- 學位論文
以鹼性無電鍍鎳銅製備超級電容電極材料之研究
The Preparation of Nickel-Copper Materials for Supercapacitor Electrodes by Alkaline Electroless Plating
摘要
銅基材料之低成本、高導電性、高的環境友善性與好的電位儲存能力(0~1.0V)，使其成一種高潛力的超級電容電極材料。本研究使用無電鍍法(Electroless Plating Process)在鈦基板上製備銅鎳/鎳銅膜來作為超級電容電極材料，為了進一步提高無電鍍膜之比電容值，利用7M硝酸在40℃下進行蝕刻使得膜層表面產生多孔性結構的黑膜。在硼酸系統中改變鎳離子濃度和pH值，而在醋酸鈉系統中改變銅離子濃度和蝕刻時間，探討經過蝕刻後膜層顯微結構與成份的變化，並利用循環伏安法、充放電測試和交流阻抗分析測量其電化學性質以及計算其比電容值。另外，並進一步討論鎳銅磷膜顯微結構和比電容性質的關係。 實驗結果顯示，當無電鍍銅之初鍍膜的表面形貌明顯不同外，含不同比例鎳銅膜的表面形貌均類似，由大小為1-5μm之島狀物所組成，而島狀物則由大小0.2-0.5μm之銅鎳顆粒堆疊而成。在醋酸鈉系統中，在低銅離子濃度時，鎳銅磷膜為單一非晶相，隨著銅離子濃度的增加 (> 6 g/L)，磷含量隨著降低且形成多晶相，而且膜層中的實際銅鎳比遠高於鍍液中銅鎳比。初鍍膜比電容並不高，約為9-16 F/g，而與銅鎳比無明顯關係。銅離子濃度與磷含量越高之膜層，進行硝酸蝕刻時不易產生選擇性的溶解。對於鎳銅磷膜，在銅離子濃度較低時(< 1.5 g/L)，會發生選擇性的蝕刻，膜的鎳、磷量會上升而銅含量則會下降，進而形成島狀和石筍狀的多孔結構。在銅離子濃度1 g/L且蝕刻5秒時，在掃描速率10 mV/s獲得最佳的比電容值約440 F/g，而利用充放電量測更高達470 F/g，比起蝕刻前比電容值增加了約30倍。當進一步減少銅離子濃度時，比電容值卻明顯的降低，有可能是因為磷含量的增加，使得鎳磷膜不易被蝕刻。另外，以充放電測試與循環伏安測試所得的比電容相近，並無明顯差異。根據交流阻抗分析可以發現，銅離子濃度1 g/L在三者之中具有最小的電荷傳輸電阻和最高的離子擴散能力，使得其比電容值的表現最為優異，經過1000次循環伏安測試，其比電容變化在10 %以內。因此說明了鎳銅磷膜經過酸蝕刻後，確實能有效增加其比電容值且表現出高的CV循環壽命，在超級電容電極應用上有很大的潛力。
並列摘要
In this study, the nickel-copper-phosphorus (Ni-Cu-P) alloy films on titanium substrate for supercapacitor electrodes were prepared by electroless plating process. Electroless plating can be carried out without power supply and less demanding on the environment. In order to increase the specific capacitance of Ni-Cu-P alloy films and porous structures on the surface of films were formed by acid etching. The electrochemical properties and specific capacitance were measured by cyclic voltammetry and charge/discharge test. In addition, the effect of nickel ion concentration and pH value of the boric acid system as well as the copper ion concentration and etching time of the sodium acetate system on characteristics of Ni-Cu-P films were further explored in details. The experimental results show that the Ni-Cu-P films with different compositions reveal a similar surface morphologies for the boric acid system. It’s composed of islands with sizes of 1-5 μm, while islands are composed of copper-nickel particles with sizes of 0.2-0.5 μm. For the sodium acetate system with low copper ion concentration, the Ni-Cu-P films are a single amorphous phase. With the increase of copper ion concentration (> 6 g/L), the phosphorus content decreases and the formation of polycrystalline phase occurs. The actual copper-nickel ratio of the films is much higher than that in the bath. The specific capacitance of the films after etching is about 9-16 F/g. The films with high copper and phosphorus content are not easy to produce selective dissolution by acid etching. For Ni-Cu-P films, selective etching occurs when the copper ion concentration is low (< 1.5 g/L), the nickel and phosphorus contents of the films are increased, while the copper content is decreased. Therefore, the island-like and stony-like porous structure are formed. When the copper ion concentration is 1 g/L and etching time is 5 seconds, the highest value of the specific capacitance achieve about 440 F/g at the scan rate of 10 mV/s and 470 F/g at current density of 1 A/g. After etching, the specific capacitance is increased 30 times. Once the copper ion concentration is further decreased, the specific capacitance is decreased significantly. The reason may be that the increase of phosphorus content makes the etching resistance of nickel-phosphorus film increase resulting in the formation of non-porous structure with less surface area. According to the result of EIS analysis, it can be found that the copper ion concentration of 1 g/L has the smallest charge transfer resistance and the highest ion diffusion ability among the three ones, this leads to the better performance of the electrochemical reactions. After 1000 cycles of CV, the change of specific capacitance is less than 10%. It’s shown that the nickel-copper-phosphorus film can increase its specific capacitance effectively after acid etching and be applied as supercapacitor electrodes.