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Redox flow batteries using aqueous organic-based electrolytes are promising candidates for developing cost-effective grid-scale energy storage devices. However, a significant drawback of these batteries is the cross-mixing of active species through the membrane, which causes battery performance degradation. To overcome this issue, here we report size-selective ion-exchange membranes prepared by sulfonation of a spirobifluorene-based microporous polymer and demonstrate their efficient ion sieving functions in flow batteries. The spirobifluorene unit allows control over the degree of sulfonation to optimize the transport of cations, whilst the microporous structure inhibits the crossover of organic molecules via molecular sieving. Furthermore, the enhanced membrane selectivity mitigates the crossover-induced capacity decay whilst maintaining good ionic conductivity for aqueous electrolyte solution at pH 9, where the redox-active organic molecules show long-term stability. We also prove the boosting effect of the membranes on the energy efficiency and peak power density of the aqueous redox flow battery, which shows stable operation for about 120 h (i.e., 2100 charge-discharge cycles at 100 mA cm −2 ) in a laboratory-scale cell. Aqueous organic redox flow batteries are promising for grid-scale energy storage, although their practical application is still limited. Here, the authors report highly ion-conductive and selective polymer membranes, which boost the battery’s efficiency and stability, offering cost-effective electricity storage.

Membranes with fast and selective ion transport are widely used for water purification and devices for energy conversion and storage including fuel cells, redox flow batteries and electrochemical reactors. However, it remains challenging to design cost-effective, easily processed ion-conductive membranes with well-defined pore architectures. Here, we report a new approach to designing membranes with narrow molecular-sized channels and hydrophilic functionality that enable fast transport of salt ions and high size-exclusion selectivity towards small organic molecules. These membranes, based on polymers of intrinsic microporosity containing Tröger’s base or amidoxime groups, demonstrate that exquisite control over subnanometre pore structure, the introduction of hydrophilic functional groups and thickness control all play important roles in achieving fast ion transport combined with high molecular selectivity. These membranes enable aqueous organic flow batteries with high energy efficiency and high capacity retention, suggesting their utility for a variety of energy-related devices and water purification processes. Ion-selective membranes are widely used for water purification and electrochemical energy devices but designing their pore architectures is challenging. Membranes with narrow channels and hydrophilic functionality are shown to exhibit salt ions transport and selectivity towards small organic molecules.

The thermal distillation of crude oil mixtures is an energy-intensive process, accounting for nearly 1% of global energy consumption. Membrane-based separations are an appealing alternative or tandem process to distillation due to intrinsic energy efficiency advantages. We developed a family of spirocyclic polytriazoles from structurally diverse monomers for membrane applications. The resulting polymers were prepared by a convenient step-growth method using copper-catalysed azide–alkyne cycloaddition, providing very fast reaction rates, high molecular weights and solubilities in common organic solvents and non-interconnected microporosity. Fractionation of whole Arabian light crude oil and atmospheric tower bottom feeds using these materials enriched the low-boiling-point components and removed trace heteroatom and metal impurities (comparable performance with the lighter feed as the commercial polyimide, Matrimid), demonstrating opportunities to reduce the energy cost of crude oil distillation with tandem membrane processes. Membrane-based molecular separation under these demanding conditions is made possible by high thermal stability and a moderate level of dynamic chain mobility, leading to transient interconnections between micropores, as revealed by the calculations of static and swollen pore structures.Thermal fractionation of petroleum consumes large amounts of energy. Here stable microporous polymers are synthesized using click chemistry, which have similar performance to commercial polyimides for the fractionation of light crude oils and successful application to heavy feeds under realistic conditions.

Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. However, their structural characterisation represents a significant challenge. Fe-BTC, and the commercial equivalent Basolite® F300, are MOFs with incredibly diverse catalytic ability, yet their disordered structures remain poorly understood. Here, we use advanced electron microscopy to identify a nanocomposite structure of Fe-BTC where nanocrystalline domains are embedded within an amorphous matrix, whilst synchrotron total scattering measurements reveal the extent of local atomic order within Fe-BTC. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. This demonstrates the applicability of this computational approach towards the modelling of other amorphous MOF systems with potential generality towards all MOF chemistries and connectivities. We find that the structures of Fe-BTC and Basolite® F300 can be represented by models containing a mixture of short- and medium-range order with a greater proportion of medium-range order in Basolite® F300 than in Fe-BTC. We conclude by discussing how our approach may allow for high-throughput computational discovery of functional, amorphous MOFs. The structures of amorphous MOFs are challenging to characterise. Here the authors use electron microscopy and pair distribution function methods, coupled with a polymerisation-based algorithm to determine the atomic structure of Fe-BTC, demonstrating the power of this computational approach.

The rational design of disordered frameworks is an appealing route to target functional materials. However, intentional realisation of such materials relies on our ability to readily characterise and quantify structural disorder. Here, we use multivariate analysis of pair distribution functions to fingerprint and quantify the disorder within a series of compositionally identical metal–organic frameworks, possessing different crystalline, disordered, and amorphous structures. We find this approach can provide powerful insight into the kinetics and mechanism of structural collapse that links these materials. Our methodology is also extended to a very different system, namely the melting of a zeolitic imidazolate framework, to demonstrate the potential generality of this approach across many areas of disordered structural chemistry. Structural disorder in materials is challenging to characterise. Here, the authors use multivariate analysis of atomic pair distribution functions to study structural collapse and melting of metal–organic frameworks, revealing powerful mechanistic and kinetic insight.

Porous crystals made to order Controlling and predicting the structural properties of porous molecular crystals would have important implications in gas adsorption, separation and catalysis applications, but remain an unmet goal. This paper introduces a new concept of modular assembly at the molecular level for the formation of porous crystalline solids. Different large chiral molecules with intrinsic nanosize pores, or porous modules, self-assemble through chiral recognition during co-crystallization to produce solid porous frameworks. The three-dimensional structure of the final material can be predicted theoretically. The paper explores four different, albeit analogous, porous modules, which form four different porous solids. Nanoporous molecular frameworks 1 , 2 , 3 , 4 , 5 , 6 , 7 are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores 7 rather than, for example, the functional group localization found in the reactive sites of enzymes 8 . This is a potential limitation for ‘one-pot’ chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores 9 , 10 , 11 , 12 , 13 , 14 , 15 . In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally 16 , 17 , allowing in silico materials design strategies 18 . The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules.

Chiral π -conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2′-dicyano[6]helicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2′-dicyano[6]helicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently ‘turned on’ or ‘turned off’. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies. The properties of chiral conjugated molecules, such as the absorption and/or emission of circularly polarized light or electron transport, are highly anisotropic. Now it has been shown that templating layers can control the orientation and anisotropic properties of small chiral molecules in bulk thin films useful for a range of emerging technologies.

Here we report a two-step, hierarchical synthesis that assembles a trigonal prismatic organic cage into a more symmetric, higher-order tetrahedral cage, or ‘cage of cages’. Both the preformed [2+3] trigonal prismatic cage building blocks and the resultant tetrahedral [4[2+3]+6]cage molecule are constructed using ether bridges. This strategy affords the [4[2+3]+6]cage molecule excellent hydrolytic stability that is not a feature of more common dynamic cage linkers, such as imines. Despite its relatively high molar mass (3,001 g mol −1 ), [4[2+3]+6]cage exhibits good solubility and crystallizes into a porous superstructure with a surface area of 1,056 m 2  g −1 . By contrast, the [2+3] building block is not porous. The [4[2+3]+6]cage molecule shows high CO 2 and SF 6 uptakes due to its polar skeleton. The preference for the [4[2+3]+6]cage molecule over other cage products can be predicted by computational modelling, as can its porous crystal packing, suggesting a broader design strategy for the hierarchical assembly of organic cages with synthetically engineered functions.

Highly permeable and selective membranes are desirable for energy-efficient gas and liquid separations. Microporous organic polymers have attracted significant attention in this respect owing to their high porosity, permeability and molecular selectivity. However, it remains challenging to fabricate selective polymer membranes with controlled microporosity that are stable in solvents. Here we report a new approach to designing crosslinked, rigid polymer nanofilms with enhanced microporosity by manipulating the molecular structure. Ultrathin polyarylate nanofilms with thickness down to 20 nm are formed in situ by interfacial polymerization. Enhanced microporosity and higher interconnectivity of intermolecular network voids, as rationalized by molecular simulations, are achieved by using contorted monomers for the interfacial polymerization. Composite membranes comprising polyarylate nanofilms with enhanced microporosity fabricated in situ on crosslinked polyimide ultrafiltration membranes show outstanding separation performance in organic solvents, with up to two orders of magnitude higher solvent permeance than membranes fabricated with nanofilms made from non-contorted planar monomers. Here it is shown how ultrathin and microporous polymer membranes, fabricated using sterically contorted monomers, can achieve enhanced performance for solvent-based separations.

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