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

A binder-free cobalt phosphate hydrate (Co3(PO4)2·8H2O) 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)2·8H2O 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)2·8H2O/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).