陰極沈積製備鎳鈷氫氧化物及其在超級電容器的應用

Preparation of Ni-Co hydroxide by cathodic deposition and the applications on supercapacitors

周宇軒(Chou, Yu Hsuan)

指導教授 ： 胡啟章

國立清華大學/工學院/化學工程學系/碩士(2015年)

摘要

本研究使用電化學陰極沈積法製備鎳鈷氫氧化物((Ni-Co)(OH)2)，並將材料應用在超級電容器上。實驗內容主要可分為三部分，第一部分為利用實驗設計法探討影響(Ni-Co)(OH)2電化學表現的因素，並找出製備上之最佳條件組合。第二部分為合成(Ni-Co)(OH)2和奈米碳管的複合材料，以提高單位面積電容，並組裝成非對稱超級電容器，期望提升材料於電動車等儲能裝置上實際應用價值。第三部分探討不同基材對陰極沈積(Ni-Co)(OH)2的影響，找出造成電化學表現差異的因素，並利用化學氣相沈積將石墨烯附著於不同基材上，以下簡要地討論各章所包含的內容。
第一部分藉由陰極沈積合成(Ni-Co)(OH)2，並以24全因素實驗設計進行分析，選定探討的四個因素分別如下，前驅物中鎳鈷比例、前驅物之pH值、沈積溫度及電流密度，目的為將(Ni-Co)(OH)2的比電容和高速掃描下的電容維持率提升。利用全因素實驗設計產生的回歸模型，進行陡升實驗，得到的最佳條件如下，Ni2+/(Ni2++Co2+)=0.35，pH值為3.60，沈積溫度為70℃，電流密度為5 mA/cm2。(Ni-Co)(OH)2的比電容可達1218.5 F g-1 (5 mV s-1)，且100 mV s-1下電容維持率仍有71.8%。最後將最佳條件之(Ni-Co)(OH)2作為正極，活性碳作為負極，組裝成非對稱電容器，其可從0.166 V充電至1.6 V，且在10 A g-1下擁有16.7 W h kg-1的能量密度和7.2 kW kg-1的功率密度。
第二部分藉由先在石墨電極表面塗布奈米碳管，再將(Ni-Co)(OH)2依前章得到之最佳條件沈積於此，重複此兩步驟合成似三明治層狀結構之複合材料，其單位面積電容可提升至1.55 F g-1。此外，從SEM圖發現，脈衝-休止法沈積相較於定電流沈積，能使(Ni-Co)(OH)2沈積入奈米碳管的孔隙中，整體材料在高速充放電下電容提升，此方法使活性材料利用率增加。藉由充放電測試，含有四層(Ni-Co)(OH)2的複合材料，電流密度2 A g-1下，單位面積電容高達3.68 F cm-2。最後將單層(Ni-Co)(OH)2之奈米碳管複合材料作為正極，活性碳作為負極，組裝成非對稱電容器，其可從0.166 V充電至1.6 V，且在10 A g-1下擁有17.1 W h kg-1的能量密度和7.2 kW kg-1的功率密度。
第三部分將化學氣相沈積石墨烯後的泡沫鎳、不鏽鋼網和鈦片作為不同集電板，並於沈積上(Ni-Co)(OH)2後，比較發現泡沫鎳上之(Ni-Co)(OH)2分佈均勻且具高孔洞性，1 A g-1下比電容高達1593 F g-1，且因活性材料高達6.3 mg cm-2，單位面積電容提升至9.9 F cm-2。最後將此材料作為正極，活性炭作為負極，組裝成非對稱電容器，其可從0.2 V充電至1.65 V，且在10 A g-1下擁有21.8 W h kg-1的能量密度和7.2 kW kg-1的功率密度。

關鍵字

超級電容器 ； 氫氧化物 ； 石墨烯 ； 奈米碳管 ； 氫氧化鎳 ； 氫氧化鈷

並列摘要

This study is about the preparation of (Ni-Co)(OH)2 by cathodic deposition method and its applications on supercapacitors. The experiments were divided into three parts. The first part was focused on the design of experiment, which was used to study the factors that influence electrochemical performance of the (Ni-Co)(OH)2 and find an optimal condition for this synthesis. The second part was focused on synthesizing a sandwich-like (Ni-Co)(OH)2/carbon nanotubes (CNT) composite in order to increase the areal capacitance, then assembled as asymmetric supercapacitor to enlarge energy density. The goal is to enhance its potential for practical applicatipons. In the third part, we used chemical vapor deposition (CVD) to grow graphene on different substrates which acted as the current collectors for cathodic deposition of (Ni-Co)(OH)2. Then, we discussed the reasons that affected the electrochemiacal performance of (Ni-Co)(OH)2/graphene composite. The followings are the contents of each part.
In the first part, we deposited the (Ni-Co)(OH)2 by cathodic deposition and made a 24 full factorial design of experiment (DOE). The four factors chosen were as below, Ni2+/(Ni2++Co2+), pH value of the precursor solution, deposition temperature, and deposition current. The goal is to increase the specific capacitance and improve the rate capability of the (Ni-Co)(OH)2. Finally, we did a steepest ascent experiment according to the regression model obtained from DOE, and the optimal conditions were obtained as below, 0.35 of Ni2+/(Ni2++Co2+), 3.60 of pH value, 70℃ of deposition temperature, and 5 mA/cm2 of current density. The highest specific capacitance was 1218.5 F g-1 (at 5 mV s-1) and rate retention (100 mV s-1) was 71.8%. Finally, using the optimal (Ni-Co)(OH)2 as the cathode combined with activated carbon (AC), the assembling asymmetric supercarpacitor can charge from 0.166 V to 1.6 V, exhibiting a energy density of 16.7 W h kg-1 and a power density of 7.2 kW kg-1 at 10 A g-1.
In the second part, the sandwich-like were (Ni-Co)(OH)2/CNT exhibited a improved areal capacitance of 1.55 F cm-2. Seen from the SEM images, compared to the galvanostatic method, the pulse-rest method facilitated the (Ni-Co)(OH)2 depositing into the pores of CNT, which further improved the utilization of active materials and increase the specific capacitance and redox reversibility of the composite (Ni-Co)(OH)2/CNT. The composite (Ni-Co)(OH)2/CNT containing four layers of hydroxides exhibited a areal capacitance of 3.68 F cm-2 at 2 A g-1. Besides, combined with AC, the assembling asymmetric supercapacitor can charge from 0.166 V to 1.6 V, exhibiting a energy density of 17.1 W h kg-1 and a power density of 7.2 kW kg-1 at 10 A g-1.
In the third part, comparing the composites (Ni-Co)(OH)2/graphene grown on different substrates including Ni foam, stainless steel mesh, and Ti foil, we found that (Ni-Co)(OH)2/graphene on Ni foam was uniformly deposited and highly porous, exhibiting the highest specific capacitance of 1593 F g-1 and areal capacitance of 9.9 F cm-2 . Besides, combined with AC, the assembling asymmetric supercapacitor can charge from 0.2 V to 1.6 V, exhibiting a energy density of 17.1 W h kg-1 and a power density of 7.2 kW kg-1 at 10 A g-1.

並列關鍵字

Supercapacitor ； Hydroxide ； Graphene ； Carbon nanotube ； Nickel hydroxide ； Cobalt hydroxide

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