Full-Temperature All-Solid-State Ti3C2Tx/Aramid Fiber Supercapacitor with Optimal Balance of Capacitive Performance and Flexibility

Full-temperature all-solid-state flexible symmetrical fiber supercapacitors (FSCs) are assembled by using montmorillonite flake/polyvinyl alcohol organic hydrogel (F-MMT/PVA OHGE) as the electrolyte and separator and Ti₃C₂T_x/ANF-5% (T/A-5) fiber as the electrode, in which T/A-5 fiber is prepared by using delaminated Ti₃C₂T_x nanosheets as assembled units and 5% of aramid nanofiber (ANF) as the functional additive using a wet spinning method in a coagulated bath with 0.5 m FeCl₂ solution. The T/A-5 hybrid fiber exhibits a specific capacity of 807 F cm⁻³ in 3 m H₂SO₄ electrolyte, a superior mechanical strength of 104 MPa, and a high conductivity of 1025 S cm⁻¹. The assembled F-MMT/PVA OHGE T/A-5 FSC not only shows a specific capacitance of 295 F cm⁻³ and a capacitance retention of 91% at a current density of 5 A cm⁻³ after 10 000 charging/discharging cycles, but also a maximum volumetric energy density of 26.2 mWh cm⁻³. Meanwhile, the assembled device displays good flexibility and excellent capacitance in a wide temperature range of −40 to 80 °C, the electrochemical performance of the FSC is maintained under varying degrees of bending. This study provides an effective strategy for designing and assembling of full-temperature all-solid-state symmetrical flexible FSCs with the optimal balance of capacitive performance and flexibility.     

Hierarchical Integrated Hybrid Structural Electrodes Based on Co-N/C and Mo-doped NiCo-LDH@Co-N/C Anchored on MX/CF for High Energy Density Fiber-Shaped Supercapacitor

The judicious design of highly electrochemically active materials on 1D fiber substrate to form a hierarchical integrated hybrid structure is an efficient technique to improve the limited cylindrical space and volumetric energy density of fiber-shaped supercapacitors (FSCs). Herein, a 3D negative electrode, consisting of vertically aligned interconnected mesoporous Co-N/C leaf-like structure on 1D MXene-carbon fiber (Co-N/C@MX/CF) is prepared by controlling the composition and morphology. At the same time, a 3D positive electrode is also prepared by introducing Mo in NiCo-LDH anchored on Co-N/C@MX/CF (Mo-NiCo-LDH@Co-N/C@MX/CF) by electrodeposition method. Benefitting from the systematic hierarchical structures with highly accessible surface area, adequate pore size and easy permeation of electrolyte, both positive and negative electrodes demonstrate highly improved electrochemical performance with areal capacity/capacitance of 0.96 mAh cm⁻²/4.55 mF cm⁻² at a current density of 3.86 mA cm⁻², respectively. Furthermore, the fiber-shaped solid-state hybrid supercapacitor (FSHSC) based on Mo_1.5NiCo-LDH@Co-N/C@MX/CF(+)//Co-N/C_0.5@MX/CF(−) is fabricated, exhibiting compelling energy density of 86.72 mWh cm⁻³ at a power density of 480.30 mW cm⁻³ with an outstanding capacitance retention of 80.2% after 20000 galvanostatic-charge-discharge cycles. This study puts forward a new perspective on the development of highly efficient FSCs for practical application.     

Redox Poly-Counterion Doped Conducting Polymers for Pseudocapacitive Energy Storage

Conducting polymers (CPs) have been widely studied for electrochemical energy storage. However, the dopants in CPs are often electrochemically inactive, introducing “dead-weight” to the materials. Moreover, commercial-level electrode materials with high mass loadings (e.g., >10 mg cm⁻²) often encounter the problems of inferior electrical and ionic conductivity. Here, a redox-active poly-counterion doping concept is proposed to improve the electrochemical performance of CPs with ultra-high mass loadings. As a study prototype, heptamolybdate anion (Mo₇O₂₄⁶⁻) doped polypyrrole (PPy) is synthesized by electro-polymerization. A 2 mm thick PPy electrode with mass loading of ≈192 mg cm⁻² reaches a record-high areal capacitance of ≈47 F cm⁻², competitive gravimetric capacitance of 235 F g⁻¹, and volumetric capacitance of 235 F cm⁻³. With poly-counterion doping, the dopants also undergo redox reactions during charge/discharge processes, providing additional capacitance to the electrode. The interaction between polymer chains and the poly-counterions enhances the electrical conductivity of CPs. Besides, the poly-counterions with large steric hindrance could act as structural pillars and endow CPs with open structures for facile ion transport. The concept proposed in this work enriches the electrochemistry of CPs and promotes their practical applications.     

Aqueous Ammonium-Ion Supercapacitors with Unprecedented Energy Density and Stability Enabled by Oxygen Vacancy-Enriched MoO3@C

The use of non-metal charge carriers such as ammonium (NH₄⁺) in electrochemical energy storage devices offers advantages in terms of weight, element abundance, and compatibility with aqueous electrolytes. However, the development of suitable electrodes for such carriers lags behind other technologies. Herein, we present a high-performance anode material for ammonium-ion supercapacitors based on a MoO₃/carbon (MoO₃@C) composite. The NH₄⁺ storage performance of such composites and their practical application prospects are evaluated both in a three-electrode configuration and as symmetric supercapacitors. The optimized material reaches an unprecedented specific capacitance of 473 F·g⁻¹ (158 mAh·g⁻¹; 1592 mF·cm⁻²) at a current density of 1 A·g⁻¹, and 92.7% capacitance retention after 5000 cycles in a three-electrode set-up. This outstanding performance is related to the presence of oxygen vacancies that enhance the composites’ ionic/electronic transportation and electrochemical reaction site, while at the same time facilitating the formation of hydrogen bonds between NH₄⁺ and the host material. Using the optimized composite, symmetric supercapacitors based on an (NH₄)₂SO₄ gel electrolyte are fabricated and demonstrated to provide unmatched energy densities above 78 Wh·kg⁻¹ at a power density of 929 W·kg⁻¹. Besides, such devices are characterized by extraordinary capacitance retention of 97.6% after 10,000 cycles.     

Tailoring Ultrahigh Energy Density and Stable Dendrite-Free Flexible Anode with Ti3C2Tx MXene Nanosheets and Hydrated Ammonium Vanadate Nanobelts for Aqueous Rocking-Chair Zinc Ion Batteries

Exploiting Zn metal-free anode materials would be an effective strategy to resolve the problems of Zn metal dendrites that severely hinder the development of Zn ion batteries (ZIBs). However, the study of Zn metal-free anode materials is still in their infancy, and more importantly, the low energy density severely limits their practical implementations. Herein, a novel (NH₄)₂V₁₀O₂₅ · 8H₂O@Ti₃C₂T_x (NHVO@Ti₃C₂T_x) film anode is proposed and investigated for constructing “rocking-chair” ZIBs. The NHVO@Ti₃C₂T_x electrode shows a capacity of 514.7 mAh g⁻¹ and presents low potential which is 0.59 V (vs Zn²⁺/Zn) at 0.1 A g⁻¹. The introduction of Ti₃C₂T_x not only affords an interconnected conductive network, but also stabilizes the NHVO nanobelts structure for a long cycle life (84.2% retention at 5.0 A g⁻¹ over 6000 cycles). As a proof-of-concept, a zinc metal-free full battery is successfully demonstrated, which delivers the highest capacity of 131.7 mAh g⁻¹ (mass containing anodic and cathodic) and energy density of 97.1 Wh kg⁻¹ compared to all reported aqueous “rocking-chair” ZIBs. Furthermore, a long cycling span of 6000 cycles is obtained with capacity retention reaching up to 92.1%, which is impressive. This work is expected to provide new moment toward V-based materials for “rocking-chair” ZIBs.     

H-BN-Encapsulated Uncooled Infrared Photodetectors Based on Tantalum Nickel Selenide

Uncooled broadband spectrum detection, spanning from visible to mid-wave-infrared regions, offers immense potential for applications in environmental monitoring, optical telecommunications, and radar systems. While leveraging proven technologies, conventional mid-wave-infrared photodetectors are encumbered by high dark currents and the necessity for cryogenic cooling. Correspondingly, innovative low-dimensional materials like black phosphorus manifest weak photoresponse and instability. Here, tantalum nickel selenide (Ta₂NiSe₅) infrared photodetectors with an operational wavelength range from 520 nm to 4.6 µm, utilizing a hexagonal boron nitride (h-BN) encapsulation technique are introduced. The h-BN encapsulated metal-Ta₂NiSe₅-metal photodetector demonstrates a responsivity of 0.86 A W⁻¹, a noise equivalent power of 1.8 × 10⁻¹¹ W Hz^−1/2, and a peak detectivity of 8.75 × 10⁸ cm Hz^1/2 W⁻¹ at 4.6 µm under ambient conditions. Multifaceted mechanisms of photocurrent generation in the novel device prototype subject are scrutinized to varying wavelengths of radiation, by characterizing the temporal-, bias-, power-, and temperature-dependent photoresponse. Moreover, the photopolarization dependence is delved and concealed-target imaging is demonstrated, which exhibits polarization angle sensitivity and high-fidelity imaging across the visible, short-wave, and mid-wave-infrared bands. The observations, which reveal versatile detection modalities, propose Ta₂NiSe₅ as a promising low-dimensional material for advanced applications in nano-optoelectronic device.     

Bimetal Organic Framework–Ti3C2Tx MXene with Metalloporphyrin Electrocatalyst for Lithium–Oxygen Batteries

The gravest oxidation of MXenes has become a critical problem due to the formation of metal oxides, leading to the loss of their intrinsic properties. Herein, bimetallic cobalt–manganese organic framework (CMT) directly grown on a Ti₃C₂T_x MXene sheet via solvothermal treatment to obtain strong oxidation resistance in an open structured application and to enhance electrocatalytic properties for oxygen evolution and reduction reaction is reported. Inspired by ligand chemistry, the carboxyl acids in tetrakis(4–carboxyphenyl)porphyrin acting as an organic linker are grafted with the surface terminators of Ti₃C₂T_x MXene through the Fischer esterification and substitution reaction of fluorine, thereby greatly enhancing the antioxidation stability. Furthermore, the as-formed metalloporphyrin structure and unpaired electrons, produced between CMT and Ti₃C₂T_x MXene during solvothermal treatment, improve their electrocatalytic activity, durability, and electrical conductivity through an electron hopping mechanism. Consequently, the CMT@MXene demonstrates high stability as a bifunctional electrocatalyst at a fixed specific capacity of 1000 mAh g⁻¹ and a current density of 500 mA g⁻¹ for 247 cycles in lithium–oxygen (Li O₂) battery. This approach suggests new strategies for the synergistic coupling of MXenes and MOFs for future open structured applications.     

High-Performance Ultraviolet Photodetectors Enabled by van der Waals Schottky Junction Based on TiO2 Nanorod Arrays/Au-Modulated Ti3C2Tx MXene

Two-dimensional transition metal carbides and nitrides (MXenes) show tremendous potential for optoelectronic devices due to their excellent electronic properties. Here, a high-performance ultraviolet photodetector based on TiO₂ nanorod arrays/Ti₃C₂T_x MXene van der Waals (vdW) Schottky junction by all-solution process technique is reported. The Ti₃C₂T_x MXene modulated by the Au electrode increases its work function from 4.41 to 5.14 eV to form a hole transport layer. Complemented by the dangling bond-free surface of Ti₃C₂T_x, the Fermi-level pinning effect is suppressed and the electric-field strength of the Schottky junction is enhanced, which promotes charge separation and transport. After applying a bias of −1.5 V, the photovoltaic effect is favorably reinforced, while the hole-trapping mechanism (between TiO₂ and oxygen) and reverse pyroelectric effect are largely eliminated. As a result, the responsivity and specific detectivity of the device with FTO/TiO₂ nanorod arrays/Ti₃C₂T_x/Au structure reach 1.95 × 10⁵ mA W⁻¹ and 4.3 × 10¹³ cm Hz^1/2 W⁻¹ (370 nm, 65 mW cm⁻²), respectively. This work provides an effective approach to enhance the performance of photodetectors by forming the vdW Schottky junction and choosing metal electrodes to modulate MXene as a suitable charge transport layer.     

2D Titanium Carbide (MXene) Based Films: Expanding the Frontier of Functional Film Materials

2D titanium carbide (Ti₃C₂T_x) MXene films, with their well-defined microstructures and chemical functionality, provide a macroscale use of nano-sized Ti₃C₂T_x flakes. Ti₃C₂T_x films have attractive physicochemical properties favorable for device design, such as high electrical conductivity (up to 20 000 S cm^–1), impressive volumetric capacitance (1500 F cm^–3), strong in-plane mechanical strength (up to 570 MPa), and a high degree of flexibility. Here, the appealing features of Ti₃C₂T_x-based films enabled by the layer-to-layer arrangement of nanosheets are reviewed. We devote attention to the key strategies for actualizing desirable characteristics in Ti₃C₂T_x-based functional films, such as high and tunable electrical conductivity, outstanding mechanical properties, enhanced oxidation-resistance and shelf life, hydrophilicity/hydrophobicity, adjustable porosity, and convenient processability. This review further discusses fundamental aspects and advances in the applications of Ti₃C₂T_x-based films with a focus on illuminating the relationship between the structural features and the resulting performances for target applications. Finally, the challenges and opportunities in terms of future research, development, and applications of Ti₃C₂T_x-based films are suggested. A comprehensive understanding of these competitive features and challenges shall provide guidelines and inspiration for the further development of Ti₃C₂T_x-based functional films, and contribute to the advances in MXene technology.     

Fe2VO4 Nanoparticles Anchored on Ordered Mesoporous Carbon with Pseudocapacitive Behaviors for Efficient Sodium Storage

Iron vanadates are attractive anode materials for sodium-ion batteries (SIBs) because of their abundant resource reserves and high capacities. However, their practical application is restricted by the aggregation of materials, sluggish reaction kinetics, and inferior reversibility. Herein, Fe₂VO₄ nanoparticles are anchored on the ordered mesoporous carbon (CMK-3) nanorods to assemble 3D Fe₂VO₄@CMK-3 composites, by solvothermal treatment and subsequent calcination. The resulting composites provide abundant active sites, high electrical conductivity, and excellent structural integrity. The pseudocapacitive-controlled behavior is the dominating sodium storage mechanism, which facilitates a fast charge/discharge process. The Fe₂VO₄@CMK-3 composites exhibit stable sodium-ion storage (219 mAh g⁻¹ under 100 mA g⁻¹ after 300 cycles), good rate performance (144 mAh g⁻¹ at 3.2 A g⁻¹), and excellent cycling performance (132 mAh g⁻¹ at 1 A g⁻¹ with capacity retention of 96.4% after 800 cycles). When coupled with a NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the sodium-ion full cell displays excellent cycling stability (94 mAh g⁻¹ after 500 cycles at 500 mA g⁻¹). These findings point to the potential of Fe₂VO₄@CMK-3 for application as anodes in SIBs.     

Flexible Carbon Dots-Intercalated MXene Film Electrode with Outstanding Volumetric Performance for Supercapacitors

2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo-capacitive mechanism, and high density. However, layer-restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots-intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion-accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA-derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots-intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm⁻³ at 1 A g⁻¹), superior rate capability (662.5 F cm⁻³ at 1000 A g⁻¹), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H₂SO₄. Additionally, an all-solid-state symmetric supercapacitor based on the carbon dots-intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L⁻¹. This study provides a simple yet efficient strategy to construct high-volumetric performance MXene film electrodes for advanced supercapacitors.     

High-Pressure Synthesis and Thermal Conductivity of Semimetallic θ-Tantalum Nitride

The lattice thermal conductivity (κ_ph) of metals and semimetals is limited by phonon-phonon scattering at high temperatures and by electron-phonon scattering at low temperatures or in some systems with weak phonon-phonon scattering. Following the demonstration of a phonon band engineering approach to achieve an unusually high κ_ph in semiconducting cubic-boron arsenide (c-BAs), recent theories have predicted ultrahigh κ_ph of the semimetal tantalum nitride in the θ-phase (θ-TaN) with hexagonal tungsten carbide (WC) structure due to the combination of a small electron density of states near the Fermi level and a large phonon band gap, which suppress electron-phonon and three-phonon scattering, respectively. Here, measurements on the thermal and electrical transport properties of polycrystalline θ-TaN converted from the ε phase via high-pressure synthesis are reported. The measured thermal conductivity of the θ-TaN samples shows weak temperature dependence above 200 K and reaches up to 90 Wm⁻¹K⁻¹, one order of magnitude higher than values reported for polycrystalline ε-TaN and δ-TaN thin films. These results agree with theoretical calculations that account for phonon scattering by 100 nm-level grains and suggest κ_ph increase above the 249 Wm⁻¹ K⁻¹ value predicted for single-crystal WC when the grain size of θ-TaN is increased above 400 nm.     

Optimized Ti?O Subcompounds and Elastic Expanded MXene Interlayers Boost Quick Sodium Storage Performance

To develop quick-charge sodium-ion battery, it is significant to optimize insertion-type anode to afford fast Na⁺ diffusion rate and excellent electron conductivity. First-principles calculations reveal the Ti O subcompound superiority for Na⁺ diffusion following Ti(II) O > Ti(III) O > Ti(IV) O. Hence, in situ growth of amorphous Ti O subcompounds with rich oxygen defects based on Ti₃C₂T_x-MXene is developed. Meanwhile, the composite presents expanded MXene interlayer spacing and much enhanced conductivity. The synergistic effect of enhanced electron/ion conduction gives a high capacity of 107 mAh g⁻¹ at 50 A g⁻¹, which gives 50% and 150% increasements compared with one counterpart without valence adjustment and another one without MXene expansion. It only needs 20 s (at 30 A g⁻¹) to complete the discharge/charge process and obtains a capacity of 144.5 mAh g⁻¹, which also shows a long-term cycling stability at quick-charge mode (121 mAh g⁻¹ after 10000 cycles at 10 A g⁻¹). The enhanced performance comes from fast electron transfer among Ti O subcompounds contributed by rich-defect amorphous TiO_2–x, and a reversible change of elastic MXene with interlayer spacing between 1.4 and 1.9 nm during Na⁺ insertion/extraction process. This study provides a feasible route to boost the kinetics and develop quick-charge sodium-ion battery.     

Reassembly of MXene Hydrogels into Flexible Films towards Compact and Ultrafast Supercapacitors

The freestanding MXene films are promising for compact energy storage ascribing to their high pseudocapacitance and density, yet the sluggish ion transport caused by the most densely packed structure severely hinders their rate capability. Here, a reassembly strategy for constructing freestanding and flexible MXene-based film electrodes with a tunable porous structure is proposed, where the Ti₃C₂T_x microgels disassembled from 3D structured hydrogel are reassembled together with individual Ti₃C₂T_x nanosheets in different mass ratios to form a densely packed 3D network in microscale and a film morphology in macroscale. The space utilization of produced film can be maximized by a good balance of the density and porosity, resulting in a high volumetric capacitance of 736 F cm⁻³ at an ultrahigh scan rate of 2000 mV s⁻¹. The fabricated supercapacitor yields a superior energy density of 40 Wh L⁻¹ at a power density of 0.83 kW L⁻¹, and an energy density of 21 Wh L⁻¹ can be still maintained even when the power density reaches 41.5 kW L⁻¹, which are the highest values reported to date for symmetric supercapacitors in aqueous electrolytes. More promisingly, the reassembled films can be used as electrodes of flexible supercapacitors, showing excellent flexibility and integrability.     

Alternative-Ultrathin Assembling of Exfoliated Manganese Dioxide and Nitrogen-Doped Carbon Layers for High-Mass-Loading Supercapacitors with Outstanding Capacitance and Impressive Rate Capability

Manganese dioxide (MnO₂) materials have received much attention as promising pseudocapacitive materials owing to their high theoretical capacitance and natural abundance. Unfortunately, the charge storage performance of MnO₂ is usually limited to commercially available mass loading electrodes because of the significantly lower electron and ion migration kinetics in thick electrodes. Here, an alternatively assembled 2D layered material consisting of exfoliated MnO₂ nanosheets and nitrogen-doped carbon layers for ultrahigh-mass-loading supercapacitors without sacrificing energy storage performance is reported. Layered birnessite-type MnO₂ is efficiently exfoliated and intercalated by a carbon precursor of dopamine using a fluid dynamic-induced process, resulting in MnO₂/nitrogen-doped carbon (MnO₂/C) materials after self-polymerization and carbonization. The alternatively stacked and interlayer-expanded structure of MnO₂/C enables fast and efficient electron and ion transfer in a thick electrode. The resulting MnO₂/C electrode shows outstanding electrochemical performance at an ultrahigh mass loading of 19.7 mg cm⁻², high gravimetric and areal capacitances of 480.3 F g⁻¹ and 9.4 F cm⁻² at 0.5 mA cm⁻², and rapid charge/discharge capability of 70% capacitance retention at 40 mA cm⁻². Furthermore, asymmetric supercapacitor based on high-mass-loading MnO₂/C can deliver an extremely high energy of 64.2 Wh kg⁻¹ at a power density of 18.8 W kg⁻¹ in an aqueous electrolyte.     

Towards All-Solid-State Polymer Batteries: Going Beyond PEO with Hybrid Concepts

To go beyond polyethylene oxide in lithium metal batteries, a hybrid polymer/oligomer cell design is presented, where an ester oligomer provides high ionic conductivity of 0.2 mS cm⁻¹ at 40 °C within thicker composite cathodes with active mass loadings of up to 11 mg cm⁻² (LiNbO₃-coated) LiNi_0.6Mn_0.2Co_0.2 (NMC622), while a 30 µm thin scaffold-supported polymer electrolyte affords mechanical stability. Corresponding discharge capacities of the hybrid cells exceed 170 mAh g⁻¹ (11 mg cm⁻²) or 160 mAh g⁻¹ (6 mg cm⁻²) at rates of either 0.1 or 0.25 C. Multilayer pouch cells are projected to enable energy densities of 235 Wh L⁻¹ (6 mg cm⁻²) and even up to 356 Wh L⁻¹ (11 mg cm⁻²), clearly superior to other reported polymer-based cell designs. Polyester electrolytes are environmentally benign and safer compared to common liquid electrolytes, while the straightforward synthesis and affordability of precursors render hybrid polyester electrolytes suitable candidates for future application in solid-state lithium metal batteries.     

A Self-Healing Volume Variation Three-Dimensional Continuous Bulk Porous Bismuth for Ultrafast Sodium Storage

Bismuth (Bi) has attracted considerable attention as promising anode material for sodium-ion batteries (NIBs) owing to its suitable reaction potential and high volumetric capacity density (3750 mA h cm⁻³). However, the large volumetric expansion during cycling causes severe structural degradation and fast capacity decay. Herein, by rational design, a self-healing nanostructure 3D continuous bulk porous bismuth (3DPBi) is prepared via facile liquid phase reduction reaction. The 3D interconnected Bi nanoligaments provide unblocked electronic circuits and short ion diffusion path. Meanwhile, the bicontinuous nanoporous network can realize self-healing the huge volume variation as confirmed by in situ and ex situ transmission electron microscopy observations. When used as the anode for NIBs, the 3DPBi delivers unprecedented rate capability (high capacity retention of 95.6% at an ultrahigh current density of 60 A g⁻¹ with respect to 1 A g⁻¹) and long-cycle life (high capacity of 378 mA h g⁻¹ remained after 3000 cycles at 10 A g⁻¹). In addition, the full cell of Na₃V₂(PO₄)₃|3DPBi delivers stable cycling performance and high gravimetric energy density (116 Wh kg⁻¹), demonstrating its potential in practical application.     

Controllable Patterning of Porous MXene (Ti3C2) by Metal-Assisted Electro-Gelation Method

Since discovered in 2011, transition metal carbides or nitrides (MXenes) have attracted enormous attention due to their unique properties. Morphology regulation strategies assembling 2D MXene sheets into 3D architecture have endowed the as-formed porous MXene with a better performance in various fields. However, the direct patterning strategy for the porous MXene into integration with multifunctional and multichannel electronic devices still needs to be investigated. The metal-assisted electro-gelation method the authors propose can directly generate porous-structured MXene hydrogel with a tunable feature. By electrolyzing the sacrificial metal, the released metal cations initiate the electro-gelation process during which electrostatic interactions occur between cations and the MXene sheets. A high spatial resolution down to micro-meter level is achieved utilizing the method, enabling high-performance hydrogels with more complex architectures. Electronics prepared through this metal-assisted electro-gelation process have shown promising applications of the porous MXene in energy and biochemical sensing fields. Energy storage devices with a capacitance at 33.3 mF cm⁻² and biochemical sensors show prominent current responses towards metabolites (sensitivity of H₂O₂: 165.6  µ A mm ⁻¹ cm⁻²; sensitivity of DA: 212 nA  µ m ⁻¹ cm⁻²), suggesting that the metal-assisted electro-gelation method will become a prospective technique for advanced fabrication of MXene-based devices.     

Nanostructured CuO/PANI composite as supercapacitor electrode material

An in-situ polymerization method has been employed to prepare CuO/PANI nanocomposite. The prepared samples have been characterized by X-ray diffraction (XRD), FTIR spectroscopy, field emission scanning electron microscopy (FESEM), and BET analysis. Application of the prepared samples has been evaluated as supercapacitor material in 1 M Na₂SO₄ solution using cyclic voltammetry (CV) in different potential scan rates, ranging from 5 to 100 mV s⁻¹, and electrochemical impedance spectroscopy (EIS). The specific capacitance of CuO/PANI has been calculated to be as high as 185 F g⁻¹, much higher than that obtained for pure CuO nanoparticles (76 F g⁻¹). Moreover, the composite material has shown better rate capability (75% capacitance retention) in various scan rates in comparison with the pure oxide (30% retention). EIS results show that the composite material benefits from much lower charge transfer resistance, compared to CuO nanoparticles. Moreover, much better cyclic performance has been achieved for the composite material.     

A New Candidate in Polyanionic Compounds for Potassium Ion Battery Anode: MXene Derived Carbon Coated π-Ti2O(PO4)2

Intercalation-type reaction that occurs in polyanion materials is considered to be a facile way to counter the mismatched relationship between the large K⁺ and compact host structure for potassium ion batteries (PIBs). However, the large “dead” weight and poor conductivity introduced by the polyanion framework severely limit the electrochemical performance of polyanion anodes. Herein, a new rigid K⁺ host of 1D π-Ti₂O(PO₄)₂ with carbon-coated (TOP@C) is simply synthesized through a simple Ti₃C₂T_x-derived method. The density functional theory (DFT) calculations and experimental results show that the potassium storage properties are unquestionably improved by the small cell volume change during cycling, the intercalation pseudo-capacitance energy storage mechanism, and the large K-storage tunnels with lower migration energy (0.23 eV) of TOP@C anode (134.5 mAh g^-1 after 2000 cycles at 1.0 A g^-1). The TOP@C//PTCDA full batteries, which clearly illustrate their promising application in advanced PIBs, successfully achieved a high energy density of 119.4 Wh kg^-1 and a power density up to 632.8 W kg^-1 with regard to the total mass of TOP@C and PTCDA.