2D MXene materials have the advantages of versatile chemical composition, tunable layer thickness, and facile functionalization nature, and can be used as catalysts for the hydrogen evolution reaction (HER). However, tuning the thermal stability and activation of in-plane activity remain a challenge. We apply high-throughput density functional theory (DFT) calculations, together with a machine learning framework, to identify 2D MXene ordered binary alloy (OBA) activity trends and guide HER catalyst design. 2D MXenes of M_n+1X_nO₂ (n = 1, 2, 3; X = C, N) and OBA HER catalysts of M₂M′X₂O₂ and M₂M′₂X₃O₂ with 3d, 4d and 5d transition metal electrons were enumerated by screening, followed by catalytic activity, thermal stability, and conductivity computations. Our results indicate that 110 kinds of experimentally unexplored 2D MXene OBAs with thermostability and outstanding HER activity surpassing that of noble metal platinum were selected. Especially, the titanium element is mainly contained in the ideal catalysts of 2D MXene OBAs, which is consistent with the MXenes synthesized by experiments. Further, we show that descriptors developed using the AdaBoost ensemble learning model could accurately predict and uncover the essential geometric and chemical origin of HER activity, which is very consistent with the electronic insights. The advanced research strategy, which combines high-throughput computing with machine learning, shows robust ability for evaluating the activity trends and designing new complicated catalysts.

Functional dynamic molecular crystals have drawn increasing interest in exploring next-generation flexible and smart materials. Molecular rotors, as a typical type of dynamic material, are good candidates that can exhibit bulk properties and functionalities. Herein, we report a molecular rotor crystal as a model system to show a unique structural phase transition-related ferroelasticity. The molecular rotor is dumbbell shaped containing a freely rotating axial rotator and multiple peripheral tert-butyl groups on the two plates with restricted motions. The crystal undergoes a ferroelastic structural phase transition at 263 K with unconventional inverse temperature symmetry breaking (ITSB), i.e., a higher-symmetric low-temperature paraelectric phase (point group mmm) vs. a lower-symmetric high-temperature ferroelastic phase (point group 2/m). Combined crystallographic and NMR spectroscopy studies reveal that unequal motions of the peripheral tert-butyl rotators and anisotropic steric repulsion among the molecules are the key cooperative intermolecular interactions to drive a concerted molecular movement to result in the unique ferroelastic phase transition with ITSB. Our study may open avenues for designing and exploring new types of dynamic functional materials.

Ultrafine Nb₂O₅–NbC nanocrystallites embedded in a CNF matrix were in situ constructed guided by a PS modulator. The assembled batteries containing the Nb₂O₅–NbC/CNF-PS interlayer exhibit restrained polysulfide shuttling, enhanced redox kinetics.

As a typical two-dimensional (2D) MXene, Ti₃C₂O₂ has been considered as a potential material for high-performance hydrogen evolution reaction (HER) catalyst, due to its anticorrosion and hydrophilic surface. However, it is still a challenge to improve the Ti₃C₂O₂ surficial HER catalytic activity. In this work, we investigated the HER activity of Ti₃C₂O₂ after the surface was doped with S, Se, and Te by the first principles method. The results indicated that the HER activity of Ti₃C₂O₂ is improved after being doped with S, Se, Te because the Gibbs free energy of hydrogen adsorption (ΔG_H) is increased from −2.19 eV to 0.08 eV. Furthermore, we also found that the ΔG_H of Ti₃C₂O₂ increased from 0.182 eV to 0.08 eV with the doping concentration varied from 5.5% to 16.7%. The HER catalytic activity improvement of Ti₃C₂O₂ is attributed to the local crystal structure distortion in catalytic active sites and Fermi level shift leads to the p-d orbital hybridization. Our results pave a new avenue for preparing a low-cost and high performance HER catalyst.