Surface copper immobilization by chelation of alizarin complexone and electrodeposition on graphite electrodes, and related hydrogen sulfide electrochemistry; matrix isolation of atomic copper and molecular copper sulfides on a graphite electrode

Abstract

Abstract The irreversibly adsorbed alizarin complexone (AC) was employed to immobilize and maintain Cu II ions on the graphite electrode. The coordination chemistry between the adsorbed alizarin complexone ligand and the Cu II ion on the surface was examined by surface cyclic voltammetry. Upon reduction of the Cu II center to a Cu 0 atom, a submonolayer of individual atoms of Cu 0 rather than a continuous layer is formed on the electrode surface. The immobilized surface displays electrocatalytic activity towards the oxidation of sulfide ion from [S 2− ] ion to S 0 . The electrocatalytic activity for the sulfide oxidation on a [Cu II (AC)] − adsorbed electrode is shown to be essentially identical with that of a electrode that contains an electrodeposited submonolayer of Cu 0 . The active catalyst in both cases is identified to be a submonolayer of cupric sulfide. The electrochemistry of the Cu 0 submonolayer-coated electrode in aqueous solution containing hydrogen sulfide was also examined. When the modified electrode was polarized from −1.1 V to 0.2 V, three electrode processes were observed. The first, near −0.7 V, is a surface reaction between surface Cu 0 and adsorbed [S 2− ] ion to form a submonolayer of cuprous sulfide. The second appeared near −0.23 V and is another surface process between Cu 2 S and adsorbed sulfide ion to form a submonolayer of cupric sulfide. The third reaction is the electrochemical oxidation of sulfide ion catalyzed by CuS to form sulphur which deposits on the electrode surface when the potential is positive of −0.2 V.