Electrocatalytic Activity and Stability of Titania-Supported Platinum- Palladium Electrocatalysts for Polymer Electrolyte Membrane Fuel Cell Sheng-Yang Huang, Prabhu Ganesan, and Branko N. Popov* Center for Electrochemical Engineering, Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29208, United States * S Supporting Information ABSTRACT: Titania-supported platinum-palladium electrocata- lysts (PtPd/TiO 2 ) were synthesized and investigated as alternative catalysts for the oxygen reduction reaction (ORR). Transmission electron microscope images revealed a uniform distribution of metal nanoparticles (d M =3-5 nm) on the TiO 2 support. An increase in ORR activity has been observed with an increase in the Pd content of the bimetallic alloy up to 30%, and beyond this composition, the decrease in catalytic activity has been found to be due to the blocking of Pt active sites by a large amount of Pd in the catalyst. The PtPd/TiO 2 electrocatalyst with a Pt/Pd composition of 70:30 shows activity comparable to that of a commercial Pt/C catalyst (TKK) in rotating ring-disk electrode studies. The accelerated durability test results show good stability for the PtPd/TiO 2 electrocatalysts at high potentials in terms of minimum loss in the Pt electrochemical surface area. The high stability of the PtPd/TiO 2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of polymer electrolyte membrane-based fuel cell cathode catalysts. KEYWORDS: titania, corrosion resistance support, platinum, palladium, oxygen reduction reaction, proton exchange membrane fuel cell 1. INTRODUCTION Fuel cells are regarded as clean energy sources for the future. The polymer electrolyte membrane fuel cell (PEMFC) is emerging as a promising candidate in the portable electronics and automobile industries due to its high power density and portability. 1-4 Carbon-supported platinum (Pt/C) and plati- num-based alloy catalysts are the most commonly used cathode catalysts for PEMFCs. Alloying Pt with other transition metals, such as Fe, Co, and Ni, can increase the catalytic activity and sometimes the stability of these catalysts for the oxygen reduction reaction (ORR). This effect may be attributed to the formation of alloys with favorable Pt-Pt interatomic distances or Pt crystal orientations in the Pt alloys that facilitate oxygen reduction and mitigate Pt sintering/dissolution. 5-7 Consid- erable efforts have been made to improve the durability and stability of Pt/C cathode catalysts in PEMFCs. Among all the known reasons for the low electrocatalyst durability, the loss of electrochemical surface area (ECSA) due to corrosion of the catalyst support and subsequent agglomeration of Pt nano- particles deposited on the support have been recognized as the most important issues to be addressed. 8-10 Electrochemical oxidation of the carbon support (eq 1) 11-13 causes microstructural degradation and surface chemical changes, which eventually lead to a loss of ECSA. + → + + = ° + − E C 2H O CO 4H 4e ( 0.207 V vs NHE at 25 C) 2 2 0 (1) The corrosion rate of carbon increases drastically at high electrode potentials. Carbon corrosion also leads to electrically isolated Pt particles that are detached from the support. Moreover, it is worth noticing that Pt also plays an important role in accelerating the carbon corrosion. 14,15 These effects result in a rapid degradation of the Pt catalyst and thus shorten the lifetime of the PEMFC. The cost of Pt-based catalysts is another obstacle for the commercialization of fuel cell vehicles due to the world’s limited Pt reserves. Therefore, many recent studies have focused on decreasing Pt loadings and increasing Pt utilization in fuel cells while maintaining satisfactory activity and stability. These efforts include the design of novel catalysts, 16,17 the use of new support materials, 18,19 and the optimization of electrode structure and fabrication methods, 15,20,21 However, it is still Special Issue: Electrocatalysis Received: February 5, 2012 Revised: March 22, 2012 Published: April 5, 2012 Research Article pubs.acs.org/acscatalysis © 2012 American Chemical Society 825 dx.doi.org/10.1021/cs300088n | ACS Catal. 2012, 2, 825-831