Improving the thermal conductivity of zeolite adsorbents is essential for enhancing the efficiency of thermal swing adsorption (TSA) processes in CO2 capture. In this work, zeolite Y was combined with two types of carbon-based thermal conductive enhancers, expanded natural graphite (ENG) and graphene nanosheets (GRA), to form zeolite-carbon composites. Structural analysis confirmed that the incorporation of carbon additives did not damage the zeolite framework, although the addition of non-porous carbon led to a decrease in surface area and micropore volume. Measurements with a transient hot disk method revealed that the incorporation of ENG and GRA could remarkably enhance the thermal conductivity of zeolite Y-carbon composites. A 7-fold increase in thermal conductivity, from 0.107 to 0.762 Wm-1K-1, was achieved by adding 5wt.% of GRA, whereas a comparable improvement with ENG required a much higher loading of about 30 wt.%. Infrared thermography on packed composite powder on a heated plate indicated that the heat transfer through the composites with improved thermal conductivity is significantly faster compared to plain zeolite. CO2 adsorption measurements indicated that both additives reduced the CO2 uptake capacity, but the loss was significantly smaller for the graphene composites (at 5 wt.% addition), which retained most of the micropore volume. Ideal adsorbed solution theory calculations further showed that the zeolite Y-GRA composites maintained reasonably high CO2/N2 selectivity, though lower than pristine zeolite Y. In conclusion, the zeolite-graphene composites present a promising pathway to improve the intrinsic thermal limitations of zeolite sorbents, enabling faster heating and cooling cycles and improved productivity in TSA-based carbon capture systems.

The transition towards safe, low-carbon, efficient energy storage and transportation is supported by the development of solid-state ammonia storage systems. Chemisorbents including alkaline earth metal halides (AEMHs), such as strontium chloride (SrCl2), have been studied for ammonia (NH3) sorption and delivery due to their high NH3 uptake. However, the volume expansion/shrinkage of AEMHs during sorption/desorption cycle significantly compromises their practical use. To improve structural stability, structuring additives (zeolites, graphite, metal-organic frameworks) have been studied, but often rely on nonrenewable components or complex fabication techniques, hindering scalability. In this study, microfibrillated cellulose (MFC) wa used as a structuring matrix for SrCl2, forming a highly porous composite called FCSr throuh a simple freeze-casting/drying with varying solid/water ratios. The resulting structure reched a porosity as high as 97% and was characterized by SEM, XMT, and FTIR. FCSr specimens could be loaded up to 90wt% of SrCl2 salt resulting in a gravimetric NH3 uptake of 43.5mmol.g-1, with mechanical and structural integrity and sorption kinetics 2.4 times faster than SrCl2 bulk of the same mass. In this study, sorption kinetics benefited from lower-density structures that promoted NH3 diffusion, though increased porosity reduced mechanical strength. A figure of merit analysis revealed that an optimal balance between sorption performance and structural integrity was achieved at 60wt% of SrCl2 in the structured composite.

Icing phenomena on wind turbine blades and components are a major problem, causing downtimes that increase maintenance costs, reducing the blade’s lifespan, or in severe cases, even leading to component damage. A nanofiber-based bi-layer liquid-infused surface (BLIS) coating was prepared and characterized, combining good adhesion to wind turbine blades with low ice adhesion. The BLIS coating was produced by a new method combining electrospinning and a heat treatment step, containing a poly ethyl-2-cyanoacrylate (PECA)-based adhesive layer, a slippery layer of poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer, and an infiltrated perfluoropolyether lubricant. Thermogravimetric analysis (TGA) was used to ensure the thermal stability of the polymers in the nanofiber coating layers and to optimize the heat treatment process of the layers. Microstructural changes were studied by scanning electron microscopy (SEM) and surface roughness measurements. Contact angle measurements and sliding velocity tests on wind turbine blade segments at icing conditions of 0 °C and +5 °C indicate that the water sliding properties of the BLIS coating were improved compared to uncoated blades. In addition, coated blade segments showed a 50% lower ice adhesion strength than uncoated blades.

Solid-state ammonia storage supports the transition towards safe and efficient low-carbon energy storage and transportation. Alkaline earth metals halides (AEMHs) based materials, such as strontium chloride (SrCl2), can be utilized to efficiently store ammonia with high capacity and mitigate ammonia toxicity but suffer from large volume expansion during ammonia absorption and slow thermal desorption kinetics. Here, SrCl2 was structured into SrCl2-carbon nanofiber composites (SrCs) by electrospinning and a subsequent three-step carbonization process. Polyvinylpyrrolidone (PVP) was used as a carrier polymer in water/ethanol solution in electrospinning and as a carbon source for stabilizing SrCs with high SrCl2 loadings. Chemical and structural changes of the nanofiber structures during carbonization were investigated with different surface characterization techniques, including XRD, SEM, and FTIR. The SrCs could be loaded with up to 90 wt% of SrCl2 salt, resulting in remarkable high, and stable ammonia sorption uptake capacity of 671 mg/g over four cycles, mechanical integrity and more than 4 times faster desorption kinetics compared to SrCl2 powder.

Bimetallic Metal-Organic Frameworks (MOFs) of silver, copper and the ligand benzene 1,3,5-tricarboxylate (AgCu-BTC MOFs), derived from Cu-BTC (HKUST-1), have been synthesized by fast co-precipitation method and investigated for CO2 reduction reaction (CO2RR). Three AgCu-BTC MOF variants were synthesized with varying Ag content: AgCu-1 (9.4 at.%), AgCu-2 (12.5 at.%), and AgCu-3 (16.5 at.%). A range of structural characterization techniques, including SEM-EDS, XRD, FTIR, and XPS, were utilized, revealing the formation of low-crystalline AgCu-BTC MOF with Ag+1 in an ionic state coordinated to the BTC framework. The investigation focused on CO2 reduction using humidified CO2 gas with bimetallic AgCu MOFs as electrocatalysts in a zero-gap MEA setup. The setup included a gas diffusion electrode (GDE) with a Sustainion Anion exchange membrane and bicarbonate as the anolyte. Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) showed that the AgCu-3 MOF, with the highest silver content (16.5 at.%), exhibited a lower onset potential at -0.65 V vs Ag/AgCl compared to pristine Cu-BTC MOF owing to the better activity with Ag inclusion. Constant potential (CP) experiments combined with product analysis indicated that AgCu-3 MOF predominantly produced CO and H2 as the main products, achieving a faradaic efficiency of approximately 60% for CO production and 5% for hydrogen production. Moreover, reducing the humidity level in the inlet CO2 gas stream from 80% to 20% RH increased CO production by 2-fold, simultaneously suppressing the HER. This reduction in humidity resulted in an increased local concentration of CO2 at the catalyst site, leading to an enhanced CO2RR rate. SEM and FTIR investigations after the CP experiment demonstrated the instability of the AgCu-3 MOF, revealing substantial morphological changes under humid CO2 conditions.

A modified Metal-Organic Framework UiO-66-NH2-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO2 reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH2 catalyst. The highest energy-to-fuel conversion efficiency of 1.06 % towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the photoelectrodes in photoelectrochemical electrolyzers can impact the CO2 reduction efficiency and selectivity.

CO2 capture and conversion using structured porous sorbents and catalysts is a solution to help the decarbonization of emission-intensive industries. Furthermore, porous sorbents have recently been considered for direct air capture to achieve negative CO2 emissions. Several new prototypes and swing adsorption technologies for CO2 capture use structured lami- nates and honeycomb sorbents to lower the energy penalty and improve process efficiency and kinetics. The challenges lie in tailoring and optimizing structured sorbents for their CO2 working capacity, selectivity over other components, the effect of impurities and humidity, mass and heat transfer kinetics, and mechanical and chemical durability, which are specific to the exhaust system and flue gas composition. Recent de- velopments in the structuring of sorbents are reviewed with a focus on the scalable approaches to improve the performance of postcombustion CO2 capture and direct air capture processes.

The Cover Feature illustrates the importance of porous carbon fiber layers (CFLs) to the activity and selectivity of photocathodes for the CO2 reduction reaction (CO2RR) in a zero-gap gas-phase photoelectrolyzer. The wettability of the CFL modulates the local environment on the yellow-colored metal organic framework catalyst (UiO-66-NH2). Hydrophobic CFL-based photocathodes lead to CO2RR, producing liquid hydrocarbons such as formate, methanol and ethanol. In contrast, hydrophilic, wetted CFL-based photocathodes favor HER. More information can be found in the Research Article by A. Kaiser and co-workers.

Enzymatic conversion processes face challenges in controlling oligosaccharide molecular weight (Mw). Enzymatic membrane reactors (EMRs) with immobilized enzymes address this, but direct enzyme immobilization on the membrane surface can lead to deactivation and reduced hydrolysis efficiency. This study proposes a novel EMR configuration: a three-layer structure. An electrospun porous fibrous layer, modified with PDA, TA, and APTES, serves as a mechanical support layer. A commercial separation membrane is positioned below. This configuration enhances enzyme activity and selectivity. Using a "fouling-induced" technique, immobilized activity of the enzyme (i.e. dextranase) significantly increased to 11.5 mu mol-isomaltose/min, surpassing incubationimmobilized dextranase (0.075 mu mol-isomaltose/min). The additional layer preserves catalytic patterns, reducing fouling and ensuring high selectivity. The EMR configuration excels in producing low Mw oligosaccharides. The catalytic layer achieves 11.3 mu mol-isomaltose/min, while the membrane exhibits exceptional selectivity and stability. The hydrophilic RC10 membrane with small pores performs best. This study highlights the potential of the EMR system for efficient production of stable low Mw oligosaccharides. Insights into optimizing enzyme immobilization strategies and membrane selection benefit enzymatic conversion processes.

The synthesis of metal-organic frameworks (MOFs) and their processing into structures with tailored hierarchical porosity is essential for using MOFs in the adsorption-driven gas separation process. We report the synthesis of modified Cu-MOF nanocrystals for CO2 separation from CH4 and N-2, prepared from DABCO (1,4-diazabicyclo[2.2.2] octane) and 9,10 anthracene dicarboxylic acid linkers with copper metal salt. The synthesis parameters were optimized to introduce mesoporosity in the microporous Cu-MOF crystals. The volumetric CO2 adsorption capacity of the new hierarchical Cu-MOF was 2.58 mmol g(-1) at 293 K and 100 kPa with a low isosteric heat of adsorption of 28 kJ mol(-1). The hierarchical Cu-MOF nanocrystals were structured into mechanically stable pellets with a diametral compression strength exceeding 1.2 MPa using polyvinyl alcohol (PVA) as a binder. The CO2 breakthrough curves were measured from a binary CO2-CH4 (45/55 vol%) gas mixture at 293 K and 400 kPa pressure on Cu-MOF pellets to demonstrate the role of hierarchical porosity in mass transfer kinetics during adsorption. The structured hierarchical Cu-MOF pellets showed stable cyclic CO2 adsorption capacity during 5 adsorption-desorption cycles with a CO2 uptake capacity of 3.1 mmol g(-1) at 400 kPa and showed a high mass transfer coefficient of 1.8 m s(-1) as compared to the benchmark zeolite NaX commercialized binderless granules, suggesting that the introduction of hierarchical porosity in Cu-MOF pellets can effectively reduce the time for CO2 separation cycles.

Hydrogen production using oxygen transport membrane reactors has attracted widespread attention. However, the structural stability of membrane materials under harsh reducing atmospheres is still a significant challenge. Gadolinium doped cerium oxide (CGO) presents high ionic conductivity and good reducing resistance but is limited by its poor electronic conductivity. Herein, a 2 mol.% cobalt-doped Ce0.8Gd0.2O2-8 (CoCGO) ultrathin membrane was manufactured by thin-film technology and applied to hydrogen production from water splitting (WS) with simultaneous syngas production through partial oxidation of methane (POM). Two catalysts, La0.4Sr0.6CoO3-8 (LSC) and Ni/Al2O3, were utilized for promoting WS and POM, respectively. Hydrogen pro-duction rate above 1.8 mL min-1 cm-2 and methane conversion of around 80 % were achieved, and no noticeable degradation was detected during 100 h operation, suggesting its prospective stability advantages as a membrane reactor for hydrogen production from water.

The adsorbed natural gas (ANG) concept uses a high-capacity adsorbent packed in the fuel tank allowing high-density fuel storage at a reduced pressure (30-60 bar). One major problem of ANG is during a fast tank filling: generation of heat of adsorption is not released fast, increasing the temperature of the adsorbent and reducing its storage capacity. In this work, we have evaluated the temperature evolution of a storage tank packed with HKUST-1 and subjected to a fast filling of methane under different external heat transfer conditions. When the tank is operated in adiabatic regime, the sudden temperature excursion damaged the HKUST-1 adsorbent with a reduction of 10% of its surface area. To enhance heat transfer and protect the integrity of the adsorbent, the MOF was packed inside 3D printed metal lattices with different lengths. The experiments showed a significant enhancement of the heat transfer which can be particularly beneficial for larger storage tanks. (c) 2023 Published by Elsevier Ltd on behalf of Institution of Chemical Engineers.

Despite the growing use of organic or mixed solvents in zeolite processing, most studies focus only on aqueous suspension systems. We investigated the colloidal characteristics of submicron-sized zeolite NaA in mixed ethanol-water solvents. The effects of the mixing ratio of solvents and various additives on the dispersion of the zeolite powders were studied. The zeolite NaA particles were destabilized in solvent mixtures at a high ethanol-to-water ratio, a reduction in the zeta potential was observed, and the destabilization was rationalized by the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory. An improved stabilization of the zeolite NaA suspensions was achieved in ethanol-rich solvent mixtures using nonionic low molecular weight organic additives, but not with their ionic counterparts such as anionic, cationic surfactants or inorganic acids or bases. Polyethylene glycol (PEG)-400 was found to be a good dispersant for the submicron-sized zeolite NaA particles in the ethanol-water mixtures, which was attributed to its interaction with the zeolite surface, leading to an increased zeta potential. The PEG-stabilized zeolite suspensions led to low suspension viscosities as well as uniform and consistent spin-coated films.

This review summarizes recent progress on dual-phase oxygen transport membranes. Existing challenges, research strategies and future application areas are discussed.

Oxygen transport membranes have the potential to deliver pure and cheap oxygen to chemical reactors, combustors, gasifiers etc., given that geometry, microstructure and material properties are optimized. This work demonstrates the first successful preparation of dual-phase tubular, asymmetric oxygen transport membranes consisting of a new electronic conductor LaCr0.85Cu0.10Ni0.05O3-δ mixed with (Sc2O3)0.10(Y2O3)0.01(ZrO2)0.89 as ionic conductor. Challenges related to Cr-volatility were overcome by using Fe2O3 as a sintering aid. The sintering aid decreased mismatches in shrinkage and thermal expansion between the four layers in the asymmetric membrane and decreased the sintering temperature such that the Cr-volatility was suppressed. The membranes reached an oxygen flux of 0.28 ml∙min−1∙cm−2 in an air/N2 atmosphere at 950 °C. Furthermore, the membranes showed a stable oxygen flux after exposure to different atmospheres, including air/CO2 and air/H2 gradients. The successful fabrication of stable, asymmetric, tubular membranes opens the possibility for future integration in syngas or oxy-combustion applications.

Ceramic materials with high surface area, large and open porosity are considered excellent supports for enzyme immobilization owing to their stability and reusability. The present study reports the electrospinning of aluminum silicate nanofiber supports from sol-gel precursors, the impact of different fabrication parameters on the microstructure of the nanofibers and their performance in enzyme immobilization. A change in nanofiber diameter and pore size of the aluminum silicate nanofibers was observed upon varying specific processing parameters, such as the sol-composition (precursor and polymer concentration), the electrospinning parameters and the subsequent heat treatment (calcination temperature). The enzyme, alcohol dehydrogenase (ADH), was immobilized on the aluminum silicate nanofibers by physical adsorption and covalent bonding. Activity retention of 17% and 42% was obtained after 12 d of storage and repeated reaction cycles for physically adsorbed and covalently bonded ADH, respectively. Overall, the immobilization of ADH on aluminum silicate nanofibers resulted in high enzyme loading and activity retention. However, as compared to covalent immobilization, a marked decrease in the enzyme activity during storage for physically adsorbed enzymes was observed, which was ascribed to leakage of the enzymes from the nanofibers. Such fibers can improve enzyme stability and promote a higher residual activity of the immobilized enzyme as compared to the free enzyme. The results shown in this study thus suggest that aluminum silicate nanofibers, with their high surface area, are promising support materials for the immobilization of enzymes.

Calcium chloride (CaCl2) impregnated zeolite A and strontium chloride (SrCl2) impregnated zeolite A and X composite granules were evaluated as ammonia sorbents for automotive selective catalytic reduction systems. The SrCl2-impregnated zeolite A granules showed a 14% increase in ammonia uptake capacity (8.39 mmol g-1) compared to zeolite A granules (7.38 mmol g-1). Furthermore, composite granules showed 243% faster kinetics of ammonia sorption (0.24 mmol g-1 min-1) compared to SrCl2 (0.07 mmol g-1 min-1) in the first 20 min. The composite CaCl2/SrCl2 impregnated zeolite A granules combined the advantages of the zeolites and CaCl2/SrCl2, where the rapid physisorption from zeolites can reduce the ammonia loading and release time, and chemisorption from the CaCl2/SrCl2 offers abundant ammonia capacity. Moreover, by optimizing the content of SrCl2 loading, the composite granules maintained the granular form with a crushing load of 17 N per granule after ammonia sorption-desorption cycles. Such structurally stable composite sorbents offer an opportunity for fast ammonia loading/release in automotive selective catalytic reduction systems.

Porous materials such as metal-organic frameworks (MOFs) with high theoretical volumetric gas uptake capacity are promising materials for gas storage and separation, but the structuring for practical applications is challenging. Herein, we report a general and feasible strategy to combine electrospinning with a phase conversion method to decorate polyacrylonitrile nanofibers (PAN NFs) with Cu-MOF (HKUST-1). The strategy is based on the combination of surface pretreatment of the NFs with Cu(OH)2 and a subsequent phase conversion into HKUST-1 crystals (PC-HKUST-1). A significant higher loading of HKUST-1 in the PAN NF matrix was achieved by the phase conversion method compared with direct electrospinning of MOF slurries or in-situ growth of MOF crystals on NFs. As a result, the hierarchical structured PC (phase conversion)-HKUST-1 NFs revealed the highest gravimetric storage capacity of 86 cm3 g−1 (STP) at 3500 kPa and 298 K for methane (CH4), which is higher than other HKUST 1 NFs reported previously. The improved CH4 uptake can be explained by the high loading of HKUST-1 due to the high availability of Cu-ions localized on the surface of the NFs during the phase conversion process, resulting in high surface area and excellent gas access of the phase converted HKUST-1. Thus, the developed strategy of structuring MOFs could be of interest for the fabrication of tailor-made MOF NF architectures for other energy and environmental applications.

Polyacrylonitrile (PAN) nanofibers were prepared by electrospinning and coated with zeolitic imidazolate framework-8 (ZIF-8) by a phase conversion growth method and investigated for CO2 capture. The PAN nanofibers were pre-treated with NaOH, and further coated with zinc hydroxide, which was subsequently converted into ZIF-8 by the addition of 2-methyl imidazolate. In the resulting flexible ZIF-8/PAN composite nanofibers, ZIF-8 loadings of up to 57 wt% were achieved. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) showed the formation of evenly distributed submicron-sized ZIF-8 crystals on the surface of the PAN nanofibers with sizes between 20 and 75 nm. X-ray photoelectron spectroscopy (XPS) and carbon-13 nuclear magnetic resonance (13C NMR) investigations indicated electrostatic interactions and hydrogen bonds between the ZIF-8 structure and the PAN nanofiber. The ZIF-8/composite nanofibers showed a high BET surface area of 887 m2 g-1. CO2 adsorption isotherms of the ZIF-8/PAN composites revealed gravimetric CO2 uptake capacities of 130 mg g-1 (at 298 K and 40 bar) of the ZIF-8/PAN nanofiber and stable cyclic adsorption performance.

Three examples of porous ceramics in energy applications are described: catalysts, solid oxide cells (SOCs) and porous separation membranes. Ceramics offer properties, such as high temperature stability, chemical durability, conductivity, mechanical strength and abrasive resistance, which make these materials attractive for high performance applications. Porous ceramics are used directly as catalysts or as catalysts supports. Ceramic catalysts are typically oxide ceramics such as transition metal oxides (TMO), microporous zeolites and perovskites. Porous ceramics for catalysis are structured in the form of granules, extrudates, honey combs and laminates to carry catalytic active metals and offer large surface area, efficient mass and heat transfer properties, low pressure drop and appreciable mechanical strength. SOCs are ceramic electrochemical devices that convert chemical energy into electrical energy and vice versa, as fuel cells or electrolyzers. These devices consist of an electrolyte and two electrodes and the electrolyte separates the two electrodes. While the porous electrodes are mainly electronic conductors, the electrolyte is an ionic conductor. Different architectures, materials and fabrication techniques as well as the physical and structural characteristics of SOC, which influence directly the SOC performance are discussed. Porous ceramic membranes have a market in micro, ultra and nanofiltration for waste water treatment, in desalination processes and gas separation that do not allow the use of polymeric membranes. Ceramic membranes usually consist of a hierarchical porous multilayer architecture with a macroporous support and a number of additional layers that are successively reduced in pore size and thickness, depending on the application. Suitable materials, the ceramic fabrication steps and the challenges to prepare separation layers in respect to increasing demands on the membrane separation processes are explained.