本文選題：固體氧化物燃料電池 + 氧的還原反應(yīng)��； 參考：《吉林大學(xué)》2016年博士論文

【摘要】：固體氧化物燃料電池(SOFC)由于其清潔、高效的特點(diǎn)已經(jīng)受到世界越來(lái)越廣泛的關(guān)注,成為了未來(lái)能源系統(tǒng)中不可或缺的電源裝置。傳統(tǒng)的SOFC由于操作溫度過高(1000 oC),容易引起材料老化、材料間界面反應(yīng)及高的成本投入等問題。有效的解決這些問題的途徑是降低SOFC的操作溫度(600-800 oC)。但電解質(zhì)的歐姆損失,特別是陰極的極化損失也隨著操作溫度的降低顯著增大。隨著電解質(zhì)新型材料和薄膜技術(shù)的研發(fā),已基本解決了電解質(zhì)的歐姆損失問題。因此,提高陰極的催化活性,降低陰極的極化損失成為了降低電池操作溫度的關(guān)鍵,是中溫固體氧化物燃料電池(IT-SOFC)發(fā)展的重要方向。分析陰極反應(yīng)機(jī)制,優(yōu)化陰極反應(yīng)步驟,進(jìn)而提高陰極反應(yīng)速率是提高催化活性的重要途徑。通過發(fā)展新型電極材料提高電化學(xué)反應(yīng)速率是當(dāng)今IT-SOFC研究的主線之一。ABO3型鈷基鈣鈦礦氧化物具有較高的電子-離子混合導(dǎo)電能力與氧催化還原能力,成為了IT-SOFC的主要陰極材料。本文以鈷基混合導(dǎo)電陰極材料和電解質(zhì)復(fù)合陰極材料為主要研究對(duì)象,研究了材料的化學(xué)組成、微觀結(jié)構(gòu)、反應(yīng)機(jī)制等因素對(duì)陰極性能產(chǎn)生的影響。通過調(diào)控材料的組成與結(jié)構(gòu),對(duì)材料性能優(yōu)化的可行途徑進(jìn)行探索,并探討了影響材料電化學(xué)性能的規(guī)律與物理、化學(xué)本質(zhì),旨在分析出陰極的氧的還原反應(yīng)步驟,找到降低陰極極化損失,提高陰極催化活性的關(guān)鍵,并為促進(jìn)IT-SOFC的發(fā)展提供一定的材料與技術(shù)儲(chǔ)備。主要研究?jī)?nèi)容如下:1.鈣鈦礦型氧化物Ba Co0.7Fe0.2Nb0.1O3-δ(BCFN)具備很好的電子-離子混合導(dǎo)電能力,作為IT-SOFC陰極材料表現(xiàn)出了較好的電化學(xué)性能。但是,影響此材料性能的主要因素,氧的還原反應(yīng)的主要步驟,以及控制反應(yīng)速率的主要過程仍沒有系統(tǒng)的研究。因而,為了進(jìn)一步探索BCFN材料的整體反應(yīng)過程,提高氧的還原反應(yīng)速率,提升陰極性能,我們選擇在A位摻Sr來(lái)分析其性能優(yōu)化的可行性和根本原因。采用固相法合成Ba1-x Srx Co0.7Fe0.2Nb0.1O3-δ(B1-x Sx CFN,x=0.0,0.1,0.2,0.3,0.4)陰極材料,研究發(fā)現(xiàn),B1-x Sx CFN材料在1000 oC燒結(jié)10 h后,形成了單相的立方鈣鈦礦結(jié)構(gòu)。摻雜之后,材料的熱膨脹系數(shù)降低。陰極的極化電阻(RP)隨著Sr的摻雜量先減小后增大,當(dāng)Sr的摻雜量為x=0.2時(shí),RP值最小。Sr的適當(dāng)摻雜提高了小極化子的濃度,使小極化子和氧空位達(dá)到了最佳濃度比,材料的導(dǎo)電能力增強(qiáng),電化學(xué)性能提高。電化學(xué)反應(yīng)機(jī)制研究表明,陰極上的反應(yīng)包括氧的解離吸附和擴(kuò)散過程;氧原子得電子生成氧離子過程;氧離子在三相界面處和氧空位結(jié)合生成晶格氧過程。對(duì)沒摻Sr的BCFN樣品,在氧分壓1 atm-0.01 atm變化范圍內(nèi),限速步驟為氧原子得電子生成氧離子過程;而對(duì)于Sr的摻雜量為0.2的B0.8S0.2CFN樣品,在氧分壓大于0.1 atm時(shí),氧原子得電子生成氧離子過程為限速步驟,當(dāng)氧分壓小于0.1 atm時(shí),限速步驟為氧的解離吸附和擴(kuò)散過程。電解質(zhì)支撐的單電池B1-xSx CFN/SDC/Ni0.9Cu0.1-SDC的功率密度隨著Sr含量的增多,先增大后減小,當(dāng)Sr的含量x為0.2時(shí),表現(xiàn)出最好的電化學(xué)性能。2.B0.8S0.2CFN作為IT-SOFC陰極材料表現(xiàn)出了優(yōu)異的性能。為了增強(qiáng)材料的離子導(dǎo)電性,提高氧的還原反應(yīng)速率,我們對(duì)B0.8S0.2CFN材料進(jìn)行了相應(yīng)的改性研究,將電解質(zhì)材料SDC與B0.8S0.2CFN(BSCFN)混合制成復(fù)合陰極材料,目的是改善氧的還原反應(yīng)過程,提高陰極性能。研究結(jié)果表明,BSCFN與SDC間沒有相反應(yīng),化學(xué)相容性良好。復(fù)合后熱膨脹系數(shù)降低,與電解質(zhì)SDC的熱膨脹系數(shù)更加接近,提高了陰極與電解質(zhì)的熱匹配性。SDC的加入改善了材料的微觀結(jié)構(gòu),拓展了三相界面的長(zhǎng)度,改善了材料的電化學(xué)性能,當(dāng)復(fù)合30 wt.%SDC時(shí)陰極表現(xiàn)出最好的性能,在800 oC時(shí)其RP比純BSCFN陰極的RP小很多。利用交流阻抗譜技術(shù)對(duì)比研究了BSCFN陰極和BSCFN-30SDC復(fù)合陰極在SDC電解質(zhì)上的反應(yīng)機(jī)制,研究結(jié)果表明:氧分壓大于0.05 atm時(shí)氧離子和氧空位結(jié)合生成晶格氧過程為限速步驟,氧分壓小于0.05 atm時(shí)氧的解離吸附和擴(kuò)散過程為限速步驟。復(fù)合后陰極的電化學(xué)活性增強(qiáng)的主要原因?yàn)閺?fù)合后反應(yīng)速率的加快,SDC離子導(dǎo)電相的引入使得反應(yīng)過程由三步縮短為兩步,氧原子得電子后直接和氧空位結(jié)合生成晶格氧,大大提高了反應(yīng)速率,陰極上的氧的還原反應(yīng)活性增強(qiáng)。800 oC時(shí),電解質(zhì)支撐的單電池BSCFN-x SDC|SDC|Ni0.9Cu0.1-SDC的功率密度分別為620.37,656.79,717.56和663.00 m Wcm-2,這表明BSCFN-30SDC是很有前景的IT-SOFC陰極材料。3.在BCFN這類電子-離子混合導(dǎo)電材料中,電子電導(dǎo)往往比離子電導(dǎo)高幾個(gè)數(shù)量級(jí),因而進(jìn)一步提高陰極性能的一種有效途徑就是提高離子電導(dǎo)率。引入A位離子缺陷對(duì)鈣鈦礦型陰極材料的晶體結(jié)構(gòu)、氧空位濃度和熱膨脹系數(shù)都可能產(chǎn)生影響,進(jìn)而改變陰極的反應(yīng)過程。因而,我們采用固相法制備了Ba1-xCo0.7Fe0.2Nb0.1O3-δ(B1-xCFN,x=0,0.05,0.10,0.15)系列陰極材料,通過XRD、SEM、交流阻抗譜以及單電池的測(cè)試,研究其A位缺位對(duì)晶體結(jié)構(gòu)、熱膨脹以及電化學(xué)反應(yīng)的影響。研究發(fā)現(xiàn),B1-xCFN經(jīng)過1000oC燒結(jié)10個(gè)小時(shí)后,完全形成立方鈣鈦礦結(jié)構(gòu),晶胞體積隨著A位缺位量的增加并不呈線性變化關(guān)系,B0.9CFN的晶胞體積最大,說明A位離子的缺陷更多的是產(chǎn)生氧空位,而不是使B位金屬離子升價(jià)。隨著缺位量的增加,孔隙率下降,B0.9CFN陰極的孔隙率最小。當(dāng)缺位量增加為0.15時(shí)(即B0.85CFN),由于顆粒團(tuán)聚使得孔隙率增加。隨著A位Ba含量的減少,界面極化電阻減小,當(dāng)x=0.10時(shí),即B0.90CFN在800oC時(shí),界面極化電阻下降約66.2%。在氧分壓大于0.01 atm時(shí),氧離子和氧空位結(jié)合生成晶格氧過程為限速步驟,當(dāng)氧分壓為0.01 atm時(shí),氧的解離吸附和擴(kuò)散過程為限速步驟。Ba缺陷引起的氧空位的增多,使得氧原子得電子后直接和氧空位結(jié)合生成晶格氧,反應(yīng)速率提升,陰極的氧的還原反應(yīng)活性增強(qiáng)。半電池的阻抗譜和單電池性能結(jié)果顯示,在800 oC時(shí)B0.90CFN表現(xiàn)出良好的陰極催化活性。4.為了繼續(xù)提升材料中的離子電導(dǎo)率,我們采用在材料中復(fù)合離子導(dǎo)電的電解質(zhì)的方法。研究結(jié)果表明,經(jīng)1000 oC燒結(jié)10個(gè)小時(shí)后,復(fù)合材料中的B0.9CFN和SDC仍保持各自相結(jié)構(gòu),沒有雜相生成。電化學(xué)反應(yīng)機(jī)制研究表明,氧分壓大于0.05 atm時(shí)氧離子和氧空位結(jié)合生成晶格氧過程為限速步驟,氧分壓小于0.05 atm時(shí)氧的解離吸附和擴(kuò)散過程為限速步驟。其電化學(xué)性能提高的原因?yàn)?離子導(dǎo)電相SDC的加入影響了氧原子得電子后和氧空位生成晶格氧的電荷轉(zhuǎn)移過程和氧的解離吸附和擴(kuò)散過程,加快了這兩個(gè)過程的反應(yīng)速度。當(dāng)SDC的含量達(dá)到30 wt.%時(shí),復(fù)合陰極具有最小的RP。復(fù)合后陰極材料的孔隙率增加,B0.9CFN-30SDC具有足夠的孔隙率和合適的顆粒尺寸。陰極內(nèi)部形成連續(xù)的B0.9CFN導(dǎo)電相的同時(shí)也形成了連續(xù)的SDC離子擴(kuò)散通道。
[Abstract]:Solid oxide fuel cell (SOFC) has been paid more and more attention in the world because of its clean and efficient characteristics. It has become an indispensable power device in the future energy system. Traditional SOFC is easy to cause material aging, intermaterial interface reaction and high cost input due to the high operating temperature (1000 oC). The way to solve these problems is to reduce the operating temperature of SOFC (600-800 oC). However, the ohm loss of the electrolyte, especially the polarization loss of the cathode, is also significantly increased with the decrease of operating temperature. With the development of new electrolyte materials and film technology, the problem of Ohm loss in electrolytes has been solved basically. Therefore, the catalysis of the cathode is improved. The key of reducing the operating temperature of the battery is the activity of reducing the polarization loss of the cathode. It is an important direction for the development of the medium temperature solid oxide fuel cell (IT-SOFC). The analysis of the mechanism of the cathode reaction, the optimization of the cathodic reaction step, and the improvement of the reaction rate of the cathode are an important way to improve the catalytic activity. The improvement of the new electrode material is improved. The electrochemical reaction rate is one of the main lines of current IT-SOFC research..ABO3 Co based perovskite oxide has high electronic and ion mixed conductivity and oxygen catalytic reduction ability. It has become the main cathode material of IT-SOFC. This paper studied the Co based mixed cathode materials and electrolyte complex cathode materials as the main research object. The effects of the chemical composition, microstructure and reaction mechanism of the material on the performance of the cathode were investigated. The feasible way to optimize the properties of the materials was explored by regulating the composition and structure of the materials, and the laws and the physical and chemical nature of the electrochemical properties of the materials were discussed, in order to find out the steps of the reduction reaction of the oxygen in the cathode. The key to reduce the cathodic polarization loss and improve the catalytic activity of the cathode is to provide a certain material and technical reserve for the development of IT-SOFC. The main contents are as follows: 1. the perovskite type oxide Ba Co0.7Fe0.2Nb0.1O3- Delta (BCFN) has good electrical and ionic mixed electrical conductivity, which shows good electricity as a IT-SOFC cathode material. However, the main factors affecting the properties of the material, the main steps of the oxygen reduction reaction and the main process of controlling the reaction rate are still not systematically studied. Therefore, in order to further explore the overall reaction process of the BCFN material, improve the rate of oxygen reduction reaction and improve the performance of the cathode, we choose to analyze the A bit with Sr. The feasibility and fundamental reason for its performance optimization. Ba1-x Srx Co0.7Fe0.2Nb0.1O3- Delta (B1-x Sx CFN, x=0.0,0.1,0.2,0.3,0.4) cathode material was synthesized by solid phase method. It was found that B1-x Sx CFN material formed a single-phase cubic perovskite structure after 1000 oC sintering of 10 h. After doping, the thermal expansion coefficient of the material was reduced. The polarization of the cathode was polarized. When the doping amount of Sr is reduced first and then increased, when the doping amount of Sr is x=0.2, the proper doping of RP value.Sr increases the concentration of the small polaron, which makes the small polaron and the oxygen vacancy reach the optimum concentration ratio, the electrical conductivity of the material is enhanced and the electrochemical performance is improved. The electrochemistry reaction mechanism study shows that the reaction on the cathode includes oxygen. The process of dissociation adsorption and diffusion; oxygen atoms generate oxygen ions by electrons; oxygen ions combine with oxygen vacancies to produce lattice oxygen processes at the three-phase interface and oxygen vacancies. In the range of oxygen partial pressure of 1 atm-0.01 ATM, the speed limiting step for oxygen atoms to generate oxygen ions by oxygen atoms, while the doping amount of Sr is 0.2 B0.8S0.. 2CFN sample, when oxygen partial pressure is greater than 0.1 ATM, oxygen atom generates oxygen ion process as a speed limiting step. When oxygen partial pressure is less than 0.1 ATM, the speed limit step is oxygen dissociation adsorption and diffusion process. The power density of the electrolyte supported single cell B1-xSx CFN/SDC/Ni0.9Cu0.1-SDC increases with the increase of Sr content, and then decreases, when the Sr content is contained. When the amount of X is 0.2, the best electrochemical performance.2.B0.8S0.2CFN shows excellent performance as a IT-SOFC cathode material. In order to enhance the ionic conductivity of the material and increase the rate of the oxygen reduction reaction, we have made a corresponding modification to the B0.8S0.2CFN material, and mixed the electrosolution material SDC and B0.8S0.2CFN (BSCFN) into the composite. The purpose of the cathode material is to improve the reduction process of oxygen and improve the performance of the cathode. The results show that there is no reaction between BSCFN and SDC, and the chemical compatibility is good. The thermal expansion coefficient of the composite decreases and the thermal expansion coefficient of the electrolyte SDC is closer, and the thermal matching of the cathode and the electrosolution is improved by the addition of.SDC. The structure expands the length of the three-phase interface and improves the electrochemical performance of the material. When the composite is 30 wt.%SDC, the cathode shows the best performance. At 800 oC, the RP is much smaller than the RP of the pure BSCFN cathode. The reaction mechanism of the BSCFN cathode and the BSCFN-30SDC composite cathode on the SDC electrolyte is compared by the AC impedance spectroscopy, and the results of the study are studied. It is shown that the process of oxygen ion and oxygen vacancy combined to produce lattice oxygen is a speed limiting step when oxygen partial pressure is greater than 0.05 ATM, and oxygen partial pressure is less than 0.05 ATM, the dissociation adsorption and diffusion process of oxygen is the speed limiting step. The main reason for the electrochemical activity enhancement of the composite cathode is the acceleration of the recombination reaction rate and the introduction of the SDC ion conductive phase. The process is shortened from three steps to two steps, and the oxygen atom is directly combined with the oxygen vacancy to generate lattice oxygen, which greatly improves the reaction rate. When the oxygen reduction reaction on the cathode increases.800 oC, the power density of the electrolyte supported single cell BSCFN-x SDC|SDC|Ni0.9Cu0.1-SDC is 620.37656.79717.56 and 663 m Wcm-2, respectively. The bright BSCFN-30SDC is a promising cathode material for the IT-SOFC cathode material.3. in the BCFN type electron ion mixed conductive material, the electronic conductance is often several orders of magnitude higher than the ionic conductance. Therefore, an effective way to further improve the performance of the cathode is to improve the ionic conductivity. The crystal junction of the Perovskite Cathode material is introduced by the introduction of the A ionization defect. The oxygen vacancy concentration and thermal expansion coefficient may affect the reaction process of the cathode. Therefore, we have prepared the Ba1-xCo0.7Fe0.2Nb0.1O3- Delta (B1-xCFN, x=0,0.05,0.10,0.15) series cathode materials by solid phase method. Through the XRD, SEM, AC impedance spectroscopy and single battery test, the crystal structure and thermal expansion of the A bit vacancy on the crystal structure were studied. The effect of expansion and electrochemical reaction was found. It was found that the cubic perovskite structure was completely formed after B1-xCFN 1000oC sintering for 10 hours. The cell volume was not linearly dependent on the increase of the A bit vacancy, and the largest cell volume of B0.9CFN showed that the defects of A bit ions were more than the B bit metal ions. With the increase of the vacancy, the porosity decreases and the porosity of the B0.9CFN cathode is the smallest. When the vacancy increase is 0.15 (B0.85CFN), the porosity increases because of the particle agglomeration. With the decrease of A Ba content, the polarization resistance of the interface decreases. When x=0.10, B0.90CFN at 800oC, the interfacial polarization resistance decreases about 66.2%. at oxygen partial pressure. At 0.01 ATM, the formation of lattice oxygen by oxygen ions and oxygen vacancies is a speed limiting step. When the oxygen partial pressure is 0.01 ATM, oxygen dissociation adsorption and diffusion process is the increase of oxygen vacancy caused by the speed limiting step.Ba defect. The oxygen atom is formed into lattice oxygen directly and oxygen vacancy, and the reaction rate increases and the oxygen reduction of the cathode is reduced. The reaction activity was enhanced. The impedance spectrum of the semi battery and the performance of the single cell showed that at 800 oC B0.90CFN showed a good cathodic catalytic activity.4. in order to continue to improve the ionic conductivity in the material. We adopted a method of conducting a composite ion conductive electrolyte in the material. The results showed that the composite material was prepared after 1000 oC sintering for 10 hours. The B0.9CFN and SDC still maintain their respective phase structure and have no phase formation. The electrochemical reaction mechanism studies show that oxygen ion and oxygen vacancies combine to produce lattice oxygen process when oxygen partial pressure is greater than 0.05 ATM is a speed limiting step, and oxygen partial pressure is less than 0.05 ATM, the dissociation adsorption and diffusion process of oxygen is a limiting step. The reason for the improvement of electrochemical performance is that the oxygen partial pressure is less than 0.05 ATM The addition of the ionic conductive phase SDC affects the process of charge transfer and the dissociation adsorption and diffusion process of oxygen atom after the electrons and oxygen vacancies produce the lattice oxygen. The reaction speed of the two processes is accelerated. When the content of SDC reaches 30 wt.%, the porosity of the cathode material with the minimum RP. composite is increased, B0.9CFN-30S DC has enough porosity and suitable particle size. A continuous B0.9CFN conductive phase is formed inside the cathode, and a continuous SDC ion diffusion channel is formed.

【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TM911.4
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本文編號(hào)：1785163