Unprecedented Structural Sensitivity toward Average Terrace Width: Nafion Adsorption at Pt{hkl} Electrodes

Abstract

Ultrathin Nafion overlayers ranging from 0 to 3.3 nm in thickness have been deposited on platinum single crystal electrodes in order to study their voltammetric behavior as a function of both Nafion surface coverage and platinum surface step density. Unusual structural sensitivity of Nafion-induced voltammetric peaks ascribable to Nafion interactions with step sites is observed as a function of average terrace width. For stepped surfaces containing both {111} and {100} terraces, average terrace widths of 2–3 atoms give rise to the most intense Nafion-step electrosorption peaks. Rapid quenching of the Nafion-step voltammetric peaks is observed as the average terrace width is gradually increased until for >5 atom wide terraces all such electrochemical features are completely attenuated. This rapid diminution of the step-Nafion voltammetric peak, within just three atoms of terrace width, is unprecedented, and a parallel with the “splitting” of hydrogen underpotential deposition (HUPD) step peaks in perchloric acid aqueous electrolyte for closely spaced steps is noted. On the basis of these measurements, it is suggested that Nafion is a molecular probe of adsorbed OH species on Pt electrodes.