Chem. J. Chinese Universities ›› 2023, Vol. 44 ›› Issue (2): 20220528.doi: 10.7503/cjcu20220528

• Physical Chemistry • Previous Articles     Next Articles

Electrochemical Impedance Spectroscopy and Kinetics of Chloride Ion Removal by Electroadsorption

SUN Zhumei1,2, FU Jie1, LI Xin1, WANG Haifang1, LU Jing1, TONG Tianxing2, ZHU Mingfei2, SHU Yude2, WANG Yunyan2,3()   

  1. 1.School of Environmental and Safety Engineering,North University of China,Taiyuan 030051,China
    2.School of Metallurgy and Environment,Central South University,Changsha 410083,China
    3.Chinese National Engineering Research Center for Control and Treatment of Heavy Metals Pollution,Changsha 410083,China
  • Received:2022-08-10 Online:2023-02-10 Published:2022-11-18
  • Contact: WANG Yunyan E-mail:wyy@csu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(52004256);the China Postdoctoral Science Foundation(2021M703651)

Abstract:

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.

Key words: Chloride ion, Capacitive deionization, Electrochemical impedance spectroscopy, Dynamics, Relaxation time

CLC Number: 

TrendMD: