where E SURF+H , E SURF , and 4E H stand for the total energy of the surface with a monolayer of hydrogen, the total energy of the clean surface and the total energy of an isolated hydrogen atom. To convert E H,b to the Gibbs free energy for H ads formation (ΔG H,ads ), the procedure of Nørskov et al. was used (ΔG ads (H) = E H,b + 1/2E H2 + 0.24 eV, E H2the total energy of an isolated H 2 molecule).