Electrocatalytic Evaluation of Shape-Dependent Platinum Nanocatalysts towards Methanol Oxidation Reaction
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Electrocatalytic Evaluation of Shape-Dependent Platinum Nanocatalysts towards Methanol Oxidation Reaction Hong Wu1, Yuxuan Wang1, Nathan Porter2, Cuikun Lin3 and Jiye Fang1,2,* 1 Materials Science & Engineering Program and 2Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902 3 Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069
ABSTRACT Electrocatalytic activity and stability of platinum nanocubes and nanospheres were comparatively investigated towards methanol oxidation reaction. The results indicate that the {100}-bounded Pt nanocubes exhibit not only higher catalytic activity but also higher stability compared with the mixed crystallographic facet-terminated Pt nanospheres. INTRODUCTION Low temperature fuel cells such as direct methanol fuel cells (DMFCs) have been studied extensively as an alternative power source for portable applications [1-3]. Platinum (Pt) nanocrystals (NCs) are considered as excellent catalysts in DMFCs due to their improved catalytic performance compared with bulk crystals [4-6]. Much effort has been devoted to manipulate the size-[7] and shape-controlled [8] Pt NCs. It has been reported that the electrocatalytic activity and reaction stability of Pt NCs are highly dependent on their shape and surface structure [10,11,12]. Therefore, it is worthwhile to study a small molecule oxidation behavior on Pt NCs with different surface structures. In this work, we report our comparative study of electrocatalytic performance on {100}-terminated nanocubes (NCbs) and multicrystallographic facet-bounded nanospheres towards methanol oxidation reaction (MOR). EXPERIMENTAL DETAILS Chemicals Platinum acetylacetonate (Pt(acac)2, 49.3-49.8% Pt), chloroform (>99.8 %), tri(ethylene glycol) (3EG, 99%) were received from Alfa Aesar. Poly(vinyl pyrrolidone) (PVP, 29,000 MW), oleic acid (OA, 90%), and oleylamine (OAm, 70%) are Sigma-Aldrich products. Chromium hexacarbonyl (Cr(CO)6, 99%) was obtained from Strem Chemicals. Anhydrous ethanol (200 proof), and hexane (98.5%) were purchased from AAPER and BDH, respectively. Perchloric acid (HClO4, 70%, double distilled) was obtained from GFS Chemicals and methanol (99.8%) from J.T. Baker. Nafion Solution (5%) was provided by Clean Fuel Cell Energy. All chemicals were used as received. Synthesis method The method of Pt NCb preparation was adopted from an approach developed previously [12]. Instead of W(CO)6 used in the previous method, Cr(CO)6 was used to obtain high-quality Pt NCs. In a typical experiment, 0.197 g of Pt(acac)2, 8.0 mL of OAm, and 2.0 mL of OA were loaded into a three-neck flask and heated to 140oC under argon stream protection. With vigorous
stirring, 0.050 g of Cr(CO)6 was added into the mixture. The temperature was raised to 200 oC and maintained for 10-40 minutes. The resultant products were collected by centrifugation after adding certain amount of absolute ethanol, and washed with anhydrous hexane for at least two cycles. Finally, the isolated NCs were dispersed in hexan
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