燃料轉換效率於多元金屬催化劑之理論計算研究：硫毒化反應與甲醇氧化反應

Abstract

本篇論文以第一性原理計算幾個不同的異質催化反應在燃料電池的應用，包括 (1) 第二章討論硫毒化與移除於BaZrO3陽極的反應， (2) 第三章討論甲醇裂解反應於鉑—石墨烯之性質， (3) 第四章討論甲醇氧化反應 (MOR) 與甲酸氧化反應 (FAOR) 於鉑三元合金 (PtRuM, M=Fe, Ti) 陽極之性質。 第二章節中，計算結果發現燃料中含有的H2S(g)會毒害催化劑表面，此為強放熱反應，然而，移除硫化物為吸熱反應。表示硫毒化為一自發性發生且難避免的反應。研究發現水的加入可以幫助硫化物的移除。除此之外，我們還列出了反應熱與自由能以及電池電動勢之間的關聯性，以此探討電池偏壓以及H2S(g)與H2O(g)的氣體分壓對於硫化反應的影響。第三章討論以石墨烯為擔體之鉑催化劑對於甲醇吸附的性質差異。根據石墨烯與鉑的結合角度可分為0o和30o角，研究結果發現甲醇可吸附在鉑團簇上，但對於鉑層吸附較弱。此種差異可以應用於材料的保護層。第四章討論配位基效應與雙官能基效應對於MOR與FAOR於鉑釕三元合金 (PtRuM, M=Fe, Ti) 上造成的反應差異。鐵的加入可使周圍電子離域化，而鈦的加入可使電子更局域化。總體來看，PtRuTi可以幫助MOR與FAOR更容易進行反應，而鐵的加入幫助不大。

Our present work utilized the first-principle calculations to investigate several important heterogeneous catalytic reactions in the fuel cells applications, including (1) sulfur poisoning and removal reactions on BaZrO3 based anodes in Chapter 2, (2) Methanol decomposition reaction on Pt layers and Pt clusters supported by graphene in Chapter 3, (3) Methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR) on PtRuM (M=Fe, Ti) trimetallic anode in Chapter 4. In Chapter 2, our computational results found that the poisoning reaction from gas-phase H2S, fuel contamination, to bulk sulfide formation in highly exothermic, while the sulfur removing reaction from sulfide to gas-phase SO2 formation by small amount of H2O is endothermic, indicating the poisoning behavior is spontaneous and rapid and hard to avoid. Additionally, we utilized the thermodynamic corrections for the Gibbs free energy calculation to reveal the effects of bias potential and partial pressures of H2S and H2O. In Chapter 3, we initially constructed Pt layers and clusters on graphene supporter and found two types of models as the beneath graphene has 0o and 30o rotations, G0-Pt (or G0-Pt37) and G30-Pt (or G30-Pt37). Furthermore, we examined methanol adsorption on them and found that methanol can tightly adsorbed on the Pt clusters while is loose on Pt layers, in comparing with their (111) surfaces. The results explain the inertness of graphene supported Pt layers that is applicable for the protection-layer materials. In Chapter 4, we examined the ligand and bifunctional effects of MOR and FAOR between PtRuM (M=Fe, Ti) ternary materials. Introducing Fe in PtRu makes the neighboring electrons more delocalized; in contrast, Ti makes PtRu more localized. As a result, PtRuTi can assist MOR and FAOR, but PtRuFe cannot.