以均苯四甲酸合成雙金屬鎳-鈷金屬有機框架應用於不對稱超級電容器之研製

Abstract

超級電容器(Supercapacitors)依其能量儲存機制可分為電雙層電容器(Electrical double-layers capacitors, EDLC)與擬電容器(Pseudocapacitor)兩大類，比起傳統的電容器擁有更優異的比功率、比電容值以及循環壽命，故在電動車與消費性電子產品的應用前景受到注目。金屬有機框架(Metal organic framework, MOF)是利用金屬離子與有機配體(organic ligand)所合成的高比表面積材料，其高比表面積的結構使MOF具有與碳材相同的電雙層電容特性，而金屬離子的氧化還原能力使MOF具有與金屬氧化物相同的擬電容特性，故非常適合用於儲能元件的電極材料。然而，目前儲能領域的研究已廣泛使用Ni、Co金屬離子搭配對苯二甲酸(Terephthalic acid, TPA))、均苯三甲酸(Trimesic acid, TMA))等有機配體進行合成，而目前在儲能領域並沒有文獻使用均苯四甲酸(Pyromellitic acid, PMA))進行NiCo-MOF的開發。因此，本研究致力於開發一款新型的NiCo-MOF，利用一步驟水熱法搭配Ni、Co金屬離子與均苯四甲酸有機配體進行NiCo-MOF(PMA)之開發，並同時合成文獻常見之NiCo-MOF(TPA)、NiCo-MOF(TMA)一同進行比較。本研究所開發具有蒲公英結構且擁有超高比表面積的NiCo-MOF(PMA)，其比表面積高達500.7 m2/g，與文獻常見花狀結構的NiCo-MOF(TPA) (6.91 m2/g)與蒲公英狀結構的NiCo-MOF(TMA) (20.66 m2/g)比較下，顯示NiCo-MOF(PMA)擁有更優異的比表面積性能。根據恆電流充放電量測結果顯示，在1 A/g的電流密度下NiCo-MOF(TPA)的比電容值為1000 F/g、NiCo-MOF(TMA)的比電容值為864 F/g、NiCo-MOF(PMA)的比電容值為918.8 F/g，此結果證實NiCo-MOF(PMA)的電化學性能可媲美NiCo-MOF(TPA)及NiCo-MOF(TMA)。當電流密度增加到10 A/g時NiCo-MOF(PMA)仍保有61.1%的倍率性能，且在10 A/g的電流密度下經過10000次充放電循環後仍具有64.3%的電容維持率。本研究也將實驗結果與文獻進行比較，證實本研究所開發的NiCo-MOF(PMA)有機會能成為超級電容器有潛力的電極材料。最後，為了驗證實際應用能力，使用NiCo-MOF(PMA)作為正極材料、活性碳作為負極材料，開發一款不對稱超級電容器，並成功點亮1顆綠光LED燈與排列有NTNU圖樣的40顆並聯綠光LED燈，證實本研究所開發之不對稱超級電容器具有作為儲能元件的實際應用能力。Supercapacitors can be divided into electrical double-layers capacitors (EDLC) and pseudocapacitor according to their energy storage mechanism. Compared with traditional capacitors, they have better specific power, specific capacitance and cycle life, so the application prospects in electric vehicles and consumer electronics have attracted attention. Metal organic framework (MOF) is a high specific surface area material synthesized by using metal ions and organic ligands. Its high specific surface area structure makes MOF have the same EDLC characteristics as carbon materials. The redox ability of metal ions makes MOF have the same pseudocapacitor characteristics as metal oxides, so it is very suitable for electrode materials of energy storage elements. However, the current research in the field of energy storage has widely used Ni, Co metal ions with terephthalic acid (TPA) and trimellitic acid (TMA) for synthesis. There is no literature in the field of energy storage using pyromellitic acid (PMA) to development NiCo-MOF.Therefore, this research is devoted to development of a new type of NiCo-MOF, using a one-step hydrothermal method with Ni, Co metal ions and pyromellitic acid organic ligands for the development of NiCo-MOF(PMA), and at the same time synthetic common literature NiCo-MOF(TPA) and NiCo-MOF(TMA) are compared together. This research has developed NiCo-MOF(PMA) with a dandelion structure and an ultra-high specific surface area. Its specific surface area is as high as 500.7 m2/g, which is comparable to the flower-like structure of NiCo-MOF(TPA) (6.91 m2/g) and dandelion-like structure of NiCo-MOF(TMA) (20.66 m2/g) the comparison shows that NiCo-MOF(PMA) has better specific surface area performance. According to the constant current charge and discharge measurement results, the specific capacitance of NiCo-MOF(TPA) is 1000 F/g, NiCo-MOF(TMA) is 864 F/g and NiCo-MOF(PMA) is 918.8 F/g at a current density of 1 A/g. This result confirms that the electrochemical performance of NiCo-MOF(PMA) is compared to NiCo-MOF(TPA) and NiCo-MOF(TMA). When the current density increases to 10 A/g, NiCo-MOF(PMA) still maintains a rate capability of 61.1%, and it still has a capacitance retention rate of 64.3% after 10,000 charge-discharge cycles at a current density of 10 A/g. This study also compares the experimental results with the literature, confirming that the NiCo-MOF(PMA) developed in this research has the opportunity to become a potential electrode material for supercapacitors.Finally, in order to verify the practical application ability, NiCo-MOF(PMA) was used as the positive electrode material and activated carbon as the negative electrode material to develop an asymmetric supercapacitor, and successfully lighted one green LED lamp and forty parallel green LED lamps with NTNU pattern. It is confirmed that the asymmetric supercapacitor developed in this research has the practical application ability as an energy storage element.