On the Importance of Geometry in Open Bipolar Electrochemistry Configurations for Corrosion Studies
Authors: Kazem Ghamsari Amin K , Braun Trevor Michael , Alexander Christopher Lewis 
Published: November 2022

This work aims to optimize cell geometry with finite element modeling to ameliorate open Bipolar electrochemistry (BPE) and split BPE setups, increase the faradaic current through the bipolar electrode to trigger localized corrosion on the anodic region, and study the corrosion behavior of anodic films when activated as bipolar electrodes under thermostatic condition.
The advent of Bipolar electrochemistry (BPE) stems from a series of investigations on fluidized bed electrodes conducted by Fleischmann et al. in the 1970s.[1] Since then, and mainly in the recent decade, BPE has been profoundly scrutinized and exploited in disparate fields such as electrodeposition[2,3], synthesis of Janus particles, propulsion of microparticles, corrosion of stainless steel[4,5], anodizing[6], biosensors, and water treatment. Additionally, it has been studied in miscellaneous formats including split BPE, 2D BPE, and array BPE. Fundamentally, BPE is performed by applying an electric field between two inducing electrodes through an electrolytic medium in which an electronic conductor is immersed. The electronic conductor is indirectly polarized such that one end becomes anodic and the other cathodic thus creating two poles of charge.
Due to lack of direct contact to the bipolar electrode, direct monitoring of the current and potential of the bipolar electrode is not viable. However, indirect measurement of current and potential through the integration of BPE with electrogenerated chemiluminescence (ECL), surface plasmon resonance imaging (SPRi), and scanning vibrating electrode technique (SVET) have been proven feasible. In studies that coupled BPE and ECL as well as in corrosion studies of a stainless-steel bipolar electrode, an apparent curvature of the equipotential lines, specifically near the extremities of the bipolar electrode, is noticed[7,8], although it has not been addressed to date. This nonlinearity of potential can be related to the non-uniform electric field in the electrolyte and can be precluded via manipulation of cell geometry.
The major benefit of using BPE for corrosion studies compared to traditional three-electrode techniques with direct polarization is the presence of a continuum of applied potentials distributed along the length of the bipolar electrode in the direction of the electric field. The distribution of potential results in distinct corrosion behaviors that may be analyzed along the length of the metal. Nevertheless, the challenge is to configure the experimental setup in a way that promotes a one-dimensional distribution of applied potential on a 2d surface while ensuring the polarization is high enough to produce the necessary corrosion response. Doing so allows one to study pitting characteristics such as pit initiation rates and distribution as well as pit growth rate from post-analysis of pit size distributions.

References

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Figure 1