Room temperature hydrogen absorption by Mg and MgTiFe nanocomposites processed by high-energy ball milling

Mg - 40 wt % TiFe nanocomposite was prepared by high-energy ball milling, HEBM, aiming improved hydrogen absorption at room temperature (RT). Four processing routes were chosen to separately investigate the effects of TiFe addition, HEBM processing and dispersion of TiFe particles, being: Route 1 – mechanical mixture of Mg and TiFe powders; Route 2 – HEBM of Mg + TiFe at 400 rpm for 12 h; Route 3 – HEBM of pure Mg at 400 rpm for 12 h to be used as reference; and Route 4 – HEBM of Mg + TiFe at 600 rpm for 36 h. In this case, TiFe was previously milled with ethanol to improve its refinement level. It is shown that the synergetic effects of TiFe addition, HEBM processing and thermal activation – involving the creation of MgTiFe interfaces, the refinement and distribution of TiFe and also the presence of free Fe – lead to good hydrogenation kinetics at RT in MgTiFe nanocomposite. It is also shown for the first time that the milled pure Mg can absorb hydrogen at RT.     

CoAl spinel oxide modified ordered mesoporous alumina supported cobalt-based catalysts for Fischer–Tropsch synthesis

A series of CoAl spinel oxide modified ordered mesoporous alumina with different CoAl₂O₄ contents were synthesized by a facile one-pot evaporation induced self-assembly (EISA) method. Then they were first investigated as supports for Cobalt-based catalysts for Fischer–Tropsch synthesis (FTS). The results from testing the catalysts clearly showed that the catalysts modified with CoAl₂O₄ exhibited higher catalytic activity than the common ordered mesoporous alumina catalysts. A volcano-type dependence of the catalytic activity with the contents of CoAl₂O₄ in the supports was observed. The results from in situ XRD revealed that the cobalt phase of the reduced catalysts modified with CoAl₂O₄ were more likely to be HCP rather than FCC. As inferred from in situ CO-FTIR and CO-TPD results, the CO dissociation ability was enhanced by increasing the content of the CoAl₂O₄ modification in the supports. Such a volcano-type dependence of catalytic activity with the contents of CoAl₂O₄ in the supports was due to the combination of two factors. One was the generation of the HCP cobalt, which exhibited a higher CO dissociation ability. The other was the synergistic effect of lower reducibility and the degree of dispersion. Meanwhile, when the Co/Al ratios was 0.08 and 0.12 in the supports, the catalysts showed higher C5⁺ selectivity than other catalysts, which was mainly due to their high Co site density on the catalysts surface.     

On the covalence in H2AuX (X = F–I)

Theoretical investigations on the H₂AuX (X = F–I) series have been performed at the CCSD(T) theoretical level with extended basis sets and the T-shaped stable structures were found. Mechanisms of Au-X and Au?H₂ interactions were explored by NBO analysis, natural resonance theory, electron density deformation analyses, delocalization index and visualized by reduced density gradient analyses. Periodic trends are found in the bond length, stability and covalent nature of the Au-X interactions. For Au?H₂ interactions, the delocalization index values and the electron density difference analysis show the “charge-shift covalent” type of interaction.     

Preparation and performances of CuCo spinel coating on ferritic stainless steel for solid oxide fuel cell interconnect

A compact and adherent CoCu spinel coating on ferritic stainless steel was developed by electroplating a CoCu alloy layer followed by oxidation. The CoCu alloy was oxidized into a three-layer structure consisted of a thinner CuO outer layer, a middle thicker Cu_0.92Co_2.08O₄ layer and an inner Co₃O₄ layer after an oxidation treatment of 2 h at 800 °C in air. The three-layer oxide structure was transformed into a double-layer scale with a (Co,Cr,Cu,Mn,Fe)₃O₄ spinel outer layer and an inner Cr-rich oxide layer after an oxidation of 500 h at 800 °C in air. The CuCo coating enhanced the oxidation resistance of the alloy and served as a diffusion barrier against the outward migration of Cr elements. Meanwhile, the area specific resistance (ASR) of the scale for the CuCo coated alloy was significantly lower than that for the bare sample.     

Production and electrochemical characterization of MgNi alloys by molten salt electrolysis for Ni–MH batteries

MgNi alloys are produced by molten salt electrolysis and diffusion method on a nickel plate in KClNaCl based melts. Structure, alloy composition and electrochemical properties of these alloys are evaluated. Electrolyte composition and applied current density parameters are studied for the characterization of the alloys. It is found that MgNi alloys with 45 wt% to 49 wt% Ni content which can be defined as MgNi–type alloys, have both higher discharge capacity and good retaining rate (72%). These alloys are mainly composed of Mg₂Ni phases and displayed a maximum discharge capacity of 384 mAhg^?1. Increased Ni content is advantageous for the enhancement of the cycle life. At the same time, the discharge capacity of MgNi alloy electrode is found to be decreasing. The highest capacity retaining (85%) rate is observed in the highest Ni content alloys (72 wt% Ni).Electrochemical impedance spectroscopy and potentiodynamic polarization measurements show that the controlling–step of the discharge process changed from a mixed rate–determining process at lower depth of discharge to a mass transfer controlled process at higher depth of discharge. The charge transfer resistance increases from 0.5 Ω to 23 Ω with increasing depth of discharge.     

First-principles GGA + U calculation investigating the hydriding and diffusion properties of hydrogen in PuH2+x, 0 ≤x≤ 1

The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (H_i) in “perfect” PuH_2+x (0 $\le x\le$ 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra H_i atom interacts much further with surrounding host atoms in PuH₃ than in other Pu hydride matrixes. The minimum migration paths of a H_i atom in PuH_2+x are characterized by the image nudged elastic band (CINEB) method. The H_i atom diffuses in PuH₂, PuH_2.25, and PuH₅ matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable I_H-site plays a dominant role for the H_i migration into the O-site in PuH_2.75. The diffusion path of the H_i atom in PuH₃ is I_Pu $\to$ I_H0160 $\to$ I_PU path with the lowest migration energy of 0.72 eV, which concludes the H_i has relatively higher mobility in PuH₃. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH₂, PuH₃, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors.