- 學位論文
奈米複合碳材應用於能源元件之研究
Nano-Carbon Composites for Energy Device Applications
摘要
本研究利用觸媒催化化學氣相沉積法，搭配乙炔氣及奈米鎳金屬分別做為碳源及觸媒，將奈米碳管均勻裝飾於聚丙烯氰(polyacrylonitrile)活性碳纖維表面，形成擁有雙階層粗糙表面(奈米碳管與微米級活性碳纖維)之三維複合碳結構。表面水滴接觸角測試証實植入奈米碳管能改變表面結構，提升固、液、氣三相接觸面之不連續性，減少液滴與基材表面接觸面積，將原本疏水介面轉換為超疏水介面。此外，本研究搭配次微米之二氧化矽球及奈米碳管於活性碳纖表面，開發出一種穩定且具有低水滴遲滯角之超疏水結構。吾人利用改良之Cassie-Baxter模型進行分析，以探討三階層粗糙度對固液接觸面比例之影響。 另一方面，複合碳材於硫酸電解質中之電化學行為，證實奈米碳管的植入不但改善電極內部之分散電容效應及電位降，也同時提供更多高效率充放電下之電雙層電容。批覆奈米碳管於碳紙上之複合碳材，經氣相氧化法表面改質後，擁有不同之表面氧化程度。實驗結果顯示，表面氧化改質可提升複合碳材之親水性及電化學比電容量，要歸因於氧化處理後，碳材表面擁有更多活性位置提供電雙層吸附(電雙層電容)及氧化還原反應(假電容)。除了氧化改質外，本研究利用以下流程進行胺官能機團之批覆，包括(i) 化學氧化、(ii) 醯氯化處理、(iii) 胺化改質。經胺化改質之複合碳材經測試，其擁有高電化學比電容量、高充放電效率、高穩定性與高庫倫效率。 第三部分，本研究利用新穎之微波輔助還原法，合成奈米級電化學白金觸媒於複合碳材表面。在經過1000次電化學循環測試後發現，白金觸媒不只擁有高電化學活性(高電化學比表面積)，更呈現高循環穩定性。一維線材結構之奈米碳管，其高導電性有助於白金觸媒更有效地進行電化學氧化還原反應。換句話說，奈米碳管之存在，不只做為觸媒載體，並能提供觸媒與氣體擴散層間之電子傳導通道。此外，本研究以利用微波輔助還原法製備不同之高活性及高穩定性之雙金屬觸媒(白金-鈷、白金-錫)，並應用於甲醇氧化反應(白金-鋅)。實驗結果證實，兩階段之微波輔助還原法能有效提升雙金屬觸媒之活性、抗毒化能力及長效穩定性。
並列摘要
A chemical vapor deposition was employed for decorating the carbon nanotubes (CNTs) onto polyacrylonitrile-based active carbon fabrics (ACF), using acetylene and Ni nanoparticle as carbon precursor and catalyst, respectively. The contact angle of water significantly increases which confirms that the wettability of carbon fabric has shifted to superhydrophobicity due to the structural transformation. Besides, a stable superhydrophobic surface with low contact angle hysteresis using microscale carbon fabrics decorated with submicroscale SiO2 spheres and CNTs is created. A modified Cassie-Baxter model analyzes that the combined effect of SiO2 spheres and CNTs contributes a high area fraction of a water droplet in contact with air, leading to superhydrophobicity. On the other hand, the electrochemical behavior of the carbon electrodes in H2SO4 indicated that the presence of nanotubes not only decreases the distributed capacitance effect and IR drop but also induces double-layer formation and high-rate capability. Gaseous oxidation of carbon papers (CPs) decorated with CNTs with varying degrees of oxidation was conducted to investigate the influence of surface oxides on the performance of electrochemical capacitors. Both superhydrophilicity and specific capacitance of the oxidized CNT/CP composites were found to increase upon oxidation treatment. Amino-functionalization of CNTs attached to CP has been achieved using one synthesis protocol: (i) chemical oxidation, (ii) acyl chlorination, and (iii) amidation. The N-modified CNT/CP capacitor exhibits an enhanced capacitance, high-rate capability, and capacitance stability with high coulombic efficiency. A facile microwave-assisted polyol (MP) approach to synthesize catalysts on carbon composite was presented. The Pt deposits, with an average size of 3–5 nm were uniformly coated over the surface of oxidized CNTs. The Pt catalysts showed not only fairly good electrochemical activity but also durability after a potential cycling of > 1000 cycles. CNTs significantly reduced both connect and charge transfer resistances. With the aid of CNTs, well-dispersed Pt catalysts enable the reversibly rapid redox kinetic since electron transport efficiently passes through a one-dimensional pathway. Bimetallic catalysts with high and stable electrochemical activity toward sulfuric acid (Pt-Co, Pt-Sn) and methanol oxidation (Pt-Zn) were proposed. Experimental results confirmed that two-stage MP synthesis enables the improvement of electrochemical activity, antipoisoning ability and long-term durability of the binary catalyst.