Facile synthesis of fibrous, mesoporous Ni1 − xO nanosponge supported on Ni foam for enhanced pseudocapacitor applications

Fibrous mesoporous Ni1 − xO nanosponge with excellent pseudocapacitive properties was synthesized by controlled calcination of [Ni(H2O)4(4-nba)2]·2H2O; a 4-nitrobenzoate (4-nba) coordinated compound. Control experiments with compounds such as [Ni(H2O)6](4-nba)2·2H2O; a non-coordinated 4-nba compound and the [Ni(H2O)6]Cl2, without any 4-nba resulted in the formation of only agglomerated NiO nanoparticles. This proved the significance of 4-nba ligation with Ni2+ in [Ni(H2O)4(4-nba)2]·2H2O to produce highly porous, sponge-like nanostructures, without the need of hydrothermal or solvothermal treatment. The detailed structural characterization confirmed the formation of highly crystalline, mesoporous Ni1 − xO nanosponge. Further, the results obtained from electrochemical investigation by cyclic voltammetry and galvanostatic charge–discharge studies demonstrated that the fibrous, nanosponge-like Ni1 − xO exhibited good electrochemical properties with a high specific capacitance of 1236.84 Fg−1 at a current density of 1 Ag−1 and excellent capacitance retention of ~ 95% even after 10000 charge–discharge cycles at the current density of 6 Ag−1. The improved pseudocapacitive performance and extremely high cycling stability were attributed to extensive mesoporous network, effective distribution of electroactive sites and an improved electrode–electrolyte interaction due to fibrous and spongy nature of the material. The synthesis process is simple and scalable for industrial applications.