Electrochemical investigation of flower-like sodium cobalt phosphate-based materials and activated carbon derived from cocoa pod husks as potential electrode for asymmetric supercapacitor

Abstract

This study presents a hydrothermal synthesis of a flower-like sodium cobalt phosphate (Co₃H₁₈Na₄P₄₁O₂₄) material, both in pristine form and as composites with varying masses of graphene foam (GF). The electrochemical performance of these materials is thoroughly investigated, with Co₃H₁₈Na₄P₄₁O₂₄/10mg GF showing the best specific capacity (52mAh g^-1 at 1 A g^-1 in 1 M KOH). The kinetic analysis using Dunn's approach indicates that the material's charge storage is predominantly diffusion-controlled (76%). Furthermore, activated carbon derived from cocoa pod husks exhibits promising capacitive performance (148 F g^-1 at 1 A g^-1). When assembled into a full asymmetric device (Co₃H₁₈Na₄P₄₁O₂₄/10mg GF as the positive electrode and cocoa pod husk-derived activated carbon as the negative electrode), the device achieves a specific capacity of 23 mAh g^-1, an energy density of 18 W h kg^-1, and a power density of 0.3996 kW kg^-1. Notably, it retains 97.8% of its capacity over 10,000 cycles at 10 A g^-1, demonstrating excellent stability. This work highlights the potential of Co₃H₁₈Na₄P₄₁O₂₄/10 mg GF composites in energy storage applications, particularly in high-performance supercapacitors.