www.afm-journal.de FULL PAPER © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 3570 www.MaterialsViews.com wileyonlinelibrary.com Yuan Zhang,* Metini Janyasupab, Chen-Wei Liu, Xinxin Li, Jiaqiang Xu,* and Chung-Chiun Liu 1. Introduction Platinum (Pt) is the most commonly used catalyst for the appli- cation of fuel cells. However, using a Pt catalyst in fuel cells can cause serious technological issues. Pt can be poisoned by CO and/or other contaminants during the oxidation of the fuel. Also, the durability of the electrode materials are critical, and Pt is not durable. [1,2] There has been considerable interest in developing more efficient and stable electrocatalysts to overcome these limitations. A frequently used strategy to design highly efficient catalysts in DMFCs is the use of multicomponent catalysts, such as random alloys, intermetallic alloys, near surface alloys, and core/shell par- ticles. [3–6] The advantage of bimtallic or multi-metallic alloy materials is that their properties may be tuned by not only their size and geometries, but also by their com- position. [4,7,8] The synergistic effect of multi- component catalysts has been discussed by many researchers. [9–11] For instance, alloying iridium (Ir) with a secondary metal (Sn), both bifunctional effects and electronic modification between the two components in DEFC reaction can be opti- mized by controlling the different ratio of Sn and Ir atoms. [12] The control of morphology for improving the properties of nanomaterials has been carried out in multiple applications, such as catalytic and sensor applications. [13,14] From the elec- tronic structure aspect, small metal nanoparticles, particularly in the size range below ∼5 nm, are defined in the “mitohe- drical” region, [15,16] in which pronounced nanosize effects can be found. Its highly accessible surface area appears in a fun- damentally difference from the bulk. Serious Ostwald ripening and associated crystallite growth (minimizing the total surface energy), usually occurred when the surface energy increased with decreasing particle size, further resulting in the loss of surface area in the electrocatalysts based fuel cell environ- ments. [17,18] In order to avoid this phenomenon, organic cap- ping agents are used to stabilize nanoparticles in relatively mild conditions. Unfortunately, these capping agents affect the catalyst surface resulting in reduced activity of the catalyst due to diffusion limitations and/or blocking of active sites. [19] Therefore, turning bimetallic nanoparticles into 3D porous materials may be preferred over separate nanoparticles due to their stability and comparable active surface area. [20–23] The 3D porous nanostructure is comprised of interconnected metallic particles or filaments, which provide a larger surface area and facilitates the effective transport of reactants and products. Therefore, the electrocatalytic performance of the catalysts can be improved. The 3D porous nanostructures have been studied extensively, [24,25] however, the investigation of 3D porous nano- structures constructed using alloy nanoparticles as building blocks has been rather limited. [21,26] Three Dimensional PtRh Alloy Porous Nanostructures: Tuning the Atomic Composition and Controlling the Morphology for the Application of Direct Methanol Fuel Cells A strategy for the synthesis of PtRh alloy 3D porous nanostructures by controlled aggregation of nanoparticles in oleylamine is presented. The atomic ratio between the two components (Pt and Rh) is tuned by varying the concentration of precursor salts accommodating the oxidation of methanol. The morphology of PtRh alloy nanostructure is controlled by elevating the temperature of the reaction system to 240 °C. The prepared 3D porous nanostructures provide a high degree of electrochemical activity and good durability toward the methanol oxidation reaction compared to those of the commercial Pt/C (E-TEK) and PtRh nanoparticles. Therefore, the 3D alloy porous nanostructures provide a good opportunity to explore their catalytic properties for methanol oxidation. DOI: 10.1002/adfm.201200678 Y. Zhang, Prof. J. Xu Department of Chemistry Shanghai University Shanghai 200444, China E-mail: xujiaqiang@shu.edu.cn Y. Zhang, M. Janyasupab, Prof. C.-C. Liu Department of Chemical Engineering Case Western Reserve University Cleveland, OH 44106, USA E-mail: yxz412@case.edu C.-W. Liu Institute of Material Sciences and Engineering National Central University Chung-Li 320, Taiwan X. Li State Key Laboratory of Transducer Technology Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050, China Adv. Funct. Mater. 2012, 22, 3570–3575