We report a dual-interfacial engineering approach that uses a sub-20 nm polycrystalline MOF-74 shell as a transition phase to engineer the MOF–polymer interface. The application of a shell MOF layer divides the original single interface problem into two interfaces: MOF–MOF and MOF–polymer, which can be individually addressed. The greater external surface area created by the uneven MOF-74 shell containing high-density open metal sites allows the MOF to interact with 300% polymer at the interface compared to traditional MOF, thereby ensuring good interfacial compatibility. When applied on UiO-66-NH2, its respective mixed-matrix membranes exhibit a simultaneous increase of CO2/CH4 separation selectivity and CO2 permeability with increasing MOF loading, implying a defect-free interface. When applied on MOF-801, the mixed-matrix membranes exhibit an ethylene/ethane separation selectivity up to 5.91, a drastic 76% increase compared to that of the neat polymer owing to a “gas focusing” mechanism promoted by the preferred pore orientation in the MOF-74 layer. This represents one of the most selective ethylene/ethane separation membranes reported to date.

Solar steam generation has attracted interest in recent years as a clean source for power generation and water treatment. To achieve a high rate of steam generation, it is important for the solar evaporator to not only have high photothermal conversion efficiency but also have a large effective surface area for water evaporation. Herein, we report the use of PVA-based composite hydrogels as the solar evaporator, which inner channel sizes were adjusted through an ice-templating method. Although PVA hydrogels have been actively pursued as a promising material for solar steam generation, the influence of inner channel sizes to material performance has not yet been well investigated. Up to this point, the inner channel sizes of most reported PVA-based solar evaporators have been in the range of several to a few tens of micrometers. In this study, we have narrowed the channel size down to submicrometer range by suppressing growth of ice crystals while freezing the hydrogels. Strong capillary force induced by the narrow channels facilitated transport of water over long distances. Therefore, even when the hydrogel was molded into a pillar structure with length of several centimeters, water could be rapidly transported from one end to another, allowing effective evaporation at much increased heights compared to hydrogels with larger channel sizes. The increase in surface area for water evaporation led to a steam generation rate of 6.35 kg m–2 h–1 per water surface area covered by the evaporator under 1 sun illumination (100 mW cm–2), which is significantly higher than previously reported values.

Lithium-rich layered oxides have received great attention due to their high energy density as cathode material. However, the progressive structural transformation from layered to spinel phase triggered by transition-metal migration and the irreversible release of lattice oxygen leads to voltage fade and capacity decay. Here, we report a Fe, Cl codoped and Co-free Li-rich layered cathode with significantly improved structural stability. It is revealed that the Fe and Cl codoping can facilitate the Li-ion diffusion and improve the rate performance of the materials. Moreover, the calculations show that the structural stability is enhanced by Fe and Cl codoping. As a result, the Fe and Cl codopant reduces the irreversible release of lattice oxygen, mitigates voltage fade, and improves the first-cycle Coulombic efficiency. This work provides a low-cost, environmentally friendly, practical strategy for high-performance cathode materials.

Transition metal dichalcogenides, especially MoS2-based materials, have been actively investigated for application as high-performance electrode materials for metal-ion batteries. To further improve the electrochemical behavior of the electrode, it is important to have a strong fundamental understanding of the metal-ion intercalation mechanism. However, much uncertainty and disagreement remain on the structural evolution of MoS2 during the intercalation process due to its complexity. Therefore, in this study, results from multiple approaches including in situ and ex situ X-ray diffraction, in situ Raman spectroscopy, and density functional theory calculations are integrated to construct a comprehensive picture of the structural changes in MoS2 for the different alkali metal (Li, Na, and K) ion battery systems. In addition, the reversibility of such structural changes at different depths of intercalation is further examined. Several notable observations are made in the process. For example, rather than the K1.0MoS2 phase reported in previous studies, a stable K1.5MoS2 phase is identified instead. Also, we find that lithium ions cannot be completely pulled out even at a low concentration of intercalation, which explains the irreversible discharge/charge profile observed for the lithium-ion system. Furthermore, the different alkali metal systems show difference in stability of the Mo–S bond, influencing the cycle stability of the battery. This study demonstrates the value of combining multiple in situ techniques with density functional theory calculations for providing physical insight into the intercalation process and accelerating the rational design of electrode materials for metal-ion batteries.

The rapid development of miniaturized electronic devices has stimulated strong interest in planar microsupercapacitors. Titanium carbide nanosheets (Ti 3 C 2 T x ) have long been considered as an attractive electrode material for such capacitors, given their high pseudocapacitance along with large surface area. State-of-the-art studies with thin films of the nanosheets prepared by methods such as spray-coating have shown specific areal capacitances of a few tens of mF cm −2 and volumetric capacitances of up to 357 F cm −3 . However, most of these results have been obtained from films with thickness over the micrometer range; with the strong interest in portable and transparent devices, it would be favorable to develop ultrathin films with comparable or even improved performance. Herein, the Langmuir−Blodgett (LB) technique is used to produce films of Ti 3 C 2 T x nanosheets with a controllable number of layers, from a single monolayer up to 20 layers. Specific areal capacitances of 1.21 and 5.89 mF cm −2 were obtained from 10 and 20 layer films, respectively, with a retention of ∼90% after 500 cycles. In particular, the thickness of the 20 layer film is ∼140 nm, which gives a volumetric capacitance of nearly 421 F cm −3 . This remarkable performance is attributed to the flat and uniform deposition of the nanosheets in high density for each layer, enabled by the LB technique. This work demonstrates how the LB technique could be utilized for creating high-performance electrodes for planar microsupercapacitors, in particular with film thickness significantly smaller than what can be typically achieved by other methods.