Structural and chemical promotion of platinum electrodes

An ultra-high vacuum/electrochemistry system has been developed to enable clean transfer of platinum single crystal electrodes to and from an electrochemical environment. This allows surface characterisation by LEED, XPS, LEISS, TPD and cyclic voltammetry.Using this system the electro-oxidation of CO on the Pt(110) and Pt(533) surfaces has been investigated. On Pt(110) this is found to be dependent on the CO adsorption potential. Adsorption at 0.45V, gave a single sharp peak at 0.74V, whilst adsorption at 0.05V results in a broader peak at lower potential (0.71V) and also the observation of a 'prepeak' at 0.43V. This difference is attributed to the ability of oxygen to adsorb at the surface which gives rise to two different oxidation mechanisms. On the Pt(533) surface, at low coverages, a single peak at 0.82V is observed due to CO at the step. At higher coverages the oxidation wave broadens to lower potentials (0.78V) as for Pt(111). At saturation coverages a single sharp peak is found at 0.82V, the step CO being more stable to oxidation than terrace CO.Similarly, investigations of the oxidation of CO at the gas/solid interface on Pt(533) reveals that CO adsorbed at the step is more stable than terrace CO. Four peaks are observed at 220K, 300K, 430K and 500K. The first three peaks have been assigned to reaction of COterr + Ostep, COterr + Oterr and COstep + Ostep respectively. The origin of the fourth peak is unclear.The modification of the surfaces with bismuth is also investigated. Bismuth adsorption on Pt(110) in vacuum is found to produce a series of ordered overlayers on the unreconstructed surface and blocks the adsorption of H2, CO and O2. Bismuth adsorbs preferentially at the step site on Pt(533), resulting in a blocking of H2 and CO at the surface. Oxygen adsorption does not follow a simple blocking curve, which is interpreted as an effect on the dissociation of the oxygen molecule at this surface as found on Pt(111).