Stable Layered Structure Research Articles

Structural stability and enhanced electrochemical performance of Co-free Li-rich layered Mn-based Li1.2Mn0.6Ni0.2O2 cathodes via F doping at the O site of lithium-ion batteries

Li-rich Mn-based Co-free layered oxides (LLOs) are promising cathode materials for lithium-ion batteries (LIBs). However, they exhibit capacity loss and low initial Coulombic efficiency. Herein, an F-doped Li1.2Mn0.6Ni0.2O1.9F0.10 material has been prepared by the high-temperature solid-state method, with numerous oxygen vacancies on the surface to accelerate Li + transport. The electrochemical performance of Li1.2Mn0.6Ni0.2O1.9F0.10 considerably improved after the treatment. A high-capacity retention of 86.9 % after 100 charge/discharge cycles at 1C was achieved for Li1.2Mn0.6Ni0.2O1.9F0.10. Results revealed that F doping replaces part of O2−, forming more force between the TM-F bonds (compared to the TM-O bond), which inhibits the cation mixing phenomenon. The layered structure stability of the material is improved after F doping, and the migration energy barrier of Li+ is reduced, which promotes the migration of Li+, thereby improving the electrochemical performance of Li1.2Mn0.6Ni0.2O2.

Precisely designed 3-stage calcination strategy for lithium-rich manganese-based cathodes with improved cycling performance

The poor cycling performance of Li-rich manganese-based (LMR) cathodes is one of the challenges that need to be urgently overcome. Enhancing the stability of the layered structure responsible for lithium-ion diffusion is an effective way to improve the cycling performance. Layered structures are mainly formed during the high-temperature solid-phase reaction, whereas the prolonged and constant-high-temperature calcination conditions in conventional calcination procedure may pose a threat to the layered structural stability. Thus, in order to optimize the formation environment of layered structures under high-temperature solid-phase reaction, we have designed suitable temperature-controlled strategies for each stage of layered structure formation, gradual maturation, and post-treatment, respectively, referred to as the 3-stage calcination strategy. This calcination strategy contributes to the formation of a more ordered and stable layered structure, which significantly improves the cycling performance of LMR cathodes (capacity retention rate of 85.2 % after 200 cycles at 1C). The shortening of the constant high temperature calcination time helps to further reduce the production cost of the batteries. The design concept of this work is to regulate the formation process of layered structures in stages, which provides inspiration for the efficient and controllable synthesis of electrode materials with excellent structural stability at low production cost.

Organic-inorganic coupled Ti3CN MXene achieving the excellent sodium-ion storage performance

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) are attracting considerable attention due to their unique multilayered structure. However, the practical application of MXenes as electrode materials is hampered by sluggish ions diffusion kinetics and serious volume variation during charging and discharging cycles. Herein, the organic-inorganic coupled Ti3CN (Ti3CNNHSA) composites were constructed by anchoring succinic acid (SA) molecules into the interlayer of Ti3CN. The anchored SA molecules contribute pillar effects to increase interlayer spacing and inhibit the volume contraction during Na+ ions extraction processes, as well as strain effects to mitigate volume expansion during Na+ ions insertion processes. Consequently, the Ti3CNNHSA composites not only exhibit the increased interlayer spacing and rapid ions transfer paths but also deliver the enhanced structural stability and maximum utilization of layered structure, realizing extraordinary cycle stability and high rate capability. The Ti3CNNHSA exhibits a superior capacity retention of 95.2% after 400 cycles at 0.1 A g-1. The Ti3CNNHSA//AC sodium-ion capacitor (SIC) also displays a capacity retention of 84.1% after 1200 cycles at 1.0 A g-1 and a high energy density of 76 Wh kg-1 at the power density of 200 W kg-1. Such an organic-inorganic coupled Ti3CNNHSA sheds light on the development of 2D layered materials.

Tailoring Pseudo-Graphitic Domain by Molybdenum Modification to Boost Sodium Storage Capacity and Durability for Hard Carbon.

Hard carbon (HC) stands out as the most prospective anode for sodium-ion batteries (SIBs) with significant potential for commercial applications. However, some long-standing and intractable obstacles, like low first coulombic efficiency (ICE), poor rate capability, storage capacity, and cycling stability, have severely hindered the conversion process from laboratory to commercialization. The above-mentioned issues are closely related to Na+ transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content. Herein, constructing molybdenum-modified hard carbon solid spheres (Mo2C/HC-5.0), both the ion transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content are comprehensively improved. Specifically, Mo2C/HC-5.0 with higher pseudo-graphitic carbon content provides a large number of active sites and a more stable layer structure, resulting in improved sodium storage capacity, rate performance, and cycling stability. Moreover, the lower defect density and specific surface area of Mo2C/HC-5.0 further enhance ICE and sodium storage capacity. Consequently, the Mo2C/HC-5.0 anode achieves a high capacity of 410.7mA h g-1 and an ICE of 83.9% at 50mA g-1. Furthermore, the material exhibits exceptional rate capability and cycling stability, maintaining a capacity of 202.8mA h g-1 at 2 A g-1 and 214.9mA h g-1 after 800 cycles at 1 A g-1.

Hydrophobic modification enhances the microstructure stability of the catalyst layer in alkaline polymer electrolyte fuel cells.

Alkaline polymer electrolyte fuel cells (APEFCs) have achieved notable advancements in peak power density, yet their durability during long-term operation remains a significant challenge. It has been recognized that increasing the hydrophobicity of the catalyst layer can effectively alleviate the performance degradation. However, a microscopic view of how hydrophobicity contributes to the stability of the catalyst layer microstructure is not clear. Here, we construct a membrane electrode assembly (MEA) with enhanced structural stability and durability by incorporating polytetrafluoroethylene (PTFE) particles into the catalyst layer. MEAs modified by this approach exhibit stabilized voltage platforms in current step tests and reduced hysteresis in current-voltage polarization curves during operation, indicating the critical role of PTFE in the removal of the excess water within the catalyst layer. Fuel cells with PTFE modification show more than 45% increase in electrochemical durability. By characterizing with field-emission scanning electron microscopy (FE-SEM) the surface and the internal microstructures of MEAs after durability tests, we find that the catalyst layers modified by PTFE experience much less reduction in porosity and less agglomeration of the solid components. These findings elucidate the microscopic mechanisms by which hydrophobicity promotes a more stable catalyst layer structure, thereby enhancing the durability of APEFCs. This research advances our understanding of hydrophobicity's impact on catalyst layer stability and offers a practical method to enhance the durability of APEFCs.

Lithium salt preprocessing calcination strategy for a more stable layered structure of lithium-rich manganese-based cathodes

The poor cycling performance of lithium-rich manganese-based (LMR) cathodes limits their practical applications. The stability of the layered structure is closely related to the cycling performance. The high-temperature solid-state reaction between transition metal oxides (TMOs) and lithium salts promotes the formation of the layered structure, which determines the quality of the layered structure. Considering the influence of physicochemical changes of the lithium salt on the formed layered structural stability, in this work, the calcination strategy includes a short period of holding time near the melting point of Li2CO3, referred to as the lithium salt preprocessing calcination strategy, which allows the molten Li2CO3 to be fully contacted with TMOs at relatively low temperatures, alleviating the problem of Li in the thermal decomposition products of Li2CO3 not easily further reacting with TMOs. Compared to the conventional calcination procedure, this new calcination strategy reduces the oxygen vacancy concentration as well as the relative Mn3+ content on the surface of the cathodes, which significantly improves the cycling performance. In addition, the shortening of the constant high temperature calcination time effectively reduces the production energy consumption, which provides a reference for the future efficient and low-cost synthesis of electrode materials with excellent cycling performance.

Protons intercalation induced hydrogen bond network in δ-MnO2 cathode for high-performance aqueous zinc-ion batteries

Birnessite-type MnO2 (δ-MnO2) exhibits great potential as a cathode material for aqueous zinc-ion batteries (AZIBs). However, the structural instability and sluggish reaction kinetics restrict its further application. Herein, a unique protons intercalation strategy was utilized to simultaneously modify the interlayer environment and transition metal layers of δ-MnO2. The intercalated protons directly form strong O H bonds with the adjacent oxygens, while the increased H2O molecules also establish a hydrogen bond network (O H···O) between H2O molecules or bond with adjacent oxygens. Based on the Grotthuss mechanism, these bondings ultimately enhance the stability of layered structures and facilitate the rapid diffusion of protons. Moreover, the introduction of protons induces numerous oxygen vacancies, reduces steric hindrance, and accelerates ion transport kinetics. Consequently, the protons intercalated δ-MnO2 (H-MnO2-x) demonstrates exceptional specific capacity of 401.7 mAh/g at 0.1 A/g and a fast-charging performance over 1000 cycles. Density functional theory analysis confirms the improved electronic conductivity and reduced diffusion energy barrier. Most importantly, electrochemical quartz crystal microbalance tests combining with ex-situ characterizations verify the inhibitory effect of the interlayer proton environment on basic zinc sulfate formation. Protons intercalation behavior provides a promising avenue for the development of MnO2 as well as other cathodes in AZIBs.

Na-deficient P2-type layered oxide cathodes for practical sodium-ion batteries

Sodium-ion batteries (SIBs) have attracted enormous attention as candidates in stationary energy storage systems, because of the decent electrochemical performance based on cheap and abundant Na-ion intercalation chemistry. Layered oxides, the workhorses of modern lithium-ion batteries, have regained interest for replicating their success in enabling SIBs. A unique feature of sodium layered oxides is their ability to crystallize into a thermodynamically stable P2-type layered structure with under-stoichiometric Na content. This structure provides highly open trigonal prismatic environments for Na ions, permitting high Na+ mobility and excellent structural stability. This review delves into the intrinsic characteristics and key challenges faced by P2-type cathodes and then comprehensively summarizes the up-to-date advances in modification strategies from compositional design, elemental doping, phase mixing, morphological control, and surface modification to sodium compensation. The updated understanding presented in this review is anticipated to guide and expedite the development of P2-type layered oxide cathodes for practical SIB applications.

Multi-metal ions co-regulated vanadium oxide cathode toward long-life aqueous zinc-ion batteries

Interlayer intercalation engineering shows great feasibility to improve the structure stability of the layered oxides. Although high Zn-storage capability has been attained based on the pillar effect of multifarious intercalants, an in-depth understanding the synergistic effect of intercalated multiple metal ions is still in deficiency. Herein, alkali metal ion K+, alkaline earth metal ion Mg2+ and trivalent metal ion Al3+ are introduced into the VO interlayer of V2O5. Due to the different electronegativity and hydrated ion radius of K+, Mg2+ and Al3+, adjusting the relative proportions of these metal ions can achieve an appropriate interlayer spacing, stable layer structure and regular morphology, which facilitates the transport kinetics of Zn2+. Under the synergistic effect of pre-intercalated multi-metal ion, the optimal tri-metal ion intercalated hydrated V2O5 cathode exhibits a high specific capacity of 382.4 mAh g−1 at 0.5 A g−1, and long-term cycling stability with capacity retention of 86 % after 2000 cycles at the high current density of 10 A g−1. Ex-situ and kinetic characterizations reveal the fast charge transfer and reversible Zn2+ intercalation mechanism. The multi-ion engineering strategy provides an effective way to design desirable layered cathode materials for aqueous zinc-ion batteries.

Demulsification of W/O emulsions induced by terahertz pulse electric fields-driven hydrogen bond disruption of water molecules

Demulsifying highly stable W/O emulsions, composed of heavy oil and water, is crucial for simplifying crude oil processing, reducing production costs, and mitigating environmental pollution. In these emulsions, aromatic components in the oil phase stack via π-π interactions, while hydrogen bonds stabilize the water phase. This leads to the creation of a strong oil-water interface through electrostatic attraction, ultimately hindering water droplet coalescence and oil-water separation. In this study, a 1.0 THz pulse electric field is introduced to effectively disrupt the hydrogen bond network among water molecules by inducing hydrogen bond resonance. This disruption contributes to increased water mobility in the oil phase, weakened stability of the oil-water interface film, and facilitates efficient water droplet coalescence in the oil phase. The results show that throughout the demulsification process, the average number of hydrogen bonds per water molecule rapidly decreases from 1.41 to 1.08 within 100 ps. The upper and lower limits of hydrogen bond lifetimes decrease by 8.12 ps and 3.24 ps, respectively. This indicates a significant disruption in the stability of hydrogen bonds between water molecules. Concurrently, the terahertz pulse electric field disrupts the initially stable oil-water interface film of the emulsion system, leading to a noteworthy reduction in the oil-water interface tension from 54.3 to 39.2 mN·m−1. The self-diffusion coefficient of water molecules increases from 1.33 to 2.62 Å2·ps−1, signifying that water molecules are more inclined to penetrate the interfacial region between the two phases. Additionally, the terahertz pulse electric field induces alterations in the arrangement of water molecules, resulting in the rearrangement of electrons in the water phase and disrupting the originally stable electrical double layer structure of the oil-water interface. This study provides novel insights into the development of efficient and environmentally friendly electric demulsification technologies, holding significant potential for widespread industrial applications.

Facile synthesis and electrochemical investigation of graphitic carbon nitride/manganese dioxide incorporated polypyrrole nanocomposite for high-performance energy storage applications

Abstract Manganese dioxide (MnO2) nanoparticles were modified by graphitic carbon nitride (GCN) and polylpyrrole (Ppy) to enhance their electrochemical performance. The surface influence, crystalline structure, and electrochemical performance of the Ppy/GCN/MnO2 material were characterized and compared with those of pristine MnO2. It is found that surface modification can improve the structural stability of MnO2 without decreasing its available specific capacitance. The electrochemical properties of synthesized Ppy/GCN/MnO2 electrode were evaluated using cyclic voltammetry (CV) and AC impedance techniques in 5 M KOH electrolyte. Specific capacitances of 486, 815, 921, and 1377 F/g were obtained for MnO2, Ppy/MnO2, GCN/MnO2, and Ppy/GCN/MnO2, respectively, at 5 A/g. This improvement is attributed to the synergistic effect of GCN and Ppy in the Ppy/GCN/MnO2 electrode material. The Ppy/GCN/MnO2 electrode in KOH has average specific energy and specific power densities of 172 Wh kg−1 and 2065 W kg−1, respectively. Only 2 % of the capacitance’s initial value is lost after 10,000 cycles. The resulting Ppy/GCN/MnO2 nanocomposite had very stable and porous layered structures. This work demonstrates that Ppy/GCN/MnO2 nanomaterials exhibit good structural stability and electrochemical performance and are good materials for supercapacitor applications.

2D Halide Perovskites for High-Performance Resistive Switching Memory and Artificial Synapse Applications.

Metal halide perovskites (MHPs) are considered as promising candidates in the application of nonvolatile high-density, low-cost resistive switching (RS) memories and artificial synapses, resulting from their excellent electronic and optoelectronic properties including large light absorption coefficient, fast ion migration, long carrier diffusion length, low trap density, high defect tolerance. Among MHPs, 2D halide perovskites have exotic layered structure and great environment stability as compared with 3D counterparts. Herein, recent advances of 2D MHPs for the RS memories and artificial synapses realms are comprehensively summarized and discussed, as well as the layered structure properties and the related physical mechanisms are presented. Furthermore, the current issues and developing roadmap for the next-generation 2D MHPs RS memories and artificial synapse are elucidated.

MXene-Stabilized VS2 Nanostructures for High-Performance Aqueous Zinc Ion Storage.

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti3C2Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g-1 at 0.2 A g-1. Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

Unveiling the electronic properties of BiP[formula omitted] triphosphide from bulk to graphene-based heterostructures by first-principles calculations

In our study, we investigated the structural and electronic properties of bismuth triphosphide (BiP3) in its bulk, few-layer, and monolayer forms. We found that BiP3 in bulk exhibits a metallic stable layered structure. The exfoliation energy of 1.07 J/m2 indicates ease exfoliation, comparable to other triphosphides. The band gap varies with thickness, transitioning from semiconductor–metal between four to five layers, influenced by interlayer coupling and quantum confinement. We also investigated the heterostructure created by depositing graphene (G) on few-layer BiP3. In monolayer (G/m-BiP3) and bilayer (G/2L-BiP3) forms, a metal–semiconductor junction is formed, characterized by weak vdW interactions at the interface and exhibiting p-type Schottky contacts. We observed that the Schottky Barrier Height (SBH) can be modulated by altering the interlayer distance between G and BiP3. This adjustment allows transitions between n-type and p-type Schottky contacts in G/m-BiP3 and the formation of an ohmic contact in G/2L-BiP3. Furthermore, applying an electric field affects the SBH, leading to similar transitions and the development of an ohmic contact. Additionally, our study shows that n-doping in graphene increases with the number of BiP3 layers and external electric field application. These properties position BiP3 few-layer as a promising material for nanoelectronic, optoelectronic, and graphene-based devices.

Electrochemical evaluation and structural characterization of polythiophene surfaces modified with PbO/PbS for energy storage applications

Polythiophene (PTh) was modified with nanoparticles of lead oxide (PbO) and lead sulfide (PbS) to enhance its electrochemical performance. The surface characteristics, crystalline structure, and electrochemical behavior of the PTh/PbO/PbS material were analyzed and compared with pristine PTh. Surface modification was found to enhance the structural stability of PTh without compromising its specific capacitance. The electrochemical properties of the synthesized PTh/PbO/PbS electrode were assessed using cyclic voltammetry (CV) and AC impedance techniques in a 3 M KOH electrolyte. Specific capacitances of 245, 620, 716, and 992 F/g were achieved for PTh, PTh/PbO, PTh/PbS, and PTh/PbO/PbS, respectively, at 5 A/g. This enhancement is attributed to the synergistic effect of Pb2+ ions in the PTh/PbO/PbS electrode material. The PTh/PbO/PbS electrode in KOH exhibited average specific energy and specific power densities of 972 Wh kg−1 and 6086 W/kg, respectively, with only a 4% decrease in capacitance after 10000 cycles. The resulting PTh/PbO/PbS nanocomposite displayed highly stable and porous layered structures. This study underscores the favorable structural stability and electrochemical performance of PTh/PbO/PbS nanomaterials, positioning them as promising materials for supercapacitor applications.

Studies on improved stability and electrochemical activity of metal oxides/sulfides‐based polymer nanocomposites for energy storage applications

AbstractPoly (3‐methylthiophene) (P3MT) was modified by nickel oxide (NiO) and nickel sulfide (NiS) nanoparticles to enhance its electrochemical performance. The surface influence, crystalline structure, and electrochemical performance of the P3MT/NiO/NiS material were characterized and compared with that of pristine P3MT. It is found that surface modification can improve the structural stability of P3MT without decreasing its available specific capacitance. The electrochemical properties of synthesized P3MT/NiO/NiS electrode were evaluated using cyclic voltammetry and alternating current impedance techniques in 3 M KOH electrolyte. Specific capacitances of 253, 764, 932, and 1434 F g−1 were obtained for P3MT, P3MT/NiO, P3MT/NiS, and P3MT/NiO/NiS, respectively at 5 A g−1. This improvement is attributed to the synergistic effect of Ni2+ ions in the P3MT/NiO/NiS electrode material. The P3MT/NiO/NiS electrode in KOH has average specific energy and specific power densities of 1032 Wh kg−1 and 6192 W/kg, respectively. Only 2% of the capacitance's initial value is lost after 10,000 cycles. The resulting P3MT/NiO/NiS nanocomposite had very stable and porous layered structures. This work demonstrates that P3MT/NiO/NiS nanomaterials exhibit good structural stability and electrochemical performance, and are good material for supercapacitor applications.Highlights The P3MT/NiO/NiS nanocomposite is fabricated and characterized as supercapacitor electrode. The incorporation of NiO/NiS in the poly (3‐methylthiophene) has improved the electrochemical performance. The P3MT/NiO/NiS electrodes retained 98% of their specific capacitance after 10,000 cycles. The P3MT/NiO/NiS nanocomposite electrode showed specific capacitance of 1434 F g−1 at 5 A g−1. The stability of the nanocomposite was enhanced without altering its morphology and chemical structure.

Synchronous organic-inorganic co-intercalated ammonium vanadate cathode for advanced aqueous zinc-ion batteries

Vanadium-based cathode materials are attractive for aqueous zinc-ion batteries (AZIBs) owing to the high capacity from their open frameworks and multiple valences. However, the cycle stability and rate capability are still restricted by the low electrical conductivity and trapped diffusion kinetics. Here, we propose an organic–inorganic co-intercalation strategy to regulate the structure of ammonium vanadate (NH4V4O10, NVO). The introduction of Al3+ and polyaniline (PANI) induces the optimized layered structure and generation of urchin-like hierarchical construction (AP-NVO), based on heterogeneous nucleation and dissolution–recrystallization growth mechanism. Owing to these favorable features, the AP-NVO electrode delivers a desirable discharge capacity of 386 mA h g−1 at 1.0 A g−1, high-rate capability of 263 mA h g−1 at 5.0 A g−1 and excellent cycling stability with 80.4% capacity retention over 2000 cycles at 5.0 A g−1. Such satisfactory electrochemical performance is believed to result from the enhanced reaction kinetics provided by the stable layered structure and a high intercalation pseudo-capacitance reaction. These results could provide enlightening insights into the design of layered vanadium oxide cathode materials.

Two-dimensional carbon rich titanium carbide (TiC3) as a high-capacity anode for potassium ion battery

In recent years, two-dimensional (2D) materials, particularly MXenes such as titanium carbide, have gained significant interest for energy storage applications. This study explores the use of potassium-adsorbed TiC3 nanosheets as potential anode materials for potassium ion batteries (KIBs), utilizing first-principles calculations. The investigated electronic, mechanical, and thermal properties of TiC3 demonstrate its suitability as an anode material. The incorporation of potassium into the host material enhances electronic conductivity while maintaining a stable layered structure. Our findings reveal promising adsorption behavior of potassium in TiC3, leading to a high theoretical specific capacity of 958 mAh/g, coupled with a low energy barrier of 0.19 eV for potassium migration, which is indicative of superior electrochemical performance. Moreover, despite the high potassium content, the electrode material shows limited volume expansion of 11.3 %, suggesting good cyclability. Additionally, the equilibrium distance between potassium and TiC3, measured at 3.11 Å, exceeds that of lithium and TiC3 (2.56 Å), potentially augmenting the material’s flexibility. Consequently, TiC3 emerges as a promising candidate for KIB anode materials.

Order-disorder transition during shear thickening in bidisperse dense suspensions

Shear thickening of multimodal suspensions has proven difficult to understand because the rheology depends largely on the microscopic details of stress-induced frictional contacts at different particle size distributions (PSDs). Our discrete particle simulations below a critical volume fraction ϕc over a broad range of shear rates and PSDs elucidate the basic mechanism of order–disorder transition. Around the theoretical optimal PSD (relative content of small particles ζ1= 0.26), particles order into a layered structure in the Newtonian regime. At the onset of shear thickening, this layered structure transforms to a disordered one, accompanied by an abrupt viscosity jump. Minor increase in large-large particle contacts after the order–disorder transition causes apparent increase in radial force along the compressional axis. Bidisperse suspensions with less regular but stable layered structure at ζ1= 0.50 show good fluidity in the shear thickening regime. This work shows that in inertial flows where particle collisions dominate, order–disorder transition could play an essential role in shear thickening for bidisperse suspensions.

N/S co-doped Nb2CTx MXene as the effective catalyst for improving the hydrogen storage performance of MgH2

While MgH2 has high hydrogen storage capacity, its high dehydrogenation temperature and sluggish de-/hydrogenation rate have hindered practical application. In the present work, a non-metallic element (N, S) co-doped Nb2CTx MXene catalyst (N/S-Nb2CTx) is employed to improve the hydrogen storage property of MgH2. The dehydrogenation activation energy of MgH2+N/S-Nb2CTx composite is reduced to 70.00 kJ mol–1 H2, which is much lower than that of MgH2+Nb2CTx (99.44 kJ mol–1 H2) and Milled-MgH2 (133.19 kJ mol–1 H2). The composite can release about 4.78 wt% of H2 within 30 min at 225 °C and uptake about 4.00 wt% of H2 within 80 min even at 30 °C under 30 bar H2, which is significantly better than most of the reported MgH2+Nb-based-catalyst composites. The mechanism analysis reveals that the stable layered structure of the N/S-Nb2CTx catalyst provides enough nucleation sites for MgH2/Mg, and the in-situ formed substances (Nb, NbO2) play the role of elongating Mg–H bond. Besides, the N, S co-doped effectively enhances the ability of multivalent Nb elements to promote the electron transfer between Mg2+ and H–, and it promotes the diffusion of hydrogen through weakening the interaction between Nb and H atoms, thus the de-/hydrogenation kinetics and cyclic stability of MgH2 is significantly improved. This work not only proves that Nb2CTx can effectively enhance its catalytic activity by N and S co-doping, but also provides a MXene-based catalyst design concept for highly efficient hydrogen storage catalysts.