博碩士論文 973409001 完整後設資料紀錄

DC 欄位 語言
DC.contributor材料科學與工程研究所zh_TW
DC.creator魏宇晨zh_TW
DC.creatorYu-Chen Weien_US
dc.date.accessioned2012-2-1T07:39:07Z
dc.date.available2012-2-1T07:39:07Z
dc.date.issued2012
dc.identifier.urihttp://ir.lib.ncu.edu.tw:88/thesis/view_etd.asp?URN=973409001
dc.contributor.department材料科學與工程研究所zh_TW
DC.description國立中央大學zh_TW
DC.descriptionNational Central Universityen_US
dc.description.abstract在本研究中,吾人致力於製備高活性之PdCo/C觸媒以利用於陰極氧氣還原反應(ORR),並且利用改質及製程控制,如調控pH值、添加氧化飾(CeO2)、氧化熱處理及添加元素金等方法,用以製備組成及結構可調控之電催化PdCo/C觸媒,並增益其ORR活性。本研究利用沉澱沉積法(DP)合成金屬重量為20 wt. %之PdCo/C觸媒,並以氫氣還原。所研製觸媒其結構、形貌、表面組成以及電催化特性之關係將利用粉末X光繞射儀(XRD)、X光吸收光譜(XAS)、穿透式電子顯微鏡(TEM)、光電子能譜儀(XPS)、程式溫度還原儀(TPR)和各種電化學量測方法進行深入探討。 本論文中研究主題分成四部分,第一部分為控制Pd/Co原子比為3/1的PdCo/C之製程參數,在反應過程中將pH值精準控制至9、11及13,而觸媒分別在390和620 K的氫氣中還原。研究指出,pH值將會顯著影響Pd及Co離子的沉澱速率進而影響觸媒的結構、表面組成及ORR活性。表面及電化學結果顯示高pH值(pH = 11和13)和高還原溫度(620 K)的製備條件會導致製備出的PdCo/C觸媒表面富含Co氧化物種而使ORR活性下降。反之,在pH=9及低還原溫度(390 K)的條件下所製備的觸媒可形成良好的Pd-Co合金、表面富含Pd組成及良好的ORR活性。 第二部分之研究重點為探討經CeO2改質之PdCo/C觸媒其ORR活性增益和表面組成的關係。利用DP法製備添加不同含量CeO2 (10 ~ 20 wt. %)的PdCo/C觸媒,並分別在390和620 K的氫氣中還原。研究結果發現雖然Co離子能在620 K下被完全還原,然而390 K的還原溫度可防止觸媒合金顆粒團聚和Co物種的表面偏析。此外,添加15 wt. %的CeO2 (Ce15)及低還原溫度(390 K)的製程條件可使觸媒表面富含Pd而形成Pd skin / alloy core結構。因此,Ce15有最佳的ORR活性,相較於未經改質的PdCo/C觸媒,其活性約提升了2.3倍,此乃因CeO2添加促進了合金顆粒的分散及表面物種的改變,因此對PdCo/C觸媒而言,CeO2為一結構及表面改質劑,能用來大幅提升觸媒ORR之活性。 第三部分為將第一部分所製備之PdCo/C觸媒進一步進行氧化後熱處理(320 ~ 620 K)。並以XPS的結果定義表面氧化程度(DSO)用以解釋觸媒ORR活性提升和表面氧化程度之關係。研究結果顯示提升觸媒活性的最佳氧化溫度為520 K,於此條件所改質之觸媒其表面由PdO所組成。此外,PdCo/C觸媒也以H2或CO熱處理,在此條件下觸媒合金顆粒之大小並無顯著改變。結果顯示:氧化過的PdCo/C觸媒較其它熱處理的觸媒有較佳的ORR活性,由此可推斷觸媒活性的提升主要是因為形成PdO物種及100 % DSO值,而非大尺寸效應所致。 第四部分合成不同原子比例之三元Pd75Co25-xAux/C(x = 5~25)觸媒,並系統性的探討金元素的添加對於觸媒的結構、表面組成及活性之影響。由XRD的結果可知添加金進入Pd-Co系統內將會導致形成非均質之合金結構。同時,XAS結果顯示金的添加會使得觸媒的異相原子混合度大幅度提升,特別是添加了15 at. %的金(Pd75Co10Au15/C, Au15)。由TPR結果可知當金添加量大於15 at. %時,觸媒的表面組成將由富含Pd之表面逐漸變成Pd,Au及合金相共存之表面組成。此外,經過金修飾過後的觸媒其合金顆粒大小約在4.9 ~ 5.4奈米之間,其中又以Au15的合金顆粒分佈尺寸最為集中。電化學特性分析發現,相較於Pd/C及Pd75Co25/C樣品,Au15的Pd質量活性分別提升了4和2.5倍。Au15能有良好的ORR活性主要是因為異相原子混合度的提升、較為集中的合金顆粒尺寸分佈、較大的電化學活性面積及多相共存之表面組成所致。 zh_TW
dc.description.abstractIn this study, the highly effective PdCo/C catalysts toward oxygen reduction reaction (ORR) are prepared. The preparation and modification approaches, including the control over pH values, addition of ceria (CeO2), oxidation heat treatment and incorporation of Au are used to synthesize Pd-Co/C with tunable structure and surface compositions and high catalytic activity. The PdCo/C catalysts with 20 wt. % metal loading are synthesized through the deposition-precipitation (DP) method and reduced under H2 atmosphere. The fundamental understanding of relationship between structures, morphologies, surface species and electrochemical properties is studied by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and various electrochemical measurements. The study is divided into four parts. In the 1st part, the PdCo/C alloy catalysts with a Pd/Co atomic ratio of 3/1 are prepared at various pH values (pH = 9, 11 and 13) and reduced at 390 or 620 K under H2 atmosphere. The pH value affects the deposition and reduction rates of Pd and Co ions significantly and thus the structures, surface species and ORR activity of the PdCo/C catalysts are also influenced. Due to the enhancement of Co surface segregation and the formation of Co oxides on the alloy surface, the deterioration of ORR activity for PdCo/C catalysts prepared under the high pH values (pH = 11 and 13) and high temperature (620 K) is observed. On the other hand, the alloy catalysts deposited at pH = 9 and reduced at 390 K have well-formed Pd-Co alloy structure, Pd-rich surface and excellent ORR activity. In the 2nd part, the ORR activity enhancement and surface species alteration of PdCo/C alloy catalysts with various Ce additions (10 ~ 20 wt. %) is studied. The electrocatalysts are prepared and subsequently reduced at 390 or 620 K. Although Co ions can be fully reduced only at 620 K, the reduction process conducted at 390 K can prevent the Pd-Co alloys from grain growth and undesired surface Co segregation. The addition of 15 wt. % CeO2 (Ce15) along with low reduction temperature (390 K) into the Pd-Co system promotes the enrichment of Pd surface species, resulting in the formation of a Pd skin / alloy core structure. As a consequence, Ce15 can present the superior ORR activity with a 2.3-fold improvement as compared to the un-modified, and CeO2 acting as a textural promoter and surface modifier for the PdCo/C alloy catalysts, can significantly improve their ORR activity. In the 3rd part, the PdCo/C catalysts prepared in the 1st part are further oxidation treated at various temperatures (To = 320 ~ 620 K) and the oxidation induced improvement of the ORR activity for PdCo/C is investigated. Based on the XPS characterization, a new term, degree of surface oxidation (DSO), is proposed to illustrate the relationship between ORR activity enhancement and surface oxidation extent of the PdCo/C. The optimal temperature for the promotion of ORR activity on various oxidized samples is 520 K where its surface is majorly comprised of PdO. Besides, various heat treatment atmospheres (H2 and CO) are applied on Pd-Co system without changing their particle size. It is clearly evident that the PdCo/C catalysts oxidized at 520 K exhibit a better performance relative to that of the non-oxidized ones, confirming that the improved ORR activity is solely ascribed to the formation of surface PdO species with 100 % DSO value rather than the large particle size effect. In the 4th part, ternary catalysts of Pd75Co25-xAux/C with varying x content (x = 5 ~ 25) are synthesized and the role of Au in altering structures, surface conditions and electrochemical properties of PdCo/C catalysts is systematically investigated. XRD results reveal that the incorporation of Au into Pd-Co system contributes to the formation of inhomogeneous alloy structure. Meanwhile, the fine structural details determined by XAS indicates that Au improves the heteroatomic intermix extent of alloy nanocatalysts significantly, especially for the Pd75Co10Au15/C (Au15) catalysts. TPR results suggest that the Pd-rich surface gradually changes to Pd, Au and alloy mixed surface species when Au content is larger than 15 at. %. All of the Au-modified PdCo/C catalysts have the particles size of ca. 4.9 ~ 5.4 nm and Au15 has the narrowest size distribution among all catalysts. For the electrochemical properties, the Pd mass activity of Au15 is ca. 4-fold and 2.5-fold higher than that of Pd/C and Au0 (Pd75Co25/C). Thus, it is demonstrated that Au15 displays the excellent ORR performance due to the improved extent of heteroatomic intermix in bulk structure, narrow size distribution, large electrochemical surface area (ECSA) and the concomitant multiple coexisting species predominated on the outermost surface. en_US
DC.subjectX光吸收光譜zh_TW
DC.subject異相原子混合度zh_TW
DC.subject表面氧化程度zh_TW
DC.subject電化學活性面積zh_TW
DC.subjectPdCoAuzh_TW
DC.subject氧還原反應zh_TW
DC.subjectPdCozh_TW
DC.subjectpH值zh_TW
DC.subject氧化飾zh_TW
DC.subject程溫式還原儀zh_TW
DC.subject氧化熱處理zh_TW
DC.subjectPdCoen_US
DC.subjectPdCoAuen_US
DC.subjectOxygen reduction reactionen_US
DC.subjectX-ray absorption spectroscopyen_US
DC.subjectTemperature programmed reductionen_US
DC.subjectpH valuesen_US
DC.subjectCeriaen_US
DC.subjectOxidation treatmenten_US
DC.subjectDegree of surface oxidationen_US
DC.subjectHeteroatomic intermix extenten_US
DC.subjectElectrochemical surface areaen_US
DC.title製備、改質及鑑定高效能鈀鈷觸媒應用於陰極氧還原反應zh_TW
dc.language.isozh-TWzh-TW
DC.titlePreparation, Promotion and Characterization of High Performance PdCo/C Catalyst for the Oxygen Reduction Reactionen_US
DC.type博碩士論文zh_TW
DC.typethesisen_US
DC.publisherNational Central Universityen_US

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