Structural and electrochemical properties of manganese substituted nickel cobaltite for supercapacitor application

NiCo2O4 and NiMnxCo2−xO4−y (x ≤ 1.0) have been synthesized by a co-precipitation method, and the effects of Mn substitution for Co on the microstructural and electrochemical properties pertaining to the supercapacitor applications have been studied. Spinel structure is retained when a quarter of Co of the spinel is substituted with Mn (i.e., x = 0.5), where the Mn ions predominantly occupy the octahedral sites of the spinel lattice. The presence of Mn significantly suppresses crystal growth upon thermal treatment but tends to cause severe crystallite agglomeration. Electrodes of the materials exhibit nearly ideal electrochemical capacitor behavior in neutral electrolyte solution (1 M KCl(aq)). Mn substitution greatly enhances the specific capacitance of the spinel, giving gravimetric and superficial specific capacitances of ca. 110 F g−1 and ca. 380 μF cm−2, respectively for x = 0.5 powder. The capacitance enhancement is attributed to the facile charge-transfer characteristic of the Mn ions, as revealed by in situ X-ray absorption near-edge structure analysis.

► Single phase NiCo2O4 and NiMn0.5Co1.5O4 spinel powders as supercapacitor materials. ► The occupancy sites of Mn ions for ¼ of Co in the spinel are identified. ► The presence of Mn in the spinel lattice greatly enhances the specific capacitance. ► XANES analysis for the first time reveals the capacitance enhancement mechanism.