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 ofhaemoglobin/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 (FeCl$_3$) as an oxidant. The HPCs were characterized through Fourier transform infrared spectra, scanning electron microscopy and simultaneous thermogravimetric analysis. Electrochemical capacitance ($C_s$, 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 (V s$^{−1}$) ranging from 0.001 to 0.2. HPCs with 30% (w/w) of Hb have shown the highest Cs of 294.00 as compared with 112.00 for pure PIN at a scan rate of 0.001 V s$^{−1}$. Successivescans of HPC electrodes show a capacitive decline of $\sim$2% during the first 1000 cycles at a scan rate of 0.1 V s$^{−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.

Doping of haemoglobin (Hb) into polypyrrole (PPy) has afforded polymer composites (PCs) with improved semiconducting behaviour with retained thermal stability. Process of doping was conducted through cationic surfactantassisteddilute polymerization of pyrrole (0.12 mol dl$^{-1}$) in the presence of ferric chloride oxidant (1.85${\times}$10$^{-2}$ mol dl$^{-1}$) supplemented with requisite weight fractions of Hb (10 and 20%; w/w). Physicochemical features of PCs were examined through diverse spectral, thermal and microscopic methods. Thermogravimetric analysis (TG) coupled with differential thermal analysis and differential thermogravimetry reveals two-step decomposition of PCs at common TG onset with Hb and PPy (200°C). Energy of activation and frequency of thermal degradation of Hb, PPy and related PCs have been evaluated and compared through Coats–Redfern (CR) and Horowitz–Metzger (HM) methods. CR method reveals substantial modification in free energy change of thermal degradation (${\Delta}$G, kJ mol$^{-1}$) of PCs (132.90) over PPy (13.09). Doping of Hb (20 wt%) has rendered shift in energy bandgap of PPy from 3.09 to 2.99 eV. Working electrodes (WEs) were derived from PCs in the presence of sulphonated polysulphone binder in graphite matrix and investigated for direct current conductivity (${\sigma}$DC) measurement under four-probe conditions at temperature range 313–373 K. Arrhenius plots reveal progressive trend in carrier activation energy (meV) of PCs ranging from 1.08 to 1.16 up to 20 wt% doping of Hb. The present study delivers a viable method of preparation of WE from Hb-doped PPy with sustained semiconducting behaviour up to 373 K.