Binary transition metal oxides (BTMOs) possess higher reversible capacity, better structural stability and electronic conductivity, and have been widely studied to be novel electrode materials for supercapacitors.

In this work, a facile hydrothermal approach for the shape-controlled synthesis of NiCo2S4 architectures is reported. Four different morphologies, urchin-, tube-, flower-, and cubic-like NiCo2S4 microstructures, have been successfully synthesized by employing various solvents. The obtained precursors and products have been characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. It is revealed that the supersaturation of nucleation and crystal growth is determined by the solvent polarity and solubility, which can precisely control the morphology of NiCo2S4 microstructures. The detailed electrochemical performances of the various NiCo2S4 microstructures are investigated by cyclic voltammetry and galvanostatic charge-discharge measurements. The results indicate that the tube-like NiCo2S4 exhibits promising capacitive properties with high capacitance and excellent retention. Its specific capacitance can reach 1048 F g(-1) at the current density of 3.0 A g(-1) and 75.9% of its initial capacitance is maintained at the current density of 10.0 A g(-1) after 5000 charge-discharge cycles.

Luminescent nanothermometers have shown competitive superiority for contactless and noninvasive temperature probing especially at the nanoscale. Herein, we report the inherently Eu /Eu codoped Sc O nanoparticles synthesized via a one-step and controllable thermolysis reaction where Eu is in-situ reduced to Eu by oleylamine. The stable luminescence emission of Eu as internal standard and the sensitive response of Eu emission to temperature as probe comprise a perfect ratiometric nanothermometer with wide-range temperature probing (77-267 K), high repeatability (>99.94%), and high relative sensitivity (3.06% K at 267 K). The in situ reduction of Eu to Eu ensures both uniform distribution in the crystal lattice and simultaneous response upon light excitation of Eu /Eu . To widen this concept, Tb is codoped as additional internal reference for tunable temperature probing range.

Hierarchical mesoporous spinel NiCo₂O₄ was synthesized by a facile hydrothermal method assisted by polyvinylpyrrolidone (PVP) and a post annealing treatment. The synthesized hierarchical mesoporous NiCo₂O₄ presents a hierarchical mesoporous structure with diameters of 5.0 and 25 nm, respectively. Compared to conventional flower-like NiCo₂O₄, the hierarchical mesoporous structured NiCo₂O₄ exhibits excellent supercapacitor performance. The specific capacitance can reach 1619.1 F g(-1) at a current density of 2.0 A g(-1). When the current density is increased to 10.0 A g(-1), a specific capacitance of 571.4 F g(-1) can be obtained. Furthermore, the hierarchical mesoporous structured NiCo₂O₄ presents excellent stability. The outstanding electrochemical performance of the hierarchical mesoporous NiCo₂O₄ reveals its potential to be a promising material for use in supercapacitors, and also inspires continued research on binary metal oxides as energy transformation materials.