Electrode potential-dependent anion chemisorption and surface bond polarization as assessed by Density Functional Theory

The electrostatic field-dependent energetics of low-coverage halogen chemisorption oil (I I 11) planes of platinum, gold, silver and mercury are examined of Density Functional Theory (DFT) using finite metal clusters with the primary aim of describing such behavior in relation to potential-dependent halide adsorption at electrochemical interfaces. The general relationship between the field-dependent and electrode potential-dependent adsorption energies of such neutral and ionic species is clarified in terms of the static surface-adsorbate dipole moment, mu(S). The sensitivity of the DFT-based mu(S) values to the metal cluster size and geometry is examined. Better agreement with experimental low-coverage. Its estimates, obtained from work function-coverage data at metal-vacuum interfaces, requires metal clusters extending to at least second-nearest-neighbor atoms in the surface plane. The mu(S) DFT values for metal-halogen bonding are also compared with experimental estimates extracted from electrochemical thermodynamic data. The markedly (greater than or equal to2-3-fold) larger -mu(S) values for the latter reflect the role of inner-layer solvation in inducing greater surface bond polarization. Comparable increases in -mu(S) values calculated from DFT are also obtained by including interfacial solvent molecules modeled as dielectric spheres. The sensitivity of the dipole moment to the interfacial field as deduced by DFT is also noted in relation to observed electrochemical behavior.