A eutectic mixture catalyzed straight forward production of functional carbon from Sargassum tenerrimum for energy storage application

Abstract

Here, we present a sustainable and scalable approach for synthesizing functionalized nanomaterials directly from an abundant natural seaweed resource coupled with a green eutectic mixture. The study utilized crushed seaweed granules obtained from fresh brown seaweed Sargassum tenerrimum (ST) and a eutectic mixture generated through the complexation of urea and a metal salt, which act as both solvent and catalyst to facilitate the straightforward production of metal oxide functionalized nanomaterials. Subjecting seaweed granules and the eutectic mixture to pyrolysis at temperatures between 700 °C and 900 °C in a nitrogen (N₂) atmosphere resulted in the formation of ST-derived carbon (STC) functionalized with β-MnO₂. The nanoneedles thus synthesized were examined for their electrochemical properties in both three-electrode and two-electrode configurations, employing 6 M KOH and 1 M Na₂SO₄ as electrolytes. Within the three-electrode framework, β-MnO₂ functionalized STC at 800 °C (MSTC-8) displayed a remarkable specific capacitance, of 685.1 F g⁻¹ in alkaline electrolyte and 308.3 F g⁻¹ in neutral electrolyte at 0.1 A g⁻¹, demonstrating a superior performance compared to MSTC-7 and MSTC-9. Additionally, two-electrode experiments and evaluations of cyclic stability were performed on MSTC-7, MSTC-8, and MSTC-9 symmetric supercapacitors. The fabricated symmetric supercapacitor in Na₂SO₄ with the operational voltage window up to 1.7 V, achieved a maximum energy density of 45.5 Wh/kg and a power density of 172.66 W kg⁻¹. Moreover, the current investigation highlights the enduring performance of MSTC-8//MSTC-8 symmetric supercapacitor, with a capacitance retention of 95 % and 80 % over 20,000 cycles in KOH and Na₂SO₄ electrolytes respectively.