The Mechanism of Enhanced Electrocatalytic Water Splitting on S-Doped NiFe2O4/Ni-Fe Alloy@Copper Foams

Abstract The development of bifunctional catalysts with subtle structures, high efficiencies and good durabilities for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is crucial for overall water splitting. In this work, a multicomponent S-doped NiFe2O4/Ni-Fe micronano flower electrocatalyst was synthesized rapidly on foam copper using a simple one-step constant current electrodeposition method. The introduction of S leads to the transformation of the microsphere structure of the Ni-Fe alloy into a cauliflower-like morphology and induces changes in the surface electronic structure, significantly enhancing the catalytic performance for the HER and OER. The S-NiFe2O4/Ni-Fe alloy/CF showed low overpotentials of 220 mV and 66 mV at 10 mA cm-2 in 1.0 M KOH for the OER and HER, respectively. High durability OER and HER performances were demonstrated through 60 h of chronopotentiometry and 6000 CV cycles test. Excellent overall water splitting electrocatalytic activity was observed in the S-NiFe2O4/Ni-Fe alloy/CF‖S-NiFe2O4/Ni-Fe alloy/CF two-electrode system. In particular, active-phase NiOOH, a highly active substance for OER, can be controllably formed in the reaction process owing to the nanoflower structure of multi-layer sulfur which slows down the dissolution of NiFe2O4/Ni-Fe alloy. These results suggest that this composite structure is a promising bifunctional electrocatalyst.