Supercapattery Based on Binder-Free Co 3 (PO 4 ) 2 ·8H 2 O Multilayer Nano/Microflakes on Nickel Foam.

A binder-free cobalt phosphate hydrate (Co3 (PO4 )2 ·8H2 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 Co3 (PO4 )2 ·8H2 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 Co3 (PO4 )2 ·8H2 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 ).