2D/2D W-MoSe₂@Ti₃C₂ MXene heterostructure harnesses high-rate lithium–oxygen batteries: momentous roles of high-valence metal sites and interfacial bridge-oxygen bonding

Abstract

The synergistic integration of high-valence metal sites and interfacial bridge-oxygen bonding plays a pivotal role in the construction of valid bifunctional electrocatalysts for accelerating oxygen electrode redox kinetics and promoting the practical implementation of lithium–oxygen batteries. Herein, high-valence tungsten dopants induced the formation of 2H-MoSe₂, which was successfully anchored on the layered Ti₃C₂ MXene matrix (W-MoSe₂@MXene) with an interfacial bridge-oxygen bonding structure, affording a porous and vertical staggered nanosheet array network architecture. Consequently, the Li–O₂ battery assembled with the as-prepared W-MoSe₂@MXene cathode delivers high discharge specific capacity (12442.6 mA h g⁻¹) and favorable cycling lifespan (over 194 cycles) at 1 A g⁻¹. Notably, stable operation is also maintained over 61 cycles at an ultra-high current density of 5 A g⁻¹. Experimental analysis in combination with density functional theory (DFT) calculation reveals that the synergistic interaction between high-valence W dopants and bridge-oxygen bonds facilitates spatial charge redistribution and accelerates charge transfer, thereby lowering the theoretical discharge–charge overpotential and enhancing electrode reaction kinetics. This work offers a feasible design paradigm for the construction of MXene-based oxygen electrode catalysts toward high-rate Li–O₂ batteries.

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Kai Zeng

Kai Zeng is currently working as an assistant professor at the Institute of Smart City and Intelligent Transportation, Southwest Jiaotong University, China. He received his B.S. degree in new energy materials and devices from the Southwest Petroleum University in 2017 and obtained his PhD degree in new energy science and engineering from the Soochow University in 2022. His research interests focus on the design, fabrication and application of advanced electrocatalysts for water electrolysis, metal–air batteries, fuel cells, etc.

1. Introduction

Lithium–oxygen (Li–O₂) batteries, featuring an exceptionally high theoretical energy density (∼3500 Wh kg⁻¹) and unique open-system oxygen cathode configuration, have emerged as one of the most promising next-generation energy storage technologies to meet the escalating global energy demands.^1–3 The fundamental electrochemical process involves the reversible formation and decomposition of lithium peroxide (2Li + O₂ ↔ Li₂O₂, E⁰ = 2.96 V) during discharge and charge, respectively.^4,5 However, beyond the challenges associated with lithium metal anodes (such as dendrite formation and surface corrosion), the inherently sluggish kinetics at the oxygen cathode led to high overpotentials, poor rate capability and limited cycling stability, which collectively impede the practical application of Li–O₂ batteries.^6,7 To address these limitations, considerable efforts have been devoted to developing cathode electrocatalysts with tailored structures and superior catalytic activity. Various catalysts, including noble metals,^8,9 transition metal compounds (e.g., oxides and phosphides)^10,11 and carbon-based architectures^12,13 have been explored to accelerate the oxygen reduction/evolution reaction (ORR/OER) and optimize the adsorption energies of critical intermediates as well as promote efficient decomposition of discharge products.

Two-dimensional (2D) materials, such as transition metal chalcogenides and MXenes, have emerged as a vibrant class of nanomaterials owing to their high aspect ratios, tunable surface chemistries and remarkable mechanical flexibility.^14–16 Nevertheless, their practical implementation is often compromised by pronounced self-restacking behavior and intrinsic limitations to individual material systems. Constructing 2D/2D heterostructures is pivotal for circumventing the inherent constraints of single-component systems. In particular, interfacial bridge-oxygen bonds with M₁–O–M₂ configuration have recently attracted growing attention due to their superior electrical conductivity and structural stability, which can effectively modulate Li₂O₂ formation/decomposition pathways and promote redox reaction kinetics.^17,18 For example, a 2D/2D MoS₂/Ti₃C₂ MXene heterostructure with an interconnected network was successfully fabricated, leveraging the synergistic effect of high-capacitance MoS₂ and high-rate Ti₃C₂ MXene to deliver excellent electrochemical performance in a flexible capacitance device.¹⁹ Similarly, ample Ir–O–Mn bonds were successfully incorporated into an Ir/MnO_x catalyst, serving as effective charge-transfer channels between IrO_x clusters and the MnO_x matrix.²⁰ Sun et al. reported interfacial oxygen bridge engineering between MoO_x and an MXene matrix (MoO_x@Ti₃C₂ MXene), which functioned as a promising cathode catalyst for Li–O₂ batteries. Consequently, the Li–O₂ battery assembled with the MoO_x@Ti₃C₂ MXene catalyst exhibited favorable discharge–charge polarization (0.75 V) and remarkable cycling stability (over 300 cycles). Density functional theory (DFT) analysis revealed that the bridge-oxygen bonding maximizes the advantages of electronic structure manipulation and Li₂O₂ formation.²¹

The high-valence metal doping (e.g. Zr⁴⁺, Nb⁵⁺, and Mo⁶⁺) strategy can effectively tune local electron density and induce spatial charge redistribution, while simultaneously acting as active sites for the oxygen electrode reaction and accelerating the reaction kinetics via optimizing intermediate adsorption and lowering energy barriers.^22,23 Zeng and co-workers reported that the incorporation of high-valence metal sites (e.g., Zr⁴⁺ and Mo⁶⁺) generates sufficient unfilled antibonding orbitals through optimized d–p orbital hybridization between metal and non-metal atoms. This electronic configuration is conducive to diminish charge transfer barriers and lower the free energy of the rate-determining step (O* → OOH*).²⁴ Li et al. designed a conductive nickel catecholate framework with strengthened Ni–O covalency and high-valence Ni³⁺ species (Ni^III-NCF), which facilitated electron transport and favored the formation of nanosheet-like Li₂O₂, achieving a superior rate capability and cycling stability.²⁵ Consequently, the synergistic modulation of high-valence metal centers and interfacial oxygen bridge bonds is poised to reshape the electronic structure and local coordination environment. However, the correlation and underlying cooperative interaction mechanism between the specific high-valence metals and interfacial bridge-oxygen bonding are yet to be unveiled, particularly in 2D/2D metal selenides and MXene heterostructures.

Inspired by the aforementioned considerations, high-valence W-doped MoSe₂ nanosheets anchored on the 2D layered Ti₃C₂ MXene matrix (W-MoSe₂@MXene) with ample bridge-oxygen bonds, featuring a porous and vertical staggered nanosheet array network architecture, is successfully constructed and acts as a favorable cathode for Li–O₂ batteries. As a result, the Li–O₂ battery assembled with the W-MoSe₂@MXene cathode possesses a promising specific capacity of 12442.6 mA h g⁻¹ and excellent cycling lifespan (over 194 cycles) at 1 A g⁻¹, which is superior to that of MoSe₂@MXene (5568.3 mA h g⁻¹, 104 cycles) and MXene (4823.2 mA h g⁻¹, 67 cycles). Notably, the W-MoSe₂@MXene-based cathode can even stably cycle over 108 and 61 cycles at ultra-high current densities of 3 and 5 A g⁻¹, respectively. DFT calculation results reveal that the synergistic interaction between high-valence metal sites and bridge-oxygen bonds is beneficial to optimize the adsorption/desorption of Li₂O₂ and accelerate the charge transfer kinetics, thereby lowering the theorical overpotentials of the discharge and charge process.

2. Experimental section

2.1 Chemicals

Ti₃AlC₂ MAX was purchased form Jilin 11 Technology Co., Ltd. Lithium fluoride (LiF), ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O), selenium dioxide (SeO₂), sodium tungstate dihydrate (Na₂WO₄·2H₂O), ethylenediamine (EDA), hydrochloric acid (HCl), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), polyvinylidene fluoride (PVDF), ethanol and acetylene black were purchased from Sinopharm Chemical Reagent Co. Ltd. All the chemicals have been used without further purification.

2.2 Synthesis of W-MoSe₂@MXene

The Ti₃C₂ MXene suspension was synthesized via the previously reported methods. A typical solvothermal method followed by calcination treatment was adopted for the synthesis of the W-MoSe₂@MXene cathode. First, (NH₄)₆Mo₇O₂₄·4H₂O (0.26 mmol), Na₂WO₄·2H₂O (0.12 mmol) and SeO₂ (0.4 mmol) were added to the appropriate MXene suspension (22.5 mL) and ultrasonicated for 20 min. Then, EDA (37.5 mL) was slowly added to the above solution and stirred vigorously for 15 min at room temperature to generate a homogenous reaction solution. After that, the reaction solution was transferred to a parapolyphenyl autoclave (100 mL) and maintained at 200 °C for 20 h. The above solution was centrifuged and washed with DI water and ethanol several times, and dried in a vacuum oven at 60 °C to collect the reaction product. Finally, the collected product was placed in a tube furnace and calcined at 500 °C for 2 h in a N₂ atmosphere. The same method was applied to the synthesis of MoSe₂@MXene, except that Na₂WO₄·2H₂O is not added to the precursor solution.

2.3 Physical characterization

Scanning electron microscopy and transmission electron microscopy (SEM/Hitachi SU8010 and TEM/FEI F20) were performed to analyse the morphology and microstructure of the catalysts. Scanning TEM (STEM) with a high-angle annular dark field (HAADF) detector and energy dispersive spectroscopy (EDS) mapping were applied to acquire the element distribution. X-ray photoelectron spectroscopy (XPS, ESCALAB QXi) was performed to obtain the chemical bonding environment and valence state. X-ray diffraction (XRD) was performed to detect the crystal structure of the samples.

3. Results and discussion

The W-MoSe₂@MXene catalyst with a porous and interconnected nanosheet array structure was synthesized through a multi-step wet-chemistry strategy (Fig. 1). Ti₃C₂ MXene with a smooth multilayered nanosheet structure (Fig. S1) can be synthesized via the previously reported methods, adopting a mixture of lithium fluoride and hydrochloric acid solution to selectively etch the Al layer from the Ti₃AlC₂ MAX phase.^21,26 This process not only exposes abundant surface functional groups (e.g., –F and –O), but also induces the formation of negatively charged Ti₃C₂ MXene. Subsequently, W-doped MoSe₂ nanosheets were in situ established on the layered Ti₃C₂ MXene via a simple solvothermal treatment followed by low-temperature calcination.

Fig. 1 Schematic illustration of the fabrication of W-MoSe₂@MXene.

Scanning electron microscopy/transmission electron microscopy (SEM/TEM) were employed to investigate the morphology and microstructure of the as-prepared catalysts. As shown in Fig. 2a and b, SEM images reveal the interconnected and vertical W-MoSe₂ nanosheets randomly distributed on the surface of Ti₃C₂ MXene, which is conducive to forming a porous architecture. TEM observations further confirm the three-dimensional porous and interconnected nanosheet array structure in W-MoSe₂@MXene (Fig. 2c and d), which is favourable for facilitating mass diffusion and charge transport. High-resolution TEM (HRTEM) images show a distinct multi-phase heterostructure in W-MoSe₂@MXene, implying the existence of sufficient heterointerfaces (Fig. 2e and S2). Additionally, the characteristic lattice spacings of 0.64 and 0.26 nm are observed, corresponding to the (002) lattice plane of 2H-MoSe₂ and the (002) lattice plane of Ti₃C₂ MXene (Fig. 2f–h), respectively. Notably, the hexagonal lattice region can be visualized as depicted in Fig. 2i, proving the formation of 2H phase MoSe₂ within the W-MoSe₂@MXene heterostructure. High-angle annular dark field (HAADF) images and scanning TEM (STEM) mapping demonstrate the homogeneous distribution of Mo, W, Se, Ti and C elements throughout the W-MoSe₂@MXene matrix (Fig. 2j and k).

Fig. 2 (a and b) SEM images, (c and d) TEM images, (e–i) HRTEM images, (j) HAADF-STEM images and (k) HAADF-STEM image and EDS mapping of W-MoSe₂@MXene.

As a counterpart, the MoSe₂@MXene catalyst was fabricated by the same method without the addition of the W dopant precursor. The thus-prepared sample shows a similar three-dimensional porous structure composed of interconnected nanosheet arrays (Fig. S3 and S4). As displayed in Fig. S5, a heterophase hybrid structure is observed in MoSe₂@MXene. HRTEM analysis demonstrates interplanar spacings of 0.82 and 0.26 nm, corresponding to the (002) lattice plane of 1T/2H-MoSe₂ and (002) lattice plane of Ti₃C₂ MXene,^27,28 respectively. Notably, W doping promotes the phase transformation from the metastable 1T/2H structure to the thermodynamically favorable 2H phase, thereby enhancing the structural stability of W-MoSe₂@MXene under Li–O₂ battery operating conditions. Energy dispersive spectroscopy (EDS) mapping manifests that the Mo, Se, Ti and C are homogeneously distributed in MoSe₂@MXene (Fig. S6).

The crystal structure of MXene, MoSe₂@MXene and W-MoSe₂@MXene was assessed by X-ray diffraction (XRD) as shown in Fig. 3a. For pristine MXene, the diffraction peaks at 8.9°, 18.6°, 27.9°, 36.3°, 42.1° and 62.7°, are assigned to the (002), (004), (008), (111), (200) and (220) planes of typical Ti₃C₂ MXene,²⁹ respectively. Additionally, MoSe₂@MXene demonstrates four characteristic diffraction peaks at 12.3°, 32.4°, 38.2° and 56.3°, indexed to the (002), (100), (103) and (110) planes of MoSe₂ (JCPDS#29-0914), respectively. W-MoSe₂@MXene possesses identical diffraction peaks to MoSe₂@MXene with a slight negative shift, indicating lattice expansion due to successful W incorporation rather than secondary phase formation. This result further proves that the W-doped MoSe₂ was successfully anchored on the layered MXene.

Fig. 3 (a) XRD of Ti₃C₂ MXene, MoSe₂@MXene and W-MoSe₂@MXene. (b) Mo 3d and (c) Se 3d XPS spectra of MoSe₂@MXene and W-MoSe₂@MXene. (d) W 4f XPS spectra of W-MoSe₂@MXene. (e) Ti 2p XPS spectra and (f) O 1s XPS spectra of MoSe₂@MXene and W-MoSe₂@MXene.

The surface chemical composition and valence states of MoSe₂@MXene and W-MoSe₂@MXene samples were probed by X-ray photoelectron spectroscopy (XPS). The full XPS spectra of W-MoSe₂@MXene catalysts display the existence of W, Mo, Se, Ti, and C elements (Fig. S7). The high-resolution Mo 3d XPS spectra of MoSe₂@MXene and W-MoSe₂@MXene can be deconvoluted into two paired peaks (Fig. 3b), related to the Mo⁴⁺ (228.7 and 231.8 eV) and Mo⁶⁺ (229.5 and 232.2 eV),^30,31 respectively. Remarkably, the Mo 3d orbital binding energy of W-MoSe₂@MXene shifted positively by around 0.3 eV after the incorporation of the W dopant, indicating that W would capture the electron cloud redistribution around Mo atoms and induce spatial charge redistribution, which is mainly attributed to the electronegativity of W (2.36) being relatively higher than that of Mo (2.16).^32,33 In Se 3d XPS spectra (Fig. 3c), the two characteristic peaks at 54.2 and 55.1 eV are in good agreement with the Se 3d_5/2 and Se 3d_3/2, respectively.³⁴ In the W 4f XPS spectrum of W-MoSe₂@MXene (Fig. 3c), the peaks fitted at 37.8 and 35.9 eV can be attributed to the W 4f_7/2 and W 4f_5/2 of W⁶⁺ species (Fig. 3d), respectively, indicating the incorporation of high-valence W sites.³⁵ As shown in Fig. 3e, the Ti 2p XPS spectra demonstrate three characteristic peaks at 453.9, 458.7 and 464.5 eV, corresponding to the Ti–C, Ti–O 2p_3/2 and Ti–O 2p_1/2,³⁶ respectively. In the O 1s XPS spectra (Fig. 3f), the four peaks at 529.8, 530.8, 531.5 and 533.2 eV can be attributed to Ti–O, Ti–OH, Mo–O–Ti and surface adsorbed H₂O,^37,38 respectively. Notably, the presence of the Mo–O–Ti bond indicates the successful formation of interfacial metal–oxygen bridge sites between W-MoSe₂ and MXene. This heterointerface is expected to boost interfacial charge transfer and lower the polarization overpotential, thereby improving the electrochemical performance of Li–O₂ batteries.

The catalytic performance of the W-MoSe₂@MXene cathode was evaluated in comparison with its MXene and MoSe₂@MXene counterparts via the assembled coin type Li–O₂ batteries. The cyclic voltammetry curves of samples are shown in Fig. 4a, where W-MoSe₂@MXene possesses higher oxygen reduction reaction (ORR) onset potential (2.89 V) and lower oxygen evolution reaction (OER) onset potential (3.61 V) than those of MXene and MoSe₂@MXene, indicative of superior bifunctional catalytic performance. Additionally, the larger integrated areas of the cathodic and anodic peaks imply a better specific capacity in the W-MoSe₂@MXene-based system. Galvanostatic discharge/charge curves demonstrate that W-MoSe₂@MXene exhibits a favorable discharge and charge overpotential of 0.61 V at 100 mA g⁻¹ (Fig. 4b), which is markedly lower than that of MoSe₂@MXene (0.87 V) and MXene (1.11 V). W-MoSe₂@MXene manifests the smallest charge transfer resistance, indicative of rapid charge transport enabled by the synergistic effects of interfacial bridge-oxygen bonds and high-valence W doping (Fig. 4c). The rate performance of samples was also evaluated at a fixed specific capacity of 1000 mA h g⁻¹. As the current density increases, W-MoSe₂@MXene exhibits a significant decrease charge potential plateau than other counterparts, which is beneficial to induce a relatively low overpotential (Fig. 4d). Additionally, the W-MoSe₂@MXene cathode assembled Li–O₂ battery exhibits a favorable specific capacity of 12442.6 mA h g⁻¹ at 1 A g⁻¹, which is ∼2.23 and ∼2.56 times greater than that of MoSe₂@MXene (5568.3 mA h g⁻¹) and MXene (4823.2 mA h g⁻¹), respectively.

Fig. 4 (a) CV curves, (b) initial full discharge–charge curves at 100 mA g⁻¹, (c) EIS, (d) rate capability, and (e) galvanostatic discharge–charge curves of LOBs at a current density of 1000 mA g⁻¹ for Ti₃C₂ MXene, MoSe₂@MXene and W-MoSe₂@MXene. (f) Rate performances of W-MoSe₂@MXene-based LOBs at high current densities.

Meanwhile, to evaluate the high-rate performance of the thus-prepared catalyst, the assembled Li–O₂ battery with the W-MoSe₂@MXene cathode was evaluated at high current densities of 1–5 A g⁻¹. As shown in Fig. 4f, the charge potential plateau increases only slightly from 4.12 to 4.31 V and eventually returns to 4.18 V, implying an advantageous high-rate performance. Specifically, it can run continuously for 127 cycles at 1 A g⁻¹. Additionally, the W-MoSe₂@MXene cathode assembled Li–O₂ battery at high current densities retains a stable discharge–charge overpotential from ∼0.95 V (1 A g⁻¹) to ∼1.32 V (5 A g⁻¹) and returns to ∼0.98 V (1 A g⁻¹). However, other counterparts display relatively higher polarization overpotentials at ultra-high rates (Fig. 5a), implying the potential application of the as-prepared W-MoSe₂@MXene cathode in high-rate Li–O₂ batteries. The discharge–charge cycling life is a crucial parameter to assess the catalytic activity of Li–O₂ batteries. As depicted in Fig. 5b and S9, the W-MoSe₂@MXene-based Li–O₂ battery can effectively operate over 194 cycles with a fixed specific capacity of 1000 mA h g⁻¹ at a high current density of 1 A g⁻¹, which is evidently superior to MoSe₂@MXene (104 cycles) and MXene (67 cycles) (Fig. S10 and S11). Surprisingly, W-MoSe₂@MXene can even stably cycle over 61 cycles at an ultra-high current density of 5 A g⁻¹, indicating a favorable high current density catalytic activity.

Fig. 5 (a) Overpotential and (b) discharge–charge cycling performance at various high current densities and a fixed specific capacity of 1000 mA h g⁻¹. (c and d) SEM images and (e and f) Li 1s and Se 3d XPS spectra of the W-MoSe₂@MXene-based cathode after the 1st discharge and 1st charge. (g) EIS of the pristine cathode after the 1st discharge and 1st recharge. (h) Galvanostatic discharge–charge curves of LOBs at 1000 mA g⁻¹ for the three samples. (f) Scheme of the cycling process for W-MoSe₂@MXene-based LOBs.

To elucidate the nature of discharge products on the W-MoSe₂@MXene cathode, SEM and XPS characterization studies as well as electrochemical analysis were performed on the electrodes after discharge and subsequent recharge. As shown in Fig. 5c, the surface of the W-MoSe₂@MXene cathode is uniformly covered by densely accumulated discharge products, which is attributed to the three-dimensional porous architecture and interconnected nanosheet array of the W-MoSe₂@MXene providing abundant nucleation sites and spatial accommodation for Li₂O₂ deposition. This structural configuration facilitates efficient Li₂O₂ decomposition into Li⁺ and O₂, and enhances electron conductivity as well as supports higher specific capacities. Upon recharging (Fig. 4d), the discharge products are completely removed and the initial three-dimensional framework of the W-MoSe₂@MXene cathode is reinstated, exposing active sites for subsequent electrochemical reactions. Fig. 4e presents the high-resolution XPS spectra of Li 1s and Se 3d obtained from the cathode after the initial discharge. The emergence of a new peak centered at 54.2 eV is in good agreement with the formation of Li₂O₂.^39,40 Notably, the complete disappearance of the Li₂O₂ signal indicates full decomposition of the discharge product, underscoring the excellent reversibility of the electrochemical reaction (Fig. 4f). Additionally, high-resolution XPS spectra of Mo 3d, W 4f and Ti 2p demonstrate that the peaks after the first discharge and subsequent recharge are basically the same as in the pristine state, indicating the preservation of the chemical environment and confirming the excellent structural stability of the W-MoSe₂@MXene cathode (Fig. S12 and S13). This robust framework is beneficial to the long-term cycling stability of the MXene-based Li–O₂ battery. Electrochemical impedance spectroscopy (EIS) measurements (Fig. 5g) along with equivalent circuit modeling (Fig. S14) further elucidate the electrochemical changes during cycling.^41,42 The substantial increase in charge transfer resistance (R_ct) observed after the discharge process reflects the obstruction of ion diffusion pathways by poorly conductive and insoluble products. The R_ct returns to values comparable to those of the pristine W-MoSe₂@MXene cathode after the recharging process, indicating effective decomposition of the discharge products. The high donor number of DMSO (∼29.8 kcal mol⁻¹) promotes a solution-mediated growth pathway of Li₂O₂. Strong Li⁺ solvation by DMSO stabilizes soluble Li⁺–O²⁻ ion pairs, enabling their diffusion and disproportionation, ultimately producing the toroidal Li₂O₂ particles (Fig. 5c), which is beneficial to achieve high discharge capacities, as it is less passivating compared with thin-films Li₂O₂ typically observed in low donor number solvents.⁴³ Nonetheless, a potential challenge associated with toroidal Li₂O₂ is its incomplete oxidation during charging, which underscores the importance of W-MoSe₂@MXene catalyst design in mitigating the resulting high overpotentials. Therefore, the synergistic effect arising from the incorporation of high-valence W⁶⁺ and oxygen-bridge sites as well as the distinctive porous architecture facilitates the efficient decomposition of the in situ formed Li₂O₂ discharge product during recharging (Fig. 5h), thereby accelerating reaction kinetics and enhancing cycling performance.

To clarify the positive role of interfacial oxygen-bridge bonding and high-valence metal sites in the electronic structure and reaction free energy barrier, first-principles calculations based on the density functional theory (DFT) were performed. Density of states (DOS) analyses reveal that both W-MoSe₂@MXene and MoSe₂@MXene tend to possess the metallic conductor behavior with a continuous occupation of electrons across the Fermi level, indicative of a favorable intrinsic electronic conductivity (Fig. 6a and b). Projected DOS results further indicate that the pronounced electronic states near the Fermi level predominantly originate from Ti atoms, owing to the excellent electronic conductivity of the MXene component. Accordingly, charge density difference calculations show the apparent charge transfer between W-MoSe₂ (MoSe₂) and MXene in W-MoSe₂@MXene (MoSe₂@MXene) induced by the construction of the heterostructure with the favorable interfacial bridge-oxygen bonding (Fig. 6c and d), which is beneficial to accelerate the interface charge transfer kinetics at the catalyst–electrolyte interface.

Fig. 6 DOS of (a) MoSe₂@MXene and (b) W-MoSe₂@MXene. Difference charge of (c) MoSe₂@MXene and (d) W-MoSe₂@MXene. Free energy diagrams for the discharge–recharge reactions of (e) MoSe₂@MXene and (f) W-MoSe₂@MXene. (g) Optimized structure models of W-MoSe₂@MXene and different adsorbed intermediates (LiO₂, Li₂O₂ and (Li₂O₂)₂) on W-MoSe₂@MXene.

To probe the origin of the catalytic activity and underlying reaction pathways, the adsorption energetics of relevant intermediates and products were investigated. Voltage gaps were calculated to quantitatively assess the overpotentials by using the definitions U_ORR = U_eq − U_DC and U_OER = U_C − U_eq for the discharge (ORR) and charge (OER) process.^44,45 Optimized structure models of key intermediates/products on W-MoSe₂@MXene and MoSe₂@MXene are depicted in Fig. 6g, S15 and S16, respectively. As shown in Fig. 6e, the MoSe₂@MXene catalyst exhibits substantial ORR and OER theoretical overpotentials of 2.06 and 2.39 V, respectively, reflecting its limited catalytic activity. The as-prepared W-MoSe₂@MXene catalyst possesses significantly lower theoretical overpotentials of 1.75 V and 1.91 V for the ORR and OER (Fig. 6f), respectively, confirming that W doping effectively enhances bifunctional oxygen electrocatalysis. The significantly reduced voltage gaps induced by the synergistic effect between high-valence W sites and interfacial bridge-oxygen bonding are expected to improve energy efficiency, suppress parasitic reactions and thereby ultimately prolong the cycling lifespan of lithium–oxygen batteries.

4. Conclusions

In summary, the incorporation of a high-valent metal dopant triggered an in situ phase transformation to form a 2H-MoSe₂ catalyst anchored on layered Ti₃C₂ MXene (W-MoSe₂@MXene) as a favorable air-electrode for Li–O₂ batteries, affording a three-dimensional porous network of interconnected nanosheets and a distinctive Mo–O–Ti interfacial bridge bonding structure. As a result, the W-MoSe₂@MXene-based Li–O₂ battery delivers a high specific capacity of 12442.6 mA h g⁻¹ and excellent cycling performance (over 194 cycles) at 1 A g⁻¹. Remarkably, it retains stable operation for 108 cycles at an ultrahigh current density of 3 A g⁻¹ with a fixed specific capacity of 1000 mA h g⁻¹. The superior electrochemical performance can be attributed to the following reasons: (1) the hierarchical porous nanosheet array network provides high surface area and sufficient space for reversible deposition and decomposition of discharge products; (2) the synergistic effect of high-valence dopants and interfacial oxygen bridge bonding between W-MoSe₂ and the Ti₃C₂ MXene matrix promotes spatial charge redistribution and enhances interfacial charge transfer kinetics; (3) DFT calculations reveal that the high-valence metal sites effectively lower the reaction energy barrier for oxygen reduction and evolution reactions, thus accelerating reaction kinetics. This work opens an avenue for the rational construction of heterophase hybrid catalysts for advanced application in Li–O₂ batteries.

Author contributions

Kai Zeng: writing original draft, writing – review & editing, conceptualization, funding acquisition. Ming Chao: investigation, formal analysis. Lanxiang Huang: data curation, methodology. Hongwei Tao: investigation, data curation. Zhengyou He: conceptualization, resources. Yibing Li: validation, conceptualization. Zhihui Sun: writing – review & editing, methodology.

Conflicts of interest

The authors declare no competing financial interest.

Data availability

The data supporting the findings of this study are available within the manuscript and its SI. Data will be made available upon reasonable request to the corresponding author. See DOI: https://doi.org/10.1039/d5ta05976c.

Acknowledgements

We gratefully acknowledge the financial support provided by the Sichuan Science and Technology Program (2024NSFSC0990), “Tianfu Emei” Youth Talent Program in Sichuan Province, Leshan West Silicon Materials Photovoltaic New Energy Industry Technology Research Institute (2024GYKF3), Huzhou Key Laboratory of Smart and Clean Energy (24CE04) and the China Postdoctoral Science Foundation (2025M770923).

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Footnote

† K. Zeng and M. Chao contributed equally to this work.

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