Ni-Co PBA-decorated CNTs as battery-type cathode materials for potassium-ion hybrid capacitors

Recently, considerable attention has been given to Prussian blue analogues (PBAs) as efficient battery-type electrode materials for devising advanced hybrid supercapacitors. In this study, nickel hexacyanocobaltate (NiHCC) was considered as a PBA system to successfully synthesize carbon nanotubes- (CNTs) and carbon nanofibers- (CNFs) hybridized NiHCC nanocomposites following a single-step hydrothermal process and the corresponding battery-type electrochemical storage behavior was investigated in 3 M KOH. All the synthesized electrodes exhibited battery-type charge storage mechanisms with excellent stability. The NiHCC-CNT composite (NiHCC@CNT) electrode, in particular, exhibited excellent charge storage capacity (348 mAh g-1 at 1 Ag-1) owing to its high electrochemically active surface area, low charge transfer resistance, and efficient utilization of redox centers for K+ ion storage. Moreover, the hybrid capacitor constructed using NiHCC@CNT exhibited excellent cycling stability over 5000 cycles with a maximum energy density of 59 W h Kg- 1 at a power density of 1798 W Kg-1. This work demonstrates the potential of NiHCC@CNT composite as a cathode material for K+ ion supercapacitors.