An in situ infrared and electrochemical study of oxalic acid adsorption at stepped platinum single crystal electrodes in the [formula omitted] zone

Abstract

Oxalic acid adsorption has been studied at platinum single crystal electrodes belonging to the [0 1 ̄ 1] zone. Cyclic voltammetry and charge displacement experiments have been combined with in situ external reflection infrared experiments and results compared with those previously reported for the Pt(1 1 1) and Pt(1 0 0) electrodes. The spectroscopic data confirm the potential dependent behaviour of oxalic acid adsorption derived from the electrochemical experiments. At the same time, the infrared spectra show distinct CO stretching bands for adsorbates on (1 0 0) and (1 1 1) terraces. As previously concluded for Pt(1 0 0) and Pt(1 1 1) electrodes, oxalate and bioxalate anions are adsorbed, respectively, at the (1 0 0) and (1 1 1) terraces for potentials above 0.30 V. Oxalate and bioxalate anions adsorb at edge and step sites at potentials lower than at terrace sites. For Pt(2 n−1,1,1) = Pt(S)[ n(1 0 0) × (1 1 1)], bands are observed at potentials higher than 0.20 V that can be assigned to oxalate anions adsorbed at (1 0 0) edge sites and bioxalate adsorbed at (1 1 1) step sites. In the case of Pt( n+1, n−1, n−1) = Pt(S)[ n(1 1 1) × (1 0 0)] electrodes, bands for oxalate anions adsorbed at the (1 0 0) step sites appears at potentials lower than bands for bioxalate adsorption at the (1 1 1) terrace sites. For all the stepped surfaces, adsorbed CO is slowly formed at the step sites in the hydrogen adsorption region. The extent of this process can be minimised during the collection of the infrared spectra by taking the reference spectrum at 0.20 V.