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There are two distinctly different subsurface oxygen peaks, with one related to lattice defects/Cu vacancy (henceforth: O SB Cu,vac sb ) at 531.6 eV and interstitial oxygen (O SB int sb ) intercalated in the metallic Cu structure at 533.7 eV. There is a Cu SB 2 sb O layer buried underneath a reduced copper film, and this is based on the relative intensity changes as a function of photon energy and the dominating metallic copper signal in Cu spectra. Climate change makes it essential that we develop alternatives to fossil-based resources for our energy and chemical needs. The O SB int sb species is here thought of as the oxygen dissolved from Cu oxide that, upon interaction with copper lattice vacancy sites, may form O SB Cu,vac sb . [Extracted from the article]

Subsurface oxygen has been proposed to be crucial in oxide‐derived copper (OD‐Cu) electrocatalysts for enhancing the binding of CO intermediates during CO2 reduction reaction (CO2RR). However, the presence of such oxygen species under reductive conditions still remains debated. In this work, the existence of subsurface oxygen is validated by grazing incident hard X‐ray photoelectron spectroscopy, where OD‐Cu was prepared by reduction of Cu oxide with H2 without exposing to air. The results suggest two types of subsurface oxygen embedded between the fully reduced metallic surface and the Cu2O buried beneath: (i) oxygen staying at lattice defects and/or vacancies in the surface‐most region and (ii) interstitial oxygen intercalated in metal structure. This study adds convincing support to the presence of subsurface oxygen in OD‐Cu, which previously has been suggested to play an important role to mitigate the σ‐repulsion of Cu for CO intermediates in CO2RR. [ABSTRACT FROM AUTHOR]