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  • 學位論文

陰極沉積鈷-(鎳)氫氧化物於多孔基材之擬電容特性研究

Pseudocapacitive Properties of Co-(Ni) Hydroxide on Porous Substrate by Cathodic Deposition

指導教授 : 王朝弘
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摘要


三維結構基材有助於提升擬電容材料之比電容量以及在高速率充放電能維持良好的穩定性,因此可應用於增進電化學表現。本研究製備兩種不同結構的基材,三維多孔銅支架與次微米鎳線陣列。第一部份利用定電流方式將氫氧化鈷沉積於多孔電極與鎳線電極。第二部分則為定電壓共沉積鈷鎳氫氧化物於兩種結構基材,調控不同濃度比例之硝酸鈷與硝酸鎳溶液,控制氫氧化物之鈷鎳組成,並找出最佳比例之條件。由於三維多孔性的立體結構具有較高的表面積,可大幅提高活性物質之附著量以及與電解液的接觸面積,並探討附著量對於擬電容性能之表現。本研究也利用以鎳為主的基材在鹼性溶液中會生成氫氧化鎳之特點,探討氫氧化鎳的生成對於電容器整體性能之影響。 利用定電流方式沉積氫氧化鈷,其沉積庫倫數由1庫倫(1C)增加至5C,1C條件具有最高的比電容量1067 F/g,不過單位重量之電容量隨著附著量增加則逐漸下降。Co(OH)2/多孔電極經過3000圈的循環測試,電容量保持穩定沒有任何衰退,即使在高電流密度下測試,仍可維持在99%,因為電解液會與基材上的鎳反應生成氫氧化鎳,進而補償了Co(OH)2電容量的損失,有助於維持電容器之循環壽命。定電壓沉積鈷鎳氫氧化物(Ni0.14Co0.86(OH)2)之最佳比例為2:1,電容量可達1771 F/g,在高電流密度充放電測試,電容量僅下降11%,比起平面電極有更好的穩定性。當沉積庫倫數提高至5C,每單位面積之電容量為2.0 F/cm2。Ni0.14Co0.86(OH)2/多孔電極在循環壽命也有優異表現,經過5000圈的測試,電容量僅下降7%。 另一部分製備鈷鎳氫氧化物/鎳線電極,其電容量為1566 F/g (0.27 F/cm2),在高電流度充放電還可維持在1383 F/g(88%),鎳線電極對於活性材料之性能提升有限,其表現與多孔電極差異不大。本研究使用鎳為主的基材,在循環測試過程中會生成Ni(OH)2,有助於維持循環穩定性,不過Ni(OH)2的存在確實會影響Co(OH)2之氧化還原行為,使氧化還原峰電位產生偏移以及額外電容量的貢獻。Co(OH)2與Ni0.14Co0.86(OH)2沉積於兩種三維結構的電荷集流體,在電容量、高速率充放電穩定性以及循環壽命表現皆優於平面電極,顯示三維電極確實有助於提升擬電容特性表現。

並列摘要


3D structured electrodes can enhance specific capacitance of pseudo-capacitive materials and improve its high-rate stability. In this study, we prepared two different 3D current collectors, porous Cu frameworks coated with Ni and sub-micron Ni rods array. Co(OH)2 and NixCo1–x(OH)2 were cathodically deposited on the electrodes by galvanostatic and potentiostatic electrodeposition methods, respectively. The Co/Ni ratios of NixCo1–x(OH)2 were controlled by adjusting the concentration ratios of Co /Ni ions in plating solutions. 3D structured electrodes having large surface area not only accommodate the deposited amount of active materials but also increase the contact area with electrolytes. The most important finding is that the capacitance gradually increased owing to the formation of Ni(OH)2 on the Ni-based electrode during cycle testing. The Co(OH)2 was deposited on the porous Ni/Cu substrate by galvanostatic electrodeposition. Various amounts of Co(OH)2 were by increasing deposition charge from 1 coulomb(C) to 5C on the electrode area of 2.27cm2. For the 1C-deposited electrode, the specific capacitance was as high as 1067 F/g. With increasing the deposition charge, the specific capacitance gradually decreased. Notably, the Co(OH)2 capacitance on the porous electrode had no significant decay upon 3000 cycles, even at a high current density. This is because the self-formation of Ni(OH)2 on the porous Ni electrodes can contribute additional capacitance to compensate for the decay of Co(OH)2. Moreover, the Ni0.14Co0.86(OH)2 deposited on the porous electrode exhibited a high specific capacitance of 1771 F/g (0.68 F/cm2) and excellent rate capability of 1583F/g (89%) at a high current density. The Ni0.14Co0.86(OH)2 capacitance on the porous electrode was much higher than that on the planar electrode. For the 5C-depsoited sample, the areal capacitance was 2.0 F/cm2. Furthermore, the Ni0.14Co0.86(OH)2/porous electrode also had excellent cycle performance, the specific capacitance decreased only 7% after 5000 cycles. The NixCo1–x(OH)2 was also deposited on Ni-rods array electrode. It exhibited a specific capacitance of 1566 F/g (0.27/cm2) and a rate capability of 1383F/g (88%). Compared to the porous electrode, the active materials deposited on rod array electrode can not further improve electrochemical properties. The above results demonstrated that 3D structure current collector helps to increase specific capacitance, enhance rate capability and improve cycling performance.

參考文獻


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