电吸附除氯过程的电化学阻抗谱及动力学研究

Electrochemical Impedance Spectroscopy and Kinetics of Chloride Ion Removal by Electroadsorption

借助三电极体系,基于电化学交流阻抗谱图,提出了一种对已吸附Cl−的活性炭再次吸附一个Cl−弛豫时间的测定方法,根据弛豫时间确定速率控制步骤.研究了阳极电势、预处理时间和预处理浓度对电化学过程的影响,基于得到的电化学交流阻抗谱图上的参数,求出不同条件下电吸附Cl−的弛豫时间及覆盖度.结果表明,不同条件下得到的复数平面图均由一个容抗弧和一个感抗弧构成,分别代表Cl−在阳极上发生电荷转移的过程和Cl−在活性炭电极上的吸附过程.增加阳极极化可有效缩短弛豫时间,阳极极化时,弛豫时间为2.0×10^(−5)s;增加预处理时间,弛豫时间逐渐增加,预处理时间为180 min时,弛豫时间增加到4.9×10^(−5)s;预处理浓度对弛豫时间的影响可忽略.弛豫时间分析结果表明,Cl−吸附速率比扩散速率小,吸附是电吸附过程的速率控制步骤.电极表面的覆盖度较低,仅有10^(−4)数量级.

The dynamics of electroadsorption faces the problem of large experimental workload,and can’t directly reveal the rate control steps.In this study,a method to determine the relaxation time of Cl^(−) adsorbed on activated carbon was proposed based on electrochemical impedance spectroscopy.The speed control step was determined according to the relaxation time.The effects of anode potential,pretreatment time and pretreatment concentration on the electrochemical process were studied.Based on the obtained electrochemical impedance spectroscopy,the relaxation time and coverage of electroadsorbed Cl^(−) under different conditions were obtained.The results show that the Nyquist plots obtained under different conditions are composed of a capacitive reactance arc and an inductive reactance arc,which represent the charge transfer process of Cl^(−) on the anode and the adsorption process of Cl^(−) on the activated carbon electrode,respectively.The relaxation time can be effectively shortened by anode polarization.When the anode polarization is applied,the relaxation time is 2.0×10^(−5) s.With the increase of pretreatment time,the relaxation time gradually increases.When the pretreatment time is 180 min,the relaxation time increases to 4.9×10^(−5) s.The effect of pretreatment concentration on relaxation time is negligible.The relaxation time shows that the adsorption rate of Cl^(−) is slower than the diffusion rate,and adsorption is the speed control step of the electroadsorption process.The electrode surface coverage is low,only 10^(−4) orders of magnitude.This method is more accurate and intuitive than the kinetic model fitting to determine the control steps,and provides a theoretical and methodological basis for the study of electroadsorption process dynamics.