A time effect in the early stages of a surface oxidation of a Pt(111) plane in alkaline solution

Abstract

A time effect in the early stages of surface oxidation of a Pt(111) plane in 0.1 M NaOH solution was studied by examining the reduction parts of the j/E profile recorded after holding the potential for various times at several values at the end of anodic-going sweeps. The processes associated with the two peaks, which appear in the anodic part of the voltammogram, are assigned to the early stages of a surface oxidation. Two OHad states are suggested based on the existence of reversibly or weakly bound OHad species and irreversibly or strongly bound OHad species. The reversibly bound OHad species are involved in the "normal" structure of the butterfly peak, while the irreversibly adsorbed OHad species can be obtained only by the slow diffusion of a part of the initially electrosorbed OH species from sites with low to sites with higher binding energies. The irreversibly reduced OHad species cannot be completely removed from the surface causing, therefore, some permanent transformation of the initial state of the surface. This kind of species was not detected in the area of the second oxidation peak. The phenomena observed in the reduction part of the j/E profile induced by a time effect in the second peak could be associated with a place-exchange mechanism between oxygen containing species, whatever they are, and the platinum surface.

Vremenski efekat u toku oksidacije Pt(111) elektrode u 0,1 M NaOH je ispitivan u oblasti prvog i drugog oksidacionog pika koji odgovaraju početku oksidacije površine, a pojavljuju se na potencijalima relevantnim za oksidaciju alkohola. Zadržavanjem potencijala u oblasti prvog tzv. "leptir" pika detektovane su dve vrste OHad čestica. Reverzibilne OHad čestice čine "normalnu" strukturu "leptir" pika, dok se ireverzibilne OHad čestice mogu dobiti samo vremenski zavisnom difuzijom dela inicijalno adsorbovanih reverzibilnih OHad čestica. Ireverzibilne OHad čestice su čvrsto vezane za površinu i ne mogu se potpuno ukloniti sa površine uzrokujući transformaciju površine u odnosu na njeno inicijalno stanje. Zadržavanje potencijala u oblasti drugog oksidacionog pika nema za posledicu stvaranje ireverzibilnih OHad čestica. Reverzibilne i ireverzibilne OHad čestice imaju značajnu ulogu u procesu oksidacije alkohola. Reverzibilne OHad čestice su aktivni intermedijeri u reakciji, dok ireverzibilne OHad čestice deluju kao tzv. katalitički otrovi.