Okra-Derived Hierarchical Porous Structured Activated Carbon Tuning with Metal-Oxide for Advanced Supercapacitors

A hybrid supercapacitor is designed to fulfill the need for power and energy density by utilizing the composite of activated carbon and metal oxide. Naturally abundant bio-waste (Okra) has been explored to develop porous activated carbon for supercapacitors due to their easy availability, excellent specific surface area, a wide range of micro and mesopore structures giving extremely high performance, and a cost-effective synthesis approach. The bio-waste precursors have excellent microstructural properties, heteroatoms, and mineral content, which outline their subsequent effect on electrochemical performances. Moreover, the surface modification of carbon materials depending upon the pre-processing, carbonization, and etching by chemical activation method is explored, showing the impact on the capacitance. The electrode material is synthesized by freeze-drying biomass precursor followed by carbonization, acid treatment, and one-step activation. Its physicochemical properties are studied by characterization techniques like FESEM, EDS, XRD, Raman, TEM, BET, FTIR, XPS, and TGA analysis. Here, hierarchical honeycomb-structured porous activated carbons giving high surface area were synthesized from okra biowaste by the combination of chemical treatment and heat treatment at different temperatures, facilitating ion penetration and ion diffusion on the electrode-electrolytes interface, and the abundant macropores can serve as ion-buffering reservoirs. Transition metal oxide is synthesized by co-precipitation technique, having a unique characteristic. The electrochemical measurements CV, GCD, EIS, and cyclic stability tests are performed in an electrolyte solution using a carbon-metal oxide composite electrode, giving ultra-high specific capacitance and cyclic stability with high energy and power density. Here in this work carbon matrix is enriched with co-doped heteroatom facilitating the pseudo behavior with the enhancement of electrical conductivity and its hierarchical porous structure, providing easy accessibility to the electrolyte ions. The charge storage mechanism is explored in detail better to understand the dependence between physiochemical and electrochemical properties. Accordingly, we can tune the properties for individual applications. This work provides a facile, scalable synthesis route to get okra-derived activated carbon and transition metal oxide to achieve outstanding super-capacitive performance without compromising energy density.