Controllable hydrogen production from NaBH4 hydrolysis promoted by acetic acid

Numerous catalysts have been widely investigated for accelerating hydrogen production from NaBH₄ hydrolysis. However, these catalysts are usually complicated in structures, costly in fabrication, and hazardous for environment. In this work, cheap and environment-friendly acetic acid, CH₃COOH, is employed to promote NaBH₄ hydrolysis to produce hydrogen in a considerable rate. The experimental results demonstrate that the addition of suitable amount of CH₃COOH into NaBH₄ solutions stabilized with NaOH could dramatically accelerate the hydrolysis reaction. Additionally, the start/stop of NaBH₄ hydrolysis could be controlled by adding acid or base into the solution to realize “go-as-you-please” on-site hydrogen production.     

Ruthenium-Imine catalyzed KBH4 hydrolysis as an efficient hydrogen production system

The present study focused on the increasing of hydrogen evolution through hydrolysis of potassium borohydride in the presence of Ruthenium complex catalyst. It is the first time to use the Ru-Imine complex catalyst in KBH₄ hydrolysis reaction to hydrogen evolution. The new Ru complex was synthesized from the tetradentate Imine ligand namely 4,4′-methylenebis (2,6-diethyl)aniline-3,5-di-tert-butylsalisylaldimine and Ru salt under the inert atmosphere. Ru-Imine complex was fully characterized by Elemental Analysis, Infrared Spectroscopy, Scanning Electron Microscope, X-Ray Diffraction Analysis, Brunauer-Emmett-Teller Surface Area Analysis and Transmission Electron Microscopy. By the synthesized Ru-Imine complex catalyst, the potassium borohydride hydrolysis reaction resulted in a lower energy barrier with 20,826 kJ/mol activation energy (Ea) for nth order kinetic model and 18,045 kJ/mol for Langmuir-Hinshelwood (L-H) kinetic model. According to the results Ru-complex was highly active and stable catalyst in KBH₄ hydrolysis reaction to hydrogen evolution with 45,466 mL H₂/g_cat.min and 76,815 mL H2/g_cat.min hydrogen generation rates at 30 °C and 50 °C respectively. Moreover Ru-Imine complex catalyst displayed 100% stability even at fifth recycle.     

Effect of phosphoric acid addition on the hydrogen production from hydrolysis of NaBH4 with Cu based catalyst

Cu based catalysts were synthesized in water and methanol solvents by chemical reduction with sodium borohydride (NaBH₄). The obtained catalyst was used to catalyze the NaBH₄ hydrolysis reaction with phosphoric acid (H₃PO₄) including different concentrations. Surface morphology and structural properties of the Cu based catalysts prepared in water and methanol solvents were studied using by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area measurements and Fourier-transform infrared spectroscopy (FTIR) analyses, respectively. The catalytic activity of the catalysts has been tested by measuring the hydrogen production rate by the acidified hydrolysis of NaBH₄. The maximum hydrogen production rates in the hydrolysis reaction including 0.25 M H₃PO₄ using the Cu based catalyst prepared in water and methanol solvents were 825 and 660 ml g^?1min^?1, respectively. At the same time, the hydrogen production experiments were carried out from this hydrolysis reaction with only H₃PO₄ and NaBH₄ interactions without using Cu metal catalyst. The activation energy obtained based on the nth order reaction model was found to be 61.16 kJ mol^?1.     

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.     

Semi-methanolysis reaction of potassium borohydride with phosphoric acid for effective hydrogen production

The methanol and water solvents were used for the production of hydrogen from potassium borohydride. In addition, phosphoric acid was selected as the green catalyst so that this semi-methanolysis reaction would be more effective for the first time. The semi-methanolysis of potassium borohydride is investigated depend on potassium borohydride, phosphoric acid concentrations and temperatures. The maximum normalized hydrogen production rate obtained from this semi-methanolysis reaction with 1 M phosphoric acid as a catalyst was 5779 ml min ^?1 g^?1. In addition, this semi-methanolysis reaction was completed in 5 s. Kinetic studies have been carried out with the power law kinetic model. The activation energy obtained for this semi-methanolysis reaction is 1.45 kJ mol^?1.     

Morphology and location manipulation of Fe nanoparticles on carbon nanofibers as catalysts for ammonia decomposition to generate hydrogen

Ammonia decomposition over Fe-based catalysts is a typical structure sensitive reaction, and the shape-controlled synthesis of Fe nanoparticles based on catalytic chemical vapor deposition (CCVD) method appears to be an effective method toward enhanced catalytic activity. The objective of this work is to understand effects of the reaction parameters on structural and textural properties of the resultant Fe catalysts and thus catalytic ammonia decomposition performance. The as-obtained catalysts are characterized by multiple techniques (N₂ physisorption, XRD, SEM, TEM, and Raman spectroscopy). Both the morphology and location of Fe nanoparticles are found to strongly depend on the partial pressure of H₂ as well as the growth time of CNFs. The long polyhedron shaped Fe nanoparticles on CNFs exhibit the highest activity among the prepared catalysts, which are relatively higher than the activities of the reported Fe based catalysts. The possible explanation for the good catalytic performance was proposed.     

Investigation of multi-metal catalysts for stable hydrogen production via urea electrolysis

It has been shown that urea electrolysis is a viable method for wastewater remediation and simultaneous production of valuable hydrogen. Inexpensive nickel catalyst is optimal for the oxidation of urea in alkaline media but improvements are needed to minimize surface blockage and increase current density. Multi-metal catalysts were investigated by depositing platinum group metals on a nickel substrate. Rhodium and nickel proved synergistic to reduce surface blockage and increase catalyst stability. Rh-Ni electrodes reduced the overpotential for the electro-oxidation of urea and improved the current density by a factor of 200 compared to a Ni catalyst.     

Shaggy-like Ru-clusters decorated core-shell metal-organic framework-derived CoOx@NPC as high-efficiency catalyst for NaBH4 hydrolysis

Achieving high catalytic performance with the lowest possible amount of noble metal is critical for any catalytic applications. Herein, we report a controllable method of preparing low Ru loaded, N-doped porous carbon embedded with cobalt oxide species (Ru/CoO_x@NPC) using core-shell metal-organic framework (MOF) as a template. The optimized catalyst exhibits a highly powerful yet stable performance of H₂ production through sodium borohydride (NaBH₄) hydrolysis. The Ru/CoO_x@NPC catalyst shows a fast H₂ generation rate (8019.5 mL min^?1 g_cat^?1), high turnover frequency (1118.6 mol min^?1 mol_Ru^?1), and reusability. The carbonized ZIF-8 core and the ZIF-67 outer shell supplies a porous carbon moiety that not only improves the conductivity and but also provides uniform distribution of the active sites. The XPS analysis indicates that there is a strong electronic interaction between Co species and Ru species. The superior catalytic performance can be attributable to the large specific surface area as well as the synergy between Co-oxide and Ru clusters.     

Highly efficient electrocatalytic hydrogen production via MoSx/3D-graphene as hybrid electrode

Molybdenum sulfide (MoS_x) has recently emerged as a promising catalyst for the hydrogen evolution reaction (HER) in water splitting that may replace the noble metal, such as platinum, as a cost-effective and high catalytic materials. It has been reported that two-dimensional structured MoS_x exhibit significant amount of exposed S-edge, which can be an active electrocatalytic catalyst for hydrogen production. However, the current reports mainly focusing on the planar electrode, where the catalyst utilization and the number of active sites are limited due to the lower exposed specific surface area (SSA) of supporting electrodes. In this work, we utilize the freeze-drying method to produce a porous three-dimensional (3D) structure assembled by graphene flakes. The as-prepared 3D graphene scaffold shows high surface area, high porosity while low density, which makes it as an ideal conductive electrode for supporting of MoS_x catalysts. Moreover, it was found out that the crystallinity of MoS_x, controlled by thermolysis temperature of thiosalts precursor ((NH₄)₂MoS₄), shows significantly influence the performance of HER. The optimized annealing temperature for the designed hybrid electrodes (MoS_x/3D-graphene) was found to create a lot of active sites, which facilitate the electrocatalytic performance for water splitting (overpotential of 163 mV @10 mA/cm² and a Tafel slope of 41 mV/dec). The study provides a potential material, which could pave the way for future applications of hydrogen energy.     

Dye-sensitized cobalt catalysts for high efficient visible light hydrogen evolution

In this work, high efficient non-noble metal cobalt cocatalysts implanted on the surface of graphene (G) by one-step photoreduction and in-situ chemical deposition methods for hydrogen evolution were reported. XRD and TEM characterizations showed that the Co and CoS_x nanoparticles were deposited on the graphene surface as Co/G and CoS_x/G composites. CoS_x/G and Co/G nanohybrids exhibited high photocatalytic activities for hydrogen evolution sensitized by Eosin Y (EY). The amounts of H₂ evolution reached 708.5 and 675.5 μmol over the EY-sensitized CoS_x/G and Co/G nanohybrids irradiated under visible light with wavelength longer than 420 nm in 3 h respectively. The apparent quantum efficiency (AQE) of 8.71% over EY-Co/G was accomplished under 520 nm illumination. The fluorescence results indicated that the lifetime of excited electron was remarkably increased. Graphene might promote the photogenerated electrons transfer from excited dye to the hydrogen evolution active sites such as Co or CoS_x, and consequently enhance photocatalytic hydrogen evolution efficiency.     

Nickel catalysts obtained from hydrotalcites by coprecipitation and urea hydrolysis for hydrogen production

Nickel hydrotalcites were subjected to synthesis using two methods: coprecipitation and urea hydrolysis. The thermal decomposition of the hydrotalcite precursors produced mixed oxides corresponding to the active phases or final catalysts.     

Devices for producing hydrogen via NaBH4 and LiH hydrolysis

Chemical hydrides have already been pointed out as great potential hydrogen storage materials. In this paper, the hydrolysis of two solid hydrides, namely sodium borohydride (NaBH₄) and lithium hydride (LiH) was studied to check their performance as hydrogen generators. The simplicity of the reactor design, the absence of high pressure or very high temperatures as well as the benignity of the spent fuel make this hydrogen storage approach conceptually feasible. Several devices have been developed and tested. The devices have been designed to generate hydrogen flows in the 0.5-1.0 L min⁻¹ range. Batches up to 500 g of sodium borohydride powder were hydrolyzed with liquid water. 10.0 wt. % nickel acetate was used as catalyst. Hydrogen flows in the desired range have been continuously produced for several hours (up to 30 h). Due to the high reactivity lithium hydride was hydrolyzed without any catalyst. In this case batches of about 50 g have been hydrolyzed with steam for 4 h.     

PVP-stabilized platinum nanoparticles supported on modified silica spheres as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

Ammonia borane (AB) is considered to be a promising solid hydrogen carrier. In this work, poly(N-vinyl-2-pyrrolidone) (PVP)-protected platinum nanoparticles are supported on γ-methacryloxypropyltrimethoxysilane (γ-MPS) modified silica spheres (Pt-PVP/SiO₂(M)), which are firstly used as highly efficient catalysts for hydrolysis of AB. Platinum nanoparticles possess a tiny size of 2–3 nm and are uniformly dispersed over modified silica spheres. Pt-PVP/SiO₂(M) catalysts with a Pt loading amount of 1.30 wt% show the highest catalytic activity with a turnover frequency (TOF) value of 371 mol_H2 mol_Pt^?1 min^?1 (866 mol_H2 mol_Pt^?1 min^?1 corrected for the surface atoms) at 25 °C. The activation energy is calculated to be 46.2 kJ/mol. Furthermore, owing to the synergistic effect between the modifier of silica spheres and the capping agent of metal nanoparticles, Pt-PVP/SiO₂(M) catalysts have a higher loading amount (8.7 and 6.5 times) and TOF value (4.8 and 5.5 times) than the counterparts prepared without γ-MPS and PVP, respectively.     

Carbon-supported Ni3B nanoparticles as catalysts for hydrogen generation from hydrolysis of ammonia borane

We report the preparation of Ni₃B and carbon-supported Ni₃B (denoted as Ni₃B/C) nanoparticles, and their catalytic performance for hydrogen generation from hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB). Ni₃B and Ni₃B/C were prepared via a chemical reduction and crystallization in tetraethylene glycol solution. The obtained Ni₃B catalysts are in well-defined crystalline state and Ni₃B/C catalysts have a high dispersion in the carbon. The hydrogen generation measurement shows that the carbon-supported Ni₃B presents enhanced catalyst activity during hydrolytic dehydrogenation of AB. Among the as-prepared Ni₃B/C catalysts, Ni₃B/C with 34.25 wt% Ni₃B loading displays the best catalytic activity, delivering a high hydrogen release rate of 1168 mL min⁻¹ g⁻¹ and the lower activation energy of 46.27 kJ mol⁻¹. The kinetic results show that the hydrolysis is a first-order reaction in catalyst concentration, while it is a zero-order in AB concentration. Furthermore, the Ni₃B/C is a recyclable catalyst under mild reaction conditions, indicating that the carbon-supported Ni₃B is a promising catalyst for AB hydrolytic dehydrogenation.     

Nickel-based perovskite catalysts with iron-doping via self-combustion for hydrogen production in auto-thermal reforming of Ethanol

Iron-doped LaNiO₃ catalysts with a perovskite structure were prepared via self-combustion and tested in auto-thermal reforming (ATR) of ethanol. Characterizations of temperature-programmed surface reaction (TPSR), X-ray diffraction (XRD), physical N₂ adsorption, and temperature-programmed reduction (TPR) were carried out. The results indicate that LaNiO₃ perovskite structure was successfully formed via self-combustion. With iron-doping in LaNiO₃, the perovskite structure still remains, in the form of solid solution La(Ni, Fe)O₃, where iron is reducible and the nickel-iron alloy forms after the reduction. In addition, the surface area of the iron-doped samples increased. The TPSR results indicate that with iron-doping, the activity for adsorbed ethanol species is modified and a higher activity for methane transformation is achieved. As a result, an LNF10 sample (LaNi_0.90Fe_0.10O₃) with both nickel and nickel-iron alloy shows better performance in ATR: the ethanol conversion is near 100%, while the selectivity to by-products, such as ethylene, ethane, acetaldehyde and methane, is decreased, and CO₂ is the main carbon-containing product; consequently, a hydrogen yield near 3.0 mol H₂/mol EtOH is obtained and remains stable in the 30-h test of ATR.     

Highly efficient acid-treated cobalt catalyst for hydrogen generation from NaBH4 hydrolysis

The effect of cobalt-based catalysts, i.e. CoCl₂(20 wt% Co)/Al₂O₃ treated by different acids, on NaBH₄ hydrolysis was investigated. Five acids were used: oxalic acid, citric acid, acetic acid, sulfuric acid and hydrochloric acid. Two ways of acid treatment were considered: (i) ex-situ addition of acid to CoCl₂(20 wt% Co)/Al₂O₃ at room temperature and (ii) in-situ addition by mixing CoCl₂, Al₂O₃ and acid (one-step process). Both ways showed that adding an acid to the catalyst contributed to an important increase of the catalytic activity towards the NaBH₄ hydrolysis. The best performances were obtained with the catalysts treated with either HCl or CH₃COOH as the global activity of CoCl₂(20 wt% Co)/Al₂O₃ was increased up to 50%.     

Investigation of ZrFe2-type materials for metal hydride hydrogen compressor systems by substituting Fe with Cr or V

In this study, the effects of partial substitution of Fe, in the ZrFe₂-system alloys, by Cr or V are presented. The two studied alloys, ZrFe_1.8V_0.2 and ZrFe_1.8Cr_0.2, have been synthesized by high frequency induction-levitation melting under inert Ar atmosphere. The induction furnace was equipped with a water-cooled copper crucible that permits the rapid solidification of the alloy after the melting. The crystal structures of the investigated alloys have been studied by the Rietveld analysis of the obtained X-ray diffraction (XRD) patterns. The microstructure has been observed by a scanning electron microscope (SEM) on polished samples of the alloys. Their hydriding properties have been studied with a high pressure Sievert's type apparatus, up to 200 bar. All pressure–composition–temperature (PCT) measurements have been obtained at 20, 60 and 90 °C. Two high temperature activation cycles have been conducted prior to PCT measurements. The results showed almost the same uptake for the alloys after identical activation and lowering of the plateau pressure in both cases.     

Facile construction of phosphate incorporated graphitic carbon nitride with mesoporous structure and superior performance for H2 production

Novel mesoporous phosphate incorporated g-C₃N₄ (CNM-Px) polymeric material was synthesized via a facile hydrothermal-calcination method, using melamine as precursor and phosphoric acid as dopant. The successful incorporation of phosphate into the framework of g-C₃N₄ nanosheets was verified by XRD, FT-IR and XPS characterizations and the possible formation mechanism was put forward. The as-fabricated CNM-Px samples were applied to photocatalytic hydrogen evolution reaction and exhibited remarkably improved photocatalytic performance both under simulated sunlight and visible light irradiation. The concentration of phosphoric acid was also well tuned and the optimal concentration was 2.5 mol L^?1. The hydrogen evolution rate of the optimized sample CNM-P2.5 (the concentration of treating phosphoric acid was 2.5 mol L^?1) reached 8163 μmol g^?1 h^?1 under simulated sunlight irradiation, which is 3.7 times higher than that of pristine g-C₃N₄ (CNM). It also showed dramatically improved hydrogen evolution rate under visible light irradiation, which was 2105 μmol g^?1 h^?1, about 6.7 times higher than that of CNM. The excellent photocatalytic activity of CNM-Px samples is due to the synergic advantages of larger surface area and reduced recombination of photo-generated electrons and holes. This study paves the way for tailoring design and synthesis of highly active metal-free carbon nitride materials for photocatalytic hydrogen evolution.     

Mesoporous silica supported cobalt catalysts for hydrogen generation in hydrolysis of ammonia borane

Mesoporous silica supported cobalt boride (Co–B) catalysts are rationally designed for hydrogen generation in ammonia–borane hydrolysis reactions under ambient conditions. Cobalt boride catalysts are supported on three different mesoporous silica, including beta-zeolite seeded MCM-41 (Co@M41S) and traditional MCM-41 (Co@M41T) via chemical adsorption onto functionalized surface with 3-trihydroxysilylpropylmethylphosphonate (THPMP), and one-step co-precipitation into mesoporous silica framework (Co@M41C). Our preparation strategies provide two insights to the reactions: first, cobalt oxide species are intrinsically deposited as ultra-small nanoparticles (<2 nm) on mesoporous silica supports; subsequently the nanoparticles are converted to active Co–B catalysts by reduction with sodium borohydride (SB). Three catalysts exhibit significant differences in catalytic reactivities with hydrogen production rates ranked in an order of Co@M41S > Co@M41T > Co@M41C. Detailed analysis of the coordination environments from in situ X-ray absorption spectroscopy (XAS) results confirm reducibility in SB. Amorphous nature of Co–B catalysts are responsible for efficient catalytic activity in Co@M41S and Co@M41T. Ammonia temperature programmed desorption (NH₃-TPD) demonstrates support acidity that correlates to the degree of high dispersity and effective reducibility to Co–B. Effects from catalyst sizes, reducibility in SB treatment and surface acidity are studied in detail to compare catalytic reactivities among three types of supports.     

Evaluation of tungsten carbide as the electrocatalyst support for platinum hydrogen evolution/oxidation catalysts

WC was investigated as an electrocatalyst support material for a monolayer-equivalent of Pt and the Pt/WC system was evaluated as an electrocatalyst for the HER and HOR and compared to commercial Pt/C. It was found that Pt/WC lost only 4% of its activity during aging, which was significantly better than Pt/C, which lost more than 20% of its activity under identical operating conditions. Most of the degradation of the Pt/WC performance was due to the decomposition of impurity WO_x species on the support surface from synthesis that was identified by XPS. The activity and mechanism for the HER and HOR were also quantitatively evaluated. It was found that the reaction kinetics for the HER and HOR in both catalyst systems, Pt/WC and Pt/C, were identical, proceeding through the Volmer–Heyrovsky mechanism with an apparent activation energy of approximately 35 kJ/mol.