Enhanced Stability of a Carbon Monoxide Monolayer Adsorbed on Platinum under Electrochemical Control Probed by Sum-Frequency Generation Spectroscopy
Résumé
We establish a new procedure to study the steady state adsorption of carbon monoxide (CO) at the surface of platinum under electrochemical control over a wide potential range in aqueous acidic solution. Using highly concentrated solutions of CO in perchloric acid medium enables the formation of a tightly packed and very stable CO monolayer at the surface of the metal, which allows cyclic voltammetry in the [−1200;+1500 mV] potential range (vs Ag/AgCl). We use sum-frequency generation (SFG) spectroscopy to show the unusual stability of the monolayer: going toward negative potentials, hydrogen evolution is first blocked then strongly quenched; toward positive potentials, CO oxidation is prevented as a consequence of its dense packing as a "frozen" monolayer. Diluting CO concentration by a factor of 10 is enough to recover most of the usual properties of the CO/Pt(110) interface, still maintaining the high stability of the CO adlayer. Such a protocol can be applied to any problem for which a CO poisoning mechanism has to be scrutinized or as a model of very stable electrochemical interfaces for fundamental studies.
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