Sustainable organic electrodes using black soldier fly-derived melanin for zinc-ion hybrid capacitors

Abstract

Pressing environmental challenges require focused research on sustainable solutions in the domains of energy, water, food, land, and climate. The pigment eumelanin has recently been positioned as a promising candidate for solving issues in health, sensors, and energy storage. However, the low solubility of eumelanin in aqueous solvents, difficult film processibility, and high cost have hindered the material from wide deployment. Here, we propose melanin extracted from the black soldier fly, Hermetia illucens (Mel-BSF), as a sustainable alternative for the preparation of organic electrodes in energy storage applications. Mel-BSF displays pseudocapacitive behaviour with a high potential window, good electrochemical stability, and higher maximum capacity (91.8 mAh g−1) compared to synthetic eumelanin (17.3 mAh g−1) as the working electrode material in zinc-ion hybrid capacitors using an ionic liquid electrolyte. Structural and surface investigations reveal that additional aliphatic compounds, potentially lipids present after Mel-BSF refinement, significantly increase the film stability and redox centre availability. Eumelanin is a promising pigment for use in energy storage applications but has limitations hindering its wide usage. Here, melanin extracted from the black soldier fly is used to prepare electrodes with higher performance than synthetic melanin in zinc-ion hybrid capacitor applications.