Water Oxidation Catalysis on the Nitrogen-Deficient SrNbO2 N(001) Surface

Perovskite oxynitrides are a promising class of photocatalysts to drive the oxygen evolution (OER) half reaction of water splitting. They are however known to be less stable than pure oxides and may lose nitrogen, in particular in the early stages of their operation. Under OER conditions, nitrogen vacancies are likely to be filled with oxygen, thus altering the stoichiometry of the surface. Here, we investigate, using density functional theory calculations, the effect of this substitution on the surface electronic structure and catalytic activity under OER conditions. We show that the investigated oxynitride SrNbO2N, due to the multivalent nature of the Nb cations, behaves differently than the related SrTaO2N. In particular, we show that under OER conditions, the substitution of N by O does enhance the reactivity, which is optimal around 3/4 substitution, given the ideal balance of excess charge injection and the suppression of O-N dimer formation. These results highlight the rich surface chemistry of oxynitrides, which strongly depends on the surface stoichiometry that represents a potential tuning knob for the activity of these materials.

Automated summary

By using density functional theory calculations, the effect of oxygen substitution for nitrogen on the surface electronic structure and catalytic activity of SrNbO2N under OER conditions was investigated. It was found that the substitution of nitrogen by oxygen does enhance reactivity, especially at around 3/4 substitution ratio.