Using Gibbs Energies to Calculate the Pt(111) Hupd Cyclic Voltammogram

The cyclic voltammogram for hydrogen on Pt(111) has been calculated using potential-dependent Gibbs reduction energies obtained by the Interface 1.0 code. The reversible potentials, U rev, are predicted by the equilibrium condition where the Gibbs energy of the oxidized reactant plus an electron and the Gibbs energy of the reduced product, when graphed as functions of electrode potential, cross and are equal at the reversible potential. Reversible potentials are calculated for 12 different coverages of H(ads), and a third-order analytic function is fit to the results. Using the derivative of this function, the experimental voltage scan rate, and the experimentally observed maximum H(ads) coverage, the cyclic voltammogram can be calculated. With the Langmuir isotherm contribution −TΔS added to the Gibbs energies, the width of the predicted voltammogram and its maximum current density compare favorably with measurements from the literature. In detailed shape, the predicted current densities are curved more than the experimental ones near the maximum values, which is a feature ensured by the addition of the Langmuir term, which has an inflection at 0.5 ML coverage. This suggests the need for modification of the Langmuir isotherm near 0.5 ML coverage and possibly subtle improvements to the surface models used.