Equilibrium electroconvective instability

Area of Science:

• Electrochemistry
• Fluid Dynamics
• Surface Science

Background:

• Hydrodynamic instability in concentration polarization at charged interfaces is typically attributed to nonequilibrium electro-osmosis.
• Previous models assumed perfect charge selectivity, limiting the understanding of instability mechanisms.
• Neither equilibrium electro-osmosis nor bulk electroconvection were thought to cause instability in perfectly selective solids.

Purpose of the Study:

• To investigate the role of non-perfect charge selectivity in hydrodynamic instability at charged interfaces.
• To explore the possibility of equilibrium electroconvective instability.
• To propose an experimental method for distinguishing between equilibrium and nonequilibrium instability origins.

Main Methods:

• Theoretical analysis of hydrodynamic instability at a charge-selective interface.
• Relaxing the assumption of perfect charge selectivity in theoretical models.
• Analyzing the conditions for equilibrium electroconvective instability.

Main Results:

• Relaxing the assumption of perfect charge selectivity allows for equilibrium electroconvective instability.
• This finding challenges the long-held attribution of instability solely to nonequilibrium electro-osmosis.
• A simple experimental test is proposed to differentiate between equilibrium and nonequilibrium origins.

Conclusions:

• Hydrodynamic instability in concentration polarization can be driven by equilibrium electroconvection.
• The degree of charge selectivity at the interface is crucial in determining the instability mechanism.
• Further experimental validation is needed to confirm the proposed instability mechanisms and diagnostic test.