Synthesis of microporous Ni/NiO nanoparticles with enhanced microwave absorption properties

The fabrication of microporous metal materials with many potential applications is challenging due to their high chemical activities and the difficulty in controlling the pore size. By adjusting the reaction condition and the composition of the Ni-Al nanoparticle precursor, we have successfully produced the microporous Ni nanoparticles (NPs) of 22 nm by chemical dealloying method. During the passivation process, the microporous Ni NPs covered with NiO shell are generated as the result of surface oxidation. The micropores range from 0.6 to 1.2 nm in diameter with a large surface area of 68.9 m²/g. Due to the elimination of Al atoms during dealloying process, the crystalline size of the microporous Ni NPs is sharply decreased to 2-5 nm. The specific architecture offers the microporous Ni/NiO NPs a small microwave reflection coefficient (RC) and a wide absorption bandwidth (RC ≤ -10 dB) of -49.1 dB and 5.8 GHz, much better than the nonporous counterpart of -24.1 dB and 3.7 GHz. The enhanced microwave absorption performance has been interpreted in terms of the micropore structure, core/shell structure and nanostructure effects.