Abstract 1. Active sites for Cu/ZnO catalysts (ActivesitesforCO2hydrogenationtomethanolonCu/ZnOcatalysts) In recent years, carbon dioxide...
1. Active sites on Cu/ZnO catalysts
(Active sites for CO2 hydrogenation to methanol on Cu/ZnO catalysts)
In recent years, active sites in commercial copper/zinc oxide/alumina (Cu/ZnO/Al2O3) catalysts for hydrogenation of carbon dioxide (CO2) to methanol, ie Zn-Cu bimetallic sites or ZnO-Cu interface sites A heated debate. Kattel et al. reported a direct comparison of the activity of typical catalysts ZnCu and ZnO/Cu for methanol synthesis. They combine x-ray photoelectron spectroscopy, density functional theory, and kinetic Monte Carlo simulation to identify and characterize the reactivity of each catalyst. Both experimental and theoretical results show that ZnCu undergoes surface oxidation under the reaction conditions, which causes the surface Zn to transform into ZnO, so that ZnCu can reach the same Zn coverage activity in ZnO/Cu. The results of Kattel et al. highlight the importance of the synergy at the interface between Cu and ZnO in promoting the synthesis of methanol from the formic acid intermediate. (Science DOI: 10.1126/science.aal3573)
2. Layered two-dimensional perovskite edge states for efficient internal exciton dissociation
(Extremely efficient internal exciton dissociation through edgestates in layered 2D perovskites)
Understanding and controlling the current charge and energy flows in semiconductor quantum wells enables high efficiency optoelectronic devices. The two-dimensional Ruddlesden-Popper perovskite is a solution-processable quantum well whose band gap can be adjusted by changing the thickness of the perovskite layer to limit electron holes. Photogenerated electrons and holes in classical quantum confinement systems are strongly constrained by Coulomb interactions or excitons. Blancon et al. reported the photophysical mechanism of a Ruddlesden-Popper perovskite film with a thickness greater than two perovskite crystal units (>1.3 nm), which is a lower energy associated with the local intrinsic electronic structure at the edge of the perovskite layer. State dominated. These energy states provide a direct way to dissociate excitons into free carriers with longer lifetimes, thereby significantly improving the performance of optoelectronic devices. (Science DOI: 10.1126/science.aal4211)
3. Grain boundary stability controls the hardening and softening of very fine nanocrystalline metals
(Grain boundary stability governs hardening and softening in extremely fine nanograined metals)
Conventional metals follow the classical Hall-Pitt relationship, and the smaller the grain, the harder it is. However, this relationship is ineffective in the case of grains of some nano-sized alloys, and softening occurs. Hu et al. found that the plastic deformation mechanism and hardness of very fine nano-metal grains can be adjusted by adjusting the stability of grain boundaries (GB). Electrodeposited nickel-molybdenum (Ni-Mo) nano-grain samples were subjected to GB conditioning and softened at grain sizes below 10 nm. The GB stabilized by relaxation and separation of Mo, the nano-grain samples achieved ultra-high hardness and had a plastic deformation mechanism dominated by the extension of dislocations. Grain boundary stability provides an alternative to the production of novel nanograin metals with exceptional properties. (Science DOI: 10.1126/science.aal5166)
4. Low temperature hydrogen production catalyst Pt/α-MoC
(Low-temperaturehydrogen production from water and methanol using Pt/α-MoC catalysts)
Polymer electrolyte membrane fuel cells (PEMFCs) are hydrogen-fueled and are an attractive power supply system. However, prior to use, the required hydrogen is generated in situ from a stable liquid, ensuring storage and transportation safety. In this regard, the use of methanol is particularly attractive because it is inexpensive and capable of recombining with water to release high quality hydrogen (18.8 wt.%). However, the traditional methanol vapor recombination method needs to be carried out at high temperatures (200-350 degrees Celsius). Therefore, the research focus of automotive and portable PEMFCs has been the liquid phase recombination (APRM) of methanol. This approach requires a more energy efficient, simpler, and more dense device design to directly integrate the PEMFC stack. However, there is still a need for an effective PEMFC catalyst. Lin et al. disperse Pt at the atomic level on α-MoC, so that hydrogen can be efficiently produced by APRM. The average conversion frequency of this process reaches 18,046 mol H2 per mol Pt per hour, far exceeding the previously reported low temperature. APRM catalyst. They attributed this excellent hydrogen production performance to the excellent activity of α-MoC to promote water decomposition and the synergistic effect of Pt and α-MoC co-activation and recombination of methanol.
5. Electron-hole exchange block and memoryless composite of colloidal quantum dot photoexcited film
(Electron–hole exchange blockade and memory-less recombination in photoexcitedfilms of colloidal quantum dots)
Understanding the charge transport and complex kinetics in photoexcited colloidal quantum dot (QD) solids is critical for their application in optoelectronic devices. Fidler et al. studied the transient photocurrents of electrically coupled, device-level PbSe QD films. It was observed that the amplitude of the photocurrent detected after excitation with a short pulse of 100 fs is virtually independent of the temperature above 6 K, indicating the tunneling mechanism of the previous photoconductivity. The late-time signal exhibits significant thermal activation characteristics, and its characteristic energy is surprisingly robust and independent of the specific type of QD surface treatment. Fidler et al. attribute this phenomenon to the involvement of intrinsic fine structure states, particularly electron-hole exchange interactions, which create an energy barrier for electron-hole separation between adjacent quantum dots. At room temperatures well above the maximum activation energy, the relaxation of the light guide is dominated by unpaired recombination, which involves moving band edge carriers and their opposite signs (pre-existing and photoexcited) present in the interstitial state. Low mobility carriers. When the photocurrent relaxation time is directly related to the instantaneous carrier density, the process causes no memory kinetics. (Nature Physics DOI: 10.1038/NPHYS4073)
6. Functional electronic inversion layer at the wall of the ferroelectric domain
(Functionalelectronic inversion layers at ferroelectric domain walls)
Due to its unique electronic properties, ferroelectric domain walls have a good prospect as a functional two-dimensional material. Of particular interest is the so-called charged wall, where a mismatch in polarity results in a localized, diverging electrostatic potential that requires charge compensation and thus a change in electronic structure. These walls can exhibit significantly enhanced electrical conductivity and serve as circuit paths. However, the development of full-domain wall devices also requires walls with controllable outputs to simulate electronic nano-elements such as diodes and transistors. Mundy et al. demonstrated electric field control of ferroelectric domain wall electron transport and reversible transformation from resistive to conductive at charged walls in semiconductor ErMnO3, correlating the inversion layer as the formation and final activation of charge transport channels . These findings provide new insights into domain wall physics in ferroelectrics and predict the possibility of designing basic digital components for full-domain circuits. (Nature Materials DOI: 10.1038/NMAT4878)
7. Mixed periodicity in van der Waals heterojunction
(Periodic potentials in hybrid van derWaals heterostructures formed by supramolecular lattices on graphene)
The rise of 2D materials has made it possible to form heterostructures that are held together by weaker van der Waals interactions. In such a van der Waals heterostructure, the occurrence of a two-dimensional periodic potential significantly changes the electronic structure of the monolith within the stack, thereby adjusting the properties of the material. However, these periodic potentials are determined by the mechanical alignment of adjacent 2D materials, which is both cumbersome and time consuming. Studies by Gobbi et al. have shown that when graphene is covered by a self-assembled supramolecular lattice, a stable programmable 1D periodic potential can occur over a region extending over 104 nm2. Also, the amplitude and sign of the potential can be changed by using the photosensitive molecule or its reaction product without changing its period. In this respect, supramolecular lattice/double-layer graphene exhibits a mixed analog of a completely inorganic van der Waals heterostructure, highlighting the rich prospects of creating special materials through molecular design. (Nature Communications DOI: 10.1038/ncomms14767)
8. Characteristics of interaction-induced helical band gap in nanowire quantum dot contact
(Signatures of interaction-inducedhelical gaps in nanowire quantum point contacts)
Spin momentum locking in semiconductor devices with strong spin-orbit coupling (SOC) is considered to be an important prerequisite for the formation of the Majorana bound state. This helical state is predicted to be affected by strong Rashba SOC and spin mixing in one-dimensional (1D) nanowires (characterized by characteristic endogenous phenomena in conductance). Heedt et al. reported direct experimental observations of the intrinsic conductance characteristics of the lowest 1D sub-band of InAs nanowires, revealing the formation of helix. Surprisingly, this feature is also very prominent in the absence of a magnetic field. This phenomenon indicates that the exchange interaction has a significant impact on the transmission in the device. Heedt et al. attributed the generation of the èµ energy gap to the spin-flip two-particle backscatter. The full electrification of ideal spiral transmission may have important implications for topological quantum computing. (Nature Physics DOI: 10.1038/NPHYS4070)
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