Kitty Nijmeijer

Formation of macrovoids in the membrane structure is a common occurrence in the process of nonsolvent-induced phase separation (NIPS), yet it is often undesired due to low structural homogeneity, poor performance, and introduction of weak mechanical points. Here, we introduce an ether-based solvent, 2,5,7,10-tetraoxaundecane (TOU), for fabrication of macrovoid-free polysulfone (PSf) ultrafiltration (UF) membranes. We investigate how strong polymer–solvent affinity, high chain entanglement, and high viscosity influence the phase-inversion process and promote the formation of homogeneous membrane structures during NIPS. Membranes prepared from PSf/TOU dope solutions exhibited stable sponge-like morphology, without macrovoids, in contrast to PSf membranes prepared from the more common solvent N-methyl-2-pyrrolidone (NMP), which typically display large fingerlike macrovoids. For PSf/TOU systems, mixing ethanol and water in the coagulation bath led to fabrication of porous, permeable membranes while maintaining the macrovoid-free morphology. Membrane performance was further optimized by changing the polymer concentration and the addition of a pore-forming agent in the dope solution. The best-performing membranes showed pure water permeance between 149 and 204 L·m–2·h–1·bar–1 and a bovine serum albumin rejection around 90%. This work establishes TOU as a previously unexplored yet effective solvent for NIPS fabrication of PSf UF membranes, enabling precise control over membrane structure and effective suppression of macrovoid formation and ultimately broadening the design space for PSf membranes.

Organic aerogels are an advanced class of lightweight materials with ultralow thermal conductivity and high porosity, widely used in applications such as thermal insulation, energy storage, and aerospace engineering. Among them, polyimide aerogels stand out for their excellent thermal stability, mechanical strength, and chemical resistance. However, their permanently cross‐linked networks make them non‐recyclable, posing a significant sustainability challenge. Here, a novel closed‐loop recycling approach for polyimide aerogels based on dynamic Diels–Alder chemistry is presented, utilizing an aerogel–sol–aerogel (ASA) process. Matrimid, a commercial polyimide, is post‐functionalized with furfurylamine to form a furan‐modified poly(amide‐imide) (PAI‐FU), which reacts with bismaleimide via a Diels–Alder reaction to create a thermally reversible cross‐linked aerogel network. The resulting poly(amide‐imide) aerogels (PAIAs) exhibit low bulk density (≈ 0.15 g cm ⁻³ ), high porosity (> 87%), ultralow thermal conductivity (16.0 mWm ⁻¹ K ⁻¹ ), excellent thermal stability ( T _d5% ≈ 400 °C), and remarkable mechanical strength (≈ 3.4 MPa). More importantly, PAIAs can be depolymerized at elevated temperatures into soluble oligomers that can be reconstructed into fresh aerogels without catalysts or purification steps. The recycled PAIAs retain their nanostructural morphology and key aerogel‐specific properties, demonstrating efficient closed‐loop recycling. This approach paves the way for advanced and sustainable thermally superinsulating materials.

Background sodium chloride in hydrochloric acid and sodium hydroxide solutions leads to large overpotentials when a bipolar membrane (BPM) is operated under forward bias (FB). Under FB polarization, the accumulation of salt ions at the junction hinders the transport of H⁺ and OH^– ions, thus increasing the mass transport resistance and lowering the water recombination rate. The “ionic blockade” phenomenon is mainly observed if the base is contaminated with Cl^– ions due to the poor OH^–/Cl^– selectivity of the BPM’s anion exchange layer (AEL). This shortcoming is successfully reduced by modifying the AEL with a sub-micrometer thick poly­(benzimidazole) (PBI) coating. Ionic crosslinking between the AEL and PBI leads to a denser interface that enhances the size exclusion of Cl^– ions. Furthermore, the negative charges of deprotonated benzimidazole units at the basic operating conditions contribute to the Donnan exclusion of Cl^– ions, while the OH^– ions can still hop between the alkaline-doped free volumes of the PBI film. The enhanced OH^–/Cl^– selectivity prevents the accumulation of Cl^– ions at the junction and leads to lower overpotentials during the forward bias operation of BPMs in salt-contaminated acid and base. As a result, the PBI-coated BPM has a peak power density 1.6 times higher than that of an uncoated BPM when harvesting electrical energy from a pH gradient. The BPM modification also benefits flow battery applications, as the calculated BPM voltaic efficiency at 100 A/m² (dis)­charge current density is increased from −3.7% to 57% with the addition of the PBI coating.

Bipolar membranes (BPMs) with a layer-by-layer (LbL) assembled montmorillonite (K30 MMT) clay-polyelectrolyte (PE) composite junction coated onto a sulfonated poly(ether ether ketone (SPEEK)) electrospun support are prepared, characterized and their water dissociation performance is analyzed. In particular, the focus is on the effect of the presence of the K30 MMT clay as a catalyst for water dissociation, the bilayer number (three, six, and nine), and the PE strength (poly(ethylenimine) (PEI) as a weak PE and poly(diallyl dimethylammonium chloride) (PDADMAC) as a strong PE) on the BPM performance. The BPMs are prepared by electrospinning and hot pressing SPEEK and the Fumion FAA-3 polymer. Adding the composite multilayers in the BPM junction decreases the membrane area resistance in reverse bias from 560 to 21 Ohms cm² for the best-performing modified BPM. The bilayer number has limited influence on the overall membrane resistance, while the PDADMAC BPMs outperform the PEI BPMs due to the higher and more stable PE and clay adsorptions. Electrochemical impedance spectroscopy shows that the depletion layer thickness decreases exponentially with the number of bilayers as the water dissociation reaction becomes less dependent on the junction electric field. Furthermore, the higher Donnan exclusion at the modified junctions improves the BPM permselectivity 3-fold compared to the BPM containing no catalyst. Altogether, these improvements lead to 6.7 times less energy being used in BPM electrodialysis for the production of acid and base when a BPM with composite LBL junction is used compared to a BPM without catalyst. Thus, adding MMT clay composite LbL catalyst to BPM junctions is a promising method to improve the efficiency and reduce the energy consumption of electrochemical processes that rely on BPMs.

The continued advancement of electrochemical technologies requires an increasingly detailed understanding of the microscopic processes that control their performance, inspiring the development of new multi-modal diagnostic techniques. Here, we introduce a neutron imaging approach to enable the quantification of spatial and temporal variations in species concentrations within an operating redox flow cell. Specifically, we leverage the high attenuation of redox-active organic materials (high hydrogen content) and supporting electrolytes (boron-containing) in solution and perform subtractive neutron imaging of active species and supporting electrolyte. To resolve the concentration profiles across the electrodes, we employ an in-plane imaging configuration and correlate the concentration profiles to cell performance with polarization experiments under different operating conditions. Finally, we use time-of-flight neutron imaging to deconvolute concentrations of active species and supporting electrolyte during operation. Using this approach, we evaluate the influence of cell polarity, voltage bias and flow rate on the concentration distribution within the flow cell and correlate these with the macroscopic performance, thus obtaining an unprecedented level of insight into reactive mass transport. Ultimately, this diagnostic technique can be applied to a range of (electro)chemical technologies and may accelerate the development of new materials and reactor designs.

The continued advancement of electrochemical technologies requires an increasingly detailed understanding of the microscopic processes that control their performance, inspiring the development of new multi-modal diagnostic techniques. Here, we introduce a neutron imaging approach to enable the quantification of spatial and temporal variations in species concentrations within an operating redox flow cell. Specifically, we leverage the high attenuation of redox-active organic materials (high hydrogen content) and supporting electrolytes (boron-containing) in solution and perform subtractive neutron imaging of active species and supporting electrolyte. To resolve the concentration profiles across the electrodes, we employ the in-plane imaging configuration and correlate the concentration profiles to cell performance with polarization measurements under different operating conditions. Finally, we use time-of-flight neutron imaging to deconvolute concentrations of active species and supporting electrolyte during operation. Using this approach, we evaluate the influence of cell polarity, voltage bias, and flow rate on the concentration distribution within the flow cell and correlate these with the macroscopic performance, thus obtaining an unprecedented level of insight into reactive mass transport. Ultimately, this diagnostic technique can be applied to a range of (electro)chemical technologies and may accelerate the development of new materials and reactor designs.

The wire-electrospun layer arrangement and composition of dense SPEEK/PFSA/PVDF membranes for long-term hydrogen-bromine flow battery operation is investigated to ensure durable performance with <50% PFSA utilization and ≤60 μm membrane thickness.

Biomaterials often contain large quantities of water (50-98%), and with the current transition to a more biobased economy, drying these materials will become increasingly important. Contrary to the standard, thermodynamically inefficient chemical and thermal drying methods, dewatering by membrane separation will provide a sustainable and efficient alternative. However, biomaterials can easily foul membrane surfaces, which is detrimental to the performance of current membrane separations. Improving the antifouling properties of such membranes is a key challenge. Other recent research has been dedicated to enhancing the permeate flux and selectivity. In this review, we present a comprehensive overview of the design requirements for and recent advances in dewatering of biomaterials using membranes. These recent developments offer a viable solution to the challenges of fouling and suboptimal performances. We focus on two emerging development strategies, which are the use of electric-field-assisted dewatering and surface functionalizations, in particular with hydrogels. Our overview concludes with a critical mention of the remaining challenges and possible research directions within these subfields.