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

Abstract

Pt(1 1 1) is modified with an overlayer of C6H6 ads by immersion in 005 or 050 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 Gamma(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 005 or 0 50 M HClO4 + 1 mM C6H6 are assigned to H-UPD adsorption and desorption Repetitive cycling of C6H6-modified Pt(1 1 1) in 005 or 050 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)