Turning mango kernel waste into high-energy porous carbon: a sustainable electrode material for high-performance supercapacitors with exceptional stability

This study explores the sustainable production of high-performance supercapacitor electrodes from waste mango kernels, addressing the growing need for eco-friendly energy storage solutions. Porous carbon materials were synthesized via pyrolysis at varying temperatures (700, 800, 900, and 1000 °C), designated as MK7, MK8, MK9, and MK10, respectively. The synthesized carbon was obtained via a simple and eco-friendly carbonization, yielding a highly porous structure with a large specific surface area of 1348.9 m² g⁻¹, for MK9 material as confirmed by BET analysis. Raman spectroscopy revealed a high degree of graphitization with D and G bands, indicating the presence of both disordered and graphitic carbon domains. SEM imaging showed a well-developed, interconnected porous morphology, while XRD patterns confirmed the amorphous nature with partially crystalline domains. The resulting carbon materials were evaluated for their electrochemical performance in supercapacitor applications. Electrochemical characterization revealed that the MK9 sample, pyrolyzed at 900 °C, exhibited the highest specific capacitance of 205.8 F g⁻¹, surpassing the performance of the other samples. To optimize device performance, symmetric supercapacitors were fabricated using a CR2032 coin cell configuration with different electrolytes and concentrations. The KOH electrolyte device demonstrated a maximum power density of 5137.86 W kg⁻¹, an energy density of 12.32 W h kg⁻¹, and a specific capacitance of 112.4 F g⁻¹. Furthermore, this device exhibited excellent cycling stability, maintaining its performance over 100 000 galvanostatic charge–discharge cycles. A practical demonstration showed the ability of the device to power a red LED for approximately 15 minutes. These results highlight the potential of utilizing waste biomass, specifically mango kernels, for sustainable and efficient supercapacitor development.