Adsorption grand potential of OH on metal oxide surfaces

Context

Describing chemical processes at solid–liquid interfaces as a function of a fixed electron chemical potential presents a challenge for electronic structure calculations and is essential for understanding electrochemical phenomena. Grand Canonical Density Functional Theory (GCDFT) allows treating solid–liquid interfaces in such a way that studying the influence of a fixed electron potential arises naturally. In this work, GCDFT is used to compute the adsorption grand potential (AGP), a key parameter for understanding and predicting the behavior of adsorbates on surfaces. We focused on the adsorption of an OH molecule on three metallic surfaces commonly used in electrochemical processes, such as the oxygen evolution reaction (OER). Our study aims to offer insights into how AGP can be used to compare adsorption strengths under different fixed electron chemical potentials, which is crucial for designing efficient electrode materials. By determining the average number of electrons self-consistently under varying chemical potentials, we showed how one can distinguish between electron acquisition and depletion during the adsorption process, offering a deeper understanding of the adsorbate–surface interactions.

Methods

The approach used in this work employs the Kohn–Sham-Mermin formulation of the Grand Canonical Density Functional Theory. The computations were performed using the periodic open-source density functional theory software, JDFTx, with the Garrity-Bennett-Rabe-Vanderbilt library of ultrasoft pseudopotentials. Calculations were made using truncated Coulomb potentials and the auxiliary Hamiltonian method with the PBE exchange–correlation functional, along with DFT-D2 long-range dispersion corrections. The implicit solvation model CANDLE was used to describe the electrolyte with a 1 M concentration.