First-Principles Investigation of Surface p<i>K</i><sub>a</sub> and\nthe Behavior of Acids at Aqueous–Metal Interfaces

Several computational\nmethods were reported for the accurate determination\nof p<i>K</i><sub>a</sub> values in a solvent medium, but\nthe research on surfaces and interfaces is limited. This study reports\na new method for accurately determining the surface p<i>K</i><sub>a</sub> (*p<i>K</i><sub>a</sub>) of acids on surfaces.\nThe *p<i>K</i><sub>a</sub> is defined as the function of\nthe adsorption energies of neutral acids and their deprotonated form.\nIn the suggested method, the estimated proton solvation-free energy\nvalue is not required, a fact that increases the accuracy of the results.\nThe *p<i>K</i><sub>a</sub> values of various organic and\ninorganic acids on the (111) surfaces of Ag, Au, and Pt were evaluated.\nThe results are validated with available experimental results on various\nsurface coverage ratios. The results point out that weak acids adsorbed\non the metal-aqueous interface are orders of magnitude stronger acids\nthan those in homogeneous solutions. The shift of the p<i>K</i><sub>a</sub>s is largest on platinum. These results are of major\nimportance in electrochemistry and heterogeneous catalysis.