The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (Tc) up to 55 K, has attracted worldwide research efforts over the past ten years. So far, all these FeSCs structurally adopt FeSe-type layers with a square iron lattice and superconductivity can be generated by either chemical doping or external pressure. Herein, we report the observation of superconductivity in an iron-based honeycomb lattice via pressure-driven spin-crossover. Under compression, the layered FePX3 (X = S, Se) simultaneously undergo large in-plane lattice collapses, abrupt spin-crossovers, and insulator-metal transitions. Superconductivity emerges in FePSe3 along with the structural transition and vanishing of magnetic moment with a starting Tc ~ 2.5 K at 9.0 GPa and the maximum Tc ~ 5.5 K around 30 GPa. The discovery of superconductivity in iron-based honeycomb lattice provides a demonstration for the pursuit of transition-metal-based superconductors via pressure-driven spin-crossover.

Spin-crossover (SCO) is generally regarded as a spectacular molecular magnetism in 3d-3d metal complexes and holds great promise for various applications such as memory, displays, and sensors. In particular, SCO materials can be multifunctional when a classical light- or temperature-induced SCO occurs along with other cooperative structural and/or electrical transport alterations. However, such a cooperative SCO has rarely been observed in condensed matter under hydrostatic pressure (an alternative external stimulus to light or temperature), probably due to the lack of synergy between metal neighbors under compression. Here, we report the observation of a pressure-driven, cooperative SCO in the two-dimensional (2D) honeycomb antiferromagnets MnPS and MnPSe at room temperature. Applying pressure to this confined 2D system leads to a dramatic magnetic moment collapse of Mn (d) from S = 5/2 to S = 1/2. Significantly, a number of collective phenomena were observed along with the SCO, including a large lattice collapse (∼20% in volume), the formation of metallic bonding, and a semiconductor-to-metal transition. Experimental evidence shows that all of these events occur in the honeycomb lattice, indicating a strongly cooperative mechanism that facilitates the occurrence of the abrupt pressure-driven SCO. We believe that the observation of this cooperative pressure-driven SCO in a 2D system can provide a rare model for theoretical investigations and lead to the discovery of more pressure-responsive multifunctional materials.

It is a serious challenge to develop photoanodes with fast charge separation efficiency and surface reaction kinetics. Herein, the N doped carbon dot modified WO3 nanoflake (NCDs/WO3) is constructed by impregnation method. The resulting NCDs/WO3 exhibits an excellent photocurrent density of 1.42 mA cm−2 (1.0 V vs saturated calomel electrode, SCE) in 1 m H2SO4 solution under AM 1.5 G irradiation, which is 2.25 times higher than that of the pristine WO3. In addition, the onset potential of NCDs/WO3 photoanode represents a cathodic shift of 70 mV, indicating the charge separation and transfer process are both promoted. These results demonstrate N doped CD modified WO3 can further enhance the conductivity and electrochemical activity surface area, which contributes to the higher photoelectrochemical (PEC) performance. This work provides an efficient strategy for the development of doping carbon material with heteroatoms to increase the charge transfer and charge separation efficiency in PEC water oxidation.

In two‐dimensional (2D) amorphous nanosheets, the electron–phonon coupling triggered by localization of the electronic state as well as multiple‐scattering feature make it exhibit excellent performance in optical science. VS2 nanosheets, especially single‐layer nanosheets with controllable electronic structure and intrinsic optical properties, have rarely been reported owing to the limited preparation methods. Now, a controllable and feasible switching method is used to fabricate 2D amorphous VS2 and partial crystallized 2D VO2(D) nanosheets by altering the pressure and temperature of supercritical CO2 precisely. Thanks to the strong carrier localization and the quantum confinement, the unique 2D amorphous structures exhibit full band absorption, strong photoluminescence, and outstanding photothermal conversion efficiency.

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