Venice's macroalgae-derived active material for aqueous, organic, and solid-state supercapacitors

Abstract

In this study, self-doped porous activated biochar derived from Venice lagoon's Sargassum brown macroalgae (ABS) has been successfully prepared through thermochemical carbonization (pyrolysis) followed by CO 2 physical activation and used as electrodes for supercapacitor (SC) applications. The ABS exhibits a remarkable specific surface area of 821 m 2 g-1 and heteroatoms (N, O, and S) doping, both key features to attain high-performance carbon-based SC electrodes. The electrochemical performances of ABS-based SCs were assessed in three different electrolytes. Two are aqueous (i.e., 1 M H 2 SO 4 and 8 M NaNO 3), while the third one is the prototypical organic, namely 1 M TEABF 4 in acetonitrile. In these three electrolytes, the ABS-based electrodes exhibited specific capacitance values (C g) of 109.5, 79.0, and 64.3Fg-1 , respectively, at a current density of 0.1 Ag-1. The capacitive performance resulted in SC energy densities of 3.45 Wh kg 1 at 22.5 W kg 1 , 6.3 Wh kg 1 at 36.1 W kg 1 , and 12.4 Wh kg 1 at 57.4 W kg 1 and maximum power densities of 147, 222, and 378 kW kg 1 in the acidic, quasi-neutral aqueous electrolyte and organic electrolyte, respectively. The ABS electrodes were used to realize a flexible solid-state SC based on the sulfonated polyether ether ketone (SPEEK):functionalized niobium disulfide flakes (f-NbS 2) composite membrane. The flexible solid-state SC displayed a remarkable 97% C g retention even under various mechanical stresses, including bending up to 1000 times and folding angles up to 180 • , while keeping a Coulombic efficiency above 98%. This study reveals ABS as a promising sustainable source of active materials for SCs. The remarkable performance of ABS-based SCs can be attributed to their multi-scale porosity, heteroatom doping, and enhanced surface wettability, providing abundant active sites for charge accumulation, and efficient electrolyte diffusion, thus highlighting its potential as a sustainable solution for energy storage applications.