Oxalic acid assisted rapid synthesis of mesoporous NiCo2O4 nanorods as electrode materials with higher energy density and cycle stability for high-performance asymmetric hybrid supercapacitor applications.

In this study, mesoporous nickel cobaltite (NiCo2O4) nanorods as electrode materials for high-performance hybrid supercapacitor were fabricated onto Ni foam by a simple and cost effective oxalic acid (OA) assisted rapid co-precipitation method. The effects of different metal precursors (NCO-Nitrate, NCO-Chloride and NCO-Acetate) on the electrochemical capacitive properties were studied. FE-SEM analysis confirmed that all samples exhibited highly dense mesoporous NiCo2O4 nanorods vertically grown on the surface of Ni foam with excess accessible surfaces and unique sizes and morphologies. The resultant NiCo2O4 nanorod electrodes (for NCO-Nitrate, NCO-Chloride and NCO-Acetate) delivered the maximum specific capacitances of 790, 784, 776 F g-1 at the current density of 1 A g-1 with ultra-high capacitance retention of 82.27, 81.63 and 81.71% even at 20 A g-1 and excellent cyclic stability of 84.25, 83.33 and 83.24% capacitance retention at 5 A g-1 after 5000 cycles. The asymmetric supercapacitor (ASC) device was also sandwiched by using NCO-Nitrate as positive electrode and N-doped graphene hydrogel (NGH) as negative electrode. The fabricated ASC device delivered superior energy density (42.5 W h kg-1) at high power density (746.34 W kg-1) with excellent long cyclic stability (90% initial capacitance retention after 5000 cycles at 5 A g-1).