LAUSR

Abstract A new composite material was obtained using a simple activation process of biochar (BC) and high performance supercapacitor (SC) electrodes were fabricated. BC was attained by carbonization of infested ash tree residue at 700 °C and was then chemically activated in an Ag 2 SO 4 /HNO 3 solution. The physical properties of the activated – Ag/BC composite product and the electrochemical properties of electrodes fabricated with this composite material were investigated and compared with properties of electrodes fabricated with activated biochar (a-BC). The a-BC was obtained by activation of BC in HNO 3 . Experimental results with the Ag/BC composite based electrodes show favourable electrochemical performance. A high specific capacitance of 494 F g −1 was achieved in an aqueous LiN((SO 2 CF 3 ) 2 ) electrolyte, which is almost 31.4% higher than that of the a-BC based electrodes (376 F g −1 ) and 42% higher than was previously reported (335 F g −1 [Kouchachvili et al. (2015)]) using the identical aqueous electrolyte. Also, high cycling stability with a specific capacitance retention of 98.6% was demonstrated after 2000 cycles. Symmetric SC cells were therefore assembled with the Ag/BC composite and the a-BC based electrodes. The former cell has since shown an excellent energy density of 12.8 Wh kg −1 that is 37% higher than the energy density of the later SC cell (8 Wh kg −1 ), whereas the power density of both SC cells remained the same (366 W kg −1 at a charge/discharge current of 1.3 mA).