Earth-abundant, nickel-containing perovskite oxides (ANiO3) are highly active materials for the oxygen evolution reaction (OER). The strong nickel-oxygen (Ni-O) covalency in ANiO3, tunable by A-site chemical substitution, contributes to both bulk and surface material properties such as the formation of oxygen vacancies (vO●●) and OER activity. In this talk we discuss results from a recent ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) investigation of several OER-relevant adsorbates on a series of La1-xSrxNiO3-δ (LSNO, 0 ≤ x ≤ 0.5) epitaxial thin films in humid environments (1.5 x 10-5 – 0.2 % relative humidity (RH)). Here we harness the ability of AP-XPS to observe occupied electronic structure and to quantify speciation and coverage of adsorbate species in situ, relating these observations to ex situ activity measurements and proposed vO●●-mediated OER mechanisms. We observe several indicators of increased Ni-O covalency with Sr content in LSNO, which correspond to observed increases in OER activity with Sr content. Quantitative determination of OER-relevant adsorbates indicates an increased affinity for under-coordinated oxygen on LSNO with higher Sr content films. We consider these two observations in conjunction with ex situ observations of pH-dependent OER activity, characteristic of an vO●●-mediated OER mechanism, to consider the implications of this study on these mechanisms.

Probing adsorbates on La1-xSrxNiO3-δ surfaces under humid conditions: Implications for the oxygen evolution reaction

ACS Spring Meeting 2021

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