Electrocatalytic reduction of molecular oxygen using a poly(terthiophene carboxylic acid) appended by 1,5-diaminonaphthalene copper complex

The conducting polymer electrochemically obtained from a newly synthesized 5,2': 5', 2"-terthiophene-3'-carboxylic acid monomer was modified with 1,5-diaminonaphthalene by covalent bonding, and the modified electrode was complexed with copper ions. All modifications were characterized by Fourier transform infrared spectroscopy (FTIR), electron spectroscopy for chemical analysis (ESCA), and cyclic voltammetry (CV) techniques. The electrode modified with copper ions caused a positive shift in the peak potential for oxygen reduction to 0.30 V when compared to the absence of copper in the modified electrode. An ESCA study indicates the participation of Cu(I) species in the process of catalytic reduction of oxygen. The kinetics for oxygen reduction was studied by rotating ring-disk voltammetry. The results reveal 3.6 electrons participating in the reduction of oxygen with about 75% conversion to water in an aqueous medium of 0.1 M KNO3. The kinetic study also indicates the presence of an inner sphere mechanism between copper and oxygen during the latter's reduction. The calculated rate constant from the kinetic study on the electrocatalytic reduction of oxygen was found to be higher when compared to other copper complexes adsorbed on the carbon electrode surface. This modified electrode was also tested for the estimation of oxygen content in an aqueous solution. (C) 2002 The Electrochemical Society.