Fabrication and Morphological Control of a Palladium Film with a Three-Dimensional Nano-Network Structure as a Hydrogen
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.82
Fabrication and Morphological Control of a Palladium Film with a Three-Dimensional NanoNetwork Structure as a Hydrogen Gas Sensing Material using Organic Acid Chelation Takuji Ube, Akizumi Kawamoto, Tomoya Nishi, and Takashi Ishiguro Tokyo University of Science, Department of Materials Science and Technology
Abstract
Nano-porous palladium (Pd) thin films could potentially be applied to hydrogen gas sensing materials with high sensitivity and selectivity. In our previous study, a nano-porous Pd film was fabricated with a three-dimensional network structure from an AlPd mother alloy film by a dealloying method using the chelating ability of an organic acid. This process was simple and environmentally friendly because it only required organic acid in a ppm concentration, and did not exhaust a strong acid waste solution, including heavy metal ions. This method was modified to improve the Pd purity of the dealloyed specimen, reaction rate, and morphology control. In this study, the existence of a composition undulation pattern was shown in the AlPd mother alloy film, and its effects on the morphology of the dealloyed specimen were evaluated. Furthermore, this pattern could be controlled by N2 gas addition to the Ar sputtering gas during the preparation of the AlPd mother alloy film.
INTRODUCTION Thin film materials contain a high specific area and uniformity in large areas even in small amounts than those of bulk materials. Thin films of noble metals can be applied as catalytic materials[1-3] and/or highly sensitive gas sensing materials[4, 5]. Moreover, the fabrication of a porous thin film could increase the specific surface area and could require less resources. Palladium (Pd) is a metal that can be applied to a hydrogen occlusion material[6] or hydrogen permeable material and could potentially be applied to a hydrogen gas sensor or catalytic material. However, Pd has shown an expansion property when occluding hydrogen atoms in a crystal structure, and this destroys the macroscopic structure. Therefore, a pure Pd thin film could not be used in
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practical applications. This study aimed to overcome this disadvantage of the Pd film by a creating a nano-porous structure that can realize a large specific area and stress relieving mechanism. In general, dealloying methods are used to fabricate nano-porous metals. Dealloying is a corrosion process, where the base metals are selectively dissolved into an electrolyte solution, and a more noble metal is retained to form a porous structure[7-9]. A combination of base and noble metals is selected to show a wide solid solution phase range on the binary-phase diagram. There are some metals that contain a wide solubility limit with Pd, such as Ni, Co, and C
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