【作者】 周永军；

【导师】 吕喆；

【作者基本信息】 哈尔滨工业大学 ， 物理学， 2014， 博士

【摘要】 固体氧化物燃料电池（SOFC）以其所具有的转换效率高、燃料选择灵活和污染排放少等优点获得了越来越多的关注。目前，提高SOFC阴极的催化活性以适应更低的工作温度和寻找具有抗碳沉积和硫中毒的新型阳极材料都是该技术走向实用化需要解决的问题，钙钛矿型的稀土-过渡族复合氧化物是解决这两个问题的首选材料。稀土元素的替代、碱土元素的掺杂和引入贵金属催化剂都是优选和改善阴极和阳极材料性能的几种主要的实验研究手段，在这方面已经有大量实验结果的报道。但是，目前关于不同材料之间所存在的性能差异现象的起因，贵金属催化剂在阴极氧还原过程中的作用，以及LaCrO3基氧化物比Ni基阳极更耐硫毒化的现象等方面还缺乏足够详实的微观机制分析。事实上，对于电极反应机制、不同表面位置的催化活性以及它们对表面结构和缺陷的依赖性等方面的信息目前仍难以完全通过实验测量直接获得，这方面实验观测的缺失需要借助第一性原理计算加以弥补。第一性原理计算模拟能够提供电子结构、几何参数、相关能量和中间吸附物等多种信息，是一种有助于阐明电极反应机制的研究方法。本论文研究了气体分子在ABO3型氧化物表面的吸附机制，验证了贵金属的引入促进了O2分子解离吸附的实验结论，阐明了LaCrO3基阳极材料比传统的Ni基阳极具有更好抗硫性的原因。基于密度泛函理论的第一性原理计算了体相LaMnO3的电子结构以及以6层薄片(Slab)周期结构为模型，重点研究了Ag原子与LaMnO3(001)表面相互作用的电子性质，同时对O2分子在Ag预吸附和纯净的LaMnO3(001)表面的吸附情况进行对比分析，进一步揭示O2-LaMnO3吸附体系相互作用机理。研究贵金属原子（Ag、Pt、Pd）在La1xSrxMnO3(001)表面的吸附性能及O2分子在La1xSrxMnO3(001)表面的吸附和解离机制。研究贵金属原子吸附对O2分子在La1xSrxMnO3(001)表面吸附的催化作用，进而探讨贵金属原子和O2分子间相互作用机理；研究结果表明贵金属原子预吸附表面后，使O2分子的吸附能由0.495eV提高到0.591～1.118eV，键长和键布局的结果表明贵金属原子的预吸附促进O2分子的解离，从理论上验证了贵金属的负载促进了O2分子解离吸附的实验结论。基于密度泛函理论的GGA+U方法对PrMnO3(001)面的表面性能及氧在表面的吸附性质进行了探讨，结果表明PrO-终端面的表面褶皱大于MnO2-终端面，说明PrO-终端面比MnO2-终端面更粗糙；两个终端面第一层和第二层的距离都是收缩的；相反，对于两个终端面的第二层和第三层的距离都是膨胀的。在PrMnO3(001)的MnO2-终端和PrO-终端两个面的氧空位形成能分别为2.764eV和3.624eV，这表明在MnO2-终端面更容易产生氧空位。体相PrMnO3的氧空位形成能为3.226eV，Sr掺杂体相PrMnO3后，氧空位形成能减小到0.333eV。采用密度泛函理论研究了H2S、SH和S在钙钛矿氧化物LaCrO3(001)表面的吸附机制。H2S分子更容易吸附在LaO-终端面的O位，H2S在表面吸附后，电子由衬底向吸附物转移，同时H2S分子内部电荷重新分布。SH和S更容易吸附在Cr位，键布局和态密度的结果表明吸附原子和表面Cr原子形成杂化；预测了硫基物在LaCrO3(001)表面的吸附能的顺序为H2S＜SH＜S。从吸附能的角度，分析了LaCrO3相比于传统的Ni-YSZ阳极材料表现出更好的抗硫性的原因。更多还原

【Abstract】 Solid oxide fuel cell (SOFC) as power generator has attracted considerable attention due to their high energy conversion efficiency, excellent fuel flexibility and low level of pollutant emission. At present, increasing the SOFC cathode catalytic activity at lower temperature and looking for new anode materials with resistance to carbon deposition and sulfur poisoning are needed to solve the problem for the practical technology. Rare earth-transition metal composite perovskites oxide is the preferred material to solve the problems. Rare earth element replacement, alkaline element doping and noble metal catalysis loading are main experimental means for optimization and improvement of cathode and anode material performance. A large number of experimental results have been reported. However, detailed microscopic mechanism analysis is still lack about the cause of the performance difference of different material, the role of noble metal catalysis for oxygen reduction reaction in cathode, and LaCrO3oxide is more resistant to sulfur poisoning phenomenon than Ni-based anode. In fact, the reaction mechanism of electrode, catalytic activity of different surface positions and their reliance on surface structure and defect, which are difficult to be directly obtained by experimental measurement. The first-principles calculation can make up for the loss. The first-principle calculation has proved to be a powerful tool to elucidate reaction mechanism as the technique can provide electronic structure, geometrical parameters, related energy and adsorbed intermediate species. The adsorption mechanisms of gas molecules on ABO3-type oxide surface are studied in paper. The experimental conclusion which noble metal loading promoted the O2molecule dissociation adsorption is verified. We have clarified the reason which LaCrO3based anode material is more sulfur-tolerant than traditional Ni-based anode.Bulk LaMnO3electronic structure has been investigated using first-principles calculation based on the density functional theory. We calculate electronic properties of interaction between Ag atom and LaMnO3(001) surface with6layer slab model. The comparative analysis of O2molecule adsorption properties on pure LaMnO3(001) surface and Ag loaded surface is implemented. We reveal the interaction mechanism of the O2-LaMnO3adsorption system.The adsorption properties of noble metal atoms (Ag、Pt、Pd) on La1xSrxMnO3(001) and the mechanisms of O2molecule adsorption and dissocation on La1xSrxMnO3(001) surface have been investigated. We further analysis noble metal catalytic role for O2molecule adsorption and the interaction mechanisms between O2molecule and noble metal atoms. Results indicate that the adsorption energies of O2molecule increase from0.495eV to0.591～1.118eV due to pre-adsorbed noble metal atoms. Bond length and bond population show the pre-adsorbed noble metal atoms facilitate O2molecule dissociate to O atoms. We theoretically verified the experiment conclusion that the loaded noble metals promoted the O2molecule dissociative adsorption.We have investigated surface properties of the PrMnO3(001) and oxygen adsorption on surface using density functional theory with the generalized gradient approximation (GGA+U) method. The surface rumpling of the PrO-terminated surface is much larger than that of the MnO2-terminated surface and PrO-terminated surface is rough than MnO2-terminated surface. Both the PrO-and MnO2-terminated surfaces display reduction of interlayer distance of the first layer and the second layer, expansion of the second layer and the third layer. The formation energies of oxygen vacancy on MnO2-terminated surface and PrO-terminated surface are2.764eV and3.624eV, respectively. This implies that the oxygen vacancy occurs more readily at the MnO2-terminated surface as compared with the PrO-terminated surface. The formation energy of oxygen vacancy in bulk PrMnO3is3.226eV. The oxygen vacancy formation energy of bulk PrMnO3decreases from3.226eV to0.333eV due to the doped Sr.Density functional theory calculations are employed to investigate the adsorption of H2S、SH and S on the (001) surface of LaCrO3. H2S molecule adsorption is found to be stable with H2S binding preferentially at O site on the LaO-terminated surface. The adsorption of H2S molecule leads to the electrons transferring from the substrate to the molecule and the charges rearrangement within the molecule. SH and S are found to be preferentially adsorbed at the Cr site. Both bond population and PDOS analysis show that there is hybridization between adatoms and surface Cr atoms. We predict the adsorption energies of sulfur-containing species increase following the sequence H2S<SH<S on LaCrO3(001) surface. We analyze the reason that LaCrO3is more sulfur-tolerant than traditional Ni-based anode materials from the angle of adsorption energy.更多还原