Synthesis of Pt/TiO[sub 2] Nanotube Catalysts for Cathodic Oxygen Reduction

Abstract

Robust titanium oxide nanotube ͑TONT͒ arrays were formed by electrochemical anodization on various sample shapes ͑rod, screw, and foil͒, which facilitates versatility for electrode applications. From scanning electron microscopy images, it is clearly noted that irrespective of the shape of the sample, the self-organized TONT structure stands perpendicular to the surface with approximately the same width, hole size, and length, leading to its high surface area. To evaluate various TONT samples as catalyst supports for oxygen reduction in acidic solutions, a platinum ͑Pt͒ layer was deposited by both dc sputtering and evaporation. From the microscopic comparison between the sputtered and evaporated features of Pt/TONT catalysts, we found that the sputtered Pt is more conformal to the TONT surface morphology than the evaporated one, and this preserves the surface area increased by TONT formation. The cyclic voltammogram obtained from the sputtered Pt/TONT showed a somewhat higher potential value for initiating oxygen reduction than for the evaporated Pt/TONT. This is attributed to better electrochemical catalytic activity enhanced by the high surface area of the Pt layer.Ordered arrays of oxide nanotubes offer support for oxygen reduction catalysts with controlled sites to enhance the rate of the electrochemical reaction. With control of the site disposition on the arrays, one may expect to lower the amount of catalyst needed for efficient performance and to facilitate design of membrane electrode assemblies that have effective catalyst locations. This would have a major impact on fuel cell applications in renewable energy.The formation of titanium oxide ͑TiO 2 ͒ compact films has a wide literature that includes gas-phase oxidation and formation by electrochemical anodic processing ͑EAP͒. The films have been studied in many aqueous electrolytes and at a range of pH conditions. The TiO 2 films are found to be amorphous if they are formed rapidly, and are crystalline rutile if formed carefully and slowly. 1,2 Anatase and brookite are also formed under some conditions. Compact films are the dominant morphology with low porosity.There is considerable recent interest in forming nanoscopic materials with enhanced or unique properties. Nanotubes and nanowires have been synthesized in hard templates such as nanoporous alumina, 3 and bicontinuous nanomaterials have been formed by solgel processing and supercritical drying. TiO 2 nanotubes have been formed by hydrothermal processing, 4 and hydrated titanate nanotubes show proton conductivity at ambient temperatures. 5 Hydrothermal processing of titania powder in an alkaline solution at modest temperatures ͑e.g., 150°C͒ produces powders of nanotubes. 6 TiO 2 nanotube arrays have been formed in porous alumina templates. 7 Nanorods and nanodots of TiO 2 have been formed with EAP. 8 Pores in single-crystal rutile ͑TiO 2 ͒ have been formed by etching in alkaline solutions.Research in our laboratory has been described in papers on anodic formation of nanotubes of ZrO 2 and TiO 2 ͑TO...

Electrochemical oxygen reduction behaviour of platinum nanoparticles supported on multi-walled carbon nanotube/titanium dioxide composites

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Pt nanoparticles deposited on TiO2 based nanofibers: Electrochemical stability and oxygen reduction activity

“…The surface coverage with Pt nanoparticles, which had a diameter of 2 nm, could be increased by extending the deposition time. Several studies focused on utilizing TiO 2 supported Pt for the relatively sluggish oxygen reduction reaction (ORR), one of the main limiting factors with respect to the PEM fuel cell performance [4,10,11]. Lee et al described the fabrication of TiO 2 nanotubes onto which Pt was deposited through either sputtering or evaporation.…”

Preparation of Pt catalysts decorated TiO2 nanotube arrays by redox replacement of Ni precursors for proton exchange membrane fuel cells

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