Hydrogen generated from hydrolysis of ammonia borane using cobalt and ruthenium based catalysts

Ammonia borane (NH₃BH₃, AB), one kind of promising hydrogen storage materials, is hydrolyzed to produce hydrogen in presence of HCl, Co/IR-120 and Ru/IR-120 catalysts. The kinetics analysis of the AB hydrolysis shows that hydrogen production is of the first-order reaction in regard to both concentrations of ammonia borane and catalysts initially present, respectively. The hydrolyzate of ammonia borane after hydrogen evolution is also characterized with XRD, FT-IR and ¹¹B NMR. Boric acid (H₃BO₃) is found to be the dominant product in the hydrolyzate. Besides, the produced gas is discovered to contain both hydrogen and ammonia according to the GC–MS analysis and the indophenol colorimetric analysis. A possible reaction pathway on hydrogen generation from hydrolysis of ammonia borane is, accordingly, proposed based on the existence of boric acid, hydrogen and ammonia in the products. The total life cycle of ammonia borane is also proposed to illustrate formation of different intermediates during the AB hydrolysis for hydrogen generation and a possible regeneration scheme of the spent ammonia borane.     

A review on the catalysts used for hydrogen production from ammonia borane

Boron compounds have recently attracted attention in hydrogen production since they contain many hydrogen atoms. Among these compounds, ammonia borane, which has high hydrogen density (in weight basis), can be used to produce hydrogen through a hydrolysis reaction. However, since the ammonia borane solution is highly resistant to hydrolysis under ambient conditions, there is a need for active and stable catalysts to accelerate the reaction. In this review paper, unsupported and carbon-based supported metal catalysts used for hydrogen production through the hydrolysis of ammonia borane are presented. Noble metal catalysts (Ru, Rh, Pd, Pt and their binary and ternary alloys) and non-noble metal catalysts (Co, Ni, Fe, Cu and their binary and ternary alloys) were examined. The activation energy of reaction and turnover frequency (TOF) values were compared for these catalysts. Among the unsupported catalysts, it was concluded that the multi-metal catalyst systems (binary, ternary and quaternary) have higher catalytic activity than a single use of the same metals. In addition, the comparison showed that the supported catalysts are more resistant to catalytic cycles and suitable for long-term use. It was observed that CNT supported Rh (TOF = 706 mol H₂ mol cat⁻¹ min⁻¹) and graphene supported Ru (TOF = 600 mol H₂ mol cat⁻¹ min⁻¹) catalysts are the most active catalysts for the hydrogen generation from the ammonia borane at room temperature.     

Borates in hydrolysis of ammonia borane

Ammonia borane NH₃BH₃ (19.5 wt% H) is able to release hydrogen by hydrolysis in the presence of a catalyst in ambient conditions. This reaction has received considerable attention since 2006, with special focus on the catalytic material. In comparison, important aspects like the nature of the hydrolysis by-product(s) have been much less investigated while a good identification of the borate(s) is required for approaching recyclability. In this context, we present a work based on a systematic approach that aims at characterizing the hydrolysate, its stability in time, and the borate(s) recovered after drying. It is shown that the hydrolysate consists in aqueous B(OH)₃ and that the solution (catalyst-free) is stable when stored 6 months under argon atmosphere at 30 °C. The extraction of the water from the hydrolysate was performed at different conditions (vacuum, or air; from −50 to 500 °C). It is observed that the higher the temperature, the lower the hydration degree of the borates. The total dehydration, with the formation of B₂O₃, can be obtained at heating at 500 °C. The main problem with the hydrolysate is the release of NH₃ during the drying stage. A solution is to remove NH₃ after hydrolysis and to dry the NH₃-free hydrolysate. By this way, H₃B₃O₆ forms. Hence, B₂O₃ and H₃B₃O₆ could be recovered and recycled into ammonia borane. Besides the identification of the borates, the suitability of ammonia borane for hydrogen production by hydrolysis is discussed, especially in comparison with sodium borohydride NaBH₄.     

Boron-doped Cobalt nanoparticles anchored to different activated carbon supports as recyclable catalysts for enhanced alkyl-substituted amine boranes dehydrogenation

Aiming at easily recoverable and regenerated catalyst development for efficient hydrogen production from alkyl-substituted amine boranes, boron (B)-doped cobalt (Co) nanoparticles with similar composition and particle size were anchored on two different activated carbon supports: granule and pellet. The effect of different independent variables such as type active carbon support (granule or pellet), alkyl-substituted amine boranes (ammonia borane-AB, methyl amine borane-MEAB and ethylenediamine borane-EDAB), recyclability cycle on hydrogen generation rate as dependent variable were investigated via Analysis of Variance (ANOVA). In addition, compared with ammonia borane, alkyl-substituted ones showed slower hydrogen generation properties in presence catalysts: AB > MEAB > EDAB. Among B-doped Co catalysts supported with different activated carbon supports, granule type activated carbon supported one showed best catalytic performance of derivatives of borane compounds dehydrogenation, and the hydrogen generation rate (2.49–0.44 L H₂ min^?1 g^?1_Co) and TOF values (7338.52–1451.96 mol_H2 mol^?1_catmin^?1). In the bargain, granule catalysts performed good recyclability activity, maintains its high hydrogen yields and its activity only decreased % 71 even after 5 repetitive cycles.     

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.     

One-step synthesis of graphene supported Ru nanoparticles as efficient catalysts for hydrolytic dehydrogenation of ammonia borane

Ru nanoparticles supported on graphene have been synthesized via a one-step procedure using methylamine borane as reducing agent. Compared with NaBH₄ and ammonia borane, the as-prepared Ru/graphene NPs reduced by methylamine borane exhibit superior catalytic activity towards the hydrolytic dehydrogenation of ammonia borane. Additionally, the Ru/graphene NPs exhibit higher catalytic activity than its graphene free counterparts, and retain 72% of their initial catalytic activity after 4 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia borane is first order with respect to Ru concentration, the turnover frequency is 100 mol H₂ min⁻¹ (mol Ru)⁻¹. The activation energy for the hydrolysis of ammonia borane in the presence of Ru/graphene NPs has been measured to be 11.7 kJ/mol, which is the lowest value ever reported for the catalytic hydrolytic dehydrogenation of ammonia borane.     

Photoelectrocatalytic hydrolysis of ammonia borane by electrochemical deposited cuprous oxide on titanium dioxide nanotube arrays

Photoelectrocatalytic hydrolysis of ammonia borane (AB) is a promising technique for producing hydrogen gas (H₂) in the presence of an appropriate photocatalyst under light irradiation and bias. The application of cuprous oxide on titanium dioxide nanotube arrays (Cu₂O/TNA) for the photoelectrocatalytic hydrolysis of AB was studied. Cu₂O/TNA exhibited a spectral response in the ultraviolet–visible region and an onset wavelength of 600 nm. With AB in an electrolyte, Cu₂O/TNA exhibited a significant increase in its photocurrent spectral response at a bias of 0.1 V versus Ag/AgCl. The H₂ generation rate by photoelectrocatalysis (under 5-mW cm^?2 irradiation at 455 nm; bias of 0.1 V vs. Ag/AgCl) was 0.018 μmol s^?1 cm^?2, which was twice that by photocatalysis and four times those by catalysis and electrocatalysis; a Faradaic efficiency of 77% (corresponding to the oxidation reaction of AB) was also observed. Hence, Cu₂O/TNA is an efficient photoanode for photoelectrocatalytic hydrolysis of AB.     

Graphitic nanofibers supported NiMn bimetallic nanoalloys as catalysts for H2 generation from ammonia borane

Bimetallic nickel manganese nanoalloy-decorated graphitic nanofibers were prepared using electrospinning. The introduced catalysts were explored as an effective and inexpensive catalyst for H₂ generation from ammonia borane using hydrolysis. Standard techniques were used to determine the morphology and chemical composition of the nanofibers. Characterization indicated successful formation of bimetallic nickel-manganese-decorated graphitic nanofibers. Introduced effective catalysts showed a high reusability for H₂ generation using ammonia borane hydrolysis at low concentrations and temperatures. All formations of the introduced catalysts demonstrated a higher catalytic activity in H₂ generation than nickel-decorated carbon nanofibers. Samples composed of 55 wt% nickel and 45 wt% manganese showed the best catalytic activity compared with other formulations. Initial turnover frequency (TOF) of this sample was 58.2 min⁻¹, twice the TOF of the manganese-free catalyst. Kinetics and thermodynamics revealed that the catalyst concentration followed the pseudo-first order reaction while the ammonia borane concentration follow the pseudo-zero order reaction, providing activation energy of 38.9 kJ mol⁻¹.     

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.     

Magnetically recyclable Ni@h-BN composites for efficient hydrolysis of ammonia borane

The magnetic Ni@h-BN composites containing the uniform Ni nanoparticles supported on h-BN nanosheets have been prepared via a facile solvothermal method. The as-prepared samples show high catalytic performance for H₂ generation from the ammonia borane aqueous solution, especially for the Ni@h-BN with 25.0 wt% Ni content. Moreover, the Ni@h-BN composites possess a good ferromagnetic property at room temperature, endowing them with rapid magnetic separation to recycle. The kinetics of the hydrolysis of ammonia borane over the Ni@h-BN composites were further investigated in detail. It is found that the hydrogen generation was highly dependent on the catalyst amount and the reaction temperature. The activation energy of the hydrolysis reaction of ammonia borane is found to be 47.3 kJ mol^?1 over the Ni@h-BN with 25.0 wt% Ni content. Considering the good catalytic activities for H₂ release, the Ni@h-BN composites are expected to find important application in fuel cells and the related fields.     

Ammonia as a hydrogen energy carrier

The gravimetric H₂ densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H₂ tanks at the weight of 20–30ton, although the gravimetric H₂ density of liquid H₂ is 100 wt%. The volumetric H₂ densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H₂ tanks at 1–4 × 10⁴ m³. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO₂ emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H₂ density and similar to the efficiency of H₂ gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H₂<MCH. The amounts of energy consumption by N₂ production and Haber-Bosch process were below 10% compared with the value of H₂ production from water electrolysis.     

Oxygen vacancy-engaged interfacial charge transfer modulation for upgrade Rh-catalyzed hydrogen and oxygen productions

Developing efficient modulation strategies to upgrade the catalytic activity and reusability of Rh-catalyzed hydrogen evolution from ammonia borane (AB) hydrolysis are definitely profitable but remains a grand challenge. Here, we develop a stepwise activation strategy to produce highly active and reusable Rh/CoFe₂O₄-SB-H₂ with abundant oxygen vacancies and strong electronic metal-support interaction through stepwise reduction of Rh/CoFe₂O₄ precursor using sodium borohydride and H₂ as the reducing agents. Under ultrasonic irradiation, Rh/CoFe₂O₄-SB-H₂ with an ultralow Rh loading of 0.20 wt% can be utilized as an excellent catalyst for hydrogen production from room-temperature AB hydrolysis with a high turnover frequency (TOF) of 1894 min⁻¹. The TOF value could be further promoted to 15,570 min⁻¹ in the alkaline ultrasonic environment. The catalyst has a superior reusability with 75% maintaining activity of initial one in the 10^th cycle. The strong electronic metal-support interaction, rich oxygen vacancies and ultrasound irradiation promote the oxidative cleavage of the O–H bonds in attracted H₂O and thus account for high performance toward hydrogen production from AB. This catalyst can also be utilized as an active catalyst for oxygen generation from H₂O₂ decomposition. The developed strategies can be applied to upgrade the performance of other reducible metal oxides supported metal catalysts toward catalytic applications.     

Evaluation of bio-hydrogen production using rice straw hydrolysate extracted by acid and alkali hydrolysis

This study was conducted to investigate the properties of hydrolysates obtained from acid and alkali hydrolysis and to evaluate the feasibility of employing them for bio-hydrogen production. High sugar concentrations of 16.8 g/L and 13.3 g/L were present in 0.5% and 1.0% H₂SO₄ hydrolysates, respectively. However, H₂SO₄ hydrolysis resulted in large amounts of short-chain fatty acids (SCFAs) and furan derivatives, which were removed by detoxification. In bio-hydrogen production, 1.0% H₂SO₄ hydrolysate showed a 55.6 mL of highest hydrogen production and 1.14 mol-H₂/mol-hexose equivalent_added of hydrogen yield. In control and 1.0% NaOH hydrolysate, 29.7 mL and 36.9 mL of hydrogen were produced, respectively. Interestingly, relatively high acetate and butyrate production resulted in lactate reduction. Also, NH₄OH hydrolysate produced less than 10 mL of hydrogen. Thus, these results indicate that hydrogen production and metabolite distribution can vary depending on the sugars and by-product composition in the hydrolysate.     

Efficient hydrogen production from ammonia borane hydrolysis catalyzed by TiO2-supported RuCo catalysts

Hydrolysis of ammonia borane provides a reliable pathway for hydrogen production, while suitable catalysts are indispensable to make the hydrolysis reaction reach a considerable rate. In the present work, a series of TiO₂-supported RuCo catalysts have been fabricated by coprecipitation and subsequent reduction of Ru³⁺ and Co²⁺ on the surface of TiO₂ nanoparticles. Transmission electron microscopy and elemental mapping have verified the good distribution of metal species in the catalysts. The fabricated catalysts have shown excellent performance for catalyzing ammonia borane hydrolysis, especially in alkaline solutions with 0.5 M NaOH. For Ru₁Co₉/TiO₂ in which Ru/Co molar ratio is 1:9, the active energy of catalyzed ammonia borane hydrolysis is 33.25 kJ/mol, and a turnover frequency based on Ru as high as 1408 mol_H2/(mol_Ru·min) is obtained at 25 °C. Moreover, when different types of TiO₂ substrates are used, anatase TiO₂-supported catalysts show better catalytic activity than their counterparts with rutile TiO₂ as substrate or mixture of anatase and rutile TiO₂ as substrate.     

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.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.     

Simple synthesis of Cu2O–CoO nanoplates with enhanced catalytic activity for hydrogen production from ammonia borane hydrolysis

The development of inexpensive and high performing catalysts for ammonia borane (NH₃BH₃) hydrolysis is crucial for hydrogen production. In our research, a high-performance plate-like Cu₂O–CoO nanocomposite catalyst for NH₃BH₃ hydrolysis has been developed for the first time. In the hydrolytic reaction, both Cu₂O and CoO are separately inactive, while Cu₂O–CoO nanoplates show a high turnover frequency of 34.1 mol_hydrogen min⁻¹ mol_cat⁻¹, which is attributed to the synergistic effect between Cu₂O and CoO. It is interesting to discover that the induction time for the hydrolytic reaction is reduced to null when a small amount of Cu₂O is introduced into CoO. The reaction kinetics of NH₃BH₃ hydrolysis catalyzed by Cu₂O–CoO is also investigated. This work may provide other researchers some valuable insights into designing inexpensive and synergistic catalysts with enhanced catalytic activity for NH₃BH₃ hydrolysis for hydrogen production.     

Mechanistic implications of the solvent kinetic isotope effect in the hydrolysis of NaBH4

The sodium borohydride, NaBH₄, hydrolysis mechanism is studied via the H₂O/D₂O kinetic isotope effect (KIE). This reaction is of importance as NaBH₄ is considered as a hydrogen storage material. Nowadays, hydrogen is thought to be one of the most promising and efficient clean energy carriers. In order to control the rate of the hydrogen evolution reaction (HER), one has to understand the mechanism of its production. The H₂O/D₂O KIE of the reactions of NaBH₄ and NaBD₄ with water was studied in solutions containing a ratio of H₂O/D₂O = 1.00. The separation factor, α, of both reactions is α = 5.0 ± 1.0. The rate of the hydrolysis of BD₄^? in H₂O is faster than that of BH₄^?. The results point out that the rate-determining step in all hydrolysis stages is the H–OH bond scission.     

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.     

Mo-doped Ni-based catalyst for remarkably enhancing catalytic hydrogen evolution of hydrogen-storage materials

Ni-based alloys are considered as the efficient catalyst for hydrogen-storage materials decomposition. Herein, we applied an in-situ melt-quenching method to dope Mo in Ni-based alloy for catalytic hydrogen evolution from hydrogen-storage materials. Importantly, Mo doped Ni-based catalyst exhibits more than 6 times higher TOF value than that of pure Ni both in AB hydrolysis and hydrazine decomposition, because Mo acts as an electron donor to improve the reducibility of Ni. Hydrogen evolution kinetics were studied over a range of temperatures (303–353 K) and initial feed concentrations (catalyst/hydrogen-storage materials (wt/wt) ratios = 0.2–10). Under optimal reaction conditions, the H₂ evolution rate reaches 1.92 mol H₂/(mol_cat min) and 0.05 mol H₂/(mol_cat min) in the hydrolysis of ammonia borane and decomposition of hydrazine, which are 6.42 and 6.44 times higher than undoped Ni catalyst, respectively. And the apparent activation energy of ammonia borane hydrolysis and hydrazine decomposition were evaluated to be 26.66 ± 3.31 kJ/mol and 40.01 ± 3.38 kJ/mol, respectively.