Shape-Controlled Catalysts DOI: 10.1002/anie.201002888 Enhancing by Weakening: Electrooxidation of Methanol on Pt 3 Co and Pt Nanocubes** Hongzhou Yang, Jun Zhang, Kai Sun, Shouzhong Zou,* and Jiye Fang* Direct methanol fuel cells (DMFCs) are attractive energy conversion devices for powering portable electronics by converting the chemical energy of methanol directly into electricity. [1–4] To increase the methanol oxidation activity and to reduce platinum loading, bimetallic catalysts of platinum alloyed with a less expensive metal M are often used. [5–10] Among different bimetallic catalysts, Pt/Ru has attracted most attention owing to its strong methanol oxidation enhancement. The improved catalytic activity is explained by the bifunctional mechanism [5] and the electronic effect. [6, 7] In the bifunctional mechanism, the platinum sites are responsible for methanol oxidation to form adsorbed carbon monoxide (CO ads ), which poisons the catalyst surface for further fuel oxidation; the ruthenium sites provide adsorbed hydroxyl groups (OH ads ), which is the oxidant for the removal of CO ads , at a much lower potential than on platinum. In the electronic effect, the presence of ruthenium changes the electronic structure of platinum in such a way that it lowers the CO adsorption energy. These two mechanisms often operate concurrently and are often invoked to explain the activity enhancement of other Pt/M alloys. Herein we present methanol oxidation on Pt 3 Co nanocubes (NCbs), in which the enhanced methanol oxidation arises solely from the electronic effect. It has been extensively shown that methanol oxidation is a structure-sensitive reaction on platinum surfaces. The dependence of catalytic activity on particle shape for meth- anol oxidation on Pt nanocrystals (NCs) has also been revealed. [11–14] These studies underscore the importance of surface structure through particle shape control when the activities of different catalysts are compared. Recently, we also developed a robust and general approach for synthesizing NCbs consisting of binary alloys of platinum and 3d transition metals, including Pt 3 Co NCbs. [15] This approach provides a new avenue to compare methanol oxidation activity on structurally similar Pt 3 Co and Pt NCbs, thus eliminating the activity difference arising from the surface structure effect. Pt/ Co alloy nanoparticles (NPs) have been previously shown to possess a higher methanol oxidation activity compared to Pt NPs in both acidic and basic media. [8–10, 16] To the best of our knowledge, this is the first comparative study of methanol oxidation on structurally controlled Pt and Pt alloy NCs. Figure 1 a,e presents typical transmission electron micro- scopic (TEM) images of the Pt 3 Co and Pt NCbs, showing a Figure 1. a) TEM image of Pt 3 Co nanocubes (NCbs); b) HRTEM image of a single Pt 3 Co NCb; c) size-distribution histogram (frequency f versus length l) of Pt 3 Co NCbs determined using TEM image of about 200 NCs (equivalent side lengths were calculated based on the measured diagonals); d) SAED of Pt 3 Co NCbs (ca. 300 NCs, negative pattern); e) TEM image of Pt NCbs; f) HRTEM image of a single Pt NCb. [*] Dr. H. Yang, Prof. S. Zou Department of Chemistry and Biochemistry Miami University,Oxford, OH 45056 (USA) E-mail: zous@muohio.edu Dr. J. Zhang, Prof. J. Fang Department of Chemistry State University of New York at Binghamton Binghamton, NY 13902 (USA) E-mail: jfang@binghamton.edu Homepage: http://chemiris.chem.binghamton.edu/FANG Dr. K. Sun Department of Materials Science and Engineering University of Michigan Ann Arbor, MI 48109 (USA) [**] This work was supported by the NSF (DMR-0731382 and CHM- 0616436), S 3 IP, and Binghamton University. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201002888. Communications 6848  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2010, 49, 6848 –6851