Electrochemical reduction of S(IV) species in aqueous medium by glassy carbon electrodes modified with polymeric copper(II)tetra-aza-annulene complexes

The electrocatalytic reduction of SO2 in aqueous media was studied as a function of the pH at a glassy carbon electrode modified with poly[Cu(II)-5,7,12,14-tetramethyldinaphtho[b,i]-1,4,8,11-tetraaza[14]annulene] film. The best amperometric response was obtained at pH = 1 and the activity decreased upon pH increasing. The SO2 reduction potential in this condition was shifted ca. 220 mV in the anodic direction compared to the value observed in bare glassy carbon. The Tafel slope, 278.64 mV dec−1, and the charge transfer coefficient, 0.18, are consistent with some interaction between SO2 and the modified electrode. The amperometric response is linear up to a 0.1 mM SO2 concentration, the detection limit being 0.02 mM under optimized conditions.