Oxidation of methylamine and ethylamine on Pt single crystal electrodes in acid medium

Cyclic voltammetry (CV) and Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) have been combined to analyse the oxidation of methylamine and ethylamine on platinum single crystal electrodes in an acidic medium. The oxidation of both amines on Pt(hkl) electrodes gives rise to the formation of adsorbed cyanide ad-layers, which have been detected by in situ infrared spectroscopy. In the case of Pt(111) the resulting adsorbed cyanide is rather stable but, on the contrary, the adsorbed CN-like species is highly reactive on Pt(100). It yields either adsorbed NO and CO₂ when the electrode is polarised above 0.7 V or adsorbed CO below 0.4 V. The detection of adsorbed cyanide is difficult to achieve at the Pt(110) surface. In the case of ethylamine, these adsorbed species are present in lower coverage than for methylamine. The substitution of one hydrogen atom by a methyl group in the methylamine makes the amine molecule more stable. So, the behaviour of ethylamine provides evidence for its lower electrochemical reactivity when compared with that of the methylamine molecule.