Two-Dimensional Sulfonate-Functionalized Metal-Organic Framework Membranes for Efficient Lithium-Ion Sieving.

Two-dimensional (2D) membranes have shown promising potential for ion-selective separation but often suffer from the trade-off between permeability and selectivity. Herein, we report an ultrathin 2D sulfonate-functionalized metal-organic framework (MOF) membrane for efficient lithium-ion sieving. The narrow pores with angstrom precision in the MOF assist hydrated ions to partially remove the hydration shell, according to different hydration energies. The abundant sulfonate groups in the MOF channels serve as hopping sites for fast lithium-ion transport, contributing to a high Li-ion permeability. Then, the difference in affinity of the Li+, Na+, K+, and Mg2+ ions to the terminal sulfonate groups further enhances the Li-ion selectivity. The reported ultrathin MOF membrane overcomes the trade-off between permeability and selectivity and opens up a new avenue for highly permselective membranes.

High-Performance Flexible Polymer Memristor Based on Stable Filamentary Switching.

Polymer-based atomic switch memristors via the formation/dissolution of atomic-scale conductive filaments are considered as the leading candidate for next-generation nonvolatile memory. However, the instability of conductive filaments of incomplete bridge makes their switching performances unsatisfied. In this work, we report a flexible polymeric memristor using polyethylenimine incorporated with silver salt. The memristor device exhibited superior performances at room temperature with a favorable endurance, high ON/OFF ratio, good retention, and low operating voltage. These satisfactory performances are attributed to the pre-existing Ag ions in the polymer, guiding the formation of a robust Ag filament. In addition, the device shows stable bipolar switching behavior in bending conditions or after hundreds of bending cycles. In our work, we provide a simple and efficient method to construct robust filament-based memristors for flexible electronics.

Niobium Tungsten Oxides for Electrochromic Devices with Long-Term Stability.

There is a keen interest in the use of electrochromic materials because they can regulate light and heat, thereby reducing the cooling and heating energy. However, the long response time, short cycle life, and high power consumption of an electrochromic film hinder its development. Here, we report an electrochromic material of complex niobium tungsten oxides. The Nb18W16O93 thin films in the voltage range of 0 to -1.5 V show good redox kinetics with the coloration time of 4.7 s and bleaching time of 4.0 s, respectively. The electrochromic device based on the Nb18W16O93 thin film has an optical modulation of 53.1% at a wavelength of 633 nm, with the coloration efficiency of ∼46.57 cm2 C-1. An excellent electrochemical stability of 78.1% retention after 8000 cycles is also achieved. These good performances are due to the fast and stable Li-ion intercalation/extraction in the open framework of Nb18W16O93 with multiple ion positions. Our work provides a strategy for electrochromic materials with fast response time and good cycle stability.