Rational construction of uniform CoS/NiFe2O4 heterostructure as efficient bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions

•The heterostructured CoS/NiFe2O4/NF nanosheet was prepared by two-step electrodeposition method.•The influence of electrodeposition time on electrochemical property is investigated.•CoS/NiFe2O4-15/NF composite exhibits HER and OER catalytic performance with overpotentials of 116 mV and 227 mV at 10 mA cm−2 in 1 M KOH.•The CoS/NiFe2O4-15/NF||CoS/NiFe2O4-15/NF system requires 1.60 V to deliver 10 mA cm−2 for water splitting. The development of efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline environment is crucial and challenging for large-scale hydrogen energy application. Herein, a heterostructure electrocatalyst on Ni foam (NF) with CoS nanosheet coupled with NiFe2O4 was synthesized via electrodeposition method with the assistant of thiourea followed by annealing treatment. Because of the unique three-dimension structure, this self-supported catalyst possesses high intrinsic conductivity, abundant active sites and excellent durability, acting as an exceptionally durable and efficient catalyst for HER and OER. The obtained CoS/NiFe2O4-15/NF exhibits HER and OER catalytic performance with overpotentials of 116 mV and 227 mV at a current density of 10 mA cm−2 in 1 M KOH, respectively. For CoS/NiFe2O4-15/NF||CoS/NiFe2O4-15/NF two-electrode system, the electrolyser requires 1.60 V to deliver 10 mA cm−2, and negligible loss of activity is observed after working for 12 h (10 mA cm−2). Moreover, the interface between oxide and sulfide is identified to play a major part in the catalysis of OER and HER. These excellent properties of CoS/NiFe2O4-15/NF electrode advance the electronic water splitting reaction for hydrogen production. [Display omitted]