DEMS study on methanol oxidation at poly- and monocrystalline platinum electrodes: The effect of anion, temperature, surface structure, Ru adatom, and potential

Methanol oxidation on Ru-unmodified and modified polycrystalline platinum, Pt(111), and Pt(332) was studied by on-line differential electrochemical mass spectrometry (DEMS) in combination with the dual thin-layer flow-through cell. The effects of anion, temperature, surface structure of Pt electrodes, Ru adatom, and potential on methanol oxidation were discussed. Methanol oxidation on smooth polycrystalline platinum, Pt(111), and Pt(332) electrodes proceeds via the parallel pathway mechanism, and mainly forms the soluble intermediates, i.e., formaldehyde and formic acid. Anion, temperature, and surface structure of Pt electrodes markedly influence the apparent rate of methanol oxidation; however, they do not significantly alter the current efficiency of CO2, and therefore do not change the mechanism of methanol oxidation. On pure platinum electrodes current efficiency of CO2 for methanol oxidation increases from ca. 20% to 32% with the increase of potential from 0.6 to 0.8V, accompanied by the increasing Faradaic current. Ru adatoms can promote the methanol oxidation via COad to form CO2 in the low potential region (<= 0.65 V) on three platinum electrodes, leading to higher current efficiency of CO2, even ca. 100% for Pt(111)/Ru. At potentials of > 0.65V, Ru adatoms lose their cocatalytic activity for methanol oxidation.