Where G nO * is the Gibbs free energy of the nanoparticle with n oxygen atoms, G * is the Gibbs free energy of the nanoparticle with no oxygen atoms. G H 2 O and G H 2 are the Gibbs free energies of water and dihydrogen in their standard state, respectively. U SHE is the potential of the standard hydrogen electrode. The Gibbs free energies in Equation are often reduced to G = E DFT + E ZPE -T S vib for adsorbates. Considering the large size of our systems we decided to ignore zero-point and thermal contributions for the oxidized nanoparticles and reduce the Gibbs free energy to the DFT energy, G ≈ E DFT . For reference species, the total energy is computed with DFT on the isolated molecule, Zero Point Energies (ZPEs) are available elsewhere 62 (0.27 eV for H 2 , 0.56 eV for H 2 O), and entropy contributions are taken from the NIST-JANAF thermodynamic tables. In practice Equation 3 is related to the total (∆G O ) or per atom (∆ ḠO ) binding energy of oxygen atoms on the nanoparticle, using water and hydrogen as reference states.