Influence of La3+ induced defects on MnO2–carbon nanotube hybrid electrodes for supercapacitors†
Here, we report the successful coupling of La doped MnO2 nanorods (30 nm mean diameter and 1 μm mean length) with multiwalled carbon nanotubes (CNTs) via a simple in situ hydrothermal method to form a La3+:MnO2–CNT nanohybrid as well as a systematic investigation of the influence of the dopant concentration on its performance as an electrode for supercapacitors. X-ray diffraction, electron microscopy and energy dispersive X-ray analysis revealed the formation of MnO2 nanorods uniformly distributed within the CNT network. The electrochemical measurements revealed a strong positive influence of the La dopants on the performance of the MnO2–CNT nanohybrid for up to 2 mol% La, above which the performance degraded. Thus, the 2 mol% La3+:MnO2–CNT nanohybrid sample was identified as the best electrode material in this study which exhibited a specific capacitance of ∼1530 F g−1 at a current density of 1 A g−1 along with a charge retention of 92% after 5000 cycles which are both much higher than those reported previously for MnO2 based supercapacitor electrodes and thus, is a leap towards using MnO2 as a low-cost electrode for supercapacitors. The enhanced performance of the optimised 2 mol% La3+:MnO2–CNT nanohybrid originated from the combinatorial influence of the material selection, the optimised concentration of La dopants and the synergistic influence of CNTs that resulted in its lowest charge transfer resistance and highest diffusion coefficient.