Pore size matters!—a critical review on the supercapacitive charge storage enhancement of biocarbonaceous materials

A circular economy targets zero waste converting both natural and synthetic wastes to valuable products, thereby promoting sustainable development. The porous nanocarbon synthesized from bio-waste is one such product used in applications such as energy storage, catalysis, and sensors. Different techniques are employed for synthesizing carbon from the biowastes and each route results in different properties toward end-user applications. Among them, surface area and porosity are the two critical factors that influence the energy storage capabilities of these synthesized carbon nanostructures. Besides the high surface area of the bio-derived carbons, the hindrance in supercapacitive performance is owing to its low porosity. Fewer review/research papers report the porosity tuning of these carbons for their influence on enhancing the performance of energy storage devices (supercapacitors). This critical review analyses the importance of porosity in these bio-derived carbons and reviews the recent development in its synthesis techniques along with its improvement in the energy storage capability. Special attention is also delivered to identify the ambient source of biowaste for carbon electrodes (fabrication) in supercapacitors. The recent research progress in tuning the porosity of these bio-derived carbons and the influence of electrolyte with porosity in affecting its supercapacitive energy storage is elucidated here. The research challenges, future research recommendations, and opportunities in the synthesis of bio-derived porous carbon for supercapacitor applications are briefed.