Studies on the electrochemical intercalation/de-intercalation mechanism of NiMn2O4 for high stable pseudocapacitor electrodes

Abstract

Sub-micron sized polyhedral shaped NiMn₂O₄ particles were successfully prepared by a glycine assisted solution combustion method. The phase purity and the presence of functional groups in NiMn₂O₄ were revealed through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. The formation of polyhedral shaped particles was inferred by field emission scanning electron microscopy (FE-SEM). The negative temperature coefficient of resistance (NTCR) behaviour of NiMn₂O₄ was observed using a solid state impedance analyser in the measured temperature range between 30 and 180 °C. Further, electrochemical studies revealed that NiMn₂O₄ stores the charge through intercalation rather than by a capacitive mechanism. The electrode stores 91% of the specific capacitance by intercalation and 9% by a capacitive mechanism. Also, NiMn₂O₄ possesses a specific capacitance of 202 F g⁻¹ at 0.5 mA cm⁻² in 1 M Na₂SO₄ electrolyte and exhibits excellent cyclic stability over 15 000 cycles. Similarly, the fabricated asymmetric device (FeVO₄‖NiMn₂O₄) also delivers good specific capacitance (50 F g⁻¹ at 1 mV s⁻¹) and cyclic stability.