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 (80% activity of the catalyst, making the functionalized graphene sheets derived from Sargassum tenerrimum a sustainable replacement for existing precious metal-based ORR catalysts. Copyright 2016 The Royal Society of Chemistry.