Novel method of preparing CoFe2O4/graphene by using steel rolling sludge for supercapacitor

•Steel rolling sludge provide iron for CoFe2O4/graphene, which realize the recycle and environmental protection.•The prepared CoFe2O4/graphene composites have large specific surface area.•The materials show obvious Faradaic redox reactions with high specific capacity.•The incorporation of CoFe2O4 and graphene weakened agglomerations.

Steel rolling sludge containing high amounts of iron was recycled for the first time via a facile hydrothermal method and used as ferric ions source for CoFe2O4/graphene nanocomposite electrode. CoFe2O4 agglomeration is weakened by introducting graphene, which is crucial for improving efficient ions transport pathways in energy storage devices. The CoFe2O4/graphene complex exhibits a rough morphology and a porous nanostructure with a high specific surface area of 191.5 m2 g−1. The material also shows excellent Faradaic redox reactions with high specific capacity of 166.5C g−1 and 127.0C g−1 at 0.5 and 10 A g−1, respectively, which are higher than that of simple, dense CoFe2O4 particles (121.6C g−1 at 0.5 A g−1). Furthermore, the electrode demonstrates outstanding cycle stability with 79.3% capacitance retained after 5000 cycles. Hence, the proposed resource reuse strategy can be used to prepare CoFe2O4/graphene nanocomposites for supercapacitors.

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