Effect of Acid-Assisted Hydrothermal Carbonization Temperatures on the Hydrochar Properties for Supercapacitor Application

The investigation of biomass-based, cost-effective, efficient, and environmentally materials with high power density and fast ion/electron transfer is intensively carried out for the development of renewable energy storage devices. Pyrolysis and hydrothermal carbonization (HTC) are two common methods of thermochemical conversion to synthesize biomass-derived based carbon. Compared to the pyrolysis method, HTC is a more promising strategy because it can be carried out without a pre-drying process, has a high yield, low ash content, and requires a relatively low temperature (180-250 °C). The carbon produced from the HTC process is known as hydrochar. This study reports the acid-assisted hydrothermal carbonization temperature on the hydrochar properties and its application for supercapacitor electrodes. Hydrochar was synthesized from extracted avocado seed waste with potassium permanganate and sulfuric acid catalyst solution at 200 °C for 12 h. The effect of one- and two-stage HTC temperature on the hydrochar properties were compared. The hydrochar characterization includes yield, SEM, XRD, FTIR, and cyclic voltammetry analysis. According to the characterization and analysis results, hydrochar produced has the 3D porous network morphology and the highest specific capacitance of 73.54 F/g. In conclusion, hydrochar derived from avocado seed through the acid-assisted HTC can be a potential way for supercapacitor electrodes.