Iron oxide loaded biochar/polyaniline nanocomposite: Synthesis, characterization and electrochemical analysis

[Display omitted] •Supercapacitor electrode materials were synthesized from a natural cellulose residue, banana stem.•Banana stem was pyrolyzed under nitrogen atmosphere at 500 °C to produce a biochar.•Biochar was transformed into a magnetic biochar by treating it with FeCl3 and FeSO4 solution.•The surface area was enhanced from 7.97 m2g−1 to 283 m2g−1 due to magnetization.•The magnetized biochar was then made into a composite with a conducting polymer PANI.•UV-Visible and FTIR studies revealed the interactions of magnetized char with PANI.•Cyclic voltammetry studies and impedance measurements were also conducted. The value-added application of biochar in electrochemical energy storage had been explored in the present work. The biochar was derived from the local agriculture residue, banana stem (BS). BSwas pyrolyzed at 500 °C under nitrogen atmosphere for 12 h. It was transformed into magnetic biochar (MB) and magnetic biochar–polyaniline (PANI) composite. The electronic transitions around 325 and 410 nm characterized the composite formation. The distribution of the crystalline magnetite phase throughout the PANI matrix was evident from the 2θ values in and around 17.8°, 20.4°, 25.1°, 33.4° and 43.6° in the composite. The heterogeneous porosity (mesopores and micropores) of the biochar was revealed from SEM images. PANI insertion into these sites was confirmed from the disappearance of these sites after compositing. TEM images indicated the uniform distribution of magnetite nanoparticles in the composite with average grain size of 6.25 nm, which is in agreement with the data obtained from XRD (8.08 nm). The charge transfer resistance offered by MB (11.0 Ω) is greater than that of the composite (9.6 Ω), highlighting that the composite could serve as a better electrode material over MB. The MB and the composite showed specific capacitance values (Cs MB = 234.8 Fg−1, Cs composite = 315.7 Fg−1) higher than those reported in the literature with other biochars.