Interfacial electronic structure engineering on molybdenum sulfide for robust dual-pH hydrogen evolution.

Molybdenum disulfide, as an electronic highly-adjustable catalysts material, tuning its electronic structure is crucial to enhance its intrinsic hydrogen evolution reaction (HER) activity. Nevertheless, there are yet huge challenges to the understanding and regulation of the surface electronic structure of molybdenum disulfide-based catalysts. Here we address these challenges by tuning its electronic structure of phase modulation synergistic with interfacial chemistry and defects from phosphorus or sulfur implantation, and we then successfully design and synthesize electrocatalysts with the multi-heterojunction interfaces (e.g., 1T0.81-MoS2@Ni2P), demonstrating superior HER activities and good stabilities with a small overpotentials of 38.9 and 95 mV at 10 mA/cm2, a low Tafel slopes of 41 and 42 mV/dec in acidic as well as alkaline surroundings, outperforming commercial Pt/C catalyst and other reported Mo-based catalysts. Theoretical calculation verified that the incorporation of metallic-phase and intrinsic HER-active Ni-based materials into molybdenum disulfide could effectively regulate its electronic structure for making the bandgap narrower. Additionally, X-ray absorption spectroscopy indicate that reduced nickel possesses empty orbitals, which is helpful for additional H binding ability. All these factors can decrease Mo-H bond strength, greatly improving the HER catalytic activity of these materials.

Perovskite Quantum Dots Encapsulated in a Mesoporous Metal-Organic Framework as Synergistic Photocathode Materials.

Metal halide perovskite quantum dots, with high light-absorption coefficients and tunable electronic properties, have been widely studied as optoelectronic materials, but their applications in photocatalysis are hindered by their insufficient stability because of the oxidation and agglomeration under light, heat, and atmospheric conditions. To address this challenge, herein, we encapsulated CsPbBr3 nanocrystals into a stable iron-based metal-organic framework (MOF) with mesoporous cages (∼5.5 and 4.2 nm) via a sequential deposition route to obtain a perovskite-MOF composite material, CsPbBr3@PCN-333(Fe), in which CsPbBr3 nanocrystals were stabilized from aggregation or leaching by the confinement effect of MOF cages. The monodispersed CsPbBr3 nanocrystals (4-5 nm) within the MOF lattice were directly observed by transmission electron microscopy and corresponding mapping analysis and further confirmed by powder X-ray diffraction, infrared spectroscopy, and N2 adsorption characterizations. Density functional theory calculations further suggested a significant interfacial charge transfer from CsPbBr3 quantum dots to PCN-333(Fe), which is ideal for photocatalysis. The CsPbBr3@PCN-333(Fe) composite exhibited excellent and stable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities in aprotic systems. Furthermore, CsPbBr3@PCN-333(Fe) composite worked as the synergistic photocathode in the photoassisted Li-O2 battery, where CsPbBr3 and PCN-333(Fe) acted as optical antennas and ORR/OER catalytic sites, respectively. The CsPbBr3@PCN-333(Fe) photocathode showed lower overpotential and better cycling stability compared to CsPbBr3 nanocrystals or PCN-333(Fe), highlighting the synergy between CsPbBr3 and PCN-333(Fe) in the composite.

Isolated copper single sites for high-performance electroreduction of carbon monoxide to multicarbon products.

Electrochemical carbon monoxide reduction is a promising strategy for the production of value-added multicarbon compounds, albeit yielding diverse products with low selectivities and Faradaic efficiencies. Here, copper single atoms anchored to Ti3C2Tx MXene nanosheets are firstly demonstrated as effective and robust catalysts for electrochemical carbon monoxide reduction, achieving an ultrahigh selectivity of 98% for the formation of multicarbon products. Particularly, it exhibits a high Faradaic efficiency of 71% towards ethylene at -0.7 V versus the reversible hydrogen electrode, superior to the previously reported copper-based catalysts. Besides, it shows a stable activity during the 68-h electrolysis. Theoretical simulations reveal that atomically dispersed Cu-O3 sites favor the C-C coupling of carbon monoxide molecules to generate the key *CO-CHO species, and then induce the decreased free energy barrier of the potential-determining step, thus accounting for the high activity and selectivity of copper single atoms for carbon monoxide reduction.

Estimation of the spatial distribution of Frenkel defects in NiFe2O4 by simulation of HAADF-STEM images.

Accurate determination of the atomic spatial configuration of Frenkel defects is important for understanding the mechanism and fully utilizing these defects to optimize the material properties. In this study, aberration-corrected scanning transmission electron microscopy (STEM) was used to identify the Fe vacancies and Fe Frenkel defect pairs, which have not been previously investigated, in NiFe2O4 (NFO). The spatial distribution of these point defects is determined by comparing the experimental and simulated images, where the experimental image intensities are consistent with the calculated image intensities. We confirmed the stabilities of the observed point defect configurations and calculated their electronic structures using density functional theory. A comprehensive understanding of the relationship between the Frenkel defect spatial configurations and electronic properties is obtained, which provides an alternative method to regulate the NFO performance.