High-theoretical-capacity silicon anodes hold promise in lithium-ion batteries (LIBs). Nevertheless, their huge volume expansion (∼300%) and poor conductivity show the need for the simultaneous introduction of low-density conductive carbon and nanosized Si to conquer the above issues, yet they result in low volumetric performance. Herein, we develop an integration strategy of a dually encapsulated Si structure and dense structural engineering to fabricate a threedimensional (3D) highly dense Ti 3 C 2 T x MXene and graphene dual-encapsulated Si monolith architecture (HD-Si@Ti 3 C 2 T x @ G). Because of its high density (1.6 g cm −3 ), high conductivity (151 S m −1 ), and 3D dense dual-encapsulated Si architecture, the resultant HD-Si@Ti 3 C 2 T x @G monolith anode displays an ultrahigh volumetric capacity of 5206 mAh cm −3 (gravimetric capacity: 2892 mAh g −1 ) at 0.1 A g −1 and a superior long lifespan of 800 cycles at 1.0 A g −1 . Notably, the thick and dense monolithic anode presents a large areal capacity of 17.9 mAh cm −2 . In-situ TEM and ex-situ SEM techniques, and systematic kinetics and structural stability analysis during cycling demonstrate that such superior volumetric and areal performances stem from its dual-encapsulated Si architecture by the 3D conductive and elastic networks of MXene and graphene, which can provide fast electron and ion transfer, effective volume buffer, and good electrolyte permeability even with a thick electrode, whereas the dense structure results in a large volumetric performance. This work offers a simple and feasible strategy to greatly improve the volumetric and areal capacity of alloy-based anodes for large-scale applications via integrating a dual-encapsulated strategy and dense-structure engineering.

Intricate hollow carbon structures possess vital function for anchoring polysulfides and enhancing the utilization of sulfur in room-temperature sodium–sulfur batteries. However, their synthesis is extremely challenging due to the complex structure. Here, a facile and efficient strategy is developed for the controllable synthesis of N/O-doped multichambered carbon nanoboxes (MCCBs) by selective etching and stepwise carbonization of ZIF-8 nanocubes. The MCCBs consist of porous carbon shells on the outside and connected carbon grids with a hollow structure on the inside, bringing about a MCCBs structure. As a sulfur host, the multichambered structure has better spatial encapsulation and integrated conductivity via the inner interconnected carbon grids, which combines the characteristics of short charge transfer path and superb physicochemical adsorption along with mechanical strength. As expected, the S@MCCBs cathode realizes decent cycle stability (0.045% capacity decay per cycle over 800 cycles at 5 A g–1) and enhanced rate performance (328 mA h g–1 at 10 A g–1). Furthermore, in situ transmission electron microscopy (TEM) observation confirms the good structural stability of the S@MCCBs during the (de)­sodiation process. Our work demonstrates an effective strategy for the rational design and accurate construction of intricate hollow materials for high-performance energy storage systems.

We report the introduction of π-interaction sites into a series of chemically robust metal–organic frameworks (MOFs), MOF-526, -527, and -528, with progressively increased pore size, 1.9–3.7 nm, and the inclusion and release of large organic molecules in water. The mesopores in these MOFs lead to fast adsorption kinetics, whereas the π-interaction between isolated porphyrin units in the MOF backbone and polycyclic structure of the organic guests provides excellent reversibility. Specifically, seven large organic dyes were quantitatively captured by the porphyrin units of these MOFs in a 2:1 molar ratio, exhibiting unprecedented kinetics for MOFs [e.g., 4.54 × 105 L/mol for rhodamine B] at an extremely low concentration (10 ppm) in water. Rotational-echo double-resonance NMR experiments revealed that the distance between the guest molecules and porphyrin units in MOFs was in the range from 3.24 to 3.37 Å, confirming the specific π-interaction. Repetitive and reversible dynamics was achieved in these MOFs for 10 complete inclusion–release cycles without any decay in performance, which is ideally suited for the removal and recycle of large polycyclic organic molecules from water. The performance of MOF-526 rivals that of state-of-the-art carbon and polymers.

Modern technological pressure for propertydirecting structural design of Fe/oxide core−shell nanoparticles (NPs) requires the basic understanding of the formation mechanisms and the ability to effectively tune the structures. In this work, in-depth transmission electron microscopy characterization reveals the formation of an Fe/Fe 3 O 4 core−shell structure when iron NPs were oxidized at room temperature. More importantly, we present the first atomically resolved dynamical images showing the redox reactions in Fe/oxide NPs at high temperature (400−600 °C). The real-time videos show the unambiguous evidence of the reduction and incorporation of oxygen species along the specific interfaces, leading to the reduction of Fe 3 O 4 to FeO and oxidation of Fe to Fe 3 O 4 , which are further investigated based on the theoretical calculations. Meanwhile, it is found that the passive Fe 3 O 4 shell may provide the oxygen ions for the further oxidation of the Fe core at high temperature. These findings contribute to a comprehensive scenario for the structural evolution in metal/oxide nanostructures for improved device design and modeling.

From the mechanical perspectives, the influence of point defects is generally considered at high temperature, especially when the creep deformation dominates. Here, we show the stress-induced reversible oxygen vacancy migration in CuO nanowires at room temperature, causing the unanticipated anelastic deformation. The anelastic strain is associated with the nucleation of oxygen-deficient CuOx phase, which gradually transforms back to CuO after stress releasing, leading to the gradual recovery of the nanowire shape. Detailed analysis reveals an oxygen deficient metastable CuOx phase that has been overlooked in the literatures. Both theoretical and experimental investigations faithfully predict the oxygen vacancy diffusion pathways in CuO. Our finding facilitates a better understanding of the complicated mechanical behaviors in materials, which could also be relevant across multiple scientific disciplines, such as high-temperature superconductivity and solid-state chemistry in Cu-O compounds, etc.