Jatropha oilcake based biochar and hydrochar; synthesis, characterization, and comparison of their properties for supercapacitor applications

The agro-industrial by-product jatropha oilcake was efficiently converted into biochar (BC) and hydrochar (HC) respectively via pyrolysis and hydrothermal carbonization processes. The obtained BC and HC were analyzed to evaluate their physicochemical characteristics through CHNS, XRD, FTIR, Raman, BET specific surface area, and SEM analysis. Raman analysis reveals that the BC has a higher degree of graphitization and structural order, while HC offers a more disordered but electrochemically accessible, carbon matrix. Further, the specific surface areas of BC and HC are respectively found to be 3.131and 3.857 m²/g, in which HC showed higher values due to the formation of better porous structure compared to BC. Compared to BC, HC exhibits higher carbon content, richer surface functionalities, more disordered and a more uniform, microporous structure, making it an ideal candidate for capacitive energy storage applications. Furthermore, the synthesized charred products were used to fabricate symmetric supercapacitor, and their electrochemical performance was tested using a 2-electrode configuration. The fabricated supercapacitors exhibited a specific capacitance of 2.14 F/g and 3.06 F/g at 1 A/g respectively for BC and HC. The noticed superior performance of HC is mainly attributed to its superior and unique structural features.