N-regulated three-dimensional turf-like carbon nanosheet loaded with FeCoNi nanoalloys as bifunctional electrocatalysts for durable zinc-air batteries.

N-regulated three-dimensional (3D) turf-like carbon material loaded with FeCoNi nanoalloys (F-CNS-CNT), composed of carbon nanotubes (CNT) grown in situ on carbon nanosheets(CNS), was synthesized using a low-temperature solution combustion method and organic compounds rich in pyridinic-N. This distinct structure significantly expands the effective electrochemical surface area, revealing an abundance of active sites and enhancing the mass transfer capability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Both experimental observations and theoretical calculations corroborate that the synergy between the FeCoNi nanoalloy and the highly pyridinic N-doped carbon substrate optimizes the adsorption and desorption-free energy of oxygen intermediates, resulting in a remarkable improvement of intrinsic ORR/OER activity. Therefore, the derived F-CNS-CNT electrocatalyst can present a favorable half-wave potential of 0.85 V (ORR) and a lower overpotential of 260 mV (corresponding to a current density of 10 mA cm-2, OER) in alkaline media. Moreover, when employed in the air cathode of a flowable zinc-air battery, the electrocatalyst exhibits exceptional discharge and charge performance, including a high power density of 144.6 mW cm-2, a high specific capacity of 801 mAh g-1, and an impressive cycling stability of 600 cycles at a current density of 10 mA cm-2. Notably, these results markedly surpass those of the commercial catalyst Pt/C + IrO2.

Significant hydrogen generation via photo-mechanical coupling in flexible methylammonium lead iodide nanowires.

The flexoelectric effect, which refers to the mechanical-electric coupling between strain gradient and charge polarization, should be considered for use in charge production for catalytically driving chemical reactions. We have previously revealed that halide perovskites can generate orders of higher magnitude flexoelectricity under the illumination of light than in the dark. In this study, we report the catalytic hydrogen production by photo-mechanical coupling involving the photoflexoelectric effect of flexible methylammonium lead iodide (MAPbI3) nanowires (NWs) in hydrogen iodide solution. Upon concurrent light illumination and mechanical vibration, large strain gradients were introduced in flexible MAPbI3 NWs, which subsequently induced significant hydrogen generation (at a rate of 756.5 µmol g-1 h-1, surpassing those values from either photo- or piezocatalysis of MAPbI3 nanoparticles). This photo-mechanical coupling strategy of mechanocatalysis, which enables the simultaneous utilization of multiple energy sources, provides a potentially new mechanism in mechanochemistry for highly efficient hydrogen production.

Direct in situ photolithography of ultra-stable CsPbBr3 quantum dot arrays based on crosslinking polymerization.

CsPbX3 (X = Br, Cl, I) perovskite quantum dots (PQDs) are the rising star for various display applications owing to their excellent opto-electrical properties, such as an adjustable spectrum, narrow emission linewidth and high quantum yield. However, these PQDs are well known to suffer from intrinsic instability under atmospheric conditions. In this work, a novel photosensitive ligand, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (XBPO), was employed as a dual-functional reagent for PQD surface engineering. The XBPO ligand could cleave to produce phenylphosphinyl radicals and trimethylbenzoyl radicals under UV light irradiation. The phenylphosphinyl radicals with PO bonds could effectively passivate the PQD surface defects, leading to quantum yield improvement. The CsPbBr3 and CsPbI3 PQDs with XBPO modification could achieve a photoluminescence quantum yield (PLQY) of near unity and 92%, respectively. Additionally, the in situ encapsulation of the PQDs was achieved by the subsequent crosslinking polymerization, which significantly improved the stability of the PQDs against solvents and the environment. By combining a standard photolithography procedure, we demonstrated a micro-pattern of CsPbBr3 PQDs. These results establish a universal route for PQD patterning, compatible with the existing photolithography processes, which could facilitate the application of PQDs in next-generation display technology.

Dynamic Observations on Formation of Coffee-Ring Structures from the Degradation of Cesium Lead Halide Perovskite Nanocrystals.

Nanomaterials of halide perovskites have attracted increasing attention for their remarkable potential in optoelectronic devices, but their instability to environmental factors is the core issue impeding their applications. In this context, the microscopic understanding of their structural degradation mechanisms upon external stimuli remains incomplete. Herein, we took an emerging member of this material family, Cs4PbBr6 nanocrystals (NCs), as an example and investigated the degradation pathways as well as underlying mechanisms under an electron beam by using in situ transmission electron microscopy. Our atomic-scale study identified the distinct degradation stages for the NCs toward interesting coffee-ring PbBr2 structures, which are caused by the organic surface capping agents as well as surface energy of NCs. Our findings present a fundamental insight for the degradation of halide perovskite NCs and may provide indispensable guidance for their structural design and stability improvement.

Visualization of Bubble Nucleation and Growth Confined in 2D Flakes.

The nucleation and growth of bubbles within a solid matrix is a ubiquitous phenomenon that affects many natural and synthetic processes. However, such a bubbling process is almost "invisible" to common characterization methods because it has an intrinsically multiphased nature and occurs on very short time/length scales. Using in situ transmission electron microscopy to explore the decomposition of a solid precursor that emits gaseous byproducts, the direct observation of a complete nanoscale bubbling process confined in ultrathin 2D flakes is presented here. This result suggests a three-step pathway for bubble formation in the confined environment: void formation via spinodal decomposition, bubble nucleation from the spherization of voids, and bubble growth by coalescence. Furthermore, the systematic kinetics analysis based on COMSOL simulations shows that bubble growth is actually achieved by developing metastable or unstable necks between neighboring bubbles before coalescing into one. This thorough understanding of the bubbling mechanism in a confined geometry has implications for refining modern nucleation theories and controlling bubble-related processes in the fabrication of advanced materials (i.e., topological porous materials).

Fluorescence-enhanced Cs4 PbBr6 /CsPbBr3 composites films synthesized by double-films solid phase reaction method.

Due to indispensable ligands, polluted organic solution, or complex vapour deposition, stable CsPbBr3 film is hard to be prepared directly using a simple and environmentally friendly method. To improve the stability of CsPbBr3 film and its synthesis methods, the double-films solid phase reaction was developed, and Cs4 PbBr6 /CsPbBr3 composites were designed. Although the synthesized particle had a size of 2-5 µm, much larger than that of quantum dots, in ambient conditions the composites films still showed good photoluminescence properties, with the highest photoluminescence quantum yield of 80%. It had good stability against air, temperature and humidity, and even had interesting fluorescence-enhanced phenomenon after about 4 days.