Orthorhombic Cobalt Ditelluride with Te Vacancy Defects Anchoring on Elastic MXene Enables Efficient Potassium-Ion Storage

Activating Basal Plane Inert Sites of Iron Telluride for Motivational Electromagnetic Microwave Absorption

The basal plane inert sites and inadequate intrinsic dielectric relaxation are the major bottlenecks limiting the electromagnetic microwave (EMW) absorption performance of transition metal tellurides (TMTs). Here, an effective dual defect model based on electron polarization relaxation is established on iron telluride (FeTe) flakes via one-step O2 plasma treatment. Therefore, the basal plane inert sites of FeTe are activated by Te vacancies and O incorporation, which form abundant polarization centers, resulting in charge redistribution and increased dipole site density, thereby effectively optimizing dielectric relaxation loss. Consequently, the optimal EMW attenuation performance achieves a minimum reflection loss exceeding -69.6 dB at a thickness of 2.2 mm, with an absorption bandwidth of up to 4.9 GHz at a thickness of 1.3 mm. Besides, FeTe with dual defect exhibits a prominent radar cross-section reduction of 42 dBsm, indicating excellent radar wave attenuation capability. This study illustrates an innovative model system for elucidating dielectric relaxation loss mechanisms and provides a feasible approach to developing high-loss TMTs-based absorbers.

Tailoring Self-Catalytic N─Co Bonds into Heterostructure Architectures: Deciphering Polytellurides Conversion Mechanism Toward Ultralong-Lifespan Potassium Ion Storage

Transition metal tellurides (TMTes) are promising anodes for potassium-ion batteries (PIBs) due to their high theoretical specific capacity and impressive electronic conductivity. Nevertheless, TMTes suffer from persistent capacity degradation due to the large volume expansion, high ion-diffusion energy barriers, and the dissolution/shuttle of potassium polytellurides (KxTey). Herein, a heterostructured CoTe2 composite equipped with a self-catalytic center (N-CoTe2/LTTC) is developed, exploiting its low-tortuosity tunneling, chemical tunability, and self-catalytic properties to elevate cycling stability to new heights. Systematic experiments have verified that the elaborate N-CoTe2/LTTC provides a short-range and efficient electron/ion transport path, accelerates K+ diffusion kinetics, and suppresses huge volume distortion. Notably, the N─Co bonds self-catalytic center can promote the adsorption capabilities and accelerate the conversion kinetics for KxTey under the synergistic effect of heterojunction. Consequently, the optimized N-CoTe2/LTTC electrode delivers an ultralong‑lifespan cyclability (over 25 000 cycles at 2.0 A g-1, only 0.0019% capacity decay rate per cycle), outperforming those of reported Te-based anodes. Finally, the N-CoTe2/LTTC//PTCDA@450 full cell manifests impressive stability (over 4300 cycles at 2.0 A g-1). This work uncovers the impact of catalytic centers on the conversion of KxTey and provides valuable insights for rationally designing ultralong-lifespan TMTes anodes for PIBs.

Te2- modulated heterogeneous remodeling of S atoms in ultrathin ZnIn2S4 nanosheets containing S vacancies synergistically enhances CO2 photoreduction

Reconfiguration of in situ heterojunction composites without interfacial resistance by substitution of homologous anions for the formation of gradient work function differences inducing the formation of built-in electric field is an effective strategy to enhance the charge separation efficiency. Herein, Te2-/ZnIn2S4-VS (Te2-/ZIS-VS) in situ heterojunction was synthesized by substitution of Te2- ions for S2- in ultrathin ZIS containing S vacancies, which can significantly promote photogenerated charge separation, surface electron enrichment, and CO2 adsorption/activation. The presence of S vacancies and adjacent Te2-/S2- double anions, the double active sites constructed by defect engineering promote the desorption of *CO molecules while inhibiting the protonation toward *CHO, which was more favorable for selective CO2 photoreduction to CO. The experimental results showed that the CO yield of Te2-/ZIS-VS was significantly increased to 672.1 μmol g-1 h-1 compared with pristine ZIS (54.3 μmol g-1 h-1) and the CO selectivity was close to 83 %. Notably, the life cycle assessment (LCA) of Te2-/Znln2S4 nanosheets with S-vacancy was performed. The evaluation results showed that most of the 17 impact categories showed low overall impact values and were environmentally friendly. Based on the results of this LCA, suggestions were put forward to further optimize the product to reduce carbon emissions.

Ultrafast Na-Ion Storage in Amorphization Engineered Hollow Vanadium Oxide/MXene Nanohybrids for High-Performance Sodium-Ion Hybrid Capacitors

Sodium ion hybrid capacitors (SIHCs) address the high power and energy requirements in energy storage devices but face significant challenges arising from the slow kinetics and cycling instability of the anode side. Introducing atomic disorder and employing structural engineering in anode materials proves to be effective strategies for achieving rapid charge storage. Here, it is demonstrated that N-doped MXene encapsulated amorphous vanadium oxide hollow spheres (VOx@N-MXene HSs) offer multidirectional open pathways and sufficient vacancies, enabling reversible and fast Na+ insertion/extraction. Machine learning potentials, coupled with molecular simulation techniques, confirm the presence of more abundant pores within the amorphous vanadium oxide (VOx) structure. The simulation of the charging/discharging process elucidates the authentic reaction path and structural evolutions of the VOx@N-MXene HSs, providing sufficient insight into the atomic-scale mechanisms associated with these structural superiorities. The full SIHCs devices demonstrate a high energy density of 198.3 Wh kg-1, along with a long-term cycling lifespan of 8000 cycles. This study offers valuable strategies into the intricate design and exploration of amorphous electrodes, contributing to the advancement of next-generation electrochemical energy devices.

Boosting the Production of Hydrogen from an Overall Urea Splitting Reaction Using a Tri-Functional Scandium-Cobalt Electrocatalyst

The creation of highly efficient and economical electrocatalysts is essential to the massive electrolysis of water to produce clean energy. The ability to use urea reaction of oxidation (UOR) in place of the oxygen/hydrogen evolution process (OER/HER) during water splitting is a significant step toward the production of high-purity hydrogen with less energy usage. Empirical evidence suggests that the UOR process consists of two stages. First, the metal sites undergo an electrochemical pre-oxidation reaction, and then the urea molecules on the high-valence metal sites are chemically oxidized. Here, the use of scandium-doped CoTe supported on carbon nanotubes called Sc@CoTe/CNT is reported and CoTe/CNT as a composite to efficiently promote hydrogen generation from highly durable and active electrocatalysts for the OER/UOR/HER in urea and alkali solutions. Electrochemical impedance spectroscopy indicates that the UOR facilitates charge transfer across the interface. Furthermore, the Sc@CoTe/CNT nanocatalyst has high performance in KOH and KOH-containing urea solutions as demonstrated by the HER, OER, and UOR (215 mV, 1.59, and 1.31 V, respectively, at 10 mA cm-2 in 1 m KOH) and CoTe/CNT shows 195 mV, 1.61 and 1.3 V, respectively. Consequently, the total urea splitting system achieves 1.29 V, whereas the overall water splitting device obtaines 1.49 V of Sc@CoTe/CNT and CoTe/CNT shows 1.54, 1.48 V, respectively. This work presents a viable method of combining HER with UOR for maximally effective hydrogen production.

A High-Rate and Ultrastable Re2Te5/MXene Anode for Potassium Storage Enabled by Amorphous/Crystalline Heterointerface Engineering

The pursuit of anode materials capable of rapid and reversible potassium storage performance is a challenging yet fascinating target. Herein, a heterointerface engineering strategy is proposed to prepare a novel superstructure composed of amorphous/crystalline Re2Te5 anchored on MXene substrate (A/C-Re2Te5/MXene) as an advanced anode for potassium-ion batteries (KIBs). The A/C-Re2Te5/MXene anode exhibits outstanding reversible capacity (350.4 mAh g-1 after 200 cycles at 0.2 A g-1), excellent rate capability (162.5 mAh g-1 at 20 A g-1), remarkable long-term cycling capability (186.1 mAh g-1 at 5 A g-1 over 5000 cycles), and reliable operation in flexible full KIBs, outperforming state-of-the-art metal chalcogenides-based devices. Experimental and theoretical investigations attribute this high performance to the synergistic effect of the A/C-Re2Te5 with a built-in electric field and the elastic MXene, enabling improved pseudocapacitive contribution, accelerated charge transfer behavior, and high K+ ion adsorption/diffusion ability. Meanwhile, a combination of intercalation and conversion reactions mechanism is observed within A/C-Re2Te5/MXene. This work offers a new approach for developing metal tellurides- and MXene-based anodes for achieving stable cyclability and fast-charging KIBs.

Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium-Sulfur Batteries

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe2) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe2 enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe2 can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe2@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm-2, a high areal capacity of 6.1 mA h cm-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe2 as a sulfur host material for LSBs.

Evolution of Metal Tellurides for Energy Storage/Conversion: From Synthesis to Applications

Metal telluride (MTe)-based nanomaterials have emerged as a potential alternative for efficient, highly conductive, robust, and durable electrodes in energy storage/conversion applications. Significant progress in the material development of MTe-based electrodes is well-sought, from the synthesis of its nanostructures, integration of MTes with supporting materials, synthesis of their hybrid morphologies, and their implications in energy storage/conversion systems. Herein, an extensive exploration of the recent advancements and progress in MTes-based nanomaterials is reviewed. This review emphasizes elucidating the fundamental properties of MTes and providing a systematic compilation of its wet and dry synthesis methods. The applications of MTes are extensively summarized and discussed, particularly, in energy storage and conversion systems including batteries (Li-ion, Zn-ion, Li-S, Na-ion, K-ion), supercapacitor, hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and CO2 reduction. The review also emphasizes the future prospects and urgent challenges to be addressed in the development of MTes, providing knowledge for researchers in utilizing MTes in energy storage and conversion technologies.

A bimetallic sulfide FeCoS4@rGO hybrid as a high-performance anode for potassium-ion batteries

We synthesized a low metal-to-sulfur atomic ratio (0.5) FeCoS4, exhibiting high reversible specific capacity. Reduced graphene oxide was covered on the surface to improve the cycling stability and rate performance further. Density functional theory calculations show that composite materials can effectively increase the adsorption energy and enhance the diffusion kinetics.

SnTe/SnSe Heterojunction Based Ammonia Sensors with Excellent Withstand to Ambient Humidities

Non-invasive breath testing has gained increasing importance for early disease screening, spurring research into cheap sensors for detecting trace biomarkers such as ammonia. However, real-life deployment of ammonia sensors remains hindered by susceptibility to humidity-induced interference. The SnTe/SnSe heterojunction-based chemiresistive-type sensor demonstrates an excellent response/recovery to different concentrations of ammonia from 0.1 to 100 ppm at room temperature. The improved sensing properties of the heterojunctions-based sensors compared to single-phased SnTe or SnSe can be attributed to the stronger NH3 adsorptions, more Te vacancies, and hydrophobic surface induced by the formed SnTe/SnSe heterojunctions. The sensing mechanisms are investigated in detail by using in situ techniques such as diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), Kelvin probe, and a.c. impedance spectroscopy together with the Density-Function-Theory calculations. The formed heterojunctions boost the overall charge transfer efficiency between the ammonia and the sensing materials, thus leading to the desirable sensing features as well, with excellent resistance to ambient humidities.

Unveiling the Synergy of Architecture and Anion Vacancy on Bi2Te3-x@NPCNFs for Fast and Stable Potassium Ion Storage

Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi2Te3-x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi2Te3-x@NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi2Te3, suppresses structural distortion, and accelerates K+ diffusion capacity. The meticulously designed Bi2Te3-x@NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g-1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g-1 at 2.0 A g-1). Furthermore, the systematic ex situ characterization confirms that the Bi2Te3-x@NPCNFs electrode undergoes an "intercalation-conversion-step alloying" mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K+ adsorption, and fast K+ diffusion ability of the Bi2Te3-x@NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi2Te3-x@NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg-1 at a power density of 1000 W kg-1) and excellent cycling stability (1600 cycles at 10.0 A g-1), indicating their potential practical applications.

Elastic MXene conductive layers and electrolyte engineering enable robust potassium storage

The precisely engineered structures of materials greatly influence the manifestation of their properties. For example, in the process of alkali metal ion storage, a carefully designed structure capable of accommodating inserted and extracted ions will improve the stability of material cycling. The present study explores the uniform distribution of self-grown carbon nanotubes to provide structural support for the conductive and elastic MXene layers of Ti3C2Tx-Co@NCNTs. Furthermore, a compatible electrolyte system has been optimized by analyzing the solvation structure and carefully regulating the component in the solid electrolyte interphase (SEI) layer. Mechanistic studies demonstrate that the decomposition predominantly controlled by FSI- leads to the formation of a robust inorganic SEI layer enriched with KF, thus effectively inhibiting irreversible side reactions and major structural deterioration. Confirming our expectations, Ti3C2Tx-Co@NCNTs exhibits an impressive reversible capacity of 260 mA h g-1, even after 2000 cycles at 500 mA g-1 in 1 M KFSI (DME), surpassing most MXene-based anodes reported for PIBs. Additionally, density functional theory (DFT) calculations verify the superior electronic conductivity and lower K+ diffusion energy barriers of the novel superstructure of Ti3C2Tx-Co@NCNTs, thereby affirming the improved electrochemical kinetics. This study presents systematic evaluation methodologies for future research on MXene-based anodes in PIBs.

Origin of Phase Engineering CoTe2 Alloy Toward Kinetics-Reinforced and Dendrite-Free Lithium-Sulfur Batteries

Slow electrochemistry kinetics and dendrite growth are major obstacles for lithium-sulfur (Li-S) batteries. The investigations over the polymorph effect require more endeavors to further access the related catalyst design principles. Herein, the systematic evaluation of CoTe2 alloy with two polymorphs regarding sulfur reduction reaction (SRR) and lithium plating/stripping is reported. As disclosed by theoretical calculations and electrochemical measurements, the orthorhombic (o-) and hexagonal (h-) CoTe2 make a substantial difference. The reactivity origin of the CoTe2 polymorphs is explored. The higher position of d-band centers for the Co atoms on the o-CoTe2 leads to a higher displacement of the antibonding state; the lower antibonding state occupancy, the more effective the interaction with the sulfide moieties and lithium. Hence, o-CoTe2 annihilates h-CoTe2 and exhibits better catalysis and more uniform lithium deposition, consolidated by excellent performance of full cell made of o-CoTe2 . It keeps stable charging/discharging for 800 cycles at 0.5 C with only 0.055% capacity decay per cycle and even achieves an areal capacity of 6.5 mAh cm-2 at lean electrolyte and high sulfur loading of 6.4 mg cm-2 . This work establishes the mechanistic perspective about the catalysts in Li-S batteries and provides new insight into the unified solution.

Efficient Polytelluride Anchoring for Ultralong-Life Potassium Storage: Combined Physical Barrier and Chemisorption in Nanogrid-in-Nanofiber

Metal tellurides (MTes) are highly attractive as promising anodes for high-performance potassium-ion batteries. The capacity attenuation of most reported MTe anodes is attributed to their poor electrical conductivity and large volume variation. The evolution mechanisms, dissolution properties, and corresponding manipulation strategies of intermediates (K-polytellurides, K-pTex) are rarely mentioned. Herein, we propose a novel structural engineering strategy to confine ultrafine CoTe2 nanodots in hierarchical nanogrid-in-nanofiber carbon substrates (CoTe2@NC@NSPCNFs) for smooth immobilization of K-pTex and highly reversible conversion of CoTe2 by manipulating the intense electrochemical reaction process. Various in situ/ex situ techniques and density functional theory calculations have been performed to clarify the formation, transformation, and dissolution of K-pTex (K5Te3 and K2Te), as well as verifying the robust physical barrier and the strong chemisorption of K5Te3 and K2Te on S, N co-doped dual-type carbon substrates. Additionally, the hierarchical nanogrid-in-nanofiber nanostructure increases the chemical anchoring sites for K-pTex, provides sufficient volume buffer space, and constructs highly interconnected conductive microcircuits, further propelling the battery reaction to new heights (3500 cycles at 2.0 A g-1). Furthermore, the full cells further demonstrate the potential for practical applications. This work provides new insights into manipulating K-pTex in the design of ultralong-cycling MTe anodes for advanced PIBs.

Nanowire sulfide/carbon composite with high electrochemical performance in potassium-ion batteries

Transition metal chalcogenides (TMCs) have demonstrated great potential in energy storage devices due to their versatile structures and composite functionalities. However, the application of TMCs in potassium-ion batteries (PIBs) suffers from the issues of large volume expansion, polysulfide dissolution, and sluggish kinetics. To overcome these challenges, this work develops nano-flower-like MnS-Co3S4 confined in poly-pyrrole (PPY) carbon nanotube (denoted as MS-CS-PPY) as an excellent anode in PIBs. The nitrogen-doped PPY framework facilitates the interface electron transfer, confines active materials MS-CS effectively, and mitigates the volume change, thus resulting in boosted reaction kinetics and exceptional cycling stability. TMCs induce the surface capacitance and enable the chemical anchoring of the charge/discharge products during the potassium/de-potassium process. Moreover, this work reveals the potassium/de-potassium reaction mechanism, redox kinetics, and solid electrolyte interphase formation of MS-CS-PPY in different electrolytes through theoretical calculations and experimental studies. The solvation ability of electrolytes plays a vital role in manipulating the redox kinetics of the MS-CS-PPY anode material. This study offers feasible strategies for electrode design and electrolyte selection for developing TMCs negative electrodes in future PIBs.

Built-In Electric Field-Driven Ultrahigh-Rate K-Ion Storage via Heterostructure Engineering of Dual Tellurides Integrated with Ti3C2Tx MXene

Exploiting high-rate anode materials with fast K+ diffusion is intriguing for the development of advanced potassium-ion batteries (KIBs) but remains unrealized. Here, heterostructure engineering is proposed to construct the dual transition metal tellurides (CoTe2/ZnTe), which are anchored onto two-dimensional (2D) Ti3C2Tx MXene nanosheets. Various theoretical modeling and experimental findings reveal that heterostructure engineering can regulate the electronic structures of CoTe2/ZnTe interfaces, improving K+ diffusion and adsorption. In addition, the different work functions between CoTe2/ZnTe induce a robust built-in electric field at the CoTe2/ZnTe interface, providing a strong driving force to facilitate charge transport. Moreover, the conductive and elastic Ti3C2Tx can effectively promote electrode conductivity and alleviate the volume change of CoTe2/ZnTe heterostructures upon cycling. Owing to these merits, the resulting CoTe2/ZnTe/Ti3C2Tx (CZT) exhibit excellent rate capability (137.0 mAh g-1 at 10 A g-1) and cycling stability (175.3 mAh g-1 after 4000 cycles at 3.0 A g-1, with a high capacity retention of 89.4%). More impressively, the CZT-based full cells demonstrate high energy density (220.2 Wh kg-1) and power density (837.2 W kg-1). This work provides a general and effective strategy by integrating heterostructure engineering and 2D material nanocompositing for designing advanced high-rate anode materials for next-generation KIBs.

Manipulating Molecular Structure to Trigger Ultrafast and Long-Life Potassium Storage of Fe0.4 Ni0.6 S Solid Solution

Currently, the main obstacle to the widespread utilization of metal chalcogenides (MSx ) as anode for potassium-ion batteries (PIBs) is their poor rate capability and inferior cycling stability as a result of the undesirable electrical conductivity and severe pulverization of the nanostructure during large K-ions intercalation-extraction processes. Herein, an ultrafast and long-life potassium storage of metal chalcogenide is rationally demonstrated by employing Fe0.4 Ni0.6 S solid-solution (FNS/C) through molecular structure engineering. Benefiting from improved electroactivity and intense interactions within the unique solid solution phase, the electrical conductivity and structure durability of Fe0.4 Ni0.6 S are vastly improved. As anticipated, the FNS/C electrode delivers superior rate properties (538.7 and 210.5 mAh g-1 at 0.1 and 10 A g-1 , respectively) and long-term cycle stability (180.8 mAh g-1 at 5 A g-1 after 2000 cycles with a capacity decay of 0.011% per cycle). Moreover, the potassium storage mechanisms of Fe0.4 Ni0.6 S solid solution are comprehensively revealed by several in situ characterizations and theoretical calculations. This innovative molecular structure engineering strategy opens avenues to achieve high-quality metal chalcogenides for future advanced PIBs.

MXene Contact Engineering for Printed Electronics

MXenes emerging as an amazing class of 2D layered materials, have drawn great attention in the past decade. Recent progress suggest that MXene-based materials have been widely explored as conductive electrodes for printed electronics, including electronic and optoelectronic devices, sensors, and energy storage systems. Here, the critical factors impacting device performance are comprehensively interpreted from the viewpoint of contact engineering, thereby giving a deep understanding of surface microstructures, contact defects, and energy level matching as well as their interaction principles. This review also summarizes the existing challenges of MXene inks and the related printing techniques, aiming at inspiring researchers to develop novel large-area and high-resolution printing integration methods. Moreover, to effectually tune the states of contact interface and meet the urgent demands of printed electronics, the significance of MXene contact engineering in reducing defects, matching energy levels, and regulating performance is highlighted. Finally, the printed electronics constructed by the collaborative combination of the printing process and contact engineering are discussed.

Boosting cobalt ditelluride quantum-rods anode materials for excellent potassium-ion storage via hierarchical physicochemical encapsulation

The exploration of anode materials that can store large-sized K-ion to solve the poor kinetics and large volume expansion issues has become the key scientific bottlenecks hindering the development of potassium-ion batteries (PIBs). Herein, ultrafine CoTe₂ quantum rods physiochemically encapsulated by graphene and nitrogen-doped carbon (CoTe₂@rGO@NC) are regarded as anode electrodes for PIBs. Dual physicochemical confinement and quantum size effect not only enhance electrochemical kinetics but also restrain large lattice stress during repeated K-ion insertion/extraction process. Superior electronic conductivity, K-ion adsorption, and diffusion ability can be acquired for CoTe₂@rGO@NC, confirmed through first-principles calculations and kinetics study. K-ion insertion/extraction proceeds via a typical conversion mechanism relying on Co as the redox site, where the robust chemical bond of COCo plays an important role in maintaining the electrode stability. Accordingly, CoTe₂@rGO@NC contributes a high initial capacity of 237.6 mAh·g^-1 at 200 mA·g^-1, a long lifetime over 500 cycles with low-capacity decay of 0.10% per cycle. This research will lay the materials science foundation for the construction of quantum-rod electrodes.

Comprehensively Understanding the Role of Anion Vacancies on K-Ion Storage: A Case Study of Se-Vacancy-Engineered VSe2

Anion vacancy engineering (AVE) is widely used to improve the Li-ion and Na-ion storage of conversion-type anode materials. However, AVE is still an emerging strategy in K-ion batteries, which are promising for large-scale energy storage. In addition, the role of anion vacancies on ion storage is far from clear, despite several proposed explanations. Herein, by employing VSe₂ as a model conversion-type anode material, Se vacancies are intentionally introduced (labeled as P-VSe_2-x ) to investigate their effect on K⁺ storage. The P-VSe_2-x shows excellent cyclability in half cells (143 mA h g^-1 at 3.0 A g^-1 after 1000 cycles) and high energy density in coin-type full cells (206.8 Wh kg^-1 ). By applying various electrochemical techniques, the effects of Se vacancies on the redox potentials of K-ion insertion/extraction and the K-ion diffusion in electrodes upon cycling are uncovered. In addition, the structural evolution of Se vacancies during potassiation/de-potassiation using various operando and ex characterizations is revealed. Moreover, it is demonstrated that Se vacancies can facilitate the breaking of VSe bonds upon the P-VSe_2-x conversion using theoretical calculations. This work comprehensively explains the role of anion vacancies in ion storage for developing high-performance conversion-type anode materials.

Recent Advances and Perspectives of Lewis Acidic Etching Route: An Emerging Preparation Strategy for MXenes

Since the discovery in 2011, MXenes have become the rising star in the field of two-dimensional materials. Benefiting from the metallic-level conductivity, large and adjustable gallery spacing, low ion diffusion barrier, rich surface chemistry, superior mechanical strength, MXenes exhibit great application prospects in energy storage and conversion, sensors, optoelectronics, electromagnetic interference shielding and biomedicine. Nevertheless, two issues seriously deteriorate the further development of MXenes. One is the high experimental risk of common preparation methods such as HF etching, and the other is the difficulty in obtaining MXenes with controllable surface groups. Recently, Lewis acidic etching, as a brand-new preparation strategy for MXenes, has attracted intensive attention due to its high safety and the ability to endow MXenes with uniform terminations. However, a comprehensive review of Lewis acidic etching method has not been reported yet. Herein, we first introduce the Lewis acidic etching from the following four aspects: etching mechanism, terminations regulation, in-situ formed metals and delamination of multi-layered MXenes. Further, the applications of MXenes and MXene-based hybrids obtained by Lewis acidic etching route in energy storage and conversion, sensors and microwave absorption are carefully summarized. Finally, some challenges and opportunities of Lewis acidic etching strategy are also presented.

Confine, Defect, and Interface Manipulation of Fe3 Se4 /3D Graphene Targeting Fast and Stable Potassium-Ion Storage

The fast electrochemical kinetics behavior and long cycling life have been the goals in developing anode materials for potassium ion batteries (PIBs). On account of high electron conductivity and theoretical capacity, transition metal selenides have been deemed as one of the promising anode materials for PIBs. Herein, a systematic structural manipulation strategy, pertaining to the confine of Fe₃ Se₄ particles by 3D graphene and the dual phosphorus (P) doping to the Fe₃ Se₄ /3DG (DP-Fe₃ Se₄ /3DG), has been proposed to fulfill the efficient potassium-ion (K-ion) evolution kinetics and thus boost the K-ion storage performance. The theoretical calculation results demonstrate that the well-designed dual P doping interface can effectively promote K-ion adsorption behavior and provide a low energy barrier for K-ion diffusion. The insertion-conversion and adsorption mechanism for multi potassium storage behavior in DP-Fe₃ Se₄ /3DG composite has been also deciphered by combining the in situ/ex situ X-ray diffraction and operando Raman spectra evidences. As expected, the DP-Fe₃ Se₄ /3DG anode exhibits superior rate capability (120.2 mA h g^-1 at 10 A g^-1 ) and outstanding cycling performance (157.9 mA h g^-1 after 1000 cycles at 5 A g^-1 ).

Vacancy-Mediated Anomalous Emission Characteristics of Size-Confined Semiconducting CoTe2

Transition-metal tellurides (TMTs) are promising materials for "post-graphene age" nanoelectronics and energy storage applications owing to their industry-standard compatibility, high electron mobility, large spin-orbit coupling (SOC), etc. However, tellurium (Te) having a larger ionic radius (Z = 52) and broader d-bands endows TMTs with semimetallic nature, restricting their application in photonic and optoelectronic domains. In this work, we report the optical properties of the quantum-confined semiconducting phase of cobalt ditelluride (CoTe₂) for the first time, exhibiting excellent two-color band photoabsorption attributes covering the UV-visible and near-infrared regions. Furthermore, novel excitonic resonances (X) of size-varying CoTe₂ nanocrystals and quantum dots (QDs) are indicated by their temperature-dependent emission characteristics, which are attributed to the splitting of band edge states via confinement. On the other hand, the sudden rupture of the large-area CoTe₂ nanosheets via ultrasonication incorporates Co vacancy-mediated localized trap states within the band gap, which is attributed to the superior room-temperature photoluminescence (PL) quantum yield of QDs and further corroborated using Raman analysis and atomistic density functional theory (DFT) simulations. Most interestingly, the excitonic peak of CoTe₂ QDs reveals a unique positive-to-negative thermal quenching transition phenomenon, owing to the thermal activation of nonradiative surface trap states. These results introduce an exciting approach for the defect-mediated color-saturated light emission that paves the way for solution-processed telluride-based QD light-emitting diodes.

Flat-Zigzag Interface Design of Chalcogenide Heterostructure toward Ultralow Volume Expansion for High-Performance Potassium Storage

Heterostructure construction of layered metal chalcogenides can boost their alkali-metal storage performance, where the charge transfer kinetics can be promoted by the built-in electric fields. However, these heterostructures usually undergo interface separation due to severe layer expansion, especially for large-size potassium accommodation, resulting in the deconstruction of heterostructures and battery performance fading. Herein, first a stable interface design strategy where two metal chalcogenides with totally different layer-morphologies are stacked to form large K⁺ transport channels, rendering ultralow interlayer expansion, is presented. As a proof of concept, the flat-zigzag MoS₂ /Bi₂ S₃ heterostructures stacked with zigzag-morphology Bi₂ S₃ and flat-morphology MoS₂ present an ultralow expansion ratio (1.98%) versus MoS₂ (9.66%) and Bi₂ S₃ (9.61%), which deliver an ultrahigh potassium storage capacity of above 600 mAh g^-1 and capacity retention of 76% after 500 cycles, together with the built-in electric field of heterostructures. Once the heterostructures are used as an anode for potassium-based dual-ion batteries (K-DIBs), it achieves a superior full-cell capacity of ≈166 mAh g^-1 with a capacity retention of 71% after 400 cycles, which is an outstanding performance among the reported K-DIBs. This proposed interface stacking strategy may offer a new way toward stable heterostructure design for metal ions storage and transport applications.

Achieving Sustainable and Stable Potassium-Ion Batteries by Leaf-Bioinspired Nanofluidic Flow

In nature, living systems have evolved integrated structures, matching optimized nanofluidics to adapt to external conditions. In rechargeable batteries, high-capacity electrodes are often plagued by the crucial and universal bottleneck of dissolution and shuttle of active substance into electrolyte, posing obstacles of inevitable capacity degradation. Introducing the concept of intelligent nanofluidics to electrodes, a leaf-bioinspired electrode configuration with hierarchical architecture to tackle this problem is proposed. This integrated structure with fine-tuned surface pores and unobstructed interior porous media, can spatially control the anisotropic nanofluidic flux, in an efficient and self-protectable way: tailoring the outflow across the electrode's surface and free transport in interior, to ensure speedy and stable energy conversion. As proofs of concept, applications of sustainable electrodes rejuvenated from fallen leaf and spent commercial batteries, are designed with leaf-bioinspired architecture. Both KCoS₂ and KS battery systems show advanced steady cycling with effectively mitigated shuttle issues in this smart architecture (0.15% and 0.21% capacity decay per cycle), even at high areal mass loading, when compared with open porous structure (0.60% and 0.39%). This work may pave a new way from a biomimetic view to integrated electrode engineering with regulated surface shielding to conquer the universal dissolution-shuttle problems facing high-capacity materials.

The Multicomponent Synergistic Effect of Sandwich Structure Hierarchical Nanofibers for Enhanced Sodium Storage

Constructing hierarchical micro/nanostructures as anodes for sodium ion batteries is an important approach for exploiting efficient energy storage devices. Herein, sandwich structure hierarchical nanofibers composed of hollow carbon fibers as the substrate, and MoS₂ as the interlayer with Co and/or ZnS nanoparticles anchoring in carbon skeletons as the outer shell (carbon nanofiber/MoS₂ /Co-ZnS⊂NC) are prepared via a multistep reaction strategy. Profiting from the unique hierarchical structure, abundant migration channels of Na⁺ , and multicomponent synergistic effects, the rapid diffusion kinetics are ensured and the utilization of active materials is maximized. The coaxial structure can evenly disperse volumetric strain, making structural stability guaranteed. Hierarchical nanofibers deliver a high reversible capacity of 352.3 mAh g^-1 at 5.0 A g^-1 over 3000 cycles. A discharge capacity of 182.5 mAh g^-1 is retained even after 10 000 cycles at 10.0 A g^-1 as well as a high rate capacity of 202.0 mAh g^-1 up to 30 A g^-1 . The optimal atomic ratio of Co element is further verified by the kinetic analysis. The full-cells assembled with Na₃ V₂ (PO₄ )₃ cathode provide a high capacity of 179.2 mAh g^-1 at 1.0 A g^-1 for 500 cycles. Combining in situ and ex situ characterizations and theoretical calculations, possible sodium storage mechanisms and the origin of superior electrochemical properties are revealed.

P-Doped NiTe2 with Te-Vacancies in Lithium-Sulfur Batteries Prevents Shuttling and Promotes Polysulfide Conversion

Lithium-sulfur (Li-S) batteries have been hindered by the shuttle effect and sluggish polysulfide conversion kinetics. Here, a P-doped nickel tellurium electrocatalyst with Te-vacancies (P⊂NiTe_{2- x} ) anchored on maize-straw carbon (MSC) nanosheets, served as a functional layer (MSC/P⊂NiTe_{2- x} ) on the separator of high-performance Li-S batteries. The P⊂NiTe_{2- x} electrocatalyst enhanced the intrinsic conductivity, strengthened the chemical affinity for polysulfides, and accelerated sulfur redox conversion. The MSC nanosheets enabled NiTe₂ nanoparticle dispersion and Li⁺ diffusion. In situ Raman and ex situ X-ray absorption spectra confirmed that the MSC/P⊂NiTe_{2- x} restrained the shuttle effect and accelerated the redox conversion. The MSC/P⊂NiTe_{2- x} -based cell has a cyclability of 637 mAh g^-1 at 4 C over 1800 cycles with a degradation rate of 0.0139% per cycle, high rate performance of 726 mAh g^-1 at 6 C, and a high areal capacity of 8.47 mAh cm^-2 under a sulfur configuration of 10.2 mg cm^-2 , and a low electrolyte/sulfur usage ratio of 3.9. This work demonstrates that vacancy-induced doping of heterogeneous atoms enables durable sulfur electrochemistry and can impact future electrocatalytic designs related to various energy-storage applications.

Co-Construction of Solid Solution Phase and Void Space in Yolk-Shell Fe0.4Co0.6S@N-Doped Carbon to Enhance Cycling Capacity and Rate Capability for Aluminum-Ion Batteries

Rechargeable aluminum-ion batteries (AIBs), using low-cost and inherent safety Al metal anodes, are regarded as promising energy storage devices next to lithium-ion batteries. Currently, one of the greatest challenges for AIBs is to explore cathodes suitable for feasible Al³⁺ insertion/extraction with high structure stability. Herein, a facile co-engineering on solid solution phase and cavity structure is developed via Prussian blue analogues by a simple and facile sulfidation strategy. The obtained uniform yolk-shell Fe_0.4Co_0.6S@N-doped carbon nanocages (y-s Fe_0.4Co_0.6S@NC) display a high reversible capacity of 141.3 mA h g^-1 at 500 mA g^-1 after 100 cycles and a good rate capability of 100.9 mA h g^-1 at 1000 mA g^-1. The improved performance can be mainly ascribed to the dual merits of the composite; that is, more negative Al³⁺ formation energy and improved Al³⁺ diffusion kinetics favored by the solid solution phase and Al³⁺ insertion/extraction accommodable space stemmed from the yolk-shell structure. Moreover, the reaction mechanism study discloses that the reaction involves the intercalation of Al³⁺ ions into Fe_0.4Co_0.6S to generate Al_lFe_mCo_nS and elemental Fe and Co.

Recent advances of metal telluride anodes for high-performance lithium/sodium-ion batteries

Metal tellurides (MTs) have emerged as highly promising candidate anode materials for state-of-the-art lithium-ion batteries (LIBs) and sodium ion batteries (SIBs). This is owing to the unique crystal structure, high intrinsic conductivity, and high trap density of such materials. The present work delivers a detailed discussion on the latest research and progress associated with the use of MTs for LIBs/SIBs with a focus on reaction mechanisms, challenges, electrochemical performance, and synthesis strategies. Further, the prospects and future development of MT anode materials are discussed in terms of strategies to overcome the existing limitations. This review provides both an in-depth understanding of MTs and provides the driving force for expanding research on MTs for energy storage and conversion applications.