Biochar/poly(aniline-pyrrole) modified graphite electrode and electrochemical behavior for application in low-cost supercapacitor

An attempt is made to use biochar (BC), a carbon rich low-cost green material, as a platform to house conducting polymer for fabricating stable graphite electrodes for application in next generation supercapacitor devices. Here, BC is first prepared from sucrose solution using a simple hydrothermal method. The seeded chemical oxidative copolymerization of aniline and pyrrole is then carried out at identical comonomer weight ratio using BC as seed particles. Two different BC to mixed monomer (w/w) ratios (1:0.7 and 1:1) have been used and the prepared composites are named as BC/P(Ani-Py)1:0.7 and BC/P(Ani-Py)1:1 respectively. Independent of composition, both BC seed and composite particles are spherical. The smooth homogeneous surface of BC turned heterogeneous after composite formation. The average size of BC seed particles is 2.56 µm and those of composites prepared at weight ratios of 1:0.7 and 1:1.0 are 2.72 and 2.90 µm respectively. Cyclic voltammetry (CV), galvanostatic charging discharging (GCD), and electrochemical impedance spectroscopy (EIS) are used to evaluate the electrochemical properties. Comparatively, the BC/P(Ani-Py)1:1 composite modified graphite electrode exhibited the highest capacitance value (274.27 F g−1 at a current density of 1.0 A/g) and is capable of acting as a supercapacitor electrode. A long-term cycling test of the BC/P(Ani-Py)1:1 modified electrode at a current density of 5.0 A/g displayed a capacitance retention of 96.6 % after 1000 cycles of charge and discharge, indicating a very good cycle stability.