Cyclic-voltammetry behavior of Pt(1 1 1) in aqueous HClO4 + C6H6: Influence of C6H6 concentration, scan rate and temperature

Pt(1 1 1) is modified with an overlayer of C6H6 ads by immersion in 0.05 or 0.50 M HClO4 + 1 mM C6H6 and cycling in the 0.05–0.80 V vs. RHE potential range. The influence of the C6H6 concentration (1–20 mM), scan rate (10–100 mV s–1), and temperature (278–318 K) on cyclic-voltammetry (CV) features of Pt(1 1 1) and C6H6 surface excess are examined. The surface excess of C6H6, Γ(C6H6), is evaluated through its oxidative desorption. The amount of adsorbed C6H6 corresponds to a sub-monolayer with C6H6 molecules being parallel to the Pt(1 1 1) surface. As the amount of dissolved C6H6 increases, the surface excess of C6H6 increases to ca. 2 monolayers indicating that the C6H6 ads molecules adopt a tilted orientation on Pt(1 1 1). Increase of the scan rate from 10 to 100 mV s–1 does not result in any shift of the anodic peak but induces a shift of the cathodic peak towards lower potentials. An increase of temperature from 278 to 318 K shifts both cathodic and anodic peaks towards higher potentials, while at the same time reducing the peak current density. However, it does not modify the peaks’ charge density or the C6H6 surface excess. The cathodic and anodic CV peaks obtained in 0.05 or 0.50 M HClO4 + 1 mM C6H6 are assigned to HUPD adsorption and desorption. Repetitive cycling of C6H6-modified Pt(1 1 1) in 0.05 or 0.50 M HClO4 (free of C6H6) regenerates the CV profile characteristic of a well-ordered Pt(1 1 1) electrode, thus indicating that C6H6 adsorption and desorption does not disorder Pt(1 1 1).