On-Water Surface Synthesis of Two-Dimensional Polymer Membranes for Sustainable Energy Devices

Enhancing Selective Ion Transport by Stacking Covalent Organic Framework Monolayers

Nanopore-based power generation represents an efficient way for harvesting salinity gradient energy. Due to its ultrahigh ion conductivity and moderate ion selectivity, the crystalline covalent organic framework (COF) monolayer demonstrates the record-high output power density by mixing river water and seawater. To further improve energy conversion performance, it is necessary to enhance ion selectivity while achieving high membrane permeability. Here, a layer-by-layer stacking approach is developed to notably enhance the selective ion transport of ultra-thin COF layers, offering advantageous in both conversion efficiency and scalability. Under a standard NaCl salinity gradient (0.5 M/0.1 M), the ratio of ionic mobility between Cl- and Na+ increases from 1.4 to 2.9 with stacking the anion-selective COF monolayer from one to ten layers, leading to a more than seven-fold enhancement in osmotic energy conversion efficiency. By maximizing selectivity and permeability, the output power can reach 411 pW by stacking three layers in a single device. This strategy provides an effective approach for the integration of atomically thin membranes in selective mass transport applications.

Surfactant-Assisted Construction of Covalent Organic Frameworks

Covalent organic frameworks (COFs), characterized by their unique ordered pore structures, chemical diversity, and high degree of designability, have demonstrated immense application potential across multiple fields. However, traditional synthesis methods often encounter challenges such as low crystallinity and uneven morphology. The introduction of surfactants has opened up new pathways for the synthesis of COFs. Leveraging their intermolecular interactions and self-assembly properties, surfactants can effectively regulate the nucleation, growth processes, and ultimate structure and properties of COFs. This paper systematically reviews the latest research achievements and future trends in surfactant-assisted COF synthesis, emphasizing the crucial role of surfactants as key additives in the preparation of COFs. Surfactants not only facilitate uniform nucleation and growth of COFs, enhancing the crystallinity and structural order of the products but also enable precise and diverse regulation of the dimensionality, morphology, and structure of COFs. Furthermore, by influencing the dispersion and processability of COFs, surfactants enhance their practicality and workability. Finally, the paper presents some prospects for the challenges and future opportunities in this emerging research area.

Enhancing the Performance of Fluorinated Graphdiyne Moisture Cells via Hard Acid-Base Coordination of Aluminum Ions

Moisture-enabled electric generators (MEGs) are emerging as a transformative energy technology, capable of directly converting ambient moisture into electrical energy without producing pollutants or harmful emissions. However, the widespread application of MEGs is hindered by challenges such as intermittent output and low current densities, which limit power density and prevent large-scale integration. Here, a novel moisture cell based on Al ion-F coordination-specifically, a fluorinated graphdiyne (FGDY) Al-ion moisture cell (FGDY AlMC) is introduced. This new moisture cell achieves an exceptionally high mass-specific power density of 371.36 µW g-¹, stable output (0.65 V for 15 h), and broad applicability across varying humid environments. Density functional theory (DFT) calculations reveal that the large-pore molecular structure of FGDY significantly reduces the diffusion barriers for Al ions compared to other 2D carbon materials. Furthermore, the F atoms as "hard base" on FGDY effectively coordinate with "hard acid" Al ions, enhancing ionic conductivity, accelerating ion migration, and promoting the generation of a higher number of mobile cations. These combined advantages lead to a marked improvement in the performance of the FGDY AlMC. These findings position Al ion coordinated FGDY as a highly promising candidate for the development of high-performance MEG active materials.

Advances in synthetic strategies for two-dimensional conjugated polymers

Two-dimensional conjugated polymers (2D CPs) are typically represented by 2D conjugated covalent organic frameworks (COFs) that consist of covalently cross-linked linear conjugated polymers, which possess extended in-plane π-conjugation and out-of-plane electronic couplings. The precise incorporation of molecular building blocks into ordered polymer frameworks through (semi)reversible 2D polycondensation methodologies enables the synthesis of novel polymer semiconductors with designable and predictable properties for various (opto)electronic, spintronic, photocatalytic, and electrochemical applications. Linkage chemistry lays the foundation for this class of synthetic materials and provides a library for subsequent investigations. In this review, we summarize recent advances in synthetic strategies for 2D CPs. By exploring synthetic approaches and the intricate interplay between chemical structure, the efficiency of 2D conjugation, and related physicochemical properties, we are expected to guide readers with a general background in synthetic chemistry and those actively involved in electronic device research. Furthermore, the discussion will appeal to researchers intrigued by the prospect of uncovering novel physical phenomena or mechanisms inherent in these emerging polymer semiconductors. Finally, future research directions and perspectives of highly crystalline and processable 2D CPs for electronics and other cutting-edge fields are discussed.

Physics and Chemistry of Two-Dimensional Triangulene-Based Lattices

ConspectusTriangulene (TRI) and its heterotriangulene (HT) derivatives are planar, triangle-shaped molecules that, via suitable coupling reactions, can form extended organic two-dimensional (2D) crystal (O2DC) structures. While TRI is a diradical, HTs are either closed-shell molecules or monoradicals which can be stabilized in their cationic form.Triangulene-based O2DCs have a characteristic honeycomb-kagome lattice. This structure gives rise to four characteristic electronic bands: two of them form Dirac points, while the other two are flat and sandwich the Dirac bands. Functionalization and heteroatoms are suitable means to engineer this band structure. Heteroatoms like boron and nitrogen shift the Fermi level upward and downward, respectively, while bridging groups and functionalized triangulene edges can introduce a dispersion to the flat bands.The stable backbone architecture makes 2D HT-polymers ideal for photoelectrochemical applications: (i) bridge functionalization can tune the band gap and maximize absorption, (ii) the choice of the center atom (B or N) controls the band occupation and shifts the Fermi level with respect to vacuum, allowing in some cases for overpotential-free photon-driven surface reactions, and (iii) the large surface area allows for a high flux of educts and products.The spin polarization in TRI and in open-shell HTs is maintained when linking them to dimers or extended frameworks with direct coupling or more elaborate bridging groups (acetylene, diacetylene, and phenyl). The dimers have a high spin-polarization energy and some of them are strongly magnetically coupled, resulting in stable high-spin or broken-symmetry (BS) low-spin systems. As O2DCs, some systems become antiferromagnetic Mott insulators with large band gaps, while others show Stoner ferromagnetism, maintaining the characteristic honeycomb-kagome bands but shifting the opposite spin-polarized bands to different energies. For O2DCs based on aza- and boratriangulene (monoradicals as building blocks), the Fermi level is shifted to a spin-polarized Dirac point, and the systems have a Curie temperature of about 250 K. For half-filled (all-carbon) systems, the Ovchinnikov rule or, equivalently, Lieb's theorem, is sufficient to predict the magnetic ordering of the systems, while the non-half-filled systems (i.e., those with heteroatoms) obey the more involved Goodenough-Kanamori rule to interpret the magnetism on the grounds of fundamental electronic interactions.There remain challenges in experiment and in theory to advance the field of triangulene-based O2DCs: Coupling reactions beyond surface chemistry have to be developed to allow for highly ordered, extended crystals. Multilayer structures, which are unexplored to date, will be inevitable in alternative synthesis approaches. The predictive power of density-functional theory (DFT) within state-of-the-art functionals is limited for the description of magnetic couplings in these systems due to the apparent multireference character and the large spatial extension of the spin centers.