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 degrees C under a N-2 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 m(2) g(-1)), uniform pore sizes (approximate to 3.7 nm), various porous distributions and large pore volumes (0.46-0.68 cm(3) 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.