Speaker
Description
Does electrochemistry at stepped and kinked single-crystal surfaces differ significantly from that at ideal low-index surfaces? Intuitively, in a classical electrostatic picture we expect a potential-induced excess surface charge to accumulate on protruding sites. In this picture, the high local surface curvature causes strong inhomogeneous electrical fields, that then could significantly affect adsorption energetics and kinetics, but could also invalidate the averaged dipole-field interaction view commonly employed in electrochemical simulations. Here, we scrutinize this picture by evaluating several adsorbates on various adsorption sites on a high-index Pt(632) surface with first-principles density-functional theory (DFT) calculations, employing fully grand canonical solvation in its second order approximation [1]. We show that the prevalent averaged dipole-field description does indeed hold and that variations in the local electric field do not play the anticipated significant role at undercoordinated, protruding adsorption sites. Instead, the changed local environment introduces dipole variations which strongly affect the energetic dependence on electrode potential and electrolyte concentrations. We find a correlation between these dipole variations and site coordination, showing a consistent trend across adsorbates, adsorption sites, and surface terminations. On this basis we discuss how the adsorption behavior changes on defect-rich, undercoordinated surfaces in an electrochemical environment. This provides important insights for moving from ideal low-index model-surfaces towards more complex electrochemical systems.
[1] N. G. Hörmann, N. Marzari, and K. Reuter, npj Comput Mater 6, 136 (2020)
