Unraveling the structure–sensitivity of the photocatalytic decomposition of N2O on CeO2: a DFT+U study

Abstract

The photocatalytic activity of N₂O dissociation on CeO₂ strongly depends on the exposed surface termination, with the (110) surface being much more reactive than the (111) surface. However, the physical nature requires a more detailed molecular level study. Using the DFT+U method, in the present study, we intend to explore the influence of surface termination from the following three aspects: the optical absorption, transfer kinetics of electron polaron, and the photo-chemical reaction process based on comparative studies of CeO₂ (111) and (110) model surfaces. Due to the large band gap value, both CeO₂ surfaces show negligible optical absorption difference. For both surfaces, the electron polaron is preferably localized on the surface rather than in the bulk. The Ce³⁺ ion close to the oxygen vacancy repels the excited electron due to Coulomb interactions. The migration barrier of the electron polaron from the bulk to the surface on the (110) surface is slightly lower than that on the (111) surface, suggesting a higher transfer rate of the electron polaron. The dissociation process of N₂O into N₂ with and without the photoexcited electron on CeO₂ (110) and (111) surfaces is explored. On the stoichiometric CeO₂ surface, N₂O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy dramatically decreases in the presence of photoexcited or excess electrons on the CeO₂ surface. The reaction energy is related to the electronic state of dissociated O. More negative charges make O more stable and accordingly lead to higher exothermic reaction energy.