Influence of rare earth elements on porosity controlled synthesis of MnO2 nanostructures for supercapacitor applications

Nanostructured MnO2 was synthesized using a facile hydrothermal technique with potassium permanganate as a precursor. Rare earth elements, lanthanum and cerium, were used to control the porosity of the MnO2 nanostructures. Nanorod-, nanoflower-, nanoneedle-, and nanoneedles/nanopetal-shaped MnO2 nanostructures were synthesized by changing the concentration of the rare earth elements. The as-synthesized MnO2 nanorods, La – MnO2 nanoneedles, Ce – MnO2 nanoflowers, and La/Ce – MnO2 nanoneedles/nanopetals were examined using a range of physico chemical characterization techniques. Scanning electron microscopy and transmission electron microscopy – energy dispersive X-ray spectroscopy confirmed the morphology of the MnO2 nanostructures and the elemental distribution. The porous natures of the synthesized MnO2 nanostructures were analyzed by nitrogen adsorption technique. The electrochemical behavior of the MnO2 nanostructures was examined by cyclic voltammetry, charge – discharge and electrochemical impedance spectroscopy tests. The La/Ce – MnO2 nanoneedles/nanopetals electrode exhibited a high specific capacitance of 825 F g−1 at an applied current density of 10 A g−1. The La/Ce – MnO2 nanoneedles/nanopetals were also mixed with 5, 10, 15 and 20 wt% of rGO nanosheets to enhance the electrochemical behavior. The 20 [email protected]/Ce – MnO2 sample showed extraordinary electrochemical behavior; the calculated specific capacitance was 1165 F g−1 at an applied current density of 10 A g−1. A 20 [email protected]/Ce – MnO2 and activated carbon asymmetric supercapacitor coin cell device exhibited ∼93% capacitance retention after 1000 cycles. These results highlight the potential of 20 [email protected]/Ce – MnO2 as an electrode material for supercapacitor applications.