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

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 Cu1.4Mn1.6O4 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 O2 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 Cu2+ and metallic Cu. In this work we show that the polarized electrodes also reveal the presence of metallic Cu and Cu2+. The data also show that the oxide particles embedded in the polarized electrodes contain Mn3+ and Mn4+, although the Mn3+/Mn4+ ratio is different from that found in the fresh electrodes. The Cl 2p XPS data show that in the electrode polarized in O2 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.