A strong adsorption of formaldehyde in acid solutions occurs on polycrystalline Pt at a potential of 0.05 V vs RHE. Increasing HCHO concentration or increasing time at this potential, causes a shift of HCHO oxidation to higher potentials. For short adsorption times, the onset of current can be observed at potentials as low as 0.4 V. As adsorbed species, carbon monoxide and methyleneglycolate are formed, as reported before for Pt(111). But, at variance with the results for Pt(111), at polycrystalline Pt and at PtRu as well, the main oxidation product is CO2. The oxidation reaction is favored by electrodeposited ruthenium, with a maximum for Ru content between 20% and 60%. The catalytic effect is due to the promotion of COad oxidation by Ru atoms. This effect prevails to a great extent and the parallel pathway via the methyleneglycolate has only a minor weight. (c) 2007 Published by Elsevier B.V.