First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

TL;DR

This study uses advanced computational methods to determine the potential-of-zero-charge in an alumina-coated aluminum/water interface, providing insights into corrosion mechanisms and defect behavior.

Contribution

It introduces a first-principles approach to accurately predict the PZC and defect charge states at the atomic scale for corrosion-related interfaces.

Findings

Predicted PZC at -1.53 V vs. SHE for the model interface.

Calculated defect energy levels indicating oxygen vacancies are uncharged at PZC.

Estimated voltage required to form positively charged oxygen vacancies.

Abstract

The surfaces of most metals immersed in aqueous electrolytes have a several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the existence of both metal|oxide and oxide|liquid electrotlyte interfaces, and makes it challenging to correlate atomic length-scale structures with electrochemical properties such the potential-of-zero-charge (PZC). The PZC value has been shown to be correlated the pitting onset potential for corrosion. In this work, we conduct large-scale Density Functional Theory and ab initio molecular dynamics to calculate the PZC of a Al(111)|gamma-Al(2)O(3)(110)|water double-interface model within the context of aluminum corrosion. By partitioning the multiple interfaces involved into binary components with additive contributions to the overall work function and voltage, we predict the PZC to be -1.53 V vs. SHE for this model. We also calculate the orbital energy levels of defects like oxygen vacancies in the oxide, which are critical parameters in theories associated with pitting corrosion. We predict that the Fermi level at the PZC lies above the impurity defect levels of the oxygen vacancies, which are therefore uncharged at the PZC. From the PZC estimate, we predict the voltage needed to create oxygen vacancies with net positive charges within a flat-band approximation.