Theoretical Calculation of Activation Energies for Pt + H⁺(aq) + e^-(U) ↔ Pt−H:  Activation Energy-Based Symmetry Factors in the Marcus Normal and Inverted Regions

Abstract

The low coverage reversible potential for underpotential deposition of hydrogen on platinum in acid electrolyte is calculated quantum mechanically with two approaches, (i) one using the calculated reaction energy for the overall reaction and an added constant and (ii) the other based on a model of the electrochemical interface. The former yields 0.40 V and the latter 0.48 V, both close to the observed value of ∼0.40 V. Electrode-potential-dependent activation energies are calculated using the interface model for the reduction of the hydronium ion to form the Pt−H bond and for the reverse oxidation reaction over the −0.3 to 3.0 V range. To make this possible, the model explicitly excludes the hydrogen evolution reaction at the cathodic end and water oxidation at the anodic end of the potential range. Cathodic and anodic symmetry factors are determined from the slopes of the activation energy curves, which are used as models for the corresponding activation free energy curves. They are extended into the Marcus-inverted regions for oxidation and reduction. The symmetry factors add to 1.0 in the normal region and in the inverted regions and are not linear functions of the electrode potential.

Low temperature water gas shift over gold catalysts

“…Since bicarbonates could also be intermediates in the WGS (3,47) and the WGS activity was measured in the temperature range 140 -250°C, an alternative route for the WGS via an associative mechanism could be suggested. By quantum chemical calculations for the CO-H2O adsorption on Pt it was found that Ea of water adsorption is 0.86 eV when water is adsorbed dissociatively as Ha and OHa and 1.23 eV via Oa and Ha dissociation (48). The results obtained supported the associative mechanism of WGS on supported platinum and may be regarded as a confirmation of the above-mentioned two probable mechanistic routes for the WGS on gold-based catalysts.…”

Four-electron reduction of O2 over multiple CuI centers: Quantum theory

“…This may be viewed as a linear Gibbs free energy relation. For OH(ads) formation from H 2 O oxidation on Pt [23,24] and alloys of Pt [24], and the reduction of hydronium ions to H(ads) on Pt [25], reversible potential predictions that are close to observed onset potentials have been obtained. The predictions are based on the equation for DG°:…”

Direct molecular dynamics and density-functional theoretical study of the electrochemical hydrogen oxidation reaction and underpotential deposition of H on Pt(111)

“…These studies have also failed to provide a stepwise account of energy disposal in the reactive processes. Because of the complexity of the redox reactions at the electrode/electrolyte interface, a thorough understanding of the atomic details of the electrocatalysis remains to be obtained [30][31][32][33][34][35][36][37][38][39][40][41].…”

“…Ab initio correlated methods [30][31][32][33], density-functional theory (DFT) [34,35], and first-principles molecular dynamics [36,40] may be used to probe the nature of active reaction environments. Atomic-level understanding of several electrocatalytic processes and of adsorbed intermediates involved in redox reactions at the metal/water interface has recently been demonstrated by the simulation of methanol oxidation [40] and oxygen reduction on Pt [39], water activation on Pd [34], and on alloy and sequentially deposited Pt/Ru surfaces [35,41].…”