Towards Molecular-Level Understanding of Electrocatalytic Hydrogenation. A Comparison of Cyclic Voltammetric Behavior of Benzene Adsorption at Pt(111) Single Crystal Electrodes in Aqueous HClO_4 and H_2SO_4

摘要

We present new results on the influence of (C_6H)6)_(ads) on the H_(upd) and anion adsorption on the Pt(111) electrode in aqueous HClO_4. The Pt(111) electrode is modified by an overlayer of C_6H_6 _(ads) upon its cycling in the 0.05-0.80 V range in aq. acid + 1 mM C_6H_6. The (C_6H_6)_(ads) overlayer significantly changes the Hupd (underpotential deposited H) and anion adsorption, and cyclic-voltammetry (CV) profiles show a sharp cathodic peak and an asymmetric anodic one in the 0.05-0.80 V potential range. The C_6H_6 _(ads) layer blocks the perchlorate and sulphate anion adsorption but facilitates the adsorption of one monolayer of Hupd which is embedded in the Pt(111) surface. The behavior described above in aq. HClO_4 is the same as that in aq. H_2SO_4. Cycling in the 0.4-1.25 V potential range in benzene-free aq. HClO_4 results in the complete oxidation of (C_6H_6)_(ads) to CO_2, which allows the determination that a quasi full monolayer of (C_6H_6)_(ads) lies on the surface.