Regulating Functional Groups Enhances the Performance of Flexible Microporous MXene/Bacterial Cellulose Electrodes in Supercapacitors.

Ultrathin MXene-based films exhibit superior conductivity and high capacitance, showing promise as electrodes for flexible supercapacitors. This work describes a simple method to enhance the performance of MXene-based supercapacitors by expanding and stabilizing the interlayer space between MXene flakes while controlling the functional groups to improve the conductivity. Ti3C2Tx MXene flakes are treated with bacterial cellulose (BC) and NaOH to form a composite MXene/BC (A-M/BC) electrode with a microporous interlayer and high surface area (62.47 m2 g-1). Annealing the films at low temperature partially carbonizes BC, increasing the overall electrical conductivity of the films. Improvement in conductivity is also attributed to the reduction of -F, -Cl, and -OH functional groups, leaving -Na and -O functional groups on the surface. As a result, the A-M/BC electrode demonstrates a capacitance of 594 F g-1 at a current density of 1 A g-1 in 3 M H2SO4, which represents a ∼2× increase over similarly processed films without BC (309 F g-1) or pure MXene (298 F g-1). The corresponding device has an energy density of 9.63 Wh kg-1 at a power density of 250 W kg-1. BC is inexpensive and enhances the overall performance of MXene-based film electrodes in electronic devices. This method underscores the importance of functional group regulation in enhancing MXene-based materials for energy storage.

Rational design of flower-like MnO2/Ti3C2Txcomposite electrode for high performance supercapacitors.

Combining the new two-dimensional conductive MXene with transition metal oxide to build composite structure is a promising path to improve the conductivity of metal oxide. However, a critical challenge still remains in how to achieve a good combination of MXene and metal oxide. Herein, we develop a facile hydrothermal route to synthesize the MnO2/Ti3C2Txcomposite electrode for supercapacitors by synergistically coupling MnO2nanowires with Ti3C2TxMXene nanoflakes. Compared with the pure MnO2electrode, the morphology of the MnO2/Ti3C2Txcomposite electrode changes from nanowires to nanoflowers. Moreover, the overall conductivity and electrochemical performance of the composite electrode are greatly improved due to an addition of Ti3C2TxMXene. The specific capacitance of the MnO2/Ti3C2Txcomposite electrode achieves 210.8 F·g-1at a scan rate of 2 mV·s-1, while that of the pure MnO2electrode is only 55.2 F·g-1. Furthermore, the specific capacitance of the MnO2/Ti3C2Txcomposite electrode still can remain at 97.2% even after 10 000 charge-discharge cycles, revealing an excellent cycle stability. The synthesis strategy of this work can pave the way for the research and practical application of the electrode materials for supercapacitors.

One-Step Electrochemical Synthesis and Surface Reconstruction of NiCoP as an Electrocatalyst for Bifunctional Water Splitting.

We adopted a simple one-step electrochemical deposition to acquire an efficient nickel cobalt phosphorus (NiCoP) catalyst, which avoided the high temperature phosphatization engineering involved in the traditional synthesis method. The effects of electrolyte composition and deposition time on electrocatalytic performance were studied systematically. The as-prepared NiCoP achieved the lowest overpotential (η10 = 111 mV in the acidic condition and η10 = 120 mV in the alkaline condition) for the hydrogen evolution reaction (HER). Under 1 M KOH conditions, optimal oxygen evolution reaction (OER) activity (η10 = 276 mV) was also observed. Furthermore, the bifunctional NiCoP catalyst enabled a high-efficiency overall water-splitting by applying an external potential of 1.69 V. The surface valence and structural evolution of NiCoP samples with slowly decaying stability under alkaline conditions are revealed by XPS. The NiCoP is reconstructed into the Ni(Co)(OH)2 (for HER) and Ni(Co)OOH (for OER) on the surface with P element loss, acting as real "active sites".

Passive Solar-driven Interfacial Evaporation Nanosystems: Beyond Desalination Towards Multiple Applications.

Recently, passive solar-driven interfacial evaporation has become one of the fastest-growing technologies for solar energy utilization and desalination. Herein this patent, we provide an overview of other emerging and potential applications of evaporation nanosystems beyond desalination, i.e., electricity generation, organics rejection, and sterilization. These extended functions can be a benefit for energy and environmental issues.

3D Porous Compact 1D/2D Fe2 O3 /MXene Composite Aerogel Film Electrodes for All-Solid-State Supercapacitors.

2D MXene nanoflakes usually undergo serious restacking, that easily aggravates during the traditional vacuum-assisted filtration process; and thus, hinders the electrochemical performance of the corresponding film electrodes. Herein, 3D porous compact 1D/2D Fe2 O3 /MXene aerogel film electrode with an enhanced electrochemical performance is fabricated by freeze-drying assisted mechanical pressing. An introduction of 1D α-Fe2 O3 nanorods can not only alleviate the restacking of 2D MXene but also provide additional pseudocapacitance for the composite film system. Thus, the resulting Fe2 O3 /MXene aerogel film electrode shows an enhanced specific capacitance of 182 F g-1 (691 mF cm-2 ) at a current density of 1 A g-1 in 3 m H2 SO4 electrolyte as well as with 81.74% capacitance retention after 10 000 charge-discharge cycles. Besides, the addition of 1D α-Fe2 O3 nanorods has a significant contribution in the volumetric capacitance of the composite aerogel film (150 F cm-3 ), which is 2.68 times that of the pure MXene aerogel film (56 F cm-3 ). Moreover, the fabricated all-solid-state symmetric supercapacitor (SSSC) delivers a superior areal energy density of 3.61 µWh cm-2 at a power density of 119.04 µW cm-2 . This rapid-forming 3D porous, binder-free, and freestanding aerogel film provides a progressive strategy for the fabrication of MXene-based electrode for supercapacitors.

In Situ Electrosynthesis of MAX-Derived Electrocatalysts for Superior Hydrogen Evolution Reaction.

MAX phases are frequently dominated as precursors for the preparation of the star material MXene, but less eye-dazzling by their own potential applications. In this work, the electrocatalytic hydrogen evolution reaction (HER) activity of MAX phase is investigated. The MAX-derived electrocatalysts are prepared by a two-step in situ electrosynthesis process, an electrochemical etching step followed by an electrochemical deposition step. First, a Mo2 TiAlC2 MAX phase is electrochemically etched in 0.5 m H2 SO4 electrolyte. Just several hours, electrochemical dealloy etching of Mo2 TiAlC2 MAX powders by applying anode current can acquire a moderated HER performance, outperforming most of reported pure MXene. It is speculated that in situ superficially architecting endogenous MAX/amorphous carbide (MAC) improves its intrinsic catalytic activity. Subsequently, highly active metallic Pt nanoparticles immobilized on MAC (MAC@Pt) shows a transcendental overpotential of 40 mV versus RHE in 0.5 m H2 SO4 and 79 mV in 1.0 m KOH at the current density of 10 mA cm-2 without iR correction. Ultrahigh mass activity of MAC@Pt (1.5 A mgpt -1 ) at 100 mV overpotential is also achieved, 29-folds than those of commercial PtC catalysts.

Flexible MXene-Based Composite Films: Synthesis, Modification, and Applications as Electrodes of Supercapacitors.

MXenes, as a 2D planar structure nanomaterial, were first reported in 2011. Due to their large specific surface area, high ductility, high electrical conductivity, strong hydrophilic surface, and high mechanical flexibility, MXenes have been extensively explored in the development of various functional materials with desired performances. This review is aimed to summarize the current progress in synthesis, modification, and applications of MXene-based composite films as electrode materials of flexible energy storage devices. In the synthesis of MXenes, the evolution and exploration of etchants are emphasized. Furthermore, in order to develop MXene-based composite films, the components used to modify the MXene nanoflakes, including 0D, 1D, and 2D nanomaterials, are summarized, and the perspectives and research direction of such materials are also discussed.