Haemoglobin/polyindole composites: the novel material for electrochemical supercapacitors

Abstract

Conducting polymers have recently been employed with metal derivative macromolecules that have led to great improvement in the field of supercapacitor materials. The current work reports on the synthesis of a novel class of haemoglobin/polyindole composites (HPCs) through doping of haemoglobin (Hb) into a polyindole (PIN) matrix. HPCs with enhanced electrocapacitive performance were prepared through a cationic surfactant-assisted dilute solution polymerization of indole (IN) in the presence of Hb at various concentrations ranging from 10 to 30% (w/w) and ferric chloride ( $$\hbox {FeCl}_{3}$$ ) as an oxidant. The HPCs were characterized through Fourier transform infrared spectra, scanning electron microscopy and simultaneous thermogravimetric analysis. Electrochemical capacitance ( $$C_{\mathrm{s}}$$ , $$\hbox {F g}^{-1}$$ ) of graphite-based electrodes fabricated from HPCs over stainless steel in the presence of sulphonated polysulphone as a binder has been investigated in KOH solution (1.0 M) with reference to Ag/AgCl at a scan rate ( $$\hbox {V s}^{-1}$$ ) ranging from 0.001 to 0.2. HPCs with 30% (w/w) of Hb have shown the highest $$C_{\mathrm{s}}$$ of 294.00 as compared with 112.00 for pure PIN at a scan rate of $$0.001 \hbox { V s}^{-1}$$ . Successive scans of HPC electrodes show a capacitive decline of $${\sim }2\%$$ during the first 1000 cycles at a scan rate of $$0.1 \hbox { V s}^{-1}$$ in KOH (1.0 M), which indicates the appreciable electrochemical cyclic stability of the HPCs over PIN. Thus, the fabricated HPCs may serve as potential electrode material for development of electrochemical supercapacitors.