| This work consists of two parts. In the first part, the effect of the potential energy function on the charge transfer theory was studied. Use of a harmonic potential in the potential energy distance relations for charge transfer reactions at electrodes predicts non-linear Tafel lines and an inverted region for current-potential relations which are in disagreement with well established experimental laws, well known for electron and ion transfer reactions. The inverted region was analyzed in terms of harmonic and Morse type potential energy profiles. Tafel linearity is known (experimentally) to extend over more than 0.6 V for redox reactions and 1.2 V for hydrogen and oxygen evolution; it does not exceed 0.2 V using the harmonic potential energy - distance relations. Qualitatively, an inverted region can not be obtained if a realistic Morse type anharmonic potential energy profile is used. The constant value of the reorganization energy used in interpreting the experimental data to represent the inverted region needs revision. Non-linear Tafel plots for organic spacer covered electrodes can be interpreted in terms of resonance tunneling of the electron across the barrier in the spacer layer.;In the second part of this work a theoretical study of electrochemical reduction oxygen on platinum was carried out. In this latter work, multi-dimensional potential energy surfaces were constructed for the experimentally found most probable rate-determining step in electroreduction of oxygen (ERO) on Pt(111) and Pt(100) using a combination of experimental data in Morse functions and ASED-MO, a semi-empirical quantum mechanical technique. The minimum energy path for the reaction was extracted by Euler's single step method. The non-adiabacity of the electron transfer step was treated with Landau-Zener formalism and the proton tunneling was taken into account using an Eckart barrier. On this basis, the kinetic parameters, e.g., the activation energies, entropies of activation, the symmetry factors and reaction rates of the model reaction, were calculated. |
