Hierarchical MnO₂ Nanoflowers and SnO₂ Nanoparticles on Rhombohedral LaMnO₃ for 2 V Supercapacitor Electrodes

The strategy of forming hierarchical nanostructures of electroactive materials has shown enhancements in supercapacitor performances. In this study, two hierarchical electrodes are prepared by directly growing MnO₂ nanoflowers and SnO₂ nanoparticles on rhombohedral LaMnO₃ nanostructures using a facile method. An extended potential window of 2 V in a neutral aqueous electrolyte with superior electrochemical characteristics compared to pristine LaMnO₃ electrodes is exhibited by these electrodes. Moreover, LaMnO₃/MnO₂ shows the best performance among the two hierarchical nanostructures. The optimized LaMnO₃/MnO₂ electrode delivers a high capacity of 426 C g^-1 at a current density of 1 A g^-1, nearly 4.6 times compared to pristine LaMnO₃. This hierarchical electrode, due to the synergistic effect, exhibits appreciable cycling stability, outperforming the electrodes based on pristine MnO₂ and LaMnO₃. The aqueous symmetric supercapacitor fabricated using this electrode shows a capacity of 64 C g^-1 (32 F g^-1) at 1 A g^-1, with a high energy density of 17.8 Whkg^-1 at a constant power density of 2000 W kg^-1. Further, the device delivers 89% of its initial capacitance even after 10 000 charge/discharge operations at 10 A g^-1. This study presents the possibility of using these hierarchical nanostructures in high-performance aqueous electrolyte supercapacitors (SCs).