Mechanistic Studies of Formate Oxidation on Platinum in Alkaline Medium

The electro-oxidation of formate (HCOO-) on polycrystalline Pt in highly basic medium (pH = 14) has been investigated by cyclic voltammetry, differential electrochemical mass spectrometry, potential step-linear sweep voltammetry, and adsorbate stripping experiments. Low oxidation currents were observed for HCOO- oxidation indicating that HCOO- is only weakly active under these conditions. The activity of HCOO- is confined to low potentials (0.2 V < E < 0.7 V vs RHE). Our results suggest a dual pathway mechanism for HCOO- oxidation, analogous to HCOOH oxidation in acid. In the case of HCOO- oxidation, the direct and indirect pathway analogues are referred to as the primary and secondary pathways, respectively. Formation of COads from HCOO- was observed to be slow. We also find that oxidation of COads (the secondary pathway) is strongly coupled to the oxidation of HCOO- through the primary pathway. Moreover, the oxidation of COads did not appreciably enhance HCOO- oxidation through the primary pathway, signifying the presence of other inhibitory processes such as OH adsorption. Adsorbate stripping experiments revealed, in addition to COads, the presence of a stable adsorbate that can undergo oxidation. We also find that the latter can be converted to COads in the H-upd region. On the basis of the results obtained, a tentative mechanism of HCOO- oxidation in basic media is proposed.