Supercapacitors are excellent energy storage devices for electronics devices and vehicles, and other devices due to their faster charge–discharge rate, higher power density and longer life cycle than batteries.[1] However, their lower energy density is a major drawback.[2] This has led to a great deal of research to increase the specific surface area of the electrode. Considering this, the activated carbon is an excellent candidate for the electrode since it is easy to control pore size and structure. It was produced from wood and fossil raw materials. But their depletion and/or high price led to utilize biomass or bio-waste because they are abundant, inexpensive, renewable and sustainable.[3] Recently, crops are also being considered for AC preparation since they are easy to obtain despite not such low price.

In this study, barley was selected for activated carbon (AC) preparation. First, column shape samples was prepared from barley powder via pressing, followed by two-step pyrolysis. The 1st step was to at 300 °C at 0.5 °C/min heating rate, and then the 2nd pyrolysis to 400, 500 or 600 °C under N2 flow in a tube furnace. Next, the ACs were subjected to cutting into 1 mm thick disc and then grinded into 0.5 mm thickness. They were immersed in 6M KOH solution and then activated at 700 °C under N2 flow. Finally, the electrochemical properties of ACs were evaluated with a three-electrode system by cyclic voltammetry, galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). In addition, two-electrode system was also studied with the samples having highest specific capacitances. The samples were characterized by Raman, XRD, XPS, SEM and TEM, and specific surface area was also measured. Specific capacitance of 372 F/g was obtained from 400 °C pyrolysis.