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.

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The electrochemical performance of lithium ion battery was enhanced by using biochar derived from Cladophora glomerata (C. glomerata) as widespread green macroalgae in most areas of the Iran's Caspian sea coast. By the utilization of the structure of the biochar, micro-/macro-ordered porous carbon with olive-shaped structure was successfully achieved through pyrolysis at 500 °C, which is the optimal temperature for biofuel production, and was activated with HCl. The biochar and HCl treatment biochar (HTB) were applied as anode electrode in lithium ion batteries. Then, electrochemical measurements were conducted on the electrodes via galvanostatic charge-discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses. The electrochemical results indicated a higher specific discharge capacity (700 mAh g) and good cycling stability for HTB at the current density of 0.1 A g as compared to the biochar. The reason that HTB electrode works better than the biochar could be due to the higher surface area, formation functional groups, removal impurities, and formation some micropores after HCl treatment. The biochar derived from marine biomass and treatment process developed here could provide a promising path for the low-cost, renewable, and environmentally friendly electrode materials. Graphical abstract Algal-biochar into Li-ion Battery.

Electrochemical power tools are regarded as essential keys in a world that is becoming increasingly reliant on fossil fuels in order to meet the challenges of rapidly depleting fossil fuel...