A catalyst coated electrode for electrochemical formaldehyde oxidation

Abstract

Thermally prepared catalytic coatings on a titanium substrate were composed of a mixture of nanocrystals of metallic Pt and RuO2 of rutile structure and used for electrooxidation of formaldehyde. The size of the RuO2 nanocrystals increased, whereas those of Pt decreased with increasing the content of RuO2 in the mixture. At more positive potentials, the maximum catalytic activities showed the coatings with lower content of RuO2. Mechanism of formaldehyde oxidation was derived to show two reaction pathways. In the first one, H2C(OH)2 was directly oxidized to CO2, whereas COad was formed in the latter. COad is strongly adsorbed on Pt atoms, which causes blocking of these atoms and thus, preventing direct dehydrogenation of H2C(OH)2 to CO2. The overall catalytic effect of the mixture of nanocrystals was caused by the bifunctional mechanism. Thus, the Ru atoms formed the oxy species at more negative potentials than Pt. These oxy species oxidized the COad intermediates, bound to adjacent Pt atoms and accordingly, discharged them for dehydrogenation of new molecules of H2C(OH)2.