequency of 171 mol Pd^?1 h^?1 and a specific metal cost turnover frequency of 64.2 $^?1 h^?1, which were predominant among currently available Pd-based catalysts towards formic acid decomposition without any additive under room temperature.     

Cobalt nanoparticles supported on magnetic core-shell structured carbon as a highly efficient catalyst for hydrogen generation from NaBH4 hydrolysis

A novel recyclable cobalt nanocatalyst, supported on magnetic carbon with core-shell structure, was successfully synthesized by using wetness impregnation-chemical reduction method for hydrogen generation from hydrolysis of NaBH₄. The resultant nanocomposite was characterized to determine the structural and physical-chemical properties by a series of analytical techniques such as FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy), TEM (transmission electron microscopy), etc. The results demonstrated that amorphous cobalt nanoparticles were homogeneously surrounded on the surface of the support due to having abundant hydrophilic groups (such as aldehyde and hydroxyl groups) on the surface of carbon layer for the effective immobilization of metal ions. The supported catalyst showed superior catalytic performance towards the hydrolysis reaction of NaBH₄ at room temperature. The total rate of hydrogen generation and activation energy were calculated to be 1403 ml H₂ g_cat^?1 min^?1 and 49.2 kJ mol^?1, respectively, which were comparable to the values of most cobalt-based catalyst reported for hydrogen production from hydrolysis of NaBH₄. Additionally, reusability test revealed that the hydrogen in NaBH₄ substrate could be completely released within 25 min with a minimum hydrogen generation rate of 832 ml H₂ g_cat^?1 min^?1 even after five runs of hydrolytic reaction, implying the as-prepared Co/Fe₃O₄@C composite could be considered as a promising candidate catalyst for portable hydrogen fuel system such as PEMFC (proton exchange membrane fuel cells).     

In situ facile synthesis of ruthenium nanocluster catalyst supported on carbon black for hydrogen generation from the hydrolysis of ammonia-borane

Ligand-free Ru nanoclusters supported on carbon black have been synthesized in situ for the first time from the reduction of RuCl₃ by ammonia-borane concomitantly with its hydrolysis process at room temperature, and their catalytic activity has been investigated. Well dispersed Ru nanoclusters (∼1.7 nm) are stabilized and immobilized by carbon black. Due to the small size and the absence of ligands on the surface, the Ru catalysts exhibit high catalytic activity, which is partly retained after 5 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia-borane is first order with respect to Ru catalyst concentration; the turnover frequency is 429.5 mol H₂ min⁻¹ mol⁻¹ Ru. The activation energy for the hydrolysis of ammonia-borane in the presence of Ru/C catalysts has been measured to be 34.81 ± 0.12 kJ mol⁻¹, which is smaller than most of the values reported for other catalysts, including those based on Ru, for the same reaction.     

Catalytic hydrolysis of hydrazine borane for chemical hydrogen storage: Highly efficient and fast hydrogen generation system at room temperature

There has been rapidly growing interest for materials suitable to store hydrogen in solid state for transportation of hydrogen that requires materials with high volumetric and gravimetric storage capacity. B-N compounds such as ammonia-triborane, ammonia-borane and amine-borane adducts are well suited for this purpose due to their light weight, high gravimetric hydrogen storage capacity and inclination for bearing protic (N-H) and hydridic (B-H) hydrogens. In addition to them, more recent study [26] has showed that hydrazine borane with a gravimetric hydrogen storage capacity of 15.4% wt needs to be considered as another B-N compound that can be used for the storage of hydrogen. Herein we report for the first time, metal catalyzed hydrolysis of hydrazine borane (N₂H₄BH₃, HB) under air at room temperature. Among the catalyst systems tested, rhodium(III) chloride was found to provide the highest catalytic activity in this reaction. In the presence of rhodium(III) chloride, the aqueous solution of hydrazine borane undergoes fast hydrolysis to release nearly 3.0 equivalent of H₂ at room temperature with previously unprecedented H₂ generation rate TOF = 12000 h⁻¹. More importantly, it was found that in the catalytic hydrolysis of hydrazine borane the reaction between hydrazine borane and water proceeds almost in stoichiometric proportion indicating that the efficient hydrogen generation can be achieved even from the highly concentrated solution of hydrazine borane or in the solid state when water added to the solid hydrazine borane. This finding is crucial especially for on-board application of the existing system. The work reported here also includes (i) finding the solubility of hydrazine borane plus its stability against self-hydrolysis in water, (ii) the definition of reaction stoichiometry and the identification of reaction products for the catalytic hydrolysis of hydrazine borane, (iii) the collection of wealthy kinetic data to demonstrate the effect of substrate and catalyst concentrations on the hydrogen generation rate and to determine the rate law for the catalytic hydrolysis of hydrazine borane, (iv) the investigation of the effect of temperature on the rate of hydrogen generation and determination of activation parameters (E_a, ΔH^#, and ΔS^#) for the catalytic hydrolysis of hydrazine borane.     

Carbon-supported cobalt catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost transition metal catalysts with high performance are attractive for the development of on-board hydrogen generation systems by catalytic hydrolysis of sodium borohydride (NaBH₄) in fuel cell fields. In this study, hydrogen production from alkaline NaBH₄ via hydrolysis process over carbon-supported cobalt catalysts was studied. The catalytic activity of the supported cobalt catalyst was found to be highly dependent on the calcination temperatures. The hydrogen generation rate increases with calcination temperatures in the range of 200–400 °C, but a high calcination temperature above 500 °C led to markedly decreased activity. X-ray diffraction patterns reveal that the catalysts experience phase transition from amorphous Co–B to crystalline cobalt hydroxide with increase in calcination temperatures. The reaction performance is also dependent on the concentration of NaBH₄, and the hydrogen generation rate increases for lower NaBH₄ concentrations and decreases after reaching a maximum at 10 wt.% of NaBH₄.