Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/91904
標題: 白金/XC72-非晶質磷酸鐵複材觸媒之製備與分析應用於燃料電池之研究
Preparation and characterization of Pt/XC72-amorphous iron phosphate composites as catalysts for fuel cells
作者: 王彥閔
Yen-Min Wang
關鍵字: 非晶質磷酸鐵
電子導電度
乙炔碳黑
直接甲醇燃料電池
膜電極組件
Amorphous iron phosphate
Electronic conductivity
Carbon black
Direct methanol fuel cell (DMFC)
Membrane electrode assembly (MEA)
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摘要: Direct methanol fuel cell (DMFC) is a device converting fuel into electric energy, generally applied to the portable electronic products. Pt-Ru is the major binary alloy catalyst presently used in the methanol oxidation to delete CO poisoning effects which reducing Pt activity. According to our previous results, Pt nano-particles were successfully reduced on ferrous phosphate (Fe3(PO4)2·8H2O, Vivianite), assigned to Pt/Vi and then uniformly mixed with the carbon black to obtain Pt/Vi/C bi-function catalyst, revealing the excellent electrochemical activity in methanol oxidation without carbon monoxide (CO) poisoning effects. However, ferrous phosphate salts that formed by Iron(II) ammonium sulfate and Diammonium hydrogen phosphate has shown poor electronic conductivity and ion conductivity. Therefore, in this study, we attempted to prepare the precipitation of ferrous phosphate directly deposited on the acetylene carbon black, the surface of which was modified to generate more OH- radicals for strengthening the bonding between vivianite(Vi) and XC72 to improve its conductivity. Three kinds of weight ratio of XC72 to Vi 1: 3, 1: 5 and 1: 10 were prepared. There were unobvious peak in XRD, referring to amorphous iron phosphate. Then H2PtCl6 were added in for platinum reduced on XCVi composite to form Pt/XCVi 1:3, Pt/XCVi 1:5 and Pt/XCVi 1:10 catalysts and finally annealed at 100℃ for 3 hrs. The features of these catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy – live fast Fourier transform (HRTEM-Live FFT), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), Fourier transform infrared (FTIR) spectroscopy, membrane assembly electrode (MEA) and cyclic voltammetry (CV). The electric resistance has been reduced from 268.0 of Pt/Vi to 162.5, 119.0 and 137.4 Ω of Pt/XCVi 1:3, 1:5 and 1:10, respectively. The bigger amorphous iron phosphate particles of Pt/XCVi 1:3 leads to the greater resistance among Pt/XCVi catalysts. The particle size of platinum was about 3.7 nm by XRD analyses and from 3.9 to 4.5 nm observed by TEM. The electrochemical surface area (ECSA) ranged from 441.25 to 649.18 (cm2/mg) while ranged from 623.19 to 1016.89 (cm2/mg) after two times XC72 added in and assigned to Pt/XCVi/C, analysed by cyclic voltammetry of hydrogen absorption / desorption reaction. In methanol oxidation reaction (MOR), Pt/XCVi1:5 illustrates the highest mass activity 132.55 (A/gPt) and the lowest on-set potential 0.25(V). No forward or reverse current peaks were observed, indicating no CO poison effects for all Pt/XCVi catalysts. For 1000 cyclic life tests, the retained capacity of Pt/XCVi 1:3 reached up to 96.12% compared with 81.45% of Pt/XCVi 1:3/C. In membrane electrode assembly (MEA) tests, three prepared Pt/XCVi catalysts revealed the greater power density and open circuit voltage than Pt/C (Alfa) and Pt/Vi, since Fe3+ in these catalysts activated the water at low potential to yield Fe-OHads and detoxify the nearby nano-sized Pt poisoned by CO to create the opportunity for forming CO2 and H+, beside the enhanced conductivity. This argument also reasons results of MOR tests out. Obviously, both electric resistance and CO poisoning effect play the major role on the performance of catalysts in DMFC, and the Pt/XCVi improved from Pt/Vi has revealed the acceptable performance due to its enhanced conductivity and detoxifying function.
直接甲醇燃料電池是一種將甲醇燃料轉換成電能的裝置,主要應用於攜帶型電子產品上,而Pt-Ru二元合金觸媒係目前用於去除甲醇氧化過程中所產生的一氧化碳(CO)毒化Pt現象。根據本實驗室之前的成果,奈米白金粒子成功地還原於磷酸亞鐵(Fe3(PO4)2·8H2O, Vivianite)記為Pt/Vi,再與碳黑均勻混合得到Pt/Vi/C,其在甲醇氧化反應中表現出優秀的電化學質量活性,且無一氧化碳(CO)中毒現象產生,成為雙功效觸媒。然而,由硫酸亞鐵銨與磷酸氫二銨所形成的磷酸亞鐵鹽類係一種電子導電度與離子導電度均差的陶瓷。因此在本研究企圖將磷酸亞鐵直接沉積析出於乙炔碳黑上以增加其導電度,首先將乙炔碳黑置於富氧環境中使表面富含官能基OH-,強化磷酸亞鐵與乙炔碳黑之間的鍵結,亦藉此方法提升磷酸亞鐵(Vivianite)導電度。 本研究中企圖獲得改質乙炔碳黑與磷酸亞鐵三種不同重量比分別為1:3、1:5、1:10的複合載體,因XRD無明顯峰值,故稱其為XC72-非晶質磷酸鐵複材,再分別加入六氯鉑酸以進行白金還原,形成Pt/XCVi 1:3、Pt/XCVi 1:5、Pt/XCVi 1:10三種觸媒,再經100℃- 3小時熱處理,最後透過X-ray繞射(XRD)、場發射掃描式電子顯微鏡(FE-SEM)、高解析度穿透式電子顯微鏡即時富利葉轉換(HR-TEM Live-FFT)、X-ray光電子能譜(XPS)、感應耦合電漿質譜儀(ICP-MS)、富利葉轉換紅外線光譜儀(FTIR)、膜電極組件(MEA)與循環伏安法(CV)加以材料分析。 改善後的Pt/XCVi 1:3、1:5、1:10的電阻,已由Pt/Vi的268.0分別降為162.5、119.0、137.4歐姆,這些改善觸媒中,Pt/XCVi 1:3仍有較大的非晶質磷酸鐵顆粒,因而導致較高的電阻。XRD公式計算得到分散奈米白金顆粒大小為3.7 nm,而TEM觀察計算得3.9~4.5 nm,此外,循環伏安法(Cyclic Voltammetry) 測試氫氣吸/脫附反應,電化學活性表面積介於441.25-649.18(cm2/mg),在額外添加了兩倍量的碳黑於觸媒,記為Pt/XCVi/C,電化學活表面積提高至623.19-1016.89(cm2/mg);在甲醇氧化反應中,Pt/XCVi1:5有最高的質量活性132.55(A/gPt)和最低的起始電位0.25(V)且沒有明顯反應峰出現顯示無毒化反應;在1000圈循環壽命測試下,以Pt/XCVi1:3之殘留電化學活性表面積達96.12%最高,相較於Pt/XCVi 1:3/C僅81.45%。 在MEA測試下,製備的三種觸媒與Pt/C、Pt/Vi比較,Pt/XCVi表現出較高的功率密度且有較高之開路電位,除了因具有較低之阻抗外,這些觸媒裡的Fe3+在低電位活化水而產生Fe-OHads,因而創造機會使在Pt上的CO反應成CO2和H+,這些論點也適用於解釋MOR的種種現象,顯然,在DMEC裡的觸媒表現,電阻與CO中毒現象扮演了主要的角色,由Pt/Vi改善調製的Pt/XCVi確實提高了導電率和解毒功效,而已呈現可接受之性能。
URI: http://hdl.handle.net/11455/91904
其他識別: U0005-1507201516382900
文章公開時間: 10000-01-01
Appears in Collections:材料科學與工程學系

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