官能基化石墨烯承載核殼Pd9Ru@Pt奈米觸媒之甲醇催化研究

Abstract

我們開發出一種簡單又有效率的方法來官能基化石墨烯。將石墨烯懸浮液和 Nafion ionomers一起滴在碳布上製成電極，並在富有氧氣的環境下透過循環伏安法還原生成羥自由基，破壞Nafion ionomers結構進而在石墨烯材料表面上生成大量的官能基。利用與水滴接觸角的變化關係來觀察不同Nafion ionomers量下被破壞的程度，發現官能基化的程度有極限值的存在，而後分析X射線光電子能譜，計算出不同Nafion ionomers含量所產生的官能基比值，得到最佳化參數的結果。另外，利用拉曼光譜來比較官能基化前後石墨烯的結構變化。接著利用濕式迴流化學法，製備鈀釕合金奈米顆粒(Pd9Ru)觸媒於改質後的石墨烯載體上，由X光繞射儀來確認鈀釕為合金形式存在，且發現在改質後的石墨烯載體上，觸媒奈米顆粒較小，大約落在 3~4 奈米上下。此外，從穿隧電子顯微鏡影像看來，觸媒顆粒分散也較均勻。最後，再利用銅的低電位沉積製作單層白金於合金上，形成Pd9Ru@Pt的奈米顆粒觸媒，並測試甲醇氧化的催化反應，結果顯示有官能基化的合金觸媒具有較好的催化活性，且擁有較佳的白金抗毒化效果，在電化學活性面積的測試中，官能基化的觸媒擁有比無官能基化的觸媒大1.5倍的活性表面積，而經過甲醇氧化反應500圈後，電化學活性表面積各自下降了14.9% 和30.3% ，表示以耐久度來看，官能基化的觸媒有較優異的表現。

A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps (CV) are performed in 0.5 M H2SO4 aqueous solution on electrodes containing carbon cloth, graphene, and Nafion ionomers. With supply of ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomers that engenders oxygenated functional groups adsorbed onto the graphene surface. Raman analysis suggests a minor change for the graphene structure. We have explored various amounts of Nafion ionomers, to determine the optimized conditions for graphene functionalization. Contact angle wetting is used to evaluate the effect of Nafion ionomers decomposition. X-ray photoelectron spectroscopy is employed to identify relevant functional groups. Afterwards, nanoparticles of Pd9Ru are synthesized and impregnated on those functionalized graphene (FGN) via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples suggest successful formation of alloy without the presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm the average size of 3-4 nm. To prepare core-shell electrocatalysts, the Pd9Ru/FGN undergoes Cu under-potential-deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The functionalized catalyst (Pd9Ru@Pt/FGN) reveals enhanced performances for methanol electro-oxidation, which include better activity (high Ia) and stronger ability against poisoning by intermediate (Ia/Ic). The electrochemical active surface area (ECSA) for the Pd9Ru@Pt/FGN shows a value that is 1.5-fold larger over that of Pd9Ru@Pt/GN. In durability tests, Pd9Ru@Pt/FGN and Pd9Ru@Pt/GN demonstrate a loss of 14.9% and 30.3% in the ECSA, respectively after employing CV scans for 500 cycles.