Dongqi Li

Electron–phonon (e–ph) interactions govern photoinduced nonequilibrium dynamics of MXenes, determining hot-carrier relaxation and parasitic heat accumulation. However, strategies to deliberately modulate these interactions through chemical control, together with mechanistic understanding, remain underexplored. Here, we demonstrate the effective modulation of nonequilibrium e–ph interactions in Ti ₃ C ₂ T _x MXene via surface-anchored Mo ₃ S ₇ nanoclusters, which introduce a rapid energy harvesting pathway competing with intrinsic e–ph relaxation. Using mild ligand substitution, Mo ₃ S ₇ nanoclusters are densely and homogenously anchored onto Ti ₃ C ₂ T _x via coordination bonding between Mo centers and O-terminations. Femtosecond transient absorption and optical-pump terahertz-probe spectroscopy reveal an ultrafast, sub-100 fs nonthermal electron and/or energy extraction, with efficiency increasing from ~28.6 % at 1.55 eV to ~38.2 % at 3.88 eV. This excitation-energy-dependent enhancement is enabled by improved energetic alignment between hot electrons in Ti ₃ C ₂ T _x and the conduction-band manifold of Mo ₃ S ₇ . The competitive depletion of nonthermal electrons suppresses coherent A _1g phonon excitation, reducing effective e–ph interactions. Our study offers a viable strategy for modulating e–ph interactions in MXenes, advancing hot carrier relaxation and thermal management in next-generation optoelectronic devices.

Titanium carbide MXene (Ti₃C₂T ₓ ) is an emerging metallic material with promise for (opto)electronics and thermal management. Yet how photoexcitation—particularly via photogenerated thermal energy—modifies its charge carrier dynamics remains poorly understood. By combining time-resolved terahertz spectroscopy and transient reflectance measurements, we reveal a long-lived, photo-induced suppression of conductivity, which we attribute to efficient lattice heating and slow heat dissipation in Ti₃C₂T _x . A systematic variation of pump photon energy reveals that this ‘negative’ photoconductivity can equivalently be induced by lattice temperature increases, indicating a thermal origin. Repetition-rate-dependent transient reflectance measurements further show residual heat persisting over 100 ns, substantially longer than in conventional metals. Our work presents a unified understanding of photothermal effects in Ti₃C₂T ₓ and their influence on non-equilibrium charge transport, underscoring its potential for photothermal electronics and light-to-thermal energy storage applications.

Surface terminations critically govern the properties of two-dimensional transition metal carbides and/or nitrides (MXenes), yet a universal strategy to obtain MXenes with uniform and controllable terminations remains elusive. Here we introduce a ‘gas–liquid–solid’ triphasic etching strategy that employs iodine vapour, halide molten salts and MAX phases to produce MXenes with pure and precisely tunable halogen terminations (Cl, Br, I or their combinations). In this process, halide molten salts dissolve iodine via interhalogen anion formation while efficiently transporting etching by-products. The resulting MXenes retain excellent structural integrity, yielding uniformly ordered surfaces. As a representative example, Ti ₃ C ₂ Cl ₂ shows a 160-fold enhancement in macroscopic conductivity and a 13-fold enhancement in terahertz conductivity relative to conventional Cl/O-terminated Ti ₃ C ₂ , attributed to minimized electron trapping and scattering. Beyond single-halogen terminations, the gas–liquid–solid approach enables dual- and triple-halogen termination control, providing a general platform for tailoring MXene surface chemistry towards advanced (opto)electronic applications.

Catalysts featuring multiple active sites hold significant potential for CO₂ photoconversion to multi-carbon products. However, multi-metal-site catalysts typically face challenges with low yields and selectivity for ethylene production, with a lack of definitive design guidelines. Here we show that Bader charge can serve as a critical descriptor for delineating the structure–activity relationship of kesterite-like nanosheets in the reduction of CO₂ to ethylene. We propose the Bader-Regulate-Performance principle — apposite Bader charge can provide a moderate energy barrier for intermediate adsorption and C-C coupling simultaneously, thus promoting the performance for ethylene generation. Among the predicted multi-metal-site nanosheets, the Cu₂ZnSnS₄, with the appropriate Bader charge, achieves a high ethylene yield of 25.16 µmol g⁻¹ h⁻¹ with electron selectivity of 72.4% under visible light irradiation, surpassing those of reported photocatalysts under similar catalytic conditions. Our findings provide crucial insights into the design of efficient catalysts for photocatalytic CO₂ conversion to multi-carbon products.

Aluminium-based aqueous batteries hold promises for next-generation sustainable and large-scale energy storage due to the favorable metrics of Al and water-based electrolytes. However, the performance of current aluminium-based aqueous batteries falls significantly below theoretical expectations, with a critical bottleneck of realizing cathodes with high areal capacities. Herein, we present a hydrate-melt electrolyte design utilizing cost-effective AlCl₃ and organic halide salts, which enables the demonstration of aqueous Al-Br batteries with enhanced energy-power characteristics. The optimal electrolyte features suppressed water activity and loosely bound halogen anions, attributed to its unique electrolyte structure, where the majority of water molecules engage in robust ion solvation (>98% as suggested by simulations) and halogen anions reside in the outer solvation sheath of cations. These distinctive features ensure good compatibility of the electrolyte with the reversible Br⁻/Br⁰/Br⁺ conversion, enabling cathodes with a high areal capacity of 5 mAh cm⁻². Besides, the electrolyte allows for Zn-Al alloying/de-alloying with minimal polarization (around 100 mV at 5 mA cm⁻²) and a smooth alloy surface. The assembled Al-Br cell delivers an energy density (267 Wh L⁻¹, based on the volume of anode, cathode and separator) comparable to commercial Li-ion batteries and a substantial power density (1069 W L⁻¹) approaching electrochemical capacitors.

Aqueous zinc batteries are attractive for large-scale energy storage due to their inherent safety and sustainability. However, their widespread application has been constrained by limited energy density, underscoring a high demand of advanced cathodes with large capacity and high redox potential. Here, we report a reversible high-capacity six-electron-conversion Se cathode undergoing a ZnSe↔Se↔SeCl₄ reaction, with Br⁻/Br_n ⁻ redox couple effectively stabilizes the Zn | |Se cell. This Se conversion, initiated in a ZnCl₂-based hydrogel electrolyte, presents rapid capacity decay (from 1937.3 to 394.1 mAh g_Se ⁻¹ after only 50 cycles at 0.5 A g_Se ⁻¹) primarily due to the dissolution of SeCl₄ and its subsequent migration to the Zn anode, resulting in dead Se passivation. To address this, we incorporate the Br⁻/Br_n ⁻ redox couple into the Zn | |Se cell by introducing bromide salt as an electrolyte additive. The generated Br_n ⁻ species acts as a dead-Se revitalizer by reacting with Se passivation on the Zn anode and regenerating active Se for the cathode reaction. Consequently, the cycling stability of the Zn | |Se cell is improved, maintaining 1246.8 mAh g_Se ⁻¹ after 50 cycles. Moreover, the Zn | |Se cell exhibits a specific capacity of 2077.6 mAh g_Se ⁻¹ and specific energy of 404.2 Wh kg⁻¹ based on the overall cell reaction.

Surface terminations profoundly influence the intrinsic properties of MXenes, but existing terminations are limited to monoatomic layers or simple groups, showing disordered arrangements and inferior stability. Here we present the synthesis of MXenes with triatomic-layer borate polyanion terminations (OBO terminations) through a flux-assisted eutectic molten etching approach. During the synthesis, Lewis acidic salts act as the etching agent to obtain the MXene backbone, while borax generates BO₂⁻ species, which cap the MXene surface with an O–B–O configuration. In contrast to conventional chlorine/oxygen-terminated Nb₂C with localized charge transport, OBO-terminated Nb₂C features band transport described by the Drude model, exhibiting a 15-fold increase in electrical conductivity and a 10-fold improvement in charge mobility at the d.c. limit. This transition is attributed to surface ordering that effectively mitigates charge carrier backscattering and trapping. Additionally, OBO terminations provide Ti₃C₂ MXene with substantially enriched Li⁺-hosting sites and thereby a large charge-storage capacity of 420 mAh g⁻¹. Our findings illustrate the potential of intricate termination configurations in MXenes and their applications for (opto)electronics and energy storage.

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn²⁺ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn²⁺-dominated to fast-kinetics H⁺-dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV₃O₈·1.5H₂O cathode (10 mg cm⁻²) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm⁻² and a state-of-the-art energy density of 33.8 Wh m⁻², along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries.