A simple, efficient, fluorine‐free synthesis method of MXene/Ti3C2Tx anode through molten salt etching for sodium‐ion batteries

Abstract MXenes are mentioned in many applications due to their unique properties. However, the traditional etching method has a lengthy synthesis time, dangerous process, and high cost. Molten salt etching is not only short in time but also safe and simple, laying a good foundation for industrialization. Here, we compare the traditional F‐containing etching method with the molten salt etching method. Transmission electron microscopy elemental mapping images and X‐ray photoelectron spectroscopy show that the Ti3C2Tx surface end of traditional etching is terminated by –F, while the Ti3C2Tx surface end of molten salt etching is terminated by –Cl. Finally, the sodium‐ion batteries are fabricated and the performance difference of the three etching methods is compared. The results show that the capacity of 102.1 mAh g–1 can still be reached when the molten salt etching MXene material returns to 0.1 A g–1 after the current density of 5 A g–1. After 500 cycles at 1 A g–1, there is no significant loss of capacity and the Coulomb efficiency is close to 100%. This work describes that molten salt etching MXene has comparable sodium storage capacity to conventional F‐containing etched MXene, making it a potential candidate for the production of large‐scale sodium‐ion batteries

High pO₂ Flux Growth and Characterization of NdNiO₃ Crystals

Single crystals of the perovskite nickelate NdNiO3 with dimensions of up to 50 μm on edge have been successfully grown using the flux method at a temperature of 400 °C and oxygen pressure of 200 bar. The crystals were investigated by a combination of techniques, including high-resolution synchrotron X-ray single-crystal and powder diffraction and physical property measurements such as magnetic susceptibility and resistivity. Resistivity measurements revealed a metal-insulator transition (MIT) at TMIT~180 K with apparent thermal hysteresis; however, no superlattice peaks or peak splitting below TMIT, which corresponds to a structural transition from Pbnm to P21/n, was observed. The successful growth of NdNiO3 crystals at relatively low temperatures and oxygen pressure provides an alternative approach for preparing single crystals of interesting perovskites such as RNiO3 (R = Sm-Lu) and parent phases of superconducting square planar nickelates

Rational Design of a Hierarchical Candied-Haws-like NiCo₂O₄@Ni,Co-(HCO₃)₂ Heterostructure for the Electrochemical Performance Enhancement of Supercapacitors

Designing core–shell heterostructures with multicomponents, more electroactive sites, hierarchical structures, and stable geometrical configurations is an effective approach to enhance the electrochemical properties of supercapacitors. Herein, we report the fabrication of a hierarchical candied-haws-like NiCo2O4@NiCo-hydrocarbonate heterostructure on Ni foam (NiCo2O4@NiCo-HCs), which consists of NiCo2O4 nanowires acting as “rebars” that are tightly strung with NiCo-HC nanoparticles. The strong interfacial reaction between the NiCo2O4 “core” and the NiCo-HC “shell” accelerates the charge transfer within the heterostructure, while the hierarchical structure containing quantities of paths and pores provides fast ion diffusion throughout the whole electrode, hence remarkably boosting the electrochemical performance of a NiCo2O4@NiCo-HC electrode. As expected, the NiCo2O4@NiCo-HC electrode shows a high specific capacitance of 3216.4 F g–1 at a current density of 1 A g–1 and 2259.9 F g–1 even at 20 A g–1 (1.6-fold that of the NiCo2O4 electrode and 5.5-fold that of NiCo-HCs). In addition, an assembled asymmetric supercapacitor NiCo2O4@NiCo-HCs//AC delivers a high energy density of 47.46 Wh kg–1 at a power density of 708.94 W kg–1, together with 96.2% capacitance retention after 6000 cycles, surpassing most of the reported analogues. These results suggest that our hierarchical candied-haws-like heterostructure design is potential for the performance enhancement of supercapacitors