Supported Noble Metals on Hydrogen-Treated TiO2 Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells

Hydrogen-treated TiO2 nanotube (HTNT) arrays serve as highly ordered nanostructured electrode supports, which are able to significantly improve the electrochemical performance and durability of fuel cells. The electrical conductivity of HTNTs increases by approximately one order of magnitude in comparison to air-treated TNTs. The increase in the number of oxygen vacancies and hydroxyl groups on the HTNTs help to anchor a greater number of Pt atoms during Pt electrodeposition. The HTNTs are pretreated by using a successive ion adsorption and reaction (SIAR) method that enhances the loading and dispersion of Pt catalysts when electrodeposited. In the SIAR method a Pd activator can be used to provide uniform nucleation sites for Pt and leads to increased Pt loading on the H-TNTs. Furthermore, fabricated Pt nanoparticles with a diameter of 3.4nm are located uniformly around the pretreated HTNT support. The as-prepared and highly ordered electrodes exhibit excellent stability during accelerated durability tests, particularly for the HTNT-loaded Pt catalysts that have been annealed in ultrahigh purity H2 for a second time. There is minimal decrease in the electrochemical surface area of the as-prepared electrode after 1000cycles compared to a 68% decrease for the commercial JM 20% Pt/C electrode after 800cycles. X-ray photoelectron spectroscopy shows that after the HTNT-loaded Pt catalysts are annealed in H2 for the second time, the strong metalsupport interaction between the HTNTs and the Pt catalysts enhances the electrochemical stability of the electrodes. Fuel-cell testing shows that the power density reaches a maximum of 500mWcm2 when this highly ordered electrode is used as the anode. When used as the cathode in a fuel cell with extra-low Pt loading, the new electrode generates a specific power density of 2.68kWgPt1. It is indicated that HTNT arrays, which have highly ordered nanostructures, could be used as ordered electrode supports.