Microwave assisted synthesis of mesoporous NiCo2O4 nanosheets as electrode material for advanced flexible supercapacitors

Abstract

Mesoporous nickel cobaltite (NiCo₂O₄) nanosheets are synthesized using a cost effective, ultra fast and environmentally friendly microwave assisted heating method followed by a post-calcination process of the as-prepared precursors. XRD, XPS, BET, SEM, TEM and HRTEM methods are used to characterize the nanosheets. The as-prepared nanosheets with a thickness of around 2 nm possess many interparticle mesopores. The nanosheets have a mesoporous structure, high specific surface area (111.15 m² g⁻¹), large pore volume (0.3033 cm³ g⁻¹) and narrow pore size distribution (2.25–10 nm). A flexible supercapacitor working electrode of the mesoporous NiCo₂O₄ nanosheets is prepared on carbon cloth. Cyclic voltammetry, chronopotentiometry and impedance spectroscopy measurements are used to investigate the electrochemical performance of the as-prepared mesoporous NiCo₂O₄ nanosheet/carbon cloth electrode. The mesoporous NiCo₂O₄ nanosheets exhibit specific capacitances of 292.5 and 200 F g⁻¹ in 2 M KOH aqueous electrolyte at current densities of 1 and 8 A g⁻¹ respectively. The cyclic performance indicates excellent capacitance retention of 94.5% after 2000 cycles at a current density of 3 A g⁻¹. The excellent cyclic stability can be attributed to the mesoporous nature, high specific surface area, large pore volume and narrow pore distribution of the nanosheets. The synthesized mesoporous NiCo₂O₄ nanosheets using a microwave method are proved to be excellent electrode material for advanced flexible supercapacitors.