Probing adsorbates on La <sub> 1− <i>x</i> </sub> Sr <i> <sub>x</sub> </i> NiO <sub> 3− <i>δ</i> </sub> surfaces under humid conditions: implications for the oxygen evolution reaction
O. Quinn Carvalho, Prajwal Adiga, Le Wang, Jishan Liu, Endong Jia, Yingge Du, Slavomír Nemšák, Kelsey A. Stoerzinger
Abstract
Abstract 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 •• O ) and OER activity. Here we quantify the coverage of OER relevant adsorbates on a series of La 1− x Sr x NiO 3− δ (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 × 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 (Δ G ads, i ) of these OER intermediates, inferred from adsorption isotherms, in the context of proposed v •• 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.