Scanning photoelectron microscopy investigation of the initial stages of the electrochemical reduction of Cr(VI) at Pt(1 1 1) electrode

This paper reports on the electrochemical reduction of bichromate from an aqueous solution at a Pt(1 1 1) electrode studied by voltammetry and synchrotron-based photoelectron spectromicroscopy Cathodic reduction is carried out at potentials −1.5 and −2.0 eV in an electrochemical cell attached to the UHV chamber hosting the scanning photoelectron microscope (SPEM), which allowed sample transfer for SPEM analysis without exposure to the air. The Cr 2p and Pt 4f core level spectra are used as fingerprints of the Cr lateral distribution and chemical state after reduction. The Pt 4f and Cr 2p maps show inhomogeneous Cr distribution in microscopic Cr-rich and Cr-poor islands. Analysis of the Pt 4f, Cr 2p photoemission peaks recorded in these islands has disclosed that – under both reduction conditions – Cr(VI) is reduced principally to Cr(III), with ca. 10% of Cr(0) localised in the Cr-rich islands. The presence of an intermediate oxidation state has also been detected, that can be assigned to a transition state from Cr(VI) to Cr(III).

► Reduction of Cr(VI) was studied by quasi-in-situ photoelectron spectromicroscopy.
► Electroreduction of Cr(VI) at Pt(1 1 1) yields Cr-islands containing Cr(III) and Cr(0).
► A transition state between Cr(III) and Cr(VI) was found by PES in Cr-islands on Pt.