Self-assembly of NiO nanoparticles in lignin-derived mesoporous carbons for supercapacitor applications

We demonstrate the self-assembly of highly dispersed NiO nanoparticles embedded in lignin-derived mesoporous carbon (MPC) frameworks. Self-assembly is induced by evaporation of the solvent from a mixture of metal-containing liquid crystalline mesophases of lignin-derived polymers and transition metal nitrate hydrate, which yielded NiO@MPC nanostructures at 600 °C under a N2 atmosphere. The microstructure and morphology of the NiO@MPC are characterized by XRD, TEM and BET. The results show that the NiO nanoparticles are highly dispersed in a mesoporous carbon matrix. The NiO@MPC composites show metal oxide contents in the range 49–79 wt%, high surface areas (503–802 m2 g−1), uniform pore sizes (≈3.7 nm), various porous distributions and large pore volumes (0.46–0.68 cm3 g−1). Electrochemical studies were carried out by measurement of cyclic voltammetry (CV) and charge–discharge tests. The results demonstrate that the NiO@MPC composites have high specific capacitance (880.2 F g−1 at a current density of 1.0 A g−1) and display good retention. 90.9% of the specific capacitance is retained when the current density changes from 1 A g−1 to 10 A g−1 in the charge–discharge tests and 93.7% of the specific capacitance is retained after 1000 charge–discharge cycles. Thus, the NiO@MPC composites are promising supercapacitor electrode materials.