Theoretical Relations between Electronic and Ionic Work Functions, Standard Reduction Potentials for Metal Dissolution and the Corrosion Potential

Abstract

Corrosion resistance has become an important factor to consider in integrated computational materials engineering, yet generating science-based indicators of corrosion resistance for hypothetical materials remains challenging. We explore the quantitative relations between work function and corrosion potential, taking a theoretical approach that considers the relation between these thermodynamic and kinetically-determined variables. The work function is a fundamental thermodynamic property of a metallic surface in isolation, whereas the corrosion potential is kinetically determined as the potential at which the rates of anodic and cathodic processes active on the metal surface are equal. The latter quantity is therefore time dependent, as well as dependent on the material, surface preparation, ageing/history and the environment. Reasoning from Mixed Potential Theory, we develop a rationale for the correlation between the corrosion potential and the electronic work function. Two distinct Born-Haber cycles for the anodic dissolution reaction are analyzed to allow calculation of a related quantity, the ionic work function, which embodies the energy of desorption for metal cations from an electrode. The ionic work function is not only highly correlated with, but of similar magnitude to the cation hydration energy. The theoretical analysis provided herein establishes the significance of not only the electronic work function, but also the ionic work function, cation hydration energy, cohesive energy and the ionization potential as co-descriptors for the corrosion resistance of candidate corrosion resistant metal alloys, with the role of the environment to be considered in future work.