- 學位論文
量子分析鋰-空氣電池陰極鉑氮觸媒在奈米碳管/石墨烯的催化機制
Quantum Analysis on the Pt-N Catalytic Mechanism at the Carbon Nano Tube/Graphene Cathode of Lithium-Air Batteries
摘要
本研究希望藉由量子力學分析鋰空氣電池(Li-air batteries)中空氣極(air electrode)部分，以奈米碳管及graphene等導電性良好、大表面積之材料取代傳統多孔性碳材料，以提升其電子傳導能力及化學催化性能。傳統鋰空氣電池使用多孔性碳黑(carbon black)混合白金作為工作電極，其導電能力由於金屬催化物與碳黑界面問題，造成電子散失，使催化氧還原反應限制了鋰空氣電池在整體上的效率。奈米碳管摻雜白金和氮，即藉由白金及氮的摻雜改變碳管性質，進而在催化氧氣同時順勢將電子導入，使白金或是摻雜後的碳管催化能力提升。故本論文研究此材料(Pt-doped and N-doped Carbon nanotube)特性來提高鋰空氣電池效率。 在鋰空氣電池中，氧氣的還原速率將決定整體鋰空氣電池之效率，而氧氣催化速率又與白金和空氣極電子導電能力有關。因此本研究採用奈米碳管為空氣極材料摻雜白金方式使電子從白金注入奈米碳管更為容易，加上奈米碳管介於半導體到導體的導電能力與不須考量白金與奈米碳管接觸面界面電子傳導等問題，大大的提升氧氣的催化與整體鋰空氣電池效率。本論文另一嶄新研究為利用氮來取代白金摻雜碳管而使用於電極上，預期可以減少整體花費。本論文加以詳細評估其可行性，並與原白金性能比較。 本研究利用第一原理計算，建立分子尺度的奈米碳管摻雜白金及氮及奈米碳管吸附白金、並加入石墨烯(graphene)模型等，以時間獨立（time independent）的密度泛函理論（density functional theory, DFT），搭配B3LYP（Becke, three-parameter, Lee-Yang-Parr）交換相關泛函，來計算各種不同基底碳材的能隙寬、電子軌道與態密度分布（density of states, DOS）、電子雲分布，並藉由計算後之吸附能比較催化能力，分析電極在微觀下觸媒催化的各種現象。
並列摘要
The most critical process in both low temperature fuel cells and Li/air batteries is the oxygen reduction at the cathode of these electrochemical devices. The rate-limited process of the catalytic mechanism is extremely important to be fully understood in the nanoscale transport phenomena. This research intends to use computational quantum mechanics to simulate the detailed processes, including oxygen molecule adsorption, water molecule adsorption, and hydroxyl production, on a platinum atom which is doped on the surface of carbon nanotubes (CNT) and graphene nanoribbons (GNS). They are also doped with nitrogen atoms for decreasing the catalyst cost. We use the computational techniques to simulate the catalytic mechanism of the oxygen reduction at the cathode. The 1st step is to dope Pt atoms onto the CNT surface and to dope N atoms onto the graphene nanoribbons, then to observe the phenomenon of the novel electrode adsorbing the oxygen molecule in the atomistic scale. The 3rd step is to break the bond between two oxygen atoms and to generate a hydroxyl radical with one of the hydrogen atoms in the nearby water molecule. It is possible to predict the bonding energy and bond length between atoms and hence the easiness of breaking and recombination of the bonds. The detailed catalytic performance of the novel catalyst at nano scale is predicted in this research.