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Two‐dimensional transition‐metal carbides called MXenes are emerging electrode materials for energy storage due to their metallic electrical conductivity and low ion diffusion barrier. In this work, we combined Ti2CTx MXene with graphene oxide (GO) followed by a thermal treatment to fabricate flexible rGO/Ti2CTr film, in which electrochemically active rGO and Ti2CTr nanosheets impede the stacking of layers and synergistically interact producing ionically and electronically conducting electrodes. The effect of the thermal treatment on the electrochemical performance of Ti2CTx is evaluated. As anode for Li‐ion storage, the thermally treated Ti2CTr possesses a higher capacity in comparison to as‐prepared Ti2CTx. The freestanding hybrid rGO/Ti2CTr films exhibit excellent reversible capacity (700 mAh g−1 at 0.1 Ag−1), cycling stability and rate performance. Additionally, flexible rGO/Ti3C2Tr films are made using the same method and also present improved capacity. Therefore, this study provides a simple, yet effective, approach to combine rGO with different MXenes, which can enhance their electrochemical properties for Li‐ion batteries. Flexible freestanding hybrid rGO/MXene films with enhanced Li‐ion storage capacity are fabricated by vacuum‐assisted filtration method followed by a simple thermal treatment. In the hybrid films, reduced graphene oxide nanosheets act as a binder, which bridges electrochemically active conducting MXene particles. The effect of the surface functional group (‐OH) on Li‐storage performance of MXenes is evaluated. [ABSTRACT FROM AUTHOR]

Coplanar energy storage devices with interdigitated electrodes have attracted a significant amount of attention as micropower units for portable and flexible electronics, and self-powered systems. Herein, we propose a simple, cost-effective, and scalable two-step screen-printing process to fabricate flexible coplanar asymmetric microscale hybrid device (MHD) with a higher energy density compared to carbon-based microsupercapacitors. 2D titanium carbide MXene (Ti 3 C 2 T x ) with a large inlayer spacing is selected as negative electrode, and Co-Al layered double hydroxide (LDH) nanosheets are selected as positive electrode. The assembled coplanar, all-solid-state, asymmetric MHD possesses a higher energy density (8.84 μWh cm −2 ) compared to the MXene-based, coplanar, symmetric microsupercapacitors (3.38 μWh cm −2 ), and exhibit excellent flexibility and reliability, as well as cycling stability (92% retention of the initial capacitance after 10,000 cycles). Moreover, we integrate the coplanar asymmetric MHDs with the force sensing resistors as portable power source units to fabricate lightweight and inexpensive integrated force sensors, which can be used to detect applied pressure variation. The two-step screen-printing method can also be extended to other MXenes and various positive electrode materials for fabrication of coplanar asymmetric MHDs on flexible substrates. Therefore, we believe that the two-step screen-printing method opens up new avenues toward developing flexible coplanar asymmetric MHDs, thus promoting the application of MHDs based on MXenes for flexible integrated electronic devices. [ABSTRACT FROM AUTHOR]

Pseudocapacitive materials that store charges by fast redox reactions are promising candidates for designing high energy density electrochemical capacitors. MXenes – recently discovered two-dimensional carbides, have shown excellent capacitance in aqueous electrolytes, but in a narrow potential window, which limits both the energy and power density. Here, we investigated the electrochemical behavior of Ti 3 C 2 MXene in 1M solution of 1-ethly-3-methylimidazolium bis- (trifluoromethylsulfonyl)-imide (EMITFSI) in acetonitrile and two other common organic electrolytes. This paper describes the use of clay, delaminated and composite Ti 3 C 2 electrodes with carbon nanotubes in order to understand the effect of the electrode architecture and composition on the electrochemical performance. Capacitance values of 85 F g −1 and 245 F cm −3 were obtained at 2 mV s −1 , with a high rate capability and good cyclability. In situ X-ray diffraction study reveals the intercalation of large EMI + cations into MXene, which leads to increased capacitance, but may also be the rate limiting factor that determines the device performance. [ABSTRACT FROM AUTHOR]

Abstract Recently, a large family of 2D materials called MXenes have attracted much attention in the field of supercapacitors, thanks to the excellent performance demonstrated by Ti 3 C 2 MXene-based electrodes. However, research on MXenes for supercapacitor applications has been primarily focused on Ti 3 C 2 , even though there are more than 20 other members of this large family of materials already available. Studies on other MXenes are emerging, with promising results already achieved by Ti 2 C, Mo 2 C, and Mo 1.33 C in aqueous electrolytes. Yet, many other MXenes remain unexplored in aqueous supercapacitor applications. In this work, we report on the electrochemical behavior of a vanadium carbide MXene, V 2 C, in three aqueous electrolytes. Excellent specific capacitances were achieved, specifically 487 F/g in 1 M H 2 SO 4 , 225 F/g in 1 M MgSO 4 , and 184 F/g in 1 M KOH, which are higher than previously reported values for few micrometer-thick delaminated MXene electrodes. This work shows the promise of V 2 C MXene for energy storage using aqueous electrolytes. Graphical abstract Unlabelled Image Highlights • A flexible freestanding film was prepared from MXene V 2 C nanosheets. • V 2 C MXene was investigated as electrode for supercapacitors with three aqueous electrolytes. • The best performance, 487 F/g, was obtained in 1 M H 2 SO 4. • V 2 C exhibited higher specific capacitance than previously reported MXenes. [ABSTRACT FROM AUTHOR]

Flexible FeVO 4 /Ti 3 C 2 T x film had been constructed via simple vacuum assist filtration with a unique structure. Through the synergistic action of FeVO 4 and Ti 3 C 2 T x , excellent electrochemical performance is shown in lithium ion and sodium ion batteries. [Display omitted] • 3D sandwiched structure of FeVO 4 /Ti 3 C 2 T x film improves access to active sites and facilitates the Li+/Na+ insertion/extraction. • The synergistic effect of FeVO 4 and Ti 3 C 2 T x leads to superior electrochemical performance in both Li and Na ions batteries. • The reaction mechanism of lithium ion in FeVO 4 was simply verified by in-situ XRD. Ferric vanadate (FeVO 4) is a desirable anode candidate for lithium-ion battery (LIB) and sodium-ion battery (SIB) because of its high theoretical capacity, low cost and ease of synthesis. However, its practical application is hindered by its volume expansion during the Li+/Na+ insertion/extraction and low electronic conductivity. Herein, flexible and free-standing FeVO 4 /Ti 3 C 2 T x (FVO/MX) films have been made via combining FeVO 4 nanorods and Ti 3 C 2 T x MXene sheets via a simple method of vacuum assisted filtration. In the composite films, Ti 3 C 2 T x sheets act as host and FeVO 4 nanorods are uniformly deposited onto the layers. FeVO 4 nanorods are encapsulated by Ti 3 C 2 T x sheets, forming a three-dimensional network sandwich structure. The binder-free FVO/MX films exhibited superior electrochemical performance due to the synergyy between FeVO 4 and Ti 3 C 2 T x. Specifically, when FVO/MX electrode was used in a lithium-ion battery, it delivered reversible capacity of 1179 mAh g−1 and 1125 mAh g−1 after 250 cycles at a current density of 0.1 A g−1. Besides, the FVO/MX = 2:1 anode delivered a reversible capacity of 428 mAh g−1 at 5 A g−1 and 69.5% capacity was retained after 2500 cycles. Moreover, the Na-ion storage capacity reaches 129 mAh g−1 at a high current density of 5 A g−1, showing capacity retention of 81.1% after 5000 cycles. The charging and discharging mechanism of the FVO/MX based lithiumion battery was studied by in-situ XRD technique. Owing to high metallic conductivity and 2D morphology of Ti 3 C 2 T x MXene, 3D networks can be constructed by combining other active agents, suggesting that MXene is a promising host material for the next-generation flexible energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple electrodeposition method deposits PPy on the surface of Ti 3 C 2 T x to prepare a Ti 3 C 2 T x /PPy bilayer film. • The curvature change of Ti 3 C 2 T x /PPy bilayer film was improved by 57% in aqueous 1 M LiClO 4 compared to the pure PPy film. • After 10,000 cycles, the actuation performance of Ti 3 C 2 T x /PPy bilayer film can still maintain 69.2% of the initial performance. Electrochemical actuators are devices that directly convert electrical energy into mechanical energy and have a wide range of applications. MXenes have high energy density, excellent rate performance, high electronic conductivity, strong mechanical strength, and can store ions through fast intercalation mechanism, making it a promising material for actuator applications. However, the restacking of MXenes layers limits ion percolation and thus limits the actuation performance. Polypyrrole (PPy) has a large volume deformation during its redox reaction process, but its low electrical conductivity and weak mechanical strength limit its practical application. Here, we logically designed an electrochemical actuator with Ti 3 C 2 T x /PPy bilayer film as the electrode, and the Ti 3 C 2 T x layer effectively improved the electrical conductivity of Ti 3 C 2 T x /PPy and acted as the same time as current collector, co-actuation, and conductive additive, effectively accelerating the redox reaction rate of the PPy layer and increasing the performance. The curvature change of Ti 3 C 2 T x /PPy bilayer film was improved by 57% (at 5 mV/s) in aqueous 1 M LiClO 4 compared to the pure PPy film. After 10,000 cycles, 69.2% of the initial actuation performance can still be maintained. This research proves that this electrode structure design is feasible to improve the performance of actuators. [ABSTRACT FROM AUTHOR]