Synthesis of a Novel Interconnected 3D Pore Network Algal Biochar Constituting Iron Nanoparticles Derived from a Harmful Marine Biomass as High-Performance Asymmetric Supercapacitor Electrodes

Via the activation treatment on Cladophora glomerata (CG) with FeCl 3 and KOH, magnetic biochar (MBC) with olive-shaped pores and functional biochar (FBC) with a novel interconnected 3D pore network structure have been successfully prepared by a facile slow pyrolysis process to be applied as electrodes in supercapacitors. To obtain Fe composite biochar (FCBC), FBC was functionalized with HNO 3 and H 2 SO 4 for extending formation of iron oxide through the hydrothermal method. These electrodes demonstrate remarkable electrochemical behaviors, in terms of wonderful rate capability, high specific capacitance and excellent cycle stability when first served as electrodes for supercapacitors. In addition, we have successfully fabricated an asymmetric supercapacitor with high energy and power densities using FBC as the anode electrode and iron oxide/carbon composites (MBC and FCBC) as the cathode electrodes in a neutral aqueous 3 M KCl electrolyte. Because of the desirable porous structure, high specific capacitance, rate capability, and complementary potential window of the two electrodes, the asymmetric supercapacitor can be cycled reversibly in a wide potential window of 0–1.8 V and exhibits energy density 41.5 Wh kg –1 at a power density of 900 W kg –1 for FBC//FCBC. The asymmetric supercapacitor also presents stable cycling performance with 93.1% for FBC//FCBC capacitance retention at 8 A g –1 after 10000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.