Carbon-Supported Pt and Pt–Ir Nanowires for Methanol Electro-Oxidation in Acidic Media
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Direct methanol fuel cells are promising electrochemical energy conversion devices. But, more efficient and stable and less expensive catalysts are still required. Here, we successfully synthesized Pt/C and Pt0.5–Ir0.5/C, Pt0.6–Ir0.4/C, Pt0.7–Ir0.3/C, and Pt0.8–Ir0.2/C nanowires by the chemical reduction of the metallic precursors by formic acid and tested them towards methanol electro-oxidation in acidic media. Neither surfactants nor templates were used during the syntheses. The nanowires catalysts were compared with a commercial state-of-art catalyst aiming the observation of the properties improvements derived from both alloying Pt with Ir and morphology change from nanoparticles to nanowires. Well-defined and slightly agglomerated over the carbon nanowires (diameters and lengths of approximately 5 and 20 nm, respectively) were obtained, the fact that is ascribed to the 40 wt% metal loading. In addition, accelerated degradation tests showed that Pt0.6–Ir0.4/C, Pt0.7–Ir0.3/C and Pt0.8–Ir0.2/C catalysts are more stable than commercial Pt/C. All synthesized nanowires catalysts were more active towards methanol electro-oxidation than the commercial Pt/C. The Pt0.5–Ir0.5/C sample shows Pt mass activities 7 times that of commercial Pt/C. However, the Pt0.8–Ir0.2/C catalyst presented the best specific activity (6 times that of commercial Pt/C), have the highest currents in the derivative voltammetry and the oxidation potential shifts negatively 100 mV in comparison with the commercial Pt/C catalyst. Hence, the nanowires developed in this study are indicated as potential promising catalysts and can be applied successfully as direct methanol fuel cell anodes.
KeywordsChemical reduction method Methanol electro-oxidation Catalyst stability Direct methanol fuel cell Bifunctional mechanism
The authors would like to thank the CNPq (Grant Nos. 407274/2013-8, 400443/2013-9, 474261/2013-1, 304419/2015-0, and 310282/2013-6), to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES (Grant: 001), to FAPITEC/SE from Brazil, for financial support and scholarships. Moreover, we thank Profs. Ronaldo Santos Silva and Euler Araújo dos Santos from the Federal University of Sergipe and to Haoliang Huang from the University of Southampton.
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