The effect of catalyst film thickness on the magnitude of the electrochemical promotion of catalytic reactions

The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the model catalytic reaction of C 2 H 4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μ m) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μ m) films. The Faradaic efficiency Λ was found to increase moderately with increasing film thickness and to be described semiquantitatively by the ratio 2 Fr o / I 0 , where r o is the unpromoted rate and I 0 is the exchange current of the catalyst–electrolyte interface. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O 2- species, which causes electrochemical promotion.