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Abstract Recent studies of the high energy‐conversion efficiency of the nanofluidic platform have revealed the enormous potential for efficient exploitation of electrokinetic phenomena in nanoporous membranes for clean‐energy harvesting from salinity gradients. Here, nanofluidic reverse electrodialysis (NF‐RED) consisting of vertically aligned boron‐nitride‐nanopore (VA‐BNNP) membranes is presented, which can efficiently harness osmotic power. The power density of the VA‐BNNP reaches up to 105 W m⁻², which is several orders of magnitude higher than in other nanopores with similar pore sizes, leading to 165 mW m⁻²of net power density (i.e., power per membrane area). Low‐pressure chemical vapor deposition technology is employed to uniformly deposit a thin BN layer within 1D anodized alumina pores to prepare a macroscopic VA‐BNNP membrane with a high nanopore density, ≈10⁸pores cm⁻². These membranes can resolve fundamental questions regarding the ion mobility, liquid transport, and power generation in highly charged nanopores. It is shown that the transference number in the VA‐BNNP is almost constant over the entire salt concentration range, which is different from other nanopore systems. Moreover, it is also demonstrated that the BN deposition on the nanopore channels can significantly enhance the diffusio‐osmosis velocity by two orders of magnitude at a high salinity gradient, resulting in a huge increase in power density. 

Abstract Understanding the behavior of confined matter within Van der Waals (VdW) materials is complicated due to the interplay of various factors, including the VdW interaction between the interlayers, the layer interaction with the matter, and the bending strain energy of the layers to accommodate encapsulation. Herein, new insight on the magnitude of pressure and density of water entrapped within confined spaces in VdW materials is provided. This is accomplished by studying the plasmon excitation of water encapsulated between two sheets of graphene membranes in an aberration‐corrected scanning transmission electron microscope. The results indicate ≈12% maximum increase in the density of water under tight graphene encasement, where pressure as high as 400 MPa is expected. The pressure estimation from theoretical analysis considering the effect of VdW forces, Laplace pressure, and strain energy is in agreement with the experimental results. The findings of this work open new opportunities to explore the local physical state of not only water but also other liquid materials under high pressure with imaging and analytical resolutions never achieved before. 

Abstract Calcium oxalate (CaOx) is the major phase in kidney stones and the primary calcium storage medium in plants. CaOx can form crystals with different lattice types, water contents, and crystal structures. However, the conditions and mechanisms leading to nucleation of particular CaOx crystals are unclear. Here, liquid‐cell transmission electron microscopy and atomistic molecular dynamics simulations are used to study in situ CaOx nucleation at different conditions. The observations reveal that rhombohedral CaOx monohydrate (COM) can nucleate via a classical pathway, while square COM can nucleate via a non‐classical multiphase pathway. Citrate, a kidney stone inhibitor, increases the solubility of calcium by forming calcium‐citrate complexes and blocks oxalate ions from approaching calcium. The presence of multiple hydrated ionic species draws additional water molecules into nucleating CaOx dihydrate crystals. These findings reveal that by controlling the nucleation pathways one can determine the macroscale crystal structure, hydration state, and morphology of CaOx.