本文選題：密度泛函理論 + 質(zhì)子交換膜燃料電池　； 參考：《河南師范大學(xué)》2017年碩士論文

【摘要】：由于能源危機(jī)和環(huán)境問題,燃料電池在工業(yè)和科技領(lǐng)域都受到了相當(dāng)?shù)年P(guān)注。在各種不同的燃料電池中,質(zhì)子交換膜燃料電池(PEMFCs)被認(rèn)為可以作為未來零/低排放交通工具和便攜能源站中潛在的能源裝置。PEMFCs中傳統(tǒng)的電極催化劑是Pt納米顆粒負(fù)載在碳黑上。而在電化學(xué)反應(yīng)環(huán)境中碳黑容易被腐蝕,Pt基催化劑不穩(wěn)定且易CO中毒,而且Pt昂貴稀缺,對Pt的過度依賴限制了質(zhì)子交換膜電池在工業(yè)中的推廣應(yīng)用。因此,尋找廉價且高效的電催化劑是燃料電池發(fā)展道路上必須深入解決的問題。以過渡金屬碳化物(TMC)為載體的負(fù)載型納米體系,通過對載體以及負(fù)載金屬的優(yōu)化設(shè)計有望達(dá)到這個目的。本文采用基于密度泛函理論的第一性原理方法,首先研究了Ti C不同低指數(shù)面在各種化學(xué)勢和表面缺陷環(huán)境中的穩(wěn)定性和催化活性,隨后又在Ti C(001)表面上負(fù)載了小Pt團(tuán)簇(Pt_n,n=1~5),研究了它們的相互作用以及電子結(jié)構(gòu),最后構(gòu)建了單層Pd負(fù)載在Ti C(001)的表面,并計算了O_2在上面的吸附、擴(kuò)散和解離,從而為設(shè)計高效廉價的催化劑提供了理論參考。主要工作及結(jié)果如下:(1)研究了Ti C在不同晶向、截止面和化學(xué)勢情況下的表面能,同時也考慮了不同密度的表面缺陷的影響。結(jié)果表明:表面馳豫會使(001)和(110)表面出現(xiàn)褶皺,引起了(111)表面的收縮。Ti C低指數(shù)表面的相對穩(wěn)定性會隨著碳化學(xué)勢、表面缺陷和空位的密度的不同而不同,費(fèi)米能級附近的電子結(jié)構(gòu)也會受空位的影響,在實際應(yīng)用中這些都會影響到納米顆粒的形貌以及催化表現(xiàn)。(2)研究了小Pt團(tuán)簇(Pt_n,n=1~5)和Ti C(001)表面的相互作用。結(jié)果顯示,在Ti C(001)表面上單個Pt原子易于吸附在C的頂位,同時一個Pt_2團(tuán)簇傾向于形成二聚體,Pt_3團(tuán)簇形成一個線性的結(jié)構(gòu)。對于Pt_4團(tuán)簇,形成三維結(jié)構(gòu)和二維四邊形結(jié)構(gòu)具有幾乎相同的穩(wěn)定性。相比于二維構(gòu)型的Pt_5團(tuán)簇,在Ti C(001)表面上三維構(gòu)型的Pt_5團(tuán)簇更穩(wěn)定。小Pt團(tuán)簇吸附在Ti C(001)表面上伴隨著明顯的電荷轉(zhuǎn)移,使其帶上了負(fù)電。最后,計算了吸附Pt原子的d帶中心,發(fā)現(xiàn)具有2D構(gòu)型的Pt_n/Ti C催化劑具有較高的催化ORR活性的性質(zhì),可以被用作電極催化劑。(3)研究了不同覆蓋度下O_2在單層Pd負(fù)載在Ti C(001)面上的吸附,擴(kuò)散和解離。結(jié)果表明:Pd和C之間的強(qiáng)相互作用可以保證Pd單層的穩(wěn)定而不會發(fā)生團(tuán)聚現(xiàn)象。襯底Ti C(001)的存在大大地改變了Pd單層的電子結(jié)構(gòu)。負(fù)載的單層Pd的d帶中心位于費(fèi)米能級之下2.38 e V處,這跟Pt(111)表面原子的幾乎一樣。另外,MLPd跟Ti C(001)襯底的結(jié)合可以提高其吸附O_2的效率,同時減弱對O的吸附強(qiáng)度。O_2在其上的解離勢壘也很小,跟O_2的覆蓋率關(guān)系不大。O_2和O在MLPd/Ti C(001)表面相鄰的Hollow位之間的擴(kuò)散都很容易,因此該模型可以作為一個高效的ORR催化劑。
[Abstract]:Due to energy crisis and environmental problems, fuel cells have received considerable attention in industry and technology. Proton exchange membrane fuel cells (PEMFCs) are considered as potential energy devices in future zero / low emission vehicles and portable energy stations. The traditional electrode catalyst for PEMFCs is Pt nanoparticles loaded on carbon black. However, in the electrochemical reaction environment, carbon black is liable to be corroded by Pt-based catalysts, which is unstable and prone to CO poisoning, and Pt is expensive and scarce. The excessive dependence on Pt limits the application of proton exchange membrane batteries in industry. Therefore, finding cheap and efficient electrocatalysts is a problem that must be solved in the development of fuel cells. The supported nanosystem with transition metal carbide (TMC) as the carrier is expected to achieve this goal through the optimum design of the carrier and the loaded metal. In this paper, the first principle method based on density functional theory is used to study the stability and catalytic activity of different low exponent surfaces of tic in various chemical potential and surface defect environments. The interaction and electronic structure of Pt clusters were studied. Finally, the surface of single-layer PD loaded on TiCn001) was constructed, and the adsorption, diffusion and dissociation of O2 on the surface were calculated. This provides a theoretical reference for the design of efficient and cheap catalysts. The main work and results are as follows: (1) the surface energy of tic at different crystal directions, cutoff surfaces and chemical potentials is studied, and the influence of surface defects of different densities is also considered. The results show that the surface relaxation results in the appearance of folds on the surface of C001) and Y110), which causes the contraction of the surface. The relative stability of the low exponent surface of Ti C will vary with the carbon chemical potential, the density of the defects and the density of the vacancy, and the relative stability of the surface will vary with the carbon chemical potential, the density of the surface defect and the vacancy. The electronic structure near the Fermi energy level is also affected by the vacancies. In practical applications, these influences on the morphology and catalytic performance of the nanoparticles. The results show that a single Pt atom is easy to be adsorbed on the top of C on the TiCn001) surface, and a Pt_2 cluster tends to form a dimer / Pt3 cluster to form a linear structure. For Pt_4 clusters, the formation of three-dimensional and two-dimensional quadrilateral structures has almost the same stability. Compared with Pt_5 clusters with two-dimensional configuration, Pt_5 clusters with 3D configuration are more stable on Ti Cn001) surface. Small Pt clusters are adsorbed on the surface of TiCn001) with obvious charge transfer, which results in negative charge. Finally, the d band center of Pt atom adsorbed was calculated. It was found that Pt_n/Ti C catalyst with 2D configuration had higher catalytic activity of ORR. The adsorption, diffusion and dissociation of O _ (2) on the surface of single-layer PD supported on TiCn001) have been studied. The results show that the strong interaction between the two monolayers can ensure the stability of PD monolayer without agglomeration. The electronic structure of PD monolayer was greatly changed by the existence of Ti Cn001). The d band center of the monolayer PD is located at 2.38 EV below the Fermi level, which is almost the same as that of the surface atom of Ptn111). In addition, the combination of MLPd and TiCn001) substrates can improve the efficiency of O _ 2 adsorption, and weaken the adsorption intensity of O _ 2. The dissociation barrier of O _ 2 on it is also very small. The diffusion of O _ (2) and O between the adjacent Hollow sites on the surface of MLPd/Ti C _ (001) is very easy, so the model can be used as an efficient ORR catalyst.
【學(xué)位授予單位】：河南師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM911.4

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本文編號：1943879