本文選題：固體氧化物燃料電池　切入點(diǎn)：復(fù)相陰極　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：固體氧化物燃料電池(SOFC)是一種能夠?qū)⒒瘜W(xué)能直接轉(zhuǎn)化為電能的高效、環(huán)保的能源轉(zhuǎn)換裝置。在其商業(yè)化應(yīng)用的發(fā)展進(jìn)程中,運(yùn)行條件的中低溫化成為了 SOFC技術(shù)的必然趨勢(shì),但是陰極反應(yīng)的極化損失嚴(yán)重制約了 SOFC在中低溫下的性能提升,因此,設(shè)計(jì)構(gòu)建高性能的陰極和深入理解陰極的反應(yīng)機(jī)理勢(shì)在必行。本論文以典型的混合導(dǎo)體陰極La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)(LSCF)為研究對(duì)象,通過電導(dǎo)弛豫方法表征離子導(dǎo)電相Sm_xCe_(1-x)O_(2-δ)(SDC)的加入對(duì)于陰極表面氧還原反應(yīng)過程的增強(qiáng)作用,重點(diǎn)研究三相線處的反應(yīng)過程和對(duì)于整體反應(yīng)的貢獻(xiàn)率,確定氧還原反應(yīng)的反應(yīng)機(jī)理和速控步驟。第一章主要介紹了 SOFC的運(yùn)行原理和陰極的常用材料,重點(diǎn)闡述了復(fù)相材料中的性能協(xié)同增強(qiáng)現(xiàn)象,以及三相線對(duì)于陰極氧還原反應(yīng)的重要作用,隨后揭示了氧還原反應(yīng)可能的反應(yīng)機(jī)理步驟,最后對(duì)本論文的主要表征手段電導(dǎo)弛豫方法進(jìn)行了全面的介紹,包括其測(cè)試過程、理論方法、影響因素等等。為了實(shí)現(xiàn)對(duì)復(fù)相材料以及三相線處氧還原過程的表征,首先必須從理論上獲得相應(yīng)的反應(yīng)動(dòng)力學(xué)參數(shù)的表達(dá)式。第二章的工作以LSCF-SDC復(fù)相材料為研究對(duì)象,通過把表面交換系數(shù)具象化為反應(yīng)量與反應(yīng)速率的形式,基于傳統(tǒng)的單相材料的表面交換系數(shù),提出了有關(guān)復(fù)相材料表面以及三相線處氧還原反應(yīng)動(dòng)力學(xué)參數(shù)的理論推導(dǎo)方法,并且定義了三相線對(duì)于整體反應(yīng)的貢獻(xiàn)因子。此外,基于電導(dǎo)弛豫測(cè)試的氧分壓梯度和計(jì)算的氧還原反應(yīng)速率,提出了表面氧還原過程對(duì)應(yīng)的等效電勢(shì)差、交換電流密度以及極化阻抗的計(jì)算方法。第二章的工作為后續(xù)的氧還原反應(yīng)動(dòng)力學(xué)參數(shù)表征和反應(yīng)機(jī)理研究提供了理論方法和基礎(chǔ)。能夠定量表征并區(qū)分兩相界面和三相線處的反應(yīng)過程對(duì)于研究復(fù)相陰極的表面協(xié)同效果和氧還原反應(yīng)機(jī)理都是必不可少的,因此第三章的工作主要基于前面提出的理論方法,通過電導(dǎo)弛豫測(cè)試表征了 LSCF-SDC復(fù)相材料的表面氧還原反應(yīng)過程,并分別計(jì)算得到了兩相界面與三相線處的氧還原反應(yīng)量和反應(yīng)速率。結(jié)果表明加入SDC后樣品的表面交換系數(shù)增大了 5倍,證明LSCF與SDC之間存在表面協(xié)同增強(qiáng)作用。結(jié)合樣品表面微結(jié)構(gòu)的定量統(tǒng)計(jì)結(jié)果顯示,在復(fù)相材料的表面氧還原反應(yīng)過程中超過70%的氧都是通過三相線進(jìn)入氧化物體相中的。進(jìn)一步的結(jié)果表明三相線處的反應(yīng)速率并不是完全由三相線的密度決定,因?yàn)長(zhǎng)SCF的顆粒大小也會(huì)影響三相線的反應(yīng)速率,這可能與表明吸附的氧物種在LSCF表面的遷移過程有關(guān),基于實(shí)驗(yàn)結(jié)果發(fā)現(xiàn)氧在LSCF表面的最大遷移距離約為1.5 μm。為了定量表征離子導(dǎo)電相電導(dǎo)率對(duì)于三相線處氧還原反應(yīng)的影響,第四章測(cè)試了 LSCF-Sm_xCe_(1-x)O_(2-δ)復(fù)相材料的氧弛豫過程。通過上述理論方法計(jì)算得到的三相線處的貢獻(xiàn)因子隨著測(cè)試溫度的升高而降低,說明三相線在低溫時(shí)的作用更加明顯。結(jié)合三相線密度等參數(shù)的統(tǒng)計(jì)結(jié)果,發(fā)現(xiàn)三相線處的表面反應(yīng)速率隨著Sm_xCe_(1-x)O_(2-δ)的電導(dǎo)率增大而提升,在較低測(cè)試溫度時(shí),甚至表現(xiàn)為線性增長(zhǎng)。經(jīng)過基元反應(yīng)的動(dòng)力學(xué)參數(shù)的理論推導(dǎo)證明當(dāng)氧融入過程是唯一的速控步驟時(shí),三相線的反應(yīng)速率常數(shù)會(huì)隨著Sm_xCe_(1-x)O_(2-δ)的電導(dǎo)率線性增加。因此,氧的融入過程是三相線處氧還原反應(yīng)的重要速控步驟。由于三相線處的氧還原反應(yīng)過程不僅與三相線的密度相關(guān),還會(huì)受到兩相表面微結(jié)構(gòu)的影響,因此第五章主要通過調(diào)控LSCF-SDC復(fù)相樣品中的SDC相的晶粒尺寸來(lái)研究其表面形貌對(duì)于三相線處氧還原反應(yīng)過程的影響。結(jié)果表明隨著SDC初始粉體的熱處理溫度的升高,復(fù)相樣品中的SDC粒徑逐漸增大,而統(tǒng)計(jì)得到的三相線密度則逐漸減小,相應(yīng)的表面氧還原反應(yīng)速率也隨之降低。但是單位三相線長(zhǎng)度的反應(yīng)速率反而有所增加,表明三相線的實(shí)際反應(yīng)效率隨著SDC晶粒尺寸的增加而提升。這可能是因?yàn)樵谌嗑�處富集的吸附氧離子會(huì)溢流到SDC表面,進(jìn)而與SDC表面的活性氧空位相結(jié)合,這樣氧融入反應(yīng)的活性位點(diǎn)就會(huì)由三相線向SDC表面擴(kuò)展,從而提升了單位三相線的反應(yīng)效率。結(jié)果表明吸附氧離子在SDC表面的遷移距離可能不小于0.42 μm。為了直接表征多孔樣品的表面氧還原反應(yīng)過程,必須保證氣體在反應(yīng)容器內(nèi)的切換過程和樣品孔內(nèi)的擴(kuò)散過程足夠快。考慮到傳統(tǒng)的測(cè)試方法很難做到,在第六章的工作中設(shè)計(jì)了真空-電導(dǎo)弛豫測(cè)試裝置并用于表征了多孔LSCF樣品的表面氧還原反應(yīng)過程。結(jié)果發(fā)現(xiàn)測(cè)得的多孔樣品的氧還原反應(yīng)同時(shí)受到表面交換過程和氣體在孔內(nèi)的Knudsen擴(kuò)散過程的影響。在此基礎(chǔ)上,提出了多孔樣品的特征厚度的概念,可以用于比較表面交換過程和Knudsen擴(kuò)散過程的相對(duì)快慢。之后推導(dǎo)得到了包含上述兩個(gè)過程的雙參數(shù)擬合函數(shù),可以分離得到多孔樣品的氧還原反應(yīng)動(dòng)力學(xué)參數(shù)。擬合結(jié)果顯示多孔樣品的氧還原反應(yīng)速率隨著燒結(jié)溫度的升高和造孔劑含量的減少而降低,而且其表面交換系數(shù)的表觀活化能(49-70 kJ mol-1)明顯低于致密樣品(約110 kJ mol-1)。基于多孔LSCF樣品在不同氧分壓梯度和SDC浸漬量等條件下的實(shí)驗(yàn)結(jié)果,表明氧的吸附過程是多孔樣品氧還原反應(yīng)的重要速控步驟。
[Abstract]:Solid oxide fuel cell (SOFC) is a way to convert chemical energy directly into electrical energy efficient, environmentally friendly energy conversion device. In the process of the development of the commercial application in low temperature operating conditions has become the inevitable trend of SOFC technology, but loss of cathode reaction seriously restricts the promotion the performance of SOFC in low temperature therefore, imperative reaction mechanism design construction of high performance cathode and understanding the cathode. In this paper, the typical mixed conductor cathode La_ (0.6) Sr_ (0.4) Co_ (0.2) Fe_ (0.8) O_ (3- 8) (LSCF) as the research object, through the conductivity relaxation characterization of ion conducting phase Sm_xCe_ (1-x) O_ (2- 8) (SDC) enhancement to the cathode surface oxygen reduction reaction process, the reaction process focuses on the three-phase contact line and the overall response rate of contribution, to determine the reaction mechanism and the rate controlling step of oxygen reduction reaction The first chapter mainly introduces the operating principle of commonly used materials and the cathode of SOFC, focuses on the performance of the composite material of the synergistic phenomenon, as well as the important role of three-phase line for the cathodic oxygen reduction reaction, then reveals the possible reaction mechanism of oxygen reduction reaction steps, finally the main characterization methods of the conductivity relaxation relaxation methods are introduced, including the test process, theoretical methods, influencing factors and so on. In order to realize the multiphase materials and the three-phase line of the oxygen reduction process characterization, expression must first obtain the kinetic parameters from the corresponding theory. The second chapter work with LSCF-SDC composite as the research object, through the the surface exchange coefficient for concrete reaction and reaction rate in the form of the traditional single-phase materials surface exchange coefficient based on the proposed composite surface and three The theoretical derivation method of phase at the oxygen reduction reaction kinetic parameters, and the definition of the three phase for the contribution factor of the overall reaction. In addition, the electrical conductivity relaxation test of oxygen partial pressure gradient and the calculation of oxygen reduction reaction rate based on the equivalent potential of surface oxygen reduction process corresponding to the exchange current density and polarization impedance calculation method the work of the second chapter. For the oxygen reduction kinetics and reaction mechanism of the reaction parameters provides a theoretical basis and the methods. To quantitatively characterize and distinguish the reaction process and the three-phase line at the interface of the surface to study the synergistic effect of composite cathode and oxygen reduction reaction mechanism is essential, so the work of the third chapter mainly based on the methods proposed above, the conductivity relaxation test to characterize the reaction process of oxygen on the surface of LSCF-SDC composites and reduction, respectively Is the three phase of the two phase interface and the oxygen reduction reaction and the reaction rate. The results showed that after adding SDC sample surface exchange coefficient increased by 5 times, to prove the existence of surface synergistic effect between LSCF and SDC. Combined with the quantitative statistical results of sample surface micro structure, on the surface of the composite materials of oxygen reduction reaction in the process of more than 70% of the oxygen is through the three phase object into the oxidation phase. Further results show that the three-phase line at the reaction rate is not entirely by the three phase determines the density, because the reaction rate of LSCF particle size will also affect the three phase, which may be related to that of oxygen species adsorbed on the migration process of LSCF the surface of the experimental results found that the oxygen in the maximum migration distance from the LSCF surface is about 1.5 m. for quantitative characterization of ion conductive phase conductivity influence on the three-phase contact line based on oxygen reduction reaction, The fourth chapter tested LSCF-Sm_xCe_ (1-x) O_ (2- 8) oxygen relaxation process of composite materials. The contribution factor at the three phase obtained by the theoretical calculation method decreases with the increase of temperature, indicating the three-phase line when the low temperature effect is more apparent. Combined with statistical results of three-phase line density parameter that, the three-phase contact line surface reaction rate as Sm_xCe_ (1-x) O_ (2- 8) the conductivity increases at low temperature, test, even for linear growth. Theoretical derivation by kinetic parameters of reactions that when oxygen is incorporated into the process is the only rate controlling step, reaction rate constant of three-phase line with Sm_xCe_ (1-x) O_ (2- 8) to increase the conductivity of linear. Therefore, in the process of oxygen is an important speed three-phase line oxygen reduction reaction control steps. The reaction of oxygen reduction at the three-phase line not only with the three phase. The degree of correlation is also affected by the two surface micro structure, so the fifth chapter mainly through the regulation of LSCF-SDC composite samples of the SDC phase and the grain size of the surface topography effects on reaction process of three phase line oxygen reduction. The results showed that with the increase of initial SDC powder heat treatment temperature, multiphase samples SDC particle size increases, and the statistics of three phase density is gradually decreased, the corresponding surface oxygen reduction reaction rate is reduced. But the reaction rate per unit length of the three phase but increased, showed that the actual anti three phase should enhance with the increased efficiency of the grain size of SDC. This may be because the adsorption of oxygen ion enrichment in the three-phase line will overflow to the surface of SDC, and combined with the activity of oxygen vacancies on the surface of SDC, such as reaction sites of oxygen into the three phase will be extended from SDC to the surface, thus To enhance the reaction efficiency of unit three phase. The results show that the adsorption of oxygen ions in the migration distance of SDC surface may not be less than 0.42 M. in order to direct characterization of porous sample surface oxygen reduction reaction, must ensure that the switching process and the sample gas diffusion hole in the reaction vessel in the process of fast enough. Considering the traditional test method it is difficult to do, in the work of the sixth chapter in the design of the vacuum - conductivity relaxation test device and used to characterize the reaction process of oxygen on the surface of porous LSCF sample reduction. The results showed that the porous samples measured the oxygen reduction reaction is also affected by the surface exchange process and gas hole in Knudsen diffusion process. On the basis of put forward the concept, the characteristics of thickness of porous samples, can be used to compare relative speed of surface exchange process and Knudsen diffusion process is derived. After the two Double parameter fitting function, can be obtained from the porous samples of oxygen reduction reaction kinetic parameters. The fitting results show that the porous samples of oxygen reduction reaction rate decreased with the decrease and increase the content of pore forming agent and sintering temperature, and the surface exchange coefficient of apparent activation energy (49-70 kJ mol-1) was significantly lower than that of dense samples (about 110 kJ mol-1). The experimental results of porous LSCF sample pressure gradient and SDC impregnation conditions under different oxygen based on that the oxygen adsorption velocity of porous samples is an important oxygen reduction reaction controlling step.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM911.4

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