Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries

Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries Seeram Ramakrishna, Dipsikha Ganguly, Abhijitha VG, Tanwir Ansai, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7559583/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Transition-metal carbides remain underexplored as catalytic phases in energy storage despite their rich electronic structure and tunable surface chemistry. Here, we demonstrate that Fe₅C₂ nanoparticles embedded in a carbon nanotube (CNT) network act as a bifunctional catalytic–anchoring phase, simultaneously immobilizing lithium polysulfides (LiPSs) and accelerating their conversion to Li₂S. Density functional theory and ab initio molecular dynamics simulations reveal that the (510) Fe₅C₂ surface provides strong adsorption sites and promotes stepwise dissociation of higher-order polysulfides. UV–vis adsorption, potentiostatic Li₂S deposition, cyclic voltammetry, and X-ray photoelectron spectroscopy confirm Fe–S bond formation and rapid polysulfide conversion, while dynamic electrochemical impedance spectroscopy (DEIS) tracks the reduction of charge-transfer resistance during cycling. The Fe₅C₂/S/CNT bilayer cathode delivers a high initial capacity of 1450 mAh g⁻¹ at 0.1C, excellent rate capability (700 mAh g⁻¹ at 1C), and stable cycling. This multiscale investigation establishes a direct link between atomic-level catalytic interactions and enhanced electrochemical kinetics, presenting Fe₅C₂ as a design paradigm for catalytic materials in lithium–sulfur and broader metal–sulfur battery systems. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Materials science/Materials for energy and catalysis/Batteries Fe₅C₂ Transition-metal carbides Lithium–sulfur batteries Polysulfide conversion Catalytic anchoring Density functional theory (DFT) Ab initio molecular dynamics (AIMD) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Li–S batteries are considered one of the promising candidates to meet the world’s energy demand for next-generation energy storage due to their high theoretical energy density (~2600 Wh kg⁻¹) and earth-abundant, low cost sulfur cathode 1 . However, their practical development is challenged by rapid capacity fading, largely driven by the dissolution and migration of lithium polysulfides (LiPSs), the sluggish kinetics of sulfur conversion, and the intrinsically low conductivity of sulfur and its discharge products. To address these issues, multifunctional sulfur hosts capable of physically confining LiPSs and catalytically accelerating their conversion are essential 2,3 . Transition metal carbides (TMCs) have emerged as promising candidates, characterized by their metallic conductivity, strong surface polarity, and intrinsic redox catalytic activity 4–6 . Yet, their widespread adoption in Li–S batteries has been limited by complex, multi-step fabrication protocols that yield suboptimal structural and interfacial integration with conductive supports 4,7 . Among these, Hägg carbide (χ−Fe 5 C 2 ) remains notably underexplored for electrochemical energy storage 8–10 . This is surprising given its advantageous electronic structure and robust affinity for sulfur species via specific Fe–S interactions critical for polysulfide regulation. While a few reports exist on Hägg carbide for electrochemical energy conversion, most synthetic routes rely on toxic and challenging-to-handle carbon monoxide as a precursor, significantly complicating their widespread utility 7,9,10 . χ-Fe 5 C 2 presents a unique confluence of physicochemical attributes highly beneficial for Li–S chemistry. Unlike more commonly investigated carbides, it is a ferromagnetic carbide with a distinct orthorhombic structure ( Pnma ) and a high density of states at the Fermi level, conferring excellent electrical conductivity comparable to metals 11,12 . Crucially, the partially filled d-band structure of Fe atoms in χ−Fe 5 C 2 facilitates strong orbital hybridization with S-based species, promoting robust chemisorption of LiPSs. In contrast to noble metal catalysts, χ-Fe 5 C 2 provides abundant, earth-abundant catalytic sites capable of reversible Fe 2+ ↔Fe 3+ redox cycling, essential for mediating sulfur redox reactions. Its surface also facilitates dissociative adsorption of S–S bonds, enhancing LiPS conversion kinetics through a powerful bifunctional mechanism of binding and catalysis 4 . Despite these compelling features and its established role as an active phase in heterogeneous catalysis like Fischer-Tropsch synthesis, χ−Fe 5 C 2 has been largely overlooked in energy storage 8,9 . This oversight is primarily due to the formidable synthetic challenges in preparing it in a highly nanostructured, electrochemically accessible morphology with well-defined interfaces, a prerequisite for effective battery performance. To fully exploit χ−Fe 5 C 2 's catalytic potential while simultaneously addressing the inherent low conductivity and substantial volume changes of sulfur cathodes, a robust and highly conductive scaffold is indispensable. Porosity places a major role in sulfur confinement 13 . While microporous and mesoporous materials are highly effective for suppressing polysulfide shuttling, macroporous materials have proven largely ineffective for this purpose, despite their benefits in providing ample space for sulfur and efficient electrolyte transport 14 . Carbon nanotubes (CNTs) are uniquely suited for this, offering exceptional intrinsic electronic conductivity that establishes an efficient electron transport throughout the electrode architecture 15–17 . Beyond electrical transport, their interconnected, three-dimensional porous network provides a high surface area for intimate component contact, accommodates the significant volume expansion (∼80%) during lithiation, and imparts substantial mechanical stability to maintain electrode integrity over extended cycling, which is one of the key parameter to attain high energy density 13,18 . However, fabricating such a composite using conventional method typically involving separate synthesis of catalytic nanoparticles and conductive carbon followed by mechanical mixing is inherently problematic. These multi-step approaches frequently lead to poor interfacial contact, uncontrolled component agglomeration, and the introduction of impurities, severely compromising the synergistic potential of the hybrid material and hindering charge transfer to the active sites 13,18 . Herein, we introduce a fundamentally new material paradigm that directly confronts these pervasive synthetic hurdles: a nanostructured χ−Fe 5 C 2 /CNT hybrid precisely engineered through a single-step chemical vapor deposition (CVD) route utilizing hematite as the catalyst and acetylene as carbon source. This innovative approach orchestrates the concerted and synchronized initiation of Fe nucleation, in situ carburization to form χ− Fe 5 C 2 nanocrystals, and carbon nanotube (CNT) formation within a singular reaction environment. This reaction-synchronized CVD growth is transformative because it ensures atomic-scale coupling and the formation of ultra-clean, defect-free heterointerfaces directly between the growing χ−Fe 5 C 2 nanocrystals and the nascent CNT scaffold. This unprecedented direct growth mechanism, distinct from conventional assembly methods intrinsically maximizes active site accessibility and facilitates seamless electron and ion transport, critical for efficient polysulfide conversion. Our unique synthesis yields an intimately integrated hybrid architecture, entirely devoid of surfactants, binders, or additional post-processing steps, directly addressing the limitations of prior art. The resulting material capitalizes on a powerful synergistic interplay between highly active χ−Fe 5 C 2 nanocrystals and a robust, conductive, high-surface-area CNT scaffold. To our knowledge, this work constitutes the first report of using single-step CVD to engineer Hägg carbide/carbon hybrids specifically tailored for high-performance Li–S battery. It not only establishes a facile and scalable pathway for fabricating advanced functional composites but also opens entirely new possibilities for integrating underutilized transition metal carbide phases into diverse electrochemical systems by providing a blueprint for their controlled, atomic-scale integration. The χ−Fe 5 C 2 /CNT system represents a fundamentally new class of catalytic–conductive architectures, designed from the ground up for superior polysulfide regulation and sulfur redox enhancement in Li–S batteries. Synthesis and Structural Characterization The synthesis of the Fe₅C₂/CNT composite was performed using a one-step catalytic chemical vapor deposition (CVD) process. This technique involved the thermal decomposition of acetylene (C 2 H 2 ) vapor at 700 °C under an argon (Ar) atmosphere, over an Fe₂O₃ catalyst. The Fe₂O₃ was first reduced and served as nucleation sites where acetylene decomposed, and the resulting carbon atoms rapidly diffused into the Fe lattice, leading to carburization and the formation of the Fe₅C₂ phase. Concurrently, the continuous supply of carbon from the acetylene allowed for the growth of carbon nanotubes (CNTs) via a tip-growth mechanism, with the Fe₅C₂ nanoparticles acting as catalysts at their growing tips. The process's kinetics were carefully controlled by a specific flow of hydrogen and inert gas, which was essential to prevent oxidation and ensure the concurrent formation of both the Hägg carbide and the high-quality carbon nanotubes (Scheme 1). The step by step growth mechanism was elaborated in supplementary information (S1,S2). The cathode was prepared by Sulphurization carbon nanotubes using melt diffusion of sulfur at 155 o C for 12 h in argon atmosphere 19 . Electrochemical Measurements The cathode slurry was prepared by combining S/CNT, polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 8:1:1. N-methyl-2-pyrrolidone (NMP) was then added to achieve a solid content of 30 wt.% and create a uniform slurry. This slurry was coated onto an aluminium foil using the doctor-blade technique. The coated foil was dried at 60 °C for 8 hours. A second layer was then added by mixing Fe₅C₂/CNT with PVDF in a 9:1 ratio. This second slurry was coated onto the dried first layer. The thickness of the first layer was maintained at 100 μm, while the second layer was kept at 40 μm. The bilayer cathode was termed as Fe₅C₂/CNT/S. The electrode was then punched into 12-mm-diameter disks. The total sulfur loading on the cathode was maintained at 3-3.5 mg cm⁻². Electrochemical performance was evaluated using a CR2032 coin cell, assembled in an argon-filled glove box with oxygen and water levels maintained below 0.1 ppm. The cell employed a lithium metal anode and a glass fiber separator. The electrolyte was composed of 1 M lithium bis(trifluoromethane)sulfonimide (LiTFSI) in a 1:1 v/v mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME), with an additional 0.2 M lithium nitrate (LiNO₃). The E/S ratio was maintained at 10 uL mg -1 . Symmetric Cell Fabrication for CV Analysis For the fabrication of symmetric cells, Fe₅C₂/CNT/S.electrodes were used for both the cathode and anode. The cell was filled with an electrolyte consisting of 0.2 M Li₂S₆ and 1 M LiTFSI in a 1:1 v/v mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME). For comparison, S/CNT electrodes were also tested using the same cell configuration as a baseline. Li₂S Deposition Test The catholyte solution for the Li₂S deposition test was prepared by dissolving lithium sulfide (Li₂S) and elemental sulfur (S) in a 1:7 molar ratio in a tetraglyme solvent containing 1.0 M LiTFSI. The solution was stirred overnight at 60 °C to ensure complete dissolution, yielding a 0.2 M Li₂S₈ solution. The cell was assembled with 20 μL of the prepared Li₂S₈ catholyte applied to the Fe₅C₂/CNT/S cathode and 20 μL of a blank electrolyte (without Li₂S₈) added as the anolyte. A glass fiber membrane was used as the separator. The batteries were initially discharged galvanostatically to 2.06 V at a current of 0.112 mA, then subjected to a potentiostatic discharge at 2.05 V. Results and Discussions The synthesis yielded a phase-pure Hägg carbide/carbon nanotube composite, as confirmed by a suite of advanced characterization techniques. X-ray diffraction (XRD) definitively established the successful in-situ solid-state transformation of the Fe₂O₃ precursor, revealing sharp reflections exclusively indexed to orthorhombic Fe₅C₂ ( Pnma , PDF# 89-7272) with no evidence of residual iron oxides or metallic iron ( figure 1a, figure S1 ) 8,12 . The diffraction peaks at 37.07°, 39.38°, 40.83°, 41.19°, 43.45°, 44.2°, 45.1°, 47.3°, 50.8°, 54.27°, 58.3° represents the diffraction patterns of (311), (020), (- 112), (202), (021), (510), (- 312), (221), (312), (022), (- 113) crystal planes of Fe 5 C 2 . A distinct peak at 26.3° confirms the formation of the CNT scaffold. Additionally, a separate XRD analysis of a pure CNT/sulfur composite revealed the presence of an orthorhombic sulfur (S8) cathode along with the characteristic CNT peak at 26.3°, which was then utilized to create a bilayer cathode composite 20 . Mössbauer spectroscopy ( Figure 1b ) was used to determine the chemical state of iron. The spectrum showed three distinct magnetically ordered hyperfine-split sextets, which are characteristic of the unique iron sites within the Hägg carbide (Fe 5 C 2 ) structure, thereby confirming the phase purity and ruling out any non-magnetic iron phases. The broad and complex absorption features spanning a velocity range of approximately -8 mm/s to +8 mm/s, with multiple discernible dips, are consistent with the presence of magnetically ordered iron phases, which is a fingerprint of Fe 5 C 2 due to its multiple crystallographically inequivalent iron sites 21,22 . Figure 1c illustrates the crystal structure of Fe₅C₂, revealing the presence of both Fe²⁺ and Fe⁺ states. These mixed-valence iron sites are hypothesized to serve as catalytic centers for reactions within a lithium-sulfur battery. The macroscopic morphology of Fe₅C₂/CNT was observed by scanning electron microscopy and High-resolution transmission electron microscopy (HRTEM). The quasi-spherical Fe₅C₂ nanoparticles (5–15 nm) intimately anchored as the catalyst tips for the CNTs via a classic tip-growth mechanism was observed ( figure 1 d-f ). Raman spectra, with an elevated I D /I G ratio of 1.15, indicated increased structural defects and lattice strain in the CNTs due to the anchored Fe 5 C 2 nanoparticles. These defects are believed to improve the catalytic sites and structural integrity 23 . BET analysis showed a high surface area of 117 m² g -1 with a meso-microporous structure, beneficial for ion transport and sulfur confinement 5,13,16,19 . Supplementary information showed the synthesis optimization with 5 min, 10 min and 15 min exposure of acetylene decomposition on 100 mg Fe 2 O 3 . The Fe 2 O 3 precursor was fully converted to the desired Fe 5 C 2 phase after 15 minutes of acetylene decomposition. This systematic optimization process revealed a phase evolution from mixed oxides (Fe 3 O 4 , Fe 2 O 3 ), carbides (Fe-C) and pure iron (Fe) at 5 minutes to a Fe 3 O 4 and Fe-C mixture at 10 minutes, ultimately leading to the phase-pure Fe 5 C 2 material, confirmed by XRD analysis ( Supplementary information figure S1 ). Microstructures of each stages were shown in supplementary information, figure S2, which clearly depicts the change in the sizes and morphology of the Fe-constitutes in CNT. Microscopic images in figure 1(k-m) show that sulfur is successfully confined to the surface of the CNTs in the S/CNT composite. The sulfur loading was estimated to be 70 wt.% . Density Functional Theory Calculations and Experimental Correlation To elucidate the anchoring behaviour and catalytic activity of Fe₅C₂ toward lithium polysulfides (LiPSs), density functional theory (DFT) calculations were performed further 11 . A slab model was constructed using the (510) plane of Fe₅C₂, chosen for its stability and representative surface structure. The atomic arrangement of 510-Fe₅C₂ exposes three distinct adsorption sites: threefold Fe-coordinated hollow sites (3F), fourfold Fe-coordinated hollow sites (4F), and a fourfold Fe site coordinated with a central C atom (4FC) ( figure 2 ) The optimized geometries of pristine and LiPS-anchored 510-Fe₅C₂ are shown in figure 2a-f. Lower-order polysulfides (Li₂S and Li₂S₂) adsorb molecularly with anchoring strengths of –5.69 eV and –7.34 eV, respectively, with sulfur atoms preferentially binding at 3F sites while lithium atoms occupy Fe–Fe bridge, 4F, or 4FC sites. In contrast, higher-order polysulfides exhibit dissociative adsorption on the 510 surface with binding energies ranging from –8 to –12 eV ( figure 2g ). During this process, sulfur atoms occupy both 3F and 4F sites, while lithium atoms maintain similar adsorption motifs as in lower-order species. The enhanced binding arises from polar–polar interactions between the asymmetric, polar polysulfides and Fe sites, promoting dissociation of long-chain species 4 . Comparable behaviour has been reported for Na polysulfides on Fe₃N/carbon composites 24 . Ab initio molecular dynamics (AIMD) simulations provided further insight into the dissociation mechanism of Li₂S₈ on 510-Fe₅C₂. Born–Oppenheimer AIMD simulations 25,26 were performed using a canonical ensemble (NVT) 27,28 with the temperature maintained at 300 K using a Nose–Hoover thermostat with a time step of 1 fs. Starting from the optimized configuration ( figure 3a ), Fe–S bond formation at 3F sites initiated decomposition within ~0.5 ps, with one sulfur atom detaching from the Li₂S₈ ring and chemisorbing at a 3F site ( figure 3b ). Progressive bond cleavage led to further detachment by ~1.0 ps ( figure 3c ). At ~1.0 ps, a second sulfur atom broke its S-S bond and re-optimized on a 3F site. By ~1.5 ps, the structure had fully evolved into a lower-order polysulfide resembling Li 2 S 2 , with four sulfur atoms completely detached from the original ring( figure 3d ), and finally stabilizing as Li₂S ( figure 3e ). This dissociation was accompanied by an ~18 eV energy drop ( figure 3f ), consistent with earlier reports on Na₂S₈ on Fe₃N 24 . Together, these results establish Fe₅C₂ as an effective bifunctional phase capable of both anchoring and catalyzing polysulfide conversion . To experimentally validate these predictions, polysulfide adsorption and electrochemical measurements on the Fe₅C₂/CNT composite were recorded. Upon exposure to a Li₂S₆ solution, the composite induced near-complete decolorization from yellow to transparent within 10 min ( figure 4a–b ). UV–vis spectroscopy confirmed the lowering intensity of the characteristic S₆²⁻ absorption peak, highlighting its strong polysulfide-trapping ability, in line with the high binding energies predicted by DFT 29,30 . Cyclic voltammetry (CV) in symmetric cells using Fe₅C₂/CNT electrodes further revealed pronounced redox peaks and significantly enhanced current responses compared with CNT controls ( figure 4c ) 29,31 . This confirms accelerated polysulfide conversion kinetics, directly reflecting the AIMD-predicted role of Fe–S bond formation in driving Li₂S₈ dissociation. Potentiostatic Li₂S deposition tests at 2.05 V further demonstrated the catalytic effect: the Fe₅C₂/CNT electrode delivered a deposition capacity of 319.33mAh g⁻¹, far exceeding the baseline (figure 4d ). This higher capacity indicates more efficient and regulated Li₂S nucleation and growth, consistent with theoretical predictions of Fe₅C₂-facilitated stepwise polysulfide conversion. Post-mortem X-ray photoelectron spectroscopy (XPS) after deposition test provided direct chemical evidence of this catalytic role. Besides the expected Li–S (161.0–162.0 eV) and S–S (163.0–164.0 eV) peaks, Fe–S bonds were clearly identified at 162.5–163.5 eV ( figure 4e–f ) 24,27 . These bonds mirror the strong Fe–S interactions predicted in DFT and AIMD simulations, confirming the material’s chemical participation in polysulfide conversion. Elemental mapping further revealed homogeneous sulfur distribution within the composite ( figure 4g ), consistent with uniform immobilization and catalytic regulation. Electrochemical Performance and Design Implications The Fe₅C₂/CNT/S composite exhibits superior electrochemical performance and robust long-term stability, which we attribute to the bifunctional catalytic and structural role of embedded Fe₅C₂ nanoparticles. CV analysis revealed significantly higher current responses and reduced peak separation compared to CNT/S and Sulfur electrodes, with reduction peaks shifted to more positive potentials and oxidation peaks to more negative potentials ( figure 5a ). This indicates accelerated polysulfide conversion kinetics and reduced polarization, consistent with the catalytic effect observed in simulations and adsorption studies 19,23 . Galvanostatic charge–discharge tests at 0.1C yielded an initial discharge capacity of 1450 mAh g⁻¹, for Fe₅C₂/CNT/S ,substantially outperforming CNT/S (800 mAh g⁻¹) and sulfur (650 mAh g⁻¹) cathodes( figure 5b and 5c ).The overpotential observed to be lower (250 mV) indicating the better charge transfer. Discharge capacities of 1450, 1100, 750, 600 mAh g⁻¹ was recorded for Fe 5 C 2 /CNT/S at 0.1C, 0.2C, 0.5C, 1C respectively ( figure 5d ). After 100 cycles, the capacity stabilized at 700 mAh g⁻¹ with minimal decay of 0.08% per cycle, demonstrating excellent cycling stability shown in figure 5e . At higher rates, the electrode retained 700 mAh g⁻¹ at 1C, and full capacity recovery upon returning to 0.2C confirmed structural integrity and reversibility of the composite framework. Electrochemical impedance spectroscopy (EIS) further demonstrated the beneficial role of Fe₅C₂. The composite exhibited a markedly lower charge-transfer resistance (Rct ≈ 38 Ω) than CNT/S (50 Ω) and Sulfur electrodes (64 Ω), highlighting improved conductivity and reaction kinetics ( figure 5f ). Cyclic stability at 2C showed 80% retention of initial discharge capacity (552 mAh g⁻¹) at 200 th cycles and 57% retention after 700 th cycles( figure 5g ). Dynamic electrochemical impedance spectroscopy (DEIS) across 1.8–2.85 V ( figure 5h–i ) provided real-time insight into resistance evolution during cycling. The consistently low Rct for Fe₅C₂/CNT–S, particularly at the low-voltage plateau, provides direct evidence of its catalytic role in accelerating the sluggish final Li₂S conversion step 32 . By preventing electrode passivation and promoting efficient deposition, Fe₅C₂ ensures high capacity utilization and long-term stability. Conclusion This work presents a novel, single-step chemical vapor deposition (CVD) strategy for synthesizing a Fe₅C₂/CNT catalytic polysulfide shuttling inhibitor for Li-S batteries, highlighting a powerful synergy between material design, reaction engineering, and catalysis. The unique properties of Fe₅C₂ including availability of different Fe states, strong polysulfide affinity, and robust catalytic activity—make it an ideal sulfur host and polysulfide regulator. Density functional theory (DFT) calculations further confirm the strong anchoring of LiPSs on Fe₅C₂ surfaces, with higher-order polysulfides exhibiting dissociative adsorption and large binding energies. These theoretical insights reveal that Fe₅C₂ not only immobilizes LiPSs effectively but also catalyzes their stepwise conversion, thereby explaining the superior electrochemical performance. By integrating the Fe₅C₂ within a CNT matrix, our synchronous reaction pathway yields a hierarchical, highly conductive, and catalytically active hybrid that effectively addresses both the physical confinement and chemical conversion challenges of lithium polysulfides. This strategy not only introduces a previously untapped carbide phase into sulfur cathode research but also establishes a blueprint for designing multifunctional hosts through a minimal-step synthesis. This finding may open a new frontier in utilizing metal carbides for high-energy-density batteries. Declarations Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. Acknowledgements This research was conducted at Alternative Energy Nanotechnology laboratory (AENL), IIT Madras, National University of Singapore and HPCE, IIT Madras. A. V. G and B. R. K. N acknowledge the high-performance computational facilities at HPCE, IIT Madras. We further acknowledge the use of ChatGPT-4.0 in refining the English in this manuscript. References He, J. & Manthiram, A. A review on the status and challenges of electrocatalysts in lithium-sulfur batteries. Energy Storage Mater. 20 , 55–70 (2019). Manthiram, A., Chung, S. & Zu, C. Lithium–Sulfur Batteries: Progress and Prospects. Adv. Mater. 27 , 1980–2006 (2015). Yang, R. et al. Single-step laser-printed integrated sulfur cathode toward high-performance lithium–sulfur batteries. Nat. Commun. 16 , 2386 (2025). Wang, M. et al. Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium–sulfur batteries. Nanoscale 16 , 462–473 (2024). Adi, A. & Taniguchi, I. Synthesis of an Advanced Sulfur Cathode with a Porous Graphitic C/Fe 3 C Electrocatalyst and Three-Dimensional Current Collector for Li–S Batteries. Energy Fuels 37 , 14324–14333 (2023). Hu, P., Xu, P., Chen, Y., Wang, W. & Shao, J.-J. Tungsten Carbide Embedded in a Porous Carbon Nanofiber Sandwich Structure Electrode: A Strategy to Improve the Performance of Lithium–Sulfur Batteries. Langmuir 41 , 795–803 (2025). Naguib, M. et al. Two-Dimensional Transition Metal Carbides. ACS Nano 6 , 1322–1331 (2012). Wang, D., Chen, B., Duan, X., Chen, D. & Zhou, X. Iron-based Fischer–Tropsch synthesis of lower olefins: The nature of χ-Fe5C2 catalyst and why and how to introduce promoters. J. Energy Chem. 25 , 911–916 (2016). Li, Y. et al. Interfacial Fe5C2-Cu catalysts toward low-pressure syngas conversion to long-chain alcohols. Nat. Commun. 11 , 61 (2020). Wang, P. et al. Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2. Nature 635 , 102–107 (2024). Zhao, S. et al. Determining surface structure and stability of ε-Fe 2 C, χ-Fe 5 C 2 , θ-Fe 3 C and Fe 4 C phases under carburization environment from combined DFT and atomistic thermodynamic studies. Catal. Struct. React. 1 , 44–60 (2015). Kong, F. et al. Magnetic properties and electrocatalytic properties of Fe5C2 particles with different morphologies. J. Mater. Sci. Mater. Electron. 33 , 884–893 (2022). Kang, N. et al. Cathode porosity is a missing key parameter to optimize lithium-sulfur battery energy density. Nat. Commun. 10 , 4597 (2019). Zhao, C. et al. A high-energy and long-cycling lithium–sulfur pouch cell via a macroporous catalytic cathode with double-end binding sites. Nat. Nanotechnol. 16 , 166–173 (2021). Shi, Y. et al. Self-assembly of hierarchical MoSx/CNT nanocomposites (2<x<3): towards high performance anode materials for lithium ion batteries. Sci. Rep. 3 , 2169 (2013). Yan, Z. et al. Nickel sulfide nanocrystals on nitrogen-doped porous carbon nanotubes with high-efficiency electrocatalysis for room-temperature sodium-sulfur batteries. Nat. Commun. 10 , 4793 (2019). Ganguly, D., Ramanujam, K. & Sundara, R. Low-Temperature Synthesized Pt 3 Fe Alloy Nanoparticles on Etched Carbon Nanotubes Catalyst Support Using Oxygen-Deficient Fe 2 O 3 as a Catalytic Center for PEMFC Applications. ACS Sustain. Chem. Eng. 11 , 3334–3345 (2023). Li, F. et al. Recent advances in cathode materials for rechargeable lithium–sulfur batteries. Nanoscale 11 , 15418–15439 (2019). Zhang, H. et al. Fe3O4-doped mesoporous carbon cathode with a plumber’s nightmare structure for high-performance Li-S batteries. Nat. Commun. 15 , 5451 (2024). Zhang, Y. et al. “Sauna” Activation toward Intrinsic Lattice Deficiency in Carbon Nanotube Microspheres for High‐Energy and Long‐Lasting Lithium–Sulfur Batteries. Adv. Energy Mater. 11 , 2100497 (2021). Liu, X.-W. et al. Mössbauer Spectroscopy of Iron Carbides: From Prediction to Experimental Confirmation. Sci. Rep. 6 , 26184 (2016). Rao, K. R. P. M. et al. Mössbauer Study of Iron Fischer−Tropsch Catalysts during Activation and Synthesis. Energy Fuels 10 , 546–551 (1996). Ghosh, A., Garapati, M. S., Vijaya Kumar Saroja, A. P. & Sundara, R. Polar Bilayer Cathode for Advanced Lithium–Sulfur Battery: Synergy Between Polysulfide Conversion and Confinement. J. Phys. Chem. C 123 , 10777–10787 (2019). Qi, Y. et al. A Fe3N/carbon composite electrocatalyst for effective polysulfides regulation in room-temperature Na-S batteries. Nat. Commun. 12 , 6347 (2021). Barnett, R. N. & Landman, U. Born-Oppenheimer molecular-dynamics simulations of finite systems: Structure and dynamics of ( H 2 O ) 2. Phys. Rev. B 48 , 2081–2097 (1993). Ribaldone, C. & Casassa, S. Born–Oppenheimer Molecular Dynamics with a Linear Combination of Atomic Orbitals and Hybrid Functionals for Condensed Matter Simulations Made Possible. Theory and Performance for the Microcanonical and Canonical Ensembles. J. Chem. Theory Comput. 20 , 3954–3975 (2024). Xiao, Y. et al. Cationic surfactant for lithium-sulfur batteries enables efficient use of sulfur and limits lithium dendrite formation. Cell Rep. Phys. Sci. 4 , 101658 (2023). Singh, D. & Ahuja, R. Polypeptoid Material as an Anchoring Material for Li–S Batteries. ACS Appl. Energy Mater. 4 , 13070–13076 (2021). Ansari, T., Ghosh, A., Ganguly, D., Muthiah, B. & Sundara, R. Expediting Polysulfide Anchoring by Fe 3 O 4 /Reduced Graphene Oxide Composite for High‐Performance Lithium‐Sulfur Batteries. Batter. Supercaps 8 , e202400716 (2025). Chatterjee, A., Ganguly, D., Sundara, R. & Bhattacharya, S. S. Rare‐Earth Doped Configurational Entropy Stabilized High Entropy Spinel Oxide as an Efficient Anchoring/Catalyst Functional Interlayer for High‐Performance Lithium‐Sulfur Battery. Batter. Supercaps 6 , e202300082 (2023). Shen, Z. et al. Cation-doped ZnS catalysts for polysulfide conversion in lithium–sulfur batteries. Nat. Catal. 5 , 555–563 (2022). Drvarič Talian, S., Moškon, J., Dominko, R. & Gaberšček, M. The Pitfalls and Opportunities of Impedance Spectroscopy of Lithium Sulfur Batteries. Adv. Mater. Interfaces 9 , 2101116 (2022). Scheme 1 Scheme 1 is available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files Supportinginformationfe5c2.docx schem1.jpg Scheme 1: Schematic diagram of CVD grown Fe 5 C 2 /CNT synthesis Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7559583","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":511589637,"identity":"9c81e115-6ab8-4c03-ae3e-ab7694ab9032","order_by":0,"name":"Seeram Ramakrishna","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYPACGwjFQ4KWNNK1HCZBi3x787EPP3PO5xmcP8D44G0bg728AwEtBmeOJc/s3Xa72OBGArPh3DaGxI0HCGmRyDFm4N12O3HDDQY2ad42hgTDBkIOm//+M+PfbecSN5w/wP4bqMWeoBaGGzzMzLzbDiRuOJDAxgzUwjifkA6DM2nGzLLbkhNn3khslpxzTiJxAyEt8u2HHzO+3WaX2Hf+8MEPb8ps7OUJOgwBGEFqJRgMDhCvBWYvCbaMglEwCkbByAAAe0RBJMiScDcAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-8479-8686","institution":"National University of Singapore","correspondingAuthor":true,"prefix":"","firstName":"Seeram","middleName":"","lastName":"Ramakrishna","suffix":""},{"id":511589638,"identity":"19a04f2f-5b96-40ea-a4c0-c248ac10a8a0","order_by":1,"name":"Dipsikha Ganguly","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Dipsikha","middleName":"","lastName":"Ganguly","suffix":""},{"id":511589639,"identity":"a503bb8e-cc05-4c06-b291-39e5ed8e23ef","order_by":2,"name":"Abhijitha VG","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Abhijitha","middleName":"","lastName":"VG","suffix":""},{"id":511589640,"identity":"66dc81d0-6f3e-4d25-bf64-1b2dfcee529b","order_by":3,"name":"Tanwir Ansai","email":"","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"Tanwir","middleName":"","lastName":"Ansai","suffix":""},{"id":511589641,"identity":"a8143502-de99-43b6-b2c1-3f94bd2728f5","order_by":4,"name":"Anamika Ghosh","email":"","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"Anamika","middleName":"","lastName":"Ghosh","suffix":""},{"id":511589642,"identity":"c47f40ee-abb8-408b-9019-5b80331d7b92","order_by":5,"name":"Ravi N","email":"","orcid":"","institution":"Spelman College,Atlanta","correspondingAuthor":false,"prefix":"","firstName":"Ravi","middleName":"","lastName":"N","suffix":""},{"id":511589643,"identity":"5b9a99fe-9d03-4e94-84d5-414934d62835","order_by":6,"name":"B.R.K Nanda","email":"","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"B.R.K","middleName":"","lastName":"Nanda","suffix":""},{"id":511589644,"identity":"dba4daf5-3af3-4ae0-a199-4dc0e9d08abe","order_by":7,"name":"Sundara Ramaprabhu","email":"","orcid":"https://orcid.org/0000-0002-7960-9470","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"Sundara","middleName":"","lastName":"Ramaprabhu","suffix":""}],"badges":[],"createdAt":"2025-09-08 03:30:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7559583/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7559583/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91423517,"identity":"c3c87661-5ed7-43e9-955e-12d5759ad873","added_by":"auto","created_at":"2025-09-16 10:40:56","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1371197,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e XRD studies of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT, CNT/S and CNT\u003cstrong\u003e (b) \u003c/strong\u003eMossbauer study (c) structure of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT \u003cstrong\u003e(d)\u003c/strong\u003e SEM and \u003cstrong\u003e(e)\u003c/strong\u003e TEM micrographs \u003cstrong\u003e(g)\u003c/strong\u003e Raman Spectra \u003cstrong\u003e(h-i)\u003c/strong\u003e BET surface area and porosity analysis (j-l) elemental mapping of CNT|Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e \u003cstrong\u003e(m) \u003c/strong\u003eTEM micrograph of S/CNT\u003csub\u003e, \u003c/sub\u003e\u003cstrong\u003e(n\u003c/strong\u003e) EDAX spectra of S/CNT\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/345e7b83d9efad426564eae1.jpg"},{"id":91423869,"identity":"d9d172d2-58be-486b-906c-3f76f3826aaa","added_by":"auto","created_at":"2025-09-16 10:48:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":817631,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a-g)\u003c/strong\u003e DFT studies of LiPS absorption on Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e (510 plane)\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/97129d00976a1d255fae5d52.jpg"},{"id":91422688,"identity":"d0a42bf4-a41f-4c6d-9e74-e211ed4e4f8e","added_by":"auto","created_at":"2025-09-16 10:32:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":654553,"visible":true,"origin":"","legend":"\u003cp\u003eAb initio molecular dynamics (AIMD) simulation of Li\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e8 \u003c/sub\u003edissociation on 510-Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2 \u003c/sub\u003eover time configuration at 300 K(a) Initial \u003cstrong\u003e(b)\u003c/strong\u003e 0.5 ps \u003cstrong\u003e(c)\u003c/strong\u003e 1.0 ps \u003cstrong\u003e(d)\u003c/strong\u003e 1.5 ps \u003cstrong\u003e(e)\u003c/strong\u003e 4.5 ps \u003cstrong\u003e(f)\u003c/strong\u003e evolution of Li\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e8 \u003c/sub\u003e- Fe₅C₂ as a function of AIMD simulation time\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/f816597c07fd533639192131.jpg"},{"id":91423870,"identity":"605cf402-086f-4554-9f45-8fac1097cf7f","added_by":"auto","created_at":"2025-09-16 10:48:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1255813,"visible":true,"origin":"","legend":"\u003cp\u003eLiPS absorption experimental correlation:\u003cstrong\u003e (a) \u003c/strong\u003eUV-Vis spectra \u003cstrong\u003e(a) \u003c/strong\u003eOptical image\u003cstrong\u003e (c) \u003c/strong\u003esymmetric cell study with Li\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e6\u003c/sub\u003e\u003cstrong\u003e (d) \u003c/strong\u003epotentiostatic LiPS deposition\u003cstrong\u003e (e) \u003c/strong\u003eXPS survey spectra post LiPS deposition \u003cstrong\u003e(f) \u003c/strong\u003edeconvoluted S 2p spectra \u003cstrong\u003e(g)\u003c/strong\u003e elemental mapping of cycled electrode\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/a1329b0273185fc0b2efc828.jpg"},{"id":91422687,"identity":"48f88a24-485e-4ccf-9ed4-ca5db00e81b7","added_by":"auto","created_at":"2025-09-16 10:32:56","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":505813,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e CV studies of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S, CNT/S and Sulfur cathodes\u003csub\u003e, \u003c/sub\u003e\u003cstrong\u003e(b) \u003c/strong\u003eCharge discharge profile at 0.1C of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S\u003cstrong\u003e (c) \u003c/strong\u003eCharge discharge profile comparison of S Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S, CNT/S and Sulfur cathodes\u003csub\u003e , \u003c/sub\u003e\u003cstrong\u003e(d) \u003c/strong\u003eRate capability studies of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S, CNT/S and Sulfur cathodes\u003csub\u003e, \u003c/sub\u003e\u003cstrong\u003e(e\u003c/strong\u003e) Cyclic stability of\u003cstrong\u003e \u003c/strong\u003e\u0026nbsp;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S\u003cstrong\u003e \u003c/strong\u003eat 1C rate\u003cstrong\u003e (f) \u003c/strong\u003eEIS study of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S, CNT/S and Sulfur cathodes \u003cstrong\u003e(f) \u003c/strong\u003eCyclic stability of\u003cstrong\u003e \u003c/strong\u003e\u0026nbsp;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S for 700 cycles at 2C rate\u003csub\u003e \u003c/sub\u003e\u003cstrong\u003e(h-i) \u003c/strong\u003eDEIS study of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S\u003cstrong\u003e \u003c/strong\u003eafter 500 cycles.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/eb6dcefa05f2b2b8f1ba8e58.jpg"},{"id":92669498,"identity":"ca7a15da-6cd4-4479-969b-6d65799704fa","added_by":"auto","created_at":"2025-10-02 17:53:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5477906,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/3e4f3d64-701c-4b50-b466-c111ae71906d.pdf"},{"id":91422692,"identity":"cd1e376e-a395-43e1-a10b-5a74252284b8","added_by":"auto","created_at":"2025-09-16 10:32:56","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":428306,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"Supportinginformationfe5c2.docx","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/2bfe38e771c253a080282986.docx"},{"id":91422686,"identity":"ff2231b2-9a18-48eb-b167-271f9732761b","added_by":"auto","created_at":"2025-09-16 10:32:56","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":322182,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1:\u003c/strong\u003e Schematic diagram of CVD grown Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT synthesis\u003c/p\u003e","description":"","filename":"schem1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7559583/v1/664947ba57e26b0c056c9cbd.jpg"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLi\u0026ndash;S batteries are considered one of the promising candidates to meet the world\u0026rsquo;s energy demand for next-generation energy storage due to their high theoretical energy density (~2600 Wh kg⁻\u0026sup1;) and earth-abundant, low cost sulfur cathode\u003csup\u003e1\u003c/sup\u003e. However, their practical development is challenged by rapid capacity fading, largely driven by the dissolution and migration of lithium polysulfides (LiPSs), the sluggish kinetics of sulfur conversion, and the intrinsically low conductivity of sulfur and its discharge products. To address these issues, multifunctional sulfur hosts capable of physically confining LiPSs and catalytically accelerating their conversion are essential\u003csup\u003e2,3\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTransition metal carbides (TMCs) have emerged as promising candidates, characterized by their metallic conductivity, strong surface polarity, and intrinsic redox catalytic activity\u003csup\u003e4\u0026ndash;6\u003c/sup\u003e. Yet, their widespread adoption in Li\u0026ndash;S batteries has been limited by complex, multi-step fabrication protocols that yield suboptimal structural and interfacial integration with conductive supports\u003csup\u003e4,7\u003c/sup\u003e. Among these, H\u0026auml;gg carbide (\u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e) remains notably underexplored for electrochemical energy storage\u003csup\u003e8\u0026ndash;10\u003c/sup\u003e. This is surprising given its advantageous electronic structure and robust affinity for sulfur species via specific Fe\u0026ndash;S interactions critical for polysulfide regulation. While a few reports exist on H\u0026auml;gg carbide for electrochemical energy conversion, most synthetic routes rely on toxic and challenging-to-handle carbon monoxide as a precursor, significantly complicating their widespread utility\u003csup\u003e7,9,10\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026chi;-Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e presents a unique confluence of physicochemical attributes highly beneficial for Li\u0026ndash;S chemistry. Unlike more commonly investigated carbides, it is a ferromagnetic carbide with a distinct orthorhombic structure (\u003cem\u003ePnma\u003c/em\u003e) and a high density of states at the Fermi level, conferring excellent electrical conductivity comparable to metals\u003csup\u003e11,12\u003c/sup\u003e. Crucially, the partially filled d-band structure of Fe atoms in \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e facilitates strong orbital hybridization with S-based species, promoting robust chemisorption of LiPSs. In contrast to noble metal catalysts, \u0026chi;-Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e provides abundant, earth-abundant catalytic sites capable of reversible Fe\u003csup\u003e2+\u003c/sup\u003e\u0026harr;Fe\u003csup\u003e3+\u003c/sup\u003e redox cycling, essential for mediating sulfur redox reactions. Its surface also facilitates dissociative adsorption of S\u0026ndash;S bonds, enhancing LiPS conversion kinetics through a powerful bifunctional mechanism of binding and catalysis\u003csup\u003e4\u003c/sup\u003e. Despite these compelling features and its established role as an active phase in heterogeneous catalysis like Fischer-Tropsch synthesis, \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e has been largely overlooked in energy storage\u003csup\u003e8,9\u003c/sup\u003e. This oversight is primarily due to the formidable synthetic challenges in preparing it in a highly nanostructured, electrochemically accessible morphology with well-defined interfaces, a prerequisite for effective battery performance.\u003c/p\u003e\n\u003cp\u003eTo fully exploit \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e\u0026apos;s catalytic potential while simultaneously addressing the inherent low conductivity and substantial volume changes of sulfur cathodes, a robust and highly conductive scaffold is indispensable. Porosity places a major role in sulfur confinement\u003csup\u003e13\u003c/sup\u003e. While microporous and mesoporous materials are highly effective for suppressing polysulfide shuttling, macroporous materials have proven largely ineffective for this purpose, despite their benefits in providing ample space for sulfur and efficient electrolyte transport\u003csup\u003e14\u003c/sup\u003e. Carbon nanotubes (CNTs) are uniquely suited for this, offering exceptional intrinsic electronic conductivity that establishes an efficient electron transport throughout the electrode architecture\u003csup\u003e15\u0026ndash;17\u003c/sup\u003e. Beyond electrical transport, their interconnected, three-dimensional porous network provides a high surface area for intimate component contact, accommodates the significant volume expansion (\u0026sim;80%) during lithiation, and imparts substantial mechanical stability to maintain electrode integrity over extended cycling, which is one of the key parameter to attain high energy density\u003csup\u003e13,18\u003c/sup\u003e. However, fabricating such a composite using conventional method typically involving separate synthesis of catalytic nanoparticles and conductive carbon followed by mechanical mixing is inherently problematic. These multi-step approaches frequently lead to poor interfacial contact, uncontrolled component agglomeration, and the introduction of impurities, severely compromising the synergistic potential of the hybrid material and hindering charge transfer to the active sites\u003csup\u003e13,18\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eHerein, we introduce a fundamentally new material paradigm that directly confronts these pervasive synthetic hurdles: a nanostructured \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT hybrid precisely engineered through a single-step chemical vapor deposition (CVD) route utilizing hematite as the catalyst and acetylene as carbon source. This innovative approach orchestrates the concerted and synchronized initiation of Fe nucleation, \u003cem\u003ein situ\u003c/em\u003e carburization to form \u0026chi;\u0026minus; Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u0026nbsp;\u003c/sub\u003enanocrystals, and carbon nanotube (CNT) formation within a singular reaction environment. This reaction-synchronized CVD growth is transformative because it ensures atomic-scale coupling and the formation of ultra-clean, defect-free heterointerfaces directly between the growing \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u0026nbsp;\u003c/sub\u003enanocrystals and the nascent CNT scaffold. This unprecedented direct growth mechanism, distinct from conventional assembly methods intrinsically maximizes active site accessibility and facilitates seamless electron and ion transport, critical for efficient polysulfide conversion. Our unique synthesis yields an intimately integrated hybrid architecture, entirely devoid of surfactants, binders, or additional post-processing steps, directly addressing the limitations of prior art. The resulting material capitalizes on a powerful synergistic interplay between highly active \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e nanocrystals and a robust, conductive, high-surface-area CNT scaffold. To our knowledge, this work constitutes the first report of using single-step CVD to engineer H\u0026auml;gg carbide/carbon hybrids specifically tailored for high-performance Li\u0026ndash;S battery. It not only establishes a facile and scalable pathway for fabricating advanced functional composites but also opens entirely new possibilities for integrating underutilized transition metal carbide phases into diverse electrochemical systems by providing a blueprint for their controlled, atomic-scale integration. The \u0026chi;\u0026minus;Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT system represents a fundamentally new class of catalytic\u0026ndash;conductive architectures, designed from the ground up for superior polysulfide regulation and sulfur redox enhancement in Li\u0026ndash;S batteries.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis and Structural Characterization\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe synthesis of the Fe₅C₂/CNT composite was performed using a one-step catalytic chemical vapor deposition (CVD) process. This technique involved the thermal decomposition of acetylene (C\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e) vapor at 700 \u0026deg;C under an argon (Ar) atmosphere, over an Fe₂O₃ catalyst. The Fe₂O₃ was first reduced and served as nucleation sites where acetylene decomposed, and the resulting carbon atoms rapidly diffused into the Fe lattice, leading to carburization and the formation of the Fe₅C₂ phase. Concurrently, the continuous supply of carbon from the acetylene allowed for the growth of carbon nanotubes (CNTs) via a tip-growth mechanism, with the Fe₅C₂ nanoparticles acting as catalysts at their growing tips. The process\u0026apos;s kinetics were carefully controlled by a specific flow of hydrogen and inert gas, which was essential to prevent oxidation and ensure the concurrent formation of both the H\u0026auml;gg carbide and the high-quality carbon nanotubes (Scheme 1). The step by step growth mechanism was elaborated \u003cstrong\u003ein supplementary information (S1,S2).\u0026nbsp;\u003c/strong\u003eThe cathode was prepared by Sulphurization carbon nanotubes using melt diffusion of sulfur at 155\u003csup\u003eo\u003c/sup\u003eC for 12 h in argon atmosphere\u003csup\u003e19\u003c/sup\u003e. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical Measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cathode slurry was prepared by combining S/CNT, polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 8:1:1. N-methyl-2-pyrrolidone (NMP) was then added to achieve a solid content of 30 wt.% and create a uniform slurry. This slurry was coated onto an aluminium foil using the doctor-blade technique. The coated foil was dried at 60 \u0026deg;C for 8 hours. A second layer was then added by mixing Fe₅C₂/CNT with PVDF in a 9:1 ratio. This second slurry was coated onto the dried first layer. The thickness of the first layer was maintained at 100 \u0026mu;m, while the second layer was kept at 40 \u0026mu;m. The bilayer cathode was termed as Fe₅C₂/CNT/S. The electrode was then punched into 12-mm-diameter disks. The total sulfur loading on the cathode was maintained at 3-3.5 mg cm⁻\u0026sup2;. Electrochemical performance was evaluated using a CR2032 coin cell, assembled in an argon-filled glove box with oxygen and water levels maintained below 0.1 ppm. The cell employed a lithium metal anode and a glass fiber separator. The electrolyte was composed of 1 M lithium bis(trifluoromethane)sulfonimide (LiTFSI) in a 1:1 v/v mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME), with an additional 0.2 M lithium nitrate (LiNO₃). The E/S ratio was maintained at 10 uL mg\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSymmetric Cell Fabrication for CV Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor the fabrication of symmetric cells, Fe₅C₂/CNT/S.electrodes were used for both the cathode and anode. The cell was filled with an electrolyte consisting of 0.2 M Li₂S₆ and 1 M LiTFSI in a 1:1 v/v mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME). For comparison, S/CNT electrodes were also tested using the same cell configuration as a baseline.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLi₂S Deposition Test\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe catholyte solution for the Li₂S deposition test was prepared by dissolving lithium sulfide (Li₂S) and elemental sulfur (S) in a 1:7 molar ratio in a tetraglyme solvent containing 1.0 M LiTFSI. The solution was stirred overnight at 60 \u0026deg;C to ensure complete dissolution, yielding a 0.2 M Li₂S₈ solution. The cell was assembled with 20 \u0026mu;L of the prepared Li₂S₈ catholyte applied to the Fe₅C₂/CNT/S cathode and 20 \u0026mu;L of a blank electrolyte (without Li₂S₈) added as the anolyte. A glass fiber membrane was used as the separator. The batteries were initially discharged galvanostatically to 2.06 V at a current of 0.112 mA, then subjected to a potentiostatic discharge at 2.05 V.\u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cp\u003eThe synthesis yielded a phase-pure H\u0026auml;gg carbide/carbon nanotube composite, as confirmed by a suite of advanced characterization techniques. X-ray diffraction (XRD) definitively established the successful in-situ solid-state transformation of the Fe₂O₃ precursor, revealing sharp reflections exclusively indexed to orthorhombic Fe₅C₂ (\u003cem\u003ePnma\u003c/em\u003e, PDF# 89-7272) with no evidence of residual iron oxides or metallic iron (\u003cstrong\u003efigure 1a, figure S1\u003c/strong\u003e)\u003csup\u003e8,12\u003c/sup\u003e . The diffraction peaks at 37.07\u0026deg;, 39.38\u0026deg;, 40.83\u0026deg;, 41.19\u0026deg;, 43.45\u0026deg;, 44.2\u0026deg;, 45.1\u0026deg;, 47.3\u0026deg;, 50.8\u0026deg;, 54.27\u0026deg;, 58.3\u0026deg; represents the diffraction patterns of (311), (020), (- 112), (202), (021), (510), (- 312), (221), (312), (022), (- 113) crystal planes of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e. A distinct peak at 26.3\u0026deg; confirms the formation of the CNT scaffold. Additionally, a separate XRD analysis of a pure CNT/sulfur composite revealed the presence of an orthorhombic sulfur (S8) cathode along with the characteristic CNT peak at 26.3\u0026deg;, which was then utilized to create a bilayer cathode composite\u003csup\u003e20\u003c/sup\u003e. M\u0026ouml;ssbauer spectroscopy (\u003cstrong\u003eFigure 1b\u003c/strong\u003e) was used to determine the chemical state of iron. The spectrum showed three distinct magnetically ordered hyperfine-split sextets, which are characteristic of the unique iron sites within the H\u0026auml;gg carbide (Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e) structure, thereby confirming the phase purity and ruling out any non-magnetic iron phases. The broad and complex absorption features spanning a velocity range of approximately -8 mm/s to +8 mm/s, with multiple discernible dips, are consistent with the presence of magnetically ordered iron phases, which is a fingerprint of Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e due to its multiple crystallographically inequivalent iron sites\u003csup\u003e21,22\u003c/sup\u003e. \u003cstrong\u003eFigure 1c\u003c/strong\u003e illustrates the crystal structure of Fe₅C₂, revealing the presence of both Fe\u0026sup2;⁺ and Fe⁺ states. These mixed-valence iron sites are hypothesized to serve as catalytic centers for reactions within a lithium-sulfur battery. The macroscopic morphology of Fe₅C₂/CNT was observed by scanning electron microscopy and High-resolution transmission electron microscopy (HRTEM). The quasi-spherical Fe₅C₂ nanoparticles (5\u0026ndash;15 nm) intimately anchored as the catalyst tips for the CNTs via a classic tip-growth mechanism was observed (\u003cstrong\u003efigure 1 d-f\u003c/strong\u003e). Raman spectra, with an elevated I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio of 1.15, indicated increased structural defects and lattice strain in the CNTs due to the anchored Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e nanoparticles. These defects are believed to improve the catalytic sites and structural integrity\u003csup\u003e23\u003c/sup\u003e. BET analysis showed a high surface area of 117 m\u0026sup2; g\u003csup\u003e-1\u003c/sup\u003e with a meso-microporous structure, beneficial for ion transport and sulfur confinement\u003csup\u003e5,13,16,19\u003c/sup\u003e. Supplementary information showed the synthesis optimization with 5 min, 10 min and 15 min exposure of acetylene decomposition on 100 mg Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e precursor was fully converted to the desired Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e phase after 15 minutes of acetylene decomposition. This systematic optimization process revealed a phase evolution from mixed oxides (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e , Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), carbides (Fe-C) and pure iron (Fe) at 5 minutes to a Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe-C mixture at 10 minutes, ultimately leading to the phase-pure Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ematerial, confirmed by XRD analysis (\u003cstrong\u003eSupplementary information figure S1\u003c/strong\u003e). Microstructures of each stages were shown in \u003cstrong\u003esupplementary information,\u003c/strong\u003e\u003cstrong\u003efigure S2,\u003c/strong\u003e which clearly depicts the change in the sizes and morphology of the Fe-constitutes in CNT. Microscopic images in \u003cstrong\u003efigure 1(k-m)\u003c/strong\u003e show that sulfur is successfully confined to the surface of the CNTs in the S/CNT composite. The sulfur loading was estimated to be \u003cstrong\u003e70 wt.%\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDensity Functional Theory Calculations and Experimental Correlation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo elucidate the anchoring behaviour and catalytic activity of Fe₅C₂ toward lithium polysulfides (LiPSs), density functional theory (DFT) calculations were performed further\u003csup\u003e11\u003c/sup\u003e. A slab model was constructed using the (510) plane of Fe₅C₂, chosen for its stability and representative surface structure. The atomic arrangement of 510-Fe₅C₂ exposes three distinct adsorption sites: threefold Fe-coordinated hollow sites (3F), fourfold Fe-coordinated hollow sites (4F), and a fourfold Fe site coordinated with a central C atom (4FC) (\u003cstrong\u003efigure 2\u003c/strong\u003e)\u003c/p\u003e\n\u003cp\u003eThe optimized geometries of pristine and LiPS-anchored 510-Fe₅C₂ are shown in \u003cstrong\u003efigure 2a-f.\u003c/strong\u003e Lower-order polysulfides (Li₂S and Li₂S₂) adsorb molecularly with anchoring strengths of \u0026ndash;5.69 eV and \u0026ndash;7.34 eV, respectively, with sulfur atoms preferentially binding at 3F sites while lithium atoms occupy Fe\u0026ndash;Fe bridge, 4F, or 4FC sites. In contrast, higher-order polysulfides exhibit dissociative adsorption on the 510 surface with binding energies ranging from \u0026ndash;8 to \u0026ndash;12 eV (\u003cstrong\u003efigure 2g\u003c/strong\u003e). During this process, sulfur atoms occupy both 3F and 4F sites, while lithium atoms maintain similar adsorption motifs as in lower-order species. The enhanced binding arises from polar\u0026ndash;polar interactions between the asymmetric, polar polysulfides and Fe sites, promoting dissociation of long-chain species\u003csup\u003e4\u003c/sup\u003e. Comparable behaviour has been reported for Na polysulfides on Fe₃N/carbon composites\u003csup\u003e24\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eAb initio molecular dynamics (AIMD) simulations provided further insight into the dissociation mechanism of Li₂S₈ on 510-Fe₅C₂. Born\u0026ndash;Oppenheimer AIMD simulations\u003csup\u003e25,26\u003c/sup\u003e were performed using a canonical ensemble (NVT)\u003csup\u003e27,28\u003c/sup\u003e with the temperature maintained at 300 K using a Nose\u0026ndash;Hoover thermostat with a time step of 1 fs. Starting from the optimized configuration (\u003cstrong\u003efigure 3a\u003c/strong\u003e), Fe\u0026ndash;S bond formation at 3F sites initiated decomposition within ~0.5 ps, with one sulfur atom detaching from the Li₂S₈ ring and chemisorbing at a 3F site (\u003cstrong\u003efigure 3b\u003c/strong\u003e). Progressive bond cleavage led to further detachment by ~1.0 ps (\u003cstrong\u003efigure 3c\u003c/strong\u003e). At ~1.0 ps, a second sulfur atom broke its S-S bond and re-optimized on a 3F site. By ~1.5 ps, the structure had fully evolved into a lower-order polysulfide resembling Li\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003e, with four sulfur atoms completely detached from the original ring(\u003cstrong\u003efigure 3d\u003c/strong\u003e), and finally stabilizing as Li₂S (\u003cstrong\u003efigure 3e\u003c/strong\u003e). This dissociation was accompanied by an ~18 eV energy drop (\u003cstrong\u003efigure 3f\u003c/strong\u003e), consistent with earlier reports on Na₂S₈ on Fe₃N\u003csup\u003e24\u003c/sup\u003e. Together, these results establish Fe₅C₂ as an effective bifunctional phase capable of both anchoring and catalyzing polysulfide conversion\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo experimentally validate these predictions, polysulfide adsorption and electrochemical measurements on the Fe₅C₂/CNT composite were recorded. Upon exposure to a Li₂S₆ solution, the composite induced near-complete decolorization from yellow to transparent within 10 min (\u003cstrong\u003efigure 4a\u0026ndash;b\u003c/strong\u003e). UV\u0026ndash;vis spectroscopy confirmed the lowering intensity of the characteristic S₆\u0026sup2;⁻ absorption peak, highlighting its strong polysulfide-trapping ability, in line with the high binding energies predicted by DFT\u003csup\u003e29,30\u003c/sup\u003e. Cyclic voltammetry (CV) in symmetric cells using Fe₅C₂/CNT electrodes further revealed pronounced redox peaks and significantly enhanced current responses compared with CNT controls (\u003cstrong\u003efigure 4c\u003c/strong\u003e)\u003csup\u003e29,31\u003c/sup\u003e. This confirms accelerated polysulfide conversion kinetics, directly reflecting the AIMD-predicted role of Fe\u0026ndash;S bond formation in driving Li₂S₈ dissociation. Potentiostatic Li₂S deposition tests at 2.05 V further demonstrated the catalytic effect: the Fe₅C₂/CNT electrode delivered a deposition capacity of 319.33mAh g⁻\u0026sup1;, far exceeding the baseline\u0026nbsp;\u003cstrong\u003e(figure 4d\u003c/strong\u003e). This higher capacity indicates more efficient and regulated Li₂S nucleation and growth, consistent with theoretical predictions of Fe₅C₂-facilitated stepwise polysulfide conversion.\u003c/p\u003e\n\u003cp\u003ePost-mortem X-ray photoelectron spectroscopy (XPS) after deposition test provided direct chemical evidence of this catalytic role. Besides the expected Li\u0026ndash;S (161.0\u0026ndash;162.0 eV) and S\u0026ndash;S (163.0\u0026ndash;164.0 eV) peaks, Fe\u0026ndash;S bonds were clearly identified at 162.5\u0026ndash;163.5 eV (\u003cstrong\u003efigure 4e\u0026ndash;f\u003c/strong\u003e)\u003csup\u003e24,27\u003c/sup\u003e. These bonds mirror the strong Fe\u0026ndash;S interactions predicted in DFT and AIMD simulations, confirming the material\u0026rsquo;s chemical participation in polysulfide conversion. Elemental mapping further revealed homogeneous sulfur distribution within the composite (\u003cstrong\u003efigure 4g\u003c/strong\u003e), consistent with uniform immobilization and catalytic regulation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical Performance and Design Implications\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Fe₅C₂/CNT/S composite exhibits superior electrochemical performance and robust long-term stability, which we attribute to the bifunctional catalytic and structural role of embedded Fe₅C₂ nanoparticles. CV analysis revealed significantly higher current responses and reduced peak separation compared to CNT/S and Sulfur electrodes, with reduction peaks shifted to more positive potentials and oxidation peaks to more negative potentials (\u003cstrong\u003efigure 5a\u003c/strong\u003e). This indicates accelerated polysulfide conversion kinetics and reduced polarization, consistent with the catalytic effect observed in simulations and adsorption studies\u003csup\u003e19,23\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eGalvanostatic charge\u0026ndash;discharge tests at 0.1C yielded an initial discharge capacity of 1450 mAh g⁻\u0026sup1;, for Fe₅C₂/CNT/S ,substantially outperforming CNT/S (800 mAh g⁻\u0026sup1;) and sulfur (650 mAh g⁻\u0026sup1;) cathodes(\u003cstrong\u003efigure 5b and 5c\u003c/strong\u003e).The overpotential observed to be lower (250 mV) indicating the better charge transfer. \u0026nbsp;Discharge capacities of 1450, 1100, 750, 600 mAh g⁻\u0026sup1; was recorded for Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/CNT/S at 0.1C, 0.2C, 0.5C, 1C respectively (\u003cstrong\u003efigure 5d\u003c/strong\u003e). After 100 cycles, the capacity stabilized at 700 mAh g⁻\u0026sup1; with minimal decay of 0.08% per cycle, demonstrating excellent cycling stability shown in\u0026nbsp;\u003cstrong\u003efigure 5e\u003c/strong\u003e. At higher rates, the electrode retained 700 mAh g⁻\u0026sup1; at 1C, and full capacity recovery upon returning to 0.2C confirmed structural integrity and reversibility of the composite framework. Electrochemical impedance spectroscopy (EIS) further demonstrated\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ethe beneficial role of Fe₅C₂. The composite exhibited a markedly lower charge-transfer resistance (Rct \u0026asymp; 38 \u0026Omega;) than CNT/S (50 \u0026Omega;) and Sulfur electrodes (64 \u0026Omega;), highlighting improved conductivity and reaction kinetics (\u003cstrong\u003efigure 5f\u003c/strong\u003e). Cyclic stability at 2C showed 80% retention of initial discharge capacity (552 mAh g⁻\u0026sup1;) at 200\u003csup\u003eth\u003c/sup\u003e\u0026nbsp; cycles and 57% retention after 700\u003csup\u003eth\u003c/sup\u003e\u0026nbsp; cycles(\u003cstrong\u003efigure 5g\u003c/strong\u003e). Dynamic electrochemical impedance spectroscopy (DEIS) across 1.8\u0026ndash;2.85 V (\u003cstrong\u003efigure 5h\u0026ndash;i\u003c/strong\u003e) provided real-time insight into resistance evolution during cycling. The consistently low Rct for Fe₅C₂/CNT\u0026ndash;S, particularly at the low-voltage plateau, provides direct evidence of its catalytic role in accelerating the sluggish final Li₂S conversion step\u003csup\u003e32\u003c/sup\u003e. By preventing electrode passivation and promoting efficient deposition, Fe₅C₂ ensures high capacity utilization and long-term stability.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis work presents a novel, single-step chemical vapor deposition (CVD) strategy for synthesizing a Fe₅C₂/CNT catalytic polysulfide shuttling inhibitor for Li-S batteries, highlighting a powerful synergy between material design, reaction engineering, and catalysis. The unique properties of Fe₅C₂ including availability of different Fe states, strong polysulfide affinity, and robust catalytic activity\u0026mdash;make it an ideal sulfur host and polysulfide regulator. Density functional theory (DFT) calculations further confirm the strong anchoring of LiPSs on Fe₅C₂ surfaces, with higher-order polysulfides exhibiting dissociative adsorption and large binding energies. These theoretical insights reveal that Fe₅C₂ not only immobilizes LiPSs effectively but also catalyzes their stepwise conversion, thereby explaining the superior electrochemical performance. By integrating the Fe₅C₂ within a CNT matrix, our synchronous reaction pathway yields a hierarchical, highly conductive, and catalytically active hybrid that effectively addresses both the physical confinement and chemical conversion challenges of lithium polysulfides. This strategy not only introduces a previously untapped carbide phase into sulfur cathode research but also establishes a blueprint for designing multifunctional hosts through a minimal-step synthesis. This finding may open a new frontier in utilizing metal carbides for high-energy-density batteries.\u0026nbsp;\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was conducted at Alternative Energy Nanotechnology laboratory (AENL), IIT Madras, National University of Singapore and HPCE, IIT Madras. A. V. G and B. R. K. N acknowledge the high-performance computational facilities at HPCE, IIT Madras. We further acknowledge the use of ChatGPT-4.0 in refining the English in this manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHe, J. \u0026amp; Manthiram, A. A review on the status and challenges of electrocatalysts in lithium-sulfur batteries. \u003cem\u003eEnergy Storage Mater.\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 55\u0026ndash;70 (2019).\u003c/li\u003e\n\u003cli\u003eManthiram, A., Chung, S. \u0026amp; Zu, C. Lithium\u0026ndash;Sulfur Batteries: Progress and Prospects. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e27\u003c/strong\u003e, 1980\u0026ndash;2006 (2015).\u003c/li\u003e\n\u003cli\u003eYang, R. \u003cem\u003eet al.\u003c/em\u003e Single-step laser-printed integrated sulfur cathode toward high-performance lithium\u0026ndash;sulfur batteries. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 2386 (2025).\u003c/li\u003e\n\u003cli\u003eWang, M. \u003cem\u003eet al.\u003c/em\u003e Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium\u0026ndash;sulfur batteries. \u003cem\u003eNanoscale\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 462\u0026ndash;473 (2024).\u003c/li\u003e\n\u003cli\u003eAdi, A. \u0026amp; Taniguchi, I. Synthesis of an Advanced Sulfur Cathode with a Porous Graphitic C/Fe\u003csub\u003e3\u003c/sub\u003e C Electrocatalyst and Three-Dimensional Current Collector for Li\u0026ndash;S Batteries. \u003cem\u003eEnergy Fuels\u003c/em\u003e \u003cstrong\u003e37\u003c/strong\u003e, 14324\u0026ndash;14333 (2023).\u003c/li\u003e\n\u003cli\u003eHu, P., Xu, P., Chen, Y., Wang, W. \u0026amp; Shao, J.-J. Tungsten Carbide Embedded in a Porous Carbon Nanofiber Sandwich Structure Electrode: A Strategy to Improve the Performance of Lithium\u0026ndash;Sulfur Batteries. \u003cem\u003eLangmuir\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e, 795\u0026ndash;803 (2025).\u003c/li\u003e\n\u003cli\u003eNaguib, M. \u003cem\u003eet al.\u003c/em\u003e Two-Dimensional Transition Metal Carbides. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 1322\u0026ndash;1331 (2012).\u003c/li\u003e\n\u003cli\u003eWang, D., Chen, B., Duan, X., Chen, D. \u0026amp; Zhou, X. Iron-based Fischer\u0026ndash;Tropsch synthesis of lower olefins: The nature of \u0026chi;-Fe5C2 catalyst and why and how to introduce promoters. \u003cem\u003eJ. Energy Chem.\u003c/em\u003e \u003cstrong\u003e25\u003c/strong\u003e, 911\u0026ndash;916 (2016).\u003c/li\u003e\n\u003cli\u003eLi, Y. \u003cem\u003eet al.\u003c/em\u003e Interfacial Fe5C2-Cu catalysts toward low-pressure syngas conversion to long-chain alcohols. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 61 (2020).\u003c/li\u003e\n\u003cli\u003eWang, P. \u003cem\u003eet al.\u003c/em\u003e Efficient conversion of syngas to linear \u0026alpha;-olefins by phase-pure \u0026chi;-Fe5C2. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e635\u003c/strong\u003e, 102\u0026ndash;107 (2024).\u003c/li\u003e\n\u003cli\u003eZhao, S. \u003cem\u003eet al.\u003c/em\u003e Determining surface structure and stability of \u0026epsilon;-Fe\u003csub\u003e2\u003c/sub\u003e C, \u0026chi;-Fe\u003csub\u003e5\u003c/sub\u003e C\u003csub\u003e2\u003c/sub\u003e , \u0026theta;-Fe\u003csub\u003e3\u003c/sub\u003e C and Fe\u003csub\u003e4\u003c/sub\u003e C phases under carburization environment from combined DFT and atomistic thermodynamic studies. \u003cem\u003eCatal. Struct. React.\u003c/em\u003e \u003cstrong\u003e1\u003c/strong\u003e, 44\u0026ndash;60 (2015).\u003c/li\u003e\n\u003cli\u003eKong, F. \u003cem\u003eet al.\u003c/em\u003e Magnetic properties and electrocatalytic properties of Fe5C2 particles with different morphologies. \u003cem\u003eJ. Mater. Sci. Mater. Electron.\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, 884\u0026ndash;893 (2022).\u003c/li\u003e\n\u003cli\u003eKang, N. \u003cem\u003eet al.\u003c/em\u003e Cathode porosity is a missing key parameter to optimize lithium-sulfur battery energy density. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 4597 (2019).\u003c/li\u003e\n\u003cli\u003eZhao, C. \u003cem\u003eet al.\u003c/em\u003e A high-energy and long-cycling lithium\u0026ndash;sulfur pouch cell via a macroporous catalytic cathode with double-end binding sites. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 166\u0026ndash;173 (2021).\u003c/li\u003e\n\u003cli\u003eShi, Y. \u003cem\u003eet al.\u003c/em\u003e Self-assembly of hierarchical MoSx/CNT nanocomposites (2\u0026lt;x\u0026lt;3): towards high performance anode materials for lithium ion batteries. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 2169 (2013).\u003c/li\u003e\n\u003cli\u003eYan, Z. \u003cem\u003eet al.\u003c/em\u003e Nickel sulfide nanocrystals on nitrogen-doped porous carbon nanotubes with high-efficiency electrocatalysis for room-temperature sodium-sulfur batteries. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 4793 (2019).\u003c/li\u003e\n\u003cli\u003eGanguly, D., Ramanujam, K. \u0026amp; Sundara, R. Low-Temperature Synthesized Pt\u003csub\u003e3\u003c/sub\u003e Fe Alloy Nanoparticles on Etched Carbon Nanotubes Catalyst Support Using Oxygen-Deficient Fe\u003csub\u003e2\u003c/sub\u003e O\u003csub\u003e3\u003c/sub\u003e as a Catalytic Center for PEMFC Applications. \u003cem\u003eACS Sustain. Chem. Eng.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 3334\u0026ndash;3345 (2023).\u003c/li\u003e\n\u003cli\u003eLi, F. \u003cem\u003eet al.\u003c/em\u003e Recent advances in cathode materials for rechargeable lithium\u0026ndash;sulfur batteries. \u003cem\u003eNanoscale\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 15418\u0026ndash;15439 (2019).\u003c/li\u003e\n\u003cli\u003eZhang, H. \u003cem\u003eet al.\u003c/em\u003e Fe3O4-doped mesoporous carbon cathode with a plumber\u0026rsquo;s nightmare structure for high-performance Li-S batteries. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 5451 (2024).\u003c/li\u003e\n\u003cli\u003eZhang, Y. \u003cem\u003eet al.\u003c/em\u003e \u0026ldquo;Sauna\u0026rdquo; Activation toward Intrinsic Lattice Deficiency in Carbon Nanotube Microspheres for High‐Energy and Long‐Lasting Lithium\u0026ndash;Sulfur Batteries. \u003cem\u003eAdv. Energy Mater.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 2100497 (2021).\u003c/li\u003e\n\u003cli\u003eLiu, X.-W. \u003cem\u003eet al.\u003c/em\u003e M\u0026ouml;ssbauer Spectroscopy of Iron Carbides: From Prediction to Experimental Confirmation. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 26184 (2016).\u003c/li\u003e\n\u003cli\u003eRao, K. R. P. M. \u003cem\u003eet al.\u003c/em\u003e M\u0026ouml;ssbauer Study of Iron Fischer\u0026minus;Tropsch Catalysts during Activation and Synthesis. \u003cem\u003eEnergy Fuels\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 546\u0026ndash;551 (1996).\u003c/li\u003e\n\u003cli\u003eGhosh, A., Garapati, M. S., Vijaya Kumar Saroja, A. P. \u0026amp; Sundara, R. Polar Bilayer Cathode for Advanced Lithium\u0026ndash;Sulfur Battery: Synergy Between Polysulfide Conversion and Confinement. \u003cem\u003eJ. Phys. Chem. C\u003c/em\u003e \u003cstrong\u003e123\u003c/strong\u003e, 10777\u0026ndash;10787 (2019).\u003c/li\u003e\n\u003cli\u003eQi, Y. \u003cem\u003eet al.\u003c/em\u003e A Fe3N/carbon composite electrocatalyst for effective polysulfides regulation in room-temperature Na-S batteries. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 6347 (2021).\u003c/li\u003e\n\u003cli\u003eBarnett, R. N. \u0026amp; Landman, U. Born-Oppenheimer molecular-dynamics simulations of finite systems: Structure and dynamics of ( H 2 O ) 2. \u003cem\u003ePhys. Rev. B\u003c/em\u003e \u003cstrong\u003e48\u003c/strong\u003e, 2081\u0026ndash;2097 (1993).\u003c/li\u003e\n\u003cli\u003eRibaldone, C. \u0026amp; Casassa, S. Born\u0026ndash;Oppenheimer Molecular Dynamics with a Linear Combination of Atomic Orbitals and Hybrid Functionals for Condensed Matter Simulations Made Possible. Theory and Performance for the Microcanonical and Canonical Ensembles. \u003cem\u003eJ. Chem. Theory Comput.\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 3954\u0026ndash;3975 (2024).\u003c/li\u003e\n\u003cli\u003eXiao, Y. \u003cem\u003eet al.\u003c/em\u003e Cationic surfactant for lithium-sulfur batteries enables efficient use of sulfur and limits lithium dendrite formation. \u003cem\u003eCell Rep. Phys. Sci.\u003c/em\u003e \u003cstrong\u003e4\u003c/strong\u003e, 101658 (2023).\u003c/li\u003e\n\u003cli\u003eSingh, D. \u0026amp; Ahuja, R. Polypeptoid Material as an Anchoring Material for Li\u0026ndash;S Batteries. \u003cem\u003eACS Appl. Energy Mater.\u003c/em\u003e \u003cstrong\u003e4\u003c/strong\u003e, 13070\u0026ndash;13076 (2021).\u003c/li\u003e\n\u003cli\u003eAnsari, T., Ghosh, A., Ganguly, D., Muthiah, B. \u0026amp; Sundara, R. Expediting Polysulfide Anchoring by Fe\u003csub\u003e3\u003c/sub\u003e O\u003csub\u003e4\u003c/sub\u003e /Reduced Graphene Oxide Composite for High‐Performance Lithium‐Sulfur Batteries. \u003cem\u003eBatter. Supercaps\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, e202400716 (2025).\u003c/li\u003e\n\u003cli\u003eChatterjee, A., Ganguly, D., Sundara, R. \u0026amp; Bhattacharya, S. S. Rare‐Earth Doped Configurational Entropy Stabilized High Entropy Spinel Oxide as an Efficient Anchoring/Catalyst Functional Interlayer for High‐Performance Lithium‐Sulfur Battery. \u003cem\u003eBatter. Supercaps\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, e202300082 (2023).\u003c/li\u003e\n\u003cli\u003eShen, Z. \u003cem\u003eet al.\u003c/em\u003e Cation-doped ZnS catalysts for polysulfide conversion in lithium\u0026ndash;sulfur batteries. \u003cem\u003eNat. Catal.\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 555\u0026ndash;563 (2022).\u003c/li\u003e\n\u003cli\u003eDrvarič Talian, S., Mo\u0026scaron;kon, J., Dominko, R. \u0026amp; Gaber\u0026scaron;ček, M. The Pitfalls and Opportunities of Impedance Spectroscopy of Lithium Sulfur Batteries. \u003cem\u003eAdv. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 2101116 (2022).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Fe₅C₂, Transition-metal carbides, Lithium–sulfur batteries, Polysulfide conversion, Catalytic anchoring, Density functional theory (DFT), Ab initio molecular dynamics (AIMD)","lastPublishedDoi":"10.21203/rs.3.rs-7559583/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7559583/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Transition-metal carbides remain underexplored as catalytic phases in energy storage despite their rich electronic structure and tunable surface chemistry. Here, we demonstrate that Fe₅C₂ nanoparticles embedded in a carbon nanotube (CNT) network act as a bifunctional catalytic–anchoring phase, simultaneously immobilizing lithium polysulfides (LiPSs) and accelerating their conversion to Li₂S. Density functional theory and ab initio molecular dynamics simulations reveal that the (510) Fe₅C₂ surface provides strong adsorption sites and promotes stepwise dissociation of higher-order polysulfides. UV–vis adsorption, potentiostatic Li₂S deposition, cyclic voltammetry, and X-ray photoelectron spectroscopy confirm Fe–S bond formation and rapid polysulfide conversion, while dynamic electrochemical impedance spectroscopy (DEIS) tracks the reduction of charge-transfer resistance during cycling. The Fe₅C₂/S/CNT bilayer cathode delivers a high initial capacity of 1450 mAh g⁻¹ at 0.1C, excellent rate capability (700 mAh g⁻¹ at 1C), and stable cycling. This multiscale investigation establishes a direct link between atomic-level catalytic interactions and enhanced electrochemical kinetics, presenting Fe₅C₂ as a design paradigm for catalytic materials in lithium–sulfur and broader metal–sulfur battery systems.","manuscriptTitle":"Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-16 10:32:51","doi":"10.21203/rs.3.rs-7559583/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-materials","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsmat","sideBox":"Learn more about [Communications Materials](https://www.nature.com/commsmat/)","snPcode":"","submissionUrl":"","title":"Communications Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"081ba5bb-0b1e-4011-8b1a-07441454832a","owner":[],"postedDate":"September 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":54330147,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"},{"id":54330148,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Batteries"}],"tags":[],"updatedAt":"2025-10-20T22:26:09+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-16 10:32:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7559583","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7559583","identity":"rs-7559583","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}