Transients of the open-circuit potential observed during the interaction of formic acid with preliminarily adsorbed oxygen on a platinized platinum electrode

Transients of the open-circuit potential, which are observed during the interaction of formic acid with preliminarily adsorbed oxygen (O-ads) on a Pt/Pt electrode in 0.5 M H2SO4, are measured. It is established, by means of the method of cathodic potentiodynamic pulses, that the slowest interaction of formic acid with Oads occurs in the region of large coverages of the electrode surface by oxygen (theta(O) similar to 1-0.8). A presumption is put forward that the process rate in this region is defined by a direct reaction of O-ads with molecules of formic acid from the bulk solution. It is shown that the interaction of formic acid with Oads in the region of intermediate coverages (theta(O) similar to 0.8-0.2) proceeds via a mechanism of conjugated reactions. Transients of the open-circuit potential for formic acid are compared to transients for carbon monoxide obtained in analogous conditions. The substantially shorter overall time of potential decay in the case of CO (at the same concentrations) is caused by a faster reaction of CO with adsorbed oxygen in the region of large theta(O). The difference is explained by assuming that the HCOOH adsorption as opposed to CO bears a dissociative character.