Malabar spinach–derived hierarchical porous carbon for robust supercapacitors by an activation-pickling-carbonization method

Abstract

Supercapacitors have attracted considerable interests owing to their elevated power density, swift charge–discharge capabilities, and extended cycle life. The pivotal element in augmenting supercapacitor performance lies in the synthesis of porous carbon materials characterized by high specific surface area and well-developed pore architectures. This work introduces an innovative approach integrating activation, pickling, and carbonization, utilizing Malabar spinach as the carbon precursor and KOH as the activating agent for biochar-based supercapacitors. The activation process enhances the material porosity, while pickling removes the majority of non-carbon elements. Subsequent re-carbonization increases the specific surface area and porosity of carbons, resulting in a higher specific capacitance. The optimized carbons exhibit a high specific surface area (1195.37 m² g⁻¹), hierarchical porous structure, and remarkable specific capacitance (427.5 F g⁻¹ at 0.5 A g⁻¹). After 10,000 galvanostatic charge/discharge cycles at 10 A g⁻¹, the capacitance retention rate remains at 98.71% with a high Coulombic efficiency of 99.67%. Under two-electrode system testing conditions, the energy density measured 6.9 Wh kg⁻¹ while the power density reached 125.3W kg⁻¹. This work demonstrates a promising potential of combining activation, pickling, and carbonization for biomass-derived carbons, which have great potential in the application of electrochemical energy storage and conversion devices.