TY - JOUR
T1 - Nonlinear dynamics of ion concentration polarization in capacitive deionization
AU - Lee, Hyungsub
AU - Kim, Dongho
AU - Kang, Ji Yoon
AU - Bong, Ki Wan
AU - Lee, Soo Hyun
AU - Kwak, Rhokyun
N1 - Funding Information:
This work was supported by the research fund of Hanyang University ( HY-2017 ).
PY - 2019/5/15
Y1 - 2019/5/15
N2 - Capacitive deionization (CDI) is an emerging desalination technique by utilizing the electrosorption of porous electrodes. Thus far, only linear concentration profiles in bulk electrolyte between the electrodes have been observed, during ion charging (ion depletion) or ion discharging (ion enrichment). This so-called linear ion concentration polarization (ICP) can be predicted by the simple convective-diffusion model. In this study, we demonstrate that capacitive charging can induce nonlinear concentration profiles in the electrolyte. To visualize nonlinear ICP dynamics, a miniaturized CDI platform is developed to observe in situ ion concentration profiles. Determined by the ion flux mismatching of electrosorption and bulk ion transport, we discovered four ICP regimes in CDI – steady, linear ICP, delayed-nonlinear ICP, and nonlinear ICP. We directly observed the signatures of nonlinear ICP: i) flat depletion zone with extremely low ion concentration, and ii) corresponding exponential current drop. Based on this observation, two scaling models are formulated to predict i) when the nonlinear ICP occurs, and ii) the propagation speed of the flat depletion zone. To the best of our knowledge, this is the first microscopic characterization of ICP in CDI systems, and it firmly establishes the existence of nonlinear ion transport dynamics in CDI's bulk electrolyte.
AB - Capacitive deionization (CDI) is an emerging desalination technique by utilizing the electrosorption of porous electrodes. Thus far, only linear concentration profiles in bulk electrolyte between the electrodes have been observed, during ion charging (ion depletion) or ion discharging (ion enrichment). This so-called linear ion concentration polarization (ICP) can be predicted by the simple convective-diffusion model. In this study, we demonstrate that capacitive charging can induce nonlinear concentration profiles in the electrolyte. To visualize nonlinear ICP dynamics, a miniaturized CDI platform is developed to observe in situ ion concentration profiles. Determined by the ion flux mismatching of electrosorption and bulk ion transport, we discovered four ICP regimes in CDI – steady, linear ICP, delayed-nonlinear ICP, and nonlinear ICP. We directly observed the signatures of nonlinear ICP: i) flat depletion zone with extremely low ion concentration, and ii) corresponding exponential current drop. Based on this observation, two scaling models are formulated to predict i) when the nonlinear ICP occurs, and ii) the propagation speed of the flat depletion zone. To the best of our knowledge, this is the first microscopic characterization of ICP in CDI systems, and it firmly establishes the existence of nonlinear ion transport dynamics in CDI's bulk electrolyte.
KW - Capacitive deionization
KW - Desalination
KW - Ion concentration polarization
UR - http://www.scopus.com/inward/record.url?scp=85061427293&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85061427293&partnerID=8YFLogxK
U2 - 10.1016/j.desal.2019.01.032
DO - 10.1016/j.desal.2019.01.032
M3 - Article
AN - SCOPUS:85061427293
SN - 0011-9164
VL - 458
SP - 14
EP - 24
JO - Desalination
JF - Desalination
ER -