Peanut shell-derived porous carbons activated with iron and zinc chlorides as electrode materials with improved electrochemical performance for supercapacitors

This work presents a simple and efficient approach to producing a cost-effective and eco-friendly porous carbon with excellent performance for supercapacitor systems. Present study, peanut shells, a byproduct of the agricultural industry have been taken as the precursor for activated carbon (AC). ACs have been synthesized by hydrothermal treatment at 200 °C for 7 h with and without activated agents (FeCl₃ and ZnCl₂), followed by carbonization at 700 °C for 1 h 30 min. under the N₂ flow. The X-ray diffraction patterns show two broad peaks at around 23 °C and 43 °C, respectively, agreeing with the amorphous and graphitic phases in the samples. The specific surface area and pore radius of the ZnCl₂ treated sample (PS-Zn-700) are 466.2 ± 9.3 m²g⁻¹ and 1.9 nm, respectively, found to be the highest among all the samples. The PS-Zn-700 exhibits a mesoporous nature, demonstrating the capability of ZnCl₂ in building the carbon framework on the sample’s surface during the hydrothermal and carbonization treatments. The PS-Zn-700 shows a superior electrochemical performance compared to the others (PS-700 and PS-Fe-700) in 1 M H₂SO₄ electrolyte at ambient temperature. Galvanostatic charge-discharge curves show nearly-isosceles triangular features, characteristic of the EDLC behavior with a little faradic contribution from the heteroatoms (N, O) comprising functional groups. The specific capacitance (C_m) value is 101.6 F/g at 1 A/g and the energy density (E) value is 20.32 Wh kg⁻¹. The stability and durability of the samples are evaluated for 8000 cycles at 5 A/g, and the PS-Zn-700 shows a 98.5% capacitance retention rate without any shape change. Moreover, the PS-Zn-700 exhibits a low Equivalent Series Resistance (ESR) of 2.96 Ω.