Electron Mobility via Polaron Hopping in Bulk Ceria: A First-Principles Study

The outstanding catalytic properties of cerium oxides and, consequently, the broad use in heterogeneous catalysis rely on the easy Ce3+ <-> Ce4+ redox conversion. Within the two-state model of Marcus, the electron transfer associated with the redox process is governed by the electronic coupling matrix element V-AB that accounts for the interaction between the diabatic electronic states at the crossing seam. Here we present a computational analysis based on ab initio quantum mechanics theory that allows for a characterization of negative polaron structures and intrinsic polaron hopping in bulk CeO2. The relevant parameters inherent to the model: reorganization energy, activation barrier, and electronic coupling for the 4f -> 4f electron hopping are estimated for several models. Our analysis predicts an activation barrier of 0.4 eV and a transmission coefficient kappa = 0.81, confirming the earlier proposed adiabatic theory of small polaron and hopping conductivity in reduced bulk ceria.