Three-Dimensional Self-Supporting Ti3C2 with MoS2 and Cu2O Nanocrystals for High-Performance Flexible Supercapacitors

All-aerosol-jet-printed Fe3+ modified bilayers polyaniline flexible room temperature sensor with enhanced ammonia sensing properties

The rapid advancement of human-machine interaction (HMI), the Internet of Things (IoTs), and artificial intelligence (AI) has imposed greater demands on the ambient temperature wearable performance of sensors. In this study, the Fe3+ modified bilayers polyaniline (PANI) flexible room temperature ammonia sensor is prepared by all-aerosol-jet-printed. The increased protonation degree of the PANI film produced by this method was elucidated through analysis of aerosol microdroplet evaporation behavior, while the improved ammonia sensing performance of the PANI/Fe3+ dendritic structure was explained using soft and hard acid-base theory. Gas sensing tests demonstrated that the PANI/Fe3+ sensor exhibited high sensitivity to ammonia (776 % at 55 ppm), a wide detection range (547 ppb-547 ppm), as well as excellent selectivity, flexibility, and cyclic stability. These results underscore its potential for application in ambient temperature wearable fields.

Controlled synthesis of hierarchical hollow CoxNi3-xS4 towards enhanced rate capability and excellent cycling stability

The strategic design and advancement of electrode materials are crucial for the effectiveness of energy storage and conversion devices. Herein, we successfully synthesized a series of CoxNi3-xS4 hollow microspheres through a combined hydrothermal and vapor-phase sulfidation process. These microspheres are composed of interlinked nanosheets featuring uniformly distributed nanoparticles on their surfaces. This distinctive hierarchical structure integrates one-dimensional, two-dimensional and three-dimensional elements, thereby facilitating the exposure of more active sites, enhancing electrolyte-active site interactions, accelerating carrier transport, and mitigating volume expansion during cycling. Specifically, varying the molar ratios results in different nanosheet thicknesses, with higher cobalt content leading to thicker nanosheets and higher nickel content producing thinner ones. The optimized (Co1Ni2)S4 electrode material exhibits an impressive specific capacity of 204.9 mA h g-1 (1639 F g-1) at 1 A g-1, along with remarkable rate capability (holding 80.5% when the current is increased 20 times) and exceptional cycling stability (maintaining 96% of its initial capacity after 15 000 cycles). When paired with lotus pollen-derived activated carbon (AC) to form a supercapacitor device, the (Co1Ni2)S4//AC configuration reaches an energy density of 66.5 W h kg-1 at 800 W kg-1. Notably, even after 30 000 cycles, the device retains an outstanding 98% of its initial capacity while sustaining 100% coulombic efficiency. This study presents an encouraging method for the precise fabrication of advanced bimetallic sulfides with enhanced electrochemical characteristics, facilitating their broader application in energy storage technologies.

Unleashing the Full Potential of Electrochromic Heterostructured Nickel-Cobalt Phosphate for Optically Active High-Performance Asymmetric Quasi-Solid-State Supercapacitor Devices

The rational design of hybrid systems that combine capacitor and battery merits is crucial to enable the fabrication of high energy and power density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni-Co phosphate (Ni3-xCox(PO4)2·8H2O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni3-xCox(PO4)2·8H2O offered a respectable gravimetric specific capacity and marvelous capability rate (966 and 595 C g-1 at 1 and 15 A g-1) over the Ni3(PO4)2·8H2O (327.3 C g-1) and Co3(PO4)2·8H2O (68 C g-1) counterparts. Additionally, the nanoplatelets showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni3-xCox(PO4)2·8H2O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg-1 and 15998.54 W kg-1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices are capable of glowing a red LED bulb for nearly 180 s. This research paves the way to design and fabricate electroactive species via a facile approach for boosting the design of a plethora of supercapattery devices.

Tuning diffusion coefficient, ionic conductivity, and transference number in rGO/BaCoO3 electrode material for optimized supercapacitor energy storage

Due to their remarkable cycle stability and outstanding capacitance, ABO3-type perovskite materials have emerged as highly effective electrode materials, delivering remarkable electrochemical performance. In this study, BaCoO3/rGO composites with varying rGO content (0, 5, 10, and 15%), designated as PBCO, BCO-I, BCO-II, and BCO-III, were synthesized using a solvothermal process. These composites were evaluated for their potential as electrode materials in supercapacitor (SC) applications. X-ray diffraction analysis confirmed the presence of well-crystallized samples with a hexagonal phase structure. Field emission scanning electron microscopy revealed the desired level of porosity, well-defined morphologies, and uniformly distributed grains, which are beneficial for electrochemical applications. Elemental analysis verified the stoichiometric composition of the samples. Comprehensive electrochemical characterization was performed using cyclic voltammetry in a 2 M KOH solution, revealing a transition from diffusive control (EDLC) to hybrid capacitor behavior. Additionally, galvanostatic charge-discharge experiments demonstrated that the BCO-III composite exhibited a specific capacity of 90.15 C g-1, an energy density of 21.28 W h kg-1, and a power density of 531.25 W kg-1. The transference number (t +) is found to be 0.2, which means that higher current will be driven through the anion. Further, the sample BCO-III, exhibiting the highest specific capacity, was evaluated for stability and demonstrated a remarkable retention rate of 90% after 5k GCD cycles and a remarkable coulombic efficiency of 94%, with an excellent diffusion rate and ionic conductivity of about 4.51 × 10-14 cm2 s-1, 0.128 S cm-1, respectively, highlighting its significant potential for SC applications.

Lanthanide Molecular Clusters and Metal-Organic Layers Constructed by Manipulation of Substituents

Usually, complexes with different connections and shapes are constructed by regulating the substituents. However, it is extremely challenging to construct two lanthanide complexes with different dimensions by only fine-tuning the substituents of the ligands, especially the substituents (-CH3 and -CH2CH3) with almost similar physical and chemical properties. Herein, by only regulating the substituents of the multidentate chelating ligands, two lanthanide complexes with different dimensions and connection modes were successfully constructed using a multicomponent "one-pot method" under the guidance of the multidentate chelating coordination method (MCC). They are the 11-nuclear lanthanide molecular cluster (Dy11) and the metal-organic layer (2D-Dy). Specifically, when the selected ligand is an imidazole-2-carboxaldehyde derivative and its substituent is -CH3, a layered 2D-Dy is obtained. The linker [Dy(HL1)3] with a propeller configuration is formed by chelating the Dy(III) ion with an acylhydrazone ligand (HL1) formed by the condensation of three salicylhydrazides and 1-methyl-1H-imidazole-2-carboxaldehyde. The above linkers were further linked alternately with propeller-shaped [Dy(NO3)3] as a secondary building unit (SBU) to form 2D-Dy. In addition, by changing the -CH3 on the ligand to -CH2CH3, we obtained an example of Dy11 formed by epitaxial assembly of two Dy(III) ions with an hourglass-shaped Dy9 as the core, and its molecular formula is [Dy11(HL2)8(μ3-OH)8(μ4-O)2(CH3O)4(NO3)4](NO3)5 18CH3OH. The cluster Dy11 was bombarded using high-resolution electrospray ionization mass spectrometry (HRESI-MS) and the molecular ion peaks of various fragments formed were captured. Based on the above molecular ion peaks, the possible fragmentation mechanisms of Dy11 were inferred to be Dy11 → Dy4(HL2)4 → Dy3(HL2)2 → Dy2(HL2)2 → Dy(HL2)2 and Dy11 → Dy(HL2)2/Dy2(HL2)2/Dy3(HL2)2/Dy4(HL2)4. This work is one of the rare examples where fine-tuning of ligand substituents leads to the formation of complexes of different dimensions, which promotes the progress of crystal engineering of lanthanide complexes.

Enhanced peroxidase-like activity based on electron transfer between platinum nanoparticles and Ti3C2TX MXene nanoribbons coupled smartphone-assisted hydrogel platform for detecting mercury ions

BACKGROUND

Heavy metal pollution poses a serious threat to the ecological environment. Mercury ion (Hg2+) is a class of highly toxic heavy metal ions, which is bioaccumulative, difficult to breakdown, and has a significant affinity with sulfur and thiol-containing proteins, which seriously affects environmental safety and human health. Nanozyme-based sensing methods are expected to be used to detect toxic heavy metal ions. However, the application of precious metal nanozymes to develop portable sensors with simplicity, high stability, and high sensitivity has not been explored to a large extent.

RESULTS

In this paper, based on MXene's unique adsorption capacity for certain precious metal ions, PtNPs/Ti3C2TXNR composites were successfully prepared by in-situ growth of Pt nanoparticles (PtNPs) on the surface of Ti3C2TX MXene nanoribbons (Ti3C2TXNR) using the hydrothermal technique. Experimental data revealed PtNPs/Ti3C2TXNR exhibited superior peroxidase-like activity, attributed to the synergistic effect of well-dispersed ultrasmall PtNPs and electron transfer effect. Hg2+ can significantly inhibit enzyme-like activity of PtNPs/Ti3C2TXNR due to specific capture and partial in-situ reduction of PtNPs, so a colorimetric sensor was constructed for ultra-trace detection of Hg2+ with a linear range of 0.2 nM and 400 nM. Furthermore, using the portable detecting capabilities of smartphones and hydrogel, a smartphone-assisted hydrogel sensing platform of Hg2+ was constructed. Notably, the two-mode sensing platforms exhibited outstanding detection performance with LOD values as low as 15 pM (colorimetric) and 26 pM (hydrogel), respectively, superior to recently reported nanozyme-based Hg2+ sensors.

SIGNIFICANCE

Compared with other methods, the PtNPs/Ti3C2TXNR-based dual-mode sensor designed in this paper has superior sensitivity, high selectivity, simple operation and portability. In particular, the dual-output sensing strategy enables self-confirmation of detection results, greatly improving the reliability of the sensor, and is expected to be used for the on-site determination of trace mercury ions.

Improved electrochemical performance of defect-induced supercapacitor electrodes based on MnS-incorporated MnO2 nanorods

In this paper, we report the effect of MnS nanoparticles on the electrochemical performance of 1D-MnO2 stable nanorods for supercapacitor electrodes. The MnS-incorporated 1D-MnO2 (MnO2/MnS) nanorods were produced using a facile two-step hydrothermal method. Morphological investigation reveals that the incorporation of MnS nanoparticles distorts the lattice fringes and extends the interlayer spacing of the MnO2 nanorods. The structural study showed that MnS modified the structural parameters of the nanocomposite. XPS analysis revealed defects in the nanocomposite due to the generation of oxygen vacancies. The MnO2/MnS nanocomposite improves capacitive performance and has the highest specific capacitance of 305 F g-1, at a current density of 1 A g-1 with an energy density of 5.7 W h kg-1 and a power density of 449 W kg-1. The MnO2/MnS nanocomposite electrodes exhibit exceptional cyclic stability after 5000 charging and discharging cycles. With enhanced specific capacitance and excellent cyclic stability, the MnO2/MnS nanocomposite paves a new way to produce supercapacitor electrodes.

Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials

An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge-discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge-discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge-discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

Enhancement of Peroxydisulfate Activation for Complete Degradation of Refractory Tetracycline by 3D Self-Supported MoS2/MXene Nanocomplex

Antibiotic abuse, particularly the excessive use of tetracycline (TC), a drug with significant environmental risk, has gravely harmed natural water bodies and even posed danger to human health. In this study, a three-dimensional self-supported MoS2/MXene nanohybrid with an expanded layer spacing was synthesized via a facile one-step hydrothermal method and used to activate peroxydisulfate (PDS) for the complete degradation of TC. The results showed that a stronger •OH signal was detected in the aqueous solution containing MoS2/MXene, demonstrating a superior PDS activation effect compared to MoS2 or Ti3C2TX MXene alone. Under the conditions of a catalyst dosage of 0.4 g/L, a PDS concentration of 0.4 mM, and pH = 5.0, the MoS2/MXene/PDS system was able to fully eliminate TC within one hour, which was probably due to the presence of several reactive oxygen species (ROS) (•OH, SO4•-, and O2•-) in the system. The high TC degradation efficiency could be maintained under the influence of various interfering ions and after five cycles, indicating that MoS2/MXene has good anti-interference and reusability performance. Furthermore, the possible degradation pathways were proposed by combining liquid chromatography-mass spectrometry (LC-MS) data and other findings, and the mechanism of the MoS2/MXene/PDS system on the degradation process of TC was elucidated by deducing the possible mechanism of ROS generation in the reaction process. All of these findings suggest that the MoS2/MXene composite catalyst has strong antibiotic removal capabilities with a wide range of application prospects.

Pseudocapacitive Kinetics in Synergistically Coupled MoS2-Mo2N Nanowires with Enhanced Interfaces toward All-Solid-State Flexible Supercapacitors

Pseudocapacitive kinetics in rationally engineered nanostructures can deliver higher energy and power densities simultaneously. The present report reveals a high-performance all-solid-state flexible symmetric supercapacitor (FSSC) based on MoS2-Mo2N nanowires deposited directly on stainless steel mesh (MoS2-Mo2N/SSM) employing DC reactive magnetron co-sputtering technology. The abundance of synergistically coupled interfaces and junctions between MoS2 nanosheets and Mo2N nanostructures across the nanocomposite results in greater porosity, increased ionic conductivity, and superior electrical conductivity. Consequently, the FSSC device utilizing poly(vinyl alcohol)-sodium sulfate (PVA-Na2SO4) hydrogel electrolyte renders an outstanding cell capacitance of 252.09 F·g-1 (44.12 mF·cm-2) at 0.25 mA·cm-2 and high rate performance within a wide 1.3 V window. Dunn's and b-value analysis reveals significant energy storage by surface-controlled capacitive and pseudocapacitive mechanisms. Remarkably, the symmetric device boosts tremendous energy density ∼10.36 μWh·cm-2 (59.17 Wh·kg-1), superb power density ∼6.5 mW·cm-2 (37.14 kW·kg-1), ultrastable long cyclability (∼93.7% after 10,000 galvanostatic charge-discharge cycles), and impressive mechanical flexibility at 60°, 90°, and 120° bending angles.

Recent Trends in Supercapacitor Research: Sustainability in Energy and Materials

Supercapacitors (SCs) have emerged as critical components in applications ranging from transport to wearable electronics due to their rapid charge-discharge cycles, high power density, and reliability. This review offers an analysis of recent strides in supercapacitor research, emphasizing pivotal developments in sustainability, electrode materials, electrolytes, and 'smart SCs' designed for modern microelectronics with attributes such as flexibility, stretchability, and biocompatibility. Central to this discourse are two dominant electrode materials: carbon materials (CMs), primarily in electric double layer capacitors (EDLCs), and pseudocapacitive materials, involving oxides/hydroxides, chalcogenides, metal-organic frameworks, conductive polymers and metal nitrides such as MXene. Despite EDLCs' historical use, challenges such as low energy density persist, with heteroatom introduction into the carbon lattice seen as a solution. Concurrently, pseudocapacitive materials dominate recent studies, with efficiency enhancement strategies, such as the creation of hybrids based on different types of materials, surface structural engineering and doping, under exploration. Electrolyte innovation, especially the shift towards gel polymer electrolytes for flexible SCs, and the harmonization of electrode materials with SC designs are highlighted. Emphasis is given to smart SCs with novel attributes such as self-charging, self-healing, biocompatibility, and environmentally conscious designs. In summary, the article underscores the drive in sustainable supercapacitor research to achieve high energy and power density, steering towards SCs that are efficient and versatile and involving bioderived/biocompatible SC materials. This brief review is based on selected recent references, offering depth combined with an accessible overview of the SC landscape.

Designed fabrication of MoS2 hollow structures with different geometries and the comparative investigation toward capacitive properties

Hollow MoS2 cubes and spheres were synthesized by a one-step hydrothermal method with the hard template method. The structure and morphology were characterized, and their electrochemical properties were studied. It is concluded that the specific capacitance of the hollow MoS2 cubes (335.7 F g-1) is higher than that of the hollow MoS2 spheres (256.1 F g-1). The symmetrical supercapacitors were assembled, and the results indicate that the specific capacitance of the device composed of hollow MoS2 spheres (32.9 F g-1) is slightly lower than that of the hollow MoS2 cube (37.4 F g-1) device. Furthermore, the symmetrical supercapacitor (MoS2-cube//MoS2-cube) provides a maximum energy density of 4.93 W h kg-1, which is greater than that of the symmetrical capacitor (MoS2-sphere//MoS2-sphere, 3.65 W h kg-1). This may indicate that hollow molybdenum disulfide cubes with substructures have more efficient charge transfer capabilities and better capacitance characteristics than hollow spheres. After 8000 cycles, the coulombic efficiency of the two symmetrical capacitors is close to 100%. The capacity retention of the MoS2 sphere device (95.2%) is slightly higher than that of the MoS2 cube device (90.1%). These results show that the pore structure, specific surface, and active site of MoS2 with different hollow structures have a greater impact on its electrochemical properties.

Heterogeneous Cu2O-SnO2 doped polydopamine fenton-like nanoenzymes for synergetic photothermal-chemodynamic antibacterial application

Wound infections caused by drug-resistant bacteria pose a great threat to human health, and the development of non-drug-resistant antibacterial approaches has become a research priority. In this study, we developed Cu2O-SnO2 doped polydopamine (CSPDA) triple cubic antibacterial nanoenzymes with high photothermal conversion efficiency and good Fenton-like catalase performance. CSPDA antibacterial nanoplatform can catalyze the generation of hydroxyl radical (·OH) from H2O2 at low concentration (50 μg∙mL-1) under 808 nm near-infrared (NIR) irradiation to achieve a combined photothermal therapy (PTT) and chemodynamic therapy (CDT). And the CSPDA antibacterial nanoplatform displays broad-spectrum and long-lasting antibacterial effects against both Gram-negative Escherichia coli (100 %) and Gram-positive Staphylococcus aureus (100 %) in vitro. Moreover, in a mouse wound model with mixed bacterial infection, the nanoplatform demonstrates a significant in vivo bactericidal effect while remaining good cytocompatible. To conclude, this study successfully develops an efficient and long-lasting bacterial infection treatment system. This system provided different options for future studies on the design of synergistic antimicrobial therapy. Hence, the as-synthesized synergetic photothermal therapy and chemodynamic therapy nanoenzymes have rapid and long-term bactericidal ability, well-conglutinant performance and effectively preventing wound infection for clinical application. STATEMENT OF SIGNIFICANCE: Wound infections caused by drug-resistant bacteria pose a great threat to human health, and the development of non-drug-resistant antibacterial approaches has become a research priority. In this study, we developed Cu2O-SnO2 doped polydopamine (CSPDA) triple cubic yolk-like antibacterial nanoenzymes with high photothermal conversion efficiency and Fenton-like catalase effect for photothermal and Chemodynamic antibacterial therapy, Meanwhile, the nanocomposites exhibit good antibioadhesion in a natural water environment for a long-time immersion. In conclusion, this study successfully develops an efficient and long-lasting bacterial infection treatment system. These findings present a pioneering strategy for future research on the design of synergistic antibacterial and antibioadhesive systems.

Directly Sputtered Molybdenum Disulfide Nanoworms Decorated with Binder-less VN and W2N Nanoarrays for Bendable Large-Scale Asymmetric Supercapacitor

Considering the superior capacitive performance and rich redox kinetics, the two-dimensional (2D) layered molybdenum disulfide (MoS2) and transition metal nitrides (TMNs) have emerged as the latest set of nanomaterials. Direct incorporation of key materials vanadium nitride (VN) and tungsten nitride (W2N) into a MoS2 array has been achieved on cost-effective, bendable stainless steel (SS) foil via a reactive cosputtering route. Herein, we have utilized the synergistic effect of intermixed nanohybrids to develop a flexible asymmetric supercapacitor (FASC) device from MoS2-VN@SS (negative) and MoS2-W2N@SS (positive) electrodes. As-constructed FASC cell possesses a maximum operational potential of 1.80 V and an exceptional gravimetric capacitance of 200 F g-1 at a sweep rate of 5 mV s-1. The sustained capacitive performance mainly accounts for the synergism induced through unique interfacial surface architecture provided by MoS2 nanoworms and TMN conductive hosts. The sulfur and nitrogen edges ensure the transport channels to Li+/SO4-2 ions for intercalation/deintercalation into the composite nanostructured thin film, further promoting the pseudocapacitive behavior. Consequently, the supercapacitor cell exhibits a distinctive specific energy of 87.91 Wh kg-1 at 0.87 kW kg-1 specific power and a reduced open circuit potential (OCP) decay rate (∼42% self-discharge after 60 min). Moreover, the assembled flexible device exhibits nearly unperturbed electrochemical response even at bending at 165° angle and illustrates a commendable cyclic life-span of 82% after 20,000 charge-discharge cycles, elucidating advanced mechanical robustness and capacitance retentivity. The powering of a multicolor light-emitting diode (LED) and electronic digital watch facilitates the practical evidence to open up possibilities in next-generation state-of-the-art wearable and miniaturized energy storage systems.

Facile preparation of poly-(styrene-co-maleic anhydride) encapsulated Iridium(III) complexes as highly efficient electrochemiluminescence indicators for sensitive immunoassay of CYFRA 21-1

Exploring facile strategy for developing highly efficient emitters using water-insoluble luminophores has become a vital topic in electrochemiluminescence (ECL) immunoassay. In this work, an ECL-active and water-dispersive iridium(III) complex-based polymer dots (IrPdots) was fabricated by encapsulating water-insoluble tris[1-phenylisoquinolinato-C2, N] iridium(III) complexes [Ir(piq)₃] into poly-(styrene-co-maleic anhydride) (PSMA) matrix by a controllable nanoprecipitation process. The obtained IrPdots generated strong ECL signals in the presence of tri-n-propylamine (TPrA) and were used to label detection antibody (Ab₂) to act as ECL probes to indicate the signal changes when analyzing target antigen. To construct a sandwich immunosensor, Pd nanoparticles (NPs) decorated MoS₂/Ti₃C₂T_x MXene nanocomposites (MoS₂/Ti₃C₂T_x MXene/Pd) were fabricated as substrates to bind capture antibody (Ab₁), which could further amplify ECL signals via a coreaction-accelerating pathway to improve the detection sensitivity. When the cytokeratin 19 fragment 21-1 (CYFRA 21-1) was chosen as model analyte, the developed immunosensor displayed a good linear relationship ranging from 0.1 pg/mL to 50 ng/mL with a low detection limit of 95 fg/mL (S/N = 3) was achieved as well. This research proposed a facile and effective method of fabricating IrPdots as ECL probes for immunoassay using water-insoluble iridium complexes, which expanded the application scope of those water-insoluble luminophores for aqueous bioanalysis.

Formation of MXene-Derived/NiCoFe-LDH Heterostructures for Supercapacitor Applications

In this study, MXene-derived/NiCoFe-LDH heterostructures with three-dimensional interconnected porous network microstructures were prepared, leveraging the excellent electrical conductivity and growth platform provided by the MXene material. The remarkable specific capacitance of metal oxides was fully exploited. The composite exhibited high specific capacitance and excellent stability, with a specific capacitance of 1305 F g^-1 at 1 A g^-1 and a capacitance of 85.7% of the initial performance after 6000 charge/discharge tests at 10 A g^-1. A two-electrode assembly was constructed using activated carbon as the negative electrode material corresponding to 49.5 Wh kg^-1 at 800 W kg^-1, indicating that the electrodes could achieve rapid charge/discharge. The findings of this study indicate that the composite material comprising LDH/MXene has significant potential for supercapacitor applications.

Fabrication of Coral-like Polyaniline/Continuously Reinforced Carbon Nanotube Woven Composite Films for Flexible High-Stability Supercapacitor Electrodes

The electrochemical performance is significantly influenced by the structure and surface morphology of the electrode materials used in supercapacitors. Using the floating catalytic chemical vapor deposition (FCCVD) technique, a self-supporting, flexible layer of continuously reinforced carbon nanotube woven film (CNWF) was developed. Then, polyaniline (PANI) was formed in the conductive network of CNWF using cyclic voltammetry electrochemical polymerization (CVEP) in various aqueous electrolytes to produce a series of flexible CNWF/PANI composite films. The impacts of the CVEP period, electrolyte type, and electrolyte concentration on the surface morphology, doping degree, and hydrophilicity of CNWF/PANI composite films were thoroughly examined. The CNWF/PANI₁-15C composite electrode, which was created using 15 cycles of CVEP in a solution of 1 M sodium bisulfate, displayed a distinctive coral-like PANI layer with a well-defined sharp nanoprotuberance structure, a 48% doping degree, and a quick reversible pseudocapacitive storage mechanism. At a current density of 1 A g^-1, the energy density and specific capacitance reached 54.9 Wh kg^-1 and 1098.0 F g^-1, respectively, with a specific capacitance retention rate of 75.9% maintained at 10 A g^-1. Both the specific capacitance and coulomb efficiency were maintained at 96.9% and more than 98.1% of their initial values after being subjected to 2000 cycles of galvanostatic charge and discharge, demonstrating excellent electrochemical cycling stability. The CNWF/PANI₁-15C composite film, an ideal electrode material, offers a promising future in the field of flexible energy storage due to its exceptional mechanical properties (127.9 MPa tensile strength and 16.2% elongation at break).

Engineering chemical-bonded Ti3C2 MXene@carbon composite films with 3D transportation channels for promoting lithium-ion storage in hybrid capacitors

Lithium-ion capacitors (LICs) are promising energy storage devices because they feature the high energy density of lithium-ion batteries and the high power density of supercapacitors. However, the mismatch of electrochemical reaction kinetics between the anode and cathode in LICs makes exploring anode materials with fast ion diffusion and electron transfer channels an urgent task. Herein, the two-dimensional (2D) Ti3C2 MXene with controllable terminal groups was introduced into 1D carbon nanofibers to form a 3D conductive network by the electrospinning strategy. In such Ti3C2 MXene and carbon matrix composites (named KTi-400@CNFs), the 2D nanosheet structure endows Ti3C2 MXene with more active sites for Li+ ion storage, and the carbon framework is favorable to the conductivity of the composites. Impressively, Ti-O-C bonds are formed at the interface between Ti3C2 MXene and the carbon framework. Such chemical bonding in the composites builds a bridge for rapid electron transportation and quick ion diffusion in the longitudinal direction from layer to layer. As a result, the optimized KTi-400@CNFs composites maintain a good capacity of 235 mA h g-1 for 500 cycles at a current density of 5 A g-1. The LIC consisting of the KTi-400@CNFs//AC configuration achieves high energy density (114.3 W h kg-1) and high power density (12.8 kW kg-1). This paper provides guidance for designing 2D materials and the KTi-400@CNFs composites with such a unique structure and superior electrochemical performance have great potential in the next-generation energy storage fields.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/s40843-022-2268-9 and is accessible for authorized users.

One-Step Hydrothermal Synthesis of MoO2/MoS2 Nanocomposites as High-Performance Electrode Material for Supercapacitors

By only changing the ratio of Mo to S source, a distinctive single phase MoO2 or MoS2 and MoO2/MoS2 nanocomposites (NCs) are obtained through a simple one-step hydrothermal method based on CH4N2S as a sulfur source and (NH4)6Mo7O24·4H2O as a source of Mo in oxalic acid. The effect of ratio of Mo to S source on the composition, structure, and electrochemical performance are systematically researched. Due to its unique design, abundant macropores active sites in MoO2/MoS2 NCs induce superior rate property (55.30% capacitance retention to 20 from 1 A g-1) and larger specific capacitance (1667.3 F g-1 at 1 A g-1) and longer cycle life (94.75% after 5000 cycles) as used directly as an electrode. Furthermore, at a power density of 225 W kg-1, a maximal energy density of 21.85 Wh kg-1 is provided by the asymmetric supercapacitor (MoO2/MoS2//AC). The capacitance of asymmetric supercapacitor (ASC) is remarkably enhanced by 129.02% under 5000 cycles at a current density of 1.5 A g-1, demonstrating outstanding cycle property. These results imply the prepared MoO2/MoS2 NCs have promising applications in advanced energy storages. It is important and should be noted that NCs of oxide and sulfide are prepared with only a simple one-step process.

Facile Synthesis of Biocarbon-Based MoS2 Composite for High-Performance Supercapacitor Application

Nanocomposites are gaining high demand for the development of next-generation energy storage devices because of their eco-friendly and cost-effective natures. However, their short-term energy retainability and marginal stability are regarded as hindrances to overcome. In this work, we demonstrate a high-performance supercapacitor fabricated by biocarbon-based MoS₂ (Bio-C/MoS₂) nanoparticles synthesized by a facile hydrothermal approach using date fruits. Here, we report the high specific capacitance for a carbon-based nanocomposite employing the pyrolysis technique of converting agricultural biowaste into a highly affordable energy resource. The biocompatible Bio-C/MoS₂ nanospheres exhibited a high capacitance of 945 F g^-1 at a current density of 0.5 A g^-1 and an excellent reproducing stability of 92% after 10000 charge/discharge cycles. In addition, the Bio-C/MoS₂ NS showed an exceptional power density of 3800-8000 W kg^-1 and an energy density of 74.9-157 Wh kg^-1. The results would pave a new strategy for design of eco-friendly materials toward the high-performance energy storage technology.

MXenes as Emerging Materials: Synthesis, Properties, and Applications

Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure-property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor

To improve the production rate of MoS₂ nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS₂-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS₂ nanosheets on a large scale. Then, the MnO₂ nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS₂ nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS₂ nanosheets and MnO₂ nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS₂ nanosheets and MnO₂ nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS₂ nanosheets and MnO₂ nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m²/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.

Water- and Acid-Sensitive Cu2O@Cu-MOF Nano Sustained-Release Capsules with Superior Antifouling Behaviors

Marine biofouling is one of the technical bottlenecks restricting the development of the global marine economy. Among the commercial self-polishing antifouling coatings, cuprous oxide is an irreplaceable component because of its efficiency and broad-spectrum antibacterial activity. However, one of the biggest obstacles to achieving long-term antifouling is the "initial burst and final decay" of cuprous oxide in the coating. Here, we lock the copper ions by establishing an antifouling unit composed of Cu₂O (core) and Cu-based metal-organic framework (Cu-MOF, shell). Cu-MOF is densely grown in situ on the periphery of Cu₂O by acid proton etching. The shell structure of Cu-MOF can effectively improve the stability of the internal Cu₂O and thus achieve the stable and slow release of copper ions. Furthermore, Cu₂O@Cu-MOF nanocapsules can also achieve active defense by rapid and complete dissolution of Cu₂O@Cu-MOF at local acidic microenvironment (pH ≤ 5) where the adhesion of fouling organisms occurs. Super-resolution fluorescence microscopy is used to explain the sterilization mechanism. Relying on the water- and acid-sensitive properties of Cu-MOF shell, the stable, controlled and efficient release of copper ions has been achieved for the Cu₂O@Cu-MOF nanocapsules in the self-polishing antifouling coatings. Thus, these controlled-release nanocapsules make long-term antifouling promising.