Green preparation using black soybeans extract for graphene-based porous electrodes and their applications in supercapacitors

•An in situ strategy for green reduction and electrode fabrication is proposed.•The proposed process was completed in a one-pot system.•The waste product from the food processing industry is used as a green agent.•Nanotextured surfaces of electrodes can be obtained after microwave treatment.•Performance of supercapacitor is significant improved after microwave treatment.

Adopting an in situ construction strategy, green reduction of graphene oxide (GO) and the formation of an open porous structure are simultaneously completed in a one-pot process using an aqueous extract of an anthocyanin-containing plant, black soybean, as a green reducing agent. The reduced GO prepared by the aqueous extract of black soybean (BRGO), and the hydrogel of BRGO are characterized to better understand the nature of BRGO and the evolution of BRGO from GO. Graphene-based porous electrodes for supercapacitors are fabricated using the BRGO hydrogel as a primary material, and the electrochemical performance of the electrodes are further improved when the BRGO porous electrodes are treated in a microwave oven. Owing to the formation of uniformly dispersed nanoparticles on the graphene surface during the microwave treatment, the electrical conductivity of the electrodes improves by four orders of magnitude and the electroactive surface area also increases by over four times, as a consequence, the capacitance is significantly enhanced, reaching a capacitance of 268.4 F g−1 at a charging current of 0.1 A g−1.

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