O₂ Reduction Stimulates Adatom Generation on Cu(111) Catalyzing Hydrogen Evolution

Electrochemical mass spectrometry (EC-MS) was used to investigate the coupled dynamics of surface hydride formation, the oxygen reduction reaction (ORR), and the hydrogen evolution reaction (HER) on Cu(111) in perchloric acid. Starting with an Ar-saturated electrolyte, hydride formation proceeds via two overlapping cathodic waves that evolve with cycling due to the restructuring of the electrode surface, associated with the removal of residual oxide species. Grand canonical free-energy calculations indicate that the surface hydride stabilizes pristine terraces against roughening and helps to anneal vacancy-adatom defects introduced during specimen preparation. Introducing controlled amounts of O₂ markedly perturbs this behavior, shifting hydride formation to more negative potentials and accelerating HER kinetics, as revealed by EC-MS. Density functional theory and molecular dynamics simulations show that coadsorption of H with ORR intermediates (OH*/OOH*) promotes Cu(111) restructuring through adatom-vacancy formation and subsurface O incorporation. The resulting fluxional adatom sites enhance the HER activity and modulate the ORR kinetics under mixed control. Extended O₂ exposure irreversibly restructures the surface and reshapes the hydride formation waves resulting in a lasting imprint on surface reactivity that remains even after returning to nominally O₂-free conditions. These findings demonstrate that coupled adsorbates restructure Cu(111) under an electrochemical bias, generating new active sites with direct implications for the performance and stability of Cu electrocatalysts.