Elucidation of the Electrochemical Activation of Water over Pd by First Principles

摘要

The water/metal interface is critical to the performance of a number of chemical, biological, and materials systems, including electrocatalysts for fuel cells, corrosion-resistant surfaces, electrochemically deposited electronic and magnetic films, and inorganic scaffolds for biomolecular adhesion. The reactivity and electrochemical behavior of the metal/solution interface is dictated by the explicit atomic and electronic structure that forms at the interface as a response to environmental conditions, such as an applied potential. Elucidating the structure and chemistry at this interface, however, is a considerable challenge because of the large number of molecular configurations that result from factors such as the various orientations of the water molecules in the hydrogen-bonded network, the presence and formation of different ions at various positions within the interface, and the range of reactions that can occur at different applied surface potentials. Spectroscopic resolution of the molecular-level transformations that occur at this interface as a function of the applied electrochemical conditions is difficult to obtain. Although theory has made important advances in elucidating gas-phase reactions on metal substrates, there have been very few ab initio studies of the metal/solution interface in the presence of an applied potential[1]-[3] These previous studies were pioneering, as they provided insights into the reactivity of the interface. Their treatment of the metal, the solution phase, and the polarizability of the interface with potential, however, was not quantitative enough to model the detailed surface chemistry accurately. Herein, we report the development and application of an ab initio quantum mechanical approach to simulate the specific changes in the atomic structure of the water/metal interface and its reactivity as a function of applied potential. The approach is used to derive what we believe is the first interfacial electrochemical phase diagram to be developed by ab initio calculations. More specifically, we examine the activation of aqueous water over Pd(111). The results demonstrate that the polarization of the interface is critical in correctly establishing the structure and the reactivity of the interface as a function of potential.