Supercapattery Based on Binder-Free Co3(PO4)2•8H2O Multilayer Nano/Microflakes on Nickel Foam

A binder-free cobalt phosphate hydrate (Co-3(PO4)(2)center dot 8H(2)O) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co2+ and PO4-3 were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co-3(PO4)(2)center dot 8H(2)O modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g(-1) (capacitance of 1578.7 F g(-1)) at a current density of 5 mA cm(-2) and remains as high as 566.3 C g(-1) (1029.5 F g(-1)) at 50 mA cm(-2) in 1 M NaOH. A supercapattery assembled using Co-3(PO4)(2)center dot 8H(2)O/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g(-1) (volumetric capacitance of 4.44 F cm(-3)). Furthermore, the device offers a high specific energy of 29.29 Wh kg(-1) (energy density of 1.17 mWh cm(-3)) and a specific power of 4687 W kg(-1) (power density of 187.5 mW cm(-3)).