Improvement of ORR Activity and Durability of Pt Electrocatalyst Nanoparticles Anchored on TiO 2 /Cup-Stacked Carbon Nanotube in Acidic Aqueous Media Fuma Ando a , Toyokazu Tanabe a , Takao Gunji a , Takashi Tsuda a , Shingo Kaneko b , Tsuyoshi Takeda c , Takeo Ohsaka b , Futoshi Matsumoto a, * a Department of Materials and Life Chemistry, Kanagawa University, 3-27-1, Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686, Japan b Research Institute for Engineering, Kanagawa University, 3-27-1, Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686, Japan c Sankei Giken Kogyo Co., Ltd., 2-5-1 Akabane Minami Kita-ku, Tokyo 115-8588, Japan A R T I C L E I N F O Article history: Received 28 December 2016 Received in revised form 13 February 2017 Accepted 1 March 2017 Available online 2 March 2017 Keywords: Cup-stacked carbon nanotube Composite electrocatalyst Platinum Titanium dioxide Oxygen reduction reaction (ORR) A B S T R A C T Platinum nanoparticles (Pt NPs) have been selectively anchored by photodeposition on titanium oxide (TiO 2 ) matrix which is formed by hydrolysis of titanium isopropoxide on cup–stacked carbon nanotubes (CSCNT) in isopropanol, producing the composite Pt catalyst useful for oxygen reduction reaction (ORR) in acidic media, i.e., Pt NPs/TiO 2 /CSCNT. Using scanning transmission electron microscopy (STEM) with a high–angle annular–dark–field (HAADF) detector it has been clarified that Pt NPs are sunk into the TiO 2 moieties and have the unique polyhedral shape surrounded mainly by the Pt (1 1 1) and Pt (1 0 0) facets. X–ray photoelectron spectroscopy (XPS) allowed us to confirm changes in electronic properties of both Pt NPs and TiO 2 support, induced by the so-called strong metal–support interactions (SMSI) and the significantly increased ORR activity was attained in 0.1 M HClO 4 , compared with the Pt NPs deposited on CB (Vulcan carbon) and CSCNT. The surface structure of the Pt NPs was characterized by transmission electron microscopy (TEM), indicating the improved durability of the Pt NPs deposited on the TiO 2 / CSCNT, i.e., the only slight increase in the particle size after the durability test (typically 2000 times’ potential cycling at 10 mV s 1 in the potential ranges of 0.05 to 1.1 V and 1.0 to 1.5 V vs. RHE in 0.1 M HClO 4 ). The results obtained demonstrate that the anchoring of Pt NPs on the TiO 2 support material deposited on CSCNT is an effective way to enhance the ORR activity of Pt NPs by the SMSI as well as to prohibit Pt NPs from aggregating, i.e., the degradation of the ORR activity of Pt NPs. © 2017 Elsevier Ltd. All rights reserved. Introduction Recently, the development of new energy sources and improve- ments in energy efficiency in generation, conversion and storage have become some of the most pressing issues confronting today’s scientific community. In this context, the use of fuel cells that directly convert chemical energy into electricity, using electro- chemical reactions, and can reach efficiencies as high as 90% [1,2] has been presented as one of the most promising technologies. Among fuel cells, recently, there has been an increased interest in polymer electrolyte membrane fuel cells (PEMFCs) that use hydrogen and oxygen, where hydrogen is used as a fuel and oxygen as an oxidant. The oxidation of fuel produces electrons to generate electricity with only water. In order to develop PEMFCs which satisfy demands from both economical and environmental points of view and to spread the application of PEMFCs to various areas, a number of important issues must be resolved. One is the development of electrocatalyst materials for the anode and cathode where high power density has been obtained at room temperature [3]. Especially, the oxygen reduction reaction (ORR) kinetics at the cathode is very slow, even at the surface of the Pt catalyst. Therefore, a large overpotential is required for the ORR to proceed at any practical speed under the operating conditions of PEMFCs [4]. To accelerate the ORR kinetics to a practically usable level in fuel cells, there has been a strong demand for the development of cathode ORR catalysts that can solve significant cost and durability issues as well as sluggish ORR kinetics [5–10]. The carbon-supported Pt nanoparticle (NP) is a state-of-the-art cathode electrocatalyst for ORR. In order to reduce the cost of Pt NPs used in PEMFCs and to enhance their electrocatalytic activity, * Corresponding author. Tel.: +81454815661. E-mail address: fmatsumoto@kanagawa-u.ac.jp (F. Matsumoto). http://dx.doi.org/10.1016/j.electacta.2017.03.004 0013-4686/© 2017 Elsevier Ltd. All rights reserved. Electrochimica Acta 232 (2017) 404–413 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta