以超臨界流體製備金屬觸媒/奈米碳管複合材料並探討其添加對氫化鋁鋰放氫特性的影響

本研究首先分別以球磨法於氫化鋁鋰(LiAlH4)添加各種金屬、金屬氧化物與碳材並研究催化效果，找出適合的催化劑與載體，研究其添加量對催化效果之影響；再利用超臨界流體(Supercritical fluids)製備金屬觸媒/奈米碳管複合材料，以球磨法與LiAlH4均勻混合，先研究超臨界流體之製程參數對其放氫特性的影響，而後研究複合材料添加量與催化效果之關係，最後則是恆溫放氫動力學的研究，並與文獻添加中奈米Ni文獻之放氫動力學曲線做比較。分析儀器則使用X光繞射儀(X-Ray Diffractometer, XRD)與臨場X光繞射(In-situ XRD)進行晶體結構與相變化鑑定、掃描式電子顯微鏡(Scanning Electron Microscope, SEM)進行催化劑與LiAlH4球磨前後之微觀結構分析、高解析掃描穿透式電子顯微鏡(High-Resolution Scanning Transmission Electron Microscopy, HR-STEM)進行金屬顆粒於碳材上之大小及分佈分析、熱程控脫附儀(Temperature-programmed Desorption, TPD)與線上氣體量測即時分析儀(Real time gas Analyzer, RTGA)進行放氫特性研究。研究結果顯示所添加微米級之金屬如Ni、Pd、Cu、Fe等催化效果皆不顯著，然而文獻中雖然學者添加奈米Ni具有催化效果，推測是由於顆粒大小造成與文獻催化效果上的差異；金屬氧化物部分Y2O3具有些微催化效果，Nb2O5則為具有稍佳的效果，而在碳材的催化效果中以多壁奈米碳管(MWCNTs)的效果最好，添加量達50 wt%時在室溫下即可放出氫氣，石墨烯(Graphene)則次之。利用超臨界流體披覆奈米Ni於MWCNTs上形成Ni/CNT之催化效果則相當顯著，與金屬Ni之效果差異極大，10 wt% Ni/CNT催化效果更優於50 wt% MWCNTs，足以說明催化劑之尺寸效應相當大，且Ni/CNT於相同添加量下之放氫溫度低於文獻中提及效果最佳之VCl3，放氫動力學則優於文獻中之奈米Ni，證實超臨界流體法為一有效改善氫化鋁鋰放氫特性與節省催化劑使用量之製程。

關鍵字

超臨界流體；氫化鋁鋰；臨場X光繞射；熱程控脫附儀；奈米碳管；石墨烯

並列摘要

In this study, we tried to improve the hydrogen storage properties of lithium aluminum hydride (LiAlH4) by ball milling process. Additives were metal, metal oxide and carbon materials. To further improved the catalytic effect of additives, we used supercritical fluids assisted process to decorate metal particles on carbon nanomaterials, ball milled with LiAlH4 and investigated the influence of supercritical fluid parameters and metal loading on the dehydrogenation properties of LiAlH4. Analytical Instruments were X-Ray Diffractometer (XRD), In-situ XRD, Scanning Electron Microscope(SEM), High-Resolution Scanning Transmission Electron Microscopy (HR-STEM), Real time gas Analyzer (RTGA), and Temperature-programmed Desorption (TPD). The results of this study showed carbon materials had the best catalytic effect for LiAlH4 among metal, metal oxide and carbon materials, especially multi-walled carbon nanotube (with catalyst) and graphene. Moreover, compared to 50 wt% MWCNTs (with catalyst) modified LiAlH4, the dehydrogenation properties of 10 wt% Ni/CNT composites modified LiAlH4 were better.

並列關鍵字

temperature-programmed desorption (TPD) ； multi-walled carbon nanotube (MWCNTs) ； graphene ； In-situ XRD ； supercritical fluid ； lithium aluminum hydride (LiAlH4)

參考文獻

[1] International Energy Agency, Key World Energy Statistics, 2009.

[2] A. Züttel, “Materials for hydrogen storage ”, Mater. Today, 6 (2003) 24-33.

[3] L. Schlapbach, A. Züttel, “Hydrogen-storage materials for mobile applications”, Nature, 414 (2001) 353-358.

[4] B. Sakintunaa, F. Lamari-Darkrimb, M. Hirscherc, “Metal hydride materials for solid hydrogen storage:Areview”, Int. J. Hydrogen Energy, 32 (2007) 1121-1140.

[5] I. P. Jain, C. Lal, A. Jain, “Hydrogen storage in Mg: A most promising material”, Int. J. Hydrogen Energy, 35 (2010) 5133-5144.

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以超臨界流體製備金屬觸媒/奈米碳管複合材料並探討其添加對氫化鋁鋰放氫特性的影響

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