The influence of the apparent Pd coverage on Au nanoparticles on the kinetics of the hydrogen oxidation (HOR) reaction has been explored by combined experimental rotating disc and microkinetic modeling study. PdAu bimetallic electrodes with variable Pd coverage in the interval from 0.07 to 2 MLs were obtained by electrodeposition of Pd on carbon supported Au nanoparticles. The experimental rotating disc electrode curves have been analyzed with the help of a kinetic model, in order to shed light on the predominant HOR mechanism (Heyrovsky-Volmer vs. Tafel-Volmer), the nature of the rate determining step, and their dependence on the Pd coverage, and get an insight into the type of HOR intermediate. The kinetic modeling suggests that the Heyrovsky-Volmer mechanism can reproduce the experimental curves for the whole range of Pd coverages explored. However, the Tafel step cannot be fully discarded around the equilibrium potential, its eventual contribution increasing as the coverage of Pd is reduced. The results of this work support a weakly adsorbed Had intermediate in the HOR on Pd, its Gibbs energy of adsorption decreasing from positive to near-zero values with the decrease of the apparent Pd coverage, underlying the enhancement of the hydrogen oxidation activity of PdAu compared to pure Pd.
- Heyrovsky-Volmer and Tafel-Volmer mechanisms
- Hydrogen oxidation reaction
- Palladium-Gold electrodes