Hydrothermal synthesis of Co- and Ni-Doped MnO₂ nanorods for enhanced energy storage performance

Abstract

In this work, pristine, 6% Co-doped, and 6% Ni-doped MnO₂ nanorods were synthesized using the hydrothermal treatment followed by detailed study in terms of structural pattern, morphology, and electrochemical analysis. The formation of α-MnO₂ phase of the synthesized sample was confirmed by the X-ray diffraction analysis also suggesting no significant structural distortion upon addition of doping agents. Well-defined nanorod morphologies of all prepared samples was revealed by FESEM (Field-emission scanning electron microscopy), however, there was slight variation in MnO₂ nanorod size due to cobalt and nickel doping. The successful incorporation of Co and Ni into the MnO₂ lattice was confirmed by the Elemental analysis technique like EDX and X-ray photoelectron spectroscopy. Porous structure was analysed by BET and Raman active modes were confirmed by Raman spectra. Electrochemical performance of prepared samples was analysed using electrochemical impedance spectroscopy and Cyclic voltammetry measured in three electrode setup. Distinct redox peaks were seen from the CV curves, representative of prevailing pseudocapacitive behavior arising from reversible Faradaic reactions. CV measurements resulted in the specific capacitance values of 600 F g⁻¹ for pristine MnO₂, 1061 F g⁻¹ for 6% Co-doped MnO₂, and 786.04 F g⁻¹ for 6% Ni-doped MnO₂, respectively. GCD analysis at a current density of 0.4 A g⁻¹ yielded capacitance values of 500 F g⁻¹, 733.3 F g⁻¹, and 533.3 F g⁻¹ for pristine, Co-doped, and Ni-doped samples, respectively. The best cyclic stability was seen in 6% Co-doped MnO₂, which kept around 94.6% capacitance after 5000 cycles. The Co-doped sample is more stable because it has better electrical conductivity, lower charge-transfer resistance ( Rct = 0.9Ω seen in EIS results). Amongst all the samples, superior electrochemical performance was demonstrated by the Co-doped MnO₂, attributing them to increased electrical conductivity, enhanced ion diffusion, and improved redox-active sites. The present study demonstrates enhanced electrochemical results in terms of specific capacitance with Cobalt doping in pure MnO₂ respectively.