| 摘要: | 鉑基合金催化劑被廣泛運用於低溫燃料電池的陰極端。然而因鉑 (Pt)價格高昂及稀少性，且在陰極之氧化還原反應(oxygen reduction reaction, ORR)反應不佳，使得製備高效能的陰極觸媒成為燃料電池發 展的主要挑戰之一。本研究製備了具有不同形貌的碳載鉑鎳(PtNi)及 鉑鈷(PtCo)觸媒。藉由形貌的變化，改變觸媒的平面、提升表面積、 以及增加活性位點來提昇 ORR 的性能。所製備觸媒的形貌、結構、 化學組成、表面組成、以及電化學分析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)、以及旋轉盤電極 (rotating disk electrode, RDE)等儀器鑑定。
本研究分為兩個部分。在第一部分討論的是金屬負載量 20 wt. % 的 PtNi 奈米晶體(NCs)，藉由添加不同重量(0, 0.01, 0.02, 0.025 克)的 六羰化鎢[(W(CO)6)]，以控制觸媒的形貌，分別命名為 PtNi(NCs)-0、 PtNi(NCs)-1、PtNi(NCs)-2、PtNi(NCs)-3。另外再製備金屬負載量 30 wt. % 的 PtNi 奈米顆粒，命名為 PtNi(NPs) 與其他觸媒做比較。隨著 六羰化鎢[(W(CO)6)]的增加，促進奈米立方體(100 面)的增加，使經過 5000 圈循環的加速耐久度測試(ADT)後，活性只衰退原本的 17%，提 升了穩定性。這個結果意味著表面上的(100)面在溶液中被優先溶解， 保護了催化劑，此外，奈米立方體比奈米顆粒更不易溶於酸性溶液。
第二部分製備了金屬負載量 20 wt. %的 PtCo(NCs)，藉由添加不同重量(0, 0.01, 0.02, 0.025 克)的 W(CO)6，以控制觸媒的形貌，分別 命名為 PtNi(NCs)-0、PtNi(NCs)-1、PtNi(NCs)-2、PtNi(NCs)-3。另外 將金屬負載量為 30 wt. % 的商用 PtCo/C 觸媒，命名為 PtCo(NPs)與 其他觸媒做比較。支晶結構具有較大的表面積、大量活性位點以及樹 枝狀的支臂保護觸媒。結果顯示 PtCo(NCs)-1 具有良好的支晶狀結構， 且有最佳的性能表現，在 ADT 的 5000 圈循環後只衰退了原本的 2%。;Pt-based alloys catalysts have been widely used for the cathode of low temperature fuel cells; however, the main challenges of Pt-based catalysts are high price, scarcity, and sluggish kinetics of oxygen reduction reaction (ORR) at the cathode. Therefore, the preparation of highly effective cathode catalysts becomes one of the main challenges for the development of fuel cells. In this study, the carbon-support PtNi and PtCo catalysts with different morphologies have been prepared. Through the morphologies change, the ORR performance of the catalysts can be promoted owing to the modification of facets, and promotion of surface areas and active sites. The morphologies, structures, chemical compositions, surface compositions, and electrochemical analyses of the carbon-supported PtNi and PtCo 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), and rotating disc electrode (RDE), respectively.
This study is divided into two parts. In the first part, carbon-supported PtNi nanocrystals (NCs) with metal loading of 20 wt. % and different W(CO)6 additions of 0, 0.01, 0.02, 0.025 g, have been prepared and named as PtNi(NCs)-0, PtNi(NCs)-1, PtNi(NCs)-2, and PtNi(NCs)-3, respectively. Carbon-supported PtNi nanoparticles (NPs) with metal loading of 30 wt. % has also been prepared for comparison. As the W(CO)6 amount increases, the formation of nanocubes (100 facet) is also enhanced, promoting the stability during the accelerated durability test (ADT) of 5000 cycles (17 %). The results imply that the (100) facet on the surface can be preferentially dissolved, protecting the catalysts. Moreover, nanocubes are less vulnerable to dissolve in acidic media than nanoparticles.
In the second part, carbon-supported PtCo(NCs) with metal loading of 20 wt. % and with different W(CO)6 additions of 0, 0.01, 0.02, 0.025 g, have been prepared and named as PtCo(NCs)-0, PtCo(NCs)-1, PtCo(NCs)- 2, and PtCo(NCs)-3, respectively. Commercial PtCo/C catalysts with metal loading 30 wt. % named as PtCo(NPs) are used for comparison. Due to the large surface area, large numbers of active sites, and the protection of the dendrites arms, the PtCo(NCs)-1 with dendrites structure shows the best performance with the decay of 2 % during 5000 cycles of ADT. |
