Bending Resistance Covalent Organic Framework Superlattice: "Nano-Hourglass"-Induced Charge Accumulation for Flexible In-Plane Micro-Supercapacitors

Sulfur-bridged bonds enabled structure modulation and space confinement of MnS for superior sodium-ion capacitors

Manganese sulfide (MnS) is a promising converion-type anode for sodium storage, owing to the virtues of high theoretical capacity, coupled with it crustal abundance and cost-effectiveness. Nevertheless, MnS suffers from inadequate electronic conductivity, sluggish Na+ reaction kinetics and considerable volume variation during discharge/charge process, thereby impeding its rate capability and capacity retention. Herein, a novel lamellar heterostructured composite of Fe-doped MnS nanoparticles/positively charged reduced graphene oxide (Fe-MnS/PG) was synthesized to overcome these issues. The Fe-doping can accelerate the ion/electron transfer, endowing fast electrochemical kinetics of MnS. Meanwhile, the graphene space confinement with strong MnSC bond interactions can facilite the interfacial electron transfer, hamper volume expansion and aggregation of MnS nanoparticles, stabilizing the structural integrity, thus improving the Na+ storage reversibility and cyclic stability. Combining the synergistic effect of Fe-doping and space confinement with strong MnSC bond interactions, the as-produced Fe-MnS/PG anode presents a remarkable capacity of 567 mAh/g at 0.1 A/g and outstanding rate performance (192 mAh/g at 10 A/g). Meanwhile, the as-assembled sodium-ion capacitor (SIC) can yield a high energy density of 119 Wh kg-1 and a maximum power density of 17500 W kg-1, with capacity retention of 77 % at 1 A/g after 5000 cycles. This work offers a promising strategy to develop MnS-based practical SICs with high energy and long lifespan, and paves the way for fabricating advanced anode materials.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal-ion Batteries

Covalent organic frameworks (COFs) are a class of porous crystalline polymeric materials constructed by linking organic small molecules through covalent bonds. COFs have the advantages of strong covalent bond network, adjustable pore structure, large specific surface area and excellent thermal stability, and have broad application prospects in various fields. Based on these advantages, rational COFs design strategies such as the introduction of active sites, construction of conjugated structures, and carbon material composite, etc. can effectively improve the conductivity and stability of the electrode materials in the field of batteries. This paper introduces the latest research results of high-performance COFs electrode materials in alkali metal-ion batteries (LIBs, SIBs, PIBs and LSBs) and other advanced batteries. The current challenges and future design directions of COFs-based electrode are discussed. It provides useful insights for the design of novel COFs structures and the development of high-performance alkali metal-ion batteries.

All-Covalent Organic Framework Nanofilms Assembled Lithium-Ion Capacitor to Solve the Imbalanced Charge Storage Kinetics

Free-standing covalent organic framework (COFs) nanofilms exhibit a remarkable ability to rapidly intercalate/de-intercalate Li+ in lithium-ion batteries, while simultaneously exposing affluent active sites in supercapacitors. The development of these nanofilms offers a promising solution to address the persistent challenge of imbalanced charge storage kinetics between battery-type anode and capacitor-type cathode in lithium-ion capacitors (LICs). Herein, for the first time, custom-made COFBTMB-TP and COFTAPB-BPY nanofilms are synthesized as the anode and cathode, respectively, for an all-COF nanofilm-structured LIC. The COFBTMB-TP nanofilm with strong electronegative-CF3 groups enables tuning the partial electron cloud density for Li+ migration to ensure the rapid anode kinetic process. The thickness-regulated cathodic COFTAPB-BPY nanofilm can fit the anodic COF nanofilm in the capacity. Due to the aligned 1D channel, 2D aromatic skeleton and accessible active sites of COF nanofilms, the whole COFTAPB-BPY//COFBTMB-TP LIC demonstrates a high energy density of 318 mWh cm-3 at a high-power density of 6 W cm-3, excellent rate capability, good cycle stability with the capacity retention rate of 77% after 5000-cycle. The COFTAPB-BPY//COFBTMB-TP LIC represents a new benchmark for currently reported film-type LICs and even film-type supercapacitors. After being comprehensively explored via ex situ XPS, 7Li solid-state NMR analyses, and DFT calculation, it is found that the COFBTMB-TP nanofilm facilitates the reversible conversion of semi-ionic to ionic C-F bonds during lithium storage. COFBTMB-TP exhibits a strong interaction with Li+ due to the C-F, C=O, and C-N bonds, facilitating Li+ desolation and absorption from the electrolyte. This work addresses the challenge of imbalanced charge storage kinetics and capacity between the anode and cathode and also pave the way for future miniaturized and wearable LIC devices.

New insights on the preparation of amine covalent organic polymer and its adsorption properties

Dye pollution is becoming increasingly severe. This study used the Schiff base reaction to synthesize a polyaromatic ring covalent organic polymer material with amide bonds and high electronegativity named SLEL-9 to adsorb Methylene Blue (MB) and Rhodamine B (RhB). SLEL-9 was characterized by Fourier transform infra-red spectra, X-ray photoelectron spectra, Brunauer-Emmett-Teller (BET), zeta potential analysis, and other techniques. It was found that SLEL-9 material contains C-C, CN, C-N, and CO. SLEL-9 had a zeta potential of about -45 mV under neutral conditions, which proved that the material had been synthesized successfully. The BET and Langmuir surface areas of SLEL-9 were 35.187 m2 g-1 and 56.419 m2 g-1, respectively. The adsorptions of SLEL-9 on low concentration (10 mg L-1) Methylene Blue and Rhodamine B reached equilibrium within 48 h. The results showed that SLEL-9's adsorption of dye molecules are more consistent with pseudo-second-order kinetic and Langmuir isotherm model. The adsorption experiments showed that the adsorption process is a spontaneous endothermic reaction, mainly chemisorption. The maximum adsorption capacity of SLEL-9 for MB and RhB were 132.45 mg g-1 and 101.94 mg g-1. In addition, this study investigated to determine the optimal reaction parameters. The primary mechanisms of SLEL-9 adsorption of two dyes are n→π* interaction, π-π EDA interaction and electrostatic attraction. Selective adsorb ability experiment results showed that SLEL-9 could selectively adsorb MB and RhB to a certain extent. Finally, it was found that SLEL-9 can maintain over 70% adsorption capacity after five reuses and can maintain stability after soaking in different pH water and organic solvents for 120 h. SLEL-9 proved to be a promising organic covalent polymer adsorption material for the removal of Methylene Blue and Rhodamine B in water.

Recent advances in the utilization of covalent organic frameworks (COFs) as electrode materials for supercapacitors

Due to their excellent stability, ease of modification, high specific surface area, and tunable redox potentials, covalent organic frameworks (COFs) as potential electrodes in supercapacitors (SCs) have raised much research interest because these materials can enable the achievement of high electric double-layer supercapacitance and high pseudocapacitance. Here, the design strategies and SC applications of COF-based electrode materials are summarized. The detailed principles are introduced first, followed by discussions on strategies with diverse examples. The updated advances in design and applications are also discussed. Finally, in the outlook section, we provide some guidelines on the rational design of COF-based electrode materials for high-performance SCs, which we hope will inspire novel concepts for COF-based supercapacitors.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs), a rapidly developing category of crystalline conjugated organic polymers, possess highly ordered structures, large specific surface areas, stable chemical properties, and tunable pore microenvironments. Since the first report of boroxine/boronate ester-linked COFs in 2005, COFs have rapidly gained popularity, showing important application prospects in various fields, such as sensing, catalysis, separation, and energy storage. Among them, COFs-based electrochemical (EC) sensors with upgraded analytical performance are arousing extensive interest. In this review, therefore, we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry, with special emphasis on their usages in the fabrication of chemical sensors, ions sensors, immunosensors, and aptasensors. Notably, the emerged COFs in the electrochemiluminescence (ECL) realm are thoroughly covered along with their preliminary applications. Additionally, final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors, as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

NH3-Induced In Situ Etching Strategy Derived 3D-Interconnected Porous MXene/Carbon Dots Films for High Performance Flexible Supercapacitors

2D MXene (Ti3CNTx) has been considered as the most promising electrode material for flexible supercapacitors owing to its metallic conductivity, ultra-high capacitance, and excellent flexibility. However, it suffers from a severe restacking problem during the electrode fabrication process, limiting the ion transport kinetics and the accessibility of ions in the electrodes, especially in the direction normal to the electrode surface. Herein, we report a NH3-induced in situ etching strategy to fabricate 3D-interconnected porous MXene/carbon dots (p-MC) films for high-performance flexible supercapacitor. The pre-intercalated carbon dots (CDs) first prevent the restacking of MXene to expose more inner electrochemical active sites. The partially decomposed CDs generate NH3 for in situ etching of MXene nanosheets toward 3D-interconnected p-MC films. Benefiting from the structural merits and the 3D-interconnected ionic transmission channels, p-MC film electrodes achieve excellent gravimetric capacitance (688.9 F g-1 at 2 A g-1) and superior rate capability. Moreover, the optimized p-MC electrode is assembled into an asymmetric solid-state flexible supercapacitor with high energy density and superior cycling stability, demonstrating the great promise of p-MC electrode for practical applications.