Synthesis of Ti_2CT_x MXene as electrode materials for symmetric supercapacitor with capable volumetric capacitance

Two-dimensional(2D)metal carbides,MXene,present the promising application for the energy storage system.Among the MXene family,Ti_2CT_xas the lightest material,shows its unique electrochemical performance.Herein,Ti_2CT_xis synthesized by selective etching Al layer from the Ti_2Al C.With the optimized HF treating condition,Ti_2CT_xdisplays high volumetric capacitance and remarkable rate ability.Moreover,the Ti_2CT_x//Ti_2CT_xsymmetric supercapacitor is designed and assembled,which presents capable capacitance,outstanding rate performance and excellent cycling performance.The remarkable electrochemical performance is attributed to its 2D structure and high electronic conductivity.This work demonstrates the potential application of the Ti_2CT_xfor the supercapacitors and provides a template to design highperformance supercapacitors with 2D electrode materials.

Elucidation of the sodiation/desodiation mechanism in Ca_(0.5)Ti_(2)(PO_(4))_(3)/C as promising electrode for sodium batteries: New insights into the phase transitions

The structure evolution and electrochemical performance of Na SICON-type Ca_(0.5)Ti_(2)(PO_(4))_(3) for sodium batteries are presented.This phosphate was synthesized by a solid-state method,and the obtained particles were coated with carbon using sucrose.This compound crystallizes in the rhombohedral system with space group R-3.The presence of carbon in the Ca_(0.5)Ti_(2)(PO_(4))_(3)/C composite was confirmed by Raman and Thermogravimetric analysis.The electrochemical performance of Ca_(0.5)Ti_(2)(PO_(4))_(3)/C was investigated in the potential window 1.5–3.0 V vs.sodium metal at different scan rates.The compound is able to initially intercalate/deintercalate 1.6/1.15 Na per formula unit,respectively.In operando synchrotron diffraction was done in the potential window 0.02–3.0 V vs.Na|Na+and revealed the occurrence of several reaction regions upon first discharge.Up to 4 Na+ion per formula unit can be inserted during the first discharge.An intensive refinement of the synchrotron X-ray diffraction(SXRD)patterns of discharged Ca_(0.5)Ti_(2)(PO_(4))_(3) evidenced the existence of five regions depending on the sodium content while the crystal structures of new phases were elucidated for the first time where sodium insertion occurs in the unusual M3 and M’3 sites of the Na SICON structure.

Dendrite-free and anti-corrosion Zn metal anode enabled by an artificial layer for high-performance Zn ion capacitor

Aqueous zinc energy storage devices,holding various merits such as high specific capacity and low costs,have attracted extensive attention in recent years.Nevertheless,Zn metal anodes still suffer from a short lifespan and low Coulombic efficiency due to corrosion and side reactions in aqueous electrolytes.In this paper,we construct an artificial Sn inorganic layer on Zn metal anode through a facile strategy of atom exchange.The Sn layer suppresses Zn dendrite growth by facilitating homogeneous Zn plating and stripping during charge and discharge processes.Meanwhile,the Sn protective layer also serves as a physical barrier to decrease Zn corrosion and hydrogen generation.As a result,The Sn-coated anode(Sn|Zn)exhibits a low polarization voltage(~34 mV at 0.5 mAh/cm^(2))after 800 testing hours and displays a smooth and an even surface without corrosion.Moreover,the zinc ion capacitor(Sn|Zn‖activated carbon)is assembled with an enhanced capacity of 42 mAh/g and a capacity retention of 95%after 10,000 cycles at 5 A/g.This work demonstrates a feasible approach for the commercialization of aqueous Zn-based energy storage devices.

Unravelling a solution-based formation of single- crystalline kinked wurtzite nanowires： The case of MnSe

The search for a novel strategy to sculpt semiconductor nanowires （NWs） at the atomistic scale is crucial for the development of new paradigms in optics, electronics, and spintronics. Thus far, the fabrication of single-crystalline kinked semiconductor NWs has been achieved mainly through the vapor-liquid-solid growth technique. In this study, we developed a new strategy for sculpting single-crystalline kinked wurtzite （WZ） MnSe NWs by triggering the nonpolar axial-oriented growth, thereby switching--at the atomistic scale---the NW growth orientation along the nonpolar axes in a facile solution-based procedure. This presents substantial challenges owing to the dominant polar c axis growth in the solution-based synthesis of one-dimensional WZ nanocrystals. More significantly, the ability to continuously switch the nonpolar axial-growth orientation allowed us to craft the kinking landscape of types 150°, 120°, 90°, and 60°. A probabilistic analysis of kinked MnSe NWs reveals the correlations of the synergy and interplay between these two sets of nonpolar axial growth-orientation switching, which determine the actual kinked motifs. Furthermore, discriminating the side-facet structures of the kinked NWs significantly strengthened the spatially selected interaction of Au nanoparticles. We envisage that such a facile solution-based strategy can be useful for synthesizing other single-crystalline kinked WZ-type transition-metal dichalcogenide NWs to develop novel functional materials with finely tuned properties.