Electron transfer in Electrocatalysis

WOLFGANG SCHMICKLER; ELISABETH SANTOS; PAOLA QUAINO

Washington

Congreso; 11th Spring Meeting of the International Society of Electrochemistry; 2012

International Society of Electrochemistry

Electrochemical electron transfer reactions involve a change in the solvation sphere of the reactants, and thermal fluctuations to overcome the activation energy; in addition, they depend strongly on the electrode potential. Therefore, they cannot be treated by DFT alone, or only within oversimplified models. In our group we have developed our own approach, which combines electron transfer theory with DFT [1]. The basic idea is the following: DFT provides the electronic energy of the initial and the final state as a function of distance; our theory interpolates between the electronic energies in order to describe electron transfer, and introduces the coupling to the solvent together with the fluctuations. So far, we have applied our theory to hydrogen evolution both on bare metal electrodes and on a variety of nanostructured surfaces. The results are encouraging [2], and we will present a number of examples. However, hydrogen is a particularly simple case since the electronic energy of the hydrogen atom or molecule is easily obtained by DFT, and the electronic energy of the corresponding ion, the proton, is zero. An application to other reactions involves performing DFT calculations for ions, and an extension of our interpolation scheme. We have chosen the reaction: OH- (sol) = OHad + e- as a first example. Correspondingly, we have performed DFT calculations both for the OH radical and the anions ? the latter involve a few technical tricks to localize the excess negative charge. The Coulomb repulsion U between electrons on the same orbital is adjusted so that it provides the correct interpolation between the two states. With these data, we have calculated the free energy surface for this reaction at various electrode potentials.