直接甲醇燃料電池陽極用高熵合金觸媒研究

Abstract

本實驗採用葉君蔚教授所提出的高熵合金概念，選用過去被認為同樣具有抗CO毒化特性的Fe、Co、Ni、Cu、Ag與Pt形成六元奈米合金顆粒作為直接甲醇燃料電池(DMFC)陽極的催化劑，並利用濺鍍法製作催化層，以達到降低催化合金用量之目的。

使用X光繞射儀進行六元薄膜合金之結構與相鑑定，並以EDX分析組成成份，使用SEM觀察奈米顆粒微結構，最後進行電化學的CV量測以得知催化合金之甲醇氧化活性，並將CV進行前後的酸性電解液取出使用ICP-MS進行分析，確認其抗蝕性，為得知高熵合金之效應所在，本實驗並且將六元合金與二元合金之各項性質進行比較，並使用XPS分析其電子鍵能之變化量。

研究結果顯示，六元合金(Pt52Fe10Co9Ni9Cu12Ag8)僅具有fcc之單一相，並且形成數奈米的顆粒沉積在碳黑表面，催化活性約介於300-600 mA/cm2•mg左右，在沉積時間增長後，催化活性則有降低之情形，而分析進行完氧化測試的酸性電解液之結果發現其同樣具有良好的抗蝕性，沒有金屬溶出之現象。

在改變六元合金中的白金含量以進行甲醇氧化活性之研究中，發現白金含量減少會造成結晶度降低，然而仍為單一之fcc相，且其具有相似的表面形貌，由電化學分析結果可以得知52 atomic%之白金具有最佳催化活性。

對於將六元合金與二元合金進行比較之結果，發現PtCu具最佳之催化活性，而PtAg則因為容易形成較大顆粒，因此催化活性最低，六元合金則具有介於各合金間的各種性質，顯示多元成分造成的混合效應之影響。

In this study, fabrication and electrochemical characterization of high-entropy electrocatalyst on noncatalyzed gas diffusion electrode by RF sputter deposition was reported. XRD analysis of the as-deposited film exhibited a crystalline FCC phase while EDS confirmed its composition as Pt52Fe10Co9Ni9Cu12Ag8. SEM images revealed nanoparticles nodules growing on the carbon particles. Cyclic voltammetry (CV) was used to analyze its performance as anode electrocatalyst for direct methanol fuel cell. The area under CV curve was proportional to the amount of electrocatalyst deposited. However, in specific activity sample with 5 nm electrocatalyst demonstrated the highest values, 400~600 mA/cm2•mg. Our work presents invaluable information on electrochemical performance of high-entropy electrocatalyst.

High-entropy nanoparticles of PtxFe(100-x)/5Co(100-x)/5Ni(100-x)/5Cu(100-x)/5Ag(100-x)/5 (x = 22, 29, 52, 56) were then prepared by sputter deposition on pretreated carbon cloth. XRD patterns indicated crystalline FCC phases and SEM images revealed nanoparticulate nodules grown on surface of carbon particles with their average sizes increasing with deposition time. Cyclic voltammetry demonstrated enhancements of catalytic performance with increasing Pt amount. However, in specific activity Pt52Fe11Co10Ni11Cu10Ag8 exhibited the highest capability, reaching values as high as 504 and 462 mA/cm2•mg. This work provides invaluable information in unique electrocatalyst design using high-entropy concept.

Comparison of the properties of six-component alloys and binary alloys Pt-M (M= Fe, Co, Ni, Cu, Ag) were studied in last part. All the phases of binary alloys were fcc as identified by XRD. In addition, the morphologies of PtFe, PtCo, and PtCu were similar in their nodules structure to that of Pt52Fe10Co9Ni9Cu12Ag8. In contrast, PtAg formed a large particle on carbon black. The PtCu showed the highest catalytic activity, and PtAg was the poorest because of its large of particles size and weak strength of M-O bonding. The six-component alloy exhibited characteristics between each binary alloys, imply the mixing effects of the multi-components.