奈米合成氫氧化鈷及氫氧化鎳電極與超級電容器的應用

Abstract

為提升超級電容器的電化學效能表現，本實驗使用了高表面積的鎳網以及可撓式的碳纖維布作為電極製備的基材，結合自行開發之基材表面積提升法，並以奈米尺度的氫氧化鈷及氫氧化鎳氧化物，作為充放電的擬電容材料，製備過程以電化學作為原理應用並使用參電極系統，實驗共分為三部分進行探討： 第一部分為將氫氧化鈷應用於鎳網上作探討，實驗使用自行開發的鎳銅共鍍方法，製備多孔鎳奈米柱(Nanotube array, NTA)以及吸盤狀鎳奈米管柱(Sucker-like nanoporous, SNP)，將基材作表面積提升以及三維化的處理，再將氫氧化鈷沉積於鎳奈米柱與吸盤狀鎳奈米管柱上，即完成高表面積之奈米鈷超級電容電極Co-NTA與Co-SNP。隨後以1 M氫氧化鉀水溶液作為電解液，將電極作循環伏安法及恆電流充放電法的電化學效能測試，比電容值經計算後，在0.65 V的電位窗及1 A/g的測試速率下，Co-NTA及Co-SNP電極分別為2500及2900 F/g。 第二部分為將氫氧化鎳應用於碳纖維布上作探討，因應可撓式裝置的需求、電池的輕量化並兼顧高表面積的優勢，同樣使用前部分表面積提升的技術，製備可撓式奈米多孔基材(Flexible nanoporous, FNP)，再將氫氧化鎳沉積於奈米多孔基材上，完成可撓式奈米多孔鎳超級電容電極Ni-FNP。同樣在1 M氫氧化鉀水溶液內作電化學效能測試後，以0.65 V的電位窗及10 A/g的測試速率，測得Ni-FNP電極之比電容值為2000 F/g。 前兩部分實驗皆結合國家同步輻射研究中心之X光光源，於實驗站BL01C2作X光繞射光譜(XRD)、BL20A1作X光光電子能譜(XPS)以及BL01C1與BL07A1作即時X光吸收光譜(XAS)，分別作晶相鑑定、氧化價態鑑定以及即時電子轉移變化的觀察，並以掃描電子顯微鏡與穿透電子顯微鏡作形貌觀察。 第三部分的實驗為非對稱超級電容器的探討，結合前兩部分應用的氫氧化鎳與氫氧化鈷，在1 M氫氧化鉀水溶液下作雙電極的電化學測試，發現此非對稱組合可提供1.6 V的電位窗，最後結合聚乙烯醇高分子，將鹼性水溶液的電解液改質成鹼性固態電解液，再將此電極組合成固態可撓式超級電容器，電化學測試結果發現此組裝置亦可供應1.6 V的電位窗，且此組固態非對稱超級電容器在10000次充放電後，仍可原本電容值的95%，經由彎曲及扭轉測試可驗證其可撓性佳，且將裝置串聯三組後，可使紅光LED燈泡發亮一分鐘以上。

Large-area 3D supercapacitor electrodes were fabricated with a facile electrochemical deposition method which co-deposited of Ni-Cu layer, then selectively etching Cu from Ni-Cu layer to complete nickel nanotube on the selected substrates. Further cathodic depositon of Co(OH)2 or Ni(OH)2 hydroxide particles on the as-prepared nanoporous substrates, respectively. High-performance 3D porous supercapacitor electrodes had been synthesized. This research was divided into three parts: Part I: Two 3D porous structures, sucker-like nanoporous (SNP) and nanotube arrays (NTA) grew on nickel foam were used to enhanced the electrochemical performances of Co(OH)2-based supercapacitor electrodes. Both Co-SNP and Co-NTA electrodes were tested with cyclic voltammetry (CV) and galvanic charge-discharge (GCD) methods in 1M KOH aqueous electrolyte. The Co-SNP and Co-NTA electrodes exhibited specific capacitance of 2900 F/g and 2500 F/g at 1 A/g in a three electrode cell, respectively. Part II: Carbon fiber were used to synthesized a high-performance flexible Ni(OH)2-based electrodes. Large-area modified method were also used on carbon fiber substrate, which grew a flexible nanoporous (FNP) structures on the surface. The Ni-FNP electrodes were measured in 1M KOH aqueous electrolyte and exhibited a specific capacitance of 2000 F/g at 10 A/g in a three electrode cell. Both supercapacitor electrodes in part I and part II were analyzed with scanning electron microscope (SEM, SU-8010), transmission electron microscope (TEM, JEOL-JEM3000F) and energy dispersive spectroscope (EDS). The crystal structure, investigation of oxidation state, and the variation of the oxidation state during charge-discharge cycles in these electrodes were measured by X-ray diffraction (XRD) techniques at BL01C2, X-ray photoemission spectroscopy (XPS) at BL20A, and in-situ X-ray absorption spectroscopy (XAS) at BL01C1 and BL17C1 in National Synchrotron Radiation Research Center (NSRRC), respectively. Part III: Asymmetric supercapacitors (ASCs) were built with Ni(OH)2//Co(OH)2 electrodes and measured with CV and GCD in 1M KOH aqueous and solid-state electrolytes, respectively. The devices were tested in 1 M KOH electrolyte and displayed a voltage range of 1.6 V. Finally, the Ni(OH)2 and Co(OH)2 electrodes combined with base solid-state electrolyte to form a flexible solid-state asymmetric supercapacitor devices. This flexible device also performed a voltage range of 1.6 V and tested with bending and twisting experiments. Moreover, the device has remarkable cycle stability of only 5% loss after 10000 cycles. A red LED could be powered with the devices in series more than 1 minute.