PtPb nanoparticle electrocatalysts: control of activity through synthetic methods
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Solution phase synthesis of intermetallic nanoparticles without using surfactants (for catalytic applications) and subsequent control of size distribution remains a challenge: of growing interest, but not widely explored yet. To understand the questions in the syntheses of Pt containing intermetallic nanoparticles (as electrocatalysts for direct fuel cells) by using sodium naphthalide as the reducing agent, the effects of the Pt precursors’ organic ligands were investigated. PtPb syntheses were studied as the model case. In particular, methods that lead to nanoparticles that are independent single crystals are desirable. Platinum acetylacetonate, which is soluble in many organic solvents, has ligands that may interfere less with nanoparticle growth and ordering. Interesting trends, contrary to expectations, were observed when precursors were injected into a reducing agent solution at high temperatures. The presence of acetylacetonate, from the precursor, on the nanoparticles was confirmed by ATR, while SEM imaging showed evidence of morphological changes in the nanoparticles with increasing reaction temperature. A definite relationship between domain size and extent of observed residue (organic material and sodium) present on the particles could be established. By varying post-reaction solvent removal techniques, room temperature crystallization of PtPb nanoparticles was also achieved. Electrochemical activity of the nanoparticles was also much higher than that of nanoparticles synthesized by previous reaction schemes using sodium naphthalide as the reducing agent. Along with the above mentioned techniques, BET, TEM, CBED, SAED, and XRD were used as characterization tools for the prepared nanoparticles.
KeywordsElectrocatalysis PtPb Intermetallics Nanoparticles Fuel cells
This study was supported by the Basic Energy Sciences Division of the Department of Energy through Grants: DE-FG02-03ER46072 and DE-FG02-87ER4529. The authors thank Mick Thomas for help with the UHV-STEM data, John Hunt for the EPMA microprobe and John Grazul for the TEM data for which we made use of the UHV- STEM, TEM, and EPMA microprobe, laboratories of Cornell Center for Materials Research (CCMR). The BET surface area for the PtPb samples was measured in Prof. Ulrich Wiesner’s laboratory in the department of Materials Science and Engineering, at Cornell University. The BET surface area of one of the PtPb compounds (series 1, 120 °C reaction) was measured at Primet Precision Materials Inc. in Ithaca, NY. The authors would also like to thank Thomas McCarrick and Prof. J. Meinwald for helpful discussions on IR spectra.
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