NiCo2O4/FeMoO4 heterostructure as a bifunctional electrocatalyst for hydrogen and oxygen evolution reactions.

Sustainable hydrogen production requires low-cost, efficient electrocatalysts to replace precious-metal benchmarks. Here, we report a heterostructured NiCo2O4/FeMoO4 nanocomposite that exhibits bifunctional electrocatalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a three-electrode half-cell configuration. Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses confirmed heterostructure formation between conductive NiCo2O4 and redox-active FeMoO4 bearing multivalent metal species. Among the investigated NiCo2O4/FeMoO4 compositions, the 3 : 2 composite exhibited the highest electrochemical activity, demonstrating that the relative composition of the two components strongly influences the HER and OER response, requiring an overpotential of only 40 mV at 10 mA cm-2 for the HER, with a Tafel slope of 35.9 mV dec-1 and a charge-transfer resistance of 2.251 Ω, as determined by electrochemical impedance spectroscopy (EIS). The OER exhibited an overpotential of 330 mV at 10 mA cm-2, a Tafel slope of 63 mV dec-1 and a charge-transfer resistance of 19.31 Ω. The electrochemically active surface area (ECSA) indicates a higher number of accessible catalytic sites. The results demonstrate the NiCo2O4/FeMoO4 heterostructure as a low-cost and bifunctional electrocatalyst for HER/OER and establish heterostructure engineering as an effective strategy for the development of non-precious-metal catalysts for prospective water splitting technologies.