Electrochemical Lithium Storage Performance of Molten Salt Derived V_(2)SnC MAX Phase

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage.Here,we report the preparation of V_(2)SnC MAX phase by the molten salt method.V_(2)SnC is investigated as a lithium storage anode,showing a high gravimetric capacity of 490 mAh g−1 and volumetric capacity of 570 mAh cm^(−3) as well as superior rate performance of 95 mAh g^(−1)(110 mAh cm^(−3))at 50 C,surpassing the ever-reported performance of MAX phase anodes.Sup-ported by operando X-ray diffraction and density functional theory,a charge storage mechanism with dual redox reaction is proposed with a Sn-Li(de)alloying reaction that occurs at the edge sites of V_(2)SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V_(2)C layers with Li.This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.

Molten Salt-Shielded Synthesis(MS^(3))of MXenes in Air

MXenes are two-dimensional transition metal carbides and/or nitrides with unique physiochemical properties and have attracted extensive interest in numerous fields.However,current MXene synthesis methods are limited by hazardous synthesis conditions,high production costs,or difficulty in largescale production.Therefore,a general,safe,cost-effective,and scalable synthesis method for MXenes is crucial.Here,we report the fast synthesis of MXenes in the open air using a molten salt-shielded synthesis(MS^(3))method,which uses Lewis-acid salts as etchants and a low-melting-point eutectic salt mixture as the reaction medium and shield to prevent MXene oxidation at high temperatures.Carbide and nitride MXenes,including Ti_(3)C_(2)T_(x),Ti_(2)CT_(x),Ti_(3)CNT_(x),and Ti_(4)N_(3)T_(x),were successfully synthesized using the MS^(3) method.We also present the flexibility of the MS^(3) method by scaling the etching process to large batches of 20 and 60 g of Ti_(3)AlC_(2) MAX precursor in one pot.When used as negative electrodes,the prepared MS^(3)-MXenes delivered excellent electrochemical properties for high-rate Li-ion storage.

Ultraviolet-activated long-lived room-temperature phosphorescence from small organic molecule-doped polymer systems

Long-lived organic room-temperature phosphorescent(RTP)materials have attracted widespread attention because of their fantastic properties and application prospects.The current methods for developing RTP materials are mainly based on the synthesis of new chromophore molecules and crystallization engineering.However,there are great challenges in the preparation of new chromophore molecules and the use of crystalline materials.Herein,dynamic stimulus-responsive long-lived RTP systems with various emission colors are realized by doping organic chromophore molecules into polymer matrix prepared from vinyl acetate and acrylic acid.Through UV light irradiation,the growth process of long-lived RTP phenomena can be observed for up to 10 s.In particular,the phosphorescence intensity,lifetime,afterglow brightness,and quantum yield of one representative film(P2-M2)increase by 155,262,414,and 8 times after the irradiation,respectively.The unique photophysical phenomena are ascribed to the oxygen consumption characteristics of the polymer matrix under UV irradiation.Meanwhile,the information storage devices are prepared with these RTP systems.This work provides a strategy for achieving small organic molecule-doped polymer RTP systems that are easy to prepare,low-cost,and widely adaptable.

Simple Vanilla Derivatives for Long-Lived Room-Temperature Polymer Phosphorescence as Invisible Security Inks

Developing novel long-lived room-temperature polymer phosphorescence(RTPP)materials could significantly expand their application scope.Herein,a series of RTPP materials based on eight simple vanilla derivatives for security ink application are reported.Attributed to strong mutual hydrogen bonding with polyvinyl alcohol(PVA)matrix,vanilla-doped PVA films exhibit ultralong phosphorescence emission under ambient conditions observed by naked eyes,where methyl vanillate shows the longest emission time up to 7 s.Impressively,when vanilla-doped PVA materials are utilized as invisible security inks,and the inks not only present excellent luminescent emission stability under ambient conditions but also maintain perfect reversibility between room temperature and 65℃ for multiple cycles.Owing to the unique RTPP performance,an advanced anticounterfeiting data encoding/reading strategy based on handwriting technology and complex pattern steganography is developed.

Topotactic transition of Ti_(4)AlN_(3) MAX phase in Lewis acid molten salt

MAX phases and its derived two-dimensional MXenes have attracted considerable interest because of their rich structural chemistry and multifunctional applications.Lewis acid molten salt route provides an opportunity for structure design and performance manipulation of new MAX phases and MXenes,Although a series of new MAX phases and MXenes were successfully prepared via Lewis acid melt route in recent years,few work is explored on nitride MAX phases and MXenes.Herein,a new copper-based 413-type Ti_(4)CuN_(3)MAX phase was synthesized through isomorphous replacement reaction using Ti_(4)CuN_(3)MAX phase precursor in molten CuCl2.In addition,it was found that at high temperature Ti4N3Clx MXene will transform into two-dimensional cubic TiNa nanosheets with improved structural stability.