鈀鉑與鈀鉑合金觸媒對於甲乙醇氧化反應表現與機構之探討

Abstract

本研究主要探討在碳黑(XC-72)上Pt、Pd、PtPd不同比例分別為3:1, 1:1, 1:3(以下寫作Pt3Pd1,Pt1Pd1,Pt3Pd1)觸媒對於直接甲醇(乙醇)燃料電池中的甲醇(乙醇)氧化反應中的陽極反應，在實驗中所用到的合金觸媒皆為含浸法合成，並且使用XRD、SEM、EDS去鑑定物理性質，接著將觸媒放在1M KOH中曝氮氣再使用電化學CV測量ECSA，再分別利用CV及CA測量1M甲醇和乙醇的電催化活性和穩定度。結果顯示合金的活性和穩定度都優於純Pt與Pd其中Pt3Pd1有著最高的MA(1279 mA/ugPt)及SA65(mA/cm2)而Pt1Pd1有著最好的穩定性(經過90分鐘CA測試後仍有原本51%的電流)。進一步利用ex-FTIR來偵測溶液中的2,4,6電子產物(HCHO, HCOOH, CO32-)隨著CV圈數的變化來推測觸媒在MOR的機制，圖譜顯示所有的合金都有些微的差異，其差異趨勢與CA的結果相同。

The present study mechanistic investigates methanol/ethanol oxidation reactions (MOR/EOR), the anodic reactions for direct methanol/ethanol fuel cells (DMFC/DEFC), on Pt, Pd and their alloys with the ratios of Pt/Pd = 3:1, 1:1, 1:3 (denoted as Pt3Pd1, Pt1Pd1 and Pt1Pd3) on carbon black XC-72. All the metallic electrodes were fabricated by the impregnation method and characterized by X-ray diffraction (XRD), Secondary electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The fabricated electrodes were examining by cyclic voltammetry (CV) in 1 M KOH purged with N2 to determine their electrochemical surface area (ECSA). The MOR/EOR activity and stability of the electrodes were investigated by CV and chronoamperometry (CA), respectively, in 1 M methanol/ethanol in alkaline solution of 1 M KOH. The electrochemical tests showed that all the alloys has better both activity and stability than pure Pt and Pd; among them Pt3Pd1 has the best activity with mass activity (MA) =1279 (mA/ugPt)and surface activity (SA) = 65(mA/cm2), and Pt1Pd1 has the best stability (51% decay in 90 minutes CA). The MOR performance was further examined by ex-situ FT-IR to determine the variations of products of HCHO, HCOOH and CO32-(in two, four and-six electron reactions) with CV cycles. The spectroscopic results show that all the alloys have smaller variations, indicating the better stability and agreeing with the CA results.