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Cobalt sulfide materials have attracted enormous interest as low‐cost alternatives to noble‐metal catalysts capable of catalyzing both oxygen reduction and oxygen evolution reactions. Although recent advances have been achieved in the development of various cobalt sulfide composites to expedite their oxygen reduction reaction properties, to improve their poor oxygen evolution reaction (OER) activity is still challenging, which significantly limits their utilization. Here, the synthesis of Fe 3 O 4 ‐decorated Co 9 S 8 nanoparticles in situ grown on a reduced graphene oxide surface (Fe 3 O 4 @Co 9 S 8 /rGO) and the use of it as a remarkably active and stable OER catalyst are first reported. Loading of Fe 3 O 4 on cobalt sulfide induces the formation of pure phase Co 9 S 8 and highly improves the catalytic activity for OER. The composite exhibits superior OER performance with a small overpotential of 0.34 V at the current density of 10 mA cm −2 and high stability. It is believed that the electron transfer trend from Fe species to Co 9 S 8 promotes the breaking of the Co–O bond in the stable configuration (Co–O–O superoxo group), attributing to the excellent catalytic activity. This development offers a new and effective cobalt sulfide‐based oxygen evolution electrocatalysts to replace the expensive commercial catalysts such as RuO 2 or IrO 2 .
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