| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 107 === Pt and Pt-based alloys as cathode catalysts of proton exchange membrane fuel cells (PEMFCs) have been widely researched; however, their main challenges are the high cost, Pt scarcity and the sluggish kinetics of oxygen reduction reaction (ORR). On the other hand, hydrogen, a greener source of the fuel used in the anode of PEMFCs, is currently produced by steam reforming of hydrocarbons with CO2 emission. Therefore, the design of low Pt and highly efficient hydrogen evolution reaction (HER) and ORR catalysts is an important task for the practical application of PEMFCs. In this study, carbon supported Pt and PtSn catalysts with low Pt loading (Pt0.4-NCs, Pt3-NCs, and Pt3Sn1-NCs) are prepared for the HER and ORR. Besides, carbon-supported PtSn heterostructures (Pt19Sn3-H and Pt3Sn0.4-H) prepared by a mix and then heating process is used for comparison. The electrochemical properties, morphologies, structures, surface compositions, chemical compositions and HTs of the carbon-supported Pt and PtSn catalysts are analyzed by rotating disc electrode (RDE), high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Inductively coupled plasma‒optical emission spectroscopy (ICP-OES), and X-ray absorption spectroscopy (XAS), respectively.
For the HER reaction, Pt0.4-NCs and Pt3-NCs samples show high HER activity comparable to commercial Pt, due to their small size and uniform dispersion of single atoms observed by STEM. With the addition of Sn, Pt3Sn1-NCs show the best HER performance and stability attributed to the cluster morphology and the Pt-Sn heterostructure. On the other side, for the ORR reaction, Pt36Sn5 nanorods, Pt19Sn3-H and Pt3Sn0.4-H exhibit superior ORR activity on a mass basis attributed to the high ECSA of Pt NPs on SnO2 modifier, especially for Pt3Sn0.4-H, which possesses the highest mass activity at 0.85 V (MA0.85) before and after 5000 cycles among all catalysts. It is believed that Pt3Sn1 nanoclusters with single atoms are highly effective and stable HER catalysts with a overpotential of 37 and 43 mV before and after 6 h CA test, respectively. Moreover, by taking the advantages of the heterostructrures and the 2 step process, Pt3Sn0.4-H exhibits the highest MA about 613 and 245 mA/mgPt before and after 5000 cycles durability test, respectively.
|
|---|
