Reaction Acceleration of Nanoporous High-Purity Pd Film Formation by Dealloying of Al-Pd-N Film in pH-Controlled EDTA So
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.59
Reaction Acceleration of Nanoporous High-Purity Pd Film Formation by Dealloying of Al-Pd-N Film in pH-Controlled EDTA Solution Tomoya Nishi, Syuya Hasegawa, Takuji Ube, and Takashi Ishiguro Tokyo University of Science, Department of Materials Science and Technology
ABSTRACT Metallic palladium (Pd) is used for hydrogen storage and detection. Fabrication of a nanoporous (NP) Pd structure can increase the specific surface area leading to a significant improvement in the sensitivity. In our previous study, we succeeded in forming a NP-Pd film by dealloying an Al-Pd alloy film using citric acid as a chelating agent. This method was environmentally friendly but had a long reaction time and a considerable amount of Al remained after dealloying; hence, the Pd purity was reduced. In this study, we succeeded in forming a higher purity NP-Pd film faster by dealloying the nitrogen-containing Al-Pd (AlPd-N) film using ethylene-diamine-tetraacetic-acid (EDTA) as a chelating material.
INTRODUCTION Hydrogen (H2) is considered a promising next-generation energy resources due to its cleanliness, efficiency, and renewable energy [1-3]. Real-time accurate monitoring of hydrogen flow in its application is crucial to effective operation. For leak monitoring, instruments must be capable of detecting hydrogen at concentrations below 4 vol%H2 (the lower explosion limit in the air [4]). Also, H2 is colorless, odorless, and tasteless, so it cannot be easily detected by human senses [1]. Therefore, it is necessary to develop an H2 sensor with high sensitivity, excellent gas selectivity, fast response, and long-term stability [1-10]. Extensive research is being performed on this subject. Metallic Pd is widely used as a H2 sensing material because of its high affinity for H 2 adsorption at room temperature [5]. When bulk Pd is used as the H2 sensing material, the electrical resistance changes irreversibly, and the response time becomes longer [3]. Therefore, various nanostructures of Pd have been studied for the purpose of H2 sensing, namely nanoscale thin films [7, 9, 10], two-dimensional nanoporous thin films [4, 8], nanoparticles [5, 6], and nanowires [3].
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The purpose of this study is to overcome the disadvantages of Pd by creating a nanoporous structure that can realize a large specific surface area and the stress relaxation mechanism. Dealloying is the most commonly used method to produce nanoporous metal structures. In this method, the base metal is selectively dissolved in the electrolyte due to metal corrosion, and the noble metal is retained to form a porous structure [11-13]. Several metals like Ni, Co, and Cu have wide solubility limits with Pd, but the use of strong acids and bases, or an anodic oxidation process,
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