Dual Confinement Research Articles

Physical and Chemical Dual Confinement Promotes Controllable Synthesis of Loose-Structured Azine-Linked Nanofilms for Fast Molecular Separation.

Thin-film composite (TFC) membranes, featuring nanoscale film thickness and customizable pore structures, hold promise for solute-solute separations. However, achieving on-demand molecular sieving requires fine control over the membrane microstructure. Here, the concept of physical and chemical dual confinement (PCDC) is introduced to fabricate loose-structured TFC membranes via confined interfacial polymerization (IP). This concept leverages the synergistic effects of physically restricted monomer diffusion and a chemically inhibited reaction to achieve controlled nanofilm growth. Dorsal addition of the aqueous phase to the hydrogel reduces the diamine diffusion via electrostatic and H-bonding interactions within its nanopores. The prepassivation of hydrazine using acid protonation effectively weakens its ability for nucleophilic reactivity. This confined IP between twisted TFPA and short-chain hydrazine yielded loosely structured azine-linked nanofilms, which displayed a high permeability of 53.4 LMH bar-1 and effective differentiation of binary mixtures. This PCDC concept offers a useful guideline to finely tailor polymeric nanofilms for precise separations.

Sulfur Distribution Analysis in Lithium−Sulfur Cathode via Confined Inverse Vulcanization in Carbon Frameworks

AbstractLithium–Sulfur (Li–S) batteries are promising energy storage devices due to their high theoretical energy density. However, challenges such as the shuttling effect and volume expansion have significantly hindered their cycle life and capacity retention. Furthermore, the complex kinetic pathways in Li–S batteries call for advanced characterization techniques to unravel underlying mechanisms. In this study, a hollow porous carbon (HPC) is used as a microreactor, where inverse vulcanization occurs between 1,3‐diisopropylbenzene (DIB) and sulfur (S8), resulting in the creation of three‐dimensionally interconnected and well‐distributed S‐DIB in carbon frameworks. As a result, the dual confinement strategy imparts Li–S coin cells with remarkable cycling stability and capacity retention, exhibiting an impressive capacity of 866 mAh g−1 when returning to 0.1 C after 100 cycles of rate capability tests. Particularly, the Energy‐selective Backscattered (EsB) assisted Scanning Electron Microscope (SEM) technique as a novel approach is introduced to distinguish different lengths of polysulfides. Their distribution is visualized in the cross‐section view of the electrode in a micrometer range. These EsB images provide concrete indications of the sulfur evolution process and explain the capacity degradation during cycling.

Behavior of FRP-interlayer-steel confined concrete columns subjected to eccentric compression

Fiber reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) columns are proposed by bonding a filament-wound FRP tube with a concrete-filled steel tube (CFST) using grouting material to increase the corrosion resistance of CFST columns. FISC columns have high bearing capacity, benefiting from the dual confinement provided by both FRP and steel tubes on the core concrete. Despite this, the current research on the behaviors of FISC columns is limited, particularly regarding the confinement mechanism in FISC columns under eccentric compression. In this paper, a total of twenty short specimens were tested under eccentric compression, including seventeen FISC specimens, two FRP confined concrete-filled steel tubular (CCFT) columns, and one CFST specimen. Failure modes, load versus deflection curves and strain development for FISC specimens were presented and discussed, considering variations in eccentricity, FRP types, FRP thicknesses, and the ratio of FRP and steel confining indexes. Additionally, confining stresses of the FRP and steel tubes were obtained, revealing a non-uniform distribution of confinement on concrete along the sectional circumference, which decreased with increasing eccentricity. Furthermore, by regarding the concrete and grouting material as a whole unity and accounting for the influence of eccentricity, a sectional numerical analysis model for FISC columns was established and validated against test results, and the influences of steel thickness, FRP thickness, and concrete-grouting strength on the N-M correlation curves of FISC columns were investigated.

Synergistic Triple-Action morphological composite Anode: Integrating lattice Softening, Interfacial electric Fields, and dual confinement for superior Potassium-Ion battery performance

Synergistic effects could significantly improve slow redox kinetics and structural pulverization of electrodes in potassium ion batteries (PIBs); however, the performance of single synergistic designs is limited. Multi-synergistic composite, shaped by a blend of factors, substantially boosts performance, yielding outcomes that surpass single synergistic coupling design. Herein, we develop a Bi2Se3/Sb2Se3@NC@G electrode that integrates three key features for enhanced potassium-ion storage: p-n junctions enhance electron transfer through internal electric fields, dual confinement prevents K2Se dissolution into the electrolyte, and lattice softening in the Bi-Sb alloy relieves stress during potassium ion insertion/extraction. These multi-synergistic effects enable the heterostructure to exhibit superior electrochemical performance in potassium-ion batteries.The Bi2Se3/Sb2Se3@NC@G electrode demonstrates notable capacity of 640 mA h g-1 at current density of 50 mA g-1, achieving 95.5 % of its theoretical capacity, maintain stable capacity of 310 mA h g−1 after 5000 cycles at current density of 0.5 A/g with 0.002 % per cycle degradation, and exhibits the fastest rate capability up to 10 A/g (172 mA h g−1). Furthermore, potassium ion hybrid capacitor (PIHC) can achieve a high energy density of 118 Wh kg−1 and a power density of 5200 W kg−1, and full cell shows an attractive energy density of 97 Wh kg-1 and a stable performance after 250 cycling number under 1 A g-1. This study proposes an effective strategy that employs multiple synergistic coupling designs to maximize potassium-ion storage capacity, achieving a breakthrough in extending battery lifecycle.

Carbon and MXene Dual Confinement and Dense Structural Engineering Toward Construct High Performance Micron‐SiOx Anode for Li‐Ion Batteries

AbstractThe intrinsic low conductivity, low tap density, and huge volume expansion during lithium storage severely restrict the practicality of micron‐silicon suboxide (m‐SiOx). Here, a carbon and MXene dual confinement and dense structural engineering strategy is proposed to construct m‐SiOx composites (m‐SiOx@C/MXene) through in situ carbon coating and electrostatic self‐assembly process. This integrated structural achieves a conductivity of 157 S cm−1 for m‐SiOx@C/MXene, which is 7 and 2 orders of magnitude higher than m‐SiOx (5.3 × 10−5 S cm−1) and m‐SiOx@C (2.9 S cm−1), respectively. The tap density of m‐SiOx@C/MXene reaches 1.35 g cm−3, significantly greater than that of m‐SiOx (0.82 g cm−3) and m‐SiOx@C (0.75 g cm−3). The 29% volume expansion of m‐SiOx@C/MXene during lithium storage is much lower than the 228% and 162% of m‐SiOx and m‐SiOx@C. The synergistic effect of the above advantages enables m‐SiOx@C/MXene to exhibit excellent rate performance and cycle stability. When assembled into a full cell with the LiFePO4 (LFP) cathode, it features high capacity retention and energy density of 99.1% and 380 Wh kg−1 after 100 cycles at 0.2 C. This work provides new reference for the stable structural design of m‐SiOx or other materials with huge volume expansion during energy storage.

Dual confinement of RuOx nanoparticle using polar MnNiO and armored carbon for boosting water electrolysis

The poor stability of nanoparticle catalysts with catalytic activity is a significant obstacle to their industrial application. The establishment of rational nanoparticle structures to elucidate the relationship between catalyst structure and its catalytic activity and stability is crucial for constructing nanoparticle catalysts that are both highly active and stable. We propose a strategy to construct a dual-confinement effect of the nanoparticle, specifically by regulating the polarization of the MnNiO support to enhance strong oxide-support interactions (SOSI) and encapsulating the outer layer of nanoparticles with a carbon shell, which has been proven effective in improving the activity and stability of nanoparticle-based oxygen evolution reaction (OER) electrocatalysts. At a current density of 100 mA cm−2, the armor C@RuOx@MnNiO catalyst displays an overpotential of 260 mV for the OER. After the OER test for 100 h, the current density of C@RuOx@MnNiO shows no significant decay, whereas that of RuOx@MnNiO and RuOx@MnO rapidly decreases, indicating significant catalytic activity and stability of the catalyst. The assembled C@RuOx@MnNiO||Pt/C electrode demonstrates excellent alkaline water electrolysis performance in an MEA electrolyzer, requiring only a low cell voltage of 1.76 V to achieve an ampere-level current density of 1 A cm−2. In-situ electrochemical Raman spectroscopy reveals the significant interaction between nanoparticles and the polar support. The reduction in Gibbs free energy, which establishes the rate-determining step (RDS) of OER, is caused by the charge redistribution caused by polar Mn doping in RuOx@MnNiO and the coordination structure modifications, as shown by density functional theory calculations. This work provides an approach to designing efficient and stable nanoparticle electrocatalysts through the dual-confinement effect of SOSI-induced strong interactions and armor carbon layers.

Design dual confinement Ni@S-1@SiO2 catalyst with enhanced carbon resistance for methane dry reforming

Methane dry reforming is a key method for converting greenhouse gases into valuable syngas, providing a pathway for the sustainable production of valuable compounds. Yet the challenges like particle sintering and carbon deposition have hindered the widespread application of nickel-based catalysts. This study explores innovative strategies to overcome these challenges by using zeolite supports to enhance nickel dispersity and prevent carbon deposition, as well as adopting core-shell structures to prevent metal sintering and carbon deposition. In pursuit of enhancing methane dry reforming efficacy, a Ni@S-1@SiO2 dual-shell nickel-based catalyst is designed in this study to confine exposed nickel particles on the S-1 surface within a robust mesoporous silica shell, reducing nickel particle mobility and preventing active site oxidation, thereby increasing resistance to sintering and carbon deposition. Compared to conventional single-core-shell catalysts, this design significantly reduces nickel particle mobility and active site oxidation, enhancing resistance to sintering and coking. It showed virtually no carbon deposition even after a rigorous 25-h reaction at 650 °C. In-situ DRIFTS analyses provided further insights into the underlying mechanism, confirming a Langmuir-Hinshelwood mechanism and highlighting the beneficial role of formates in preventing coke deposition. This study not only advances the understanding of core-shell catalyst structures but also paves the way for optimized nickel-based catalysts in methane dry reforming, promoting a sustainable future for syngas production.

Modulating adsorption-oxidation dual sites and confinement structure of interlayered MnO2/defective rGO nanoreactor for efficient and stable catalytic ozonation of CH3SH

The design of catalyst structure and adsorption-oxidation sites is of great significance for catalytic ozonation to eliminate sulfur-containing volatile organic compounds (S-VOCs). Herein, a well-defined 2D/2D interlayered DrGO/MnO2-Vo consisting of oxygen vacancy-rich (Vo) MnO2 and defective reduced graphene oxide (DrGO) was successfully synthesized by face-to-face electrostatic self-assembly method. DrGO/MnO2-Vo with delimited void space could be employed as confined nanoreactor to boost reactive oxygen species (ROS) yields and improve mass transfer, thus achieving excellent methyl mercaptan (CH3SH) removal efficiency (82.4 %). The experimental results revealed that the DrGO/MnO2-Vo catalyst could still remove ∼74 % of CH3SH after running for 60 h at 25 ℃ with an initial concentration of 80 ppm CH3SH, 2 mg/L ozone, and a gas hourly space velocity (GHSV) of 60,000 mL/(h⋅g). The essence of the outstanding stability and durability of DrGO/MnO2-Vo lied in its role as an active dual-site catalyst, in which CH3SH was preferentially enriched on DrGO nanosheets and subsequently oxidized by ROS generated by ozone decomposition on the oxygen vacancies of MnO2 nanosheets. Additionally, the cycling redox of Mn2+/Mn3+→Mn4+→Mn2+/Mn3+ could regenerate oxygen vacancies of MnO2. This research offered novel perspectives on tackling the control issues related to S-VOCs.

Design of Ultrathin Asymmetric Composite Electrolytes for Interfacial Stable Solid-State Lithium-Metal Batteries.

Ultrathin composite electrolytes hold great promise for high energy density solid-state lithium metal batteries (SSLMBs). However, finding an electrolyte that can simultaneously balance the interfacial stability of the lithium anode and high-voltage cathode is challenging. The present study utilized the both-side tape casting technique to fabricate ultrathin asymmetric composite electrolytes reinforced with polyimide (PI) fiber membrane, with a thickness of 26.8 μm. The implementation of this asymmetric structural design enables SSLMBs to attain favorable interfacial characteristics, such as exceptional resistance to lithium dendrite puncture and compatibility with high voltages. The suppression of lithium dendrite growth and the extension of the cycle life of lithium symmetric batteries by 4000 h are both experimental and theoretically demonstrated under the dual confinement of PI fiber membrane and Li7La3Zr2O12 ceramic fibers. Furthermore, the integration of multicomponent solid electrolyte interphase and cathode electrolyte interface interfacial layers into the lithium anode and high-voltage cathode enhance theirs cycling stability. With a gravimetric/volumetric energy density of 333.1 Wh kg-1/713.2 Wh L-1, the assembled LiNi0.8Co0.1Mn0.1O2 pouch cell demonstrates exceptional safety. The extensive application of this design concept to SSLMBs enables the resolution of electrode/electrolyte interface issues.

Constructing hierarchical MoS2/WS2 heterostructures in dual carbon layer for enhanced sodium ions batteries performance

The escalating global demand for clean energy has spurred substantial interest in sodium-ion batteries (SIBs) as a promising solution for large-scale energy storage systems. However, the insufficient reaction kinetics and considerable volume changes inherent to anode materials present significant hurdles to enhancing the electrochemical performance of SIBs. In this study, hierarchical MoS2/WS2 heterostructures were constructed into dual carbon layers (HC@MoS2/WS2@NC) and assessed their suitability as anodes for SIBs. The internal hard carbon core (HC) and outer nitrogen-doped carbon shell (NC) effectively anchor MoS2/WS2, thereby significantly improving its structural stability. Moreover, the conductive carbon components expedite electron transport during charge–discharge processes. Critically, the intelligently engineered interface between MoS2 and WS2 modulates the interfacial energy barrier and electric field distribution, promoting faster ion transport rates. Capitalizing on these advantageous features, the HC@MoS2/WS2@NC nanocomposite exhibits outstanding electrochemical performance when utilized as an anode in SIBs. Specifically, it delivers a high capacity of 415 mAh/g at a current density of 0.2 A/g after 100 cycles. At a larger current density of 2 A/g, it maintains a commendable capacity of 333 mAh/g even after 1000 cycles. Additionally, when integrated into a full battery configuration with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@MoS2/WS2@NC full cell delivers a high capacity of 120 mAh/g after 300 cycles at 1 A/g. This work emphasizes the substantial improvement in battery performance that can be attained through the implementation of dual carbon confinement, offering a constructive approach to guide the design and development of next-generation anode materials for SIBs.

Atomically Precise Single-Site Catalysts via Exsolution in a Polyoxometalate-Metal-Organic-Framework Architecture.

Single-site catalysts (SSCs) achieve a high catalytic performance through atomically dispersed active sites. A challenge facing the development of SSCs is aggregation of active catalytic species. Reducing the loading of these sites to very low levels is a common strategy to mitigate aggregation and sintering; however, this limits the tools that can be used to characterize the SSCs. Here we report a sintering-resistant SSC with high loading that is achieved by incorporating Anderson-Evans polyoxometalate clusters (POMs, MMo6O24, M = Rh/Pt) within NU-1000, a Zr-based metal-organic framework (MOF). The dual confinement provided by isolating the active site within the POM, then isolating the POMs within the MOF, facilitates the formation of isolated noble metal sites with low coordination numbers via exsolution from the POM during activation. The high loading (up to 3.2 wt %) that can be achieved without sintering allowed the local structure transformation in the POM cluster and the surrounding MOF to be evaluated using in situ X-ray scattering with pair distribution function (PDF) analysis. Notably, the Rh/Pt···Mo distance in the active catalyst is shorter than the M···M bond lengths in the respective bulk metals. Models of the active cluster structure were identified based on the PDF data with complementary computation and X-ray absorption spectroscopy analysis.

Engineering Pt single atom catalyst with abundant lattice oxygen by dual nanospace confinement strategy for the efficient catalytic elimination of VOCs

Precisely constructing Pt single atom catalyst (SACs) with fine-tuned chemical environments is a vitally challenging issue, which has attracted peoples’ attentions. The activation of lattice oxygen linked to active sites is also a great challenge to heterogeneous catalysis. Herein, via a cage-encapsulating strategy, Pt single atom (SA) was accurately constructed by dual nanospace confinement of three-dimensional ordered macroporous (3DOM) CeO2 pore and Ce-MOFs nanocages. During calcination, CeO2 derived from Ce-MOF restricted the migration of Pt SA and prevented its agglomeration. With the construction of CeO2 nanocage, more active Pt-O2 bond was created. More active lattice oxygen was linked to Pt single atom. DFT calculation also confirmed VOCs molecules were more easily absorbed on the catalyst surface and CO was more easily oxidized to CO2. The 90% conversion temperature (T90) of Pt1/CeO2 @CeO2-0.2 (T90 = 268 °C) was 81 °C lower than the T90 of Pt1/CeO2 (T90 = 349 °C) on the catalytic combustion of benzene.

Nucleation-Supersaturation Dual-Drive Crystallization Strategy Enables Efficient Protein Crystallization.

A rational crystallization strategy is essential to obtain high-quality protein crystals, yet the established methods suffer from different limitations arising from the single regulation on either nucleation or supersaturation. Herein, a nucleation-supersaturation dual-driven crystallization (DDC) strategy that realizes synergistic regulation of heterogeneous nucleation sites and solution supersaturation based on dual surface and confinement effects for efficient protein crystallization is reported. This strategy relies on a p(PEGDA-co-DMAA) hydrogel template with pre-filled NaCl under designed concentrations. Once dropping hen egg white lysozyme (HEWL) protein solution on the hydrogel, the wrinkled surface provides numerous nucleation sites, while the internal structure regulates the solution supersaturation in the crystallization region through diffusion. Finally, DDC strategy can create high-quality HEWL crystals with large sizes (100-300µm), well-defined morphologies (hexagon and tetragon), and a significantly accelerated nucleation time (9-12 times faster than that achieved using the conventional hanging drop method). It also performs well at wider protein concentrations (10-50mgmL-1) and categories (e.g., achieving fast crystallization and large-size crystals of trypsin), therefore demonstrating clear advantages and great potential for efficiently fabricating protein crystals desirable for diverse applications.

Dual carbon confined MoS2 hierarchical microspheres as high-performance anode for sodium-ion batteries with superior cycling stability

Due to the growing demand in the energy market, sodium-ion batteries (SIBs) have garnered significant attention as potential energy storage devices for large-scale applications. However, the sluggish kinetics and significant volume expansion during cycling bring about the poor electrochemical behavior of SIBs. In this work, a dual carbon including internal hard carbon core and external N-doped carbon shell confined MoS2 hierarchical microspheres (HC@MoS2@NC) nanocomposites are prepared as anode for SIBs with superior cycling stability and good rate capability. The dual carbon confinement can improve the structural stability of MoS2. The dual carbon with good electronic conductivity ensures well battery rate capability of MoS2 anode. Meanwhile, the larger interlayer spacing of 10.09 Å caused by NC insertion make MoS2 store more Na+. As a consequence, the HC@MoS2@NC nanocomposite delivers a high capacity of 321 mAh g−1 at 0.1 A g−1 after 100 cycles. At large current density of 2 A g−1, a high capacity of 180 mAh g−1 can still be achieved after 1000 cycles. Even at larger current density of 5 A g−1, the capacity can still be kept at 162 mAh g−1 after 100 cycles.

Study of Superconductivity in Restricted Quantum Chromo-Dynamics in non-Abelian Gauge Theory

An Abelian Higgs model with dual superconductivity and confinement has been constructed and its string representation is described in terms of the average of Wilson loops in this QCD Abelian projection. Investigations has been carried out on monopole condensation and chromo-magnetic superconductivity within the framework of restricted quantum chromodynamics in the SU(2) gauge theory.

Dual-Confinement Effect of Nanocages@Nanotubes Suppresses Polysulfide Shuttle Effect for High-Performance Lithium-Sulfur Batteries.

The shuttle effect of lithium polysulfides (LiPSs) severely hinders the development and commercialization of lithium-sulfur batteries, and the design of high-conductive carbon fiber-host material has become a key solution to suppress the shuttle effect. In this work, a unique Co/CoN-carbon nanocages@TiO2-carbon nanotubes structure (NC@TiO2-CNTs) is constructed using an electrospinning and nitriding process. Lithium-sulfur batteries using NC@TiO2-CNTs as cathode host materials exhibit high sulfur utilization (1527 mAh g-1 at 0.2 C) and can still maintain a discharge capacity of 663 mAh g-1 at a high current density of 5 C, and the capacity loss is only 0.056% per cycle during 500 cycles at 1 C. It is worth noting that even under extreme conditions (sulfur-loading = 90%, surface-loading = 5.0mg cm-2 (S), and E/S = 6.63µL mg-1), the lithium-sulfur batteries can still provide a reversible capacity of 4 mAh cm-2. Throughdensity functional theorycalculations, it has been found that the Co/CoN heterostructures can adsorb and catalyze LiPSs conversion effectively. Simultaneously, the TiO2 can adsorb LiPSs and transfer Li+ selectively, achieving dual confinement for the shuttle effect of LiPSs (nanocages and nanotubes). The new findings provide a new performance enhancement strategy for the commercialization of lithium-sulfur batteries.

1D/3D dual carbon-supported Mott-Schottky-type Co-Co2P heterojunctions for pH-universal hydrogen evolution

The rational design of low-cost, efficient, and stable heterojunction catalysts for pH-universal hydrogen evolution is attracting increasing attention towards a sustainable hydrogen economy. Herein, a sequential spatial restriction-pyrolysis route is developed to confine Mott-Schottky-type Co-Co2P heterojunctions embedded in the one-dimensional (1D) carbon nanotube-modified three-dimensional (3D) N,P dual-doped carbon matrix (Co-Co2P@CNT//CM). The synergistic effect between the abundant Mott-Schottky heterointerfaces and the 1D/3D dual carbon confinement system enables fully exposed active sites and facilitated charge transfer dynamics, thus triggering favorable electronic structures of Co-Co2P@CNT//CM. As a result, Co-Co2P@CNT//CM heterojunctions exhibit excellent pH-universal hydrogen evolution reaction (HER) performance with overpotentials of 142, 205, and 262 mV at 10 mA cm−2 in 0.5 M H2SO4, 1.0 M KOH, and 1.0 M phosphate buffer saline (PBS), respectively. The theoretical results demonstrated that the Mott-Schottky effect can induce an oriented interfacial charge exchange between Co and Co2P. This can lower the reactive kinetic barrier and endow Co-Co2P@CNT//CM with ideal hydrogen adsorption free energy, which efficiently drives the production of H2 from electrolytic water.

Enhanced lithium storage in pomegranate-like carbon via dual confinement of lithiophilic seeds and Li deposition

The uncontrollable dendrite growth and infinite volume expansion of Li during cycling lead to low Coulombic efficiency (CE) and short cycling life, severely impeding the commercial progress of lithium metal batteries (LMBs). In this work, nitrogen-doped carbon nanospheres (CSs) with ultrafine lithiophilic ZnO nanoparticles encapsulated by interconnected pomegranate-like carbon sheets (denoted as ZnO@NPCS) have been designed and constructed to serve as novel lithium hosts. The ultrafine ZnO nanoparticles uniformly distributed in the CSs can significantly reduce the Li nucleation barrier, while the well-designed pomegranate-like carbon sheets within the CSs can provide continuous and fast electron/ion transport channels, accelerating the Li+ transfer kinetics. Moreover, the internal interconnected carbon networks can confine the lithiophilic nanoparticles, preventing them from detaching or aggregating during cycling, and meanwhile offer individual voids to accommodate deposited Li. Thus, both lithiophilic seeds and deposited Li can be well confined in the pomegranate-like structure. Such a dual-confinement effect enables the ZnO@NPCS electrode to exhibit ultralong cycling life for more than 1000 cycles with ultrahigh CE (>99.5 %) without Li dendrites growth, which is further validated by in-situ transmission electron microscopy and phase-field simulations. Therefore, this dual-confinement strategy provides an inspiring insight to design superior Li hosts for developing superior LMBs and can be extended to other battery systems.

Ternary Heteroatomic Doping Induced Microenvironment Engineering of Low Fe-N4-Loaded Carbon Nanofibers for Bifunctional Oxygen Electrocatalysis.

Fabricating highly efficient and long-life redox bifunctional electrocatalysts is vital for oxygen-related renewable energy devices. To boost the bifunctional catalytic activity of Fe-N-C single-atom catalysts, it is imperative to fine-tune the coordination microenvironment of the Fe sites to optimize the adsorption/desorption energies of intermediates during oxygen reduction/evolution reactions (ORR/OER) and simultaneously avoid the aggregation of atomically dispersed metal sites. Herein, a strategy is developed for fabricating a free-standing electrocatalyst with atomically dispersed Fe sites (≈0.89wt.%) supported on N, F, and S ternary-doped hollow carbon nanofibers (FeN4 -NFS-CNF). Both experimental and theoretical findings suggest that the incorporation of ternary heteroatoms modifies the charge distribution of Fe active centers and enhances defect density, thereby optimizing the bifunctional catalytic activities. The efficient regulation isolated Fe centers come from the dual confinement of zeolitic imidazole framework-8 (ZIF-8) and polymerized ionic liquid (PIL), while the precise formation of distinct hierarchical three-dimensional porous structure maximizes the exposure of low-doping Fe active sites and enriched heteroatoms. FeN4 -NFS-CNF achieves remarkable electrocatalytic activity with a high ORR half-wave potential (0.90V) and a low OER overpotential (270mV) in alkaline electrolyte, revealing the benefit of optimizing the microenvironment of low-doping iron single atoms in directing bifunctional catalytic activity.

Dual conductive confinement effects on enhancing Li-ion storage of NaV6O15@VO2(M)@V2C heterojunction

Exploring novel anode materials for lithium-ion batteries (LIBs) is always on the way due to the ever-increasing energy demands of the next generation electronic devices. Particularly, well-designed heterojunctions work wonders in realizing excellent lithium storage performance. Herein, 2D hierarchical NaV6O15@VO2(M)@V2C composites are constructed via one-step oxidation of Na-ion intercalated V2C MXene in CO2, where VO2(M) nanosheets are confined by NaV6O15 nanorods and V2C MXene. Attributed to the intrinsic merits of monoclinic VO2(M) and a dual conductive confinement system composed of the outer NaV6O15 nanorods and the inner V2C MXene, NaV6O15@VO2(M)@V2C exhibits superior electrochemical performance as an anode for LIBs. It delivers an outstanding reversible discharge capacity of 408.1 mAh g−1 at 100 mA g−1 after 100 cycles, as well as good cycling stability at 1 A g−1, which maintains capacity of 204.5 mAh g−1 after 400 cycles with a coulombic efficiency of 99.63%. This work proposes a novel insight into fabricating 2D hierarchical structure from various cation-intercalated MXenes with enhanced Li+ storage for LIBs.