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研究生：	蘇曼錫 Sikarwar, Manvendra Singh
論文名稱：	鑭摻雜與鎳析出對A-位置空缺含鑭/鎳鈦酸鋇之導電與微結構之影響 Effect of La doping and Ni exsolution on conduction and microstructure of A-site deficient La(x)Ba(0.8-x)Ni(y)Ti(1-y)O3-δ perovskite anode
指導教授：	方冠榮 Fung, Kuan Zong
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學及工程學系 Department of Materials Science and Engineering
論文出版年：	2024
畢業學年度：	112
語文別：	英文
論文頁數：	78
中文關鍵詞：	鈣鈦礦、溶出、微觀結構、表面形貌、電催化
外文關鍵詞：	Perovskite , Exsolution , Microstructure, Surface morphology, Electrocatalysis
相關次數：	點閱：53 下載：20
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在高溫氧化物燃料電池中，標準陽極使用Ni/YSZ (鎳/釔安定化氧化鋯)，但當使用碳氫燃料時，由鎳的催化作用，容易產生碳沉積，造成陽極劣化。以導電氧化物(如鈦酸鹽)作為陽極，可有效改善碳沉積，但其催化燃料氧化之性能則不如Ni/YSZ。因此，本研究提出針對鈦酸鋇陽極，藉鑭摻雜和鎳析出後鈣鈦礦陽極La (x) Ba (0.8-x) Ni (y) Ti (1-y) O 3-z ，進行導電性質，與微結構之量測與觀察，並探討其衍生缺陷結構之變化，進而推測其對催化性質之影響。在本研究中，不同化學組成之鈦酸鋇陽極La(x)Ba(0.8-x)Ni(y)Ti(1-y)O3-z ( x = 0, 0.16, 0.2 & 0.3) 和(y = 0.0 to 0.2)，以1150℃、8h 之條件下，進行固相反應合成。為了使鎳金屬析出於氧化物表面，La(x)Ba(0.8-x)Ni(y)Ti(1-y)O3-z 置於1200℃、8h ，通入(20 % H 2 + 80% Ar）氣體環境下，同時進行燒結和還原反應。結果，在低氧分壓環境下，氧空缺形成，同時釋出電子，使〖Ni〗^(+2)，接受電子後，還原成〖Ni〗^0 並遷移到電極表面，同時也促進Ti +4還原為Ti + 3 ，可增強電催化活性，預期高溫燃料電池性能也將隨之提升。當溫度提升至1200℃燒結8小時，則有助於氧化物電極緻密化，相對密度提高高達86%。與非燒結電極相比，緻密電極具有較高的抗再氧化性，從而具有更高的電導率。隨著鑭離子含量（0, 0.16、0.2 和0.3 或16%、20% 和30%）增加，因為當三價鑭離子取代二價鋇離子時，傾向產生更多的負電缺陷，例如更多的電子或是三價鈦離子，從而有助於提高電氣性能。所以，當 La 摻雜量達 30 %，鈦酸鋇所得的電導率可高達 64 ~72 mS/cm；當 La 摻雜量降低至 16 %時，電導率降低為 5.6 ~ 5.8 mS/cm，但仍遠高于未摻雜之BaTiO3。值得注意的是，在還原環境中，在 1200 C、12 小時，La = 30 % 時，由於La 2 O 3的釘扎效應抑制了晶粒生長並減少了晶界面積，因此當鑭濃度較高時，平均晶粒尺寸會減小，從而在還原環境中獲得更高的密度和更好的電氣性能。此外，增加了鑭含量，也明顯地使晶格常數減少，推測是由於鑭離子半徑小於鋇離子半徑，1.36 Å < 1.49 Å）。至於鎳的摻雜量提升至 20%時，在低氧分壓還原作用下，氧空缺形成，伴隨電子釋出，當鎳離子接受電子趨勢大於Ti 4+時，將造成[Ti3+]濃度減少，電子在Ti 4+/ Ti 3+之間躍遷機會減少，導電性也將隨之降低。前述之物性、化性及行為之討論，是建立於各種分析與量測技術包括: X光繞射(晶體結構、結晶性分析)，掃描式電子顯微鏡(微結構、表面形貌觀察)，四線導電性質量測等。

In high-temperature oxide fuel cells, the standard anode uses Ni/YSZ (nickel/yttrium stabilized zirconia). However, when hydrocarbon fuel is used, the catalytic effect of nickel easily produces carbon deposition, causing the anode to deteriorate. Using conductive oxide (such as titanate) as the anode can effectively improve carbon deposition, but its performance in catalyzing fuel oxidation is not as good as Ni/YSZ. Therefore, this study proposes to use lanthanum doping and nickel precipitation for barium titanate anodes to conduct electricity using the perovskite anode La(x)Ba(0.8-x)Ni(y)Ti(1-y)O3-z properties, and measurement and observation of microstructure, and explore the changes in the defect structure derived from it, and then speculate on its impact on catalytic properties. In the current research, a single-phase perovskite electrode La(x) Ba(0.8-x) Ni(y)Ti(1-y) O3-z is prepared when ( x = 0, 0.16, 0.2 & 0.3) and (y = 0.0 to 0.2) using solid-state reaction at 1150 C, 8h, which is a tetragonal crystal structure, sintered & reduced at 1200 C, 8h in 20 % H2 and 80 % Ar gas environment for reduction of 〖Ni〗^(+2) to 〖Ni〗^0 and transfer to electrode surface enhancing electrocatalytic activity, generating oxygen vacancies which promote Ti +4 to Ti+ 3 reduction, improving electrical performance for high-temperature fuel cell operation. High temperature sintering at 1200 C, 8h helped densification of electrodes improving relative density of up to 86%. Dense electrodes offer high resistance to reoxidation resulting in higher electrical conductivity in comparison to non-sintered electrodes. Lanthanum (0, 0.16, 0.2 & 0.3 or 16 %, 20 % & 30%) composition is increased because it generates more positive charge when trivalent lanthanum occupies the divalent barium site and to neutralize, more electrons are generated help in improved electrical performance. For (La =30 %), high electrical conductivity is obtained as 64 ~72 mS/cm and low for (La = 16 %) as 5.6 ~ 5.8 mS/cm which is much higher than undoped BaTiO3. It is noticed highest electrical
conductivity as 0.3 S/cm for La = 30 % at 1200 C, 12h in reducing environment. Average grain size decreases for higher lanthanum concentration because of pinning effect of La2O3 which suppresses the grain growth and reduces the phase boundary area resulting in higher density and better electrical performance in the reducing environment. It is noticed decrement in lattice constant increasing the lanthanum content (As lanthanum ionic radius is smaller than barium ionic radius, 1.36 Å < 1.49 Å). When the nickel doping amount is increased to 20%, oxygen vacancies are formed under the reduction of low oxygen partial pressure, accompanied by the release of electrons. When the tendency of nickel ions to accept electrons is greater than that of Ti 4+, the Ti3+ concentration will decrease. The opportunity for electrons to transition between Ti4+/Ti3+ is reduced, and the conductivity will also be reduced. Various characterization techniques like X-ray diffraction (XRD) are used to detect phase and crystallinity while scanning electron microscopy, energy dispersive spectroscopy, and four-wire resistance multimeter are used to analyze microstructure, surface morphology, elemental composition, and electrical conductivity. Adequate materials and microstructure designs are crucial for enhancing the performance of the Ni-exsolved perovskite anode. This study's goals are to fabricate Ni-containing perovskites with the necessary composition, examine the effect of lanthanum doping on electrical properties, analysing microstructure and surface morphology, exsolution effect on electrical performance, and determine the electrical characteristics of perovskite anodes synthesized.

1.	Introduction…………………………………………………………….............................................1
2.	Literature Review…………………………………………………......................................................... 6
2.1	Need of SOFC and SOEC………………………………………….....................................................6
2.2	Basic principle of SOC’s cell………………………………….......................................................8
2.2.1	Solid Oxide Fuel Cell (SOFC)………………………………...................................................8
2.2.2	Solid Oxide Electrolytic Cell (SOEC)………………………...............................................9
2.2.3	Constituent of SOC’s cell………………………………….................................................11
2.2.3.1	Anode………………………………………………........................................................................11 
2.2.3.2	Electrolyte………………………………………….......................................................................12
2.2.3.3	Cathode………………………………………………....................................................................12
          2.3 Anode requirements ……………………………………………….........................................12
          2.4 Types of anode materials………………………………………….........................................13
                2.4.1 Metal Fluorite Cermet………………………………..................................................14 
                2.4.2 Perovskite type………………………………………………............................................15
                     2.4.2.1 Titanium as B-site cation………………………………....................................17
                     2.4.2.2 Transition metal doping at B-site………………………..............................18
                     2.4.2.3  A-site deficiency……………………………………….........................................19
          2.5 Exsolution ………………………………………………………....................................................20  
                2.5.1 Exsolution mechanism……………………………………….......................................21 
                2.5.2 Attributes and mechanisms beneath exsolution in perovskite                                        oxides……………………………………………………..................................................................................23
                2.5.3 Exsoluted electrodes………………………………………...........................................25
                       2.5.3.1 Exsolution on stoichiometric perovskite oxide………......................25
                       2.5.3.2  Exsolution on non-stoichiometric perovskite oxide           
                       ……………………………………………………………….........................................................26
           2.6  Exsolution role in improved electrical performance……………........................27
  3. Experimental procedure…………………………………………………............................................29
           3.1 Powder preparation by solid state reaction………………………............................29
           3.2 Characterization of an electrode…………………………………...................................30
                  3.2.1 X-ray diffraction (XRD)……………………………………........................................30
                  3.2.2 Scanning Electron Microscopy……………………………...................................31
                  3.2.3 Energy Dispersive Spectroscopy…………………………...................................31
                  3.2.4 Electrical properties measurements………………………...............................31
                  3.2.5 Reduction of an electrode…………………………………....................................32
           3.3 No. of electrodes prepared……………………………………….......................................33
  4. Results and Discussion………………………………………………….............................................34
           4.1 X-ray diffraction analysis………………………………………….......................................34    
                   4.1.1 Synthesis…………………………………………………................................................34
                   4.1.2 Doping of Nickel up to 20 %..........................................................................35
                   4.1.3 Exsolution of nickel on the surface………………………................................36
                   4.1.4 Stability of an electrode……………………………………................................... 39
                   4.1.5 Effect of temperature on the extent of exsolution…………....................40
                   4.1.6 XRD analysis of electrode with higher lanthanum  
                            Concentration (La = 16%, 20% & 30%) …………………...............................41                                                                    
                   4.1.7 Ti+3/ Ti +4 redox couple generation………………………….........................42
                   4.1.8 Effect of A-site deficiency on Ni exsolution………………..........................43
           4.2 Scanning electron microscopy……………………………………....................................44
           4.3 Electrical Properties Characterization…………………………….................................48
                   4.3.1 Effect of lanthanum doping on resistance………………….........................48
                   4.3.2 Electrical conductivity measurements………………….….............................51
                   4.3.3 Effect of nickel exsolution on electrical conductivity……......................54
                   4.3.4 Effect of titanium doping………………………………….....................................56
   5. Conclusion………………………………………………………………................................................... 58
   6. References………………………………………………………………................................................... 60
                                    

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