Cation-anion double hydrolysis derived layered single metal hydroxide superstructures for boosted supercapacitive energy storage

As promising battery-type electrode materials, layered single metal hydroxides (LSHs) including alpha-Ni(OH)(2) and alpha-Co(OH)(2) based hybrid supercapacitors exhibit larger operating voltages compared with those that are based on activated carbons and double-layer capacitance mechanisms. This study proposes a novel and facile room-temperature method to fabricate alpha-Ni(OH)(2) and alpha-Co(OH)(2) superstructures by using the double hydrolysis of Ni2+ or Co2+ and NCO- without the presence of any structure directing agent. Two dimensional sheet-like building blocks of the alpha-type metal hydroxide are assembled into various elegant morphologies including a 3D interconnected hierarchical assembly (3D-ICHA), sheet-on-sheet, sheet-on-rod and other nanostructures, which depends on the cation-anion mixing mode. Significantly, the 3D-ICHA alpha-Ni(OH)(2) possesses an ultrahigh specific surface area (320.2 m(2) g(-1)) and robust porous structure. An outstanding initial specific capacity (653.1 C g(-1) at 1 A g(-1) and 406 C g(-1) at 20 A g(-1)) and an excellent cycling retention (86.2% in 20 000 cycles) were obtained for the 3D-ICHA alpha-Ni(OH)(2), which stands out from most of the state-of-the-art a-Ni(OH) 2 powder-based materials. A high-loading asymmetric capacitor with excessive activated carbon (similar to 10 mg 3D-ICHA alpha-Ni(OH) 2 vs. similar to 60 mg activated carbon) is demonstrated and it works very steadily even after 20 000 charge/discharge cycles.