Reducibility, Adsorption Energies, Surface Acidity - Fundamental Material Properties for Fast Oxygen Exchange

Recent studies have shown that surface modifications can be used to tune the high temperature oxygen exchange kinetics of a single material systematically over several orders of magnitude, shifting the focus of predictive material design from bulk descriptors, such as oxygen nonstoichiometry, diffusivity, or the O 2p band center, to a material's outermost surface and its properties. Here, we aim to identify general design principles for fast oxygen exchange based on three fundamental material properties: oxide reducibility, adsorption energetics, and surface acidity. We explain in detail how these properties relate to a material's electronic structure to facilitate guided materials discovery and design. Revisiting the example of perovskites, we discuss the connection of a material's electronic structure with its equilibrium defect chemistry and doping compensation mechanisms, and consequently to experimental observables, such as oxidation enthalpy and oxygen diffusivity. We then introduce a molecular orbital model for oxygen adsorption on mixed conducting oxide surfaces, rationalizing trends of adsorption energies with a material's chemistry and electronic structure. Using this model we explore the effect of surface modifications on adsorption energetics, partially clarifying the effect of surface acidity on oxygen exchange kinetics. For all of the above, we present detailed ab-initio calculations that translate our concepts to realistic material systems. Our results illustrate that both a shallow bulk O 2p band center and a basic surface tuned towards a low work function are key for fast oxygen exchange kinetics on pristine surfaces and we discuss corresponding material design strategies. Lastly, we explore implications for durability requirements under operating conditions.