Experimental and computational investigation of Cu–N coordination bond strengthened polyaniline for stable energy storage

Cu–N coordination bond strengthened polyaniline (PANI-Cu) grown on carbon paper is designed to improve capacitive performance of conductive polymer supercapacitor. The cross-linking porous PANI-Cu nanofibers are synthesized via electro-polymerization and hydrothermal coordination process. Cu–N coordination bond strengthens interaction of PANI polymer molecular chain, contributing to improving its cycling stability. Copper cation with high redox potential promotes the conversion from benzene ring to quinone ring of PANI, contributing to improving its electroactivity. In comparison with PANI, PANI-Cu presents specific capacitance increasing from 350 to 825 F g−1 at 1 A g−1, rate capacitance retention increasing from 78 to 84% at a raising current density of 1–10 A g−1, cycling capacitance retention increasing from 61 to 91% at 5 A g−1 for 1000 cycles, rate capacitance recovery increasing from 84.0 to 96.7% at a recovering current density of 10–1 A g−1. The simulation calculation reveals that PANI-Cu has higher density of state (4.70 eV) at Fermi energy level, lower proton doping energy (− 5.56 eV) and lower molecule orbital energy gap (0.43 eV) than PANI (3.50 eV, − 2.41 eV, 0.91 eV). The computational results of higher conductivity agree with electrochemical measurement results of higher current response and capacitance, proving superior electroactivity of PANI-Cu. Flexible PANI-Cu supercapacitor exhibits an energy density of 62.1 Wh kg−1 at a power density of 900 W kg−1 and capacity retention of 87% at 5 A g−1 for 1000 cycles, presenting stable energy storage application.