Soybean-waste-derived activated porous carbons for electrochemical-double-layer supercapacitors: Effects of processing parameters

The electrochemical performance of electrical-double-layer capacitors is dependent on the microstructures and porous structures of electrode materials, which are controlled by the processing parameters. In this work, we synthesize porous activated carbons (ACs) of submicron sizes from low-cost, ground soybean waste via hydrothermal carbonization (HTC) and facile, environment-friendly physical activation, and systematically investigate the effects of the processing parameters on the electrochemical properties of the synthesized ACs. The experimental results reveal that the activation agent of H₂O steam and high activation temperature can effectively improve the capacitance of the ACs with an optimum, specific capacitance up to 220 F/g and outstanding long-term stability over 98% after 10,000 cycles. The ACs activated with the flow of an inert gas exhibit excellent rate capabilities and relatively low electrochemical impedance. The results likely provide some guidance for the preparation of biomass-derived ACs, and help better understand the fundamental mechanisms for the energy storage in electrochemical double layer.