Supportless Platinum Nanotubes Array by Atomic Layer Deposition as PEM Fuel Cell Electrode

• A simple process for the fabrication of Pt nanotubes arrays has been developed.
• The nanotubes array is stuck on a Nafion membrane and is coated by thin Nafion film.
• Demonstration of the Pt nanotubes array MEA towards ORR in half-cell.

This work reports the fabrication and the test of a novel type of electrode for polymer electrolyte fuel cells, based on an array of oriented and self-supported platinum nanotubes. The dense array of nanotubes is produced by coating the surface of a porous Anodized Aluminum Oxide template by Pt using the Atomic Layer Deposition technique. The nanotubes have a length of around 2 μm, an external diameter of around 180 nm and 20 nm thick Pt walls. As a consequence the tubes are stiff and self-standing with no need for a supporting structure. The array of nanotubes has a density of approximately 109 tubes cm−2 and is stuck onto a Nafion® membrane with excellent adhesion. The electrochemical response of the platinum nanotubes array electrode is investigated by means of half-cell tests and it is compared with the response of a conventional electrode based on a Pt/C dispersion. The nanotubes array shows excellent surface utilization and gas accessibility. The surface specific activity of the nanotubes array towards oxygen reduction reaction is comparable to the one of the conventional electrode: 37 μA cmPt−2 vs 28 μA cmPt−2 of the Pt/C dispersion. Conversely, the mass activity still remains low: 5.5 A/gPt vs 15 A/gPt of the Pt/C dispersion, therefore future actions to decrease the Pt loading and increase the mass activity are outlined. The scale-up of this prototype of supportless nanotubes array electrode from half–cell to fuel cell size is also demonstrated, opening the way to its test under real operating conditions.

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