Carboxymethylcellulose hydrogels with stable carbon quantum dots: Enabling dynamic fluorescence modulation, automatic erasure, and secure information encryption.

Inspired by "disappear after reading", a time-modulated encryption hydrogel was synthesized by carboxymethyl cellulose with carbon quantum dots. Carboxymethyl cellulose in this system stabilized carbon quantum dots, which ensured the whole hydrogel worked well. The encryption/decryption of information depended on pH adjustment, application of EDTA and Cr (VI). Furthermore, an in-depth analysis of the fluorescence change mechanism uncovered that fluorescence quenching was potentially influenced by internal filtering effects and static quenching, which involved the amino, carboxyl, and hydroxyl groups present within the hydrogel.

Blocking Metal Nanocluster Growth through Ligand Coordination and Subsequent Polymerization: The Case of Ruthenium Nanoclusters as Robust Hydrogen Evolution Electrocatalysts.

Metal nanoclusters providing maximized atomic surface exposure offer outstanding hydrogen evolution activities but their stability is compromised as they are prone to grow and agglomerate. Herein, a possibility of blocking metal ion diffusion at the core of cluster growth and aggregation to produce highly active Ru nanoclusters supported on an N, S co-doped carbon matrix (Ru/NSC) is demonstrated. To stabilize the nanocluster dispersion, Ru species are initially coordinated through multiple Ru─N bonds with N-rich 4'-(4-aminophenyl)-2,2:6',2''-terpyridine (TPY-NH2 ) ligands that are subsequently polymerized using a Schiff base. After the pyrolysis of the hybrid composite, highly dispersed ultrafine Ru nanoclusters with an average size of 1.55 nm are obtained. The optimized Ru/NSC displays minimal overpotentials and high turnover frequencies, as well as robust durability both in alkaline and acidic electrolytes. Besides, outstanding mass activities of 3.85 A mg-1 Ru at 50 mV, i.e., 16 fold higher than 20 wt.% Pt/C are reached. Density functional theory calculations rationalize the outstanding performance by revealing that the low d-band center of Ru/NSC allows the desorption of *H intermediates, thereby enhancing the alkaline HER activity. Overall, this work provides a feasible approach to engineering cost-effective and robust electrocatalysts based on carbon-supported transition metal nanoclusters for future energy technologies.

Multifunctional Organohydrogels for pH-Responsive Fluorescent and Electrostimulus Writing.

Hydrogels have attracted widespread attention in anticounterfeiting due to their unique physical/chemical properties and designability. However, hydrogels' poor mechanical properties and sluggish response to chemical stimuli pose challenges for their wide application. A fluorescent tough organohydrogel capable of freeform writing of information is reported in this work. By incorporation of the fluorescent monomer 7-methylacryloxy-4-methylcoumarin into the polyacrylamide network in a covalently cross-linked manner while intertwining with the carboxymethyl cellulose sodium network, a fluorescent tough organohydrogel with a dual-network structure is prepared. The organohydrogel shows acid-base-mediated adjustable fluorescence through the transformation of fluorescent monomers. Ion printing and electrical stimulation design achieved free information storage and encryption. In addition, the prepared organohydrogel has good antifreezing properties and can be encrypted and decrypted at subzero temperatures. The encrypted information in the organohydrogel can be read only after UV-light irradiation. These patterned fluorescent organohydrogels should find applications in protected message displays for improved information security.

MoS2 @Polyaniline for Aqueous Ammonium-Ion Supercapacitors.

Ammonium-ion aqueous supercapacitors are raising notable attention owing to their cost, safety, and environmental advantages, but the development of optimized electrode materials for ammonium-ion storage still lacks behind expectations. To overcome current challenges, here, a sulfide-based composite electrode based on MoS2 and polyaniline (MoS2 @PANI) is proposed as an ammonium-ion host. The optimized composite possesses specific capacitances above 450 F g-1 at 1 A g-1 , and 86.3% capacitance retention after 5000 cycles in a three-electrode configuration. PANI not only contributes to the electrochemical performance but also plays a key role in defining the final MoS2 architecture. Symmetric supercapacitors assembled with such electrodes display energy densities above 60 Wh kg-1 at a power density of 725 W kg-1 . Compared with Li+ and K+ ions, the surface capacitive contribution in NH4 + -based devices is lower at every scan rate, which points to an effective generation/breaking of H-bonds as the mechanism controlling the rate of NH4 + insertion/de-insertion. This result is supported by density functional theory calculations, which also show that sulfur vacancies effectively enhance the NH4 + adsorption energy and improve the electrical conductivity of the whole composite. Overall, this work demonstrates the great potential of composite engineering in optimizing the performance of ammonium-ion insertion electrodes.

In Situ Generation of Ultrathin MoS2 Nanosheets in Carbon Matrix for High Energy Density Photo-Responsive Supercapacitors.

Stimuli-responsive supercapacitors have attracted broad interest in constructing self-powered smart devices. However, due to the demand for high cyclic stability, supercapacitors usually utilize stable or inert electrode materials, which are difficult to exhibit dynamic or stimuli-responsive behavior. Herein, this issue is addressed by designing a MoS2 @carbon core-shell structure with ultrathin MoS2 nanosheets incorporated in the carbon matrix. In the three-electrode system, MoS2 @carbon delivers a specific capacitance of 1302 F g-1 at a current density of 1.0 A g-1 and shows a 90% capacitance retention after 10 000 charging-discharging cycles. The MoS2 @carbon-based asymmetric supercapacitor displays an energy density of 75.1 Wh kg-1 at the power density of 900 W kg-1 . Because the photo-generated electrons can efficiently migrate from MoS2 nanosheets to the carbon matrix, the assembled photo-responsive supercapacitor can answer the stimulation of ultraviolet-visible-near infrared illumination by increasing the capacitance. Particularly, under the stimulation of UV light (365 nm, 0.08 W cm-2 ), the device exhibits a ≈4.50% (≈13.9 F g-1 ) increase in capacitance after each charging-discharging cycle. The study provides a guideline for designing multi-functional supercapacitors that serve as both the energy supplier and the photo-detector.

Self-activatable carbon nanotube@ruthenium-catechol coordination complex for hydrogen evolution reaction.

We report a simple metal ion-catechol coordination strategy to coat ruthenium-catechol polymer complex (TAC-Ru) on the surface of carbon nanotubes (CNT) to form a core-shell structure (abbreviated as CNT@TAC-Ru). This is achieved by firstly polymerizing catechol and boronic acid monomers on the surface of CNT to form a boronate ester polymer (BP) shell. Then, Ru3+is used to etch the BP shell, and cleave the dynamic boronate ester bond, leading to the formation of a CNT@ruthenium-catechol coordination complex based on the coordinative efficiency of the catechol group. The electrocatalytic property of the CNT@TAC-Ru composite can be activated through electrochemical cycling treatment. The as-activated CNT@TAC-Ru exhibits evidently improved hydrogen evolution reaction (HER) performance with an overpotential of 10 mV in 1.0 M KOH at a current density of 10 mA cm-2, which is better than that of commercial Pt/C (32 mV). And the long-term stability is also desirable. This work provides a pyrolysis-free method to form metal-polymer-carbon composite with high HER performance under the alkaline condition.

Facile fabrication of multifunctional cotton fabric by AgNC@boronate polymer/crosslinked chitosan.

Multifunctional cotton fabrics (M-CF) have important application prospects in intelligent home decoration and material packaging. In this work, nanoparticles (AgNC@BP) were prepared by coating the surface of silver nanocubes (AgNCs) with borate polymer. Subsequently, M-CF with electromagnetic wave (EMW) absorption, mechanical enhancement, flame-retardancy and antibacterial performances were prepared by immersing cotton fabrics (CF) into AgNC@BP/crosslinked chitosan (CS) solution. Expectantly, AgNC@BP endows AgNC@BP/CS-CF with good flame retardancy and low combustion heat release. That is, the char length of AgNC@BP/CS-CF is 7.9 cm after the vertical burning test (UL-94 V) and the peak heat release rate (pHRR) of AgNC@BP/CS-CF is reduced by 21.4% compared to pure CF. Meanwhile, the tensile strength of AgNC@BP/CS-CF is 18.8% higher than that of CF. Synchronously, the introduction of AgNC@BP can also endow M-CF with better EMW absorption, mechanical and antibacterial properties. In conclusion, this work provides a tactic for fabricating M-CF.

Three-Dimensional hybrid structure loader type flexible supercapacitor based on Polyvinyl alcohol gel and Acetylene black.

In order to overcome the structural drawbacks of layered electrodes in flexible supercapacitors, the construction of an electrode frame with high adaptability for the loading of different active materials makes the production of flexible supercapacitors simpler and more accurate. Herein, a novel loader type flexible supercapacitor with three-dimensional hybrid structure is built. In our design, the acetylene black and active material are enriched in the polyvinyl alcohol matrix, and the three-dimensional conductive network that can load different active material is formed. The active material can be selected on demand. The basic electrode (also a loader) formed by polyvinyl alcohol and acetylene black is an electronic conductor (∼1 Scm-1) with good electrochemical and mechanical performance. By loading active materials in this basic electrode, more powerful flexible electrodes can be built easily and accurately with the same steps according to the designed proportion. Electrodes constructed according to this method deliver nonnegligible surface capacity (e.g. 1.1 Fcm-2 in surface capacitance, polyaniline/carbon nanotube composite as active materials) with good response, rate performance, excellent durability (10000 times of charge-discharge), and good foldability (1000 times of folding). This pattern of carrier type electrodes provides a simple and universal strategy for manufacturing flexible supercapacitors.

Effect of morphology and phase engineering of MoS2 on electrochemical properties of carbon nanotube/polyaniline@MoS2 composites.

This paper rationally designs the morphology and phase structure of carbon nanotube/polyaniline@MoS2 (CNT/PANI@MoS2) composites, with MoS2 conductive wrapping growing vertically on the outer layer of the composites via hydrothermal method. The crystalline nature and chemical properties are characterized by X-ray diffraction (XRD), Flourier transformation infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS). Morphology and microstructures are determined by Scanning electric microscopy (SEM), Transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET). The developed composites possess excellent electrochemical properties (the specific capacitance is substantially increased by ~119%, reaching 700.0 F g-1 after wrapping by MoS2) and good cycling stability (after over 5000 cycles retains 80.8% capacitance) in three-electrode systems, which indicating that the unique morphology of MoS2 shells endow the channels to composites for rapid charge transport and ionic diffusion. Furthermore, symmetric supercapacitors devices assembled with the CNT/PANI@MoS2 composites achieve specific capacitance of 459.7 F g-1 at 1 A g-1, capacitance retention is 97.4% after 10,000 cycles and reach superior energy density of 40.9 Wh kg-1 at the power density of 400 W kg-1. This strategy of three-dimensional wrapping method may open up a new potential to relieve the dilemma of degraded performance of supercapacitor, while improving the capacitance and stability for supercapacitors.