Water Reactivity on the LaCoO3 (001) Surface: An Ambient Pressure X‑ray Photoelectron Spectroscopy Study

The reactivity of water with the (001)pc surface of epitaxial LaCoO3 (LCO) thin films was investigated as a function of relative humidity (RH) by ambient pressure X-ray photoelectron spectroscopy. Specifically, water isobars (pH2O = 100 mTorr) were performed cooling from 300 to 25 °C, reaching a final RH of ∼0.3%. Significant changes were found in the O 1s and C 1s core-level spectra at different RHs, which were deconvoluted to yield new insights into the hydroxylation and hydration of the LCO surface. Surface hydroxyl groups were found dominant, which were accompanied by minor components including (bi)­carbonates, adsorbed water, and undercoordinated/surface-dipole-influenced oxygen sites on the perovskite surface. A multilayer model was used to quantify the coverage of each species, from which the LCO (001)pc surface was found to exhibit three different regimes upon increasing RH. The water reactivity with the LCO surface proceeded by surface hydroxylatation to reach saturation (up to ∼0.5 ML), after which carbonates were found to displace hydroxyl groups, and then adsorption of water molecules.