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• VN/Mo 2 C heterointerfaces nanoparticles are monodispersed on N-doped carbon nanosheets. • Mo 2 C and VN synergistically promote the diffusion and conversion of polysulfides. • The functional separator also has excellent protective effect on the lithium anode. • The modified separator exhibits superb electrochemical performance in Li-S batteries. Lithium-sulfur (Li-S) battery is deemed as one of the optimal next-generation energy storage devices due to its low cost and high energy density. However, the shuttle effect of lithium polysulfide (LiPS), sluggish reaction kinetics, and fatal Li-dendrite growth hinder its practical applications. In this work, a bifunctional nitrogen-doped carbon nanosheet conductive framework embedded with VN-Mo 2 C heterointerfaces (VN/Mo 2 C@CNS) is reported as a separator modifier for both sulfur cathode and lithium anode. The VN/Mo 2 C@CNS can offer a synergistic effect of strong surface affinity, good catalytic activity, and small diffusion barrier to accelerate the conversion of polysulfides, which was confirmed by in-situ Raman and theoretical calculation. Moreover, the composite has good lithiophilicity, thus inhibiting the formation of dendrites and achieving uniform lithium deposition. Benefiting from the above merits, the Li-S cells with VN/Mo 2 C@CNS separator obtain desirable rate performance (687 mAh g−1 at 4 C), long cycle life of 1000 cycles (0.042 % capacity attenuation per cycle at 1 C), high areal capacity of 4.2 mAh cm−2 (under a high sulfur loading of 5.6 mg cm−2), and stable performance in protecting the Li anode (at 5 mA cm−2 for 1000 h). This work highlights a novel strategy for facilely designing heterostructures, offering valuable insights to tackle sulfur cathode and lithium anode challenges simultaneously for longevous Li-S batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Fe-Co PBA/rGO with strong interfacial chemical coupling was prepared. • The Fe-Co PBA/rGO cathode exhibited superior capacity and stability. • The strong chemical coupling between rGO and Fe-Co PBA promoted adsorption and diffusion of Al3+. • A full battery with a capacity of 53.6 mAh g−1 over 2000 cycles at 1 A g−1 was achieved. Aqueous aluminum-ion batteries (AAIBs) have emerged as cost-effective and safe alternatives to lithium-ion batteries for storing energy. However, utilizing cathode materials like Prussian blue analogs (PBAs) to accommodate different metallic charge carriers faces challenges due to their low conductivity and slow redox kinetics. To overcome these issues, we propose a novel Fe-Co PBA/rGO nanocomposite with a strong interfacial chemical coupling between Fe-Co PBA and rGO. By combining theoretical calculations with experimental analysis, we have identified the essential role of interfacial interactions in regulating the electronic state and diffusion barriers of Al3+ within the Fe-Co PBA framework. Moreover, a three-dimensional structure that is tightly enclosed by ultrathin rGO sheets was successfully formed, ensuring excellent structural stability. Ex-situ XPS and XRD investigations have further clarified the electrochemical mechanism of the Fe-Co PBA/rGO cathode, revealing reversible redox reactions between Fe2+/Fe3+ and Co3+/Co2+ states during the insertion and extraction of Al3+. These inherent properties contribute to the remarkable cycling stability of the Fe-Co PBA/rGO cathode, achieving 66.7 mAh/g at 1 A/g after 1500 cycles, and high electrochemical reversibility. Additionally, we have successfully built a MoO 3 //Fe-Co PBA/rGO full battery with a capacity of 53.6 mAh/g over 2000 cycles at 1 A/g. This outcome further emphasizes its significant potential in electronic applications related to energy storage. [ABSTRACT FROM AUTHOR]

• Established the quaternary phase diagram FePO 4 -LiFePO 4 -NaFePO 4 -KFePO 4 by DFT for the first time. • The competitive mechanism of alkali ions in FePO 4 during extraction from a salt lake is revealed. • Na 2/3 FePO 4 phase is the main reason for to decreased cyclability of FePO 4 for lithium recovery in brines. • Proposed an innovative FePO 4 regeneration process to enhance electrode performance and lifespan. The rapid expansion of lithium battery applications has resulted in a shortage of lithium resources, prompting researchers to focus on the electrochemical extraction of lithium from water resources using FePO 4 as the host material. However, a large amount of alkali metal impurity ions in brine leads to irreversible capacity loss, limiting the industrial application of FePO 4 materials in lithium extraction. The mechanism of alkali metal ions' influence on FePO 4 materials remains unclear. To address this issue, the quaternary phase diagram of FePO 4 -LiFePO 4 -NaFePO 4 -KFePO 4 and the diffusion barriers of lithium/sodium ions in FePO 4 were obtained for the first time based on the theoretical calculation of density functional theory (DFT). DFT and X-ray diffraction (XRD) refinement revealed that the inability to remove Na 2/3 FePO 4 from the FePO 4 is a critical issue affecting electrode recyclability. An innovative electrode regeneration process was proposed to enhance the lifespan of FePO4 material. The Na 2/3 FePO 4 impurity was converted to LiFePO 4 using K 2 S 2 O 8 abstersion and 0.1 mol/L LiCl lithiation regeneration process. After five rounds of regenerations, the total lithium extraction of the material could still reach 80.18 % of the extraction of the brand-new electrode, demonstrating the multiple reuses of the host material and cost savings. These innovative discoveries can advance the industrial application of electrochemical lithium extraction from FePO 4 electrode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2 O 3 /MoC@NG shows excellent rate performance and large-current long-cycle stability. • Pseudocapacitance control is the major charge–discharge mechanism. • Fe 2 O 3 /MoC@NG shows 21-time enhanced Li+ ion diffusion kinetics compared with Fe 2 O 3 @NG. • Stabilization of Li-DIBs anode structure by heterointerface bonding of Fe 2 O 3 /MoC@NG. • The transport paths of PF 6 − and Li+ ions in dual-ion batteries are studied. Lithium dual-ion batteries (Li-DIBs) technology is expected to become a leader in replacing lithium-ion batteries (LIBs) to carry out high energy/power density energy storage devices. Unfortunately, the sluggish electrochemical reaction kinetics of anode materials critically restricts their practical development. Here, a Li-DIBs is proposed by using a three-dimensional (3D) structure composed of Fe 2 O 3 /MoC heterostructure nanoparticals embedded in a hierarchical mesoporous nitrogen-doped reduction graphene oxide (Fe 2 O 3 /MoC@NG) as the anode, which has low Li+ ion diffusion barrier (0.098 eV), high Li+ ion diffusion coefficient (4.99 × 10−11 cm2 s−1) and remarkable rate property (879.2 mA h g−1 at 10 A g−1), and choosing nano-graphite as the cathode. Originating from the respective strengths of Fe 2 O 3 /MoC@NG anode and the nano-graphite cathode, the as-constructed Li-DIBs full battery displays high reversible capacity and prominent rate property (103.9 mA h g−1 at 0.05 A g−1 and 48.9 mA h g−1 at 2 A g−1). Specifically, taking advantage of density functional theory (DFT) calculations, the exact paths of PF 6 − ion intercalation into graphite cathode and Li+ ion diffusion into Fe 2 O 3 /MoC@NG anode is obtained, namely PF 6 − ion transmits along the (0 0 2) face of nano-graphite and Li+ ion diffuses along the heterointerface of Fe 2 O 3 /MoC@NG. [ABSTRACT FROM AUTHOR]

[Display omitted] • The acetonitrile (MeCN)-based catholyte for Na-CO 2 battery was successfully demonstrated with a NASICON-based hybrid cell. • The MeCN catholyte exhibited superior electrochemical performance compared to conventional TEGDME-based electrolytes. • The molecular dynamics simulations suggested that the MeCN catholyte enhances Na+ diffusion. The development of metal-CO 2 batteries has attracted intense attention because of their unique electrochemical reaction for utilization of CO 2 gas. However, unlike the alkali metal-based O 2 batteries, a limited number of combinations of aprotic electrolytes have been employed for Li(Na)–CO 2 batteries due to the sluggish reaction for the formation of the Li(Na) 2 CO 3 discharge product. Here, we demonstrate an acetonitrile (MeCN)-based catholyte for use in a hybrid cell type Na-CO 2 battery. The presence of a solid ceramic separator in our hybrid cell allows the stable operation of the MeCN catholyte-based Na-CO 2 battery, resulting in improved electrochemical characteristics such as low overpotential, high energy density, and long cycle stability compared to the conventional TEGDME-based electrolyte. In particular, results of molecular dynamics simulations suggest that the improved performance is mainly due to the enhanced Na+ diffusion in the electrolyte. The calculated barrier for Na+ diffusion in MeCN is approximately four times lower than that in TEGDME. Thus, this work provides a promising electrolyte combination and reveals the mechanism for the improved performance of the MeCN-based electrolyte used in the hybrid cell structure, promoting the development of Na-CO 2 batteries as practical secondary energy storage devices. [ABSTRACT FROM AUTHOR]

A novel ternary metal-silicon-phosphorus intramolecular hybrid flame retardant based on titanium-embedded and DOPO-functionalized POSS was synthesized for modification of EP. • A new metal–organic-inorganic hybrid Ti-POSS-bisDOPO was successfully synthesized. • The incorporation of Ti-POSS-bisDOPO into EP improved the flame retardancy of EP. • The EP/Ti-POSS-bisDOPO composites exhibited good comprehensive performances. • The presence of titanium efficiently catalyzed char formation during combustion. • Ti-POSS-bisDOPO exhibited both condensed and gas phase flame retardant mechanisms. A novel metal–organic-inorganic ternary intramolecular hybrid of N,N′-bis(methylene)-bis(dibenz[C,E][1,2]oxaphosphorin6-oxide)-propylisobutyl-amino-titanium-polyhedral oligomeric silsesquioxanes (Ti-POSS-bisDOPO) was synthesized via a feasible route including the corner-opening, corner-capping and Kabachnik-Fields reactions. The uniqueness of this compound lies in its structural design and has the function of flame retardant. Firstly, one Ti atom has been embedded into the polyhedral oligomeric silsesquioxanes (POSS) cage framework and two dibenz[C,E][1,2]oxaphosphorin6-oxide (DOPO) units with anti-burning functionality have been linked to the aminopropyl group on the corner of siliceous cage. For each molecule, the affinities of Ti-embedded POSS part and DOPO unit are different, which make Ti-POSS-bisDOPO to show the amphiphilicity. Therefore, Ti-POSS-bisDOPO could self-assemble into nanoparticle and achieve good dispersion in epoxy matrix with a particle size varying from 150 nm to 1.5 μm. Secondly, when Ti-POSS-bisDOPO was incorporated into EP matrix, the prepared EP/Ti-POSS-bisDOPO composites exhibited good comprehensive performances. Compared with pure EP, both limited oxygen index and char yield of EP/Ti-POSS-bisDOPO composites were increased greatly at a loading range of 1.5 wt%–6.0 wt%. Meanwhile, the corresponding heat release and smoke production of EP/Ti-POSS-bisDOPO were all reduced. It was observed that the interior layers of char residues were honeycomb-like multilayer structures and the exterior layers were compact, which could effectively hinder the heat transfer and gas diffusion by a barrier effect. Besides, when Ti was doped into the vertex of siliceous cage, it worked by catalyzing char formation, producing thermodynamically stable TiO 2 , and enhancing the flame retardancy. It was deduced that both condensed-phase and gas-phase flame-retardancy made contributions to the flame retardant mechanism. Overall, the metal-embedded and phosphorus-modified Ti-POSS-bisDOPO was a new kind of promising fire retardants in the field of non-halogen flame-retardant polymers. [ABSTRACT FROM AUTHOR]

• Rationally designed structure prevent the aggregation of Mn-doped MoS 2 nanosheets. • Mn-doping enhance the intrinsic electronic conductivity and Li+ diffusion rate. • The as-synthesized electrode shows high rate capacity of 659 mAh g−1 at 5 A g−1. Developing anode materials for lithium-ion batteries with excellent electrochemical performance is crucial to satisfy the requirement for energy storage. Molybdenum disulfide is recognized as a prospective anode material due to its high theoretical capacity and two-dimensional layered structure. However, its further application is mainly hindered by its poor electronic conductivity. Herein, we report Mn-doped MoS 2 nanosheets anchored on hierarchical carbon skeleton (MMSC) acting as an anode material. The as-synthesized electrode exhibits a high initial discharge capacity of 1280 mAh g−1 at a current density of 0.1 A g−1, high rate capacity (920 mAh g−1 at 2 A g−1), and long-time cycling stability (71% capacity retention after 1000 cycle). Compared to that of pristine MoS 2 electrode, the improved performance of MMSC anode can be attributed to the synergetic effects of optimized composite structure and Mn doping. The hierarchical carbon skeleton provides a larger surface area, allowing effective electrolyte penetration and preventing aggregation of MoS 2 nanosheets in charge/discharge cycles. To further understand the mechanism of the improved rate capability, calculation of corresponding atomic models according to experimental results and first-principles calculation are conducted. The calculated results prove that the Mn-doped MoS 2 (MMS) has a lower diffusion barrier of Li+ than that in pristine MoS 2. Moreover, the as-synthesized MMSC electrode also demonstrates better electronic conductivity because of the electronic injection by Mn atoms. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Janus heterostructure, namely CoSe 2 -FeSe 2 /graphite/N-doped carbon. • (CFS//g@NC) was prepared. • CFS//g@NC with dual heterojunction (p-n and Schottky junction) was used as a potassium ion battery anode. • DFT calculations reveal that the diffusion barrier of K ions on CFS//g@NC is half that on CoSe 2 or FeSe 2. • CFS//g@NC delivers a capacity of 200 mA h g−1 at a high rate of 10 A/g. • CFS//g@NC exhibits excellent cycling stability of over 2500 cycles at 0.5 A/g. Practical applications of conversion-type metal selenide electrodes in potassium ion batteries (PIBs) encounter multiple challenges, such as particle aggregation, the shuttle effect, and pulverization during cycling. We design a Janus heterostructure, namely CoSe 2 -FeSe 2 /graphite/N-doped carbon (CFS//g@NC), with dual heterojunctions (p-n and Schottky junction), which generates the synergistic effect to enhance interface charge storage and improve electrode structure integrity. When the Janus heterostructure is used as a PIB anode, it demonstrates high-rate performance up to 10 A/g, offering a capacity of 200 mA h g−1 and excellent cycling stability of over 2500 cycles at 0.5 A/g. According to the density functional theory (DFT) calculations, the diffusion barrier of K ions on CFS//g@NC is two times lower than that on CoSe 2 or FeSe 2. The distribution of n-type and p-type semiconductors in the Janus particles has been confirmed by quantitative assessment through dark-field electron microscopy. In addition to the p-n junction crossing two semiconductor interfaces, the Schottky junction between the graphite layer derived from Prussian blue analogues (PBA) and the semiconductor also creates a built-in electric field, thus enhancing ion/electron transport and increasing the diffusion of potassium ions. This work provides new insights into the architectural strategy of multi-layer heterointerfaces and offers a promising new pathway for anode design in PIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • NFCMT-0.05 material possesses a capacity retention of 83.5% after 400 cycles at 5C. • NFCMT-0.05 keeps the P2 phase structure during the sodiation/desodiation process. • NFCMT-0.05 exhibits the reversible anionic redox reaction during cycling. • DFT calculation proves the doping of Ti promotes the valence transition of Fe and Mn. P2-type layered oxides with low Na+ diffusion barriers have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to excellent cycle stability and rate performance. Among them, Co/Ni-free Fe-Mn-Cu based cathode materials have gained significant attention owing to their abundance, low cost, and environmentally friendless. However, their practical application has been hindered by irreversible phase changes during the charging/discharging process, leading to rapid capacity decay. To address this issue, the inactive element (Titanium) is introduced in Na 0.70 Fe 0.20 Cu 0.20 Mn 0.60 O 2 oxides to mitigate the detrimental phase transitions and enhance electrochemical performance by facilitating anionic redox reactions. The resulting Na 0.70 Fe 0.20 Cu 0.20 Mn 0.55 Ti 0.05 O 2 (NFCMT-0.05) cathode material exhibits a high initial discharge specific capacity of 186 mAh/g at 0.1C and superior cycling stability, with a capacity retention of 83.5% after 400 cycles at 5C between 2.0 and 4.3 V. Furthermore, the NFCMT-0.05 maintains P2 phase structure throughout the entire sodiation/desodiation process, and the reversible oxygen-related redox reaction provides additional discharge capacity for the Fe-Mn-based cathode above 4.1 V. The NFCMT-0.05 also demonstrates fast Na+ ion transfer kinetics and excellent rate performance, delivering a discharge capacity at 5C that is 60% of that at 0.1C. The DFT calculation confirms that the introduction of titanium effectively reduces the volume change and suppresses the relative slip of adjacent TMO 6 layers. As a result, Ti-doping is instrumental in improving the cycle stability of NFCMT. This work offers a low-cost strategy for constructing high-performance cathode materials for SIBs. offering promising prospects for the development of efficient and affordable energy storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enzyme-linked MXenes nanocomposites for biocatalysis and biosensing applications. • Synthesis route, functionalization, and immobilization chemistry of MXenes. • Computational attributes of enzymes involved in immobilization on MXenes. • MXene-based nanozymes as robust catalytic constructs and microfluidic reactors. • A new generation of monitoring systems to aid bioanalytical platforms. Engineered two-dimensional (2-D) MXenes-based materials with tunable characteristics and multi-functionalities have brought up new paradigms in the biosensing and catalysis of chemical compounds. The profusion of electroactive functional moieties on the surface of few/multi-layer MXenes facilitates their ability to retain biomolecules such as enzymes resulting in unique dimensions for biocatalysis and biosensing applications. As a result, the biosensing phenomenon of enzyme-linked MXenes incorporates both counterparts' electro-catalytic potential behavior and characteristics. Enzyme-linked MXenes are equipped with several noteworthy and essential features, including a large and functional surface area, tunable surface chemistry, a high capacity for anchoring biomolecules, metallic conductivity, hydrophilicity, ion transport potential, accessible diffusion barrier, excellent fluorescent and optical properties rendered MXene as appealing candidate nanocomposites to deploy and detect a variety of organic and inorganic molecules of emerging concerns. The application of enzyme-linked nanocomposites based on MXenes in biosensing platforms is expected to effectively address the unresolved challenges encountered by conventional analytical and sensing techniques in various practical settings. Considering the above-mentioned critiques and potentialities, we reviewed enzyme-linked MXenes as a fascinating interface to design, develop and deploy a new generation of monitoring systems to aid bioanalytical applications. More precisely, various challenges and obstacles connected to the synthesis processes, surface functionalization, influencing properties (such as mechanical, electrical, magnetic, and optical), and enzyme immobilization chemistry of MXenes have been highlighted with relevant examples, emphasizing their significant role in biocatalysis and biosensing applications. In the end, concluding remarks and future expectations have been outlined to document modern expansions in this area. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT calculations are performed to study the properties of S-doped MnOOH. • MnOOH nanofibers are prepared through a one-step hydrothermal method. • S doping improves the electronic/ionic transport and structural stability of MnOOH. • Ex situ XRD, Raman, XPS, and SEM tests reveal Zn2+/H+ insertion-type mechanism. • Low and high mass loading electrodes show impressive electrochemical performances. MnOOH is regarded as a product of manganese-based materials after H+ insertion. There is rare study on the Zn2+/H+ storage capability of MnOOH. Herein, MnOOH nanofibers are prepared through a one-step hydrothermal method and developed as a promising cathode. The introduction of S doping changes the crystal structure of MnOOH and is conducive to its electronic/ionic transport and structural stability, proven by density functional theory calculations and various characterizations. The reduced Zn2+ diffusion barrier of S-doped MnOOH leads to its increased Zn2+ storage capability in the test of rate capability, especially at large current density. The Zn2+/H+ insertion-type mechanism of MnOOH is revealed by ex situ XRD, Raman, XPS, and SEM tests. Therefore, this optimized material delivers a high reversible capacity of 178 mAh g−1 at 0.1 A g−1, a good rate capability of 50 mAh g−1 at 3.0 A g−1, and a long cyclic life with 108 mAh g−1 at 0.5 A g−1 over 500 cycles. Moreover, the electrode still shows satisfactory rate capability and cyclic life even at the high mass loadings of 10 and 15 mg cm−2. This work proves the Zn2+/H+ storage capability of MnOOH and its potential as a high-performance cathode in aqueous zinc ion battery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermodynamics and kinetics of photocatalytic free radical in water were summarized. • Inert diffusion barrier layer to inhibit oxidation dominant immobilization of photocatalysts. • Quantitative load stability evaluation using indentation modulus (EIT) was developed. • Cutting-edge applications directions of various types of photocatalytic reactors was proposed. Photocatalytic technology, which utilizes light energy instead of the consuming of chemical reagents, is becoming a promising purification method in various wastewater treatment occasions. Compared to conventional biological methods and advanced oxidation methods, photocatalytic technology represents great inclusion and diversity. However, the practical engineering application of photocatalytic technology is still limited, mainly because of the unsatisfied separation and recovery of catalysts and their compatibility with photocatalytic reactors. The key to conquer this problem lies in the appropriate and in-depth understanding of the interface properties of scale-up photocatalytic films and devices, specifically figuring out the reliable immobilization of photocatalysts and the development of suitable application scenarios. This review focus on the immobilized photocatalysts of photocatalytic reactors for rational engineering applications Simultaneously, different types of photocatalytic reactors are evaluated and analyzed to understand their advantages and applicability. Additionally, the state-of-art and key issues of photocatalytic technology in various water treatment engineering applications are reviewed. Furthermore, the rational operation modes of photocatalytic reactors coupling with specific engineering applications are also clarified to promote the industrial application of photocatalytic technology. [ABSTRACT FROM AUTHOR]

• A unique composite filler Gr@PDA-IPTMS-SiC was elaborately designed. • The tolerance of composite coating towards 1.5 MPa hydrogen pressure impact test was investigated. • The as-prepared coating exhibited excellent long-term anti-corrosion and enhanced hydrogen gas barrier properties. • Anti-corrosion and H 2 barrier mechanisms of the composite coating were analyzed in detail. The investigation on ordinary hydrogen barrier composite coatings has been limited in terms of corrosion and high-pressure hydrogen environments, which significantly restricts its practical and industrial applications. Herein, a unique nanohybrid two-dimensional (2D) filler, constituting poly-dopamine (PDA) functionalized graphene (Gr) nanosheets and covalently bridged silicon carbide (SiC) nanoflakes assisted by 3-Isocyanatopropyltrimethoxysilane (IPTMS) via hydrolysis reaction, was innovatively proposed and incorporated into fluoroethylene vinyl ether resin (FEVE) to fabricate final composite coating by spin-coating technique. The hydrogen gas barrier and long-term anti-corrosion performances could be simultaneously enhanced by precisely collaborative effects of interfacial interactions fortification among Gr, SiC, and polymer phase as well as centrifugal force promoted Gr orientation during the spinning process. The optimum sample demonstrated high |Z| 0.01Hz values of 3.1 × 1011 Ω cm2 and 3.37 × 1011 Ω cm2 throughout 90 d saltwater immersion and 6-day 1.5 MPa pressurized hydrogen environment exposure respectively. Moreover, its permeability coefficient decreased by 75.66% compared to the pure sample. Other significant properties including 30d constant salt-spray attack tolerance and high adhesion strength of 12.46 MPa were also achieved to meet industrial demands. This work provided paramount inspiration for designing composite coatings for hydrogen transportation pipeline protection and hydrogen energy usage. [ABSTRACT FROM AUTHOR]

• As a promising preparation strategy for 2D MXenes, the molten-salt-assisted synthesis method has garnered significant attention in recent years owing to its numerous advantages. • Molten-salt-assisted synthesis method is elucidated through the etching mechanism, property regulation, and delamination of multi-layered MXenes. • The applications of 2D MXenes derived from the molten-salt-assisted synthesis method in energy storage and conversion. • The challenges and prospects associated with the synthesis of molten-salt-assisted synthesis methods are put forward. Two-dimensional (2D) MXenes have captured inter-disciplinary interest owing to their exceptional electronic conductivities, adjustable layered structures, and controllable interfacial functional groups. Low-cost, efficient, and amicable techniques are urgently desired for synthesizing high-quality and high-yield 2D MXene materials. Recently, molten-salt-assisted methods have been proven to be the promising processes to construct versatile 2D MXenes with metallic-level conductivity, good mechanical strength, low ion diffusion barrier and rich surface chemistries to meet the criteria for practical applications. Herein, the most up-to-date progress of molten-salt-assisted approaches for manufacturing 2D MXene materials and their synthesis mechanisms are comprehensively summarized, introducing the effect on the physical/chemical properties of the obtained MXenes compared with other common synthesis methods. Meanwhile, typical examples of MXenes obtained by tuning surface termination, interlayer spacing, size, and morphology are presented. Further, the focus turns to their structure–property relationships and applications in electrochemical energy storage and conversion, including supercapacitors, Li-batteries, Zn-ion batteries and electrocatalysis. Finally, a discussion about the challenges and prospects of the molten-salt-assisted approaches is put forward. This review will guide and encourage the future rational design and controllable synthesis of 2D MXenes with high performance based on molten-salt-assisted strategies. [ABSTRACT FROM AUTHOR]

• Interlayer defects were constructed on the (002) crystal plane of WS 2 by Ni doping. • The interlayer defect structures exhibit higher sodium storage capacity. • DFT analysis shows that defects can greatly reduce the diffusion barrier for Na+. Tungsten disulfide (WS 2) exhibits high theoretical capacity (433 mAh g−1) and unique layered structure, which is a potential anode material for sodium ion batteries. The sodium ions are diffused mainly along the (0 0 2) crystal plane of WS 2 , showing unsatisfactory Na+ diffusion kinetics leads to poor rate capacity. It is still a challenge to break through the two-dimensional diffusion of Na+ and to realize the rapid multi-dimensional transport of more Na+. In this work, the multi-dimensional migration channel structure constructed by Nickel-doped WS 2 composite, which exhibits penetrable interlayer defects on the (0 0 2) crystal plane of WS 2 nanosheets. On one hand, the interlayer defects as active sites can absorb more Na+, showing higher sodium storage capacity. On the other hand, the DFT results show that these interlayer defect structures can greatly reduce the diffusion barrier for Na+ migration along the vertical direction of (0 0 2) crystal plane of WS 2. The structure expands the diffusion of Na+ from two-dimensional plane to multi-dimensional, which enables high speed sodium and potassium ion storage kinetics. This work provides a new idea for improving ion diffusion and accelerating electrochemical reaction kinetics of other transition metal layered compounds. [ABSTRACT FROM AUTHOR]

• MSs and MCs are the promising host anodes for SIBs because of their substantial capacity and impressive redox reversibility. • The layered structure and large surface area provide substantial potential for intercalating more Na ions, thus maximizing the storage capacity. • MSs and MCs reveal very low diffusion barriers for Na migration indicating the hasty sodiation/desodiation processes. • This study substantially impacts the rational design of the next generation of 2D MSs and MCs as anode materials for SIBs. Both sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs) operate on a similar principle and are striking for energy storage purposes. Although some electrode materials adapt favorably to LIBs, they are not pertinent for SIBs systems because Na+ (0.98 Å) has a significantly bigger diameter as compared to Li+ (0.69 Å). The use of two-dimensional (2D) materials as anodes for SIBs has established tremendous advancement in the last decade through their exceptional 2D layered structure, infinite planar lengths, and highly disclosed active sites. 2D materials assist the current SIB anode materials as profitable successors. To resolve the energy storage crisis, superior quality anode materials are essential for rechargeable next-generation SIBs. Among all anode materials, layered metal sulfides (MSs) and metal carbides (MCs) are the promising host anodes for SIBs because of their substantial capacity and impressive redox reversibility. The distinctive structures of 2D MCs and MSs provide an innovative era to surmount the challenges in anode materials like structural collapse, volume change, small storage capacity, and confined phase variation. The layered structure and large surface area provide substantial potential for intercalating and hosting more Na ions, thus maximizing the storage capacity. This review delineates some influential 2D MCs and MSs for anodic uses. In this review, we analyze theoretical and experimental techniques for scrutinizing predicted anode materials, electronic characteristics, and electrochemical performances, and they are reported to be beneficial for SIBs. Furthermore, the future perspective and the material design are described. The light shaded on the 2D MCs and MSs is anticipated to identify new anode materials for SIBs. [ABSTRACT FROM AUTHOR]

• A double site doped layered P 2-K 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 O 2 cathode is designed. • The expanded layer spacing of K doping provides a higher electrochemical capacity. • A combined analysis of first-principles calculation simulation and experimental verification. • The regulation of cycling stability by setting the cut-off voltage are provided. • It shows excellent cycling performance and environmental exposed stability. P 2-type Ni/Mn layered oxides have attracted intensive interest as a kind of promising cathode materials because of their high specific capacities and unique 2D Na+ diffusion path. However, the poor stability and irreversible phase transition at high voltage during charge and discharge process greatly hinders its practical applications. Herein, a novel double site substitution strategy is reported that large-sized K+ is riveted in the prismatic Na+ sites and Cu2+ is occupies in the transition metal sites. The K+ doping lead to the lattice expansion along c -axis, which facilitating sodium ions transport. In addition, the double sites substitution improves the stability of the materials exposed in air and water environments. A combined analysis of first-principles calculation simulation and experimental verification determining that larger interlayer spacing decreases the diffusion barrier of sodium ions. The as-prepared multiple-layer oriented P 2-K 0.05 Na 0.67 Mn 0.6 Ni 0.3 Cu 0.1 O 2 shows excellent rate performance, fast sodium ion transport ability and superior cycling performance with a high-capacity retention of 91.2 % at a high current density of 1 A g−1 after 1800th cycles. Therefore, this work provides a new insight for the design of stable and high-performance cathode materials for sodium ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • CRED, Rietveld refinement and HAADF-STEM prove the insertion of 1, 2, 3-BQ into V 2 O 5. • (1, 2, 3-BQ)-VO shows excellent rate and cycling performances in Zn(CF 3 SO 3) 2. • In the electrolyte with Al3+, (1, 2, 3-BQ)-VO shows much enhanced cycling performance. • It is observed dynamic reversible disorder–order conversion on the (00 l) facets. • The inserted Al3+ can improve the crystallinity of the charged (1, 2, 3-BQ)-VO. It was synthesized oxygen-deficient (1, 2, 3-BQ)-VO formulated as (1, 2, 3-BQ) 0.25 V 2 O 5 ·0.5H 2 O (BQ = benzoquinone) via a facile one-step hydrothermal technique. Continuous rotation electron diffraction (cRED), Rietveld refinement and spherical aberration-corrected transmission election microscopy unravel the successful pre-intercalation of the BQ organic species into the layered vanadium oxide, in which two neighboring V-O-V monolayers are observed with the (0 0 1) facet as the division plane. (1, 2, 3-BQ)-VO possesses a good electrochemical property in 3 M Zn(CF 3 SO 3) 2. And in the electrolyte with Al3+, it shows improved rate capability and remarkably enhanced cycling performance. Its average capacity is up to an unprecedented value of 446/400 mAh/g at 0.2/1 A/g with a capacity retention exceeding 100 % over 550 cycles at 1 A/g (411 mAh/g), which is associated with the dynamic reversible conversion between disorder and order on the (001) facets. The inserted Al3+ into the inner channel of (1, 2, 3-BQ)-VO during the discharge process, not only acts as the interlayer pillar to prevent the collapse of the layered structure, but also can improve the crystallinity of the charged (1, 2, 3-BQ)-VO sample due to the more ordered atomic arrays from the interlayer (00 l) facets. And the dual pillars of BQ and Al3+ in the sample can boost the exposure of active sites, thus enhance the storage capacity. In addition, density functional theory (DFT) calculations disclose a small Zn2+ diffusion barrier of 0.85 eV in (1, 2, 3-BQ)-VO. Moreover, it is found that the electrolyte with Al3+ is not only beneficial for the modification of the (1, 2, 3-BQ)-VO cathode, but also can inhibit the Zn dendrite formation at the Zn anode. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monolayer graphene with partial wetting transparency decreases the interaction between substrates and perovskite. • CsPbBr 3 grown on substrates with graphene shows changed orientation, improved crystallinity and enlarged grains. • Graphene could regulate the doping level of CsPbBr 3. • CsPbBb 3 photodetector with graphene shows better device performance. Tuning the structural and electronic properties of halide perovskite material is an effective method to promote its device performance. Increasing the grain size can decrease grain boundaries and further reduce defects. Regulating the band structure will improve the separation and extraction efficiency of carriers. In this work, high-quality CsPbBr 3 films with increased crystallinity, better preferential orientation and improved carrier dynamics are achieved, using partial wetting transparent monolayer graphene as an interlayer. It is demonstrated that graphene can partially shield the surface potential field of the substrates, resulting in a changed preferred orientation of the CsPbBr 3. The reduced interaction between the substrates and the perovskite effectively decreases the diffusion barrier of adatoms, increasing the grain size and crystallinity. Besides, the presence of graphene also tunes the band structure of the perovskite with increased p-type doping, which changes the band offset at perovskite substrate interface. An improved charge extraction can be achieved on perovskite/G/ITO interface due to increased band offset while a reduced charge extraction is observed on perovskite/G/Au interface. As a result, the corresponding photodetector with graphene demonstrates better performance than that without graphene. Our study will provide more ideas for tuning the perovskite structure and energy bands to achieve better device performance. [ABSTRACT FROM AUTHOR]

• Ti 3 C 2 T x MXene provides zincophilic sites for dendrite-Free zinc deposition. • The ZnO@MXene anode achieves ultra-long cycle stability at a high rate. • The average discharge specific capacity of this work can attain 625 mAh·g−1. Although Zn-Ni battery is a potential energy storage system, the anode zinc electrode often faces dendrite, passivation and deformation problems, which tend to be exacerbated at high current densities particularly, and severely hamper its practical applications. Zinc oxide was modified with 2D transition metal carbides/nitride (ZnO@MXene) firstly for the purpose of broadening the application scenarios of zinc alkaline secondary batteries. A variety of characterizations and density functional theory (DFT) calculations certify that highly conductive MXene matrix provides a high-speed electron transfer channel and its low ionic diffusion barrier and excellent ionic diffusion mobility of MXene can quickly reduce the ion concentration gradient at the solid–liquid interface, which weakens the concentration polarization. Also, MXene can tune the diffusion behavior to induce homogeneous deposition of zinc via the zinc-oriented-O groups, forming well-dispersed "seed points" to realize uniform nucleation and inhibiting dendrite growth. Therefore, ZnO@MXene as the anode of a Zn-Ni battery can keep its capacity of 594mAh·g−1 after 1500 cycles at 10C. That reaches 90% of its initial capacity (596mAh·g−1), suggesting superb specific capacity, rate performance, and cycle life span. [ABSTRACT FROM AUTHOR]

[Display omitted] • f-FePSe 3 /CNT hybrids were prepared as anodes for potassium ion storage devices. • f-FePSe 3 /CNT hybrids enhance electronic conductivity and promote K+ diffusion. • The f-FePSe 3 /CNT anodes perform 472.1 mA h g−1 at 0.05 A/g and 124.9 mA h g−1 at 10 A/g. • The potassium-ion battery with f-FePSe 3 /CNT anode was cycled 500 times. • The hybrid capacitor with f-FePSe 3 /CNT anode provides an energy/power density of 54.7 W h kg−1/5790.8 W kg−1. Given the layered crystal structure and tunable composition, ternary metal phosphorus trichalcogenides (MPCh 3) is an attractive anode material for potassium-ion batteries with higher surface activity and mobility than their binary analogues. However, how to improve the electronic conductivity, ion diffusion, and maintain high reversible potassiation/depotassiation processes are the main key issues for the development of MPCh 3 -based electrodes with high rate and long cycle life. For example, theoretically, FePSe 3 has a layered crystal structure with high electronic conductivity and low diffusion barrier, yet their K+-based electrochemical performance not well demonstrated. Here, we report a mechanical exfoliation method to prepare few-layer FePSe 3 -carbon nanotube (f-FePSe 3 /CNT) hybrids for use as high-efficiency K+ storage anodes. Electrochemical performance, kinetic analysis, reaction mechanism analysis, and density functional theory calculations show that this strongly coupled 1D-2D hybrids promotes the reaction and diffusion of potassium ions, giving full play to the inherent advantages of materials with different dimensions. Therefore, the f-FePSe 3 /CNT PIB anodes exhibit high capacity (472.1 mA h g−1, 0.05 A/g), high rate (124.9 mA h g−1, 10 A/g), and cycling stability (>1000 cycles), which significantly exceeds the performance of its binary analogue, here FeSe. In addition, the full cells of potassium-ion battery and hybrid capacitor coupled with f-FePSe 3 /CNT anodes exhibit good cycling stability (500 cycles) and high energy/power density of 54.7 W h kg−1/5790.8 W kg−1, respectively, revealing its practical applications in a wide range of K+-based storage systems. We believe that this work will provide a universal strategy for effectively activating the K+ electrochemical performance on a wide range of layered materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • N,O codoping and atomic-interface engineering is performed on WS 2. • Interoverlapped superstructure of unilamellar N, O co-doped WS 2 and C is obtained. • The unique structure maximizes atomic-interface contact area between WS 2 and C. • The unique structure has ultralow bandgap and K+ diffusion energy barrier. • The unique structure shows ultrafast K+ storage performances. WS 2 is a promising anode for potassium-ion batteries due to its high theoretical capacity and unique layered structure. However, the intercalation-dominated K+ storage, large K+ diffusion barrier energy, and poor intrinsic electrical conductivity limit its practical application. Based on these problems, a synergetic effect of N, O codoping and atomic-interface engineering is performed for WS 2, in which interoverlapped superstructure of unilamellar N, O co-doped WS 2 and C (NO-WS 2 -C) is designed to maximize the atomic-interface contact area between WS 2 and carbon. The unique NO-WS 2 -C enables the occurrence of the conversion reaction between WS 2 and K+, which produces vast ultrasmall W nanoparticles (∼2 nm), resulting in the construction of a space charge zone on the W surface to enhance K+ storage. Furthermore, density functional theory calculations indicate that the unique NO-WS 2 -C possesses a low bandgap (0 eV) and K+ diffusion energy barrier (0.2 eV) to boost K+ transport. Consequently, an ultrafast K-ion storage capability (107.8 mAh/g at 20C), and an ultralong cycling life over 5000 cycles at 5C with an extremely low capacity loss per cycle of 0.007 % are obtained, which are the best among previously reported WS 2 -based anodes.. [ABSTRACT FROM AUTHOR]

[Display omitted] • The precipitates V 2 O 5 and Li 1.2 V 9 O 22 formed after heat treatment of V 2 O 5 -TeO 2 -Li 2 O. • Conversion of [VO 5 ] to [VO 4 ] changed the structure of [TeO 4 ] to [TeO 3 ]. • LiV 3 O 8 precipitated after 200 cycles promoting the reaction kinetics and capacity. • Different mechanisms of nanocrystals formation during cycling and thermal induced. • DFT model reveals lower diffusion barriers and higher electronic conductivity. V 2 O 5- TeO 2 (VT) is one of the promising vanadium-based materials for electrodes in Li-ion batteries, but its application is impeded by its low conductivity and poor capacity retention. The initial cyclic efficiency of V 2 O 5 -TeO 2 -Li 2 O(VTL) is enhanced by the addition of Li 2 O, implying that the pre-intercalation of Li-ions significantly improves the performance. The thermal treatment of VTL leads to the formation of V 2 O 5 and Li 1.2 V 9 O 22 crystals in the polycrystalline state (VTL-X). The VT, VTL and VTL-X exhibited specific capacitie of 821.9, 842.1, and 867.2 mAh g−1, respectively for the 1st cycle with respective retention rates of 19.6%, 19.5% and 27.5% after 1000 cycles. To elucidate the reaction mechanism, a structural simulation diagram of VTL during the heat treatment is modeled for the first time. The conversion of [VO 5 ] to [VO 4 ] transformed the structure of [TeO 4 ] into [TeO 3 ]. The DFT model reveals that the highest diffusion barriers for VTL and VTL-X are 0.49 eV and 0.16 eV, respectively. After crystallization, the conductivity and specific capacity of the resulting electrode material are significantly improved. LiV 3 O 8 precipitated after 200 cycles promotes the reaction kinetics and specific capacity. The synergistic effect of precipitating crystals impacts the glass structure, electrochemical reversibility, and reaction kinetics enormously, revealing the pivotal function of nanocrystal in regulating the battery cycling stability. The formation mechanism of nanocrystals during cycling is entirely different from thermal induced crystallization. The crystallization of glass electrodes during battery cycles helps to unfold the properties of glassy materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aerogel-structured MnO 2 was assembled by defect-rich ultrathin nanosheets. • V doping and oxygen vacancies manipulate electronic structure of the MnO 2. • The MnO 2 shows enhanced electrical conductivity and fast Zn2+ diffusion ability. • The MnO 2 cathode presents markedly boosted electrochemical performance. Rechargeable MnO 2 //Zn zinc-ion batteries (ZIBs) gain increasing attention as prospective candidates for large-scale energy storage applications, but MnO 2 cathode materials are afflicted by intrinsic low electrical conductivity, sluggish Zn2+ diffusion kinetics and unstable crystal structure during Zn2+ insertion/extraction. Herein, we report the scalable synthesis of an aerogel-structured MnO 2 (A-MnO 2) assembled by defect-rich ultrathin nanosheets for ZIBs. For the A-MnO 2 , V doping and its induced oxygen vacancies manipulate electronic structure to enhance electrical conductivity and decrease Zn2+ diffusion energy barrier, and meanwhile, the ultrathin nanosheets-assembled aerogel structure favors the exposure of more electrochemically active sites and the shortening of ion diffusion distance. As a consequence, the A-MnO 2 is endowed with markedly boosted electrochemical kinetics and thus superior electrochemical performance than defect-free MnO 2 nanorod counterpart. Furthermore, flexible ZIB devices with both impressive flexibility and outstanding electrochemical properties can be realized using the A-MnO 2 cathode material. This work is expected to promote the practical application of MnO 2 //Zn ZIBs. [ABSTRACT FROM AUTHOR]

• A sub-micron CIGS solar cell with the conversion efficiency of 18.9% was fabricated. • Optimum SiO 2 can effectively regulate the Na content in CIGS. • The optimized Na can optimize the Mo/CIGS interface and CIGS/CdS interface. • The optimized Na can improve carrier separation and passivate recombination. Alkali metal Na is beneficial to the performance of CuInGaSSe thin film solar cells. This work studies the addition and optimization of a sputtering SiO 2 barrier layer on the soda-lime glass to optimize the Na content that diffuses into the absorber layer from the SLG. The resulting Se content and distribution, the influence and change of the MoSe 2 thickness are studied. Also, the changes in quality of the p-n junction and the defects of the absorption layer are studied. Last, the resulting carrier separation and changes in the carrier recombination rate of each part of the absorber are analyzed. For sub-micron CuInGaSSe devices, it is clear that untreated soda-lime glass provides excessive amounts of Na. After optimization and analysis of the barrier layer thickness, the average conversion efficiency is increased by 34% compared with the sub-optimal sample, and the efficiency reaches 18.9%. [ABSTRACT FROM AUTHOR]

• An interface-free integrative graphitic carbon network film (IGCN) was prepared. • Lattice defects and large layer distance of IGCN formed by Ar/S/H plasma etching. • The ED-IGCN exhibits high rate durable cyclability with obvious discharge plateau. • The pseudo-capacitive mechanism and contributed a lot to the fast K-storage kinetics. In the K-storage process, graphitic carbon exhibits unique practical plateau potential but suffers terrible rate and cycle performance, because its perfect long-range ordered carbon structure, small lattice space and high contact/interface resistance are still bottlenecks to limit the kinetics and structural stability. Herein, we prepare a novel interface-free integrative graphitic carbon network film on a large scale, and enlarged its lattice distance and reasonably introduce defects (ED-IGCN) to boost kinetics and cyclability via a plasma-enhanced etching/S-doping process. Typically, the ED-IGCN entails ultra-thin hollow graphitic units (diameter ∼ 10 nm, shell wall ∼ 1 nm) interconnected by sp2 hybrid covalent bonds, providing an interface-free highly conductive network. Additionally, the defective long-range ordered carbon arrangement and enlarged lattice distance ensured numerous open channels and shortened pathways with low diffusion barrier for boosting the fast (de)potassiation kinetics. When applied in PIB, the ED-IGCN anodes delivered a high reversible capacity of 408 mAh g−1 at 20 mA g−1, and ultra-high rate and long-term cyclability without expensing its unique discharge plateau. The capacity maintained up to 91.1 mA h g−1 after 10,000 cycles at 5 A g−1 with a capacity retention of ∼ 60% (∼51% after 11,000 cycles), which is not inferior to that of any graphitic carbon reported previously. We separated the diffusive capacity, and pseudo-/double-layer capacitive contributions, and verified that the plasma treating process enhanced the capacitive K-storage mechanism which give great contribution to the fast kinetics. A full-cell based on potassium Prussian blue (KPB) cathode and ED-IGCN anode delivered an initial reversible capacity of 177 mAh g−1 at 1000 mA g−1, and retained ∼ 70% after 50 cycles, further demonstrating the ultra-high rate capability of ED-IGCN in practical application. The results provide new insights into the design and structure regulations of graphitic carbon for fast-charging batteries with stable working voltages and an understanding of the diffusion acceleration mechanism in graphitic carbon materials. [ABSTRACT FROM AUTHOR]

• Oxygen vacancy-mediated N doping strategy is purposed to modify nano-TiO 2. • The doped TiO 2 displays the highest doping concentration of N of 13.8 atom%. • High N doping level favors the diffusion kinetics of Li+/electron. • The doped TiO 2 exhibits excellent Li+ storage capability. Substitutional nitrogen (SN) doping is an effective approach to simultaneously enhance the ionic diffusion kinetics and increase the electronic conductivity of TiO 2 being as host for lithium-ion storage. Nevertheless, achieving SN doping with high concentration in well-crystallized TiO 2 nano-particles is still a great challenge. Herein, guided by density functional theory (DFT) calculations, an oxygen vacancy-mediated SN doping strategy is purposed to modify the surface structure of TiO 2 nano-particles. A reduced TiO 2-x amorphous layer with rich oxygen vacancy on the surface of TiO 2 nano-particles brings about high doping concentration of SN (∼13.8 atom%) and thus a TiO 2 @TiO 2-x -SN core@shell heterojunction is constructed. The high doping concentration of SN in TiO 2-x -SN shell of TiO 2 @TiO 2-x -SN heterojunction favors the diffusion kinetics of Li+ due to the formation of local electric field at its heterointerface region and reduced diffusion barrier of Li+. Moreover, TiO 2 @TiO 2-x -SN heterojunction shows a decreased band gap of 2.37 eV after increasing the doping concentration of SN, facilitating the transport of electrons. Thus, the TiO 2 @TiO 2-x -SN electrode displays high reversible specific capacity of 362.7 mAh g−1 at 0.1C and ultra-long cycling structural stability (with a capacity retention of 76.1% after 5000 cycles at 20C). A Li+ hybrid capacitor, assembled by activate carbon cathode and pre-lithitated TiO 2 @TiO 2-x -SN anode, shows high energy/power densities (114.8 Wh kg−1/305.1 W kg−1 and 90.2 Wh kg−1/5659.8 W kg−1). This work paves a way for developing high concentration of heteroatom doping metallic oxides and offers comprehensive understandings for the relationship between doping concentration of heteroatoms and energy storage mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic passivation by Na+ and SCN− suppresses nonradiative loss in C-PSCs. • Na+ is incorporated at the A-site of CsPbI 2 Br enhancing the I− diffusion barrier. • SCN− plays a role in regulating the crystal growth dynamics of CsPbI 2 Br formation. • HTM-free carbon-based CsPbI 2 Br solar cells with efficiency of 14.63%. Hole transport material (HTM)-free carbon-based all-inorganic perovskite solar cells (C-PSCs) possess excellent thermal stability and low cost, which promise an alternative to replace the conventional organic–inorganic hybrid PSCs. The additive method is an effective approach to enhance the performance of PSCs by improving the quality of perovskite films. Herein, the synergistic passivation strategy of alkali metal and halogenoid ions in NaSCN additive is adopted to suppress nonradiative recombination in CsPbI 2 Br films. The Na+ is incorporated at the A-site of CsPbI 2 Br cell that enhances the I− diffusion barrier energy from 0.229 eV to 0.401 eV, suggesting suppressed iodide vacancy. Moreover, the SCN− plays a role in regulating the crystal growth dynamics during the CsPbI 2 Br film formation process, reducing defect density. This synergistic passivation strategy effectively improves the perovskite film quality, and increases the recombination resistance and the carrier extraction efficiency of CsPbI 2 Br films, therefore reducing nonradiative recombination loss in the final device. The assembled HTM-free carbon-based all-inorganic CsPbI 2 Br perovskite solar cells present a champion PCE of 14.63% (V OC = 1.267 V, J SC = 14.31 mA/cm2, fill factor (FF) = 0.807), which is among the best performances in the carbon-based all-inorganic perovskite solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quantitatively control surface barriers via modifying ZSM-5 zeolite surface. • A higher reaction rate achieved with the increase of surface permeability. • Spatiotemporally visualize evolution of guest molecules in zeolite crystals. • Enhance zeolite accessibility to increase reaction rate by lowering surface barriers. Mass transfer of guest molecules is crucial for zeolite catalysis. Compared to intracrystalline diffusion, the surface barriers in zeolite catalysis have been less understood. Taking furfuryl alcohol oligomerization catalyzed by ZSM-5 zeolites as model reaction, here we present a single-crystal level study and gain insight into the surface barriers induced spatiotemporal evolution of oligomer products using structured illumination microscopy (SIM). It is shown that, as a result of the enhanced accessibility to zeolite crystals, promoting the surface permeability leads to the increase in catalytic reaction rate that is characterized as the generation rate of oligomer products. [ABSTRACT FROM AUTHOR]

High-performance flexible sodium-ion batteries based on carbon sphere-supported hierarchical Nb2CTx MXene/MoS 2 composites, which excellent specific capacity, cycle stability and rate performance. It has a specific capacity of 196 mAh g-1 at a current density of 20 A g-1. In addition, this design scheme can also be extended to other application scenarios. [Display omitted] • Hollow carbon sphere could make electrode three-dimensional. • MXene-bonded 3D hierarchical structure could reduce the charge transfer path. • Nb 2 CT x /MoS 2 @CS anode have outstanding cycle stability for Na ion storage. • MXene-bonded electrode have certain flexibility. Hand-made Nb 2 CT x /MoS 2 @CS//NVP full battery could reach to 90° bending. Sodium-ion batteries, as a promising alternative to the lithium-ion battery, have attracted extensive attention. However, due to the larger ion radius and higher standard reduction potential, the sodium-ion batteries still face poor cycle stability and relatively low energy density problems. In this work, a carbon sphere-supported Nb 2 CT x MXene/MoS 2 hierarchical structure has been designed and synthesized through hydrothermal and electrostatic self-assembly methods. The design strategy successfully improves the utilization efficiency of the MoS 2 carbon sphere as a support skeleton and reducing the diffusion path length of Na ions, leading to an improved specific capacity and rate performance. Moreover, Nb 2 CT x sheets also effectively inhibit the capacity attenuation caused by MoS 2 shedding, thus achieving the long cycle life of the sodium-ion battery. As a result, the carbon-supported MXene/MoS 2 anode delivers an ultrahigh reversible capacity, long cycling stability, and superior capacity retention rate. Notably, the carbon-supported MXene/MoS 2 anode can also obtain a considerable capacity of 196 mAh g−1 at a current density of 20 A g−1. The full cell of SIBs was assembled, and the flexibility of the battery was tested. The density functional theory simulation results show that the sodium ion has a smaller diffusion barrier under this material design strategy. [ABSTRACT FROM AUTHOR]

[Display omitted] • High surface energy of PA induced low-energy-barrier orientation crystallization. • The morphology of Al-CDC was transformed from 3D crystals to 2D nanosheets. • Ultrathin films provided high adsorption efficiency and low diffusion barrier. • The composite yields optimum selectivity of CH 4 /N 2 among available adsorbents. • Hydrophobic shell enhanced the water and recycling stability of composite. Development of materials with high efficiency and long-life cycles for CH 4 /N 2 separation is of importance for coal-bed methane purification. Herein, a composite was prepared by in-situ growing the specific aluminum-based metal–organic framework (MOF) with trans -1,4-cyclohexanedicarboxylicacid as ligand (Al-CDC) on the internal macroporous surface of polyacrylates (PA). Due to the surface-induced low-energy-barrier orientation crystallization, the morphology of Al-CDC was transformed from three-dimensional (3D) crystals to two-dimensional (2D) nanosheets, forming ultrathin films with higher adsorption efficiency and lower diffusion barrier. As a result, the adsorption efficiency can be increased by 1.73 times compared with bulk Al-CDC and the selectivity of CH 4 /N 2 (50/50, v/v) mixed gas is 13.75, which is the highest value reported so far. Furthermore, the hydrophobic feature of PA enhanced the water and recycling stability of composite, providing promising adsorbent for coal-bed methane purification using pressure swing adsorption process. [ABSTRACT FROM AUTHOR]

[Display omitted] • • The interplanar distance of MoS 2 is expanded from 0.62 nm to 0.885 nm. • • Li+/Mg2+ hybrid-ion batteries realize the Li+/Mg2+ co-intercalation even at 1000 mA g−1. • • A "boost effect" of intercalated Li+ on Mg2+ was found and demonstrated. • • A reversible capacity of 123.3 mAh g−1 was exhibited at 1000 mA g−1 after 2000 cycles. Li+/Mg2+ hybrid-ion batteries (LMIBs), integrating the merits of lithium ion batteries (LIBs) and magnesium ion batteries (MIBs) are considered as an attractive alternative of next generation metal secondary batteries. Due to the sluggish solid-state diffusion kinetic induced by the strong Coulombic interaction between Mg2+ and host materials, pristine MoS 2 with interplanar distance of 0.62 nm exhibits inferior electrochemical performance for LMIBs with only Li+ intercalation. Herein, we report an oxygen-incorporated MoS 2 (O-MoS 2) nanoflower anchored on graphene (O-MoS 2 /G) with the interplanar distance of O-MoS 2 from 0.62 nm expanded to 0.885 nm. Even at 1000 mA g−1, the expanded interlayer spacing can still ensure the Mg2+ and Li+ intercalation/deintercalation into/from the host material simultaneously. Meanwhile, this configuration can effectively reduce the diffusion barrier of metal ions, increase the intercalated number of ions, and enhance the stability of structure. In addition, we found and demonstrated the intercalated Li+ had a boosting effect to the intercalation kinetics of Mg2+. Compared with the MIBs, the migration energy barriers of Mg2+ under the existence of Li+ intercalating into MoS 2 is reduced from 0.36 eV to 0.16 eV, meanwhile the corresponding intercalation capacity and diffusion coefficient of Mg2+ are 1.38 and 7.1 times as large as MIBs. As expect, the O-MoS 2 /G exhibits superior rate capability and cycling performance with a reversible capacity of 123.3 mAh g−1 after 2000 cycles charge–discharge processes at 1000 mA g−1. [ABSTRACT FROM AUTHOR]

Schematic illustration of the synthesis routes of MnSe⊂3DCNM by typical sol–gel and selenation methods. [Display omitted] • MnSe ⊂ 3DCNM are synthesized via a facile sol–gel and selenation route. • The 3DCNM are beneficial for the generation of intermediate Li x MnSe phase. • The phase transformation of Mn (α → β) can decrease diffusion energy barriers. • MnSe ⊂ 3DCNM-1.92 show excellent electrochemical performances for half and full cells. Manganese selenide (MnSe), a conversion-type anode for Lithium-ion batteries with low cost and high specific capacity, is impeded the development by drastic volume changes and poor kinetics in Li+ insertion/desertion processes. In this study, we successfully synthesized uniform MnSe nanoparticles anchored in 3D carbon nanosheet matrix (MnSe ⊂ 3DCNM) via a facile sol–gel and selenation route. The obtained 3DCNM contributes high surface area, increased active sites for N-doping, excellent electric conductivity and stable nanostructure to MnSe ⊂ 3DCNM, thereby leading to full lithiation/delithiation reactions, excellent electrochemical kinetics and buffer volume expansion of MnSe nanoparticles. Among these MnSe ⊂ 3DCNM materials, MnSe ⊂ 3DCNM-1.92 exhibits superior cycle stability with a stable reversible capacity of 665.5 mA h g−1 after 200 cycles and excellent rate capabilities in half cells. When combined with LiMn 2 O 4 cathode, the MnSe ⊂ 3DCNM-1.92//LiMn 2 O 4 full cells also exhibit excellent electrochemical properties. The kinetic analysis and EIS results demonstrate the generation of intermediate Li x MnSe phase and the irreversible phase transformation of α-MnSe → β-MnSe with decreased diffusion energy barriers mainly facilitate MnSe ⊂ 3DCNM-1.92 to exhibit high specific capacity, superior Li+ and electron transport kinetics. This facile strategy provides a guideline for the other transition metal selenides with high surface areas and stable nanostructures apply in storage systems, electrocatalysis, and semiconductors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of disordered and ordered S vacancies on Na+ storage in VS 2 nanosheets were investigated. • The disordered S vacancies provided an extra ion diffusion pathway perpendicular to the VS 2 plane with a lower Na+ diffusion barrier of 0.229 eV. • The VS 2 with disordered S vacancies exhibited rapid rate capability and ultra-long cycle stability. Slow diffusion kinetics of Na+ in electrode is a major obstacle for the rate capability of Na-ion batteries. In this work, super-fast Na+ diffusion in a VS 2 anode was achieved by creating ordered (OSV-VS 2- x) or disordered S vacancies (DSV-VS 2- x) in VS 2 nanosheets under a H 2 /Ar reduction atmosphere. Both the disordered and ordered S vacancies can improve the Na+ diffusion kinetics in VS 2. Especially, disordered S vacancies provided an extra ion diffusion pathway perpendicular to the VS 2 plane, which significantly reduced the Na+ diffusion barrier of DSV-VS 2- x to 0.229 eV, much smaller than the 0.473 eV for VS 2 and 0.401 eV for OSV-VS 2- x. Taking this advantage, the DSV-VS 2- x nanosheets exhibited impressive rate capability (117 mA·h·g−1 at 100 C) and ultra-long cycle life (~100% capacity retention after 5000 cycles at 50 C) in the 1.0–3.0 V voltage window. About 95% of the capacity was attributed to a pseudocapacitive process. The vacancy engineering strategy proposed in this work could significantly improve the rate capability of VS 2 and other transition metal dichalcogenides. This technology that combines the high rate performance of supercapacitors with the high energy density of rechargeable batteries would promote the development of high power energy storage devices. [ABSTRACT FROM AUTHOR]

• An in-situ surface barium engineering method is proposed to suppress lithium dendrite growth. • The growth behaviors of lithium are investigated after Ba-modification. • Diffusion barriers of lithium on the Ba-modified surface are probed by first principle calculation. • Ba engineered lithium metal anode enables 5 V-class lithium metal batteries. Lithium metal is well-known as the most promising anode material for lithium batteries due to its high capacity and lowest working potential. However, the inevitable dendrite growth of lithium is the key issue that restricts the commercialization of the lithium metal batteries (LMBs). Here, a facile in-situ surface barium engineering method is proposed to suppress the dendrite growth of lithium at ambient temperature. By first principle calculation, it is found that the diffusion barrier of lithium atom is significantly reduced by interfacial Ba-Li alloy. The experiments prove that the lithium dendrite is suppressed in commercial carbonate electrolyte and a smooth surface morphology is obtained even at a high area density of 4 mAh cm−2. A high energy 5 V-class lithium metal full battery is assembled and tested. Results reveal that 5 V-class lithium metal batteries with Ba engineered lithium metal anode show stable cycling performance and high rate capacity, indicating that the interfacial Ba-Li alloy can act as effective protection strategy to suppress the lithium dendrite. The results may be useful for the developing of dendrite-free lithium metal anode and other metal anodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrafine Mo 2 C embedded porous N-doped carbon spheres with rGO wrapping are developed. • Record high capacity and rate capability for Mo 2 C based sodium storage are achieved. • Unique double-carbon coatings with high conductivity effectively stabilized the structure. • DFT confirmed strong interfacial interaction between Mo 2 C and C promoted Na+ diffusion. • This design with ultrahigh Li+/Na+ storage performance is promising for broad energy use. As a model compound for transition metal carbides, Mo 2 C is considered as a promising anode material for sodium ion batteries (SIBs) due to its excellent electrical conductivity and low Na+ diffusion barriers. However, the low capacity and poor rate capability strongly limit its practical applications. Nanostructuralization of active materials combined with conductive matrix incorporation may address this issue. Inspired by this concept, we herein propose a rational strategy to create a special structure with ultrafine Mo 2 C nanoparticles encapsulated in porous N-doped carbon spheres wrapped by rGO. The well-defined double-carbon coating effectively limited the growth/agglomeration of Mo 2 C and provided highly conductive network to stabilize capacity. Theoretical calculations disclose hetero-interaction between components favorably promoted Na+ diffusion kinetics. Impressively, such composite with excellent cyclic stability showed a record high reversible capacity (332.9 mA h/g at 0.1 A/g) and rate capability (155.7 mA h/g at 5 A/g) of Mo 2 C based materials for SIBs. [ABSTRACT FROM AUTHOR]

A synergetic promotion of sodium ion storage in the titania nanosheets has been achieved by doping the oxide nanosheets with Fe and heteroassembling them with the conductive reduced graphene oxide, showing an over 6 folds capacity enhancement compared with the original titania nanosheets. • A joint promotion improved sodium ion storage in titania nanosheets over 6 folds. • rGO stabilized structure and increased electrical conductivity of the composites. • Fe doping improved capacity of composites to 378.8 mA h g−1 at 0.1 A g−1. • Ti 0.67 Fe 0.3 O 2 /rGO showed a capacity of 287.4 mA h g−1 at 1 A g−1 after 3000 cycles. Titania has been taken as one promising anode material for sodium ion batteries because of its long cycling stability and suitable working voltage. One of the main bottlenecks for its use is the low capacity. To overcome this challenge, in this work, restacked two dimensional (2D) titania nanosheets, which has an open edge and enlarged interlayer spacing for the ion diffusion, have been doped with Fe elements and hetero-assembled with the conductive reduced graphene oxide (rGO). The conductive rGO added increased the charge transfer at the interface of anode and electrolyte, decreased the diffusion barrier of Na+ inside the composites and increased the stability of titania nanosheet during the charge and discharge process, increasing the capacity and long cycle stability of the anode. The high concentration doping of Fe in the titania nanosheets further decreased the Na+ diffusion barrier, increased the electrical conductivity of the composites and greatly increased the storage sites of Na+. The as obtained superlattice composites of Ti 0.67 Fe 0.3 O 2 /rGO showed a sodium ion capacity of 378.8 mA h g−1 at 0.1 A g−1 after 100 cycles, which is the highest values among all reported Ti and Fe oxide materials. It still delivered a stable capacity of 287.4 mA h g−1 at high current charge density (1 A g−1) after a long cycling process (3000 cycles). [ABSTRACT FROM AUTHOR]

• The feasibility of 2D metallic B 2 C was studied for Li/Na ion batteries. • The B 2 C possesses an extremely high capacity for Li/Na ions storage. • The B 2 C exhibits low average open circuit voltages and fast Li/Na ions diffusion. • The Li/Na-B 2 C systems maintain the metallic properties during adsorption. Two-dimensional (2D) materials have garnered extensive enthusiasm and become the promising candidates as electrode materials for rechargeable ion batteries owning to their high surface area and excellent electrical, thermal and mechanical properties. Recently, a new stable 2D material named B 2 C was theoretically proposed and possesses metallic properties. Due to its light weight and intrinsic advantage of transportation of electrons, we further assess the feasibility of B 2 C monolayer to serve as Li and Na ion batteries (LIBs/NIBs) anode material by using first-principles calculations. The results reveal that B 2 C exhibits a very high theoretical capacity of 1596 mAh·g−1 for both LIBs and NIBs. Impressively, the structure of B 2 C can be well maintained at the maximum concentration (Li 2 B 2 C/Na 2 B 2 C) at 400 K, suggesting its good thermal stability. Moreover, B 2 C offers moderate average open circuit voltages (Li: 0.57 V, Na: 0.43 V) and fast motilities with lower diffusion barriers (Li: 0.49 eV, Na: 0.23 eV). Finally, B 2 C can maintain metallic properties during the whole Li/Na ion insertion processes, meaning that the material has a favorable electronic conductivity. Our findings demonstrate that metallic B 2 C could be a potential LIBs/NIBs anode material with high performance. [ABSTRACT FROM AUTHOR]

• The non-stoichiometric nickel ferrite was exploited for CO 2 splitting. • Cation diffusion mitigates the high-temperature sintering and boosts CO 2 splitting. • The non-stoichiometric nickel ferrite demonstrates extremely high CO yield. • 100% reactivity remaining for NF-60 after multiple high-temperature redox cycles. The thermochemical splitting of CO 2 into CO based on redox reaction demonstrates great promising for clean energy production. However, the redox material inevitably suffers from high-temperature sintering, leading to an increased ion diffusion barrier that deactivates the bulk phase. In this study, a distinct strategy is demonstrated to neutralize the adverse effect of sintering by engineering a non-stoichiometric nickel ferrite for the CO 2 splitting. It maintains a very high CO yield over multiple consecutive cycles, performing better than state-of-the-art redox materials. Extensive characterizations and first principles calculations reveal that the bulk cation diffusion boosts the splitting reaction. Such cation diffusion mode in the non-stoichiometric ferrite provides a more accessible diffusion path for the bulk reaction, leading to accelerated CO 2 splitting kinetics. Meanwhile, high stability is demonstrated for the non-stoichiometric nickel ferrite with 100% of the initial reactivity maintaining often 20 redox cycles. Our findings guide to design newly anti-sintering redox materials toward highly efficient energy conversion and production. [ABSTRACT FROM AUTHOR]

• The potassium storage mechanisms of MXenes were briefly explained. • The applications of various modified MXenes in potassium ion batteries were comprehensively summarized. • The advantages and challenges of MXenes in potassium ion batteries were pointed out. • This review proposed several promising strategies to improve the potassium storage performances of MXenes. MXenes, a new kind of two-dimensional (2 D) materials derived from MAX phases, have shown wide application prospects in metal-ion batteries due to their unique structural and electronic properties. Particularly, the diffusion barrier of K+ on MXenes is very low, indicating that MXenes may have excellent rate performance when applied to potassium ion batterie (PIBs) as anodes. However, pristine MXenes are not suitable to be used as anodes for PIBs due to their low theoretical potassium storage capacity and rapid capacity decline. Here, the potassium storage mechanisms of MXenes are briefly introduced. Besides, this review summarizes the applications of various modified MXenes in PIBs, with emphasis on the relationship between structure and electrochemical performances. Through the analysis of various modification methods, it is hoped that the future development direction of MXenes in PIBs can be seen, so as to provide enlightenment for readers. [ABSTRACT FROM AUTHOR]

• Compared with TiO 2 (1 0 1), Se(1 0 1) has a larger adsorption energy of [AlCl 4 ]−. • The porous nanosphere TiO 2 provides sites for the redox reaction of selenium. • TiO 2 @Se-rGO exhibits a discharge capacity of 225.8 mAh g−1 after 500 cycles. At present, because of the low energy density of aluminium-based batteries, rGO coated porous nanospheres TiO 2 @Se (TiO 2 @Se-rGO) was prepared by electrostatic effect as cathode material for Al-Se batteries. In Al-Se batteries, rGO coating has three functions: firstly, rGO uniform coating improves the dynamic properties of electrons and ions by increasing the diffusion or transfer rate; secondly, it avoids the diffusion of some selenides and dissolves them into the electrolyte to affect the electrochemical properties; lastly, the coating can stabilize the nanostructure and avoid the volume expansion or structural collapse during cycling. In addition, the porous nanosphere TiO 2 provides sites for the redox reaction of selenium, and can also avoid the dissolution of selenide. Most importantly, the density functional theory (DFT) shows that compared with TiO 2 (1 0 1), Se(1 0 1) has a larger adsorption energy of [AlCl 4 ]− and a smaller diffusion barrier of [AlCl 4 ]−. Therefore, TiO 2 @Se-rGO exhibits excellent electrochemical performance in Al-Se batteries. The initial discharge capacity reaches 1127.3 mAh g−1 at 0.2 A g−1, and the capacity is 208.7 mAh g−1 even at 1 A g−1. The discharge capacity is still as high as 225.8 mAh g−1 after 500 cycles at 0.5 A g−1. Therefore, TiO 2 @Se-rGO shows a clear advantage in the cathode material of aluminum-based batteries. [ABSTRACT FROM AUTHOR]

• UiO-67/NSC was applied in simultaneous adsorbing and sensing TC for the first time. • UiO-67/NSC exhibits high TC adsorption capacity over a wide pH range (pH 2.0–7.0). • 2D structure in UiO-67/NSC can alleviate diffusion barrier and enhance mass transfer. • UiO-67/NSC can effectively recognize TC with a low detection limit (0.063 mg/L). Discharged tetracycline (TC) seriously threatens human health and environmental safety. Herein, we developed a novel 3D flower-on-sheet structure of Zr-metal organic framework adsorbent with the assistant of N,S co-doped carbon dots as heterogeneous nucleation (UiO-67/NSC) for selective and effective removal of TC residue from contaminated water. Functional groups of UiO-67/NSC acts as a tentacle to identify TC molecules, and TC-adsorbed NSC can be separated easily by incorporating in UiO-67 structure. Hierarchical UiO-67/NSC exhibited excellent recognition performance with a wide sensitive range (0.08–20.0 mg/L) and low detection limit (0.063 mg/L) for TC. Particularly, vertically oriented 2D nanosheets in UiO-67/NSC alleviate the diffusion barrier and enhance mass transfer between adsorption sites and TC molecules, endowing it with an ability that can improve the TC adsorption capacity of parent UiO-67 to 427.35 mg/g. UiO-67/NSC with 0D structure has no significant toxic effect on human cells (HepG2 and Caco-2), which demonstrate the prepared hybrid structure is safety in practical application. Our data indicate the great potential of UiO-67/NSC as an innocuous, bifunctional, smart adsorbent for the effective detection and removal of TC residues, and we not only provide a rational design of advanced metal organic framework-based hierarchical adsorbents, but also shed light on an available method to toxic antibiotic residue recognition and water remediation. [ABSTRACT FROM AUTHOR]

• The few-layered MoS 2 nanosheets with different phase contents were prepared by an efficient controllable phase engineering. • The optimized material shows outstanding specific capacity and excellent long cycling performances. • The mechanisms involved were elucidated by systematical characterizations. • The DFT simulations reveal that the 1T phase MoS 2 has much lower Zn diffusion energy barriers. Recently, aqueous rechargeable Zn-ion batteries have attracted extensive attention, owing to their low-cost, high operational safety and environmental friendliness. However, the aqueous zinc-ion battery is still in a very infant stage, and the main challenge is to develop the ideal cathode due to the sluggish kinetics and low reversibility of divalent zinc ions. Herein, for the first time, we report controllable phase engineered few-layered MoS 2 nanosheet as cathode materials for rechargeable aqueous Zn-ion batteries and systematically study their performance. We found that the obtained MoS 2 with different phase contents showed distinct performance in the rechargeable aqueous zinc-ion battery. In particular, the MoS 2 nanosheets with ~70% 1T phase content displays excellent specific capacity and shows outstanding long-term cyclic stability. The mechanisms involved were clarified by not only comprehensive characterizations, but also the density functional theory (DFT) simulations that reveal the 1T phase MoS 2 has much lower Zn diffusion energy barriers. This study provides new insight into the effect of different phases on the performance of MoS 2 -based electrodes and will improve our understanding of developing better cathodes for the aqueous rechargeable Zn-ion batteries. [ABSTRACT FROM AUTHOR]

A facile structural refining for Sb film anode is firstly applied in SIBs by increasing the working pressure. Compared with Sb@0.2Pa and Sb@1Pa, the Sb@3Pa anode exhibits improved performance, stemming from its refined architecture. Surprisingly, the progressive in-situ electrochemically-driven Cu-Sb alloying can be probed upon cycling onward and further clarified by operando XRD, ex-situ SEM and DFT calculations. • A scalable structural refining for sputtered Sb film via altering working pressure. • The Sb@3Pa anode exhibits better performance owing to refined structure. • The (de)sodiation mechanism of Sb anodes was probed utilizing operando XRD. • In-situ electrochemically-driven Cu-Sb alloying is firstly observed in SIBs. Sb is a promising anode for sodium ion batteries (SIBs) but held back from practical application owing to its pulverization induced by dramatic volumetric variation. Herein, we propose a simple pressure-induced regulation strategy to efficiently refine nanoscale column-channel architecture of Sb layer by magnetron sputtering, which is easily manipulated and reproductive in practical conditions. The refining process under high working pressure can be ascribed to the synergistic effects from the shadow effect, the low kinetic energy of sputtered Sb atoms and high diffusion barrier on substrate. As benchmarked with Sb@0.2Pa and Sb@1Pa electrodes, the Sb@3Pa anode exhibits significantly enhanced electrochemical performance owing to structural refining effect generated by the elevated working pressure, effectively accelerating the ion/electron transfer and mitigating the volumetric variations. Notably, the progressive in-situ electrochemically-driven alloying in Sb layer on the Cu substrate to form Cu x Sb with the gradient Cu/Sb content is detected and further rationalized by operando XRD, ex-situ SEM and DFT calculations. Simultaneously, the formed Cu-Sb layer yields a novel (de)sodiation mechanism of Cu x Sb 1−x ↔ Na y Cu x Sb 1−x ↔ Na 3 Cu x Sb 1−x after the 1st discharge. [ABSTRACT FROM AUTHOR]

• Optimization of catalyst particles in a fixed-bed methanation reactor. • Optimal particle design: active particle core encapsulated by inert diffusion barrier. • Stoichiometric and undiluted feed to industrial scale reactor is possible. • Optimized particle-reactor system shows reduced thermal sensitivity. • Optimized particle-reactor system is suited for dynamic and flexible reactor operation. Power-to-Methane is a concept for energy storage harvested from renewable sources, for instance solar and wind power. A flexible operation of catalytic fixed-bed methanation reactors, according to the availability of energy, eliminates the need to store intermediate reactants in large buffer units. This requires reliable heat management, as the heat generation of the methanation reaction is a challenge even at steady-state conditions. For this purpose, many studies have been conducted on the reactor scale, but knowledge on how the catalyst particle design can influence reactor behavior is rather limited. Therefore, a heterogeneous reactor model is used in this study to investigate the influence of particle activity, permeability and heat conductivity on reactor performance. Subsequently, a nonlinear program is formulated and solved to find the optimal particle design depending on these three properties and their radial distribution in the catalyst particles. The designs include spherical particles with uniform properties (Case 1), particles with two uniform zones of different properties (Case 2) and particles with radially variable properties (Case 3). Optimization, subsequent sensitivity analyses and dynamic simulations reveal that reactors filled with particles of Case 2 should exhibit a particle core with high activity, which is surrounded by an inert, low-permeability shell (so-called 'egg-yolk' particles). In this way, the reactor shows a reduced parametric sensitivity and a high methane yield at the same time. In comparison to reactors filled with particles of Case 1, they also exhibit a favorable behavior for dynamic and flexible reactor operation. The benefit of further particle zones to increase reactor performance appears insignificant, as shown by the results of Case 3. [ABSTRACT FROM AUTHOR]