Search

The creation of vacancies and/or pores into two‐dimensional materials, like graphene and MXenes, has shown to increase their performance for sustainable applications. However, a simple and affordable method with controlled and tailorable vacancy concentration and/or pores size remains challenging. Herein, a simple and reproducible method is presented for controlled synthesis of Mo1.74CTz MXene with randomly distributed vacancies and pores, obtained from selective etching of both Ga and Cr in the Cr‐alloyed MAX‐phase like precursor Mo1.74Cr0.26Ga2C. Structural and compositional analysis of the 3D alloy show ≈13% Cr on the metal site, homogeneously distributed between different particles and within the atomic structure. After etching, it translates to Mo1.74CTz MXene, exhibiting defect‐rich sheets. Notably, the incorporation of Cr facilitates a shorter etching time with an improved yield compared to Mo2CTz. The Mo1.74CTz MXene displays excellent electrochemical properties, almost doubling the capacitance values (1152 F cm−3 and 297 F g−1 at 2 mV s−1 scan rate), compared to its pristine counterpart Mo2CTz. The presented method and obtained results suggest defect engineering of MXenes through precursor alloying as a pathway that can be generalized to other phases, to further improve their properties for various applications. [ABSTRACT FROM AUTHOR]

MXenes have shown great potential as an emerging two-dimensional (2D) material for micro-supercapacitors (MSCs) due to their high conductivity, rich surface chemistry, and high capacity. However, MXene sheets inherently tend to lay flat on the substrate during film formation to assemble into compact stacked structures, which hinders ion accessibility and prolongs ion transport paths, leading to highly dependent electrochemical properties on the thickness of the film. Here, we demonstrate a vertically aligned Ti3C2Tx MXene based micro-supercapacitor with an excellent electrochemical performance by a liquid nitrogen-assisted freeze-drying method. The vertical arrangement of the 2D MXene sheets allows for directional ion transport, enabling the vertical-MXene based MSCs to exhibit thickness-independent electrochemical properties even in thick films. In addition, the MSCs displayed a high areal capacitance of 87 mF cm−2 at 10 mV s−1 along with an excellent stability of ∼87.4% after 10 000 charge–discharge cycles. Furthermore, the vertical-MXene approach proposed here is scalable and can be extended to other systems involving directional transport. [ABSTRACT FROM AUTHOR]

Nb4C3Tx MXene has shown extraordinary promise for various applications owing to its unique physicochemical properties. However, it can only be synthesized by the traditional HF‐based etching method, which uses large amounts of hazardous HF and requires a long etching time (> 96 h), thus limiting its practical application. Here, an ultra‐efficient and environmental‐friendly H2O‐assisted supercritical etching method is proposed for the preparation of Nb4C3Tx MXene. Benefiting from the synergetic effect between supercritical CO2 (SPC‐CO2) and subcritical H2O （SBC‐H2O）, the etching time for Nb4C3Tx MXene can be dramatically shortened to 1 h. The as‐synthesized Nb4C3Tx MXene possesses uniform accordion‐like morphology and large interlayer spacing. When used as anode for Li‐ion battery, the Nb4C3Tx MXene delivers a high reversible specific capacity of 430 mAh g−1 at 0.1 A g−1, which is among the highest values achieved in pure‐MXene‐based anodes. The superior lithium storage performance of the Nb4C3Tx MXene can be ascribed to its high conductivity, fast Li+ diffusion kinetics and good structural stability. [ABSTRACT FROM AUTHOR]

Highlights: Porous MXene (p-MC) films with 3D-interconnected ion transmission paths are constructed by NH3-induced in situ etching strategy. The flexible p-MC film electrodes exhibit a superior capacitance of 688.9 F g−1 with a good rate capability. The as-assembled p-MC solid-state flexible supercapacitors reveal superior electrochemical performance (99.7 F g−1 at 1 A g−1) and excellent flexibility.2D MXene (Ti3CNTx) has been considered as the most promising electrode material for flexible supercapacitors owing to its metallic conductivity, ultra-high capacitance, and excellent flexibility. However, it suffers from a severe restacking problem during the electrode fabrication process, limiting the ion transport kinetics and the accessibility of ions in the electrodes, especially in the direction normal to the electrode surface. Herein, we report a NH3-induced in situ etching strategy to fabricate 3D-interconnected porous MXene/carbon dots (p-MC) films for high-performance flexible supercapacitor. The pre-intercalated carbon dots (CDs) first prevent the restacking of MXene to expose more inner electrochemical active sites. The partially decomposed CDs generate NH3 for in situ etching of MXene nanosheets toward 3D-interconnected p-MC films. Benefiting from the structural merits and the 3D-interconnected ionic transmission channels, p-MC film electrodes achieve excellent gravimetric capacitance (688.9 F g−1 at 2 A g−1) and superior rate capability. Moreover, the optimized p-MC electrode is assembled into an asymmetric solid-state flexible supercapacitor with high energy density and superior cycling stability, demonstrating the great promise of p-MC electrode for practical applications. [ABSTRACT FROM AUTHOR]

Abstract: Approaching state‐of‐the‐art areal and volumetric capacitances while maintaining high‐power characteristic is a big challenge that promotes practical application of flexible solid‐state micro‐supercapacitors (MSCs), which have recently attracted great attention with the rapid development of flexible microelectronics. Herein, it is reported that freestanding extrahigh conductive Ti3C2Tx (MXene) films with excellent flexibility and effectively controlled thickness ranging from 1–21 µm performed as excellently scalable and flexible solid‐state MSCs owing to their ultrahigh underlying electrical conductivity (up to 1.25 × 105 S m−1) and self‐functionalized surfaces (O, OH, and F terminations). Amazingly, freestanding conductive Ti3C2Tx based flexible solid‐state MSCs with interdigital electrodes and polyvinyl alcohol/sulfuric acid (PVA/H2SO4) gel electrolyte display outstanding areal capacitances of 340 mF cm−2 at 0.25 mA cm−2 based on the two working electrodes. Moreover, the maximum corresponding volumetric capacitance and energy density of flexible solid‐state MSCs reach up to 183 F cm−3 and 12.4 mWh cm−3, which is on the topmost level among all the unconventional supercapacitors to date. Compared with materials currently used in MSCs, this freestanding conductive Ti3C2Tx shows potential and scalability in increasing overall micro‐supercapacitor performance, which evidently sheds light on promising application of freestanding conductive MXenes for next‐generation flexible, portable, and integrated MSCs. [ABSTRACT FROM AUTHOR]

Nb 4 C 3 T x MXene has shown extraordinary promise for various applications owing to its unique physicochemical properties. However, it can only be synthesized by the traditional HF-based etching method, which uses large amounts of hazardous HF and requires a long etching time (> 96 h), thus limiting its practical application. Here, an ultra-efficient and environmental-friendly H 2 O-assisted supercritical etching method is proposed for the preparation of Nb 4 C 3 T x MXene. Benefiting from the synergetic effect between supercritical CO 2 (SPC-CO 2 ) and subcritical H 2 O （SBC-H 2 O）, the etching time for Nb 4 C 3 T x MXene can be dramatically shortened to 1 h. The as-synthesized Nb 4 C 3 T x MXene possesses uniform accordion-like morphology and large interlayer spacing. When used as anode for Li-ion battery, the Nb 4 C 3 T x MXene delivers a high reversible specific capacity of 430 mAh g -1 at 0.1 A g -1 , which is among the highest values achieved in pure-MXene-based anodes. The superior lithium storage performance of the Nb 4 C 3 T x MXene can be ascribed to its high conductivity, fast Li + diffusion kinetics and good structural stability., (© 2023 Wiley-VCH GmbH.)

MXene-based microsupercapacitors (MSCs) have promoted the development of on-chip energy storage for miniaturized and portable electronics due to the small size, high power density and integration density. However, restricted energy density and operating voltage invariably create obstacles to the practical application of MSCs. Here, we report a symmetric MXene-based on-chip MSC, achieving an ultrahigh energy density of 75 mWh cm -3 with high operating voltage of 1.2 V, which are almost the highest values among all reported symmetric MXene MSCs. The adjustment strategy of acetone on the viscosity and surface tension of MXene ink, along with the natural sedimentation strategy, can effectively prevent the orderly stacking of MXene sheets. Further, we developed an all-in-one Si-electronics with three series MSCs through laser-etching technology, obviously presenting high integration capacity and processing compatibility. Thus, this work will contribute to the development of high integration all-in-one electronics with high energy density MXene-based MSCs.

Solid-state composite polymer electrolytes (CPEs) usually suffer from intrinsic low ionic conductivity and a solid-solid interface, badly inhibiting their widespread commercial application in all-solid-state Li-metal battery (ASSLMB) energy storage. Herein, a synergetic strategy using strong Lewis acid-base and weak hydrogen bonds was employed for self-assembly in situ construction of three-dimensional (3D) network-structured poly(ethylene oxide) (PEO) and SiO 2 CPEs (PEO@SiO 2 ). Ascribed to this synergistically rigid-flexible coupling dynamic strategy, a harmonious incorporation of monodispersed SiO 2 nanoparticles into PEO could remarkably reduce crystallinity of PEO, significantly enhancing the ionic conductivity (∼1.1 × 10 -4 S cm -1 at 30 °C) and dramatically facilitating solid electrolyte interface stabilization (electrochemical stability window > 4.8 V at 90 °C). Moreover, the PEO@SiO 2 -based ASSLMBs possess excellent rate capability over a wide temperature range (∼105 mA h g -1 under 2 C at 90 °C), high temperature cycling capacity (retaining 90 mA h g -1 after 100 cycles at 90 °C), and high specific capacity (146 mA h g -1 under 0.3 C at 90 °C). Unambiguously, these high ionic conductivity CPEs along with excellent flexibility and safety can be one of the most promising candidates for high-performance ASSLMBs, evidently revealing that this synergistically rigid-flexible coupling dynamic strategy will open up a way to exploit the novel high ionic conductivity solid-state electrolytes.