Phosphorous – Containing Activated Carbon Derived From Natural Honeydew Peel Powers Aqueous Supercapacitors

Abstract

The introduction of phosphorous (P), and oxygen (O) heteroatoms in the natural honeydew chemical structure is one of the most effective, and practical approaches to synthesizing activated carbon for possible high-performance energy storage applications. The performance metrics of supercapacitors depend on surface functional groups and high-surface-area electrodes that can play a dominant role in areas that require high-power applications. Here, we report a phosphorous and oxygen co-doped honeydew peel-derived activated carbon (HDP-AC) electrode with low surface area for supercapacitor via H₃PO₄ activation. This activator forms phosphorylation with cellulose fibers in the HDP. The formation of heteroatoms stabilizes the cellulose structure by preventing the formation of levoglucosan (C₆H₁₀O₅), a cellulose combustion product, which would otherwise offer a pathway for a substantial degradation of cellulose into volatile products. Therefore, heteroatom doping has proved effective, in improving the electrochemical properties of AC-based electrodes for supercapacitors. The specific capacitance of HDP-AC exhibits greatly improved performance with increasing carbon-to-H₃PO₄ ratio, especially in energy density and power density. The improved performance is attributed to the high phosphorous doping with a hierarchical porous structure, which enables the transportation of ions at higher current rates. The high specific capacitance of 486, and 478 F/g at 0.6, and 1.3 A/g in 1 M H₂SO₄ electrolyte with a prominent retention of 98.5 % is observed for 2 M H₃PO₄ having an impregnation ratio of 1 : 4. The higher yield of HDP-AC could only be obtained at an activation temperature of 500 °C with an optimized amount of H₃PO₄ ratio. The findings suggest that the concentration of heteroatoms as surface functional groups in the synthesized HDP-AC depends on the chosen biomass precursor and the processing conditions. This work opens new avenues for utilizing biomass-derived materials in energy storage, emphasizing the importance of sustainable practices in addressing environmental challenges and advancing toward a greener future.