Facet dependence for CeO ₂ as a potential ammonia oxidation electrocatalyst studied by DFT

The transition toward a carbon-free energy system requires energy carriers that are both sustainable and practical to scale. Ammonia is a promising candidate due to its high energy density, established infrastructure, and compatibility with renewable electricity. A key challenge in direct ammonia fuel cells (DAFCs) development is the lack of inexpensive, active, and poison-resistant anode catalysts capable of efficiently carrying out the ammonia oxidation reaction (AOR). Ceria (CeO 2 ) related materials have shown potential for AOR and adjacent reactions, however, a comprehensive mechanistic understanding of AOR on pristine ceria surfaces has not previously been established. This density functional theory (DFT) study examines CeO 2 (111), CeO 2 (110), and CeO 2 (100) for AOR. CeO 2 (100) was found to be the most active surface with the least positive limiting potential of 1.16 V and a potential determining step (PDS) of *NH 3 → *NH 2 for the Gerischer-Mauerer mechanism, whereas the Oswin-Salomon mechanism has a more positive limiting potential of 1.33 V due to the PDS being *NH 2 → *NH. In comparison, CeO 2 (111) and CeO 2 (110) possessed limiting potentials of 1.38 V and 1.33 V respectively, both with a PDS of *NH 2 → *NH for the Gerischer-Mauerer and Oswin-Salomon mechanisms. Among oxide materials, the activity of CeO 2 (100) is improved over NiO due to possessing a lower limiting potential for AOR. Introducing vacancies into CeO 2 may further improve its activity toward AOR.