Self‐Assembly of MXene‐Surfactants at Liquid–Liquid Interfaces: From Structured Liquids to 3D Aerogels

2D transition metal carbides and nitrides (MXenes), a class of emerging nanomaterials with intriguing properties, have attracted significant attention in recent years. However, owing to the highly hydrophilic nature of MXene nanosheets, assembly strategies of MXene at liquid–liquid interfaces have been very limited and challenging. Herein, through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface, we report the formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), which can significantly enhance the interfacial activity of MXene nanosheets. More importantly, this simple assembly strategy opens a new platform for the fabrication of functional MXene assemblies from mesoscale (e.g., structured liquids) to macroscale (e.g., aerogels), that can be used for a range of applications, including nanocomposites, electronic devices, and all‐liquid microfluidic devices.     

Visual Chemical Detection Mechanism by a Liquid Gating System with Dipole‐Induced Interfacial Molecular Reconfiguration

Chemical detection has a wide range of applications. The detection of a certain substance is so vital that new detection mechanisms with features such as low‐cost, accessibility, and readily available visual markers are in demand. Herein, a liquid‐gating‐based chemical‐detection mechanism is reported, which has a dynamic gas/liquid interface due to dipole‐induced interfacial molecular reconfiguration. The mechanism exhibits a sensitive relationship between the dipole‐force‐induced rearrangement of interfacial molecules and transmembrane gating behavior. These features can be utilized to create visual markers for detection by converting the analyte‐mediated interfacial interaction to a pressure‐driven marker movement. This “green” detection mechanism requires no electrical energy input and has readily available markers for anyone to observe directly. This new mechanism opens a window for a more in‐depth exploration of combining liquid‐gating mechanisms with detection mechanisms.     

Electroless Formation of Hybrid Lithium Anodes for Fast Interfacial Ion Transport

Rechargeable batteries based on metallic anodes are of interest for fundamental and application‐focused studies of chemical and physical kinetics of liquids at solid interfaces. Approaches that allow facile creation of uniform coatings on these metals to prevent physical contact with liquid electrolytes, while enabling fast ion transport, are essential to address chemical instability of the anodes. Here, we report a simple electroless ion‐exchange chemistry for creating coatings of indium on lithium. By means of joint density functional theory and interfacial characterization experiments, we show that In coatings stabilize Li by multiple processes, including exceptionally fast surface diffusion of lithium ions and high chemical resistance to liquid electrolytes. Indium coatings also undergo reversible alloying reactions with lithium ions, facilitating design of high‐capacity hybrid In‐Li anodes that use both alloying and plating approaches for charge storage. By means of direct visualization, we further show that the coatings enable remarkably compact and uniform electrodeposition. The resultant In‐Li anodes are shown to exhibit minimal capacity fade in extended galvanostatic cycling when paired with commercial‐grade cathodes.     

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation

Herein, we describe a new class of porous composites comprising metal–organic framework (MOF) crystals confined in single spherical matrices made of packed covalent‐organic framework (COF) nanocrystals. These MOF@COF composites are synthesized through a two‐step method of spray‐drying and subsequent amorphous (imine‐based polymer)‐to‐crystalline (imine‐based COF) transformation. This transformation around the MOF crystals generates micro‐ and mesopores at the MOF/COF interface that provide far superior porosity compared to that of the constituent MOF and COF components added together. We report that water sorption in these new pores occurs within the same pressure window as in the COF pores. Our new MOF@COF composites, with their additional pores at the MOF/COF interface, should have implications for the development of new composites.     

A Robust Solid Electrolyte Interphase Layer Augments the Ion Storage Capacity of Bimetallic‐Sulfide‐Containing Potassium‐Ion Batteries

Metal–organic framework‐derived NiCo_2.5S₄ microrods wrapped in reduced graphene oxide (NCS@RGO) were synthesized for potassium‐ion storage. Upon coordination with organic potassium salts, NCS@RGO exhibits an ultrahigh initial reversible specific capacity (602 mAh g^?1 at 50 mA g^?1) and ultralong cycle life (a reversible specific capacity of 495 mAh g^?1 at 200 mA g^?1 after 1 900 cycles over 314 days). Furthermore, the battery demonstrates a high initial Coulombic efficiency of 78 %, outperforming most sulfides reported previously. Advanced ex situ characterization techniques, including atomic force microscopy, were used for evaluation and the results indicate that the organic potassium salt‐containing electrolyte helps to form thin and robust solid electrolyte interphase layers, which reduce the formation of byproducts during the potassiation–depotassiation process and enhance the mechanical stability of electrodes. The excellent conductivity of the RGO in the composites, and the robust interface between the electrodes and electrolytes, imbue the electrode with useful properties; including, ultrafast potassium‐ion storage with a reversible specific capacity of 402 mAh g^?1 even at 2 A g^?1.     

Anisotropically Electrochemical–Mechanical Evolution in Solid‐State Batteries and Interfacial Tailored Strategy

All‐solid‐state batteries have attracted attention owing to the potential high energy density and safety; however, little success has been made on practical applications of solid‐state batteries, which is largely attributed to the solid–solid interface issues. A fundamental elucidation of electrode–electrolyte interface behaviors is of crucial significance but has proven difficult. The interfacial resistance and capacity fading issues in a solid‐state battery were probed, revealing a heterogeneous phase transition evolution at solid–solid interfaces. The strain‐induced interfacial change and the contact loss, as well as a dense metallic surface phase, deteriorate the electrochemical reaction in solid‐state batteries. Furthermore, the in situ growth of electrolytes on secondary particles is proposed to fabricate robust solid–solid interface. Our study enlightens new insights into the mechanism behind solid–solid interfacial reaction for optimizing advanced solid‐state batteries.     

The Effect of Methylammonium Iodide on the Supersaturation and Interfacial Energy of the Crystallization of Methylammonium Lead Triiodide Single Crystals

It is very important to study the crystallization of hybrid organic–inorganic perovskites because their thin films are usually prepared from solution. The investigation on the growth of perovskite films is however limited by their polycrystallinity. In this work, methylammonium lead triiodide single crystals grown from solutions with different methylammonium iodide (MAI):lead iodide (PbI₂) ratios were investigated. We observed a V‐shaped dependence of the crystallization onset temperature on the MAI:PbI₂ ratio. This is attributed to the MAI effects on the supersaturation of precursors and the interfacial energy of the crystal growth. At low MAI:PbI₂ ratio (<1.7), more MAI leads to the supersaturation of the precursors at lower temperature. At high MAI:PbI₂ ratio, the crystal growing plans change from (100)‐plane dominated to (001)‐plane dominated. The latter have higher interfacial energy than the former, leading to a higher crystallization onset temperature.     

Stabilizing Liquids Using Interfacial Supramolecular Polymerization

The strong electrostatic interactions at the oil–water interface between a small molecule, 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphyrin, H₆TPPS, dissolved in water, and an amine terminated hydrophobic polymer dissolved in oil are shown to produce a supramolecular polymer surfactant (SPS) of H₆TPPS at the interface with a binding energy that is sufficiently strong to allow an intermolecular aggregation of the supramolecular polymers. SPSs at the oil–water interface are confirmed by in situ real‐space atomic force microcopy imaging. The assemblies of these aggregates can jam at the interface, opening a novel route to kinetically trap the liquids in non‐equilibrium shapes. The elastic film, comprised of SPSs, wrinkles upon compression, providing a strategy to stabilize liquids in non‐equilibrium shapes.     

A Rutile TiO2 Electron Transport Layer for the Enhancement of Charge Collection for Efficient Perovskite Solar Cells

Interfacial charge collection efficiency has demonstrated significant effects on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, crystalline phase‐dependent charge collection is investigated by using rutile and anatase TiO₂ electron transport layer (ETL) to fabricate PSCs. The results show that rutile TiO₂ ETL enhances the extraction and transportation of electrons to FTO and reduces the recombination, thanks to its better conductivity and improved interface with the CH₃NH₃PbI₃ (MAPbI₃) layer. Moreover, this may be also attributed to the fact that rutile TiO₂ has better match with perovskite grains, and less trap density. As a result, comparing with anatase TiO₂ ETL, MAPbI₃ PSCs with rutile TiO₂ ETL delivers significantly enhanced performance with a champion PCE of 20.9 % and a large open circuit voltage (V_OC) of 1.17 V.     

Interfacial Defect Engineering for Improved Portable Zinc–Air Batteries with a Broad Working Temperature

Atomic‐thick interfacial dominated bifunctional catalyst NiO/CoO transition interfacial nanowires (TINWs) with abundant defect sites display high electroactivity and durability in the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations show that the excellent OER/ORR performance arises from the electron‐rich interfacial region coupled with defect sites, thus enabling a fast‐redox rate with lower activation barrier for fast electron transfer. When assembled as an air‐electrode, NiO/CoO TINWs delivered the high specific capacity of 842.58 mAh g_Zn^?1, the large energy density of 996.44 Wh kg_Zn^?1 with long‐time stability of more than 33 h (25 °C), and superior performance at low (?10 °C) and high temperature (80 °C).     

Revealing an Interconnected Interfacial Layer in Solid‐State Polymer Sodium Batteries

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na‐metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid‐state polymer Na‐metal batteries, using a high mass loaded Na₃V₂(PO₄)₃ cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability.     

Coagulated SnO2 Colloids for High‐Performance Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Stability

Organic–inorganic perovskite solar cells with a planar architecture have attracted much attention due to the simple structure and easy fabrication. However, the power conversion efficiency and hysteresis behavior need to be improved for planar‐type devices where the electron transport layer is vital. SnO₂ is a promising alternative for TiO₂ as the electron transport layer owing to the high charge mobility and chemical stability, but the hysteresis issue can still remain despite the use of SnO₂. Now, a facile and effective method is presented to simultaneously tune the electronic property of SnO₂ and passivate the defects at the interface between the perovskite and SnO₂. The perovskite solar cells with ammonium chloride induced coagulated SnO₂ colloids exhibit a power conversion efficiency of 21.38 % with negligible hysteresis, compared to 18.71 % with obvious hysteresis for the reference device. The device stability can also be significantly improved.