Specificity of electrochemical reactivity of small aliphatic oximes to geometries of Pt(111) and (100) surfaces

Oximes are organic compounds with a characteristic NOH group derived by condensation of carbonyl-groups with NH2OH. In acidic or neutral solutions they undergo electrolytic reduction to primary amines. The present paper reports some examples of surface lattice specificity of electrochemical adsorption and reduction behaviour for two small aliphatic oximes: formamidoxime (FNOH) and acetaldehyde oxime (ANOH) at two low index, Pt(111) and (100), single-crystal planes in 0.5 M H2SO4 solution. In H2SO4, both FNOH and ANOH undergo electrocatalytic reduction involving upd H on Pt(111), where the FNOH species ultimately forms a species leading to poisoning of the Pt surface, while ANOH becomes reduced to ethylamine, without such effects arising. These effects are manifested as striking differences in the cyclic voltammetric profiles for these surfaces. In the case of Pt(100), the behaviour of FNOH implies a reversible cooperative chemisorption of the species with HSO4− ion on the Pt surface (as previously found with guanidine), which process prevails over reductive scission, the latter, however, being the principal process at the Pt(111) surface. FTIR spectroscopy confirms the role of chemisorption. In addition, impedance spectroscopy performed at the Pt(111) surface in 0.5 M H2SO4 provides confirmatory information for interpretation of the voltammetric profiles, and reactivity of FNOH and ANOH molecules. The roles of Faradaic reduction coupled with electrosorption, including participation of diffusion control, are clearly distinguishable.