increasing by the abundant WN bond. To the best of our knowledge, the experimental synthesis of 2D nitrogen-rich tungsten nitrides is not reported in literature because of the harsh synthesis condition, stemming from the sluggish reaction thermodynamics of penetrating nitrogen into tungsten lattice. [9] Overall, high pressure and temperature (P-T) synthetic method (5 GPa and 880-2570 K) was adopted to prepare various nitrogen-rich tungsten nitrides such as W 2 N 3 , W 3 N 4 . [10] However, this harsh synthesis condition is laborious to control the morphology of tungsten nitrides, especially for the 2D structure. [11][12][13][14] As an alternative strategy, ammoniating tungsten metals or compounds are extensively studied to produce tungsten nitrides. [9,15] Yet, the reaction is always incomplete, leading to low nitrogen ratio in final products with unreacted tungsten precursor (tungsten, tungsten oxides, etc.). [16] Consequently, developing a facile and real-world synthetic strategy, with favorable reaction thermodynamics and facile morphology control for 2D nitrogen-rich tungsten nitrides, is highly desired but still thought provoking.Herein, we synthesize atomically thin 2D nitrogen-rich hexagonal W 2 N 3 (h-W 2 N 3 ) nanosheets via salt-templated method at atmospheric pressure for the first time. In this strategy, h-W 2 N 3 2D transition metal nitrides, especially nitrogen-rich tungsten nitrides (W x N y , y > x), such as W 3 N 4 and W 2 N 3 , have a great potential for the hydrogen evolution reaction (HER) since the catalytic activity is largely enhanced by the abundant WN bonding. However, the rational synthesis of 2D nitrogen-rich tungsten nitrides is challenging due to the large formation energy of WN bonding. Herein, ultrathin 2D hexagonal-W 2 N 3 (h-W 2 N 3 ) flakes are synthesized at atmospheric pressure via a salt-templated method. The formation energy of h-W 2 N 3 can be dramatically decreased owing to the strong interaction and domain matching epitaxy between KCl and h-W 2 N 3 . 2D h-W 2 N 3 demonstrates an excellent catalytic activity for cathodic HER with an onset potential of −30.8 mV as well as an overpotential of −98.2 mV for 10 mA cm −2 . ElectrocatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Zero thermal expansion materials are crucial for manufacturing high-precision devices, but most of these materials discovered so far are inorganic. Organic zero thermal expansion materials are rare due to the need for precise control over the complex supramolecular interactions between organic groups in order to modulate their thermal expansion properties. Here, we report a novel organic crystalline supramolecular rotor, [(3-chloro-1-adamantylammonium)(18-crown-6)]ClO4, which exhibits planar positive–zero–negative thermal expansion along the a- and c-axes, with zero thermal expansion behavior in the range of 250–317 K. X-ray single-crystal structures, differential scanning calorimetry (DSC) measurements, and molecular dynamics simulations disclosed that such unique transition in thermal expansion results from the static–swing–rotation transition of 18-crown-6 in the crystal structure.

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