Due to their unique properties and diversity, two-dimensional (2D) nanomaterials have attracted tremendous interest from the scientific community in recent years, especially for energy storage applications. Herein, we present a strategy to prepare flexible and conductive MXene/graphene (reduced graphene oxide, rGO) supercapacitor electrodes by using electrostatic self-assembly between positively charged rGO with poly(diallyldimethylammonium chloride) and negatively charged MXene nanosheets. After electrostatic assembly, rGO nanosheets are inserted in-between MXene layers. As a result, the self-restacking of MXene nanosheets is effectively prevented, leading to a considerably increased interlayer spacing. Accelerated diffusion of electrolyte ions enables more electroactive sites to become accessible. The as-prepared freestanding MXene/rGO-5wt% electrode displays a volumetric capacitance of 1040 F cm -3 at a scan rate of 2 mV s -1 and anThis article is protected by copyright. All rights reserved.3 impressive rate capability with 61% capacitance retention at 1 V s -1 . Moreover, the film electrode exhibits long cycle life with almost no capacitance decay after 20,000 cycles. More importantly, our binder-free, symmetric supercapacitor fabricated with MXene/rGO-5wt%shows a maximum volumetric energy density of 34.6 Wh L -1 and an ultrahigh volumetric power density up to 74.4 kW L -1 , which is among the highest values reported for carbon and MXene based materials in aqueous electrolytes. This work not only provides fundamental insight into the effect of interlayer spacing on the electrochemical performance of 2D hybrid materials, but also sheds light on the design of next-generation flexible, portable and highly integrated supercapacitors with high volumetric and rate performances.

We report on the synthesis of the first two-dimensional transition metal nitride, Ti4N3-based MXene. In contrast to the previously reported MXene synthesis methods - in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions - here a molten fluoride salt is used to etch Al from a Ti4AlN3 powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti4N3Tx, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti4N3 and terminated Ti4N3Tx were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti4N3 are predicted to be metallic. Bare Ti4N3 is expected to show magnetism, which is significantly reduced in the presence of functional groups.

Influences from solvents on charge storage in titanium carbide MXenes. (2019) Nature Energy, 4 (3). 241-248.

Two-dimensional (2D) heterostructured materials, combining the collective advantages of individual building blocks and synergistic properties, have spurred great interest as a new paradigm in materials science. The family of 2D transition-metal carbides and nitrides, MXenes, has emerged as an attractive platform to construct functional materials with enhanced performance for diverse applications. Here, we synthesized 2D MoS -on-MXene heterostructures through in situ sulfidation of Mo TiC T MXene. The computational results show that MoS -on-MXene heterostructures have metallic properties. Moreover, the presence of MXene leads to enhanced Li and Li S adsorption during the intercalation and conversion reactions. These characteristics render the as-prepared MoS -on-MXene heterostructures stable Li-ion storage performance. This work paves the way to use MXene to construct 2D heterostructures for energy storage applications.

properties of novel transparent electrode materials include high transmittances (>85%) in the UV and visible regions and low sheet resistances ( R s ), in the range of 0.01-1 kΩ sq −1 . In addition, the new materials should be mechanically robust for fl exible touch screen and organic lightemitting diode applications. On top of excellent optoelectronic and mechanical properties, low cost of production per unit area and feasibility of large-scale fabrication are key factors determining their industrial success. [ 1a , 2 ] Among numerous materials being considered for transparent electrode applications, 2D graphene is arguably the most studied in the past few years. [ 1e , 3 ] Transparent conductive graphene fi lms are mainly produced by two methods: direct chemical vapor deposition (CVD) or solution-processing of reduced graphene oxide (rGO). [ 4 ] Although the CVD method results in high-performance fi lms, their high fabrication cost and size limitations have hindered their commercialization. Several solution-processing methods, such as spray coating, spin coating, and dip coating, have also been employed to fabricate thin fi lms from rGO solutions. [ 5 ] However, the transparent fi lms produced by such methods exhibit high R s (1-1000 kΩ sq −1 ), mainly due to defects (functional groups) and inter-fl ake resistance. [ 6 ] The development of novel materials for transparent conductive fi lms and suitable methods for their large-scale and low-cost production remains a challenge.Recently, a new class of 2D transition metal carbides and/or nitrides, so-called MXenes, was discovered. [ 7 ] Both theoretical and experimental results indicate that most MXenes exhibit metallic conductivity, hydrophilicity, high mechanical strength, and can act as intercalation hosts. [ 8 ] They have shown great promise as electrodes in supercapacitors, Li-ion and other types of batteries, fuel cells, reinforcement for polymers, adsorbents, and sensors. [ 9 ] Upon delamination, colloidal MXene solutions contain large quantities of ≈1 nm-thick 2D fl akes with lateral sizes up to several micrometers, which are perfect for solution processing.