Ti2CT2 MXene as Anodes for Metal Ion Batteries: From Monolayer to Bilayer to Pillar Structure

Ti3C2Tx MXene Composite with Much Improved Stability for Superior Humidity Sensors

MXenes have attracted tremendous attention in electromagnetic interference shielding, energy storage, and gas and humidity detections because of their ultralarge surface area and abundant functional groups. However, their poor stability against hydration and oxidation makes them challenging for long-term storage and applications. Herein, we proposed and demonstrated a Ti3C2Tx MXene composite-based humidity sensor, of which the stability is pronouncedly enhanced by introducing an O2 adsorption competitor of extracted bentonite (EB). All the results of TEM, XPS, and Raman spectroscopy show that the oxidation of the Ti3C2Tx MXene is significantly suppressed by the introduction of EB. Its excellent performance in humidity detection further confirms the effectiveness of EB in improving the stability. An ultrahigh response value of 6400% and an ultrafast response time of 1 s at 85% RH are observed, suggesting promising prospects for superior humidity detection of the Ti3C2Tx MXene composite. Furthermore, its feasibility for flexible humidity detection was also examined on a PET substrate, which exhibited high flexibility and excellent discrimination in speaking words.

First principles study on monolayer GeTe as an anode material for multivalent ion batteries

Finding suitable anode materials for multivalent ion batteries (MuIBs) is the key to improving theoretical capacity, reducing development costs and enhancing the safety of energy storage batteries. In recent years, monolayer GeTe has been reported as an anode material in monovalent ion batteries, but it has not received much attention in MuIBs. This article uses first principles methods based on density functional theory (DFT) to explore the application prospects of monolayer GeTe with a unique serrated wrinkled layer structure as an anode material for multivalent metal ion (Al3+/Mg2+/Ca2+) batteries. The research results show that Al3+, Mg2+ and Ca2+ have low diffusion barriers (0.47, 0.35 and 0.61 eV) on monolayer GeTe, indicating its excellent diffusion ability and fast charge discharge rate during the charging and discharging process. Reasonable open circuit voltages (0.62, 0.85 and 0.64 V) and theoretical specific capacities higher than those of commercial graphite anode materials (624.6, 446.1 and 446.1 mA h g-1) indicate that monolayer GeTe has the ability to store Al3+/Mg2+/Ca2+. Finally, molecular dynamics simulations (MD) are used to calculate the adsorption energy and density field of ions during their movement on the surface of monolayer GeTe, demonstrating the stable adsorption ability of monolayer GeTe and the strong interaction between the two. This article reveals that monolayer GeTe can be used as a promising candidate anode material for MuIBs.

Designing a Se-intercalated MOF/MXene-derived nanoarchitecture for advancing the performance and durability of lithium-selenium batteries

Lithium-selenium batteries have emerged as a promising alternative to lithium-sulfur batteries due to their high electrical conductivity and comparable volume capacity. However, challenges such as the shuttle effect of polyselenides and high-volume fluctuations hinder their practical implementation. To address these issues, we propose synthesizing Fe-CNT/TiO2 catalyst through high-temperature sintering of an amalgamated nanoarchitecture of carbon nanotubes decorated metal-organic framework (MOF) and MXene, optimized for efficient selenium hosting, leveraging the distinctive physicochemical properties. The catalytic features inherent in the porous Se@Fe-CNT/TiO2 nanoarchitecture were instrumental in promoting efficient ion and electron transport, and lithium-polyselenide kinetics, while its inherent porosity could play a crucial role in inhibiting electrode stress during cycling. This nanoarchitecture exhibits remarkable battery performance, retaining 99.7% of theoretical capacity after 425 cycles at 0.5 C rate and demonstrating 95.8% capacity retention after 2000 cycles at 1 C rate, with ∼100% Coulombic efficiency. Additionally, the Se@Fe-CNT/TiO2 electrode exhibited an impressive recovery of 297.5 mAh/g (97.9%) capacity after undergoing 450 cycles at a charging rate of 10 C and a discharging rate of 1 C. This synergistic integration of MOF- and MXene-derived materials unveils new possibilities for high-performance and durable LSeBs, thus advancing electrochemical energy storage systems.

Pillaring Behavior of Organic Molecules on MXene: Insights from Molecular Dynamics Simulations

Pillaring MXene with organic molecules is an effective approach to expand the interlayer spacing and increase the accessible surface area for enhanced performance in energy storage applications. Herein, molecular dynamics simulations are employed to explore the pillaring effect of six organic molecules on Ti3C2O2. The interlayer spacing and structural characteristics of MXene after the insertion of different organic molecules are examined, and the influence of the type and quantity of organic molecules on the pillared MXene structure is systematically investigated. The results demonstrate that the inserted molecules are influenced by interactions between MXene layers, resulting in a thinner morphology. Effective pillar support on MXene is achieved only when a specific quantity of organic molecules is inserted between the layers. Furthermore, different organic molecules occupy distinct surface areas on MXene when acting as pillars. Pillaring molecules with a Pi-conjugated ring structure require a larger surface area on MXene, whereas those with a branched structure occupy a smaller surface area. Additionally, organic molecules containing oxygen functional groups tend to aggregate due to hydrogen bonding, impeding their diffusion within MXene sheets. Considering the interlayer expansion of MXene, surface area occupation, and diffusion characteristics, the isopropylamine demonstrates the most favorable pillaring effect on MXene. These findings provide valuable insights into the design and application of pillared MXenes in energy storage and other applications. Further studies on the properties and applications of the optimized pillared MXene structures will be conducted in the future.

Flower-like Layered NiCu-LDH/MXene Nanocomposites as an Anodic Material for Electrocatalytic Oxidation of Methanol

Direct methanol fuel cell (DMFC) technology has grabbed much attention from researchers worldwide in the realm of green and renewable energy-generating technologies. Practical applications of DMFCs are marked by the development of highly active, efficient, economical, and long-lasting anode catalysts. Layered double hydroxide (LDH) nanohybrids are found to be efficient electrode materials for methanol oxidation. In this study, we synthesized NiCu-LDH/MXene nanocomposites (NCMs) and investigated their electrochemical performance for methanol oxidation. The formation of NCM was verified through field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and X-ray photoemission spectroscopy (XPS) analyses. The cyclic voltammetry, chronoamperometry, and electron impedance spectroscopy techniques were carried out to assess the electrocatalytic ability of the methanol oxidation reaction. The incorporation of MXene enhanced the methanol oxidation 2-fold times higher than NiCu-LDH. NCM-45 exhibited high peak current density (86.9 mA cm^-2), enhanced electrochemical active surface area (7.625 cm²), and long-term stability (77.8% retention after 500 cycles). The superior performance of NCM can be attributed to the synergistic effect between Ni and Cu and, further, the electronic coupling between LDH and MXene. Based on the results, NCM nanocomposite is an efficient anodic material for the electrocatalytic oxidation of methanol. This study will open the door for the development of various LDH/MXene nanocomposite electrode materials for the application of direct methanol fuel cells.