| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 101 === Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. In this study, highly effective carbon supported PtM (M= Au, Pd, or Cu) nanoparticles (NPs), Pt and PtM nanorods (NRs) prepared by formic acid method (FAM) are studied for their activity and durability toward oxygen reduction reaction (ORR). The structures, surface compositions, chemical compositions, morphologies, electrochemical properties and local structural parameters of prepared catalysts are characterized by X-ray diffraction (XRD), 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.
The study is divided into three parts. In the first part, the 45 wt% PtM NPs are prepared by FAM successfully. The ORR activity and long-term durability of the PtM NPs is better than that of the Pt/C after 1000th potential cycles of accelerated durability test (ADT), especially PtAu NPs. The promotion of ORR performance is attributed to the modified electronic structure of the surface Pt and oxophilicity through the underlying Au sublayer.
In the second part, the 45 wt% Pt and PtM NRs catalysts with an average diameter of 3 nm and length of 10-20 nm are prepared by FAM. The number of unoccupied d-states (hTs) extracted from Pt LIII and LII –edge of XAS spectra show that PtCu and PtPd NRs have lower unfilled Pt d-states, indicating more d-band electrons transfer from the metal to Pt and a decrease of the adsorption strength of oxygenated adsorbates. The as-prepared Pt and PtM NRs have significantly enhanced ORR activity with an electrons transfer number per oxygen molecule of more than 3.8. Besides, after ADT of 1000 cycles, PtCu NRs display a mass activity of 34.4 mA cm−2 mg-1 Pt, which is nearly 2.2 times higher than that of commercial Pt/C. Thus, these results lead to the conclusion that the promotional effect of Pt and PtM NRs may be attributed to the 1D morphology, favorably enhancing the electrochemical activity and stability of ORR.
In the third part, the LSV results exhibit that the current density of PtCu NRs and Pt/C in HClO4 is about 3.0 and 1.5 times higher than that in H2SO4 because strongly adsorbed sulfate (or bisulfate) anions block the ORR active sites on Pt, especially on Pt (111) surface.
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