Catalyst Interfaces between two chemically dissimilar materials can strongly influence the functionalities and performance for a wide range of applications. Standing-wave X-ray Photoemission Spectroscopy (SW-XPS) can overcome some of the limitations of conventional XPS technique by combining spectroscopic and scattering techniques, which makes it very suitable for investigating material interfaces. The reporter studied single crystalline LaNiO₃ (LNO) thin films to understand the factors governing the oxygen evolution reaction (OER) electrocatalytic activity. By using SW-XPS, The reporter is able to directly probe the differences in surface chemistry of LNO induced by processing temperature, which is linked to electro-catalytic activity and durability. Moreover, by using in situ ambient-pressure SW-XPS (SWAPPS), the reporter  obtained insights into the potential distribution across the electric double layers (EDLs) at LNO/alkaline electrolyte interfaces. The reporter used tender X-ray SW-XPS to reveal individual contribution from each layer in the valence band structure of PdCoO₂. These two examples highlight the power and versatilities of SW-XPS in shedding light into the chemical and electronic heterogeneity across material interfaces.