Ultrasonic-assisted preparation and characterization of hierarchical porous carbon derived from garlic peel for high-performance supercapacitors

•Application of ultrasonic waves to the preparation of porous carbon for supercapacitors.•Ultrasonic-assisted impregnation of porous carbon helps to regulate pore structure to improve electrochemical performance.•The mechanism of action of ultrasonic waves in the impregnation process and subsequent activation processes.•A porous carbon preparation strategy with simple synthesis method and excellent performance is proposed. Ultrasonic-assisted impregnation is used to synthesize physically modified garlic peel-based 3D hierarchical porous carbons (PCs), and the effect on PCs is investigated by changing ultrasonic time. The results show that ultrasonic waves can effectively peel off surface attachments of the carbonized product, so that activator has a better mass transfer process and create more active sites. The connectivity of 3D pore network is enhanced as well, so the structure and electrochemical properties of garlic peel-based porous carbon (GBPC) are improved. The ultrasonic disperser is used as an ultrasonic generator, specific conditions are as follows: ultrasonic frequency is 40 kHz, ultrasonic power is 500 W, and ultrasonic time is 0, 3, 6, and 9 min, respectively. With the increase of ultrasonic time, impurities again block the pore structure during dynamic movement, resulting in a decrease in electrochemical performance. Specifically, the performance of GBPC-6 is the most excellent, the specific surface area (SSA) increases from 2548 m2 g−1 to 3887 m2 g−1, the specific capacitance increases from 304 F g−1 to 426 F g−1 at a current density of 1 A g−1 in a two-electrode test system. Energy density and cycle performance are also improved at the same time, which are attributed to rational structure. In addition, the effectiveness of the strategy of ultrasonic-assisted synthesis has been confirmed on another precursor material–scallion, meaning that this work proposes a new and simple modification method for improving the performance of biomass-based PCs.