Hydrochromic materials that can reversibly change color upon water treatment have attracted much attention owing to their potential applications in diverse fields. Herein, for the first time, we report that space‐confined CsPbBr3 nanocrystals (NCs) are hydrochromic. When CsPbBr3 NCs are loaded into a porous matrix, reversible transition between luminescent CsPbBr3 and non‐luminescent CsPb2Br5 can be achieved upon the exposure/removal of water. The potential applications of hydrochromic CsPbBr3 NCs in anti‐counterfeiting are demonstrated by using CsPbBr3 NCs@mesoporous silica nanospheres (around 100 nm) as the starting material. Owing to the small particle size and negatively charged surface, the as‐prepared particles can be laser‐jet printed with high precision and high speed. We demonstrate the excellent stability over repeated transformation cycles without color fade. This new discovery may not only deepen the understanding of CsPbX3, but also open a new way to design CsPbX3 materials for new applications.

No abstract

Molybdenum disulfide (MoS 2) is one of the most important two-dimensional materials after graphene. Monolayer MoS 2 has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS 2 's synthesis techniques are more developed. Here, we review the recent developments in the synthesis of hexagonal MoS 2 , where they are categorized into top-down and bottom-up approaches. Micromechanical exfoliation is convenient for beginners and basic research. Liquid phase exfoliation and solutions for chemical processes are cheap and suitable for large-scale production; yielding materials mostly in powders with different shapes, sizes and layer numbers. MoS 2 films on a substrate targeting high-end nanoelectronic applications can be produced by chemical vapor deposition, compatible with the semiconductor industry. Usually, metal catalysts are unnecessary. Unlike graphene, the transfer of atomic layers is omitted. We especially emphasize the recent advances in metalorganic chemical vapor deposition and atomic layer deposition, where gaseous precursors are used. These processes grow MoS 2 with the smallest building-blocks, naturally promising higher quality and controllability. Most likely, this will be an important direction in the field. Nevertheless, today none of those methods reproducibly produces MoS 2 with competitive quality. There is a long way to go for MoS 2 in real-life electronic device applications.

Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.

The oxygen reduction reaction (ORR) is of significant importance in the development of fuel cells. Now, cobalt-nitrogen-doped chiral carbonaceous nanotubes (l/d-CCNTs-Co) are presented as efficient electrocatalysts for ORR. The chiral template, N-stearyl-l/d-glutamic acid, induces the self-assembly of well-arranged polypyrrole and the formation of ordered graphene carbon with helical structures at the molecular level after the pyrolysis process. Co was subsequently introduced through the post-synthesis method. The obtained l/d-CCNTs-Co exhibits superior ORR performance, including long-term stability and better methanol tolerance compared to achiral Co-doped carbon materials and commercial Pt/C. DFT calculations demonstrate that the charges on the twisted surface of l/d-CCNTs are widely separated; as a result the Co atoms are more exposed on the chiral CCNTs. This work gives us a new understanding of the effects of helical structures in electrocatalysis.

In comparison with oil-based cracking technologies, the on-purpose dehydrogenation of propane (PDH) is a more eco-friendly and profitable approach to produce propylene. By means of density functional theory calculations, the present work reveals that the single vanadium (V) atom anchored on graphitic carbon nitride (V1/g-C3N4) may serve as a promising single-atom catalyst for non-oxidative PDH with industrially practical activity, selectivity, and thermal stability. The high activity of V1/g-C3N4 for PDH is attributed to the low-coordinated 3d orbitals of single V atoms, while the propylene selectivity is originated from the inhibition of the di-σ binding mode of propylene on the single V atoms. This work provides a guideline to design and screen out promising single-atom catalysts for selective dehydrogenation of alkanes.

Pd is the only metal that can catalyze electrochemical CO 2 reduction to formate at close-to-zero overpotential. It is unfortunately subjected to severe poisoning by trace CO as the side product and suffers from deteriorating stability and selectivity with increasing overpotential. Here, we demonstrate that alloying Pd with Cu in the form of twodimensional nanodendrites could enable highly stable and selective formate production. Such unique bimetallic nanostructures are formed as a result of the rapid in-plane growth and suppressed out-of-plane growth by carefully controlling a set of experimental parameters. Thanks to the combined electronic effect and nanostructuring effect, our alloy product catalyzes CO 2 reduction to formate with remarkable stability and selectivity under the working potential as cathodic as −0.4 V. Our results are rationalized by computational simulations, evidencing that Cu atoms weaken the *CO adsorption and stabilize the *OCHO adsorption on neighboring Pd atoms.

Hybrid metal/COF stack multilayers and patterned COF films were fabricated via the flexible combination of solvothermal deposition and compatible film processing techniques.