Self-Assembled Nickel Pyrophosphate-Decorated Amorphous Bimetal Hydroxides 2D-on-2D Nanostructure for High-Energy Solid-State Asymmetric Supercapacitor.

To obtain a supercapacitor with a remarkable specific capacitance and rate performance, a cogent design and synthesis of the electrode material containing abundant active sites is necessary. In present work, a scalable strategy is developed for preparing 2D-on-2D nanostructures for high-energy solid-state asymmetric supercapacitors (ASCs). The self-assembled vertically aligned microsheet-structured 2D nickel pyrophosphate (Ni P O ) is decorated with amorphous bimetallic nickel cobalt hydroxide (NiCo-OH) to form a 2D-on-2D nanostructure arrays electrode. The resulting Ni P O /NiCo-OH 2D-on-2D array electrode exhibits peak specific capacity of 281 mA hg (4.3 F cm ), excellent rate capacity, and cycling stability over 10 000 charge-discharge cycles in the positive potential range. The excellent electrochemical features can be attributed to the high electrical conductivity and 2D layered structure of Ni P O along with the Faradic capacitance of the amorphous NiCo-OH nanosheets. The constructed Ni P O /NiCo-OH//activated carbon based solid-state ASC cell operates in a high voltage window of 1.8 V with an energy density of 78 Wh kg (1.065 mWh cm ) and extraordinary cyclic stability over 10 000 charge-discharge cycles with excellent energy efficiency (75%-80%) over all current densities. The excellent electrochemical performance of the prepared electrode and solid-state ASC device offers a favorable and scalable pathway for developing advanced electrodes.