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Redox flow batteries (RFBs) are promising for large-scale long-duration energy storage owing to their inherent safety, decoupled power and energy, high efficiency, and longevity. Membranes constitute an important component that affects mass transport processes in RFBs, including ion transport, redox-species crossover, and the net volumetric transfer of supporting electrolytes. Hydrophilic microporous polymers, such as polymers of intrinsic microporosity (PIM), are demonstrated as next-generation ion-selective membranes in RFBs. However, the crossover of redox species and water migration through membranes are remaining challenges for battery longevity. Here, a facile strategy is reported for regulating mass transport and enhancing battery cycling stability by employing thin film composite (TFC) membranes prepared from a PIM polymer with optimized selective-layer thickness. Integration of these PIM-based TFC membranes with a variety of redox chemistries allows for the screening of suitable RFB systems that display high compatibility between membrane and redox couples, affording long-life operation with minimal capacity fade. Thickness optimization of TFC membranes further improves cycling performance and significantly restricts water transfer in selected RFB systems.

Flow batteries are promising for long-duration grid-scale energy storage. Future terawatt-scale deployment of flow batteries will require substantial capital cost reduction, particularly low-cost electrolytes and hydrocarbon ion exchange membranes. However, integration of hydrocarbon membranes with novel flow battery chemistries in commercial-scale stacks is yet to be demonstrated. Here we report the pilot scale synthesis and roll-to-roll manufacturing of sulfonated poly(ether ether ketone) (SPEEK) membranes and demonstrate their high hydroxide conductivity and chemical stability in kW-scale alkaline-based flow batteries. After exposure to a 5 mol L-1 NaOH solution at 60 °C for 41 days, the SPEEK membrane still enabled a stable alkaline zinc-iron flow battery performance for more than 650 cycles (more than 650 hours) at high current densities (80 to 160 mA cm-2 ). Furthermore, the membrane was integrated in flow battery stacks with power up to 4000 W, which demonstrated a high energy efficiency of 85.5% operated at 80 mA cm-2 and long term stable operation over 800 h as well as substantial cost savings relative to Nafion membranes. This work illustrates a potential pathway for manufacturing and upscaling of next-generation cost-effective flow batteries based on low-cost hydrocarbon membranes developed in past decades to translate to large scale applications for longduration energy storage.

Redox flow batteries (RFBs) have great potential for long-duration grid-scale energy storage. Ion conducting membranes are a crucial component in RFBs, allowing charge-carrying ions to transport while preventing the cross-mixing of redox couples. Commercial Nafion membranes are widely used in RFBs, but their unsatisfactory ionic and molecular selectivity as well as high costs limit the performance and the widespread deployment of this technology. To extend the longevity and reduce the cost of RFB systems, inexpensive ion-selective membranes are highly desired that concurrently deliver low ionic resistance and high selectivity towards redox-active species. In this work, high-performance RFB membranes are fabricated from blends of carboxylate- and amidoxime-functionalized polymers of intrinsic microporosity (PIMs) that exploit the beneficial properties of both polymers. The enthalpy-driven formation of cohesive interchain interactions, including hydrogen bonds and salt bridges, facilitates the microscopic miscibility of the blends, while ionizable functional groups within the sub-nanometer pores allow optimization of membrane ion transport functions. The resulting microporous membranes demonstrate fast cation conduction with low crossover of redox-active molecular species, enabling improved power ratings and reduced capacity fade in aqueous RFBs using anthraquinone and ferrocyanide as redox couples. This article is protected by copyright. All rights reserved.

Gas-separation membranes are a critical industrial component for a low-carbon and energy-efficient future. As a result, many researchers have been testing membrane materials over the past several decades. Unfortunately, almost all membrane-based testing systems are home-built, and there are no widely accepted material standards or testing protocols in the literature, making it challenging to accurately compare experimental results. In this multi-lab study, ten independent laboratories collected high-pressure pure-gas permeation data for H2, O2, CH4, and N2 in commercial polysulfone (PSf) films. Equipment information, testing procedures, and permeation data from all labs were collected to provide (1) accepted H2, O2, CH4, and N2 permeability values at 35 °C in PSf as a reference standard, (2) statistical analysis of lab-to-lab uncertainties in evaluating permeability, and (3) a list of best practices for sample preparation, equipment set-up, and permeation testing using constant-volume variable-pressure apparatuses. Results summarized in this work provide a reference standard and recommended testing protocols for pure-gas testing of membrane materials.

IL@MOF (IL: ionic liquid; MOF: metal-organic framework) materials have been proposed as a candidate for solid-state electrolytes, combining the inherent non-flammability and high thermal and chemical stability of the ionic liquid with the host-guest interactions of the MOF. In this work, we compare the structure and ionic conductivity of a sodium ion containing IL@MOF composite formed from a microcrystalline powder of the zeolitic imidazolate framework (ZIF), ZIF-8 with a hierarchically porous sample of ZIF-8 containing both micro- and mesopores from a sol-gel synthesis. Although the crystallographic structures were shown to be the same by X-ray diffraction, significant differences in particle size, packing and morphology were identified by electron microscopy techniques which highlight the origins of the hierarchical porosity. After incorporation of Na0.1EMIM0.9TFSI (abbreviated to NaIL; EMIM = 1-ethyl-3-methylimidazolium; TFSI = bis(trifluoromethylsulfonyl)imide), the hierarchically porous composite exhibited a 40% greater filling capacity than the purely microporous sample which was confirmed by elemental analysis and digestive proton NMR. Finally, the ionic conductivity properties of the composite materials were probed by electrochemical impedance spectroscopy. The results showed that despite the 40% increased loading of NaIL in the NaIL@ZIF-8micro sample, the ionic conductivities at 25 °C were 8.4 × 10-6 and 1.6 × 10-5 S cm-1 for NaIL@ZIF-8meso and NaIL@ZIF-8micro respectively. These results exemplify the importance of the long range, continuous ion pathways contributed by the microcrystalline pores, as well as the limited contribution from the discontinuous mesopores to the overall ionic conductivity.

International audience; Ring-opening polymerization (ROP) of propylene oxide (PO) is achieved at 25 °C either in bulk or in solution, using N-heterocyclic carbenes (NHCs) and triisobutylaluminum (i-Bu3Al) as a bicomponent catalytic system. Transfer to monomer was not observed and poly(propylene oxide)s with predictable molar masses up to 60 000 g·mol−1 and low dispersities were obtained. In presence/absence of an alcohol as the initiator, the polymerization of PO follows anionic or zwitterionic ROP mechanisms, respectively. The addition of the Lewis acid strongly improves the efficiency of NHCs for the polymerization of substituted epoxides. It is established that i-Bu3Al is involved both in the formation of an initiating/propagating complex of moderate basicity/nucleophilicity and in the coordination of PO, enabling the activation of the monomer towards the complexed nucleophilic active species. Block copolyethers are also prepared by PPO chain extension experiments. All (co)polyethers were thoroughly characterized by 1H NMR spectroscopy, SEC and MALDI-TOF mass spectrometry as means to prove the control and benefit of this NHC approach for epoxides ROP.

Membranes with fast and selective transport of protons and cations are required for a wide range of electrochemical energy conversion and storage devices, such as proton‐exchange membrane (PEM) fuel cells and redox flow batteries. Here we report a new approach to designing solution‐processable ion‐selective polymer membranes with both intrinsic microporosity and ion‐conductive functionality. This was achieved by synthesizing polymers with rigid and contorted backbones, which incorporate hydrophobic fluorinated and hydrophilic sulfonic acid functional groups, to produce membranes with negatively‐charged subnanometer‐sized confined ionic channels. The facilitated transport of protons and cations through these membranes, as well as high selectivity towards nanometer‐sized redox‐active molecules, enable efficient and stable operation of an aqueous alkaline quinone redox flow battery and a hydrogen PEM fuel cell. This membrane design strategy paves the way for producing a new‐generation of ion‐exchange membranes for electrochemical energy conversion and storage applications.

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 Troger’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.

International audience; Triggered by raised environmental awareness and the rising requirements for sustainable polymers such as degradable or recyclable polymers, studies on ring-opening (co)polymerization (ROP/ROCP) of (bio-based) cyclic monomers (e.g., cyclic esters, lactides, epoxides etc.) have been booming in recent years. Renewable five-membered γ-butyrolactone (γBL) and derivatives would thus be a desirable feedstock to produce poly(γ-butyrolactone) (PγBL) and different (bio-based) functional polyesters. Their copolymerization with other cyclic monomers could also afford an alternative to tune the properties of the resulting materials. Although γBL was traditionally regarded "non-polymerizable", some progresses were made recently concerning the ROP/ROCP of γBL and derivatives. More importantly, some polyesters could be totally depolymerized back to their monomers by thermal or chemical treatment. This review is specially focused on ROP of γ-lactones and their copolymerization with other cyclic monomers by different catalytic/initiating systems, including Lewis/Brønsted acids, organic bases and alkali metal compounds, organometallic compounds, and cooperative bicomponent catalytic systems. The depolymerization process of some obtained polyesters is also discussed.

International audience; Propylene oxide (PO) is polymerized by metal-free ring-opening 11 polymerization (ROP) at 25 °C using N-heterocyclic carbenes (NHCs) and 12 triethylborane (Et 3 B) as a bicomponent catalytic system. Poly(propylene oxide)s with 13 predictable molar mass up to 60 000 g.mol-1 and low dispersity (Ð < 1.10) were 14 obtained without the occurrence of undesirable transfer reaction to the monomer. In 15 presence of an alcohol as the initiator, the ROP of PO follows an anionic mechanism 16 assisted by monomer activation improving the efficiency of NHCs for the 17 polymerization of substituted epoxides. Et 3 B is involved both in the formation of a 18 complexed active center and in the activation of PO. Interestingly, 19 dihydroxytelechelic PPOs can be readily synthesized not only using 1,4-20 benzenedimethanol but also water, both serving as difunctional initiators. Block

Large-scale energy storage is becoming increasingly critical to balancing renewable energy production and consumption. Organic redox flow batteries, made from inexpensive and sustainable redox-active materials, are promising storage technologies that are cheaper and less environmentally hazardous than vanadium-based batteries, but they have shorter lifetimes and lower energy density. Thus, fundamental insight at the molecular level is required to improve performance. Here we report two in situ nuclear magnetic resonance (NMR) methods of studying redox flow batteries, which are applied to two redox-active electrolytes: 2,6-dihydroxyanthraquinone (DHAQ) and 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy) dibutyrate (DBEAQ). In the first method, we monitor the changes in the H NMR shift of the liquid electrolyte as it flows out of the electrochemical cell. In the second method, we observe the changes that occur simultaneously in the positive and negative electrodes in the full electrochemical cell. Using the bulk magnetization changes (observed via the H NMR shift of the water resonance) and the line broadening of the H shifts of the quinone resonances as a function of the state of charge, we measure the potential differences of the two single-electron couples, identify and quantify the rate of electron transfer between the reduced and oxidized species, and determine the extent of electron delocalization of the unpaired spins over the radical anions. These NMR techniques enable electrolyte decomposition and battery self-discharge to be explored in real time, and show that DHAQ is decomposed electrochemically via a reaction that can be minimized by limiting the voltage used on charging. We foresee applications of these NMR methods in understanding a wide range of redox processes in flow and other electrochemical systems., W.Z. and C.P.G. acknowledge support from Centre of Advanced Materials for Integrated Energy Systems (CAM-IES), via EPSRC grant number EP/P007767/1. E.W.Z., R.J. and C.P.G. acknowledge support from Shell. E.W.Z. acknowledges support from the Manifest exchange programme via EPSRC grant number EP/N032888/1. T.L. acknowledges support from the Schlumberger Fellowship, Darwin College. E.J. acknowledges support from the Swedish Research Council. We thank A. Brookfield for assistance with the EPR measurement; P. A. A. Klusener from Shell, H. Bronstein, I. Fleming, D. S. Wright, K. Märker, C. Xu, P. C. M. M. Magusin from the University of Cambridge and E. Castillo-Martínez from Universidad Complutense de Madrid for discussions; R. Tan from Imperial College London and D. Lyu, Y. Kim, Y. Jin, and J. Lu from the University of Cambridge for assistance setting up the redox flow battery. A.W. and Q.S. acknowledge Imperial College start-up funding and CAM-IES seed funding. J.C.G. acknowledges support from the Spanish Ministry of Science, Innovation and Universities through a Ramon y Cajal Fellowship (RYC-2015-17722) and the Retos Project (MAT2017-86796-R).

Understanding the behavior of bacteria near biodegradable surfaces is critical for the development of biomedical and antibiofouling materials. By using digital holographic microscopy (DHM), we investigated the three-dimensional (3D) behavior of Escherichia coli and Pseudomonas sp. in lipase-containing aquatic environments near dynamic surfaces constructed by biodegradable poly(ε-caprolactone) (PCL)-based polymers in real time. As the enzymatic degradation rate increases, the percentage of near-surface subdiffusive bacteria and consequently, the irreversible adhesion decreases. Atomic force microscopy (AFM) measurements reveal that the adhesion force between bacteria and the surfaces decreases with an increasing degradation rate. In addition, the degradation products elicit a negative chemotactic response in E. coli, further driving them away from the dynamic surfaces through more frequent tumbling motion. Our study clearly demonstrates that bacterial adhesion can be reduced on dynamic surfaces formed by degradable polymers.

The formation of two‐dimensional (2D) oriented porous organic cage crystals (consisting of imine‐based tetrahedral molecules) on various substrates (such as silicon wafers and glass) by solution‐processing is reported. Insight into the crystallinity, preferred orientation, and cage crystal growth was obtained by experimental and computational techniques. For the first time, structural defects in porous molecular materials were observed directly and the defect concentration could be correlated with crystal growth rate. These oriented crystals suggest potential for future applications, such as solution‐processable molecular crystalline 2D membranes for molecular separations.

Triggered by environmental concerns and the rising demands for metal-free polymers in e.g. bio-related and microelectronic applications, studies on organocatalytic polymerization have been launched and developed unprecedentedly during the last 15 years. A wide range of organic molecules are now available in polymer chemists' toolbox to choose from as catalysts for polymerization of (hetero) cyclic and polar vinyl monomers. Apart from the intrinsic merits such as lower toxicity and better solubility compared with (transition) metal catalysts/initiators, organocatalysts have also shown, in many cases, excellence to achieve high polymerization rates and/or good control (selectivity). In addition, particular natures and catalytic/activating mechanisms of organocatalysts have led to new opportunities for rational design and efficient synthesis of macromolecular architectures, i.e. chain structures, topological structures and functionalities. This mini-review is specially themed on pathways to construct copolymer chain structures by organocatalytic copolymerization of mixed type monomers (comonomers bearing different polymerizing moieties) and will be sectioned by different comonomer combinations, including cyclic monoesters of different sizes, cyclic monoesters and lactides, cyclic esters and cyclic carbonates or epoxides, heterocycles and vinyl monomers.

The development of adsorption and membrane-based separation technologies toward more energy and cost-efficient processes is a significant engineering problem facing the world today. An example of a process in need of improvement is the separation of C8 aromatics to recover para-xylene, which is the precursor to the widely used monomer terephthalic acid. Molecular simulations were used to investigate whether the separation of C8 aromatics can be carried out by the porous organic cages CC3 and CC13, both of which have been previously used in the fabrication of amorphous thin-film membranes. Metadynamics simulations showed significant differences in the energetic barriers to the diffusion of different C8 aromatics through the porous cages, especially for CC3. These differences imply that meta-xylene and ortho-xylene will take significantly longer to enter or leave the cages. Therefore, it may be possible to use membranes composed of these materials to separate ortho- and meta-xylene from para-xylene by size exclusion. Differences in the C8 aromatics’ diffusion barriers were caused by their different diffusion mechanisms, while the lower selectivity of CC13 was largely down to its more significant pore breathing. These observations will aid the future design of adsorbents and membrane systems with improved separation performance.

Large-scale energy storage is becoming increasingly critical to balancing renewable energy production and consumption

Hydrogen oxidation and oxygen reduction are two crucial energy conversion reactions, which are shown to be both strongly affected by the presence of intrinsically microporous polymer coatings on electrodes. Polymers of intrinsic microporosity (PIMs) are known to possess extremely high internal surface area and ability to bind gases under dry conditions. It is shown here that both, hydrogen- and oxygen gas binding into PIMs, also occurs under wet or “triphasic” conditions in aqueous electrolyte environments (when immersed in 0.01 M phosphate buffer at pH 7). For two known PIM materials (PIM-1 and PIM-PY), nanoparticles are formed by an anti-solvent precipitation protocol and then cast as a film onto platinum or glassy carbon electrodes. Voltammetry experiments reveal evidence for hydrogen and oxygen binding. Both, PIM-1 and PIM-PY, locally store hydrogen or oxygen gas at the electrode surface and thereby significantly affect electrocatalytic reactivity. The onset of oxygen reduction on glassy carbon is shifted by 0.15 V in the positive direction.

Chemical looping with oxygen uncoupling (CLOU) and chemical looping air separation (CLAS) are novel and potentially promising processes for the combustion of solid fuels (e.g. biomass) for power generation with inherent CO2 capture. Redox-experiments at 850–950 °C confirmed that copper manganese spinel oxides are promising oxygen carriers for these processes, as they combine a relatively high O2 release capacity and fast O2 release kinetics. Furthermore, this work presents a novel method to calculate the O2 partial pressure equilibrium and the heat of O2 release from observed rates of reaction. To demonstrate this method, oxygen carriers were prepared via mechanical mixing and co-precipitation with varying molar Cu:Mn ratios and synthesis conditions, thereby tuning material properties and the pore structure. The precursors and calcined materials were characterised, and the crystalline phases were determined using X-ray diffraction. The insights from the post cycling analysis of the oxygen carriers and the experimentally obtained O2 release capacities were combined to elucidate the redox-reactions relevant for the two processes. It was found that the presence of a higher partial pressure of O2 during the O2 release results in the formation of different (perovskite-like) phases than those occurring during the decomposition in an O2-free environment. The oxygen carriers demonstrated excellent stability at CLOU and CLAS process conditions during extended redox cycling (100 cycles in a thermo-gravimetric analyser and 50 cycles in a fluidised bed reactor), showing no significant loss of reactivity or O2 release capacity and a high resistance towards attrition and agglomeration. The degree of degradation after 100 cycles was in the order: temperature swing (CLAS)

The copolymerization of e-caprolactone (CL) with its structural isomer, δ-hexalactone (HL), or trimethylene carbonate (TMC) catalysed by diphenyl phosphate was investigated. Copolymers with molar fraction of CL units ranging from 54% to 95% were obtained. Molecular characterization exhibited random distribution of the two monomeric units (CL/HL or CL/TMC), owing to the extensive occurrence of transesterification scrambling reactions at high temperature. Compared with poly(e-caprolactone) (PCL), the copolymers showed reduced crystallinity and enhanced enzymatic degradability as revealed by the analysis with differential scanning calorimetry and quartz crystal microbalance with dissipation, respectively. Interestingly, the incorporation of HL units showed a more profound impact than TMC. It is therefore considered that organocatalytic copolymerization with HL, a bio-renewable lactone, can serve as an effective method to regulate the properties of PCL.

A base-to-base organocatalytic approach has been developed for one-pot synthesis of poly(ethylene oxide)-block-polyesters and poly(ethylene oxide)-based polyurethanes. Ethylene oxide is first polymerized from a diol in the presence of a phosphazene superbase; then a thiourea is added to be deprotonated by the strongly basic alkoxide, which attenuates the basicity of the catalytic system and thus allows for controlled polymerization of the subsequently added cyclic ester from the polyether chain end or for step-growth polymerization of an added diisocyanate with the macrodiol which is free from anionic homopolymerization of the diisocyanate. The approach shows several advantages in addition to the one-pot facile character, e.g., a wide applicability toward different “second monmers” including (but not limited to) e-caprolactone, l-lactide, and diisocyanate, and a low amount of “second catalyst” required as the deprotonated thiourea itself serves as the mildly or weakly basic organocatalyst. Impact of the N...

Multiblock-like amphiphilic polyurethanes constituted by poly(ethylene oxide) and biosourced betulin are designed for antifouling and synthesized by a convenient organocatalytic route comprising tandem chain-growth and step-growth polymerizations. The doping density of betulin (D-B) in the polymer chain structure is readily varied by a mixed-initiator strategy. The spin-coated polymer films exhibit unique nanophase separation and protein resistance behaviors. Higher D-B leads to enhanced surface hydrophobicity and, unexpectedly, improved protein resistance. It is found that the surface holds molecular-level heterogeneity when D-B is substantially high due to restricted phase separation; therefore, broad-spectrum protein resistance is achieved despite considerable surface hydrophobicity. As D-B decreases, the distance between adjacent betulin units increases so that hydrophobic nanodomains are formed, which provide enough landing areas for relatively small-sized proteins to adsorb on the surface.

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Polyamide thin film composite (PA TFC) membranes are synthesized from interfacial polymerization using two amines in the aqueous phase. The conventional monomer, m-phenelynediamine (MPD), is partially replaced by a linear monomer, 1,3–diamino-2-hydroxypropane (DAHP). The water permeability of the membranes improves by around 22% (to 2.67±0.09 L m −2 h −1 bar −1 ) while keeping the same high salt rejection (96–98%) at an optimum DAHP/MPD ratio of 12.8%. While developing the control PA TFC membrane we introduce a washing step and show that the support surface should be free from surface protective coatings to achieve high water flux (2.18±0.08 L m −2 h −1 bar −1 ). Incorporating DAHP units into the polyamide network improves the water flux through the membranes fabricated on both original and washed supports. The surface morphologies of polyamide films change significantly with introduction of DAHP, from large ridge-and-valley structure to enlarged nodular structures. High resolution SEM images show an ultrathin polyamide thin film with a thickness that is reduced with addition of DAHP. These influences of DAHP, namely a reduction in the selective layer thickness, an alteration in surface morphology, changes in internal molecular packing and hydrophilicity, are suggested as factors behind the improved water permeability.

We report the fabrication and electrochemical performance of a flexible thin film supercapacitor with a novel nanostructured composite electrode. The electrode was prepared byin situcoprecipitation of two-dimensional (2D) MnO2nanosheets at room temperature in the presence of carbon nanofibers (CNFs). The highest specific capacitance of 142 F/g was achieved for CNFs-MnO2electrodes in sandwiched assembly with PVA-H4SiW12O40·nH2O polyelectrolyte separator.

Mixed matrix membranes (MMMs) for gas separation applications have enhanced selectivity when compared with the pure polymer matrix, but are commonly reported with low intrinsic permeability, which has major cost implications for implementation of membrane technologies in large-scale carbon capture projects. High-permeability polymers rarely generate sufficient selectivity for energy-efficient CO2 capture. Here we report substantial selectivity enhancements within high-permeability polymers as a result of the efficient dispersion of amine-functionalized, nanosized metal–organic framework (MOF) additives. The enhancement effects under optimal mixing conditions occur with minimal loss in overall permeability. Nanosizing of the MOF enhances its dispersion within the polymer matrix to minimize non-selective microvoid formation around the particles. Amination of such MOFs increases their interaction with thepolymer matrix, resulting in a measured rigidification and enhanced selectivity of the overall composite. The optimal MOF MMM performance was verified in three different polymer systems, and also over pressure and temperature ranges suitable for carbon capture. Mixed matrix membranes can separate CO2 from flue gas mixtures but increasing selectivity without sacrificing permeability remains challenging. Selectivity can be increased with little loss in permeability by using nanoparticulate, amine-functionalized metal–organic framework fillers.

Towards the Rational Design of Multi-Functional Materials M. Roussenovaa,∗, D.J. Hughes, J. Enrione, P. Diaz-Calderon, E. Sivaniah, Q. Song, J. Ubbink, P. Beavis, A. Swain and M.A. Alam H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK Department of Food Science and Technology, Universidad de Santiago de Chile Av. Ecuador 3343, Estacion Central, Santiago, Chile University of Cambridge, Cavendish Laboratory, Biological and Soft Systems Section, Cambridge CB3 0HE, UK Food Concept & Physical Design The Mill , Muhleweg 10, CH-4112 Fluh, Switzerland AWE, Aldermaston, Reading, RG7 4PR, UK

“Ionic diode” (or current rectification) effects are potentially important for a range of applications including water purification. In this preliminary report, we observe novel ionic diode behaviour of thin (300 nm) membranes based on a polymer of intrinsic microporosity (PIM-EA-TB) supported on a poly-ethylene-terephthalate (PET) film with a 20 μm diameter microhole, and immersed in aqueous electrolyte media. Current rectification effects are observed for half-cells with the same electrolyte solution on both sides of the membrane for cases where cation and anion mobility differ (HCl, other acids, NaOH, etc.) but not for cases where cation and anion mobility are more alike (LiCl, NaCl, KCl, etc.). A pH-dependent reversal of the ionic diode effect is observed and discussed in terms of tentatively assigned mechanisms based on both (i) ion mobility within the PIM-EA-TB nano-membrane and (ii) a possible “mechanical valve effect” linked to membrane potential and electrokinetic movement of the membrane as well as hydrostatic pressure effects. Keywords: Electrokinetic effects, Salt separation, Membrane potential, Nanofluidics, Iontronics, Electrophysiology

Chemical-looping combustion (CLC) of fuels via the cyclic reduction and oxidation of an oxygen carrier is a novel process for CO2 capture. CaSO4 has emerged as an alternative material with much lower cost and higher oxygen storage capacity compared to metal oxide based oxygen carrier. In principle, CaSO4 is reduced by CO and H2 (coal gasification products) generating CaS, CO2 and H2O, and then the solid product CaS is regenerated back to CaSO4 in air. Research on the reactions of CaSO4 and CaS is not only important for understanding the reaction mechanism and parameters for the new CLC technology but also of high interest in understanding the sulfur chemistry in fluidized bed combustion and gasification. This paper focuses on the reduction reaction of CaSO4 with CO to CaS and CO2 (CaSO4 + 4CO → CaS + 4CO2) by thermodynamics, characterization and kinetics analysis. Phase diagram of CaSO4–CaO–CaS indicates the operation regime of reduction–oxidation cycle by delicate control of temperature and partial pressure of reaction gases. The kinetics of the reduction reaction of a low cost natural anhydrite as oxygen carrier was investigated in an isothermal differential bed reactor where a thin layer of CaSO4 particles were exposed to a plug flow of CO balanced by N2. Prior to the kinetics modeling, extensive physical and chemical characterization analyses, such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), and N2 adsorption–desorption were carried out to understand the reaction mechanism. External mass transfer and heat effects were minimized and the operation regime for intrinsic kinetics was determined. The experimental data was described with a gas–solid shrinking unreacted core model (SCM) with both chemical reaction control and product layer diffusion resistance considered.

A chemical looping process using the redox reactions of iron oxide has been used to produce separate streams of pure H 2 and CO 2 from a solid fuel. An iron oxide carrier prepared using a mechanical mixing technique and comprised of 100 wt.% Fe 2 O 3 was used. It was demonstrated that hydrogen can be produced from three representative coals – a Russian bituminous, a German lignite and a UK sub-bituminous coal. Depending on the fuel, pure H 2 with [CO] ≲50 vol. ppm can be obtained from the proposed process. The cyclic stability of the iron oxide carrier was not adversely affected by contaminants found in syngas which are gaseous above 273 K. Stable quantities of H 2 were produced over five cycles for all three coals investigated. Independent of the fuel, SO 2 was not formed during the oxidation with steam, i.e. the produced H 2 was not contaminated with SO 2 . Since oxidation with air removes contaminants and generates useful heat and pure N 2 for purging, it should be included in the operating cycle. Overall, it was demonstrated that the proposed process may be an attractive approach to upgrade crude syngas produced by the gasification of low-rank coals to pure H 2 , representing a substantial increase in calorific value, whilst simultaneous capturing CO 2 , a greenhouse gas.

Chemical-looping combustion (CLC) is a new combustion technology with inherent separation of CO2. Most of the previous investigations on CLC of solid fuels were conducted under atmospheric pressure. A pressurized CLC combined cycle (PCLC-CC) system is proposed as a promising coal combustion technology with potential higher system efficiency, higher fuel conversion, and lower cost for CO2 sequestration. In this study pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor. CVRD iron ore particles were exposed alternately to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasified with 87.2% steam/N2 mixture and oxidation with 5% O2 in N2 at 970 °C. The operating pressure was varied between 0.1 MPa and 0.6 MPa. First, control experiments of steam coal gasification over quartz sand were performed. H2 and CO2 are the major components of the gasification products, and the operating pressure influences the gas composition. Higher concentrations of CO2 and lower fractions of CO, CH4, and H2 during the reduction process with CVRD iron ore was achieved under higher pressures. The effects of pressure on the coal gasification rate in the presence of the oxygen carrier were different for pyrolysis and char gasification. The pressurized condition suppresses the initial coal pyrolysis process while it also enhances coal char gasification and reduction with iron ore in steam, and thus improves the overall reaction rate of CLC. The oxidation rates and variation of oxygen carrier conversion are higher at elevated pressures reflecting higher reduction level in the previous reduction period. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM–EDX) analyses show that particles become porous after experiments but maintain structure and size after several cycles. Agglomeration was not observed in this study. An EDX analysis demonstrates that there is very little coal ash deposited on the oxygen carrier particles but no appreciable crystalline phases change as verified by X-ray diffraction (XRD) analysis. Overall, the limited pressurized CLC experiments carried out in the present work suggest that PCLC of coal is promising and further investigations are necessary.

A pressurized chemical-looping combustion combined cycle (PCLC) system is proposed for solid fuels combustion with potential high system efficiency, improving the fuel conversion and lowering the cost for CO2 sequestration. In this study, pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor focusing on cyclic performance. CVRD iron ore particles were exposed alternately for 20 cycles to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasified with 87% steam/N2 mixture and oxidation with 5% O2 in N2 at 970 °C at atmospheric pressure (0.1 MPa) and a typical elevated pressure of 0.5 MPa. With increasing number of redox cycles, more pyrolysis gases are oxidized by the oxygen carrier. At elevated pressure, the char gasification is intensified with negligible gasification intermediate products released. The CO2 fraction increases from 80% to approximate 90% after 10 cycles at atmospheric pressure. At elevated pressures, the average CO2 fr...

Ethylene production from petroleum or natural gas is an energy intensive process. Bio-ethanol catalytic dehydration to ethylene is an attractive alternative for oil based ethylene. Catalytic dehydration conversion of bio-ethanol to ethylene using HZSM-5 modified by 3 wt% rare earth metal (lanthanum) was carried out in a laboratory bioreactor. The physicochemical properties of the catalyst were characterized. The stability test showed that ethanol conversion and selectivity over this catalyst could be maintained above 98% for more than 950 h. The regenerated catalyst also displayed high reactivity and stability of up to 830 h can be obtained. The effects of temperature, liquid hourly space velocity, particle size of catalyst, and bio-ethanol partial pressure on products formation rate were investigated. The external and internal diffusion resistances were eliminated and the kinetic control range was identified. An apparent kinetics model was used to describe the dehydration reaction of ethanol over 3 wt% La-HZSM-5 catalyst, and the kinetic parameters were determined.

Chemical-looping combustion of biomass was carried out in a 10 kWth reactor with iron oxide as an oxygen carrier. A total 30 h of test was achieved with the same batch of iron oxide oxygen carrier. The effect of the fuel reactor temperature on gas composition of the fuel reactor and the air reactor, the proportion of biomass carbon reacting in the fuel reactor, and the conversion of biomass carbon to CO2 in the fuel reactor was experimentally investigated. The results showed that the CO production from biomass gasification with CO2 was more temperature dependent than the CO oxidation with iron oxide in the fuel reactor, and an increase in the fuel reactor temperature produced a higher increase for the CO production from biomass gasification than for the oxidation of CO by iron oxide. Although the conversion of biomass carbon to CO2 in the fuel reactor decreased with the increase of the fuel reactor temperature, there was a substantial increase in the proportion of biomass carbon reacting in the fuel react...

Chemical-looping combustion (CLC) is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO2. A reactivity study of CaSO4 oxygen carrier in CLC of methane was conducted in a laboratory scale fixed bed reactor. The oxygen carrier particles were exposed in six cycles of alternating reduction methane and oxidation air. A majority of CH4 reacted with CaSO4 to form CO2 and H2O. The oxidation was incomplete, possibly due to the CaSO4 product layer. The reactivity of CaSO4 oxygen carrier increased for the initial cycles but slightly decreased after four cycles. The product gas yields of CO2, CH4, and CO with cycles were analyzed. Carbon deposition during the reduction period was confirmed with the combustible gas (CO+H2) in the product gas and slight CO2 formed during the early stage of oxidation. The mechanism of carbon deposition and effect was also discussed. SO2 release behavior during reduction and oxidation was investigated, and the possible formation mechanism and mitigation method was discussed. The oxygen carrier conversion after the reduction decreased gradually in the cyclic test while it could not restore its oxygen capacity after the oxidation. The mass-based reaction rates during the reduction and oxidation also demonstrated the variation of reactivity of CaSO4 oxygen carrier. XRD analysis illustrated the phase change of CaSO4 oxygen carrier. CaS was the main reduction product, while a slight amount of CaO also formed in the cyclic test. ESEM analysis demonstrated the surface change of particles during the cyclic test. The reacted particles tested in the fixed bed reactor were not uniform in porosity. EDS analysis demonstrated the transfer of oxygen from CaSO4 to fuel gas while leaving CaS as the dominant reduced product. The results show that CaSO4 oxygen carrier may be an interesting candidate for oxygen carrier in CLC.

A novel biomass, autothermal, fast pyrolysis reactor with a draft tube and an internal dipleg dividing the reactor into two interconnected beds is proposed. This internally interconnected fluidized beds (IIFB) reactor is designed to produce high-quality bio-oil using catalysts. Meanwhile, the pyrolysis by-products, i.e., char, coke and non-condensable gases, are expected to burn in the combustion bed to provide the heat for the pyrolysis. On the other hand, the catalysts can be regenerated simultaneously. In this study, experiments on the hydrodynamics of a cold model IIFB reactor are reported. Geldart group B and D sand particles were used as the bed materials. The effects of spouting and fluidizing gas velocities, particle size, static bed height and the total pressure loss coefficient of the pyrolysis bed exit, on the flow patterns and pressure drops of the two interconnected beds are studied. Six distinct flow patterns, i.e., fixed bed (F), periodic spouted/ bubbling bed (PS/B), spouted bed with aeration (SA), spout-fluidized bed (SF), spout-fluidized bed with slugging (SFS) and spouted bed with backward jet (SBJ) are identified. The investigations on the pressure drops of the two beds show that both of them are seen to increase at first (mainly in the F flow pattern), then to decrease (mainly in the PS/B and SA flow patterns) and finally to increase again (mainly in the SA and SF flow patterns), with the increase of the spouting gas velocity. It is observed that a larger particle size and lower static bed height lead to lower pressure drops of the two beds.

There are growing concerns about increasing emissions of greenhouse gases and a looming global warming crisis. CO2 is a greenhouse gas that affects the climate of the earth. Fossil fuel consumption is the major source of anthropogenic CO2 emissions. Chemical looping combustion (CLC) has been suggested as an energy-efficient method for the capture of carbon dioxide from combustion. A chemical-looping combustion system consists of a fuel reactor and an air reactor. The air reactor consists of a conventional circulating fluidized bed and the fuel reactor is a bubbling fluidized bed. The basic principle involves avoiding direct contact of air and fuel during the combustion. The oxygen is transferred by the oxygen carrier from the air to the fuel. The water in combustion products can be easily removed by condensation and pure carbon dioxide is obtained without any loss of energy for separation. With the improvement of numerical methods and more advanced hardware technology, the time required to run CFD (computational fluid dynamic) codes is decreasing. Hence, multiphase CFD-based models for dealing with complex gas-solid hydrodynamics and chemical reactions are becoming more accessible. To date, there are no reports in the literature concerning mathematical modeling of chemical-looping combustion using FLUENT. In this work, the reaction kinetics models of the (CaSO4 + H2) fuel reactor is developed by means of the commercial code FLUENT. The effects of particle diameter, gas flow rate and bed temperature on chemical looping combustion performance are also studied. The results show that the high bed temperature, low gas flow rate and small particle size could enhance the CLC performance.

Chemical-looping combustion is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO 2 . Chemical-looping combustion of methane with calcium sulfate as a novel oxygen carrier was conducted in a laboratory scale fixed bed reactor. The effects of reaction temperature, gas flow rate, sample mass, and particle size on reduction reactions were investigated and an optimum operating condition was determined. The results show that this novel oxygen carrier has a high reduction reactivity and stability in a long-time reduction/oxidation test. The conversions of CH 4 increased with a higher temperature, smaller gas flow rate, larger sample mass and smaller particle size. The suitable reaction temperature seems to be around 950 °C. Low temperatures lead to a low CH 4 conversion, but a significant SO 2 formation was observed at a higher temperature. The release of SO 2 , CO, H 2 via a series of side reactions, carbon deposition and agglomeration were also discussed. The formation of SO 2 , CO, H 2 , and carbon can be avoided by optimization of the operating conditions.

Chemical-looping combustion is an indirect combustion technology with inherent separation of the greenhouse gas CO{sub 2}. The feasibility of using NiO as an oxygen carrier during chemical-looping combustion of coal has been investigated experimentally at 800-960{degree}C in the present work. The experiments were carried out in a fluidized bed, where the steam acted as the gasification-fluidization medium. Coal gasification and the reaction of oxygen carrier with the water gas take place simultaneously in the reactor. The oxygen carrier particles exhibit high reactivity above 900{degree}C, and the dry basis concentration of CO{sub 2} in the exit gas of the reactor is nearly 95%. The flue gas composition as a function of the reactor temperature and cyclic reduction number is discussed. At 800-960{degree}C, the dry basis concentration of CO{sub 2} in the flue gas presents a monotonously increasing trend, whereas the dry basis concentration of CO, H{sub 2}, and CH{sub 4} decreases monotonously. The concentrations of CO{sub 2}, CO, H{sub 2}, and CH{sub 4} in the flue gas as a function of cyclic reduction number present a para-curve characteristic at 900{degree}C. With the increase of cyclic reduction number, the dry basis concentration of CO{sub 2} decreases remarkably, while the dry basis concentrationsmore » of CO, H{sub 2}, and CH{sub 4} increase rapidly. Moreover, the peak value of H{sub 2} concentration is less than that of CO. The performance of the NiO-based oxygen carriers was also evaluated using an X-ray diffractometer and a scanning electron microscope to characterize the solid residues of oxygen carrier. The results indicate that NiO is one of the suitable oxygen carriers for chemical-looping combustion of coal.« less

Chemical-looping combustion (CLC) is a promising combustion technology for gaseous and solid fuel with efficient use of energy and inherent separation of CO2. The concept of a coal-fueled CLC system using calcium sulfate (CaSO4) as oxygen carrier is proposed in this study. Reduction tests of CaSO4 oxygen carrier with simulated coal gas were performed in a laboratory-scale fluidized bed reactor in the temperature range of 890−950 °C. A high concentration of CO2 was obtained at the initial reduction period. CaSO4 oxygen carrier exhibited high reactivity initially and decreased gradually at the late period of reduction. The sulfur release during the reduction of CaSO4 as oxygen carrier was also observed and analyzed. H2 and CO conversions were greatly influenced by reduction temperature. The carbon deposition ratio was found to be quite low. The oxygen carrier conversion and mass-based reaction rates during the reduction at typical temperatures were compared. Higher temperatures would enhance reaction rates ...

Chemical-looping combustion (CLC) is a promising technology for the combustion of gas and solid fuel with efficient use of energy and inherent separation of CO2. In this study, the cyclic test of a CaSO4-based oxygen carrier (natural anhydrite) in alternating reducing simulated coal gas and oxidizing conditions was performed at 950 °C in a fluidized bed reactor at atmospheric pressure. A high concentration of CO2 was obtained in the reduction. The H2 and CO conversions and CO2 yield increased initially and final decreased significantly. The release of SO2 and H2S during the cyclic test was found to be responsible for the decrease of reactivity of a CaSO4 oxygen carrier. The oxygen carrier conversion after the reduction reaction decreased gradually in the cyclic test. Through the comparison of mass-based reaction rates as a function of mass conversion at typical cycles, it was also evident that the reactivity of a CaSO4 oxygen carrier increased for the initial cycles but finally decreased after around 15 c...

The catalytic activity and kinetic behavior of catalytic reforming of methane with carbon dioxide over activated carbon were investigated as a function of reaction temperature, gas hourly space velocity (GHSV), and partial pressures of CH4 and CO2. The CH4 and CO2 conversions were greatly influenced by the reaction temperature in the range of 850−1050 °C. The apparent activation energies for CH4 and CO2 consumption and CO and H2 production were 32.63 ± 1.06, 25.54 ± 1.79, 24.81 ± 3.06, and 32.99 ± 2.58 kcal/mol, respectively. The curves of reaction rates versus GHSV showed various trends at different temperatures and indicated 7500 mL/h·g-cat was sufficient for operation in the kinetic regime. The reaction rate of methane and carbon dioxide over activated carbon was affected significantly by the partial pressures. Under a higher CO2 pressure, the excess CO2 reacted with H2 through the reverse water−gas shift (RWGS) reaction. The predictions of the CH4 and CO2 reaction rates based on a semiexperimental for...

Computational fluid dynamics (CFD) modeling, which has recently proven to be an effective means of analysis and optimization of energy-conversion processes, has been extended to coal gasification in this paper. A 3D mathematical model has been developed to simulate the coal gasification process in a pressurized spout-fluid bed. This CFD model is composed of gas−solid hydrodynamics, coal pyrolysis, char gasification, and gas phase reaction submodels. The rates of heterogeneous reactions are determined by combining Arrhenius rate and diffusion rate. The homogeneous reactions of gas phase can be treated as secondary reactions. A comparison of the calculated and experimental data shows that most gasification performance parameters can be predicted accurately. This good agreement indicates that CFD modeling can be used for complex fluidized beds coal gasification processes.