First-principles based quantification of charged species redistribution at electrochemical interfaces: Model system of zirconium oxide

Modeling local distribution of charged ions and ionic defects at electrochemical interfaces is key to understanding related electrochemical processes. Based on the grand canonical approach which defines the electrochemical potential of individual charged species, a unified treatment of defects in solid oxide and ions on water side can be established. In this work, we apply this framework to the system of ZrO₂/water interface. Density functional theory calculations are performed to obtain defect formation energy in the oxide materials and ab initio molecular dynamics is used to assess the formation free energy of H⁺ and OH^- ions in water at different distances from the ZrO₂ surface. The results are fed into a continuum model which produces the equilibrated distribution of these charged species. The continuum model considers explicitly both ion adsorption and defect segregation in the vicinity of the interface, and the diffuse layer and space charge layer in the extended area. Such a unified description reveals the influence of interfacial chemistry on oxide defect chemistry, and vice versa. This framework based on the grand canonical approach allows easy inclusion of additional charged species into the system and offer a general tool for studying electrochemical interfaces.