【作者】 张丹丹；

【导师】 刘慧玲；

【作者基本信息】 吉林大学 ， 物理化学， 2018， 硕士

【摘要】 近年来,直接甲醇燃料电池（DMFC）被认为是一种高效、低污染的可再生清洁能源,它具有很多优良的特性,如在室温下能快速启动、对环境友好、燃料来源丰富以及能量密度高等优点。甲醇的催化分解是直接甲醇燃料电池中关键反应步骤之一,因此寻找一种有效、稳定的阳极催化剂更是重中之重。在众多甲醇燃料电池阳极催化剂中,类富勒烯结构引起了越来越多的科学研究人员的注意,它独特的物理和化学性质在许多方面都有潜在的应用。本文我们选用类富勒烯Al₁₂N₁₂和Al₁₂N₁₂Pt纳米笼作为直接甲醇燃料电池的阳极催化剂,来模拟甲醇的分解和氧化过程。文章中采用密度泛函理论（DFT）研究了在Al₁₂N₁₂和Al₁₂N₁₂Pt纳米笼表面上甲醇的吸附、脱氢和氧化反应。在阳极催化层上,甲醇溶液主要和水氧化成二氧化碳、电子和质子。电极反应式为CH₃OH-6e^-+H₂O→6H⁺+CO₂。由反应式可以看出,水作为反应物参与阳极的氧化反应,所以我们同时还研究了在催化剂表面上水的吸附和分解。结果表明,铂金属原子可以封装在Al₁₂N₁₂纳米笼内形成Al₁₂N₁₂Pt纳米笼电催化剂。优化后的几何结构显示甲醇和水分子都更倾向于吸附在笼中铝原子的上方。甲醇在表面有两种分解过程。一种是从O-H键断裂（途径I）开始,另一种从C-O键断裂（途径II）开始。计算结果得出,与甲醇第一步分解反应中C-O键断裂相比,O-H键的断裂被认为是最有利的甲醇初始分解途径。此外,我们优化确定了所有中间体、过渡态和最终产物的反应能垒和反应能等几何结构参数。通过对甲醇分解氧化的吸附能和反应能垒等相关数据进行分析,与Al₁₂N₁₂笼催化剂相比,Al₁₂N₁₂Pt催化剂对甲醇催化分解的吸附能和能垒值略有降低,没有较大的竞争优势。尽管如此,内嵌了Pt原子的Al₁₂N₁₂笼型的电催化剂可以使整个催化循环能量变化趋于平缓。总而言之,Al₁₂N₁₂和Al₁₂N₁₂Pt纳米笼可以作为有效的催化剂,实现甲醇分子的氢分离,并将一氧化碳分子氧化成二氧化碳分子。希望本文的研究结果可以为直接甲醇燃料电池阳极催化剂材料的设计和开发提供一定的参考价值。更多还原

【Abstract】 In recent few years,the DMFC（direct methanol fuel cell）is considered to be an efficient and nonpolluting power source in virtue of its excellent characters,such as quick start-up in room temperature,environmental friendliness,abundant source as well as the high hydrogen-to-carbon ratio.The catalytic decomposition of CH₃OH is one of the crucial steps in DMFC,therefore an efficient catalyst to enhance the reaction is desirable.Among those DMFC anode materials,fullerene-like structures are drawing scientific researchers’increasing attention due to their specific physical and chemical properties with potential applications in many aspects.In this work,we selected fullerene-like Al₁₂N₁₂2 and Al₁₂N₁₂Pt nanocage as the direct methanol fuel cell’s anode catalyst to simulate the decomposition and oxidation process of methanol.The density functional theory（DFT）has been used to investigate the methanol adsorption,decomposition and oxidation as well as the water adsorption and decomposition on the clean and Pt-encapsulated Al₁₂N₁₂2 cages.On the anode catalytic layer,methanol solution is mainly oxidized by water to form carbon dioxide,electrons and protons.The electrode reaction equation is as CH₃OH-6e^-+H₂O→6H⁺+CO₂.It is shown that platinum metal atom can be encapsulated within the Al₁₂N₁₂2 cage thus forming Pt-encapsulated Al₁₂N₁₂2 cage electrocatalyst.According to the reaction results,CH₃OH and H₂O both prefer to be adsorbed on the Al atom top site.Two dehydrogenation pathways have been presented.One pathway starts with O-H bond broken（pathway I）and the other starts with C-O bond broken（pathway II）.Calculated results show that O-H bond scission is the significantly favorable reaction pathway than C-O bond scission on the cage surface.Furthermore,the structures of the intermediates,transition states and products,the corresponding energy barriers and reaction energies are confirmed.The results also show that the adsorption energies and energy barriers of CH₃OH and H₂O dissociation are cut down slightly with the aid of the platinum atom.Nevertheless,Pt-encapsulated Al₁₂N₁₂2 cage makes the potential energy surface changes smooth than pure Al₁₂N₁₂2 cage.In conclusion,Al₁₂N₁₂2 and Pt-encapsulated Al₁₂N₁₂2 cages could be served as effective catalysts to take the hydrogen atoms off the methanol and oxidize the CO molecules into CO₂ molecules.We hope that the results of this study could be useful for designing and developing of catalyst materials.更多还原