Using Brewery Waste and Green Deep Eutectic Solvent for High Performance Sustainable Supercapacitors

Abstract

Sustainable energy storage devices are intensively sought with the goal to produce nontoxic and easily recycling devices with minimum to zero environmental impact. Porous carbon materials made from biomass waste in combination with the use of green solvent like deep eutectic solvent (DES) make the perfect combination to produce sustainable supercapacitors. In this work, a bio-compatible DES composed of betaine and urea is used in combination with a sodium perchlorate (NaClO₄) solution (20% water content) to form hybrid DES electrolyte with improved ionic conductivity, reduced viscosity and enhanced electrochemical performances. This hybrid DES was used as electrolyte in a symmetric supercapacitor employing porous activated carbon derived from spent grains. The carbon material was prepared via a one-step carbonization and activation process at 900°C, resulting in a hierarchical porous structure with interconnected sheet-like morphology, exhibiting high specific surface area of 1828 m² g^-1 and a total pore volume of 1.06 cm³ g^-1. Electrochemical testing in aqueous 1 M H₂SO₄ revealed a specific capacitance of 253 F g^-1 at 0.25 A g^-1, with 54.5% retention at 10 A g^-1, demonstrating excellent rate capability. Furthermore, using hybrid DES electrolyte, the symmetric device demonstrated excellent operating voltage of 2.6 V with an energy density up to 53.8 Wh kg^-1 and a maximum power density of 9.8 kW kg^-1, along with 78% capacitance retention after 10,000 cycles. These findings highlight the potential of green, non-toxic and low-cost modified Betaine: Urea DES electrolytes in the development of high-performance, sustainable supercapacitors using biomass-derived carbon materials.

Keywords

betaine / deep eutectic solvent / energy storage / supercapacitors / urea / waste

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