DOI: 10.1002/cssc.201200828 Supported Noble Metals on Hydrogen-Treated TiO 2 Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells Changkun Zhang, [a, b] Hongmei Yu,* [a] Yongkun Li, [a, b] Yuan Gao, [a, b] Yun Zhao, [a, b] Wei Song, [a] Zhigang Shao,* [a] and Baolian Yi [a] Introduction Polymer exchange membrane fuel cells (PEMFCs) have re- ceived considerable attention as promising energy conversion devices for both stationary and mobile applications because of their zero or low emissions and high power densities at low temperatures. [1] However, there are several issues that hinder the commercialization of PEMFCs such as high cost, low reli- ability, and poor long-term durability. [1, 2] Many materials can be used as catalyst supports to increase the electrochemical sur- face area (ECSA). Carbon materials such as Vulcan XC72 are common supports because of their large surface area, good electronic conductivity, and favorable pore structure. However, carbon oxidation during fuel-cell operation leads to significant degradation because of aggregation and dissolution of Pt par- ticles. [3] Metal oxides (e.g., SnO 2 , [4] WO x , [5] CeO 2 , [6] MnO 2 , [7] and TiO 2 [8] ) that have high stability under fuel-cell operating condi- tions are beneficial for improving the catalytic performance of catalysts. This is because of strong metal–support interactions (SMSIs) between the metals and the metal oxides, which can promote absorption of oxygen or fuels onto the catalyst sur- face. [9] In particular, TiO 2 has been extensively applied in dye- sensitized solar cells (DSSCs) and fuel cells. [10] The main limitation for the large-scale application of PEMFCs is cost. Therefore, cost reduction is important for the emerging fuel cell industry. Recently, highly oriented nanostructured elec- trodes with lower Pt loadings and higher ECSAs have attracted considerable attention. A unique nanostructured thin film (NSTF) electrode, which consists of oriented nanometer-sized crystalline organic whiskers [1a] can enhance specific activity of the catalysts as well as reduce the loss of ECSA. TiO 2 nanotube (TNT) arrays also offer high specific surface areas for catalysts with controllable sites; they hold promise to be used as highly ordered electrodes in fuel cells. Anodized TNT arrays were initially investigated by the Grimes group. [11] Self-organized TNTs can be grown electro- chemically in a fluoride-containing electrolyte that is either water-based or organic. The influence of fluoride content, anodization voltage, water content, and temperature on the TNT morphology has been investigated by many research- Hydrogen-treated TiO 2 nanotube (H–TNT) 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 H–TNTs 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 H–TNTs help to anchor a greater number of Pt atoms during Pt electro- deposition. The H–TNTs 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 uni- form nucleation sites for Pt and leads to increased Pt loading on the H-TNTs. Furthermore, fabricated Pt nanoparticles with a diameter of 3.4 nm are located uniformly around the pre- treated H–TNT support. The as-prepared and highly ordered electrodes exhibit excellent stability during accelerated durabil- ity tests, particularly for the H–TNT-loaded Pt catalysts that have been annealed in ultrahigh purity H 2 for a second time. There is minimal decrease in the electrochemical surface area of the as-prepared electrode after 1000 cycles compared to a 68 % decrease for the commercial JM 20 % Pt/C electrode after 800 cycles. X-ray photoelectron spectroscopy shows that after the H–TNT-loaded Pt catalysts are annealed in H 2 for the second time, the strong metal–support interaction between the H–TNTs and the Pt catalysts enhances the electrochemical stability of the electrodes. Fuel-cell testing shows that the power density reaches a maximum of 500 mW cm 2 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 2.68 kW g Pt 1 . It is indicated that H–TNT arrays, which have highly ordered nanostructures, could be used as ordered electrode supports. [a] C. Zhang, Prof. H.Yu, Y. Li, Y. Gao, Y. Zhao, Dr. W. Song, Prof. Z. Shao, Prof. B. Yi Fuel Cell System and Engineering Laboratory Dalian Institute of Chemical Physics, Chinese Academy of Sciences 457 Zhongshan Road, Dalian 116023 (PR China) Fax: (+ 86) 411-84379185 E-mail : hmyu@dicp.ac.cn zhgshao@dicp.ac.cn [b] C. Zhang, Y. Li, Y. Gao,Y. Zhao Graduate University of Chinese Academy of Science Beijing 100039 (PR China) # 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemSusChem 2013, 6, 659 – 666 659 CHEMSUSCHEM FULL PAPERS