Nanoporous metal materials with many potential applications have been synthesized by a chemical dealloying approach. The fabrication of nanoporous metal nanoparticles (NPs), however, is still challenging due to the difficulties in producing suitable nanoscale precursors. Herein, nanoporous Co NPs of 31 nm have been successfully prepared by dealloying Co-Al NPs, and surprisingly they possess micropores in a range from 0.7 to 1.7 nm and a large surface area of 50 m(2) g(-1). The crystalline size of the microporous NPs is 2-5 nm. Through the passivation process, the microporous Co NPs covered with CoO (Co@CoO) are generated as a result of the surface oxidation of Co. They exhibit better microwave absorption properties than their nonporous counterpart. An enhanced reflection loss (RL) value of -90.2 dB is obtained for the microporous Co@CoO NPs with a thickness of merely 1.3 mm. The absorption bandwidth corresponding to the RL below -10 dB reaches 7.2 GHz. The microwave absorption mechanism is discussed in terms of micropore morphology, core@shell structure and nanostructure. This novel microporous material may open new routes for designing high performance microwave absorbers.

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In order to improve the hydrogen storage properties of Mg, Mg@Mg 17 Al 12 ultrafine particles (UFPs) with 7, 22 and 27 at% Al have been successfully prepared by a hydrogen plasma-metal reaction (HPMR) approach. These UFPs are nearly spherical in shape with an average size of about 150 nm. The Mg particle core is a single crystal, and the Mg 17 Al 12 particle shell of 2-5 nm thickness effectively suppresses the formation of MgO. The formation mechanism of the core-shell structure is interpreted in terms of Mg-Al phase transformation. The Mg 17 Al 12 shell disproportionates into MgH 2 and Al upon hydrogenation, and is recovered after hydrogen release. The morphology and size of these UFPs are not obviously changed during the sorption cycle, whereas the Mg particle core changes from single crystal into the polycrystalline form of 2-4 nm size. The hydrogen sorption kinetics and storage capacity of the Mg@Mg 17 Al 12 UFPs decreased with increasing Al content. Mg-7 at.% Al can absorb 5.7 wt% H 2 at 523 K and 7.0 wt% H 2 at 673 K. It can release 6.0 wt% H 2 within 30 minutes at 623 K and 6.2 wt% H 2 within 3 minutes at 673 K. The catalytic effect and oxidation resistance of the Mg 17 Al 12 shell, and the nanostructure of the Mg core accelerate the hydrogen diffusion, with low hydrogen absorption and desorption activation energies of 49.3 and 105.5 kJ mol À1 , respectively.

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