Probing adsorbates on La1-x Sr x NiO3-δ surfaces under humid conditions: implications for the oxygen evolution reaction

Earth-abundant nickel-containing perovskite oxides (ANiO(3)) are highly active materials for the oxygen evolution reaction (OER). The strong nickel-oxygen (Ni-O) covalency, tunable by A-site chemical substitution, contributes to both bulk and surface material properties like the formation of oxygen vacancies (v (center dot center dot) ( O )) and OER activity. Here we quantify the coverage of OER relevant adsorbates on a series of La1-x Sr (x) NiO3-delta (LSNO, 0 <= x <= 0.5) epitaxial thin films exposed to humid environments by ambient pressure x-ray photoelectron spectroscopy. While all LSNO film compositions investigated here have comparable hydroxide coverages at the relative humidities (RHs) probed (1.5 x 10(-5) - 0.2%RH), the amount of under-coordinated surface oxygen increases notably with Sr content. We interpret differences in the free energy of adsorption (Delta G (ads,i )) of these OER intermediates, inferred from adsorption isotherms, in the context of proposed v (center dot center dot) ( O )-mediated OER mechanisms, consistent with the pH-dependent OER activity observed here for LSNO. We find that Sr incorporation enhances the affinity of LSNO surfaces for these under-coordinated oxygen species, in line with calculations in the literature.

Automated summary

Nickel-containing perovskite oxides, such as LSNO, are highly active materials for the oxygen evolution reaction due to strong nickel-oxygen covalency. The addition of strontium enhances the affinity of LSNO surfaces for under-coordinated oxygen species, providing insights into the OER mechanisms mediated by oxygen vacancies. The study demonstrates the importance of surface composition in determining the OER activity of perovskite oxides.