Ultrafast Pd/AAO Nanowell Hydrogen Sensor
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Ultrafast Pd/AAO nanowell hydrogen sensor Jianjiang Lu, Shufang Yu+, H. Hau Wang,* Argonne National Laboratory, Materials Science Division, Argonne, IL 60439 Corresponding author: [email protected]
Abstract: Anodized aluminum oxide (AAO) membranes consist of highly uniform and aligned nanopores with pore diameters ranging between 10 and 200 nm. Based on these nanoporous materials, we developed a new AAO nanowell structure that was synthesized through short-term anodization of aluminum foil. The nanowell structure was made of shallow wells that were oriented in a hexagonally close packed configuration with well diameter around 50 nm and depth less than 100 nm. The chemical composition was amorphous alumina on aluminum substrate. Thin palladium film was then fabricated on the surface of the as-synthesized AAO nanowell to prepare a Pd/AAO nanowell structure. These devices demonstrated unexpectedly high hydrogen sensitivity. The response time ranged from a few hundred milliseconds to a few seconds with hydrogen concentration between 1 and 0.05%. They also showed modest responses at hydrogen concentration as low as 5 ppm.
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Introduction: Researches on the fabrication of fast responding and sensitive hydrogen sensors are called for the preparation of the forthcoming hydrogen economy. Currently, commercial hydrogen sensors suffer from their lengthy response time and high cost. In addition, the working temperatures are usually high. Therefore, explorations for new methods that lead to inexpensive, convenient and fast response hydrogen sensors are crucial for the future application of hydrogen fuel. Palladium metal has long been recognized as the desired material for hydrogen sensing.[1-2] In principle, Pd metal swells upon exposure to hydrogen gas that results in resistance change. Recent advances in the synthesis of Pd nanostructure based hydrogen sensors lead to a series of new results. These studies[3-5] showed that Pd nanostructure based hydrogen sensors are promising due to decrease in response time. In particular, Pd nanoparticle based hydrogen sensors respond to hydrogen gas in milliseconds.[3] The challenge here therefore is how to find an appropriate carrier that can load these palladium nano-particles and functions as a sensor. Anodized aluminum oxide (AAO) membranes consist of highly uniform and aligned nanopores with the pore diameter ranging between 10 and 200 nm.[6] AAO nanowell structure can be synthesized through short-term anodization of aluminum metal. Herein, we report that the thin AAO nanowell structure is an excellent substrate for hydrogen sensing because not only does it provide a rough surface with large surface areas which is a perfect medium for supporting Pd nanostructures but also the surface are weakly conductive for better electronic measurements. AAO nanowell hydrogen sensors that are coated with Pd nanostructure can be achieved either by thermal evaporation or
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coating Pd metal through chemical route on AAO nanowell surface. This paper will illus
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