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  • 學位論文

功能性二氧化矽氣凝膠與過渡金屬氧化物氣凝膠於節能與儲能之應用

Applications of Functional Silica Aerogels and Transition Metal Oxide Aerogels in Energy Saving and Storage

指導教授 : 呂世源
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摘要


本研究採用溶膠-凝膠法搭配不同種類乾燥技術製備二氧化矽氣凝膠、複合氣凝膠與過渡金屬氣凝膠,並成功將其分別應用於節能與儲能材料上,展現氣凝膠特殊之物理與化學特性。於節能材料研究上,分為三大部分,逐漸由室溫隔熱材研究,發展至高溫隔熱材。首先,為了降低二氧化矽氣凝膠之傳統製作成本,本研究採以多次表面疏水化改質技術,搭配常壓乾燥,取代傳統超臨界乾燥,成功製備出具有低密度與低熱傳導係數之二氧化矽氣凝膠。其中也針對單次、多次與無疏水化改質之二氧化矽氣凝膠作物理與化學特性之分析,由於具有疏水之表面結構,此氣凝膠也可於室溫環境下,在不受環境濕氣之影響下,長時間應用。 進一步為了改善純二氧化矽氣凝膠之脆性,增強其機械強度,本研究採以單一步驟之快速高分子摻合技術,於二氧化矽氣凝膠骨架中,添加高分子,成功製備具有高機械強度與低熱傳導係數之複合氣凝膠,本實驗搭配前述開發之多次表面疏水化改質技術,於常壓乾燥下製備。除了進行機械強度之量測,所摻合之高分子具有高溫300oC之熱穩定性,因此也嘗試將其應用於高溫300oC下之節能上。最後,因為純二氧化矽氣凝膠屬於低消光係數材料,不適用於高溫500oC以上之節能應用,因此本研究以快速摻合技術,搭配超臨界乾燥,將具有高溫500oC熱穩定性之奈米碳纖維添加至二氧化矽氣凝膠中,成功製備出具有高溫低熱傳導係數之複合氣凝膠,並進行長效高溫隔熱測試,其中也針對消光係數進行不同摻合比例之比較與量測。 於儲能材料應用上,本研究採以對溫度與濕氣敏感性較低之金屬非烷氧化物(金屬硝酸物與金屬氯化物),取代敏感性高之金屬烷氧化物進行溶膠-凝膠反應。為了觸發水解與縮合反應,反應過程中,添加環氧化物做為觸發反應之添加物,以達成濕凝膠之製備,最後再以超臨界乾燥,製備出具有高比表面積與介孔洞特性之過渡金屬氣凝膠。高比表面積與介孔洞特性之材料於超電容應用上具有極高之應用價值,由於氧化鈷是一種低成本之過渡金屬,並且透過電雙層與擬電容之儲能型式進行儲能,因此本研究,採以非烷氧化物為前驅物成功第一個製備出具有高比表面積與介孔洞特性之氧化鈷氣凝膠。高比表面積之氧化鈷氣凝膠提供高活性表面積進行電雙層與擬電容機制,進行儲能。製備之氧化鈷氣凝膠於200oC熱處理後,具有高比電容(623 F/g)與極佳之可逆性。本研究也製備具有微孔之氧化鈷與介孔洞氧化鈷氣凝膠進行比較,結果顯示,介孔洞可降低電解質之傳輸阻力,於超電容之應用下,展現較佳之性能。 接續氧化鈷氣凝膠於超電容之應用,由於鎳原子摻合至氧化鈷中,所形成之氧化鎳鈷(NiCo2O4)相對於純氧化鈷與純氧化鎳具有較高之電子導電性。因此本研究採以非烷氧化物為前驅物,搭配超臨界乾燥成功第一個製備出NiCo2O4氣凝膠。將其應用於超電容材料上,高比表面積與介孔洞的特性作用下,展現極高之比電容值(1400 F/g)。本實驗也針對不同熱處理溫度,與純氧化鈷與純氧化鎳進行物理特性與化學特性之比較。

並列摘要


In this dissertation, silica aerogels, composite aerogels, and transition metal oxide aerogels were synthesized via sol-gel processes with various drying procedures, and further applied in energy saving and storage. Because of the novel chemical and physical properties of aerogels, excellent performances in thermal insulation and specific capacitances were achieved. This dissertation is divided into five main parts, three in energy saving and two in energy storage. In energy saving, pure silica aerogels with low density, good hydrophobicity, low thermal conductivity were successfully synthesized via a sol-gel process with multiple surface modification (MSM) treatments followed by ambient pressure drying. The chemical and physical properties of MSM samples were compared to those of single surface modification (SSM) and non-modification (NSM) samples. Because of their hydrophobic surfaces, these silica aerogels are suitable for long term usage. The fragility of pure silica aerogels however makes it difficult to apply in monolithic form. A facile one-step polymer-incorporation sol-gel process, together with a surface modification and an ambient pressure drying processes, was further developed to prepare silica-poly(vinylpyrrolidone) composite aerogels. These composite aerogels are with high hydrophobicity (static contact angle >120o), good mechanical strength (Young’s modulus of bending >30 MPa), and low high-temperature thermal conductivity (0.063 W/m-K at 300 oC), which are critical characteristics for practical applications of aerogels, particularly in energy saving areas, for long-term usage and large scale production. Furthermore, in order to apply silica aerogels at high temperatures (300oC~500 oC), carbon nanofibers were incorporated into the mesoporous network of silica aerogels to obtain opacified monolithic aerogels at concentrations as high as 20 wt % through an accelerated-gelation sol-gel process. The incorporation of carbon nanofibers enhanced the dimensional stability of the silica aerogels and suppressed the thermal radiations that became dominant at high temperatures, to achieve an ultralow thermal conductivity of 0.050 W/m-K at 500 oC, whereas maintaining a thermal stability above 500 oC (much better than the conventional high-temperature thermal insulation materials: 0.3 W/m-K at 500 oC for glass fibers, 0.1 W/m-K at 527 oC for alumina fused brick, and 1.7 W/m-K at 527 oC for sillimante). In energy storage, metal alkoxide precursors, which were highly sensitive to heat and moisture, were replaced by non-alkoxide precursors (metal nitrate and metal chloride) to prepare transition metal oxide aerogels. High specific surface area and mesoporous structure of aerogels were ideal for supercapacitor applications. This idea was successfully demonstrated for the first time by taking cobalt oxide aerogels as an example. Cobalt oxide aerogels of excellent supercapacitive properties, including high specific capacitances (the highest ever reported for cobalt oxides, >600 F/g at a high mass loading of 1 mg/cm2) and onset frequencies, and excellent reversibility and cycle stability, were successfully synthesized with an epoxide addition procedure by using cobalt nitrate as the precursor. The present development makes possible the low cost production of high performance supercapacitors of the asymmetric type. Mesoporous materials of high specific surface area, porosity, electronic conductivity, as well as electrochemical activity, and multiple oxidation states/structures are desired for next generation supercapacitors. These requirements for material characteristics can be met by the nickel cobaltite (NiCo2O4) aerogels prepared from an epoxide-driven sol-gel process. In this work, nickel cobaltite aerogels of ultrahigh specific capacitance (1400 F/g under a mass loading of 0.4 mg/cm2 at a sweep rate of 25 mV/s from 0.04 to 0.52 V in a 1 M NaOH solution), excellent reversibility, and outstanding cycle stability were synthesized with a chloride based epoxide addition procedure for the first time. The post-gel-drying calcination temperature was found to play a critical role in producing the preferred products. Nickel cobaltite aerogels of outstanding supercapacitive properties were obtained with a starting Ni/Co ratio of 0.5 and post-gel-drying calcination temperature of 200 oC, achieving an optimal combination of composition, crystallinity, specific surface area, pore volume, and pore size. The development of the present work makes possible the low cost production of next generation, ultrahigh performance supercapacitors of the asymmetric type.

參考文獻


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被引用紀錄


余宗軒 (2012). 具磁性可回收之可見光應答光觸媒於光催化分解水產氫之研究 [master's thesis, National Tsing Hua University]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0016-2002201315140667

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