Preparation And Electrochemical Property Of Nanostructured Magnesium

Nanoporous metals have great applications in the fields of sensing, catalysis and energy storage, due to its special bicontinuous "ligament-pore" nanostructure. Current researches of the nanoporous metals are concentrating on metals with high chemical stability. But about the active metals, such nanoporous Mg, few studies have been done. Thus in this paper, the preparation, characterization and electrochemical property of nanoporous Mg are studied.The current preparation methods of nanoporous metals can be subdivided into templated synthesis and dealloying, which involve in elctrochemical reduction and elctrochemical corrosion. However, as an active metal, Mg is very easy to be corroded, which makes the former two methods unsuitable for the preparation of Nanoporous Mg. Thus in this paper, physical vapor deposition (PVD) method was explored to prepare the nanoporous Mg.Firstly, Mg nanoparticles were prepared by PVD method. The preparation route was evaporating Mg powders at 500?600 ? under an Ar flow of 80-120 cm3·min-1, and depositing Mg vapor onto water-cooled copper foil. Diameters of the Mg nanoparticles were determined to be 10?50 nm.Secondly, by controlling the vacuum level, evaporation temperature and substrate, Mg nanowires were prepared by PVD method. The preparation route was evaporating Mg powders in a tube furnace in a high vacuum level and depositing Mg vapor on stainless steel mesh. The results showed that the vacuum level played a key role in the formation of Mg nanowires. Moreover, with the increase of evaporation temperature and deposition distance, Mg NWs become thicker and longer and finally transformed into micron particles. The as-prepared Mg NWs were determined to be 75 nm in diameter and 1.25 um in length. Depending on the experimental results, the formation process was explained by bond length-binding energy theory, and the formation mechanism that Mg NWs tend to giow in the [11-20] direction was proposed.Based on the preparation of Mg NPs and Mg NWs, by changing the deposition mode, i.e. changing from horizontal deposition mode to vertical deposition mode, cellular nanoporous Mg was successfully prepared. The preparation route was evaporating Mg powders at 500 ?in a vacuum of 10"1 Pa in the vertical mode, and depositing Mg vapor on the stainless steel mesh. The as-prepared cellular nanoporous Mg was consist of columnar crystals. The columnar crystals had radial structures on the bottom surface, and grew layer by layer against the Mg vapor flow, and formed regular shaped nanopores of 120-380 nm on the top surface. The columnar crystals had a preferred orientation, which is found to be the [0001] direction of Mg crystal. The 3D structure of the cellular nanoporous Mg was characterized by synchrotron radiation micron-imaging, synchrotron radiation nano-imaging and 3D-FEB, and results showed that the cellular nanoporous Mg had three kinds of pores:micronpores of 2.5?3.0 ?m, nanopores of 280475 nm and nanopores of 110 nm. The calculated porosities were 11.9?18.6%,6.5?10.5% and 2.1%, respectively. According to the experimental results, the mechanism of vacancy assisted atom deposition was proposed to explain the formation of cellular nanoporous Mg:There were a lot of Mg atoms and atom groups in the Mg vapor. During the desublimation of Mg atoms and atom groups into Mg crystals, a lot of holes are formed in the Mg crystals because of the large amount of vacancies existed in the Mg vapor. Columnar crystals with a specific growth orientation were formed owing to the anisotropy existed in the growth of Mg crystals.Based on the preparation of cellular nanoporous Mg, by adding assistant gas, feathery nanoporous Mg was successfully prepared. The preparation route was evaporating Mg powders at 550 ? in the flow of alcholol vapor of 3 Pa and depositing Mg vapor on the stainless steel mesh at the height of 12 cm. The results showed that the deposition displayed micronpores of 3.3-9.4 ?m in a low magnification and displayed feathery nanostnictures in a high magnification. The 3D structures were characterized by synchrotron radiation nano-imaging and 3D-FIB, and the results showed that there were two kinds of pores in the feathery nanoporous Mg:micronpores of 1.33 ?m and nanopores of 385 nm and the calculated porosities were 72% and 80%, respectively.Finally, the electrochemical properties of cellular nanoporous Mg and feathery nanoporous Mg were examined. The results showed that in the NaCl solution, the cellular nanoporous Mg and the feathery nanoporous Mg exhibited a much lower electrode potential (-1.4 V and -1.55 V, respectively) and strong hydrogen evolution reaction.This paper has great impli. ations for the development of nanoporous metals and nanostructured Ma.