Defect engineered ternary metal spinel-type Ni-Fe-Co oxide as bifunctional electrocatalyst for overall electrochemical water splitting.

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 NiFeCoO4 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.

Structurally engineered highly efficient electrocatalytic performance of 3-dimensional Mo/Ni chalcogenides for boosting overall water splitting performance.

Hydrogen production from water splitting combined with renewable electricity can provide a viable solution to the energy crisis. A novel MoS2/NiS2/Ni3S4 heterostructure is designed as a bifunctional electrocatalyst by facile hydrothermal method to demonstrate excellent electrocatalytic performance towards overall water splitting applications. MoS2/NiS2/Ni3S4 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 MoS2/NiS2/Ni3S4 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.

Facile hydrothermal synthesis of carbon-coated cobalt ferrite spherical nanoparticles as a potential negative electrode for flexible supercapattery.

Battery type electrodes would replace the currently available pseudocapacitive electrodes by the cause of high energy density and long discharge time. In this regard, battery type carbon coated CoFe2O4 spherical nanoparticles is prepared by the facile hydrothermal method and tested as the possible negative electrode for supercapattery applications. The phase purity, electronic states of elements, and the presence of carbon is inferred through various sophisticated techniques. The calculated surface area of CoFe2O4 and carbon coated CoFe2O4 are found to be 9 and 26 m2 g-1, respectively. The morphological analysis confirms the formation of uniform CoFe2O4 nanospheres (∼25 nm) with a thin layer of carbon coating (∼2 nm). The amorphous carbon coating over CoFe2O4 nanosphere is identified via high-resolution transmission electron microscope. The observed peak and plateau regions in the cyclic voltammogram and galvanostatic charge/discharge curves reveals the battery-type charge storage behaviour of the material. The carbon coated CoFe2O4 delivers the maximum length capacitance of 9.9 F m-1 at 1 mV s-1 with a useful lifespan over 5000 cycles. The electrochemical impedance spectroscopy reveals that the carbon-coated CoFe2O4 delivers the low charge transfer resistance than CoFe2O4. Further, the fabricated supercapattery provides the energy density of 160 × 10-8 Wh cm-1 at a power density of 67.2 µW cm-1. As well as, the device shows 93% of coulombic efficiency and 75% of the specific capacitance retention over 11,000 cycles. Overall, it is believed that the carbon-coated CoFe2O4 can serve as a good candidate for flexible supercapatteries.