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.

Tailoring Monovalent Ion Sieving in Graphene-Oxide Membranes with High Flux by Rationally Intercalating Crown Ethers.

Two-dimensional membranes have shown promising potential for ion-selective separation due to their well-defined interlayer channels. However, the typical "trade-off" effect of throughput and selectivity limits their developments. Herein, we report a precise tailoring of monovalent cation sieving technology with enhanced water throughput via the intercalation of graphene-oxide membranes with selective crown ethers. By tuning the lamellar spacing of graphene oxide, a critical interlayer distance (∼11.04 Å) is revealed to maximize water flux (53.4 mol m-2 h-2 bar-1) without sacrificing ion selectivity. As a result, the elaborately enlarged interlayer distance offers improved water permeance. Meanwhile, various specific cations with remarkably high selectivity can be separated in mixed solutions because of the strong chelation with crown ethers. This work opens up a new avenue for high-throughput and precise regulation of ion separations for various application scenarios.

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.

A two-dimensional superlattice membrane enables high-performance desalination and enhanced Li ion selectivity.

Here, we report a two-dimension (2D) superlattice-like membrane composed of periodic MoS2 and GO nanosheets, which delivers enhanced salt rejection capability, high water flux, and Li ion selectivity. It opens a new perspective in assembling 2D membranes and can be utilized as a green and low-cost approach for desalination.

Low-Temperature Synthesis of Lithium Lanthanum Titanate/Carbon Nanowires for Fast-Charging Li-Ion Batteries.

Due to the lower working voltage and higher capacity, the Li-rich lithium lanthanum titanate perovskite (LLTO) anode is becoming a potential candidate for the commercial Li4Ti5O12 (LTO) Li-ion battery anode [Zhang, L. Lithium Lanthanum Titanate Perovskite as an Anode for Lithium Ion Batteries. Nat. Commun. 2020, 11, 3490]. However, a high temperature of 1250 °C is required to fabricate pure LLTO particles by the conventional solid-phase calcination method, limiting their further practical applications. Here, an in situ carbon nanospace confined method is developed to synthesize the pure LLTO with sub-nanometer grain size at an extremely low temperature of 800 °C. The LLTO precursor is confined in the in situ formed carbon nanowire matrix during heating, resulting in a shorter solid-phase diffusion distance and subsequently lower energy required for the formation of the pure LLTO phase. The low-temperature-synthesized pure LLTO/carbon composite nanowires (P-LLTO/C NWs) exhibit improved lithium storage performances than the traditionally prepared LLTO due to the fast electronic conduction of carbon and the stable carbon surface. In addition, the working potentials of P-LLTO/C||LiFePO4 and P-LLTO/C||LiCoO2 full cells are all 0.7 V higher than that of the corresponding commercial full cells with LTO as an anode, meaning much higher power energy densities (307.6 W kg-1 at 2C and 342.4 W kg-1 at 1C vs 198.4 W kg-1 and 275.2 W kg-1 for LTO||LiFePO4 and LTO||LiCoO2 full cells based on electrode materials, respectively). This low-temperature synthesis method can extend to other solid-state ionic materials and electrode materials for electrochemical devices.

Anchoring CoFe2O4 Nanoparticles on N-Doped Carbon Nanofibers for High-Performance Oxygen Evolution Reaction.

The exploration of earth-abundant and high-efficiency electrocatalysts for the oxygen evolution reaction (OER) is of great significant for sustainable energy conversion and storage applications. Although spinel-type binary transition metal oxides (AB2O4, A, B = metal) represent a class of promising candidates for water oxidation catalysis, their intrinsically inferior electrical conductivity exert remarkably negative impacts on their electrochemical performances. Herein, we demonstrates a feasible electrospinning approach to concurrently synthesize CoFe2O4 nanoparticles homogeneously embedded in 1D N-doped carbon nanofibers (denoted as CoFe2O4@N-CNFs). By integrating the catalytically active CoFe2O4 nanoparticles with the N-doped carbon nanofibers, the as-synthesized CoFe2O4@N-CNF nanohybrid manifests superior OER performance with a low overpotential, a large current density, a small Tafel slope, and long-term durability in alkaline solution, outperforming the single component counterparts (pure CoFe2O4 and N-doped carbon nanofibers) and the commercial RuO2 catalyst. Impressively, the overpotential of CoFe2O4@N-CNFs at the current density of 30.0 mA cm-2 negatively shifts 186 mV as compared with the commercial RuO2 catalyst and the current density of the CoFe2O4@N-CNFs at 1.8 V is almost 3.4 times of that on RuO2 benchmark. The present work would open a new avenue for the exploration of cost-effective and efficient OER electrocatalysts to substitute noble metals for various renewable energy conversion/storage applications.