Characterization of copper manganite oxide-polypyrrole composite electrodes cathodically polarized in acidic medium

Abstract We have studied the electrochemical behaviour induced by polarization in sandwich-type composite electrodes with the structure GC/PPy/PPy(Ox)/PPy where GC stands for glassy carbon, PPy for polypyrrole and Ox for Cu 1.4 Mn 1.6 O 4 nanoparticles. The electrodes were polarized at −0.45 V/SCE in 0.15 M KCl aqueous solution at pH 2.2 either saturated in Ar or O 2 at 25 °C. The changes occurring on these electrodes were studied using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS and XANES) techniques. In previous work we have shown that when the oxide particles are incorporated into the PPy matrix the Cu + present in the initial oxide suffers dismutation to give Cu 2+ and metallic Cu. In this work we show that the polarized electrodes also reveal the presence of metallic Cu and Cu 2+ . The data also show that the oxide particles embedded in the polarized electrodes contain Mn 3+ and Mn 4+ , although the Mn 3+ /Mn 4+ ratio is different from that found in the fresh electrodes. The Cl 2p XPS data show that in the electrode polarized in O 2 there is an enhancement of the Cl covalent contribution that appears at 200.8 eV (which is already present in the fresh electrode although with a very small intensity). This result suggests that the oxygen reduction reaction leads to an increase of the OH − concentration inside the composite electrode that explains the charge transport in PPy at negative potentials.