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[Display omitted] • Facile synthesis of structurally engineered Ternary Spinel-type NiFeCoO 4 nanoparticles. • Ni-Fe-Co elements work synergistically to enhance the electrocatalytic activity. • The defect engineered NiFeCoO 4 requires a low water splitting cell voltage of 1.67 V. Transition metal spinel oxides were engineered with active elements as bifunctional water splitting electrocatalysts to deliver superior intrinsic activity, stability, and improved conductivity to support green hydrogen production. In this study, we reported the ternary metal Ni-Fe-Co spinel oxide electrocatalysts prepared by defect engineering strategy with rich and deficient Na+ ions, termed NFCO-Na and NFCO, which suggest the formation of defects with Na+ forming tensile strain. The Na-rich NiFeCoO 4 spinel oxide reveals lattice expansion, resulting in the formation of a defective crystal structure, suggesting higher electrocatalytic active sites. The spherical NFCO-Na electrocatalysts exhibit lower OER and HER overpotentials of 248 mV and 153 mV at 10 mA cm−2 and smaller Tafel slope values of about 78 mV dec−1 and 129 mV dec−1, respectively. Notably, the bifunctional NFCO-Na electrocatalyst requires a minimum cell voltage of about 1.67 V to drive a current density of 10 mA cm−2. The present work highlights the significant electrochemical activity of defect-engineered ternary metal oxides, which can be further upgraded as highly active electrocatalysts for water splitting applications. [ABSTRACT FROM AUTHOR]

Hydrogen production from water splitting combined with renewable electricity can provide a viable solution to the energy crisis. A novel MoS 2 /NiS 2 /Ni 3 S 4 heterostructure is designed as a bifunctional electrocatalyst by facile hydrothermal method to demonstrate excellent electrocatalytic performance towards overall water splitting applications. MoS 2 /NiS 2 /Ni 3 S 4 heterostructure necessitates a low overpotential of 81 mV and 210 mV to attain a current density of 10 mA cm−2 during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Consequently, the MoS 2 /NiS 2 /Ni 3 S 4 heterostructure-based electrolyzer shows a low cell voltage of 1.54 V at 10 mA cm−2. The present work highlights the significance of the heterostructure configuration of transition metal sulfide-based electrocatalysts for electrochemical overall water splitting applications. [Display omitted] • Preparation of MoS 2 /NiS 2 /Ni 3 S 4 heterostructure by facile hydrothermal method. • Synergistically enhanced HER and OER electrocatalytic activity of MoS 2 /NiS 2 /Ni 3 S 4. • MoS 2 /NiS 2 /Ni 3 S 4 heterostructure requires a low voltage for overall water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Regulating the heterostructure interfaces towards improved water splitting performance. • NiO/NiFe 2 O 4 with higher compressive strain enhances the interfacial electrocatalytic activity. • Bifunctional NiO/NiFe 2 O 4 requires a low water splitting cell voltage of 1.56 V. The present work reports the simple preparation of NiO/ NiFe 2 O 4 heterostructures with interfacial effects as bifunctional electrocatalysts for overall water splitting. At increasing Ni/Fe precursor ratios, the evolution of NiO phases is observed in NFO heterostructures, which incorporate differential strain effects at the interface. The modulated heterojunction of NiO/NiFe 2 O 4 heterostructure incorporates compressive strain at the interfaces enhancing its electrocatalytic performances. Notably, NiO/NiFe 2 O 4 heterostructure prepared at equimolar Ni/Fe ratios (NFO-1) exhibits significant electrocatalytic performances due to modulated interfacial effects. As such, NFO-1 exhibits lower OER and HER overpotentials of about 242 mV and 106 mV for 10 mA cm−2 current density and exhibits improved water splitting activity, requiring 1.56 V to drive 10 mA cm−2 current density. The present work emphasizes the importance of modulating the heterostructures of transition metal oxides to enhance the interfacial effects as bifunctional electrocatalysts for water splitting applications. [ABSTRACT FROM AUTHOR]