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The role of alkali cations (Li(+), Na(+), K(+), Cs(+), and Be(2+)) on the blank voltammetric response and the oxidative stripping of carbon monoxide from stepped Pt single-crystal electrodes in alkaline media has been investigated by cyclic voltammetry. A strong influence of the nature of the cation on both the blank voltammetric profile and the CO oxidation is observed and related to the influence of the cation on the specific adsorption of OH on the platinum surface. Especially Li(+) and Be(2+) cations markedly affect the adsorption of OH and thereby have a significant promoting effect on CO(ads) oxidation. The voltammetric experiments suggest that, on Pt(111), the influence of Li(+) (and Be(2+)) is primarily through a weakening of the repulsive interactions between the OH in the OH adlayer, whereas in the presence of steps also, the onset of OH adsorption is at a lower potential, both on steps and on terraces.

The electrooxidation of adsorbed CO on a stepped platinum electrode in alkaline media reveals a dual role of the "active" step site in activating CO oxidation by adsorbed OH. The combination of "interrupted" chronoamperometry with cyclic voltammetry shows that there is active combination of CO and OH near or on the step site as well as a much less reactive combination of CO and OH in which the CO sits on the step and reacts with OH from the terrace.

Herein the general concepts of fuel cells are discussed, with special attention to low temperature fuel cells working in alkaline media. Alkaline low temperature fuel cells could well be one of the energy sources in the next future. This technology has the potential to provide power to portable devices, transportation and stationary sectors. With the aim to solve the principal catalytic problems at the anode of low temperature fuel cells, a fundamental study of the mechanism and kinetics of carbon monoxide as well as water dissociation on stepped platinum surfaces in alkaline medium is discussed and compared with those in acidic media. Furthermore, cations involved as promoters for catalytic surface reactions are also considered. Therefore, the aim of the present work is not only to provide the new fundamental advances in the electrocatalysis field, but also to understand the reactions occurring at fuel cell catalysts, which may help to improve the fabrication of novel electrodes in order to enhance the performance and to decrease the cost of low temperature fuel cells.

In this work we investigate the electro-oxidation of CO on Pt(111) in alkaline solution by using Fourier transform infrared spectroscopy (FTIRS), to determine the adsorption sites of the CO, the intermediate species and the final oxidation product as a function of the applied potential. Multiple CO vibration bands (on-top, bridge and 3-fold hollow site) are observed on the Pt(111) electrode, their distribution and potential dependence being strongly dependent on the surface treatment. Spectroscopic results show that the final reaction product is carbonate and suggest that adsorbed carbonate blocks the access of CO from the (111) terrace to the active sites (i.e., step and kink sites).

From a detailed analysis of the chronoamperometry of CO stripping on stepped platinum single-crystal electrodes in alkaline solution, in combination with kinetic modeling, a mechanistic and kinetic picture of the CO oxidation mechanism is derived. On Pt(111), CO oxidation starts at defect sites (steps, kinks), following a one-dimensional nucleation-and-growth mechanism, or a Langmuir-Hinshelwood mechanism with no effective competition between CO and OH. The carbonate that is formed in this reaction blocks the active oxidation sites, so that CO adsorbed on terraces further away from the defect sites can be oxidized at defects sites only very slowly. At potentials above ca. 0.75 V vs. RHE this CO is oxidized on the Pt(111) terrace. On stepped Pt electrodes, CO oxidation is also initiated at the kink (step defects) and step sites. We postulate that carbonate partially blocks the active site, but CO from the terrace still prefers to react at the steps over the terrace sites. The oxidation of terrace-bound CO at the step sites follows a competitive Langmuir-Hinshelwood mechanism. The least reactive CO on the surface is the CO that is adsorbed on the step sites, and it is oxidized by OH on terraces. Finally, on the terrace, the Tafel slope for CO stripping is close to 60 mV dec(-1), suggesting an EC mechanism, i.e. reversible OH formation followed by a chemical rate-determining step, presumably the CO + OH combination reaction. At the step site, the Tafel slope is close to 120 mV dec(-1), suggesting an electrochemical rate-determining step, ascribed to slow OH formation at the step site.

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