碳化钛负载的高效廉价燃料电池纳米催化剂的模拟与设计

发布时间：2018-05-27 21:43

本文选题：密度泛函理论 + 质子交换膜燃料电池　；参考：《河南师范大学》2017年硕士论文

【摘要】：由于能源危机和环境问题,燃料电池在工业和科技领域都受到了相当的关注。在各种不同的燃料电池中,质子交换膜燃料电池(PEMFCs)被认为可以作为未来零/低排放交通工具和便携能源站中潜在的能源装置。PEMFCs中传统的电极催化剂是Pt纳米颗粒负载在碳黑上。而在电化学反应环境中碳黑容易被腐蚀,Pt基催化剂不稳定且易CO中毒,而且Pt昂贵稀缺,对Pt的过度依赖限制了质子交换膜电池在工业中的推广应用。因此,寻找廉价且高效的电催化剂是燃料电池发展道路上必须深入解决的问题。以过渡金属碳化物(TMC)为载体的负载型纳米体系,通过对载体以及负载金属的优化设计有望达到这个目的。本文采用基于密度泛函理论的第一性原理方法,首先研究了Ti C不同低指数面在各种化学势和表面缺陷环境中的稳定性和催化活性,随后又在Ti C(001)表面上负载了小Pt团簇(Pt_n,n=1~5),研究了它们的相互作用以及电子结构,最后构建了单层Pd负载在Ti C(001)的表面,并计算了O_2在上面的吸附、扩散和解离,从而为设计高效廉价的催化剂提供了理论参考。主要工作及结果如下:(1)研究了Ti C在不同晶向、截止面和化学势情况下的表面能,同时也考虑了不同密度的表面缺陷的影响。结果表明:表面驰豫会使(001)和(110)表面出现褶皱,引起了(111)表面的收缩。Ti C低指数表面的相对稳定性会随着碳化学势、表面缺陷和空位的密度的不同而不同,费米能级附近的电子结构也会受空位的影响,在实际应用中这些都会影响到纳米颗粒的形貌以及催化表现。(2)研究了小Pt团簇(Pt_n,n=1~5)和Ti C(001)表面的相互作用。结果显示,在Ti C(001)表面上单个Pt原子易于吸附在C的顶位,同时一个Pt_2团簇倾向于形成二聚体,Pt_3团簇形成一个线性的结构。对于Pt_4团簇,形成三维结构和二维四边形结构具有几乎相同的稳定性。相比于二维构型的Pt_5团簇,在Ti C(001)表面上三维构型的Pt_5团簇更稳定。小Pt团簇吸附在Ti C(001)表面上伴随着明显的电荷转移,使其带上了负电。最后,计算了吸附Pt原子的d带中心,发现具有2D构型的Pt_n/Ti C催化剂具有较高的催化ORR活性的性质,可以被用作电极催化剂。(3)研究了不同覆盖度下O_2在单层Pd负载在Ti C(001)面上的吸附,扩散和解离。结果表明:Pd和C之间的强相互作用可以保证Pd单层的稳定而不会发生团聚现象。衬底Ti C(001)的存在大大地改变了Pd单层的电子结构。负载的单层Pd的d带中心位于费米能级之下2.38 e V处,这跟Pt(111)表面原子的几乎一样。另外,MLPd跟Ti C(001)衬底的结合可以提高其吸附O_2的效率,同时减弱对O的吸附强度。O_2在其上的解离势垒也很小,跟O_2的覆盖率关系不大。O_2和O在MLPd/Ti C(001)表面相邻的Hollow位之间的扩散都很容易,因此该模型可以作为一个高效的ORR催化剂。
[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.
【学位授予单位】：河南师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM911.4

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