Ordered Mesoporous Platinum@Graphitic Carbon Embedded Nanophase as a Highly Active, Stable, and Methanol-Tolerant Oxygen Reduction Electrocatalyst Zhangxiong Wu, †,‡ Yingying Lv, ‡ Yongyao Xia, ‡ Paul A. Webley, † and Dongyuan Zhao* ,†,‡ † Department of Chemical Engineering, Faculty of Engineering, Monash University, Melbourne, VIC 3800, Australia ‡ Department of Chemistry and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, P. R. China * S Supporting Information ABSTRACT: Highly ordered mesoporous platinum@graphitic carbon (Pt@ GC) composites with well-graphitized carbon frameworks and uniformly dispersed Pt nanoparticles embedded within the carbon pore walls have been rationally designed and synthesized. In this facile method, ordered mesoporous silica impregnated with a variable amount of Pt precursor is adopted as the hard template, followed by carbon deposition through a chemical vapor deposition (CVD) process with methane as a carbon precursor. During the CVD process, in situ reduction of Pt precursor, deposition of carbon, and graphitization can be integrated into a single step. The mesostructure, porosity and Pt content in the final mesoporous Pt@GC composites can be conveniently adjusted over a wide range by controlling the initial loading amount of Pt precursor and the CVD temperature and duration. The integration of high surface area, regular mesopores, graphitic nature of the carbon walls as well as highly dispersed and spatially embedded Pt nanoparticles in the mesoporous Pt@GC composites make them excellent as highly active, extremely stable, and methanol-tolerant electrocatalysts toward the oxygen reduction reaction (ORR). A systematic study by comparing the ORR performance among several carbon supported Pt electrocatalysts suggests the overwhelmingly better performance of the mesoporous Pt@GC composites. The structural, textural, and framework properties of the mesoporous Pt@GC composites are extensively studied and strongly related to their excellent ORR performance. These materials are highly promising for fuel cell applications and the synthesis method is quite applicable for constructing mesoporous graphitized carbon materials with various embedded nanophases. 1. INTRODUCTION Fuel cells such as direct methanol fuel cells (DMFCs) and proton exchange membrane fuel cells (PEMFCs) are highly desirable for automotive and portable electrical devices because they hold fascinating features including high energy density, low operating temperature, green emission, and ease of processing. 1,2 Their performance mainly relies on the electro- chemical activities of the electrocatalysts toward fuel oxidation reaction (e.g., methanol oxidation reaction, MOR) at the anode and oxygen reduction reaction (ORR) at the cathode. Nanostructured and/or nanoporous platinum (Pt)-containing materials are the most common attractive electrocatalysts for both the anode and cathode in these fuel cells. Currently, the unsatisfactory activity, kinetics, and durability of the Pt-based ORR catalysts and the high Pt usage are the major bottlenecks for commercializing these fuel cells. As a result, extensive research has been devoted to developing new catalysts with enhanced ORR performance, including porous Pt nanostruc- tures, 3-5 alloyed Pt nanoparticles, 6-8 carbon-supported Pt nanoparticles, 9-12 and some metal-free catalysts such as mesoporous nitrogen-enriched carbon materials. 13,14 Up to now, porous carbon-supported Pt nanoparticles are the most widely adopted ORR catalysts due to their reliable ORR performance as well as easy and scalable synthesis, such as the state-of-the-art and commercial carbon-black-supported Pt catalyst. 15 Mesoporous carbon materials themselves or supporting functional composites are essential in many potential applications such as energy storage, catalysis, and adsorption and separation. 16-20 As supports for Pt nanoparticles in electrocatalysis, they can provide high surface area for finely dispersing nanoparticles, large pore size/volume for facilitating mass diffusion, and good electrical conductivity for providing sufficient electron pathways, thus leading to high Pt mass and/ or specific activities. 9-12,21-31 However, major challenges still remain. First, the stability of the ORR electrocatalysts should be further improved. The most common support, carbon black, and some mesoporous carbon supports are mainly amorphous with high electrical resistance so that they are vulnerable to corrosion/oxidation, which can be further accelerated by the presence of Pt at high potentials (>0.7 V vs the normal hydrogen electrode, NHE), resulting in electrochemical isolation of Pt. 32 Meanwhile, the dispersed Pt nanoparticles have high surface energies and their interactions with amorphous carbon supports are fairly weak because in most Received: October 17, 2011 Published: December 15, 2011 Article pubs.acs.org/JACS © 2011 American Chemical Society 2236 dx.doi.org/10.1021/ja209753w | J. Am. Chem.Soc. 2012, 134, 2236-2245