Zinc Oxide-Enhanced Porous Activated Carbon From Waste Walnut Shells for Supercapacitor Electrodes

Abstract

This work shows the direct conversion of waste walnut shells into zinc oxide-enriched porous activated carbon (ZnO-AC_w) and focuses on its electrochemical performance analysis. The synthesis method consists of two steps: thermal carbonization and ZnCl₂ chemical activation. The XRD analysis revealed the presence of ZnO, graphitic carbon, and crystallinity of the synthesized composite material (ZnO-AC_w). The as-prepared ZnO-AC_w was found to have rod and 2 D plate-like microstructures as observed in SEM images. The elemental composition confirmed the traces of Zn, O, Al, Si elements, and graphitic carbon. The BET analysis confirmed a high specific surface area of 756 m² g⁻¹ and a mesoporous structure with an average pore radius of 16.3 Å. Electrochemical studies demonstrated a specific capacitance of 77.7 F g⁻¹ at a high current density of 5 A g⁻¹. The capacitance retention was about 80% even after the 10,000 CV cycles. The experimental findings prove the high electrochemical performance of the ZnO-enriched activated carbon, which was introduced. It also produced an energy density of 8.74 Wh kg⁻¹. This synthetic approach demonstrates the promising potential of walnut shells derived activated carbon as an electrode material for the supercapacitor.