Guotao Wu

Cobalt-catalyzed hydrogen desorption from the LiNH2–LiBH4 system

A doping of 5 wt% CoCl2 considerably decreases the dehydrogenation temperature of a mixture of LiNH2 and LiBH4. More that 8 wt% of hydrogen can be released at ca. 155 degrees C. X-Ray absorption near edge structure (XANES) spectroscopy indicated the formation of metallic Co after ball milling CoCl2 with LiNH2 and LiBH4. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements revealed that Co particles have poor crystallinity and are finely dispersed in the sample, which could lead to a high catalytic efficiency.

Hydrogen Storage Properties of Ca(BH4)2–LiNH2 System

Ca(BH(4))(2) is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its practical applications. In an effort to overcome these barriers and to adjust the thermal stability, we make a composite system Ca(BH(4))(2)-LiNH(2). Interaction of Ca(BH(4))(2) and LiNH(2) leads to decreased dehydrogenation temperatures and increased hydrogen desorption capacity in comparison to pristine Ca(BH(4))(2). More than 7 wt% of hydrogen can be detached at a temperature as low as approximately 178 degrees C from the cobalt-catalyzed Ca(BH(4))(2)-4 LiNH(2) system.

Investigations into the interaction between hydrogen and calcium nitride

The interaction between hydrogen and α-Ca3N2 has been investigated by temperature programmed adsorption–desorption and pressure–composition (P–C) isotherms and also by X-ray powder diffraction. We find that hydrogen adsorption by Ca3N2 begins at temperatures around 300 °C. Approximately 3.5 H atoms can be adsorbed by one Ca3N2 molecule. Only half of the adsorbed hydrogen can be desorbed at temperatures above 350 °C. Addition of CaH2 enhances the reversibility of H-adsorption in the Ca3N2 sample. As demonstrated in the present work, almost all of the hydrogen adsorbed by the Ca3N2–CaH2 sample (molar ratio 1 ∶ 1) can be released with Ca2NH as the final product.

Ammonia Decomposition with Manganese Nitride-Calcium Imide Composites as Efficient Catalysts.

Ammonia has high gravimetric and volumetric hydrogen densities and is, therefore, considered a promising carrier for the production of COx -free molecular H2 for forthcoming energy systems. Alkaline earth metals are generally regarded as structural promoters of catalysts and employed in numerous catalytic processes. Here, we report that calcium imide (CaNH) has a strong synergistic effect on Mn6 N5 in catalyzing the decomposition of NH3 , leading to a ca. 40 % drop in apparent activation energy. At 773 K, the H2 formation rate over a Mn6 N5 -11CaNH composite catalyst is about an order of magnitude higher than that of Mn6 N5 and comparable to the highly active Ni/SBA-15 and Ru/Al2 O3 catalysts. Analysis by means of temperature-programmed decomposition (TPD), X-ray diffraction (XRD), and X-ray absorption near edge spectroscopy (XANES) reveal that CaNH participates in the catalysis via forming a [Ca6 MnN5 ]-like intermediate, thus altering the reaction pathway and energetics. A two-step catalytic cycle, accounting for the synergy between CaNH and Mn6 N5 , is proposed.

New synthetic procedure for NaNH 2 (BH 3 ) 2 and evaluation of its hydrogen storage properties

Tremendous efforts have been devoted to the synthesis of new light element hydrides for hydrogen storage. Ammonia borane (AB) is a promising candidate possessing high hydrogen capacity and low dehydrogenation temperature. The step-wise dehydrogenation and release of by-products, however, are obstacles to its practical application. Chemical modifications of AB to synthesize new compounds or its derivatives are of practical and fundamental importance. Here we report an improved synthesis of sodium aminodiborane (NaNH2(BH3)2, NaABB), a derivative of ammonia borane. This procedure leads to high purity NaABB by reacting NaNH2 and 2 eq. AB. The dehydrogenation properties have been investigated by means of temperature programmed desorption-mass spectrometry, volumetric release, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and X-ray diffraction. In a closed vessel, NaABB can release ∼2 eq. H2 when heated at 271 °C, forming solid products of NaBH4 and highly condensed polyborazylene.

Ammonium Aminodiboranate: A Long-Sought Isomer of Diammoniate of Diborane and Ammonia Borane Dimer.

Ammonium aminodiboranate ([NH4 ][BH3 NH2 BH3 ]) is a long-sought isomer of diammoniate of diborane ([NH3 BH2 NH3 ][BH4 ]) and ammonia borane (NH3 BH3 ) dimer. Our results show that [NH4 ][BH3 NH2 BH3 ] is stable in tetrahydrofuran at -18 °C and decomposes rapidly to NH3 BH2 NH2 BH3 and H2 at elevated temperatures. The decomposition pathway is dictated by the dihydrogen bonding between H(δ+) on NH4 (+) and H(δ-) on BH3 , as confirmed by theoretical calculations. This is in contrast to the interconversion between [NH3 BH2 NH3 ][BH4 ] and (NH3 BH3 )2 , although all three have dihydrogen bonds and the same stoichiometry.

Half-metallic ferromagnetism in hypothetical wurtzite structure chromium chalcogenides

The hypothetical wurtzite structure chromium chalcogenides were investigated through first-principle calculation within density-functional theory. All compounds are predicted to be true half-metallic ferromagnets with an integer Bohr magneton of 4 mu(B) per unit. Their half-metallic gaps are 1.147, 0.885, and 0.247 eV at their equilibrium volumes for wurtzite-type CrM (M = S, Se, and Te), respectively. The half-metallicity can be maintained even when volumes are expanded by more than 20% for all compounds and compressed by more than 20%, 20%, and 5%, for CrS, CrSe, and CrTe, respectively.