Materials for hydrogen storage and the Na-Mg-B-H system

This review on materials for hydrogen storage in the solid state gives a brief discussion underlying reasons and driving forces of this specific field of research and development (the why question). This scenario is followed by an outline of the main materials investigated as options for hydrogen storage (the what exactly). Then, it moves into breakthroughs in the specific case of solid state storage of hydrogen, regarding both materials (where to store it) and properties (how it works). Finally, one of early model systems, namely NaBH₄/MgH₂ (the case study), is discussed more comprehensively to better elucidate some of the issues and drawbacks of its use in solid state hydrogen storage

Nanoporous Microtubes via Oxidation and Reduction of Cu–Ni Commercial Wires

Metallic porous microtubes were obtained from commercial wires (200–250 µm diameter) of Cu-65Ni-2Fe, Cu-44Ni-1Mn and Cu-23Ni, alloys (wt. %) by surface oxidation at 1173 K in air, removal of the unoxidized core by chemical etching, and reduction in annealing in the hydrogen atmosphere. Transversal sections of the partially oxidized wires show a porous layered structure, with an external shell of CuO (about 10 μm thick) and an inner layer of NiO (70–80 μm thick). In partially oxidized Cu-44Ni-1Mn and Cu-23Ni, Cu2O is dispersed in NiO because the maximum solubility of Cu in NiO is exceeded, whereas in Cu-65Ni-2Fe, a Cu2O shell is present between CuO and NiO layers. Chemical etching removed the unoxidized metallic core and Cu2O with formation of porous oxide microtubes. Porosity increases with Cu content because of the larger amount of Cu2O in the partially oxidized wire. After reduction, the transversal sections of the metallic porous microtubes show a series of f.c.c.-(Cu,Ni) solid solutions with different compositions, due to the segregation of CuO and NiO during oxidation caused by the different diffusion coefficients of Ni and Cu in the respective oxides. Pore formation occurs at each step of the process because of the Kirkendall effect, selective phase removal and volume contraction