藉由熱處理促進碳支撐之鈀及鈀基奈米顆粒之甲酸氧化反應;Promotion of Formic Acid Oxidation Performance of Carbon-Supported Pd and Pd-based Nanoparticles by Heat Treatment

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题名:	藉由熱處理促進碳支撐之鈀及鈀基奈米顆粒之甲酸氧化反應;Promotion of Formic Acid Oxidation Performance of Carbon-Supported Pd and Pd-based Nanoparticles by Heat Treatment
作者:	周百鴻;Chou, Pai-Hung
贡献者:	材料科學與工程研究所
关键词:	鉑鈀;鉑鈀釕;X光電子能譜;甲酸氧化反應;計時電流法;表面組成;熱處理;PdPt;PdRuPt catalysts;X-ray photoelectron spectroscopy (XPS);formic acid oxidation reaction (FAO);chronoamperometric (CA);surface composition;heat treatment
日期:	2017-07-19
上传时间:	2017-10-27 13:17:09 (UTC+8)
出版者:	國立中央大學
摘要:	在質子交換膜燃料電池(polymer electrolyte membrane fuel cells, PEMFCs)中，甲酸由於具有高能量密度及低燃料滲透質子交換膜的特性(crossover)，而被使用為陽極端。其中，低鉑含量的鉑鈀二元合金觸媒因其對甲酸氧化反應(formic acid oxidation reaction, FAO)具有優異的催化活性，而備受矚目。在本研究中，製備碳支撐之鈀，二元鉑鈀和三元鉑鈀釕觸媒，並將鉑鈀及鉑鈀釕觸媒做熱處理後，探討表面組成變遷及觸媒電化學性能之間的關係。所製備觸媒之晶體結構、表面組成、化學組成、形貌和電化學特性分別使用X光繞射儀(X-ray diffraction, XRD)、X光電子能譜(X-ray photoelectron spectroscopy, XPS)、感應耦合電漿放射光譜分析儀(inductively coupled plasma-optical emission spectrometer, ICP-OES)、高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM)和旋轉盤電極(rotating disc electrode, RDE)等儀器做分析。本研究分成兩部分。在第一部分中，碳支撐之鈀，鉑鈀和鉑鈀釕觸媒被製備於相同的還原條件中。X光電子能譜及一氧化碳剝除實驗(CO stripping)的結果顯示了低含量的鉑存在於鉑鈀及鉑鈀釕觸媒的表面，且相較於純鈀觸媒，添加鉑到鈀上展示了較優越的FAO催化活性，而釕的添加更進一步強化了觸媒對CO毒化的抗性。此外，純鈀觸媒之FAO電流前後掃比值(If/Ib ratio)要高於其他兩者，可歸因於鉑的添加，因其在前掃時的低電位範圍極易被CO毒化。第二部分，鉑鈀及鉑鈀釕觸媒各自分別於CO及O2氣氛進行熱處理。由X光繞射儀、X光電子能譜及電化學的分析，可描述了觸媒在熱處理過程中的表面組成變化，及其與催化性能之間的關係。表面鉑的含量與FAO性能表現高度相關，鉑鈀及鉑鈀釕觸媒經過O2處理後，其活性雖然上升，但經過計時電流法(chronoamperometric, CA)測試後的電流值皆展現了極低的數值，說明氧氣熱處理有助於提升活性，但卻無益於穩定性。相反的，鉑鈀及鉑鈀釕經過CO熱處理後產生表面物種還原及鉑偏析，CA之後之電流明顯提升，特別是在三元合金系統內。 ;In order to promote energy density and overcome the fuel crossover on the membrane, formic acid is considered to be an attractive fuel at the anode of polymer electrolyte membrane fuel cells (PEMFCs). Besides, the low Pt content PtPd bimetallic catalysts have been investigated due to their high catalytic activity of formic acid oxidation reaction (FAO). In this study, the carbon-supported Pd, PdPt and PdRuPt have been prepared and PdPt, PdRuPt have been heat-treated. The relationship between their surface compositions and electrochemical properties is elucidated. The lattice structures, surface compositions, chemical compositions, morphologies and electrochemical properties of prepared catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometer (ICP-OES), high resolution transmission electron microscopy (HRTEM), and rotating disc electrode (RDE), respectively. This study is divided into two parts. In the first part, carbon-supported Pd, PdPt and PdRuPt nanoparticles have been prepared at the same reduction condition. The XPS and CO stripping results reveal the small amount of Pt coverage on the surface of PdPt and PdRuPt. The addition of Pt into Pd catalysts have demonstrated great promotion of FAO performance compared to Pd/C, and Ru addition further enhances the CO tolerance of catalysts. Besides, the ratio between forward and backward peak current (If/Ib) of Pd is much higher than those of PdPt and PdRuPt, due to CO poisoning at low potential during forward scan of surface Pt. In the second part, carbon-supported PdPt and PdRuPt catalysts have been heat-treated under CO and O2 atmosphere. Based on the analysis of the XRD, XPS and electrochemical measurement, the change of surface composition during heat treatment, and the correlation between surface composition and catalytic properties of PdPt and PdRuPt catalysts is methodically elucidated. The amounts of surface Pt is related to FAO performance. O2 heat treatment can promote the FAO performance but does not have positive effect on their stability based on the chronoamperometric (CA) results. On the other side, owing to the Pt surface segregation and reduction by CO heat treatment, the mass activity (MA) after CA tests is enhanced, especially for the ternary one.
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