Design and Synthesis of Highly Porous Activated Carbons from Sargassum as Advanced Electrode Materials for Supercapacitors

The synthesis of three-dimensional porous biomass carbon was investigated using sargassum as precursor employing KOH, ZnCl 2 and H 3 PO 4 as the activators for the application as electrode materials for supercapacitors. H 3 PO 4 activation resulted in the plugging of pore structure due to the formation of crystallized phosphorus, while three-dimensional framework of porous carbons were synthesized applying ZnCl 2 and KOH. Compared with ZnCl 2 (441.14 m 2 g −1 ), larger surface area was achieved by KOH activation (2486.18 m 2 g −1 ) at 700°C, leading to the significantly better electrochemical performance. The porosity of KOH activated carbon was further improved by adjusting the activation temperature, and a high surface area of 3170.02 m 2 g −1 was obtained by two-step activation of firstly 400°C activation for 45 min and then 800°C for 2 h (KOH-400-800). KOH-400-800 electrode exhibited a high capacitance of 316 F g −1 at 1 A g −1 with good rate capacity (84% retention at 10 A g −1 ) and excellent cycling stability of 99.4% capacitance retention after 5000 cycles. The KOH-400-800 sample also showed a high energy density of 41.67 W h kg −1 and a power density of 320.51 W kg −1 at a current density of 1 A g −1 in the voltage range of 0–1 V.