Mass transfer effects on kinetics of the hydrogen oxidation reaction at Nafion film covered Pt/C rotating disk electrodes

The effects of mass transfer on the kinetics of the hydrogen oxidation reaction at the Nafion covered Pt/C electrodes immersed in 0.5 M H2SO4 was investigated using a rotating disk electrode configuration. The hydrodynamic voltammograms were analyzed to determine the kinetic parameters using the modified Koutecky–Levich equation. The permeability of H2 in the Nafion film was determined to be 2.0 × 10−5 mM cm2 s−1, which is close to that in 0.5 M H2SO4. Due to the fast intrinsic reaction rate of H2 oxidation on the Pt catalyst, the diffusion of H2 in the catalyst layer affected the overall reaction rate to a higher extent when the Pt loading or the overpotential increased. The effect of H2 diffusion in the catalyst layer on the overall reaction rate was accounted for using the effectiveness factor. The corrected exchange current density for the 20 wt% Pt/C catalyst was determined to be about 0.96 mA cm−2, based on the real Pt surface area. The results of this work may contribute to the measurement on the intrinsic electrocatalytic activity of a high surface area catalyst used in proton exchange membrane fuel cells.

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► The effect of H2 diffusion in the Pt catalyst layer on the overall HOR rate was accounted for using the effectiveness factor.
► A theoretical description of the thin-film RDE method for the determination of the kinetic parameters was presented, and the intrinsic i0 value was thus determined.
► The corrected i0 value of the Pt catalyst was determined to be 0.96 mA cm−2.