具活性碳/碳黑複合電極之正流式電容去離子系統及其操作效能與穩定性分析

A flow-through CDI system with activated carbon/carbon black composite electrode: analysis of operation performance and system stability

柯皓中(Hao-Chung Ko)

指導教授 ： 黃志彬

國立交通大學/工學院/環境工程系所/碩士(2018年)

摘要

電容去離子技術為目前極具發展潛力的脫鹽技術，其有能耗低、吸脫附快速且簡易、模組結構簡便、能源回收方便等優點。電容去離子電極材料依吸附機制，可分為以電雙層電容吸附鹽類的多孔碳材，還有以擬電容為吸附機制的金屬氧化物。其中又以多孔炭材材料取得簡易、成本較低，且電化學穩定性較高。故本研究採用活性碳/碳黑複合電極作為電容去離子電極材料。
本研究分為兩大部分，第一部分為電極之特性分析，運用電子掃描顯微鏡與熱分析儀分析電極披覆情形；以比表面積分析儀測量活性碳/碳黑複合電極之比較面積；最後使用電化學方法，定義電極之適用工作電位視窗與合適陰陽極重量配比。第二部分為電極操作效能評估與系統穩定度分析，此部分本研究以定電壓與定電流操作，評估電極在不同操作條件下之電吸附量、電荷效率與能源消耗，同時觀察系統pH與導電度隨時間之變化，探討其變化機制與對系統造成之影響。
研究顯示複合電極具有比表面積為2152 m2/g、比電容值為189.5 F/g；此外，適用工作電位視窗為-1.0 ~ 1.3 V(vs. Ag/AgCl)、適用陰陽電極重量比為1：1。在定電壓操作下，電極在施加電壓為1.5 ~ 1.8 V間有較高且穩定的吸附量、較好的電荷效率與低能源消耗；定電流操作電吸附量與能源消耗則隨著電流密度上升而增加，電流密度則相反。最後系統操作產生之pH變化，主要由電極法拉第反應(氧化還原反應)造成，而導電度之變化則歸因於pH之變動。

關鍵字

去離子 ； 電容去離子 ； 活性碳 ； 碳黑 ； 複合電極

並列摘要

Capacitive deionization (CDI) is an emerging desalination technology with potential currently. It takes advantage of low energy consumption, high rate of adsorption/desorption, convenient to energy recycle and easy to assemble. The materials of electrodes can be divided by adsorption mechanism to two kinds, electrical double layers capacitor (EDLC) for porous carbon materials and pseudocapacitor for oxide metals. For porous carbon materials, it take benefits of cheap, abundant in environment and stable. As a result, it takes activated carbon as material of electrode in this study.
This study is composed of two parts. The first part is the investigation of surface characteristics on electrode. Scanning electron microscopy (SEM) and thermogravimetric analyzer (TGA) are used for analyzing the coated situation of electrodes. Specific surface area and porosimetry analyzer is utilized for investigating the specific surface areas and pore size distribution of electrodes. Eventually, the definition of working potential window and mass distribution of anode and cathode were assessed by electrochemical analytic method. The second part is the evaluation of electrosorption ability and stability of composite electrode. In this part, constant voltage and constant current modes were applied for evaluating the adsorption capacity, charge density and energy consumption with different operation conditions. In operation, pH and conductivity were also observed continuously for investigating the mechanism of pH and conductivity fluctuations.
In this study, it showed that activated carbon (ACS25)/carbon black (XC-72) composite electrode possess specific surface area of 2152 m2/g and specific capacitance of 189.5 F/g. And the appropriate potential window ranges from -1.0 V to 1.3 V (vs. Ag/AgCl). Moreover, suitable mass of distribution between anode and cathode closes to 1:1. In the electrosorption study, there are better adsorption capacity, charge efficiency and energy consumption when applied voltage is between 1.5 V to 1.8 V in the constant voltage mode. For the constant current mode, higher the current density is, more the adsorption capacity it has, and charge efficiency and energy consumption are just the opposite trend. Eventually, the fluctuations of pH are mainly attributed to the faradaic reactions of electrode. Then, the decreasing of pH would rise the conductivity of solution.

並列關鍵字

deionization ； CDI ； activated carbon ； carbon black ； composite electrode

參考文獻

Biesheuvel, P. M., Porada, S., Levi, M., & Bazant, M. Z. (2014) "Attractive forces in microporous carbon electrodes for capacitive deionization" Journal of Solid State electrochemistry, 18(5), 1365-1376.

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