| 摘要: | 開發鉑基一維奈米材料及使用石墨烯為擔載可有效增益觸媒之活性與穩定度，本研究利用甲酸還原法(formic acid method, FAM)，製備碳或石墨烯擔載鉑
基合金(PtM, M= Cu or Pd)奈米棒(nanorods, NRs)觸媒以應用於氧氣還原反應(oxygen reduction reaction, ORR)。所製備觸媒之合金相、表面組成、化學組成、形貌、電催化活性以及未填滿 d 軌域(number of unoccupied d-states, HTs)分析分別使用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-atomic emission spectrometer, ICP-AES), 高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM), 旋轉盤電極(rotating disk electrode,RDE)以及 X 光吸收光譜(X-ray absorption spectroscopy, XAS)等儀器鑑定。
本研究分為兩部分，第一部分成功地以 FAM 製備不同比例之碳擔載Pt及PtM NRs觸媒，自X光近源吸收光譜(X-ray absorption near edge spectroscopy, XANES)所計算出之 H Ts 值，可用來鑑定與 ORR 活性有強烈關聯之 Pt 未填滿d軌域數目，其中，自 Pt 奈米顆粒(nanoparticles, NPs)至 Pt NRs，由於一維形貌的形成，使得HTs值下降，又因與不同金屬形成合金使HTs值達更低。Pt3Pd NRs具有最低之HTs值(0.3056)，表示其具有較少之 Pt未填滿d軌域，有更多電子自Pd傳至Pt，使得其ORR活性優於商用材Pt/C。同時，由於一維結構及Pd之電子修飾作用之共同效應，使得 Pt3Pd 於加速穩定度測試(accelerated durability test, ADT)後之比活性(specific activity, SA 085-1000 )優於商用材 Pt/C。
第二部分同樣使用 FAM 製備石墨烯擔載 Pt 和 PtM NRs 觸媒。XRD 分析顯示，對於石墨烯擔載之 PtPd NRs (G-PtPd NRs)而言，由於使用石墨烯擔載及與Pd 之合金作用下，將有效促進(111)及(220)面之成長，使得 ORR 活性有效提升。XAS 分析中，HTs 值因使用石墨烯擔載及第二金屬合金效應而低至 0.295，同時G-PtPd 具有最佳之 ORR 活性，其於 ADT 後之 SA 及質量活性(mass activity, MA)分別為商用材 Pt/C 之 6.5 及 2.7 倍，證實其因 Pd 之電子修飾效應及石墨烯和金屬間作用力之共同作用下，有效增益該觸媒之 ORR 活性及穩定性。;Developing the one-dimensional (1-D) Pt-based nanomaterials with graphene support can provide a great opportunity to improve their catalytic activity and durability. In this study, carbon or graphene supported Pt and PtM (M= Cu or Pd) nanorods (NRs) are prepared by the formic acid method (FAM). The structures, surface compositions, chemical compositions, morphologies, electrochemical properties and the number of unfilled d-state (H Ts ) 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 two parts. In the first part,
carbon-supported Pt and PtM NRs with different ratios are successfully prepared by FAM. The H Ts value extracted from X-ray absorption near edge spectroscopy (XANES) can be used to measure the d-band vacancies of Pt, which is strongly related to their ORR performance. The HTs value of Pt nanoparticles (NPs) is decreased due to the formation of
NRs, and further decreased due to the alloying with different metals. For Pt3Pd NRs, the H Ts value is as low as 0.3056, suggesting that they have lower unfilled Pt d-states, and more d-band electrons transfer from Pd to Pt, leading to higher ORR activities than Pt/C. Moreover, the specific activity (SA 085-1000 ) value of the Pt3Pd after accelerated durability test(ADT) is higher than that of the Pt/C. These results may be owing to the electronic modification e ff ect from Pd and 1-D structures synergistically.
In the second part, the graphene-supported Pt and PtPd NRs catalysts are prepared by FAM. XRD analysis has shown that through alloying with Pd and using graphene support for the Pt NRs (G-PtPd), the growth of (111) and (220) planes is promoted. H Ts of Pt NRs is further
decreased due to the use of graphene support and alloying. Among all catalysts, G-PtPd shows the lowest H Ts value, which is 0.295. Moreover, G-PtPd has the highest activity and durability among all catalysts in which their specific and mass activities after ADT is about 6.5 and 2.7 times higher than those of carbon-supported Pt NPs, confirming that the electronic modification effect from Pd
and graphene-metal interaction can be promoted synergistically for Pt NRs. |
