Dynamics of Ce-O bond energy upon formation of O vacancies

CeO2 offers excellent oxygen storage capacity for catalysis and energy applications. It accommodates a surprising number of oxygen vacancies (VO), yet the driving force and origin of these VO are rarely discussed. Through a combination of in situ techniques and resonant inelastic X-ray scattering (RIXS), here, we discovered that upon formation of the VO, the remaining Ce4+-O2- bond energy increases by at least 0.2 eV. Such an increase in the bond energy provides an additional enthalpy change (ΔH) in the reaction of VO formation, stabilizes the reduced CeO2 phase and explains why CeO2 can host an extensive array of VO. This work demonstrates that RIXS is effective in probing metal-oxygen bond energy, possibly under working conditions, which is an ideal method to quantify electronic structures with material performance.