利用同步輻射原位X光吸收光譜對新興能源材料電子結構之研究

Abstract

鑑於極端的全球氣候以及逐漸缺乏的自然資源，如何有效利用現有能源和尋求永續以及可再生能源已成為世界各國家發展的主要目標。目前最迫切需要發展的是具備高效率能量轉換/產生/存儲的新能源材料。在許多重要的能源材料系統中，進行反應時的原子和電子結構變化提供了對能源材料的物理以及化學性質的基本理解。基於同步輻射X光光譜學是研究物質原子和電子結構非常有力的工具。新興的臨場技術允許能源材料在工作狀態下研究上述性質。本論文透過使用（臨場）X光光譜技術著重於幾種能源相關材料的原子和電子結構。論文分為三個部分。在第一部分，透過溶膠-凝膠旋轉塗佈法製備本質以及鉬改質的五氧化二钒智慧型薄膜。臨場X光吸收光譜結果指出在氣致（電致變色）著色時，氫（鋰）的吸附將電子填入到钒的3d t2g軌道，降低釩的電荷價態。結構的調整對於氣致變色/電致變色反應是必要的。由於本質的五氧化二钒薄膜頂端的钒-氧鍵不同，鉬改質的五氧化二钒薄膜具備更快的著色效率。論文的第二部分著重於不同官能化的奈米碳管表面二氧化錳奈米片修飾應用於超級電容之研究。由於奈米碳管表面上不同的官能團導致形成不同形態的二氧化錳奈米片，進而產生不同的電容行為。臨場X光吸收光譜結果顯示奈米碳管的碳2p π*狀態以及偽電容器材料中二氧化錳隧道尺寸對於影響電容效能是非常重要的關鍵。最後，透過（臨場）X光吸收光譜和掃描穿透X光顯微儀研究氧化鋅/三氧化二鐵核殼奈米線的水分解機制。分析結果表明，氧化鋅/三氧化二鐵核殼奈米線表現出非常強的異向性效應，進而提供更高的電子傳輸能力。臨場X光吸收光譜結果表明氧化鋅（三氧化二鐵）的電洞（電子）在光電化學條件下從鋅4p（鐵 3d）軌域轉移到鐵3d（鋅 4p）軌域。

Given extreme global climate and gradual shortage of natural resources, efficiently using current energy sources and seeking sustainable and renewable energy are the primary objectives of all countries worldwide. A new energy material that has efficient energy conversion/generation/storage is urgently demanded. In many of these important energy material systems, the change in atomic and electronic structure upon reaction provide the fundamental understanding of the physical and chemical properties of an energy material. Synchrotron based-X-ray spectroscopy is very powerful tool to investigate the atomic and electronic structures of a matter. Emerging in situ techniques allow one to look into above properties under working conditions. This thesis focuses on the atomic and electronic structures of several energy materials by using (in situ) X-ray spectroscopic techniques. The thesis is cataloged into three parts. In the first part, pristine and Mo-modified V2O5 smart thin films were prepared by the sol–gel spin coating method. In situ X-ray absorption spectroscopic (XAS) results indicate that upon gasochromic (electrochromic) coloration, adsorption of hydrogen (lithium) adds electrons to the V 3d t2g orbital, lowering the charge state of vanadium. Structural modulation is essential for the gasochromic/electrochromic reaction. The Mo-modified V2O5 film exhibits faster coloration owing to the apical V–O bond differs from that in the pristine V2O5 film. Second part of the thesis reports the different functionalized carbon nanotubes (CNT) were decorated with MnO2 nanoflakes as supercapacitors by a spontaneous redox reaction. The different morphologies of nanoflaky MnO¬2 were formed owing to different functional groups created at the surface of carbon nanotubes, leading to different capacitive behaviors. In situ X-ray absorption reveals that the C 2p π* state of CNT and the tunnel size of MnO2 in pseudo-capacitor materials are critical for the capacitive performance. Finally, the water splitting mechanism of ZnO/Fe2O3 core-shell nanowires was investigated by (in situ) XAS and scanning transmission X-ray microscopy. Analytic results demonstrated that the Fe2O3/ZnO core-shell NW exhibits strong anisotropic effects and thus provides higher electron transport ability. In situ XAS demonstrated that holes (electrons) of ZnO (Fe2O3) are transferred from Zn 4p (Fe 3d) to Fe 3d (Zn 4p) state under photoelectrochemical condition.