TY - JOUR
T1 - Discharging behavior of confined bipolar electrodes
T2 - Coupled electrokinetic and electrochemical dynamics
AU - Eden, A.
AU - Scida, K.
AU - Arroyo-Currás, N.
AU - Eijkel, J. C.T.
AU - Meinhart, C. D.
AU - Pennathur, S.
N1 - Funding Information:
This work was supported by the Institute for Collaborative Biotechnologies through grants ( W911NF-09-001 and DAAD19-03-D-0004 ) from the U.S. Army Research Office. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred. Appendix A
Funding Information:
This work was supported by the Institute for Collaborative Biotechnologies through grants (W911NF-09-001 and DAAD19-03-D-0004) from the U.S. Army Research Office. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred.
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2020/1/10
Y1 - 2020/1/10
N2 - In this study we numerically investigate the intimately coupled transient electrokinetic and electrochemical dynamics of a nanoconfined bipolar electrode system, using experimental results to guide our analysis. Our recently developed 2D numerical model implements the Poisson-Nernst-Planck-Stokes system of equations to describe nanoscale chemical species transport by advection, migration, and diffusion, as well as the presence of both homogenous and heterogeneous reactions. By eschewing the assumption of electroneutrality and resolving diffuse-charge screening effects, our model uniquely accounts for a wide range of nonlinear transient effects including bipolar electrode (BPE) surface polarization, Faradaic charge accumulation, induced-charge electroosmotic flow, and ion concentration polarization. Using this model, we demonstrate that upon the removal of a polarizing electric field, excess accumulated charge at a BPE surface electrochemically discharges following the capacitive relaxation of diffuse space charge in the electrical double layers (EDLs) surrounding the BPE extremities. These EDLs continue to polarize the BPE as they relax by a process of drift-diffusion, wherein the counter-ionic space charge at each pole promotes a large influx of oppositely charged ions to restore electroneutrality. We numerically reproduced this electrokinetic enhancement effect that was first observed in a recently reported experimental system in which charged fluorophores were used as tracer molecules. Our results also support experimental evidence that, following capacitive EDL relaxation, nanoconfined BPEs can exhibit pseudocapacitance-like discharging behavior that is localized to a single end of the electrode; we experimentally linked this localization to surface oxidation of the anodic BPE pole under the applied field. In addition to providing important insight into the interplay between nanoscale electrokinetic and electrochemical phenomena that govern transient electrode processes, our model and the results presented in this work reinforce the notion that the domain of bipolar electrochemistry constitutes a promising frontier for developing “wirelessly” tunable charge storage and visual detection approaches which exploit both electrokinetic and Faradaic mechanisms.
AB - In this study we numerically investigate the intimately coupled transient electrokinetic and electrochemical dynamics of a nanoconfined bipolar electrode system, using experimental results to guide our analysis. Our recently developed 2D numerical model implements the Poisson-Nernst-Planck-Stokes system of equations to describe nanoscale chemical species transport by advection, migration, and diffusion, as well as the presence of both homogenous and heterogeneous reactions. By eschewing the assumption of electroneutrality and resolving diffuse-charge screening effects, our model uniquely accounts for a wide range of nonlinear transient effects including bipolar electrode (BPE) surface polarization, Faradaic charge accumulation, induced-charge electroosmotic flow, and ion concentration polarization. Using this model, we demonstrate that upon the removal of a polarizing electric field, excess accumulated charge at a BPE surface electrochemically discharges following the capacitive relaxation of diffuse space charge in the electrical double layers (EDLs) surrounding the BPE extremities. These EDLs continue to polarize the BPE as they relax by a process of drift-diffusion, wherein the counter-ionic space charge at each pole promotes a large influx of oppositely charged ions to restore electroneutrality. We numerically reproduced this electrokinetic enhancement effect that was first observed in a recently reported experimental system in which charged fluorophores were used as tracer molecules. Our results also support experimental evidence that, following capacitive EDL relaxation, nanoconfined BPEs can exhibit pseudocapacitance-like discharging behavior that is localized to a single end of the electrode; we experimentally linked this localization to surface oxidation of the anodic BPE pole under the applied field. In addition to providing important insight into the interplay between nanoscale electrokinetic and electrochemical phenomena that govern transient electrode processes, our model and the results presented in this work reinforce the notion that the domain of bipolar electrochemistry constitutes a promising frontier for developing “wirelessly” tunable charge storage and visual detection approaches which exploit both electrokinetic and Faradaic mechanisms.
KW - Bipolar electrochemistry
KW - Discharging dynamics
KW - Electrical double layers
KW - Induced-charge electrokinetics
KW - Nanofluidics
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U2 - 10.1016/j.electacta.2019.135275
DO - 10.1016/j.electacta.2019.135275
M3 - Article
AN - SCOPUS:85075857650
SN - 0013-4686
VL - 330
JO - Electrochimica Acta
JF - Electrochimica Acta
M1 - 135275
ER -