Deep eutectic solvent promoted one step sustainable conversion of fresh seaweed biomass to functionalized graphene as a potential electrocatalyst

Abstract

Herein we report a facile method for the scalable production of Fe₃O₄/Fe doped graphene nanosheets (Fe₃O₄/Fe–GN) from a naturally abundant seaweed resource. The granules that remained after the recovery of liquid juice from a fresh brown seaweed, Sargassum tenerrimum, were utilized as a raw material and a deep eutectic solvent (DES) generated by the complexation of choline chloride and FeCl₃ (ChoCl–FeCl₃) was employed as a template as well as a catalyst for the production of graphene nanosheets. Pyrolysis of a mixture of seaweed granules and DES at 700–900 °C under a 95% N₂ and 5% H₂ atmosphere resulted in the formation of Fe₃O₄/Fe–GN with a high surface area (220 m² g⁻¹) and high electrical conductivity (2384.6 mS m⁻¹). The synthesized nanosheets were then tested for their electrocatalytic activity in the oxygen reduction reaction (ORR) in an alkaline fuel cell. The electrocatalyst demonstrated a positive onset potential, high cathodic current density, low hydrogen peroxide formation (<5%) and ideal 4-electron transfer for the whole potential range in alkaline media. The present study successfully demonstrates the highly stable ORR activity of the electrocatalyst even after 30 000 cycles with a retention of >80% activity of the catalyst, making the functionalized graphene sheets derived from Sargassum tenerrimum a sustainable replacement for existing precious metal-based ORR catalysts.