Xin-Bo Zhang

Iron-Nanoparticle-Catalyzed Hydrolytic Dehydrogenation of Ammonia Borane for Chemical Hydrogen Storage†

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth s crust, has been studied intensively because of its very potent magnetic and catalytic properties. However, its reactivity with respect to water and oxygen, especially on a nanoscale, generally limits its applications to a non-oxidizing environment where water and oxygen are not present. Recent studies involving coating Fe nanoparticles with an outer shell have succeeded in minimizing their oxidation and agglomeration. However, the presence of protective shell around the Fe particles is unfavorable for catalytic applications, where surface Fe active sites are needed. It is therefore understandable that, to date, there has been no report on the catalytic application of Fe nanoparticles without any protective shell other than the solvent components in aqueous solution in air. Fe nanoparticles that exert their powerful catalytic ability in aqueous solution or even in air will therefore significantly benefit both academic research and practical applications of iron-based materials. The search for effective hydrogen-storage materials is one of the most difficult challenges as we move towards a hydrogen-powered society as a long-term solution to current energy problems. Ammonia borane (AB; NH3BH3) has a hydrogen content of 19.6 wt%, which exceeds that of gasoline and therefore makes it an attractive candidate for chemical hydrogen-storage applications. The development of efficient and economical catalysts to further improve the kinetic properties under moderate conditions is therefore important for the practical application of this system. Herein we report the excellent catalytic activity of Fe nanoparticles with no protective shell for the hydrolytic dehydrogenation of aqueous AB under argon and even in air at room temperature. The Fe nanoparticles were pre-synthesized by reduction of FeSO4 with NaBH4 and then AB was immediately added to the solution to be catalytically hydrolyzed (AB/FeSO4/NaBH4 1.0:0.12:0.16). The gas generated was identified by mass spectrometry and its amount was measured volumetrically. Although black Fe nanoparticles were obtained rapidly, the evolution of 134 mL of hydrogen took more than 160 min (Figure 1a). The molar ratio of hydrolytically generated H2 to

One-Step Seeding Growth of Magnetically Recyclable Au@Co Core−Shell Nanoparticles: Highly Efficient Catalyst for Hydrolytic Dehydrogenation of Ammonia Borane

Magnetically recyclable Au@Co core-shell nanoparticles were successfully synthesized in a one-step seeding-growth process within a few minutes. They were thermally stable and exhibited higher catalytic activity toward the dehydrogenation of ammonia borane than Au-Co alloy and the pure metal counterparts. This is a large enhancement in the catalytic activity of core-shell structured nanoparticles and will provide a new design principle for heterogeneous catalysis.

Liquid-Phase Chemical Hydrogen Storage: Catalytic Hydrogen Generation under Ambient Conditions

There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials.

Room-temperature hydrogen generation from hydrous hydrazine for chemical hydrogen storage.

Rhodium nanoparticles (NPs) effectively catalyze the decomposition of hydrous hydrazine to produce hydrogen under ambient reaction conditions. Rh(0) NPs with a particle size of approximately 5 nm prepared in the presence of hexadecyltrimethyl ammonium bromide show higher catalytic activity.

Bimetallic Au–Ni Nanoparticles Embedded in SiO2 Nanospheres: Synergetic Catalysis in Hydrolytic Dehydrogenation of Ammonia Borane

Gold-nickel nanoparticles (NPs) of 3-4 nm diameter embedded in silica nanospheres of around 15 nm have been prepared by using [Au(en)(2)Cl(3)] and [Ni(NH(3))(6)Cl(2)] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH(4)/NH(3)BH(3). Compared with monometallic Au@SiO(2) and Ni@SiO(2), the as-synthesized Au-Ni@SiO(2) catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H(2), the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs.

Synthesis of Longtime Water/Air-Stable Ni Nanoparticles and Their High Catalytic Activity for Hydrolysis of Ammonia−Borane for Hydrogen Generation

In this paper, two kinds of Ni nanoparticles have been successfully synthesized without and with starch as the green protective material and investigated as catalysts for generating hydrogen from ammonia borane (NH(3)BH(3), AB). Experimental investigations have demonstrated that both of the Ni nanoparticles possess high catalytic activities for H(2) generation from aqueous solution of AB. However, the catalytic activities of Ni nanoparticles without starch decrease seriously in the course of the lifetime tests. In contrast, the catalytic activities of the Ni nanoparticles with starch almost keep unchanged even after 240 h. Moreover, the XPS results show that the surface of the Ni nanoparticles in starch solution is still metallic Ni even after 240 h, while that in pure water is nickel oxide. This means that starch can successfully keep the Ni nanoparticles in aqueous solution from the oxidation in air. The present efficient, low-cost, and longtime water/air stable Ni catalyst represents a promising step toward the development of AB as a viable on-board hydrogen storage and supply material.

Magnetically Recyclable Fe@Pt Core-Shell Nanoparticles and Their Use as Electrocatalysts for Ammonia Borane Oxidation: The Role of Crystallinity of the Core

Carbon-supported Fe@Pt core-shell nanoparticle (NP) catalysts with Fe cores in different crystal states have been successfully synthesized by a sequential reduction process. Unexpectedly, in contrast to its crystallized counterpart, iron in the amorphous state exerts a distinct and powerful ability as the core for the Fe@Pt NPs. The resultant NPs are far more active for ammonia borane oxidation (by up to 354%) than the commercial Pt/C catalysts. Furthermore, these NPs combine low cost, long-term stability, and easy recovery functions.

Unique Structural Trends in the Lanthanoid Oxocarbonyl Complexes

Reactions of laser-ablated lanthanoid atoms (except for radioactive Pm) with carbon dioxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. On the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, the lanthanoid oxocarbonyl complexes have been identified. Density functional theory calculations have been performed on these products, which support the experimental assignments of the infrared spectra. Infrared spectroscopic studies of these lanthanoid complexes combined with theoretical calculations reveal that the early lanthanoid (La-Sm) oxocarbonyl complexes adopt trans configurations, the europium and ytterbium ones adopt side-on-bonded modes (Eu-(eta2-OC)O and Yb-(eta2-OC)O), and the late lanthanoid (Gd-Lu) ones adopt cis configurations. Natural bond orbital analysis indicates that the formation of the lanthanoid oxocarbonyl complexes involves the promotion of 6s and 4f electrons into the metal valence shell.

CO Adsorption on a LaNi5 Hydrogen Storage Alloy Surface: A Theoretical Investigation

Density functional theory calculations are carried out to study CO adsorption on the (001) surface of a LaNi(5) hydrogen storage alloy. At low coverages, CO favors adsorption on Ni-Ni bridge sites. With an increase in CO coverage, the decrease in the adsorption energy is much larger for Ni-Ni-CO bridge adsorption than that for Ni-CO on-top adsorption. Thus, the latter sites in the relatively stable adsorption structure are preferentially utilized at high CO coverages. The nature of the bonding between CO and the LaNi(5) (001) surface is analyzed in detail.