attraction due to their synergistic functions of hydrophilic characteristics, [1,2] superior electrical conductivities, [3] high surface area, [4] efficient electrochemical activities, [5,6] and tunable surface functional groups. [7] Ti 3 C 2 T x MXene nanosheets have been utilized as easy-to-assemble building block units for the fabrication of micro-and nanoarchitectures with multifunctionality, which have been applied to energy storage devices, [1,5,8] optoelectronics, [9,10] electromagnetic interference (EMI) shielding, [11][12][13] wireless communication, [14] and water desalination. [15][16][17] However, during the self-assembly processes, MXene nanosheets are prone to aggregate or restack due to strong van der Waals forces, which largely decreases the accessible surface area and active sites of functional MXene structures. [13,18,19] To scale the synergistic properties of MXene nanosheets to the macroscopic level, one promising strategy is through the construction of foam-like 3D structures, such as aerogels with hierarchical pores. [19,20] To date, various fabrication strategies have been adopted by incorporating external spacers/binders, [8,21] inducing crosslinking reaction between MXene nanosheets, [13,22] and utilizing supporter materials as templates. [23,24] Although these approaches have demonstrated the successful creation of MXene-based aerogels with high porosity, their electrical conductivities and electrochemical Scaling the synergistic properties of MXene nanosheets to microporous aerogel architectures requires effective strategies to overcome the nanosheet restacking without compromising MXene's advantageous properties. Traditional assembly approaches of 3D MXene aerogels normally involve external binders/templates and/or additional functionalization, which sacrifice the electrical conductivities and electrochemical activities of MXene aerogels. Herein, inspired by the hierarchal scale textures of Phrynosoma cornutum, a crumple-textured Ti 3 C 2 T x MXene platform is engineered to facilitate Mg 2+ -induced assembly, enabling conformal formation of large-area Mg 2+ -MXene aerogels without polymeric binders. Through a doctor blading technique and freeze drying, the Mg 2+ -MXene aerogels are produced with customized shapes/dimensions, featuring high surface area (140.5 m 2 g −1 ), superior electrical conductivity (758.4 S m −1 ), and high robustness in water. The highly conductive MXene aerogels show their versatile applications from macroscale technologies (e.g., electromagnetic interference shielding and capacitive deionization (CDI)) to on-chip electronics (e.g., quasi-solidstate microsupercapacitors (QMSCs)). As CDI electrodes, the Mg 2+ -MXene aerogels exhibit high salt adsorption capacity (33.3 mg g −1 ) and long-term operation reliability (over 30 cycles), showing a superb comparison with the literature. Also, the QMSCs with interdigitated Mg 2+ -MXene aerogel electrodes demonstrate high areal capacitances (409.3 mF cm −2 ) with superior power density and energy density compared with ...

Nucleation underlies the formation of many liquid-phase synthetic and natural materials with applications in materials chemistry, geochemistry, biophysics, and structural biology. Most liquid-phase nucleation processes are heterogeneous, occurring at specific nucleation sites at a solid–liquid interface; however, the chemical and topographical identity of these nucleation sites and how nucleation kinetics vary from site-to-site remain mysterious. Here we utilize in situ liquid cell electron microscopy to unveil counterintuitive nanoscale nonuniformities in heterogeneous nucleation kinetics on a macroscopically uniform solid–liquid interface. Time-resolved in situ electron microscopy imaging of silver nanoparticle nucleation at a water–silicon nitride interface showed apparently randomly located nucleation events at the interface. However, nanometric maps of local nucleation kinetics uncovered nanoscale interfacial domains with either slow or rapid nucleation. Interestingly, the interfacial domains vanished at high supersaturation ratio, giving way to rapid spatially uniform nucleation kinetics. Atomic force microscopy and nanoparticle labeling experiments revealed a topographically flat, chemically heterogeneous interface with nanoscale interfacial domains of functional groups similar in size to those observed in the nanometric nucleation maps. These results, along with a semiquantitative nucleation model, indicate that a chemically nonuniform interface presenting different free energy barriers to heterogeneous nucleation underlies our observations of nonuniform nucleation kinetics. Overall, our results introduce a new imaging modality, nanometric nucleation mapping, and provide important new insights into the impact of surface chemistry on microscopic spatial variations in heterogeneous nucleation kinetics that have not been previously observed.

Liquid-phase transmission electron microscopy (LP-TEM) enables real-time imaging of nanoparticle self-assembly, formation, and etching with single nanometer resolution. Despite the importance of organic nanoparticle capping ligands in these processes, the effect of electron beam irradiation on surface-bound and soluble capping ligands during LP-TEM imaging has not been investigated. Here, we use correlative LP-TEM and fluorescence microscopy (FM) to demonstrate that polymeric nanoparticle ligands undergo competing crosslinking and chain scission reactions that nonmonotonically modify ligand coverage over time. Branched polyethylenimine (BPEI)-coated silver nanoparticles were imaged with dose-controlled LP-TEM followed by labeling their primary amine groups with fluorophores to visualize the local thickness of adsorbed capping ligands. FM images showed that free ligands crosslinked in the LP-TEM image area over imaging times of tens of seconds, enhancing local capping ligand coverage on nanoparticles and silicon nitride membranes. Nanoparticle surface ligands underwent chain scission over irradiation times of minutes to tens of minutes, which depleted surface ligands from the nanoparticle and silicon nitride surface. Conversely, solutions of only soluble capping ligand underwent successive crosslinking reactions with no chain scission, suggesting that nanoparticles enhanced the chain scission reactions by acting as radiolysis hotspots. The addition of a hydroxyl radical scavenger, tert-butanol, eliminated chain scission reactions and slowed the progression of crosslinking reactions. These experiments have important implications for performing controlled and reproducible LP-TEM nanoparticle imaging as they demonstrate that the electron beam can significantly alter ligand coverage on nanoparticles in a nonintuitive manner. They emphasize the need to understand and control the electron beam radiation chemistry of a given sample to avoid significant perturbations to the nanoparticle capping ligand chemistry, which are invisible in electron micrographs.

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