Single Nickel Atoms on Nitrogen-Doped Graphene Enabling Enhanced Kinetics of Lithium-Sulfur Batteries

Synthesis of Vacancy-Rich NiTex-NC Catalyst under Mild Conditions for High-Performance Lithium Sulfur Batteries

Due to the slow conversion kinetics of polysulfides, the practical application of lithium-sulfur batteries faces significant challenges. Transition metal tellurides exhibit good catalytic activity and are expected to help mitigate the shuttle effect in lithium-sulfur batteries. Vacancies, as a form of defect, can further enhance the conductivity and catalytic activity of the catalysts. However, most vacancy creation is achieved by the action of strong reducing agents (such as H2, NaBH4, hydrazine, etc.). Here, we utilized the similarity in lattice parameters between NiTe and NiTe2 to adjust the extent of lattice contraction in NiTe2 by controlling the Te powder content, ultimately obtaining a Te-vacancy-rich NiTex-NC catalyst under mild conditions. The unsaturated coordination between Ni and Te provides abundant active sites for the chemical adsorption and catalytic conversion of polysulfides, thus allowing NiTex-NC to significantly lower the reaction energy barrier of polysulfides and effectively inhibit the shuttle effect. The results show that NiTex-NC can achieve a specific capacity of 589.4 mAh g-1 at a rate of 7 C, and after 1000 cycles at 2 C, the capacity decay per cycle is only 0.0278%. Even under complex conditions (with a sulfur loading of 7.5 mg cm-2 and a liquid sulfur ratio of 10 μL mg-1), it still maintains good cycling stability.

Insights into the halogen-induced p-band center regulation promising high-performance lithium-sulfur batteries

Sn-based halide perovskites are expected to solve the problems of the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) due to their high conductivity and electrocatalytic activity, but their intrinsic catalytic mechanism for LiPSs remains to be explored. Herein, halide perovskites with varying halide anions, Cs2SnX6 (X = Cl, Br, I), are purposefully designed to unveil the halogen-induced regulatory mechanism. Theoretical calculations demonstrate that increasing the halogen atomic number induces the shift of the p-band center closer to the Fermi level, which results in the localized charge distribution around halide anions and rapid charge separation/transfer at Sn sites, enhancing the adsorptive and catalytic activity and redox kinetics of LiPSs. Experimental investigations exhibit that LSBs assembled with the Cs2SnI6 modified separator deliver a high initial capacity of 1000 mA h g-1 at 2C, with a minimum decay rate of 0.068% per cycle after 500 cycles. More impressively, the Cs2SnI6 battery with a high sulfur loading (6.1 mg cm-2) and a low electrolyte/sulfur ratio (5.5 μL mg-1) achieves a remarkable reversible capacity of 768.8 mA h g-1, along with robust wide-temperature-tolerant cycling performance from -20 to 50 °C. These findings underscore the critical role of p-band center regulation in rationally designing advanced LSBs.

Co/Co3O4@NC-CNTs modified separator of Li-S battery achieving the synergistic effect of adsorption-directional migration-catalysis via built-in electric field

The shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur conversion kinetics have seriously hindered the commercial application of lithium-sulfur (Li-S) batteries. Currently, the adsorption and catalysis processes are emphasized; however, the diffusion process is often neglected. The delayed diffusion of the adsorbed LiPSs significantly reduce battery performance. Herein, the directional migration of Sn2- was realized by adjusting the characteristics of heterostructure materials. The heterostructure consists of Co with a high Fermi level and excellent catalytic activity and Co3O4 with a low Fermi level and strong adsorption ability. This configuration regulated the direction of the built-in electric field (BIEF) at the heterogeneous interface, which promoted the migration of Sn2- from Co3O4 to Co side and realised a continuous "adsorption-directional migration-catalysis" mechanism. Experimental and theoretical results indicated that the Co/Co3O4 heterostructure modified by nitrogen-doped carbon nanotubes (Co/Co3O4@NC-CNTs), as the separator of Li-S batteries, not only enhanced the adsorption of LiPSs but also accelerated the kinetic conversion process. Consequently, the battery modified by the Co/Co3O4@NC-CNTs separator exhibited a high initial specific capacity of 1423 mAh g-1 at 0.2C, and maintained 735.5 mAh g-1 at a current density of 1C after 400 cycles.

Protein-Guided Biomimetic Calcification Constructing 3D Nitrogen-Rich Core-Shell Structures Realizing High-Performance Lithium-Sulfur Batteries

Biomimetic calcification is a micro-crystallization process that mimics the natural biomineralization process, where biomacromolecules regulate the formation of inorganic minerals. In this study, it is presented that a protein-assisted biomimetic calcification method for the in situ synthesis of nitrogen-doped metal-organic framework (MOF) materials. A series of unique core-shell structures are created by utilizing proteins as templates and guiding agents in the nucleation step, creating ideal conditions for shell growth. To further understand the influence of the protein and organic ligand on the morphology of the MOF shell, the competing mechanism toward metal ions is supposed. Through systematic experiments and analyses, a strategy to construct unique precursor structures by controlling calcification nucleation is proposed. After carbonization, protein-containing precursors exhibit exceptional porous characteristics, stability, and high nitrogen content. These attributes make them promising materials as sulfur hosts in lithium-sulfur batteries (LSB). Electrochemical tests confirm that biomimetic calcification-assisted 3D carbonaceous structure can effectively immobilize dissolved polysulfides, demonstrating strong adsorption and catalytic capabilities. This discovery not only opens up new avenues for employing biomimetic calcification as a sustainable method for batteries but also enlightens the fields of materials science, catalytic chemistry, and energy storage.

Electronic Modulation and Symmetry-Breaking Engineering of Single-Atom Catalysts Driving Long-Cycling Li-S Battery

Developing efficient and durable single-atom catalysts is vitally important for the sulfur redox reaction (SROR) in Li-S battery, while it remains enormous challenging. Herein, undercoordinated Ni-N3 moieties anchored on N,S-codoped porous carbon (Ni-NSC) is obtained to enhance the SROR. The experiments and theoretical calculations indicate that the symmetry-breaking charge transfer in Ni single-atom catalyst originates from tuning effect of sulfur atoms mediated Ni-N3 moieties, which can both facilitate the chemical adsorption by formation of N-Ni⋅⋅⋅Sn 2-, and achieve a rapid redox conversion of polysulfides because of the enhanced electron transfer. As results, the Ni-NSC based Li-S battery delivers a very high initial reversible capacity (1025 mAh g-1 at 1 C), as well as outstanding cycling-stability for 2400 cycles at 2 C and 3 C, respectively. Noteworthy, the areal capacity can reach 7.8 mAh cm-2 at 0.05 C and a retention capacity of 4.7 mAh cm-2 after 100 cycles at 0.2 C for Ni-NSC based Li-S battery with sulfur loading of 5.88 mg cm-2. This work provides profound insight for rational optimizing microscopic electronic density of active site to promoting SROR in metal-sulfur batteries.

Boosting Alkaline Hydrogen Evolution Reaction by Modulating D-Band Center in Bimetallic Sulfide Ni3S2-FeS Heterointerfaces

Hydrogen evolution reaction (HER) in alkaline electrolytes is considered to be the most promising industry-scale hydrogen (H2) production method but is limited to the lack of low-cost, efficient, and stable HER catalysts. Here, a universal and scalable electrodeposition-sulfidization modulation strategy is developed to directly grow the Ni3S2-FeS heterojunction nanoarray on the commercial Ni foam (Ni3S2-FeS@NF). The as-prepared Ni3S2-FeS@NF catalyst only requires a low overpotential of 71 and 270 mV to reach the current density of 10 and 500 mA cm-2 with a long-lasting lifetime of over 200 h. Moreover, the Ni3S2-FeS@NF catalyst can operate at industrial conditions (500 mA cm-2 at 70 °C) for over 200 h stably at a low cell voltage of 1.71 V in an alkaline exchange membrane water electrolysis (AEMWE) device, which indicates a great prospect for practical application. In addition, in situ Raman experiments and density functional theory (DFT) calculations reveal that the downshift of the d-band center and interfacial synergistic actions due to the electron transfer between Ni3S2 and FeS reduce the water spitting energy barrier and optimize H/O-containing intermediates absorption, thereby improving the HER intrinsic catalytic activity. This work provides an atomic-level insight into designing efficient HER heterogeneous catalysts.

Recent progress of density functional theory studies on carbon-supported single-atom catalysts for energy storage and conversion

Single-atom catalysts (SACs) have become the forefront and hotspot in energy storage and conversion research, inheriting the advantages of both homogeneous and heterogeneous catalysts. In particular, carbon-supported SACs (CS-SACs) are excellent candidates for many energy storage and conversion applications, due to their maximum atomic efficiency, unique electronic and coordination structures, and beneficial synergistic effects between active catalytic sites and carbon substrates. In this review, we briefly review the atomic-level regulation strategies for optimizing CS-SACs for energy storage and conversion, including coordination structure control, nonmetallic elemental doping, axial coordination design, and polymetallic active site construction. Then we summarize the recent progress of density functional theory studies on designing CS-SACs by the above strategies for electrocatalysis, such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO2 reduction reaction, nitrogen reduction reaction, and electrosynthesis of urea, and electrochemical energy storage systems such as monovalent metal-sulfur batteries (Li-S and Na-S batteries). Finally, the current challenges and future opportunities in this emerging field are highlighted. This review will provide a helpful guideline for the rational design of the structure and functionality of CS-SACs, and contribute to material optimizations in applications of energy storage and conversion.

Pyrolysis-Free Synthesis of Synergistic Single-Atom/Nanocluster Electrocatalysts for Hydrogen Evolution

Constructing catalysts that simultaneously contain single atom/metal nanocluster active sites is a promising strategy to enhance the original catalytic behavior and accelerate the catalysis involving multi-electron reactions or multi-intermediates. Herein, the pyrolysis-free synthetic method is developed to integrate single atoms and nanoclusters towards highly satisfactory catalytic performances for both acidic and alkaline hydrogen electrocatalysis. The controllable pyrolysis-free strategy allows the precise modulation of the active centers, realizing the optimization of the adsorption energy and the regulation of the synergistic active components. Specially, the as-prepared catalysts with hybrid single-atom/nanocluster sites exhibited superior catalytic activities for hydrogen evolution in both acidic and alkaline media with low over-potentials at -10 mA cm-2 of 25 mV and 8.6 mV, respectively, combining with outstanding durability towards high current density and methanol poisoning. This work developed a universal synthetic strategy for the single atom/nanocluster synergy systems and addressed the superiority of hybrid single-atom/nanocluster sites.

Metal-N Coordination in Lithium-Sulfur Batteries: Inhibiting Catalyst Passivation

Lithium-sulfur (Li-S) batteries exhibit great potential as the next-generation energy storage techniques. Application of catalyst is widely adopted to accelerate the redox kinetics of polysulfide conversion reactions and improve battery performance. Although significant attention has been devoted to seeking new catalysts, the problem of catalyst passivation remains underexplored. Herein, we find that metal-N coordination has a previously overlooked role in preventing the catalyst passivation. In the case of nickel, the Ni catalyst reacts with S8 to produce NiSx compounds on the surface, leading to catalyst passivation and slow the kinetics of LiPSs conversion. In contrast, when Ni is coordinated with N (typically Ni-N4), S8 remains stable on the surface. The Ni-N4 exhibits excellent resistance to passivation and rapid kinetics of LiPSs conversion. Consequently, the sulfur cathode with Ni-N4 exhibits a high rate capability of 604.11 mAh g-1 at 3 C and maintains a low capacity decay rate of 0.046 % per cycle over 1000 cycles at 2 C. Furthermore, preventing S passivation in M-N coordination applies not only to Ni-N4 but also to various coordination numbers and transition metals. This study reveals a new aspect of metal-N coordination in inhibiting catalyst passivation, improving our understanding of catalysts in Li-S batteries.

Theoretical evaluation of monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) family as promising candidates for lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries have been considered as a potential energy storage system due to their high theoretical specific energy. However, their practical commercial application has been hindered by unresolved key issues. One promising approach to overcoming these challenges is the development of anchoring materials with exceptional performance. In this work, we conducted detailed evaluations of twelve types of MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) monolayers as potential Li-S battery electrodes through first-principles calculations. Our results indicate that these monolayers can effectively immobilize Li2Sn species, preventing them from dissolving into the electrolyte and preserving intact Li2Sn conformations. The high electrical conductivity of these monolayers can be perfectly retained after S8/L2Sn clusters adsorption. Furthermore, the MA2P4 monolayers demonstrate superior catalytic performance for the sulfur reduction reaction (SRR) compared to the MA2As4 counterparts, whereas the MA2As4 monolayers exhibit lower decomposition energy barriers. Our current work indicates that these MA2Z4 monolayers hold significant promise as electrode materials for Li-S batteries.

Immobilization and Catalytic Conversion of Polysulfide by In-Situ Generated Nickel in Hollow Carbon Fibers for High-Rate Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered promising energy-storage systems because of their high theoretical energy density, low cost, and eco-friendliness. However, problems such as the shuttle effect can result in the loss of active materials, poor cyclability, and rapid capacity degradation. The utilization of a structural configuration that enhances electrochemical performance via dual adsorption-catalysis strategies can overcome the limitations of Li-S batteries. In this study, an integrated interlayer structure, in which hollow carbon fibers (HCFs) were modified with in-situ-generated Ni nanoparticles, was prepared by scalable one-step carbonization. Highly hierarchically porous HCFs act as the carbon skeleton and provide a continuous three-dimensional conductive network that enhances ion/electron diffusion. Ni nanoparticles with superior anchoring and catalytic abilities can prevent the shuttle effect and increase the conversion rate, thereby promoting the electrochemical performance. This synergistic effect resulted in a high capacity retention of 582 mAh g-1 at 1 C after 100 cycles, providing an excellent rate capability of up to 3 C. The novel structure, wherein Ni nanoparticles are embedded in cotton-tissue-derived HCFs, provides a new avenue for enhancing electrochemical performance at high C rates. This results in a low-cost, sustainable, and high-performance hybrid material for the development of practical Li-S batteries.

The Role of Long-Range Interactions Between High-Entropy Single-Atoms in Catalyzing Sulfur Conversion Reactions

Sulfur conversion reactions are the foundation of lithium-sulfur batteries but usually possess sluggish kinetics during practical battery operation. Herein, a high-entropy single-atom catalyst (HESAC) is synthesized for this process. In contrast to conventional dual-atom catalysts that form metal-metal bonds, the center metal atoms in HESAC are not bonded but exhibit long-range interactions at a sub-nanometer distance (<9 Å). The synergistic effect between the long-range interactions and entropy changes enables the regulation of d- and π-electron states. This alteration in the electronic structure improves the adsorption and electronic conductivity of intermediate polysulfides, thereby accelerating their conversion kinetics. Consequently, this leads to a significant enhancement in specific capacities by ≈40% at high rates compared to single-atom catalysts. The resulting lithium-sulfur battery with HESAC demonstrates a remarkable areal capacity of 3.4 mAh cm-2 at 10 C. These findings provide valuable insights into the design principle of metal atom catalysts for electrochemical reactions.

Resolving the Nanostructure of Carbon Nitride-Supported Single-Atom Catalysts

Single-atom catalysts (SACs) are gathering significant attention in chemistry due to their unique properties, offering uniform active site distribution and enhanced selectivity. However, their precise structure often remains unclear, with multiple models proposed in the literature. Understanding the coordination environment of the active site at the atomic level is crucial for explaining catalytic activity. Here, a comprehensive study of SACs made of carbon nitride (CNx) containing isolated nickel atoms is presented. Using a combination of synthesis techniques and characterization methods including Fourier-transform infrared spectroscopy, X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations, the local environment of nickel active centers in CNx-supported SACs is investigated. These results challenge conventional structural models and propose a new architecture that better aligns with current experimental evidence. This new structure serves as a foundational step toward a rational approach to catalyst development and can facilitate more precise design and application of these innovative catalysts.

A Promising Approach to Ultra-Flexible 1 Ah Lithium-Sulfur Batteries Using Oxygen-Functionalized Single-Walled Carbon Nanotubes

Lithium-sulfur (Li-S) batteries represent a promising solution for achieving high energy densities exceeding 500 Wh kg-1, leveraging cathode materials with theoretical energy densities up to 2600 Wh kg-1. These batteries are also cost-effective, abundant, and environment-friendly. In this study, an innovative approach is proposed utilizing highly oxidized single-walled carbon nanotubes (Ox-SWCNTs) as a conductive fibrous scaffold and functional interlayer in sulfur cathodes and separators, respectively, to demonstrate large-area and ultra-flexible Li-S batteries with enhanced energy density. The free-standing sulfur cathodes in the Li-S cells exhibit high energy density maintaining 806 mAh g-1 even after 100 charge-discharge cycles. Additionally, oxygen-containing functional groups on the SWCNTs significantly improve electrochemical performance by promoting the adsorption of lithium polysulfides. Employing Ox-SWCNTs in both cathodes and interlayers, the study achieves high-capacity Li-S pouch cells that consistently deliver a capacity of 1.06 Ah and a high energy density of 909 mAh g-1 over 50 charge-discharge cycles. This strategy not only significantly enhances the electrochemical performance of Li-S batteries but also maintains excellent mechanical flexibility under severe deformation, positioning this Ox-SWCNT-based architecture as a viable, light-weight, and ultra-flexible energy storage solution suitable for commercializing rechargeable Li-S batteries.

Tailoring a Transition Metal Dual-Atom Catalyst via a Screening Descriptor in Li-S Batteries

The adsorption-conversion paradigm of polysulfides during the sulfur reduction reaction (SRR) is appealing to tackle the shuttle effect in Li-S batteries, especially based upon atomically dispersed electrocatalysts. However, mechanistic insights into such catalytic systems remain ambiguous, limiting the understanding of sulfur electrochemistry and retarding the rational design of available catalysts. Herein, we systematically explore the polysulfide adsorption-conversion essence via a geminal-atom model system to understand the catalyst roles toward an expedited SRR. A descriptor involving an electronic structure index (IES) and electron affinity index (IEA) is proposed, considering the geometric and electronic dictation within a Fe/M (M: 3d-block transition metal) atomic ensemble. With the aid of theoretical computation, we managed to identify the SRR thermodynamic/kinetic trends of Fe/M moieties. Guided by these findings, we in target design a Fe/V-NC dual-atom catalyst, which harvests a minimum IES and maximum IEA, accordingly demonstrating enhanced polysulfide adsorption-conversion and improved full-cell performances. Such a consistency between a computational descriptor and experimental evidence highlights the importance of an atomic catalyst screen and selection for Li-S batteries.

Ionic Liquid-Assisted Synthesis of Higher Loaded Ni/Fe Dual-Atom Catalysts in N, F, B Codoped Carbon Matrix for Accelerated Sulfur Reduction Reaction

In response to mitigating the severe shuttle effect within lithium-sulfur batteries, single-atom catalysts have emerged as one of the most effective solutions. Here, N, F, B codoped porous hollow carbon nanocages (NFB-NiFe@NC) with high Ni and Fe doping are rationally designed and synthesized using ionic liquids (ILs) as dopants. The introduction of ILs inhibits the growth of zeolitic imidazolate framework-8 (ZIF8), resulting in NFB-ZIF8 precursors with smaller particle sizes, enabling higher loading dual-atom catalysts. Meanwhile, the abundant heteroatoms increase the reactive sites and alter the carbon matrix's nonpolar intrinsic properties, thus enhancing the chemisorption of polysulfides. The synergistic interaction of the heteroatoms with Ni and Fe dual-atoms ultimately promotes the catalytic conversion kinetics of polysulfides. As a result of these beneficial properties, the cells prepared using the NFB-NiFe@NC modified separator exhibit significantly improved performance, including a high initial capacity of 1448 mAh g-1 at 0.2 C. Even at a high S-loading of 7.6 mg cm-2, the ideal area capacity of 8.38 mAh cm-2 can still be maintained at 0.1 C. New insights are provided here for designing highly loaded dual-atom catalysts for application in lithium-sulfur batteries.

Synergistic Regulation of Bidirectional Conversion of LiPSs and Li2S Using Anthraquinone as a Redox Mediator

Lithium-sulfur (Li-S) batteries are strong contenders as energy storage options in the next-generation, primarily because of their potential for delivering high energy densities. Nonetheless, their widespread commercialization faces several obstacles, including sluggish sulfur redox kinetics, the insulating properties of the Li2S discharge product, and significant reaction energy barriers. In this work, anthraquinone (AQ) was introduced as a redox mediator and incorporated onto Co-doped carbon materials through π-π interactions. The results showed that synergistic effect between AQ and Co atoms facilitated the bidirectional conversion of lithium polysulfides (LiPSs) and Li2S. During charging, AQ lowered the reaction energy barrier for Li2S oxidation and thereby enhanced the reversibility of sulfur redox reactions. Density functional theory (DFT) calculations showed that AQ-Li2Sx exhibits a lower energy for the lowest unoccupied molecular orbital (LUMO) and a higher energy for the highest occupied molecular orbital (HOMO). Experimental results demonstrated that an impressive initial discharge specific capacity of 1290 mAh g-1 was achieved by the fabricated S@AQ/Co-N-C electrode at 0.1 C. After 600 cycles at 1 C, it retained 64% of this capacity and exhibited a minimal 0.06% capacity decay rate per cycle.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Coupled Ni─Co Dual-Atom Catalyst for Guiding Sulfur and Lithium Evolutions in Lithium-Sulfur Batteries

The kinetically retarded sulfur evolution reactions and notorious lithium dendrites as the major obstacles hamper the practical implementation of lithium-sulfur batteries (LSBs). Dual metal atom catalysts as a new model are expected to show higher activity by their rational coupling. Herein, the dual-atom catalyst with coupled Ni─Co atom pairs (Ni/Co-DAC) is designed successfully by programmed approaches. The Ni─Co atom pairs alter the local electron structure and optimize the coordination configuration of Ni/Co-DAC, leading to the coupling effect for promoting the interconversion of sulfur and guiding lithium plating/striping. The LSB delivers a remarkable capacity of 818 mA h g-1 at 3.0 C and a low degeneration rate of 0.053% per cycle over 500 cycles. Moreover, the LSB with a high sulfur mass loading of 6.1 mg cm-2 and lean electrolyte dosage of 6.0 µL mgS -1 shows a remarkable areal capacity of 5.7 mA h cm-2.

Entrapment and Reactivation of Polysulfides in Conductive Amphiphilic Covalent Organic Frameworks Enabling Superior Capacity and Stability of Lithium-Sulfur Batteries

Inhibiting the shuttle of polysulfides is of great significance for promoting the practical application of lithium-sulfur batteries (LSBs). Here, an imine-linked covalent organic framework@carbon nanotube (COF@CNT) interlayer composed of triazine and boroxine rings is constructed between the sulfur cathode and the separator for polysulfides reception and reutilization. The introduction of CNT imparts the conductor characteristic to the interlayer attributed to electron tunneling in thin COF shell, and creates a hierarchical porous architecture for accommodating polysulfides. The uniform distribution of amphiphilic adsorption sites in COF microporous structure not only enables efficient entrapment of polysulfides while allowing the penetration of Li+ ions, but also provides a stable electrocatalytic channel for bidirectional conversion of active sulfur to achieve the substantially improved capacity and stability. The interlayer-incorporated LSBs deliver an ultrahigh capacity of 1446 mA g-1 at 0.1C and an ultralow capacity decay rate of 0.019% at 1C over 1500 cycles. Even at an electrolyte/sulfur ratio of 6 µL mg-1, an outstanding capacity of 995 mAh g-1 and capacity retention of 74.1% over 200 cycles at 0.2C are obtained. This work offers a compelling polysulfides entrapment and reactivation strategy for stimulating the study on ultra-stable LSBs.

Theoretical Design and Study of a Single-Atom Catalyst in Lithium-Sulfur Batteries: Edge-Type FeN4 Active Site Electron Density Redistribution Driven by Heteroatoms

Lithium-sulfur (Li-S) batteries are considered to be the most promising next-generation high energy density storage systems. However, they still face challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur oxidation-reduction kinetics. In this work, heteroatom (P and S)-doped edge-type Fe single-atom catalytic materials (FeN4S2/P2-DG) for sulfur reduction reactions (SRRs) and sulfur oxidation reactions in Li-S batteries are investigated using density functional theory calculations. Theoretical analysis suggests that compared to planar Fe-N4 fragments, the charge density accumulation around edge-type Fe-N4 fragments in S- or P-doped structures is higher. Furthermore, the doping of P or S reduces the electron filling state of Fe_3d orbitals, leading to a decrease in electron occupancy in the antibonding orbitals, which is beneficial for the formation of d-p orbital hybridization, strengthening the anchoring strength of FeN4P2/S2-DG for S8/LiPSs. Specifically, FeN4P1,2-DG showed the lowest free energy barriers (0.57 eV) for SRRs and reduced the dissociation energy barrier of Li2S from 1.85 eV (for planar FeN4-G) to 0.96 eV during the charging process, demonstrating excellent catalytic ability. Additionally, this theoretical study provides further insights into the application of graphene-supported single-atom catalyst materials as anchoring materials for Li-S batteries.

Natural biomass derived single-atom catalysts for energy and environmental applications

Single atom catalysts (SACs) excel in various chemical processes, including electrocatalysis and industrial chemistry, due to their efficiency. In contrast to chemically synthesized precursors, biomass offers a greener and more cost-effective approach for SACs fabrication. To date, over forty types of SACs have been synthesized using natural sources like starch, cellulose, lignin, hemicellulose, proteins, and chitin. These catalysts incorporate metals such as Fe, Co, Ni, Cu, Zn, Mn, and Pt. This review concentrates on the preparation of SACs from biomass, exploring innovative techniques and their extensive applications in energy conversion and environmental conservation, including but not limited to reactions involving oxygen reduction, oxygen evolution, and hydrogen evolution. It also discusses current challenges and prospective advancements in this domain. This paper updates and expands on the knowledge of SACs derived from biomass, aiming to foster the development of more effective, low-cost catalyst materials from natural sources.

Synergistic Effect of Lactam and Pyridine Nitrogen on Polysulfide Chemisorption and Electrocatalysis in Lithium Sulfur Batteries

Sulfur undergoes various changes, including the formation of negative charge-bearing lithium polysulfides during the operation of Li-S batteries. Dissolution of some of the polysulfides in battery electrolytes is one of the reasons for the poor performance of Li-S batteries. The charge injection into the sulfur and polysulfides from the electrode is also a problem. To address these issues, a small-molecule additive, 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, was designed and synthesized with carbonyl oxygen atoms and two types of nitrogen. The pyridinic nitrogen increases the electronegativity of the carbonyl oxygen atoms. The pyridinic nitrogen, carbonyl oxygen, and lactam nitrogen provide multiple binding sites concurrently to the polysulfides, which increases the binding efficiency between the additive and polysulfides. A control molecule without the pyridine moiety displayed decreased binding to lithium polysulfides. Furthermore, the band edges of lithium polysulfide and 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione are commensurate for efficient charge transfer between them, leading to the efficient electrocatalysis of lithium polysulfides. The cyclic voltammogram of the Li-S battery fabricated with 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione exhibited sharp and well-defined peaks, confirming the formation of Li2Sy (where y varies between one and eight) from S8. These Li-S batteries showed a specific capacity of 950 mA h/g at 0.5 C, with a capacity retention of 70% at the 300th cycle. The pyridine-free control molecule, 3,6-diphenyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, showed relatively poor performance in a Li-S battery.

Two-dimensional phosphorus carbides (β-PC) as highly efficient metal-free electrocatalysts for lithium-sulfur batteries: a first-principles study

Li-S batteries are considered as the next-generation batteries due to their exceptional theoretical capacity. However, their practical application is hampered by the shuttling effects of lithium polysulfides (LiPSs) and the sluggish Li2S decomposition, particularly the slow conversion from Li2S2 to Li2S. Addressing these challenges, the quest for effective catalysts that can accelerate the conversion of LiPSs and enhance the performance of Li-S batteries is crucial. In this study, we explored the electrocatalytic activity of two-dimensional phosphorus carbides (β0-PC and β1-PC) in Li-S batteries based on first-principles calculations. Our findings reveal that these materials demonstrate optimal binding strengths (ranging from 1.09 to 1.83 eV) with long-chain LiPSs, effectively preventing them from dissolving into the electrolyte. Additionally, they show remarkable catalytic activity during the sulfur redox reaction (SRR), with ΔG being only 0.37 eV for β0-PC and 0.13 eV for β1-PC. The low energy barrier induced by β-PC enhances ion migration barrier and significantly expedites the charge/discharge cycles of Li-S batteries. Furthermore, we investigated the conversion dynamics of Li2S2 to Li2S, employing the computational lithium electrode (CLE) model. The excellent performance in these aspects underscores the potential of these materials as electrocatalysts for Li-S batteries, paving the way for advanced high-efficiency energy storage solutions.

Atomic-Level Catalyst Coupled with Metal Oxide Heterostructure for Promoting Kinetics of Lithium-Sulfur Batteries

Despite the low competitive cost and high theoretical capacity of lithium-sulfur (Li-S) batteries, their practical application is severely hindered by the lithium polysulfide (LiPS) shuttling and low conversion efficiency. Herein, the electronic structure of hollow Titanium dioxide nanospheres is tunned by single Iron atom dopants that can cooperatively enhance LiPS absorption and facilitate desired redox reaction in practical Li-S batteries, further suppressing the notorious shuttle effect, which is consistent with theoretical calculations and in situ UV/vis investigation. The obtained electrode with massive active sites and lower energy barrier for sulfur conversions exhibits exceptional cycling stability after 500 cycles and high capacity under the sulfur loading of 10.53 mg cm-2. In particular, an Ah-level Li-S pouch cell is fabricated, further demonstrating that the synthetic strategy based on atomic-level design offers a promising route toward practical high-energy-density Li-S batteries.

[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N4 Single-Atom Catalysts for Efficient CO2 Electroreduction

Microenvironment regulation of M-N4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N4 and in situ generated difluorocarbene (F2C:), and enable the surface fluorocarbonation of Ni-N4, resulting in the formation of a super-hydrophobic Ni-N4-CF2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N4-CF2 to inherit both the electronic and structural configuration of the Ni-N4 sites from Ni-N4. Enhanced electrochemical CO2-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N4-CF2. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF2- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.

Regulating Sulfur Redox Kinetics by Coupling Photocatalysis for High-Performance Photo-Assisted Lithium-Sulfur Batteries

Challenges such as shuttle effect have hindered the commercialization of lithium-sulfur batteries (LSBs), despite their potential as high-energy-density storage devices. To address these issues, we explore the integration of solar energy into LSBs, creating a photo-assisted lithium-sulfur battery (PA-LSB). The PA-LSB provides a novel and sustainable solution by coupling the photocatalytic effect to accelerate sulfur redox reactions. Herein, a perovskite quantum dot-loaded MOF material serves as a cathode for the PA-LSB, creating built-in electric fields at the micro-interface to extend the lifetime of photo-generated charge carriers. The band structure of the composite material aligns well with the electrochemical reaction potential of lithium-sulfur, enabling precise regulation of polysulfides in the cathode of the PA-LSB system. This is attributed to the selective catalysis of the liquid-solid reaction stage in the lithium-sulfur electrochemical process by photocatalysis. These contribute to the outstanding performance of PA-LSBs, particularly demonstrating a remarkably high reversible capacity of 679 mAh g-1 at 5 C, maintaining stable cycling for 1500 cycles with the capacity decay rate of 0.022 % per cycle. Additionally, the photo-charging capability of the PA-LSB holds the potential to compensate for non-electric energy losses during the energy storage process, contributing to the development of lossless energy storage devices.

Practical four-electron zinc-iodine aqueous batteries enabled by orbital hybridization induced adsorption-catalysis

The successive I-/I0/I+ redox couples in the four-electron zinc-iodine aqueous battery (4eZIB) is plagued by the instability of the electrophilic I+ species, which could either be hydrolyzed or be neutralized by the I3- redox intermediates. We present an adsorption-catalysis approach that effectively suppresses the hydrolysis of ICl species and also provides an enhanced reaction kinetics to surpass the formation of triiodide ions. We elucidate that the improved stability is attributed to the pronounced orbital hybridization between the d orbitals of Fe-N4 moieties (atomic Fe supported on nitrogen doped carbon) and the p orbitals of iodine species (I2 and ICl). Such d-p orbital hybridization leads to enhanced adsorption for iodine species, increased energy barrier for proton detachment from the ICl·HOH intermediate during hydrolysis, and efficient catalysis of the iodine redox reactions with high conversion efficiency. The proposed 4eZIB demonstrates practical areal capacity (>3 mAh cm-2) with a near-unity coulombic efficiency, high energy density of 420 Wh kg-1 (based on cathode mass), and long-term stability (over 10,000 cycles). Even at -20 °C, the battery exhibits stable performance for over 1000 cycles with high iodine utilization ratio.

Ni Single-Atom Bual Catalytic Electrodes for Long Life and High Energy Efficiency Zinc-Iodine Batteries

Zinc-iodine batteries (Zn-I2) are extremely attractive as the safe and cost-effective scalable energy storage system in the stationary applications. However, the inefficient redox kinetics and "shuttling effect" of iodine species result in unsatisfactory energy efficiency and short cycle life, hindering their commercialization. In this work, Ni single atoms highly dispersed on carbon fibers is designed and synthesized as iodine anchoring sites and dual catalysts for Zn-I2 batteries, and successfully inhibit the iodine species shuttling and boost dual reaction kinetics. Theoretical calculations indicate that the reinforced d-p orbital hybridization and charge interaction between Ni single-atoms and iodine species effectively enhance the confinement of iodine species. Ni single-atoms also accelerate the iodine conversion reactions with tailored bonding structure of I─I bonds and reduced energy barrier for the dual conversion of iodine species. Consequently, the high-rate performance (180 mAh g-1 at 3 A g-1), cycling stability (capacity retention of 74% after 5900 cycles) and high energy efficiency (90% at 3 A g-1) are achieved. The work provides an effective strategy for the development of iodine hosts with high catalytic activity for Zn-I2 batteries.

Single-atom catalysts based on C2N for sulfur cathodes in Na-S batteries: a first-principles study

Several major roadblocks, including the "shuttle effect" caused by the dissolved higher-order sodium polysulfides (NaPSs), extremely poor conductivity of sulfur cathodes, and sluggish conversion kinetics of charging-discharging reactions, have hindered the commercialization of sodium-sulfur batteries (NaSBs). In our study, representative C2N-based single-atom catalysts (SACs), TM@C2N (TM = Fe, Ni and V), are proposed to improve the comprehensive performance of NaSBs. Based on first-principles calculations, we first discuss in detail the anchoring behavior of all adsorption systems, TM@C2N/(S8 and NaPSs). The results indicate that compared to pristine C2N, TM@C2N substrates exhibit a stronger capability to capture S8/NaPSs clusters through physical/chemical binding, with V@C2N showing the most outstanding capability ranging from -2.37 to -5.03 eV. The density of states analysis reveals that metallic properties can be well maintained before and after adsorption of polysulfides. More importantly, TM@C2N configurations can greatly reduce the energy barriers of charging and discharging reactions, thereby accelerating the conversion efficiency of NaSBs. It is worth mentioning that V@C2N has lower charge-discharge energy barriers and Na ion migration rates, since the embedded TM atom weakens the strong binding of Na+ in the N6 cavity of C2N. The intrinsic mechanism analysis reveals that the interaction between the d orbitals of V and the p orbitals of S leads to the weakening of Na-S bonds, which can not only effectively inhibit the shuttle effect, but also promote the dissociation of Na2S. Overall, this work not only offers excellent catalytic materials, but also provides vital guidance for designing SACs in NaSBs.

Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

Enhancing Zn2+ Storage Performance by Constructing the Interfaces Between VO2 and Co-N-C Layers

Vanadium oxides have aroused attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their low cost and high safety. However, low ion diffusion and vanadium dissolution often lead to capacity decay and deteriorating stability during cycling. Herein, vanadium dioxides (VO2) nanobelts are coated with a single-atom cobalt dispersed N-doped carbon (Co-N-C) layer via a facile calcination strategy to form Co-N-C layer coated VO2 nanobelts (VO2@Co-N-C NBs) for cathodes in AZIBs. Various in-/ex situ characterizations demonstrate the interfaces between VO2 layers and Co-N-C layers can protect the VO2 NBs from collapsing, increase ion diffusion, and enhance the Zn2+ storage performance. Additional density functional theory (DFT) simulations demonstrate that Co─O─V bonds between VO2 and Co-N-C layers can enhance interfacial Zn2+ storage. Moreover, the VO2@Co-N-C NBs provided an ultrahigh capacity (418.7 mAh g-1 at 1 A g-1), outstanding long-term stability (over 8000 cycles at 20 A g-1), and superior rate performance.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Chlorine bridge bond-enabled binuclear copper complex for electrocatalyzing lithium-sulfur reactions

Engineering atom-scale sites are crucial to the mitigation of polysulfide shuttle, promotion of sulfur redox, and regulation of lithium deposition in lithium-sulfur batteries. Herein, a homonuclear copper dual-atom catalyst with a proximal distance of 3.5 Å is developed for lithium-sulfur batteries, wherein two adjacent copper atoms are linked by a pair of symmetrical chlorine bridge bonds. Benefiting from the proximal copper atoms and their unique coordination, the copper dual-atom catalyst with the increased active interface concentration synchronously guide the evolutions of sulfur and lithium species. Such a delicate design breaks through the activity limitation of mononuclear metal center and represents a catalyst concept for lithium-sulfur battery realm. Therefore, a remarkable areal capacity of 7.8 mA h cm-2 is achieved under the scenario of sulfur content of 60 wt.%, mass loading of 7.7 mg cm-2 and electrolyte dosage of 4.8 μL mg-1.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 μmol g-1h-1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Tandem Catalysis inside Double-Shelled Nanocages with Separated and Tunable Atomic Catalyst Sites for High Performance Lithium-Sulfur Batteries

Single-atomic catalysts are effective in mitigating the shuttling effect and slow redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries, but their ideal performance has yet to be achieved due to the multi-step conversion of LiPSs requiring multifunctional active sites for tandem catalysis. Here double-shelled nano-cages (DSNCs) have been developed to address this challenge, featuring separated and tunable single-atom sites as nano reactors that trigger tandem catalysis and promote the efficient electrochemical conversion of LiPSs. This enables high capacity and durable Li-S batteries. The DSNCs, with inner Co-N4 and outer Zn-N4 sites (S/CoNC@ZnNC DSNCs), exhibit a high specific capacity of 1186 mAh g-1 at 1 C, along with a low capacity fading rate of 0.063% per cycle over 500 cycles. Even with a high sulfur loading (4.2 mg cm-2) and a low E/S ratio (6 µL mg-1), the cell displays excellent cycling stability. Moreover, the Li-S pouch cells are capable of stable cycling for more than 160 cycles. These results demonstrate the feasibility of driving successive sulfur conversion reactions with separated active sites, and are expected to inspire further catalyst design for high performance Li-S batteries.

Regulating the coordination environment of single atom catalysts anchored on C3N monolayer for Li-S battery by first-principles calculations

Owing to the extremely high theoretical specific capacity and energy density, the catalytic materials of lithium-sulfur (Li-S) batteries are widely explored. The "shuttle effect", poor electrode conductivity, and slow charge-discharge reaction dynamics are some of the key issues that have seriously hampered their commercialization process. Herein, based on the density-functional-theory (DFT), the catalytic performances of a series of single-atom catalysts (SACs) designed by regulating the N-content around coordination center in C3N (TM@N2C2/N3C/N4-C3N (TM = Ti, V, Fe, Co, Ni)), are systematically analyzed and evaluated. Among all the constructed SACs, Ti-centered configurations with fewer d electrons, especially for the Ti@N2C2-C3N, have the remarkable catalytic effect in improving the electron conductivity, trapping soluble polysulfides and accelerating the redox reaction. The in-depth mechanism indicates that the interaction between d orbital of Ti, mainly the splitting [Formula: see text] , and p orbital of S is the key factor for achieving high-effective adsorption. More importantly, the integral value of crystal orbital Hamiltonian population (ICOHP) of the Li-S bond in the adsorbed Li2S can serve as an excellent descriptor for evaluating the overall catalytic ability of substrates. Our work has vital guiding significance for designing high-performance SACs of Li-S batteries.

Phosphorous-Based Heterostructure for the Effective Catalysis of Polysulfide Reactions with Phase Changes in High-Sulfur-Loading Lithium-Sulfur Batteries

High sulfur loading and long cycle life are the design targets of commercializable lithium-sulfur (Li-S) batteries. The sulfur electrochemical reactions from Li2 S4 to Li2 S, which account for 75% of the battery's theoretical capacity, involve liquid-to-solid and solid-to-solid phase changes in all Li-S battery electrolytes in use today. These are kinetically hindered processes that are exacerbated by a high sulfur loading. In this study, it is observed that an in situ grown bimetallic phosphide/black phosphorus (NiCoP/BP) heterostructure can effectively catalyze the Li2 S4 to Li2 S reactions to increase the sulfur utilization at high sulfur loadings. The NiCoP/BP heterostructure is a good polysulfide adsorber, and the electric field prevailing at the Mott-Schottky junction of the heterostructure can facilitate charge transfer in the Li2 S4 to Li2 S2 liquid-to-solid reaction and Li+ diffusion in the Li2 S2 to Li2 S solid-state reaction. Consequently, a sulfur cathode with the NiCoP/BP catalyst can deliver a specific capacity of 830 mAh g-1 at the sulfur loading of 6 mg cm-2 for 500 cycles at the 0.5 C rate. High sulfur utilization is also possible at a higher sulfur loading of 8 mg cm-2 for 440 cycles at the 1 C rate.

The heterointerface effect to boost the catalytic performance of single atom catalysts for sulfur conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as one of the promising next-generation energy storage devices due to their characteristics of high energy density and low cost. However, the shuttle effect and sluggish conversion of lithium polysulfide (LiPs) have hindered their commercial applications. To address these issues, in our previous works, we have screened several highly efficient single atom catalysts (SACs) (MN4@G, M = V, Mo and W) with atomically dispersed transition metal atoms supported by nitrogen doped graphene based on high throughput calculations. Nevertheless, they still suffer from low loading of metal centers and unsatisfactory capability for accelerating the reaction kinetics. To tackle such problems, based on first-principles calculations, we systematically investigated the heterointerface effect on the catalytic performance of such three MN4@G toward sulfur conversion upon forming heterostructures with 5 typical two-dimensional materials of TiS2, C3N4, BN, graphene and reduced graphene oxide. Guided by efficient descriptors proposed in our previous work, we screened VN4@G/TiS2, MoN4@G/TiS2 and WN4@G/TiS2 possessing low Li2S decomposition barriers of 0.54, 0.44 and 0.41 eV, respectively. They also possess enhanced capabilities for catalyzing the sulfur reduction reaction as well as stabilizing soluble LiPs. More interestingly, the heterointerface can enhance the capability of the carbon atoms far away from the metal centers for trapping LiPs. This work shows that introducing a heterointerface is a promising strategy to boost the performance of SACs in Li-S batteries.

Kinetic Promoters for Sulfur Cathodes in Lithium-Sulfur Batteries

ConspectusLithium-sulfur (Li-S) batteries have attracted worldwide attention as promising next-generation rechargeable batteries due to their high theoretical energy density of 2600 Wh kg-1. The actual energy density of Li-S batteries at the pouch cell level has significantly exceeded that of state-of-the-art Li-ion batteries. However, the overall performances of Li-S batteries under practical working conditions are limited by the sluggish conversion kinetics of the sulfur cathodes. To overcome the above challenge, various kinetic promotion strategies have been proposed to accelerate the multiphase and multi-electron cathodic redox reactions between sulfur, lithium polysulfides (LiPSs), and lithium sulfide. Nowadays, kinetic promoters have been massively employed in sulfur cathodes to achieve Li-S batteries with high energy densities, high rates, and long lifespans. A comprehensive and timely summary of cutting-edge kinetic promoters for sulfur cathodes is of great essence to afford an in-depth understanding of the unique Li-S electrochemistry.In this Account, we outline the recent efforts on the design of sulfur cathode kinetic promoters for advanced Li-S batteries. The latest progress is discussed in detail regarding heterogeneous, homogeneous, and semi-immobilized kinetic promoters. Heterogeneous promoters, representatively known as electrocatalysts, function mainly by reducing the energy barriers of the interfacial electrochemical reactions. The working mechanism, activity regulation strategies, and reconstitution/deactivation processes of the heterogeneous promoters are reviewed to provide guiding principles for rational design. In comparison, homogeneous promoters are able to fully contact with the reaction interfaces and regulate the electron/ion-inaccessible reactants in working Li-S batteries. Redox mediators and redox comediators are typical homogeneous promoters. The former establishes extra chemical reaction pathways to circumvent the originally sluggish steps and boost the overall kinetics, while the latter fundamentally modifies the LiPS molecules to enhance their redox kinetics. For semi-immobilized promoters, the active units are generally anchored on the cathode substrate through flexible chains with mobile characteristics. Such a design endows the promoter with both heterogeneous and homogeneous characteristics to comprehensively regulate the multiphase sulfur redox reactions involving both mobile and immobile reactants.Overall, this Account summarizes the fundamental electrochemistry, design principles, and practical promotion effects of the various kinetic promoters used for the sulfur cathodes in Li-S batteries. We believe that this Account will provide an in-depth and cutting-edge understanding of the unique sulfur electrochemistry, thereby providing guidance for further development of high-performance Li-S batteries and analogous rechargeable battery systems.

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.

Anion-doped polypyrrole three-dimensional framework enables adsorption and conversion in lithium-sulfur batteries

Inhibiting the shuttle effect and propelling polysulfide conversion by introducing a suitable sulfur container has been proven as a promising strategy to enhance the cycle life of lithium-sulfur (Li-S) batteries. Here, a unique three-dimensional (3D) inter-connected framework assembled with SO42--doped polypyrrole (PPy-SO4) nanowires is proposed. The doping SO42- anion in a polymer skeleton could confine lithium polysulfides (LiPSs) by polar-polar interaction to inhibit the shuttle effect and enhance the conductivity of PPy to accelerate polysulfide conversion. Moreover, the electrostatic coupling between SO42- anion and Li+, as well as between -N+- and Sn2-, at polypyrrole /electrolyte interface can effectively regulate the redox kinetics of polysulfide. Besides, the inter-connected framework creates a large contact surface for sulfur and high-flux paths for electron transport. Consequently, the Li-S batteries assembled with PPy-SO4/S cathode exhibit a stable capacity of 501 mAh g-1 after 350 cycles at 1C, showing a low decay rate of 0.09% per cycle. Notably, the efficiency of the anion doping strategy is further verified in the pouch cell, realizing a capacity of 480 mAh g-1 after 250 cycles. This work illustrates that anion doping with rational structural design is a feasible solution to boost the electrochemical performance of Li-S batteries.

Surface design for high ion flux separator in lithium-sulfur batteries

Addressing the shuttle effect is a critical challenge in realizing practical applications of lithium-sulfur batteries. One promising avenue refers to the surface modification of separators, transitioning them from closed to open structures. In the current investigation, a high ion flux separator was devised by means of MnO2 self-assembly onto a Porous Polypropylene (PP) separator, subsequently coupling it with biochar. The separator exhibited favorable ion and electronic conductivity. Moreover, it adeptly captured and transformed polysulfides into Li2S2/Li2S, cyclically curbing the mobility of Polysulfide lithium (LiPSs). In addition, this augmentation in the kinetic conversion of LiPSs during the electrochemical process translated into an impressive discharge specific capacity and area capacity of 939 mAh/g and 4 mAh cm-2, respectively. Moreover, this innovative design methodology provides an alternative avenue for future separator designs within lithium-sulfur batteries.

High-Throughput Calculations for Screening d- and p-Block Single-Atom Catalysts toward Li2 S/Na2 S Decomposition Guided by Facile Descriptor beyond Brønsted-Evans-Polanyi Relationship

Single-atom catalysts (SACs) are promising cathode materials for addressing issues faced by lithium-sulfur batteries. Considering the ample chemical space of SACs, high-throughput calculations are efficient strategies for their rational design. However, the high throughput calculations are impeded by the time-consuming determination of the decomposition barrier (Eb ) of Li2 S. In this study, the effects of bond formation and breakage on the kinetics of SAC-catalyzed Li2 S decomposition with g-C3 N4 as the substrate are clarified. Furthermore, a new efficient and easily-obtained descriptor Li─S─Li angle (ALi─S─Li ) of adsorbed Li2 S, different from the widely accepted thermodynamic data for predicting Eb , which breaks the well-known Brønsted-Evans-Polanyi relationship, is identified. Under the guidance of ALi─S─Li , several superior SACs with d- and p-block metal centers supported by g-C3 N4 are screened to accelerate the sulfur redox reaction and fix the soluble lithium polysulfides. The newly identified descriptor of ALi─S─Li can be extended to rationally design SACs for Na─S batteries. This study opens a new pathway for tuning the performance of SACs to catalyze the decomposition of X2 S (X = Li, Na, and K) and thus accelerate the design of SACs for alkaline-chalcogenide batteries.

GO-CoNiP New Composite Material Modified Separator for Long Cycle Lithium-Sulfur Batteries

Lithium-sulfur batteries with high capacity are considered the most promising candidates for next-generation energy storage systems. Mitigating the shuttle reaction and promoting catalytic conversion within the battery are major challenges in the development of high-performance lithium-sulfur batteries. To solve these problems, a novel composite material GO-CoNiP is synthesized in this study. The material has excellent conductivity and abundant active sites to adsorb polysulfides and improve reaction kinetics within the battery. The initial capacity of the GO-CoNiP separator battery at 1 C is 889.4 mAh g-1 , and the single-cycle decay is 0.063% after 1000 cycles. In the 4 C high-rate test, the single-cycle decay is only 0.068% after 400 cycles. The initial capacity is as high as 828.2 mAh g-1 under high sulfur loading (7.3 mg cm-2 ). In addition, high and low-temperature performance tests are performed on the GO-CoNiP separator battery. The first cycle discharge reaches 810.9 mAh g-1 at a low temperature of 0 °C, and the first cycle discharge reaches 1064.8 mAh g-1 at a high temperature of 60 °C, and both can run stably for 120 cycles. In addition, in situ Raman tests are conducted to explain the adsorption of polysulfides by GO-CoNiP from a deeper level.

Transition Metal Phosphides: The Rising Star of Lithium-Sulfur Battery Cathode Host

Lithium-sulfur batteries (LSBs) with ultra-high energy density (2600 W h kg-1 ) and readily available raw materials are emerging as a potential alternative device with low cost for lithium-ion batteries. However, the insulation of sulfur and the unavoidable shuttle effect leads to slow reaction kinetics of LSBs, which in turn cause various roadblocks including poor rate capability, inferior cycling stability, and low coulombic efficiency. The most effective way to solve the issues mentioned above is to rationally design and control the synthesis of the cathode host for LSBs. Transition metal phosphides (TMPs) with good electrical conductivity and dual adsorption-conversion capabilities for polysulfide (PS) are regarded as promising cathode hosts for new-generation LSBs. In this review, the main obstacles to commercializing the LSBs and the development processes of their cathode host are first elaborated. Then, the sulfur fixation principles, and synthesis methods of the TMPs are briefly summarized and the recent progress of TMPs in LSBs is reviewed in detail. Finally, a perspective on the future research directions of LSBs is provided.

A nitrogen-rich two dimensional covalent organic framework with multiple carbonyls as a highly efficient anchoring material for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries, as next generation energy storage systems, have gained considerable attention due to their high energy density, low cost, and environmental friendliness. However, the practical applications of Li-S batteries are presently hindered by several issues, such as the low conductivity of sulfur species, the shuttle effect of polysulfides, and poor conversion efficiency in discharging/charging processes. In this study, using density functional theory (DFT)-based computations, we propose a two dimensional (2D) covalent organic framework (COF) with triquinoxalinylene (TQ) and benzoquinone (BQ) units in its skeleton, namely, TQBQCOF, as a promising sulfur host material for high-performance Li-S batteries. We have found that the TQBQCOF is a semiconductor with a band gap of 1.16 eV. After the adsorption of LiPSs the TQBQCOF becomes metallic in nature, which ensures its excellent electronic conductivity. The moderate adsorption energies of the TQBQCOF to the soluble LiPSs can effectively suppress the shuttle effect of polysulfides. Notably, the TQBQCOF also shows high catalytic activity for the sulfur reduction reactions (SRR) in the discharge process and Li2S decomposition in the charging process of Li-S batteries. The Gibbs free energy barrier for the SRR is 0.22 eV, while the decomposition barrier of a Li2S molecule on the TQBQCOF is only 0.04 eV, ensuring the rapid charging and discharging processes of Li-S batteries.

Single-atom site catalysis in Li-S batteries

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4 < x ≤ 8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

2D Materials Beyond Post-AI Era: Smart Fibers, Soft Robotics, and Single Atom Catalysts

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs), which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AI era. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.