發(fā)布時(shí)間：2018-02-13 20:46

  本文關(guān)鍵詞： 質(zhì)子交換膜燃料電池 氧還原反應(yīng)機(jī)理 密度泛函理論 缺陷石墨烯 自由能　出處：《內(nèi)蒙古工業(yè)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：質(zhì)子交換膜燃料電池(PEMFC)可以通過電化學(xué)反應(yīng)將化學(xué)能直接轉(zhuǎn)化成電能,并且因其轉(zhuǎn)換效率高,無污染等特點(diǎn),在過去的幾十年里引起了廣泛的關(guān)注。目前,貴金屬鉑(Pt)基催化劑為PEMFC的主要催化劑。但因其儲(chǔ)量低,成本高,耐久性差等問題嚴(yán)重阻礙了PEMFC廣泛的商業(yè)應(yīng)用。因此,開發(fā)廉價(jià)高效的非貴金屬或非金屬電催化劑來催化氧還原反應(yīng)(Oxygen Reduction Reaction:ORR)已成為PEMFC實(shí)現(xiàn)商業(yè)化的關(guān)鍵。近幾年,由于摻雜石墨烯以及碳納米管等sp~2納米碳材料具有優(yōu)異的導(dǎo)電性和高的比表面積等優(yōu)點(diǎn),已經(jīng)成為了非貴金屬或非金屬ORR電催化劑的重要選項(xiàng)和研究熱點(diǎn)。本論文結(jié)合量子化學(xué)計(jì)算和電化學(xué)熱力學(xué)模型分析,系統(tǒng)地研究了不同非貴金屬或非金屬摻雜缺陷石墨烯構(gòu)成的ORR電催化劑的催化性能,以及探討了摻雜含缺陷石墨烯具有催化活性的內(nèi)在機(jī)制。論文主要內(nèi)容和研究結(jié)果如下:1.磷(P)摻雜缺陷石墨烯作為氧還原反應(yīng)電催化劑的理論研究。通過形成能的計(jì)算,P摻雜雙缺陷石墨烯要比P摻雜單缺陷和Stone Wales缺陷石墨烯更易形成。針對(duì)P摻雜雙空位缺陷石墨烯,展開ORR反應(yīng)機(jī)理和自由能曲線的研究。研究結(jié)果表明,O_2分子可以有效的吸附在電催化劑表面,滿足了ORR發(fā)生的前提。隨后,在ORR機(jī)理研究中發(fā)現(xiàn)活化O_2分子可以通過三個(gè)ORR競(jìng)爭(zhēng)反應(yīng)路徑完成4e-過程且轉(zhuǎn)化為最終產(chǎn)物H_2O分子。其中動(dòng)力學(xué)最佳的路徑是O_2分子氫化形成OOH,OOH氫化形成O+H_2O的過程。這個(gè)路徑的決速步驟是最后一步,即OH氫化生成H_2O的過程。從ORR自由能曲線圖中可以得出,每一步基元反應(yīng)的吉布斯自由能都是負(fù)值,說明反應(yīng)是自發(fā)進(jìn)行的放熱過程。結(jié)合外電勢(shì)的影響,預(yù)測(cè)該體系的工作電壓是0.27 V。2.硅(Si)摻雜缺陷石墨烯作為氧還原反應(yīng)電催化劑的理論研究。研究結(jié)果表明,對(duì)于Si摻雜雙缺陷石墨烯,O_2分解和OOH氫化成O+H_2O是反應(yīng)的最佳路徑,O原子氫化生成OH是最佳路徑中的決速步驟。而對(duì)于Si摻雜單缺陷石墨烯,同一路徑下,決速步驟為第二個(gè)H_2O分子生成且需要克服相當(dāng)高的勢(shì)壘。這說明相同非金屬摻雜不同缺陷石墨烯構(gòu)型會(huì)導(dǎo)致不同的ORR催化活性發(fā)生。對(duì)于雙缺陷石墨烯,反應(yīng)的主要活性位點(diǎn)是Si以及與Si成鍵的四個(gè)C原子,這一點(diǎn)從電荷轉(zhuǎn)移和差分電荷密度可以得到證明。3.錳(Mn)和磷(P)共摻雜缺陷石墨烯作為氧還原反應(yīng)電催化劑的理論研究。結(jié)果表明,對(duì)于MnP_x(x=1-4)共摻雙缺陷石墨烯,MnP_2是最穩(wěn)定的結(jié)構(gòu)。針對(duì)MnP_2共摻雙缺陷石墨烯,反應(yīng)機(jī)理研究表明MnP_2和它相鄰的六個(gè)C原子構(gòu)成了催化活性中心,且在酸性介質(zhì)中以4e-轉(zhuǎn)移過程完成ORR催化反應(yīng)。動(dòng)力學(xué)最佳反應(yīng)路徑是O_2分子氫化形成OOH,然后OOH氫化形成O+H_2O的過程。決速步驟是第二個(gè)H_2O分子的形成。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) can convert chemical energy directly into electric energy by electrochemical reaction, and has attracted wide attention in the past decades because of its high conversion efficiency and no pollution. Pt-based catalyst of noble metal platinum is the main catalyst of PEMFC. However, due to its low storage, high cost, poor durability and other problems, the wide commercial application of PEMFC is seriously hindered. The development of cheap and efficient non-precious metal or non-metallic electrocatalysts to catalyze oxygen Reduction reaction: orr has become the key to the commercialization of PEMFC. Because of the excellent electrical conductivity and high specific surface area of sp~2 nano-carbon materials, such as graphene and carbon nanotubes, It has become an important option and research hotspot in non-noble metal or non-metallic ORR electrocatalysts. The catalytic properties of ORR electrocatalysts with different non-noble metal or non-metal doped graphene defects were systematically studied. The internal mechanism of the catalytic activity of doped graphene with defects was also discussed. The main contents and results of this paper are as follows: 1. The theoretical study of doped graphene with defect as electrocatalyst for oxygen reduction reaction. P doped double defect graphene is easier to form than P doped single defect and Stone Wales defect graphene. The mechanism of ORR reaction and the free energy curve were studied. The results showed that the molecule of ORR could be effectively adsorbed on the surface of the electrocatalyst, which satisfied the premise of the occurrence of ORR. In the study of ORR mechanism, it was found that the activation of O _ s _ 2 could be completed through three ORR competitive reaction paths and transformed into the final product H _ 2O. The best path of kinetics was that O _ 2 molecules were hydrogenated to form O _ H _ 2O via hydrogenation of O _ (2) O _ (2) O _ (2) O _ (2) O _ (2) O _ (H _ 2O). The speed step of this path is the last step, From the curve of ORR free energy, the Gibbs free energy of each step of the elementary reaction is negative, which indicates that the reaction is a spontaneous exothermic process. It is predicted that the operating voltage of the system is 0.27 V. 2.The theoretical study of the doped graphene with silicon oxide as the electrocatalyst for oxygen reduction reaction shows that, The decomposition of Si-doped graphene O _ 2 and the hydrogenation of OOH to O _ H _ 2O are the best path for the reaction. The hydrogenation of O atom to OH is the critical step in the optimal path, while for Si doped graphene with single defect, the same path is obtained. The second H2O molecule is generated and the high potential barrier must be overcome. This indicates that the same nonmetallic doped with different defects graphene configuration will lead to different ORR catalytic activity. The main active sites of the reaction are Si and four C atoms bonded to Si. This point can be proved by charge transfer and differential charge density. The structure of MNP _ XX _ XX _ (1-4) is the most stable structure. For MnP_2 co-doped with double defect graphene, the reaction mechanism studies show that MnP_2 and its adjacent six C atoms form the catalytic active center. The ORR catalytic reaction was completed by 4e- transfer process in acid medium. The best reaction path of Kinetics is the hydrogenation of O _ (2) to O _ (H _ (2)) and the hydrogenation of OOH to O _ (H _ 2O). The final step is the formation of the second H _ 2O.
【學(xué)位授予單位】：內(nèi)蒙古工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O643.36;TM911.4

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本文編號(hào)：1509063