| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 103 === In this study, Pt nanorods (NRs) with different aspect ratios and Pt3M (M= Au, Ag or Pd) NRs are prepared by the formic acid method (FAM) for the oxygen reduction reaction (ORR). For Pt nanomaterials, the effect of one-dimensional (1-D) morphology and alloying on the promotion of their ORR performance has been investigated. The structures, surface species, surface compositions, chemical compositions, morphologies, electrochemical properties and the number of unoccupied d-state (hTs) of prepared catalysts are characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometer (ICP-AES), high resolution transmission electron microscopy (HRTEM), rotating disk electrode (RDE) technique and X-ray absorption spectroscopy (XAS), respectively.
This study is divided into two parts. In the first part, the 45 wt% carbon-supported Pt and PtAu NRs with aspect ratios of 1.84, 2.34, 3.75 and 4.00 (named as Pt-1, Pt-2, Pt-3 and PtAu, respectively) are prepared via FAM. The mass activity (MA) of Pt-3 is the highest, and PtAu has lower MA than Pt-3, due to the coverage of some Pt surface atoms by Au. Nevertheless, after 1000 cycles of accelerated durability test (ADT), PtAu NRs show the best ORR activity and stability with only a decay of 24 %. The hTs value measured by XAS spectra shows that PtAu NRs have lower hTs, implying that more electrons transfer to Pt d-state, the Pt-O- binding is weaker and the ORR performance is promoted.
In the second part, the 45 wt% of carbon-supported PtAu, PtAg and PtPd NRs with a Pt core/M shell structure, aspect ratio of 4.0, and growth along (111) direction are prepared by FAM. The ORR activity of PtAu is the best among the Pt-based catalysts, and that of PtAg NRs is the second, which is 1.2 times higher than that of Pt/C. However, after 1000 cycles of ADT, due to the surface Pt segregation during ADT, the structure of PtAu becomes unstable, deteriorating the ORR performance. On the contrary, PtAg NRs show the best stability among the Pt3M catalysts with only a slight decay of 9 % attributed to the stable structure through Ag alloying during ADT.
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