鉑系觸媒與碳載體電極之電化學研究應用於直接甲醇燃料電池

Abstract

本論文研究可分為三大部分，第一部份主要是研究如何有效利用碳載體以提升觸媒的效能；第二部分主要是利用電化學去合金製程來對觸媒進行表面改質，以求提升觸媒效能；而第三部份則是利用各種檢測方式，如電化學檢測、X光吸收光譜（XAS）…等技術，討論去合金製程是如何改變觸媒進而提升觸媒效能。 在第一部分中，主要是比較不同碳載體的性質，包括碳載體XC-72R、CNCs（Carbon Nanocapsules）、BP2000以及CNTs（Carbon Nanotubes），再以脈衝式電鍍法將PtRu雙金屬奈米合金觸媒沈積在碳材上，並進一步比較已合成觸媒在各個碳載體之甲醇催化效能。實驗結果發現無電鍍鎳製程可將奈米碳管均勻分佈在碳布的各碳纖維之間，不同於傳統製程，其碳載體只能分佈在碳布表層，此有助使得觸媒的分佈更為廣泛，大大提升直接甲醇燃料電池的效能。此外，利用此一製程可直接將奈米碳管優越的物理性質或化學特性，能透過碳布而有更具體的3D化表現，而以上種種優勢也確實在本實驗中獲得證實。 在第二部分中，主要是利用濺鍍法將鐵、鈷、鎳、銅、銀等元素與Pt濺鍍於碳材上，並進一步的利用去合金製程來增進Pt多元合金觸媒的活性。實驗結果發現去合金製程能藉由提升觸媒的電化學表面積來增進觸媒氧化甲醇的效能。 在第三部分中，主要是將Cu3Pt觸媒合金進行更進一步的去合金製程研究，研究中發現，在高電位1.6 V的去合金製程下，Cu3Pt觸媒合金表面可產生新的相，推測可能為CuPt3，故此Cu3Pt合金觸媒經高電位適當的去合金處理後為一個core-shell結構；另外在XAS的研究中，可發現Cu3Pt合金觸媒經去合金處理後，仍舊為金屬態，而非氧化態，且Pt-Pt的配位數明顯上升，而Pt-Cu的配位數則明顯的下降，但整體而言中心原子Pt的配位數仍舊是屬於下降的情況，而Cu則是些微的增加。在鍵長部分，不論是Pt-Pt、Pt-Cu或是Cu-Cu，其鍵長都是增加的情況，尤其是以Pt-Pt的增加最為明顯，而以上的這一切都與Cu從Cu3Pt合金觸媒中解離有關。

This research concerns the synthesis and characterizations of nanoparticulate alloy electrocatalysts for direct methanol fuel cells. A variety of synthetic techniques were employed to obtain electrocatalysts with desirable surface composition so an enhanced catalytic activity was achieved. In the first part, pulse electrodeposition was adopted to prepare bimetallic PtRu nanoparticles on carbon supports including carbon blacks (XC-72R, BP2000), carbon nanocapsules (CNCs), and carbon nanotubes (CNTs). Comprehensive studies in both material characterizations and electrochemical analysis were carried out to validate their electro-oxidation abilities for methanol. Among these samples, the CNTs derived from the electroless route enabled a uniform distribution of PtRu that rendered a three-dimensional support for improved PtRu usage and enhanced catalytic performance. In the second part, sputter deposition was selected to form multi-component alloy (FeCoNiCuAgPt) on the carbon support, followed by a dealloying process to selectively dissolve corrosive-prone constituents leaving a Pt-dominant alloyed catalyst. We found that the dealloying process was effective in increasing the electrochemically active surface area that led to a larger methanol oxidation current. In the third part, we chose the Cu3Pt for detailed investigation on the dealloying process in which at an anodic potential of 1.6 V, the Cu3Pt was transformed to CuPt3. In this way, by appropriate dealloying treatments, the as-prepared Cu3Pt was able to form a core-shell structure in Cu3Pt@CuPt3. From X-ray absorption spectroscopy, the Cu3Pt maintained its metallic state with a notable increase in the Pt-Pt coordination number in conjunction with a reduced Pt-Cu coordination number. In addition, the bond lengths for Pt-Pt, Pt-Cu, and Cu-Cu were increased after dealloying process.