No abstract

No abstract

Zn(BH 4) 2 •2NH 3 , a new ammine metal borohydride, has been synthesized via simply ball-milling a mixture of ZnCl 2 •2NH 3 /2LiBH 4. Structure analysis shows that the subsequent complex has a monoclinic structure with unit-cell parameters of a = 6.392(4) Å, b = 8.417(6) Å, c = 6.388(4) Å and β = 92.407(4) ° and space group P2 1 , in which Zn atoms coordinate with two BH 4 groups and two NH 3 groups. The interatomic distances reported herein show that Zn-H bonding in Zn(BH 4) 2 •2NH 3 is shorter than Ca-H bonds in Ca(BH 4) 2 •2NH 3 and Mg-H in Mg(BH 4) 2 •2NH 3. This reduced bond contact leads to an increase in the ionic character of H. This study is able to show a good correlation between the reduced M-H distance and enhanced dehydrogenation behavior of the hydride material. Dehydrogenation results showed that this novel compound is able to release 8.9 wt. % hydrogen below 115 °C within 10 min without concomitant release of undesirable gases such as ammonia and/or boranes, thereby demonstrating the potential of Zn(BH 4) 2 •2NH 3 to be used as a solid hydrogen storage material.

A new ammine dual-cation borohydride, LiMg(BH(4))(3)(NH(3))(2), has been successfully synthesized simply by ball-milling of Mg(BH(4))(2) and LiBH(4)·NH(3). Structure analysis of the synthesized LiMg(BH(4))(3)(NH(3))(2) revealed that it crystallized in the space group P6(3) (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three-dimensional architecture is built up through corner-connecting BH(4) units. Strong N-H···H-B dihydrogen bonds exist between the NH(3) and BH(4) units, enabling LiMg(BH(4))(3)(NH(3))(2) to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH(4))(3)(NH(3))(2)/LiBH(4) composite is able to release over 8 wt% hydrogen below 200 °C, which is comparable to that released by Mg(BH(4))(3)(NH(3))(2). More importantly, it was found that release of the byproduct NH(3) in this system can be completely suppressed by adjusting the ratio of Mg(BH(4))(2) and LiBH(4)·NH(3). This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.

The formation of nanoporous gold by open circuit dealloying of 100 nm AgAu foils in nitric acid is investigated in situ and in real time by combining synchrotron small angle X‐ray scattering (SAXS) and X‐ray diffraction (XRD). The time dependence of the dealloying is followed as a function of acid concentration. For all concentrations, several characteristic dealloying stages are observed. Firstly, there is a fast initial dissolution stage with an increase in surface area due to pore and mound formation; this leads to strain in the nanoporous gold that results from an increase in capillary pressure. After dissolution is complete, there is rapid coarsening of the quasi‐periodic, pore–ligament morphology. During this later stage, we deduce strong strain anisotropies that can be explained by preferred crystallographic orientation of ligaments. This rapid coarsening stage is followed by a slow coarsening stage where the SAXS patterns, and hence the quasi‐periodic morphology, is self‐similar in time. There is a strong correlation between the morphology evolution and strain development, which can be explained by capillary forces.