Sustainable high-energy supercapacitors: Metal oxide-agricultural waste biochar composites paving the way for a greener future

Metal oxide-biochar composites have become a promising class of materials for supercapacitor applications. The incorporation of metal oxides into the biochar matrix offers several advantages, including improved capacitance, stability, ion diffusion, and conductivity. The synergistic interactions between metal oxides and biochar result in enhanced capacitance and stability of metal oxide-biochar composites. Biochar's porous nature makes ion transport easier, which improves energy storage capabilities and speeds up charge-discharge rates. Additionally, the addition of metal oxides and biochar improves the composites' conductivity, facilitating effective electron transport. However, several research gaps still remain despite these developments, requiring optimization of the composition and structural features as well as their synthesis approaches. Furthermore, in order to precisely control the characteristics of metal oxide-biochar composites, a greater comprehension of the mechanism underlying their creation is necessary. This agenda calls for the creation of new composites with improved electrochemical performance using diverse metal oxide precursors and biochar made from various agricultural wastes. The article summarizes recent developments in metal oxide-biochar composites made from agricultural waste for upcoming supercapacitors. We believe the findings, in terms of fundamentals, development, challenges, and future prospects, of this review would be beneficial for new readers and will facilitate the concerned research era.