All electronic structure calculations were carried out using the Vienna Ab initio Simulation Package (VASP) . Electron-core interactions were accounted for by the projector augmented wave (PAW) method 87 in the implementation of Kresse and Joubert 88 . Exchangecorrelation effects were described by the functional of Perdew, Burke, and Ernzerhof (PBE) in the generalised gradient approximation (GGA) . Respective standard deviations were computed utilising the Bayesian error estimation functional with van-der-Waals (BEEF-vdW) exchange-correlation functional . Following the scheme of Monkhorst and Pack 91 , all total energy calculations were done using a k -point mesh density of 0.15 Å -1 . A planewave cutoff energy of 340 eV was applied for the expansion of the electron one-particle wave functions into a plane-wave basis set. The DFT calculations were considered as converged when the total energy difference was less than 10 -5 eV and all forces exceeded a threshold of 10 -3 eV Å -1 . Images of CI-NEB calculations were separated by a spring constant of 5.0 eV Å -2 to guarantee the continuity of the path. Surface properties were modelled within the supercell approach introducing a vacuum region of at least 20 Å along the z-axis. Well converged symmetrical slabs with a minimum thickness of 20 Å were used to compute the respective surface energies. To examine the adsorption and diffusion properties on (100)-, (110)-and (111)-indexed surface models, 8-, 8-and 13-layer slabs were used, respectively.