| 摘要: | 質子交換膜燃料電池(proton exchange membrane fuel cells, PEMFCs) 在新興能源的發展中被廣泛地研究。然而因白金(Pt)的高價及稀少性，且在陰極之氧氣還原反應(oxygen reduction reaction, ORR)反應不佳，使得製備高效能之陰極觸媒成為一重要挑戰。本研究利用甲酸還原法製備出白金錫奈米線觸媒。隨後透過在組成以及形貌上的改變，使得觸媒藉由一維結構以及氧化錫(SnO2)的加成效應能夠具有絕佳之ORR性能。所製備觸媒之形貌、結構、化學組成、表面組成、Pt的未填滿d軌域(number of unoccupied d-states, HTs)及電化學活性分別使用高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM)、X光繞射儀(X-ray diffraction, XRD)、感應耦合電漿放射光譜分析儀(inductively coupled plasma-optical emission spectrometer, ICP-OES)、光電子能譜儀(X-ray photoelectron spectroscopy, XPS)、X光吸收光譜(X-ray absorption spectroscopy, XAS) 以及旋轉盤電極(rotating disk electrode, RDE)等儀器鑑定。
本研究結果分為兩部分，第一部分討論的是白金錫奈米線觸媒具有相同的金屬負載量(50 wt. %)及不同的組成(Pt/Sn)，分別為80/20、65/35和50/50，且分別命名為PtSn-A、PtSn-B和PtSn-C。隨著SnO2的增加，PtSn-C中Pt的氧化會被抑制，其有最低的HTs，此也成為其高質量活性(mass activity, MA)的原因之一。經由加速穩定度測試(accelerated durability test, ADT)，PtSn-A則有最好的ORR穩定度，主要歸因於高濃度的一維結構，以及高親氧性的SnO2會排斥吸附於Pt上的含氧物種(oxygen-containing species, OCS)，使其較易從Pt上脫附，進而增加Pt的活性位置。
第二部分分別製備出不同長寬比(aspect ratio)且金屬負載量同為50 wt. % 之Pt80Sn20奈米線觸媒，並分別命名為PtSn1、PtSn5、PtSn7和PtSn9。隨著長寬比的增加，不只降低了觸媒的HTs，使含氧物種對於Pt的吸附能被減弱，也改變了觸媒表面的化學狀態。在眾樣品中，PtSn9有著最佳的MA及穩定度，當10000圈ADT之後，活性只衰退了原本的24 %，在長寬比上的變化也只有19 %，其最佳的ORR性能表現是源於較大的長寬比以及SnO2的加成效應。
;In the development of emerging energy, proton exchange membrane fuel cells (PEMFCs) have been widely researched. Nevertheless, because of the high price and scarcity of Pt and the sluggish kinetics of oxygen reduction reaction (ORR) at the cathode, the preparation of highly effective cathode catalysts becomes one of the main challenges. In this study, carbon supported PtSn nanowires (NWs) have been prepared by formic acid method. Through the alternation of compositions or morphologies, the ORR performance of the catalysts can be promoted synergistically by one-dimensional (1-D) structures and SnO2 modification. The morphologies, structures, chemical compositions, surface compositions, number of unoccupied d-states (HTs), and electrochemical analyses of the carbon-supported PtSn NWs are characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometer (ICP-OES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and rotating disc electrode (RDE), respectively.
This study is divided into two parts. In the first part, carbon-supported PtSn NWs with metal loading of 50 wt. % and different Pt/Sn ratios of 80/20, 65/35, and 50/50, have been prepared and named as PtSn-A, PtSn-B, PtSn-C, respectively. The oxidation of Pt for PtSn-C can be significantly suppressed as the Sn addition increases and it has the lowest HTs, resulting in the highest mass activity (MA). After the accelerated durability test (ADT), PtSn-A has the best stability, related to the high concentration of 1-D structures and the SnO2 phase, which can lessen the binding energy between oxygen-containing species (OCS) and Pt, lead to the repulsion effect between Pt–OH and Sn oxides, and subsequently make the Pt active sites released.
In the second part, carbon-supported Pt80Sn20 NWs with metal loading of 50 wt. % and various aspect ratios of 1.00, 5.35, 7.64, and 9.65 have been investigated and named as PtSn1, PtSn5, PtSn7, and PtSn9, respectively. It is demonstrated that as the aspect ratio increases, not only the HTs is reduced, but also the chemical states are turned. When compared with other samples, PtSn9 shows the best performance with a decay of 24 and 19 % in activity and aspect ratio during 10000 cycles of ADT, respectively, ascribed to the synergistic effect of large aspect ratio and SnO2 decoration. |
