Nano-whiskers of Fe ₂ O ₃ coated with NiCo LDH grown on an iron foam substrate for overall water splitting

Transition metal-based heterostructures have attracted remarkable interest for their application in efficient water-splitting electrocatalysis. However, their application in water splitting is currently limited due to their low activity and stability at high current densities. Here, we report the rational design and synthesis of a three-dimensional nano-whisker heterostructure comprising a nickel cobalt-layered double hydroxide (NiCo LDH) deposited on iron oxide grown on an iron foam (Fe) (NiCo LDH@Fe₂O₃/Fe foam). This hierarchical architecture specifically addresses the intrinsic limitations of NiCo LDH, including low electronic conductivity and self-aggregation tendency. By combining controlled thermal oxidation and electrodeposition, the resulting catalyst exhibits remarkable catalytic performance with an overpotential of only 202 mV and 96 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, at a current density of 10 mA cm^-2 in an alkaline electrolyte. Detailed characterization and electrochemical analyses reveal that the enhanced activity stems from the synergistic interactions between Fe₂O₃ nano-whiskers and NiCo LDH nanosheets, which optimize electron transfer pathways and maximize active site accessibility. When implemented in an electrolytic cell, the catalyst demonstrates good operational stability, achieving an ultra-low cell voltage of 1.83 V at a current density of 100 mA cm^-2 for overall water splitting.