樹枝狀鉑金雙金屬觸媒之研究

Abstract

本研究利用三種不同的方法在三維樹狀金電極上修飾少量的鉑，並探討應用於直接甲醇燃料電池的催化活性和表現。製備出的鉑金雙金屬觸媒會使用X射線光電子能譜(XPS)、穿透式電子顯微鏡(TEM)和循環伏安(CV)進行結構鑑定。 首先，我們以浸泡電鍍法（IE）在樹狀金電極上修飾少量的鉑，研究發現，鉑會以類似二維的方式成長在金基材表面，而修飾了少量鉑的金電極在鹼性溶液下，對甲醇的電催化活性是較未修飾鉑的金電極來的好。再者，我們使用低濃度的氯鉑酸水溶液，添加葡萄糖作為還原劑，以無電電鍍的方式沉積鉑於金電極上。相較於未修飾鉑的金電極及大量沉積鉑的金電極，此方法製備出來的鉑金電極，對於甲醇電催化效果皆有較佳之表現。 最後，我們以銅的低電位沉積，在金電極上修飾單層銅，再以氧化還原法將單層銅置換成單層鉑，成功的在金電極上修飾一至五層之鉑層。經過電化學分析結果，修飾單層的鉑金電極有最佳的催化活性及良好的抗毒化效果。 我們的結果顯示鉑金之間的關係和對甲醇的電催化活性表現，並提供數個方法來控制鉑奈米粒子的分佈。我們製備出超低含量鉑的鉑金雙金屬觸媒，表現出優良的電催化活性及CO抗毒化效果。In this work, an ultralow or ultrathin Pt films fabricated on the nanostructure of the gold dendrites (GD) were investigated to act as novel electrodes for methanol electro-oxidation. The GD-Pt-type materials were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and cyclovoltammetry (CV). A small amount of Pt was deposited in a quasi-two-dimensional form onto the GD substrate through a simple immersion-electrodeposition (IE) method, forming nanostructured bimetallic GD-Pt catalysts. The ultrathin Pt film was also fabricated on GD through a simple way, in which only glucose and low concentration of H2PtCl4 were used. Such Pt-Au nanostructures have much higher structural stability than the bare GD. Compared with bare GD and high Pt loaded GD, the performances of methanol electro-oxidation on the low-Pt-content bimetallic film were greatly improved. The ultrathin Pt films from one to several atomic layers were also successfully decorated onto GD by utilizing under potential deposition (UPD) of Cu onto the Au or Pt surfaces, followed by in situ redox replacement reaction (RRR) of UPD Cu by Pt. The thickness of Pt layers could be controlled precisely by repeating the Cu-UPD-RRR cycles. The electrocatalytic activity of GD-Pt exhibited an interesting dependence of surface structure in electrooxidation reactions of methanol. Our results showed the relationship between nanosturcture and electrocatalytic performance towards methanol oxidation and provided a method to control the distribution of Pt nanoparticles. The resulting Au/Pt bimetallic nanocatalysts exhibited the excellent electrocatalytic activity and enhanced poison tolerance. Thus, the success in the fabrication of GD-Pt-type materials provides a new method to prepare electrocatalysts with ultralow Pt loading and high utilization, which are of great significance in energy-related applications, such as the direct methanol fuel cells (DMFCs).