Asymmetric rectified electric fields for symmetric electrolytes

TL;DR

This study demonstrates that asymmetric rectified electric fields (AREF) can be generated in symmetric electrolytes using a sawtooth voltage, with the AREF strength tunable solely by voltage waveform manipulation, advancing electrochemical control.

Contribution

It introduces a new method to generate and control AREF in symmetric electrolytes through voltage waveform design, expanding understanding beyond previous approaches.

Findings

AREF can be generated with equal diffusion coefficient electrolytes using sawtooth voltage.

The AREF strength is tunable by the voltage's time dependence.

An equivalent circuit explains the physical mechanism of AREF generation.

Abstract

In this paper, building upon the discovery of asymmetric rectified electric fields (AREF) in recent experiments [S.H. Hashemi et al., Physical Review Letters 121, 185504 (2018)], we explore the generation of AREF by applying a sawtooth-like voltage to 1:1 electrolytes with equal diffusion coefficients confined between two planar blocking electrodes. This differs from an earlier approach based on a sinusoidal AC voltage applied to 1:1 electrolytes with unequal diffusion coefficients. By numerically solving the full Poisson-Nernst-Planck equations, we demonstrate that AREF can be generated by a slow rise and a fast drop of the potential (or vice versa), even for electrolytes with equal diffusion coefficients of the cations and anions. We employ an analytically constructed equivalent electric circuit to explain the underlying physical mechanism. Importantly, we find that the strength of AREF can be effectively tuned from zero to its maximal value by only manipulating the time-dependence of the driving voltage, eliminating the necessity to modify the electrolyte composition between experiments. This provides valuable insights to control the manipulation of AREF, which facilitates enhanced applications in diverse electrochemical systems.