| 摘要: | 鉑和鉑基合金作為質子交換膜燃料電池(PEMFCs)的陰極觸媒已被廣泛地研究；然而，其主要挑戰為鉑的昂貴且稀少性以及氧氣還原反應(oxygen reduction reaction, ORR)之效率不佳。另一方面，作為在PEMFCs陽極端中較為綠色能源的燃料，氫氣，目前是透過碳氫化合物的蒸汽重整產生，亦會造成二氧化碳排放。因此，設計低鉑含量且高效析氫反應(hydrogen evolution reaction, HER)和ORR的觸媒為PEMFCs 實際應用的重要課題。本研究製備碳支撐低鉑負載的鉑和鉑錫觸媒(Pt0.4-NCs, Pt3-NCs, and Pt3Sn1-NCs) 以利用於HER和ORR反應。此外，藉由一兩步驟製程，包含混合並熱處理，以製備碳支撐鉑錫異質結構(Pt19Sn3-H and Pt3Sn0.4-H)亦用於比較。所製備觸媒之電化學性質、形貌、結構、表面組成、化學組成以及未填滿 d 軌域(number of unoccupied d-states, HTs)分別使用旋轉盤電極(rotating disk electrode, RDE)、高角度環形暗場相掃描電子顯微鏡(high angle annular dark-Field scanning transmission electron microscopy, HAADF STEM)、X 光繞射儀(X-ray diffraction, XRD)、光電子能譜儀(X-ray photoelectron spectroscopy, XPS)、感應耦合電漿原子發射光譜分析儀((inductively coupled plasma-optical emission spectrometer, ICP-OES)以及X 光吸收光譜(X-ray absorption spectroscopy, XAS)等儀器鑑定。
對於HER反應，Pt0.4-NCs和Pt3-NCs樣品由於它們的尺寸小和STEM觀察到的單原子的均勻分散，顯示出與商業Pt相當的高HER活性。隨著Sn的加入，製備的Pt3Sn1-NCs顯示出最佳的HER活性和穩定性，這可源自於團簇形貌和Pt-Sn異質結構。另一方面，對於ORR反應，因鉑奈米顆粒在氧化錫改質劑上具有高的電化學活性面積，Pt36Sn5奈米棒、Pt19Sn3-H和Pt3Sn0.4-H在質量基礎上表現出優異的ORR活性，特別是Pt3Sn0.4-H，在所有的觸媒中，在5000次循環前後，其在0.85V（MA0.85）下具有最高的質量活性。從此研究我們可以得知，具有單原子的Pt3Sn1-NCs奈米團簇是高效且穩定的HER觸媒，其在6小時計時電流試驗之前後之過電位分別為37和43 mV；此外，藉由利用異質結構和兩步法製程的優點，Pt3Sn0.4-H在耐久性試驗前後皆表現出最高的MA，分別大約是613和245 mA/mgPt。
;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. |
