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

## TL;DR

Oxygen reduction on copper surfaces creates new active sites that boost hydrogen production and change surface reactivity.

## Contribution

The study reveals how oxygen reduction and hydrogen evolution reactions interact to restructure copper surfaces and generate active adatom sites.

## Key findings

- O2 exposure shifts hydride formation to more negative potentials and enhances HER kinetics.
- Coadsorption of H with ORR intermediates promotes Cu(111) restructuring via adatom–vacancy formation.
- Extended O2 exposure irreversibly restructures the surface, leaving a lasting imprint on reactivity.

## Abstract

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.