Influence of electrochemically deposited polypyrrole layers on NiCo₂O₄-decorated carbon fiber paper electrodes for high-performance hybrid supercapacitor applications

The electrochemically polypyrrole (PPy) layer deposited on NiCo₂O₄-decorated carbon fiber paper (PPy-NiCo₂O₄@CFP) composites was prepared by a consecutive two-step process. At first, the hierarchically NiCo₂O₄-decorated CFP (NiCo₂O₄@CFP) composite was prepared by a low temperature hydrothermal method. Secondly, the PPy layer was deposited onto the NiCo₂O₄@CFP composites using an electrochemical deposition method. The potential sweeping between −0.2 and 1.0 V was performed at a scan rate of 50 mV s⁻¹ for various (0, 5, 10, 15 and 20) cycles in the presence of a pyrrole monomer. SEM images clearly indicated that the NiCo₂O₄ nanostructures were uniformly grown over the CFP. Further, the PPy layer was also uniformly hierarchically-deposited over the NiCo₂O₄@CFP composites. The surface morphologies of the obtained PPy-NiCo₂O₄@CFP composites were dramatically changed depending on the electrodeposition cycles of PPy. We have prepared various PPy-NiCo₂O₄@CFP hybrid composites with different electrodeposition cycles of PPy layers, and the effects of electrodeposited PPy layers were investigated. The PPy-NiCo₂O₄@CFP composites with the 15 cycles electrodeposited PPy layers (PPy15-NiCo₂O₄@CFP//N-rGO@CFP) showed a maximum specific capacitance of ~239 F g⁻¹ at 2 A g⁻¹ and excellent energy density of 64.95 Wh kg⁻¹ at a power density of 1400.2