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

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Nanostructured MnO<SUB>2</SUB> 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 MnO<SUB>2</SUB> nanostructures. Nanorod-, nanoflower-, nanoneedle-, and nanoneedles/nanopetal-shaped MnO<SUB>2</SUB> nanostructures were synthesized by changing the concentration of the rare earth elements. The as-synthesized MnO<SUB>2</SUB> nanorods, La – MnO<SUB>2</SUB> nanoneedles, Ce – MnO<SUB>2</SUB> nanoflowers, and La/Ce – MnO<SUB>2</SUB> 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 MnO<SUB>2</SUB> nanostructures and the elemental distribution. The porous natures of the synthesized MnO<SUB>2</SUB> nanostructures were analyzed by nitrogen adsorption technique. The electrochemical behavior of the MnO<SUB>2</SUB> nanostructures was examined by cyclic voltammetry, charge – discharge and electrochemical impedance spectroscopy tests. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals electrode exhibited a high specific capacitance of 825 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals were also mixed with 5, 10, 15 and 20 wt% of rGO nanosheets to enhance the electrochemical behavior. The 20 rGO@La/Ce – MnO<SUB>2</SUB> sample showed extraordinary electrochemical behavior; the calculated specific capacitance was 1165 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. A 20 rGO@La/Ce – MnO<SUB>2</SUB> and activated carbon asymmetric supercapacitor coin cell device exhibited ∼93% capacitance retention after 1000 cycles. These results highlight the potential of 20 rGO@La/Ce – MnO<SUB>2</SUB> as an electrode material for supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Manganese oxide nanostructures were synthesized by hydrothermal process. </LI> <LI> Lanthanum and cerium used to control the porosity of manganese oxide. </LI> <LI> La/Ce mixed MnO<SUB>2</SUB> nanoneedles/nanopetals showing good electrochemical behavior. </LI> <LI> rGO mixed La/Ce – MnO<SUB>2</SUB> was prepared to improve the storage capacity. </LI> <LI> 20rGO@ La/Ce – MnO<SUB>2</SUB> electrode exhibited high specific capacitance of 1165 F g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>