One-step electrodeposition of polyaniline/nickel hexacyanoferrate/sulfonated carbon nanotubes interconnected composite films for supercapacitor

Abstract

Sulfonated carbon nanotubes (sCNTs) were prepared by reacting concentrated sulfuric acid with carbon nanotubes (CNTs) on the defect sites. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) were used to characterize the morphology and structure of sCNTs, respectively. Subsequently, polyaniline (PANI)/nickel hexacyanoferrate (NiHCF)/sCNT interconnected composite films were electrodeposited on the platinum electrode by the one-step co-polymerization using cyclic voltammetry in an aqueous dispersion containing sCNTs. The effect of concentration of NiSO4 and K3Fe(CN)6 in the prepared solution on the morphology and structure of PANI/NiHCF/sCNTs composite films was studied by scanning electron microscopy (SEM), FTIR spectroscopy, and X-ray diffraction (XRD), respectively. The effect of concentration of NiSO4 and K3Fe(CN)6 in the prepared solution on polymerization and electrochemical performance was investigated by cyclic voltammetry (CV), galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy (EIS). One-step electrodeposition mechanism was discussed deeply. It was found that sulfonic acid groups had been attached to surface of CNTs, and sCNTs had higher dispersibility than CNTs in an aqueous dispersion. The morphology of PANI/NiHCF/sCNTs interconnected composite films was remarkably influenced by the concentration of NiSO4 and K3Fe(CN)6. The tubular packing structure appeared with the low concentration of NiSO4 and K3Fe(CN)6 in prepared solution, while the beautiful coral-like interconnected structure exhibited with 0.04 mol L−1 NiSO4 and 0.04 mol L−1 K3Fe(CN)6, which was mainly attributed to the π–π* electron stacking effect among sCNTs, NiHCF, and PANI. The specific capacitance and electroactivity of PANI/NiHCF/sCNTs composite films increased markedly with the increase of concentration of NiSO4 and K3Fe(CN)6 in prepared solution. The specific capacitance of PANI/NiHCF/sCNTs composite film was 430.77 F g−1 with 0.04 mol L−1 NiSO4 and 0.04 mol L−1 K3Fe(CN)6 due to self-doping effect of sCNT in composite films. The cycle stability of PANI/NiHCF/sCNTs composite films was enhanced with the increase of NiSO4 and K3Fe(CN)6 in prepared solution.