Flexible 3D Porous MXene Foam for High‐Performance Lithium‐Ion Batteries

2D transition‐metal carbides and nitrides, named MXenes, are promising materials for energy storage, but suffer from aggregation and restacking of the 2D nanosheets, which limits their electrochemical performance. In order to overcome this problem and realize the full potential of MXene nanosheets, a 3D MXene foam with developed porous structure is established via a simple sulfur‐template method, which is freestanding, flexible, and highly conductive, and can be directly used as the electrode in lithium‐ion batteries. The 3D porous architecture of the MXene foam offers massive active sites to enhance the lithium storage capacity. Moreover, its foam structure facilitates electrolyte infiltration for fast Li⁺ transfer. As a result, this flexible 3D porous MXene foam exhibits significantly enhanced capacity of 455.5 mAh g^?1 at 50 mA g^?1, excellent rate performance (101 mAh g^?1 at 18 A g^?1), and superior ultralong‐term cycle stability (220 mAh g^?1 at 1 A g^?1 after 3500 cycles). This work not only demonstrates the great superiority of the 3D porous MXene foam but also proposes the sulfur‐template method for controllable constructing of the 3D foam from 2D nanosheets at a relatively low temperature.     

Electrostatically Assembling 2D Nanosheets of MXene and MOF‐Derivatives into 3D Hollow Frameworks for Enhanced Lithium Storage

As an essential member of 2D materials, MXene (e.g., Ti₃C₂T_x) is highly preferred for energy storage owing to a high surface‐to‐volume ratio, shortened ion diffusion pathway, superior electronic conductivity, and neglectable volume change, which are beneficial for electrochemical kinetics. However, the low theoretical capacitance and restacking issues of MXene severely limit its practical application in lithium‐ion batteries (LIBs). Herein, a facile and controllable method is developed to engineer 2D nanosheets of negatively charged MXene and positively charged layered double hydroxides derived from ZIF‐67 polyhedrons into 3D hollow frameworks via electrostatic self‐assembling. After thermal annealing, transition metal oxides (TMOs)@MXene (CoO/Co₂Mo₃O₈@MXene) hollow frameworks are obtained and used as anode materials for LIBs. CoO/Co₂Mo₃O₈ nanosheets prevent MXene from aggregation and contribute remarkable lithium storage capacity, while MXene nanosheets provide a 3D conductive network and mechanical robustness to facilitate rapid charge transfer at the interface, and accommodate the volume expansion of the internal CoO/Co₂Mo₃O₈. Such hollow frameworks present a high reversible capacity of 947.4 mAh g^?1 at 0.1 A g^?1, an impressive rate behavior with 435.8 mAh g^?1 retained at 5 A g^?1, and good stability over 1200 cycles (545 mAh g^?1 at 2 A g^?1).     

Ionic Liquid‐Controlled Growth of NiCo2S4 3D Hierarchical Hollow Nanoarrow Arrays on Ni Foam for Superior Performance Binder Free Hybrid Supercapacitors

A significant development in the design of a NiCo₂S₄ 3D hierarchical hollow nanoarrow arrays (HNA)‐based supercapacitor binder free electrode assembled by 1D hollow nanoneedles and 2D nanosheets on a Ni foam collector through controlling ionic liquid 1‐octyl‐3‐methylimidazolium chloride ([OMIm]Cl) concentration is reported. The unique NiCo₂S₄‐HNA electrode acquires high specific capacity (1297 C g^?1 at 1 A g^?1, 2.59 C cm^?2 at 2 mA cm^?2), excellent rate capability (maintaining 73.0% at 20 A g^?1), and long operational life (maintaining 92.4% after 10 000 cycles at 5 A g^?1), which are superior to those for 1D hollow nanoneedle arrays (HNN) and 2D porous nanoflake arrays (PNF). The outstanding electrochemical performance is attributed to the novel 3D structure with large specific surface, hollow cores, high porosity as well as stable architecture. In addition, a hybrid supercapacitor applying 3D NiCo₂S₄‐HNA as the positive electrode and active carbon as the negative electrode exhibits a high energy density of 42.5 Wh kg^?1 at a power density of 2684.2 W kg^?1 in an operating voltage of 1.6 V. Robust cycling stability is also expressed with 84.9% retention after repeating 10 000 cycles at 5 A g^?1, implying their great potential in superior‐performance supercapacitors.     

Metal‐Free 2D/2D Phosphorene/g‐C3N4 Van der Waals Heterojunction for Highly Enhanced Visible‐Light Photocatalytic H2 Production

The generation of green hydrogen (H₂) energy using sunlight is of great significance to solve the worldwide energy and environmental issues. Particularly, photocatalytic H₂ production is a highly promising strategy for solar‐to‐H₂ conversion. Recently, various heterostructured photocatalysts with high efficiency and good stability have been fabricated. Among them, 2D/2D van der Waals (VDW) heterojunctions have received tremendous attention, since this architecture can promote the interfacial charge separation and transfer and provide massive reactive centers. On the other hand, currently, most photocatalysts are composed of metal elements with high cost, limited reserves, and hazardous environmental impact. Hence, the development of metal‐free photocatalysts is desirable. Here, a novel 2D/2D VDW heterostructure of metal‐free phosphorene/graphitic carbon nitride (g‐C₃N₄) is fabricated. The phosphorene/g‐C₃N₄ nanocomposite shows an enhanced visible‐light photocatalytic H₂ production activity of 571 µmol h^?1 g^?1 in 18 v% lactic acid aqueous solution. This improved performance arises from the intimate electronic coupling at the 2D/2D interface, corroborated by the advanced characterizations techniques, e.g., synchrotron‐based X‐ray absorption near‐edge structure, and theoretical calculations. This work not only reports a new metal‐free phosphorene/g‐C₃N₄ photocatalyst but also sheds lights on the design and fabrication of 2D/2D VDW heterojunction for applications in catalysis, electronics, and optoelectronics.     

Co Nanoparticles Confined in 3D Nitrogen‐Doped Porous Carbon Foams as Bifunctional Electrocatalysts for Long‐Life Rechargeable Zn–Air Batteries

Proper design and simple preparation of nonnoble bifunctional electrocatalysts with high cost performance and strong durability for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is highly demanded but still full of enormous challenges. In this work, a spontaneous gas‐foaming strategy is presented to synthesize cobalt nanoparticles confined in 3D nitrogen‐doped porous carbon foams (CoNCF) by simply carbonizing the mixture of citric acid, NH₄Cl, and Co(NO₃)₂·6H₂O. Thanks to its particular 3D porous foam architecture, ultrahigh specific surface area (1641 m² g^?1), and homogeneous distribution of active sites (C–N, Co–N_x, and Co–O moieties), the optimized CoNCF‐1000‐80 (carbonized at 1000 °C, containing 80 mg Co(NO₃)₂·6H₂O in precursors) catalyst exhibits a remarkable bifunctional activity and long‐term durability toward both ORR and OER. Its bifunctional activity parameter (ΔE) is as low as 0.84 V, which is much smaller than that of noble metal catalyst and comparable to state‐of‐the‐art bifunctional catalysts. When worked as an air electrode catalyst in rechargeable Zn–air batteries, a high energy density (797 Wh kg^?1), a low charge/discharge voltage gap (0.75 V), and a long‐term cycle stability (over 166 h) are achieved at 10 mA cm^?2.     

Sulfur‐Deficient Bismuth Sulfide/Nitrogen‐Doped Carbon Nanofibers as Advanced Free‐Standing Electrode for Asymmetric Supercapacitors

The use of free‐standing carbon‐based hybrids plays a crucial role to help fulfil ever‐increasing energy storage demands, but is greatly hindered by the limited number of active sites for fast charge adsorption/desorption processes. Herein, an efficient strategy is demonstrated for making defect‐rich bismuth sulfides in combination with surface nitrogen‐doped carbon nanofibers (dr‐Bi₂S₃/S‐NCNF) as flexible free‐standing electrodes for asymmetric supercapacitors. The dr‐Bi₂S₃/S‐NCNF composite exhibits superior electrochemical performances with an enhanced specific capacitance of 466 F g^?1 at a discharge current density of 1 A g^?1. The high performance of dr‐Bi₂S₃/S‐NCNF electrodes originates from its hierarchical structure of nitrogen‐doped carbon nanofibers with well‐anchored defect‐rich bismuth sulfides nanostructures. As modeled by density functional theory calculation, the dr‐Bi₂S₃/S‐NCNF electrodes exhibit a reduced OH^? adsorption energy of ‐3.15 eV, compared with that (–3.06 eV) of defect‐free bismuth sulfides/surface nitrogen‐doped carbon nanofiber (df‐Bi₂S₃/S‐NCNF). An asymmetric supercapacitor is further fabricated by utilizing dr‐Bi₂S₃/S‐NCNF hybrid as the negative electrode and S‐NCNF as the positive electrode. This composite exhibits a high energy density of 22.2 Wh kg^?1 at a power density of 677.3 W kg^?1. This work demonstrates a feasible strategy to construct advanced metal sulfide‐based free‐standing electrodes by incorporating defect‐rich structures using surface engineering principles.     

Novel Co2VO4 Anodes Using Ultralight 3D Metallic Current Collector and Carbon Sandwiched Structures for High‐Performance Li‐Ion Batteries

A novel spinel Co₂VO₄ is studied as the Li‐ion battery anode material and it is sandwiched with a 3D ultralight porous current collector (PCC) and amorphous carbon. Co₂VO₄ demonstrates the high capacity and excellent cyclability because of the mixed lithium storage mechanisms. The 3D composite structure requires no binders and replaces the conventional current collector (Cu foil) with a 3D ultralight porous metal scaffold, yielding the high electrode‐based capacity. Such a novel composite anode also enables the close adhesion of Co₂VO₄ to the PCC scaffold. The resulting monolithic electrode has the rapid electron pathway and stable mechanical properties, which lead to the excellent rate capabilities and cycling properties. At a current density of 1 A g^?1, the PCC and carbon sandwiched Co₂VO₄ anode is able to deliver a stable reversible capacity of about 706.8 mAh g^?1 after 1000 cycles. Generally, this study not only develops a new Co₂VO₄ anode with high capacity and good cyclability, but also demonstrates an alternative approach to improve the electrochemical properties of high capacity anode materials by using ultralight porous metallic current collector instead of heavy copper foil.     

Ultrahigh‐Sensitive Broadband Photodetectors Based on Dielectric Shielded MoTe2/Graphene/SnS2 p–g–n Junctions

2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next‐generation optoelectronics since they can be stacked layer‐by‐layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice‐mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h‐BN/p‐MoTe₂/graphene/n‐SnS₂/h‐BN p–g–n junction, fabricated by a layer‐by‐layer dry transfer, demonstrates high‐sensitivity, broadband photodetection at room temperature. The combination of the MoTe₂ and SnS₂ of complementary bandgaps, and the graphene interlayer provides a unique vdW heterostructure with a vertical built‐in electric field for high‐efficiency broadband light absorption, exciton dissociation, and carrier transfer. The graphene interlayer plays a critical role in enhancing sensitivity and broadening the spectral range. An optimized device containing 5?7‐layer graphene has been achieved and shows an extraordinary responsivity exceeding 2600 A W^?1 with fast photoresponse and specific detectivity up to ≈10¹³ Jones in the ultraviolet–visible–near‐infrared spectrum. This result suggests that the vdW p–g–n junctions containing multiple photoactive TMDs can provide a viable approach toward future ultrahigh‐sensitivity and broadband photonic detectors.     

Ultrathin 2D Mesoporous TiO2/rGO Heterostructure for High‐Performance Lithium Storage

Lithium‐ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO₂), with a high theoretical capacity (335 mAh g^?1) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO₂ is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO₂/reduced graphene (rGO) heterostructure is fabricated via a layer‐by‐layer assembly process. The synergistic effect of ultrathin mesoporous TiO₂ and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g^?1 at a current density of 200 mA g^?1 and excellent cycling stability, with a capacity of 245 mAh g^?1 maintained over 1000 cycles at a high current density of 1 A g^?1. The in situ transmission electron microscopy analysis indicates that the volume of the as‐prepared 2D heterostructures changes slightly upon the insertion and extraction of Li⁺, thus contributing to the enhanced long‐cycle performance.     

A Flexible Film toward High‐Performance Lithium Storage: Designing Nanosheet‐Assembled Hollow Single‐Hole Ni–Co–Mn–O Spheres with Oxygen Vacancy Embedded in 3D Carbon Nanotube/Graphene Network

Ternary transition metal oxides (TMOs) are highly potential electrode materials for lithium ion batteries (LIBs) due to abundant defects and synergistic effects with various metal elements in a single structure. However, low electronic/ionic conductivity and severe volume change hamper their practical application for lithium storage. Herein, nanosheet‐assembled hollow single‐hole Ni–Co–Mn oxide (NHSNCM) spheres with oxygen vacancies can be obtained through a facile hydrothermal reaction, which makes both ends of each nanosheet exposed to sufficient free space for volume variation, electrolyte for extra active surface area, and dual ion diffusion paths compared with airtight hollow structures. Furthermore, oxygen vacancies could improve ion/electronic transport and ion insertion/extraction process of NHSNCM spheres. Thus, oxygen‐vacancy‐rich NHSNCM spheres embedded into a 3D porous carbon nanotube/graphene network as the anode film ensure efficient electrolyte infiltration into both the exterior and interior of porous and open spheres for a high utilization of the active material, showing an excellent electrochemical performance for LIBs (1595 mAh g^?1 over 300 cycles at 2 A g^?1, 441.6 mAh g^?1 over 4000 cycles at 10 A g^?1). Besides, this straightforward synthetic method opens an efficacious avenue for the construction of various nanosheet‐assembled hollow single‐hole TMO spheres for potential applications.     

Ni2P@Carbon Core–Shell Nanoparticle‐Arched 3D Interconnected Graphene Aerogel Architectures as Anodes for High‐Performance Sodium‐Ion Batteries

To alleviate large volume change and improve poor electrochemical reaction kinetics of metal phosphide anode for sodium‐ion batteries, for the first time, an unique Ni₂P@carbon/graphene aerogel (GA) 3D interconnected porous architecture is synthesized through a solvothermal reaction and in situ phosphorization process, where core–shell Ni₂P@C nanoparticles are homogenously embedded in GA nanosheets. The synergistic effect between components endows Ni₂P@C/GA electrode with high structural stability and electrochemical activity, leading to excellent electrochemical performance, retaining a specific capacity of 124.5 mA h g^?1 at a current density of 1 A g^?1 over 2000 cycles. The robust 3D GA matrix with abundant open pores and large surface area can provide unblocked channels for electrolyte storage and Na⁺ transfer and make fully close contact between the electrode and electrolyte. The carbon layers and 3D GA together build a 3D conductive matrix, which not only tolerates the volume expansion as well as prevents the aggregation and pulverization of Ni₂P nanoparticles during Na⁺ insertion/extraction processes, but also provides a 3D conductive highway for rapid charge transfer processes. The present strategy for phosphides via in situ phosphization route and coupling phosphides with 3D GA can be extended to other novel electrodes for high‐performance energy storage devices.     

SnSe/MoS2 van der Waals Heterostructure Junction Field‐Effect Transistors with Nearly Ideal Subthreshold Slope

The minimization of the subthreshold swing (SS) in transistors is essential for low‐voltage operation and lower power consumption, both critical for mobile devices and internet of things (IoT) devices. The conventional metal‐oxide‐semiconductor field‐effect transistor requires sophisticated dielectric engineering to achieve nearly ideal SS (60 mV dec^?1 at room temperature). However, another type of transistor, the junction field‐effect transistor (JFET) is free of dielectric layer and can reach the theoretical SS limit without complicated dielectric engineering. The construction of a 2D SnSe/MoS₂ van der Waals (vdW) heterostructure‐based JFET with nearly ideal SS is reported. It is shown that the SnSe/MoS₂ vdW heterostructure exhibits excellent p–n diode rectifying characteristics with low saturate current. Using the SnSe as the gate and MoS₂ as the channel, the SnSe/MoS₂ vdW heterostructure exhibit well‐behavioured n‐channel JFET characteristics with a small pinch‐off voltage V_P of ?0.25 V, nearly ideal subthreshold swing SS of 60.3 mV dec^?1 and high ON/OFF ratio over 10⁶, demonstrating excellent electronic performance especially in the subthreshold regime.     

Spontaneous Formation of Noble‐ and Heavy‐Metal‐Free Alloyed Semiconductor Quantum Rods for Efficient Photocatalysis

Quasi‐1D cadmium chalcogenide quantum rods (QRs) are benchmark semiconductor materials that are combined with noble metals to constitute QR heterostructures for efficient photocatalysis. However, the high toxicity of cadmium and cost of noble metals are the main obstacles to their widespread use. Herein, a facile colloidal synthetic approach is reported that leads to the spontaneous formation of cadmium‐free alloyed ZnS_xSe_1?x QRs from polydisperse ZnSe nanowires by alkylthiol etching. The obtained non‐noble‐metal ZnS_xSe_1?x QRs can not only be directly adopted as efficient photocatalysts for water oxidation, showing a striking oxygen evolution capability of 3000 µmol g^?1 h^?1, but also be utilized to prepare QR‐sensitized TiO₂ photoanodes which present enhanced photo‐electrochemical (PEC) activity. Density functional theory (DFT) simulations reveal that alloyed ZnS_xSe_1?x QRs have highly active Zn sites on the (100) surface and reduced energy barrier for oxygen evolution, which in turn, are beneficial to their outstanding photocatalytic and PEC activities.     

3D Interconnected and Multiwalled Carbon@MoS2@Carbon Hollow Nanocables as Outstanding Anodes for Na‐Ion Batteries

Currently, the specific capacity and cycling performance of various MoS₂/carbon‐based anode materials for Na‐ion storage are far from satisfactory due to the insufficient structural stability of the electrode, incomplete protection of MoS₂ by carbon, difficult access of electrolyte to the electrode interior, as well as inactivity of the adopted carbon matrix. To address these issues, this work presents the rational design and synthesis of 3D interconnected and hollow nanocables composed of multiwalled carbon@MoS₂@carbon. In this architecture, (i) the 3D nanoweb‐like structure brings about excellent mechanical property of the electrode, (ii) the ultrathin MoS₂ nanosheets are sandwiched between and doubly protected by two layers of porous carbon, (iii) the hollow structure of the primary nanofibers facilitates the access of electrolyte to the electrode interior, (iv) the porous and nitrogen‐doping properties of the two carbon materials lead to synergistic Na‐storage of carbon and MoS₂. As a result, this hybrid material as the anode material of Na‐ion battery exhibits fast charge‐transfer reaction, high utilization efficiency, and ultrastability. Outstanding reversible capacity (1045 mAh g^?1), excellent rate behavior (817 mAh g^?1 at 7000 mA g^?1), and good cycling performance (747 mAh g^?1 after 200 cycles at 700 mA g^?1) are obtained.     

Boosting the Reversibility of Sodium Metal Anode via Heteroatom‐Doped Hollow Carbon Fibers

Sodium (Na) metal anodes stand out with their remarkable capacity and natural abundance. However, the dendritic Na growth, infinite dimensional changes, and low Coulombic efficiency (CE) present key bottlenecks plaguing practical applications. Here, heteroatom‐doped (nitrogen, sulfur) hollow carbon fibers (D‐HCF) are rationally synthesized as a nucleation‐assisting host to enable a highly reversible Na metal. The “sodiophilic” functional groups introduced by the heteroatom‐doping and large surface area (≈1052 m² g^?1) synchronously contribute to a homogenous plating morphology with dissipated local current density. High “sodiophilicity” of the D‐HCF is confirmed by first‐principle calculations and experimental results, where strong adsorption energy of ?3.52 eV with low Na⁺ nucleation overpotential of 3.2 mV at 0.2 mA cm^?2 is realized. As such, highly reversible plating/stripping is achieved at 1.0 mA cm^?2 with average CE approximating 99.52% over 600 cycles. The as‐assembled Na@D‐HCF symmetric cells exhibit a prolonged lifetime for 1000 h. A full‐cell paired with Na₃V₂(PO₄)₃ cathode further demonstrates stable electrochemical behavior for 200 cycles at 1 C along with excellent rate performance (102 mAh g^?1 at 5 C). The results clearly show the effectiveness of the D‐HCF in manipulating Na⁺ deposition and thus the significance of nucleation control in realizing dendrite‐free metal anodes.     

Micro‐Blooming: Hierarchically Porous Nitrogen‐Doped Carbon Flowers Derived from Metal‐Organic Mesocrystals

Synthesis of 3D flower‐like zinc‐nitrilotriacetic acid (ZnNTA) mesocrystals and their conformal transformation to hierarchically porous N‐doped carbon superstructures is reported. During the solvothermal reaction, 2D nanosheet primary building blocks undergo oriented attachment and mesoscale assembly forming stacked layers. The secondary nucleation and growth preferentially occurs at the edges and defects of the layers, leading to formation of 3D flower‐like mesocrystals comprised of interconnected 2D micropetals. By simply varying the pyrolysis temperature (550–1000 °C) and the removal method of in the situ‐generated Zn species, nonporous parent mesocrystals are transformed to hierarchically porous carbon flowers with controllable surface area (970–1605 m² g^?1), nitrogen content (3.4–14.1 at%), pore volume (0.95–2.19 cm³ g^?1), as well as pore diameter and structures. The carbon flowers prepared at 550 °C show high CO₂/N₂ selectivity due to the high nitrogen content and the large fraction of (ultra)micropores, which can greatly increase the CO₂ affinity. The results show that the physicochemical properties of carbons are highly dependent on the thermal transformation and associated pore formation process, rather than directly inherited from parent precursors. The present strategy demonstrates metal‐organic mesocrystals as a facile and versatile means toward 3D hierarchical carbon superstructures that are attractive for a number of potential applications.     

3D Hollow α‐MnO2 Framework as an Efficient Electrocatalyst for Lithium–Oxygen Batteries

Lithium–oxygen (Li–O₂) batteries are attracting more attention owing to their superior theoretical energy density compared to conventional Li‐ion battery systems. With regards to the catalytically electrochemical reaction on a cathode, the electrocatalyst plays a key role in determining the performance of Li–O₂ batteries. Herein, a new 3D hollow α‐MnO₂ framework (3D α‐MnO₂) with porous wall assembled by hierarchical α‐MnO₂ nanowires is prepared by a template‐induced hydrothermal reaction and subsequent annealing treatment. Such a distinctive structure provides some essential properties for Li–O₂ batteries including the intrinsic high catalytic activity of α‐MnO₂, more catalytic active sites of hierarchical α‐MnO₂ nanowires on 3D framework, continuous hollow network and rich porosity for the storage of discharge product aggregations, and oxygen diffusion. As a consequence, 3D α‐MnO₂ achieves a high specific capacity of 8583 mA h g^?1 at a current density of 100 mA g^?1, a superior rate capacity of 6311 mA h g^?1 at 300 mA g^?1, and a very good cycling stability of 170 cycles at a current density of 200 mA g^?1 with a fixed capacity of 1000 mA h g^?1. Importantly, the presented design strategy of 3D hollow framework in this work could be extended to other catalytic cathode design for Li–O₂ batteries.     

Electrospun N‐Doped Porous Carbon Nanofibers Incorporated with NiO Nanoparticles as Free‐Standing Film Electrodes for High‐Performance Supercapacitors and CO2 Capture

Carbon nanofibers (CNF) with a 1D porous structure offer promising support to encapsulate transition‐metal oxides in energy storage/conversion relying on their high specific surface area and pore volume. Here, the preparation of NiO nanoparticle‐dispersed electrospun N‐doped porous CNF (NiO/PCNF) and as free‐standing film electrode for high‐performance electrochemical supercapacitors is reported. Polyacrylonitrile and nickel acetylacetone are selected as precursors of CNF and Ni sources, respectively. Dicyandiamide not only improves the specific surface area and pore volume, but also increases the N‐doping level of PCNF. Benefiting from the synergistic effect between NiO nanoparticles (NPs) and PCNF, the prepared free‐standing NiO/PCNF electrodes show a high specific capacitance of 850 F g^?1 at a current density of 1 A g^?1 in 6 m KOH aqueous solution, good rate capability, as well as excellent long‐term cycling stability. Moreover, NiO NPs dispersed in PCNF and large specific surface area provide many electroactive sites, leading to high CO₂ uptake, and high‐efficiency CO₂ electroreduction. The synthesis strategy in this study provides a new insight into the design and fabrication of promising multifunctional materials for high‐performance supercapacitors and CO₂ electroreduction.     

3D Printing of Freestanding MXene Architectures for Current‐Collector‐Free Supercapacitors

Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1–3 nm) 2D Ti₃C₂T_x with large lateral size of about 8 µm possessing ideal viscoelastic properties are formulated for extrusion‐based 3D printing of freestanding, high specific surface area architectures to determine the viability of manufacturing energy storage devices. The 3D‐printed device achieves a high areal capacitance of 2.1 F cm^?2 at 1.7 mA cm^?2 and a gravimetric capacitance of 242.5 F g^?1 at 0.2 A g^?1 with a retention of above 90% capacitance for 10 000 cycles. It also exhibits a high energy density of 0.0244 mWh cm^?2 and a power density of 0.64 mW cm^?2 at 4.3 mA cm^?2. It is anticipated that the sustainable printing and design approach developed in this work can be applied to fabricate high‐performance bespoke multiscale and multidimensional architectures of functional and structural materials for integrated devices in various applications.     

Carbon‐Nanotube‐Confined Vertical Heterostructures with Asymmetric Contacts

Van der Waals (vdW) heterostructures have received intense attention for their efficient stacking methodology with 2D nanomaterials in vertical dimension. However, it is still a challenge to scale down the lateral size of vdW heterostructures to the nanometer and make proper contacts to achieve optimized performances. Here, a carbon‐nanotube‐confined vertical heterostructure (CCVH) is employed to address this challenge, in which 2D semiconductors are asymmetrically sandwiched by an individual metallic single‐walled carbon nanotube (SWCNT) and a metal electrode. By using WSe₂ and MoS₂, the CCVH can be made into p‐type and n‐type field effect transistors with high on/off ratios even when the channel length is 3.3 nm. A complementary inverter was further built with them, indicating their potential in logic circuits with a high integration level. Furthermore, the Fermi level of SWCNTs can be efficiently modulated by the gate voltage, making it competent for both electron and hole injection in the CCVHs. This unique property is shown by the transition of WSe₂ CCVH from unipolar to bipolar, and the transition of WSe₂/MoS₂ from p–n junction to n–n junction under proper source–drain biases and gate voltages. Therefore, the CCVH, as a member of 1D/2D mixed heterostructures, shows great potentials in future nanoelectronics and nano‐optoelectronics.