Peanut Oil Cake Biomass-Derived Hierarchical Porous Carbon by Dual Step Activation as Potential Electrodes for Fabrication of Prototype Symmetric Supercapacitor Device

Peanut oil cake biomass is a major by-product of oil industry and can be a suitable precursor for the production of biomass-based porous carbon. Herein, dual-stage activation, physical activation at 400°C, and chemical activation using KOH between 600 and 900°C are adopted to prepare hierarchical porous carbons (HPCs) from peanut oil cake biomass for use as electrode material in electrochemical supercapacitors. The textural and structural properties of the HPC were evaluated by N₂-adsorption/desorption, X-ray diffraction, Raman, FT-IR spectroscopy, and scanning electron microscopy. The prepared HPC inherited sufficient micropores and mesopores distribution with a maximum BET surface area of 640 m²/g. The electrochemical properties of the HPC electrodes were evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopic analysis. Among different HPC electrodes prepared, the carbon prepared at 800°C (HPC-P8) electrode material exhibited a high specific capacitance of 187 F/g at 0.5 A/g in 1M Na₂SO₄ electrolyte in three-electrode systems. Symmetric supercapacitors were also fabricated using HPC-P8//HPC-P8 as positive and negative electrodes using 1M Na₂SO₄ electrolyte, in a two-electrode cell configuration via split cell method. Maximum specific capacitance of 30 F/g was achieved with superior cycle stability of 93.8% capacitance retention over 5,000 cycles for the symmetric device. The device operated at a wide potential window (0–2.0 V) resulted in appreciable specific energy and power density of 15.89 Wh/kg and 493 W/kg, respectively. HPC-P8 had an ion diffusion coefficient of 7.79 × 10⁻⁸ cm²/s which is higher than the other prepared carbon samples. The symmetric device showed relatively high charge storage capacity and cyclic stability without any material degradation. The fabricated prototype portable supercapacitor module was tested for red LED glow with maximum intensity brightness up to 4 min. Thus, the present study reveals that HPC derived from peanut oil cake biomass can behave as a promising electrode material for supercapacitor applications.