Probing space charge and resolving overlimiting current mechanisms at the micro-nanochannel interface

TL;DR

This study investigates how space charge effects influence overlimiting current mechanisms in micro-nanochannels, revealing a transition from diffusion-limited to surface conduction, with experimental and theoretical insights into surface charge dynamics.

Contribution

It provides experimental evidence and theoretical analysis of space charge effects and surface charge variation at micro-nanochannel interfaces under high voltage conditions.

Findings

Extended space charge layer correlates with maximum dc resistance.

Effective surface charge varies with applied voltage.

Comparison between experimental data and models estimates surface charge changes.

Abstract

We present results demonstrating the space charge-mediated transition between classical, diffusion-limited current and surface-conduction dominant over-limiting current in a shallow micro-nanochannel device. The extended space charge layer develops at the depleted micro-nanochannel entrance at high current and is correlated with a distinctive maximum in the dc resistance. Experimental results for a shallow surface-conduction dominated system are compared with theoretical models, allowing estimates of the effective surface charge at high voltage to be obtained. In comparison to an equilibrium estimate of the surface charge obtained from electrochemical impedance spectroscopy, it is further observed that the effective surface charge appears to change under applied voltage.