Influence of cavitational and non-cavitational ultrasonic treatment on the structure and electrochemical properties of nanoporous wood activated carbon

The effect of ultrasonic radiation in the cavitational and non-cavitational modes on the properties of wood activated carbon (AC) has been investigated. The AC was synthesized from birch wood by pyrolysis at 800 ºC and activation by water vapor. The duration of the ultrasonic treatment was chosen so that the AC received the same amount of acoustic energy. It has been shown that ultrasonic treatment in the cavitational mode does not cause significant changes in the porous structure of wood activated carbon, with only the redistribution of mesopores in size taking place. The non-cavitational ultrasonic treatment not only redistributes the mesopores in size, but also forms a microporous structure of the AC. Taken together, these factors lead to an increase in the specific surface area to 719 m 2 /g as against 551 m 2 /g for the original carbon. It was found that the specific capacity of the AC after ultrasonic exposure increased to 94.8 F/g for carbon after non-cavitational treatment and 142.3 F/g for carbon after cavitational treatment as against 58.3 F/g for the original carbon. The impedance dependences at different bias voltages for supercapacitors made from both the original and treated AC were analyzed. Equivalent electrical circuits modeling impedance hodographs were constructed. To this end, the de Levie model was employed, modified by the connection of a parallel R SC C SC -link. It was established that due to the ultrasonic treatment of carbon in the cavitational mode, the density of energy states of delocalized charge carriers at the Fermi level increases, which results in the redistribution of capacitances that form an electrical double layer, and this increases the specific capacity of carbon. The increase in the specific capacity of AC after ultrasonic treatment in the non-cavitational mode is primarily attributed to the formation of a microporous structure and, consequently, an increase in the specific surface area.