  Accelerating the oxygen reduction reaction (ORR) is a main subject of
electrocatalysis research.A critical step of ORR is the formation of the
hydroperoxyl functional group (OOH*) intermediate. In this study, we
investigate the influence of defects on facilitating the creation of OOH* in a
zirconia-based cathode under hydroxyl group (-OH) adsorption. Simulations
involve tetragonal pristine ZrO2 (111) surfaces with introduced oxygen vacancy
(t-ZrO2-x) and nitrogen dopant (ZrO2-xNx). Density functional theory (DFT) is
used to calculate the competitive -OH adsorption energies on pristine and
defective surfaces. It reveals that oxynitride t-ZrO2-xNx and
under-stoichiometric oxide t-ZrO2-x exhibit the lowest and highest
susceptibility to -OH adsorption, respectively. Additionally, we have
determined the Minimum Energy Pathway (MEP) for OOH* formation on t-ZrO2,
t-ZrO2-x, and t-ZrO2-xNx with adsorbed-OH using the Nudged Elastic Band (NEB)
approach with the COMB3 potential. Our results highlight the significant
influence of defects on tuning the barrier energy of OOH* formation. The trend
in the barrier energy formation of OOH* decreases in the order of t-ZrO2-x >
pristine t-ZrO2 > t-ZrO2-xNx. We demonstrate that ZrO2-xNx is a promising
candidate for accelerating ORR due to its lower barrier energy for OOH*
creation. The findings from this study offer crucial insights for
experimentalists aiming to develop optimal non-platinum-based cathode
materials.
