ELECTROCHEMICAL DETECTION AND CHARACTERIZATION AT PT(N,N,N-2) ORIENTED ELECTRODES OF MULTIATOMIC STEP FORMATION INDUCED BY QUENCHING AT HIGH-TEMPERATURES

Results reported in this paper concern the effect of raising the tempe rature of quenching on the surface structure of flame-cleaned Pt(n,n,n - 2) surfaces. The quantitative analysis of the voltammograms obtaine d with these samples when they are quenched at 200-300-degrees-C agree s with the existence of a regular array of monoatomic steps on the sur face. Voltammograms obtained with samples with n less-than-or-equal-to 6 quenched at higher temperatures reflect the existence of a noticeab le number of multiatomic steps in the surface structure. Electrochemic al detection of such a microfaceting process may be inferred for a giv en orientation from the development of the adsorption states related t o the dimension of the (111) domains. Moreover, the experimental ratio between the changes in the (111) and (110) site densities agrees with that derived from the hard sphere model of these surfaces for the for mation of multi-atomic steps with the overall orientation of the sampl e kept constant. As a difference from results obtained with these step ped surfaces in the gas phase, step coalescence does not seem to be th e result of an oxygen-induced mechanism. Moreover, electrochemical oxy gen adsorption-desorption cycles at low coverage cause multiatomic ste ps to revert to monoatomic steps. From these results it may be. conclu ded that the microfaceting process of these vicinal surfaces is mainly a consequence of the thermal shock undergone by the sample when quenc hing at high temperature.