Co-substitution effect on the structural, electrical, and electrochemical properties of nanostructured CoxNi1-xMnP2O7 (x = 0, 0.25, 0.5, and 0.75)

Abstract

Cobalt-nickel-manganese pyrophosphate nanostructures with formula CoxNi1-xMnP2O7 were prepared via the hydrothermal method at 150 °C, with further calcinations at 500 °C. A structural analysis of CoxNi1-xMnP2O7 samples was carried out using X-ray diffraction (XRD). The effect of Co substitution on the structural, electrical, and electrochemical properties of CoxNi1-xMnP2O7 is reported. The electrochemical results show that the specific capacity increases from 59 to 205 mAh/g with increasing Co content. This study demonstrates the Co substitution effect on the mixed electrical conductivity. The temperature dependence of the dc electrical conductivity, for both pure and Co2+-doped samples, obeys the Arrhenius law. The frequency dependence of ac conductivity for the materials exhibited a Jonscher’s universal power law. The plots of pre-exponent (n) versus temperature suggested that the conduction mechanism can be described using correlated barrier hopping model. The improved electrical conductivity and electrochemical proprieties of CoxNi1-xMnP2O7 nanomaterials could be ascribed to the synergistic effect of nickel and cobalt ions. The best results have been obtained for the composition x(Co) = 0.75, where the electrical conductivity is maximum, and the Co0.75Ni0.25MnP2O7 demonstrates the highest specific capacity, implying their promising potential applications in the energy storage.