Polarography of cadmium(II) in presence of substituted alkanolamines

A study has been made of the effect of an irreversibly adsorbed iodide layer on the anodic oxidation of formic acid at a platinized platinum electrode. It is shown that, in the presence of the preadsorbed iodide layer, the oxidation process obeys the following rate expression, i=nF k^→c^α g(θ_I) exp(α_anFφ_r/RT where α≈0.75 and α_an≈0.5. This is explained in terms of the following rate-determining step, (HCOOH)_ads→C_*OOH+H⁺+e and involves the adsorption of formic acid on the iodide covered surface. A strong catalytic effect of the iodide layer is observed; the function g (θ_I) passes through two maxima at θ_I values of 0.15 and 0.53. It is suggested that these effects arise from a coverage-dependent variation of bond strength between the adsorbed iodide and platinum.