Quantum-chemical calculations of ion adsorption on slabs were performed in the Quantum Espresso software package within the generalized gradient approximation by the Perdew-Burke-Ernzerhof (PBE) functional using standard PAW pseudopotentials. Spin polarization was taken into account in the calculations and the maximum energy limit was 600 eV. The Monkhorst-Pack special point method with an electron smearing of 0.1 eV and a k-grid density of 5x5x1 by the Methfessel-Paxton method was selected for integration over the Brillouin zone. The energy convergence criterion of the selfconsistent field method was set at 10 -5 eV. The van der Waals interactions were considered within the Grimme method (DFT-D3). The relaxation of atoms in the slabs was carried out by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, the convergence criterion for the energy optimization of the atom geometry was set at 10 -4 eV and the maximum force was 0.01 eV/Å. A 72-atom graphene, a 60-atom Au(111), and a 60-atom α-Al 2 O 3 (0001) slabs with cross-sectional dimensions of 6x6, 4x4, and 4x4 unit cells, respectively, were used as the model electrodes. The adsorption energy was calculated as the energy of the optimized slab with the ion on the surface minus the energy of the slab with the ion at a distance of 9-11 Å from the surface.