Sustainable synthesis of Ni-doped activated carbon composites from agricultural waste for high-performance supercapacitor electrodes

In pursuit of sustainable energy solutions, this study presents a scalable strategy for producing high-performance supercapacitor electrodes derived from agricultural waste. Activated carbon (ACCS) was extracted from corn stover and calcium oxide (COSP) from shell powder, followed by electrochemical deposition of nickel to form Ni-ACCS/COSP composite electrodes. The composites synthesized with different ACCS/COSP concentrations (2–8 g/L) were systematically evaluated. The Ni-ACCS/COSP-6 g/L electrode demonstrated the highest electrochemical performance, delivering a specific capacitance of 223.6 mF/cm² at 5 mA/cm², a high specific surface area of 92.1 m²/g, an average pore diameter of 20 nm, increased electrical conductivity of 0.054 S/cm, and a low charge transfer resistance of 4.96 Ω. Dunn’s analysis revealed a pseudocapacitive contribution of 89.1 % at 100 mV/s, indicating rapid ion transport and efficient charge storage. An asymmetric supercapacitor (ASC) assembled with Ni-ACCS/COSP//AC electrodes demonstrated a wide operating voltage window of 1.6 V, a maximum energy density of 35.2 Wh/kg at a power density of 450 W/kg, and remarkable cycling stability, retaining 92.3 % capacitance after 5000 cycles. Practical LED illumination tests further confirmed the device’s real-world applicability. This work highlights a synergistic design strategy integrating electric double-layer capacitance and pseudocapacitance, offering a sustainable and efficient pathway for transforming agricultural waste into high-performance energy storage materials. • Dual biomass (corn stover & shell powder) used to fabricate supercapacitor electrodes. • Ni-ACCS/COSP-6 g/L electrode shows 223.6 mF/cm² capacitance and 92.3 % retention. • Electrochemical deposition integrates CaO and Ni into porous carbon network. • Asymmetric device exhibits high energy density and excellent cycling durability.