Organic-inorganic Membranes Research Articles

1,2-bis(triethoxysilyl)methane (BTESM)-derived organic–inorganic membranes with controlled sol particle size: Preparation and pervaporation dehydration performance of isopropanol aqueous solutions

1,2-bis(triethoxysilyl)methane (BTESM) is a bridged-type organoalkoxysilane, which was utilized for organic–inorganic membranes preparation via a sol–gel method to achieve high permselectivity, thus are promising for dehydration and purification of organic solvents. However, the particle size of the derived sol is crucial for membrane preparation during sol–gel processing, significantly influencing the membrane’s performance. Herein, we reported a novel strategy of controlling the sol particle size by adjusting the pH during the preparation process. BTESM-derived membranes were prepared by BTESM-H+ sol and BTESM-swing sol, which were subsequently employed for the dehydration of isopropanol (IPA) through pervaporation (PV). Compared with the BTESM-H+ sol, the particle size of the BTESM-swing sol prepared by the pH-swing method was increased from 1.3 nm to 32.7 nm. The larger particle size could hinder the permeation into the intermediate layer. Meanwhile, the dense arrangement of silica particles could efficiently retain IPA molecules, thereby substantially enhancing the rejection rate of IPA. The average particle size of the BTESM-swing sol was 18.7 nm at an acid-base ratio of 1.2 and acid-silicon ratio of 0.55, resulting a permeate flux of 1.04 kg·m−2·h−1 and separation factor of 521, while IPA rejection rate was 97.84 %. This work has shown that adjusting the pH during the process is a useful strategy of controlling the sol size for the preparation of organic–inorganic membranes. Hence, the control of sol particle size to achieve a high-performing membrane layer offers a novel approach to producing diverse membrane materials.

0.68% of solar-to-hydrogen efficiency and high photostability of organic-inorganic membrane catalyst

Solar-driven flat-panel H2O-to-H2 conversion is an important technology for value-added solar fuel production. However, most frequently used particulate photocatalysts are hard to achieve stable photocatalysis in flat-panel reaction module due to the influence of mechanical shear force. Herein, a highly active CdS@SiO2-Pt composite with rapid CdS-to-Pt electron transfer and restrained photoexciton recombination was prepared to process into an organic-inorganic membrane by compounding with polyvinylidene fluoride (PVDF). This PVDF networked organic-inorganic membrane displays high photostability and excellent operability, achieving improved simulated sunlight-driven alkaline H2O-to-H2 conversion activity (213.48 mmol m−2 h−1) following a 0.68% of solar-to-hydrogen efficiency. No obvious variation in its appearance and micromorphology was observed even being recycled for 50-times, which considerably outperforms the existing membrane photocatalysts. Subsequently, a homemade panel H2O-to-H2 conversion system was fabricated to obtain a 0.05% of solar-to-hydrogen efficiency. In this study, we opens up a prospect for practical application of photocatalysis technology.

Synergistically interface networked organic–inorganic photocatalytic membrane for highly stable Cr(VI) reduction and hydrogen production

Artificial conversion technology based on solar energy is one of most strategic artificial technologies for addressing environmental hazards and energy crisis. However, micro/nano-sized particulate catalysts mostly have the drawbacks of unstable microstructure and difficult recovery, which inevitably limits the practical application of photocatalysis technology. In order to overcome the defects of most inorganic particulate photocatalysts, a novel organic–inorganic photocatalytic membrane based on highly active Bi4Ti3O12/CdS composite and polyvinylidene fluoride (PVDF) was processed for simulated sunlight (SSL)-driven Cr(VI)-to-Cr(III) (CTC) reduction and H2O-to-H2 (HTH) conversion. Due to the maximum light harvesting capacity and synergistically electronic interaction of this synergistically interface networked organic–inorganic membrane, it possesses accelerated dynamics for separating/transferring photoexcitons and restraining photoexciton recombination, thereby outstanding CTC reduction rate (1.25 × 10-2 min−1) and HTH conversion rate (7.45 mmol∙m−2∙h−1) were achieved under SSL-irradiation, and highly stable photoactivity was maintained even being recycled for dozens of times owing to the convenient separation/recovery performance and stable organic–inorganic matrix. Subsequently, a panel reactor for wastewater purification was constructed to achieve 6.5 × 10-3 min−1 of CTC reduction rate under SSL-irradiation. This study provides a prospective insight for application of photocatalysis technology based on the membrane materials.

Conception of Hybrid Organic-Inorganic Membrane as New Electrolyte in All Solid-State Battery

All-solid-state lithium batteries (ASSBs) are considered like the next generation of electrochemical energy storage devices because of their safety and their high energy density up to 400Wh/kg. The all-solid-state battery is composed of a positive electrode (e.g., NMC (Li(Ni1∕3Mn1∕3Co1∕3)O2)), a negative one (Li), and a solid electrolyte, which is the critical component, composed of inorganic compound and/or solid polymer electrolyte (SPE) [1]. On the one hand, SPE have the advantage of an easy shaping with the technique already used in the manufacture of batteries and their flexibility allows obtaining a good interface with the electrode materials [2]. On the other hand, inorganic compounds generally have high ionic conductivity (10-3S/cm), they are stable electrochemically vs Li/Li+ and their transport number is close to 1 to promote the diffusion/migration of Li+ ions only. In order to combine the advantages of both types of materials, hybrid materials have been designed [3].First, a new adaptable polymer matrix based on PEO derivatives has been developed. A solvent-free synthesis has been designed from liquid and commercial precursors Poly(ethylene glycol) methyl methacrylate (PEGM) and Poly(ethylene glycol) dimethacrylate (PEGDM). These latter were copolymerized with Lithium 3-[(trifluoromethane)sulfonamidosulfonyl] propyl methacrylate (MTFSLi). The anion TFSI- is thus grafted to the PEO network, allowing exclusively the diffusion of the Li+ ion. This polymer matrix can be thus classified as single-ion conductor. In addition, the proportions between PEGM and PEGDM, acting as crosslinker, can be easily tuned. The PEGDM proportion controls the cross-linking density which modifies not only the glass transition temperature (Tg), but also the storage modulus (E’) and the free volume, and consequently the ionic conductivity of the polymer matrix which is the main property required for SPE. Finally, a ratio of PEGM:PEGDM (80:20) allows obtaining homogeneous SPE, self-standing and soft at room temperature, amorphous with a Tg of -41°C. The EO/Li ratio was then modulated in single-ion networks with the MTFSLi proportion, and an optimum in ionic conductivity of 2.10-7 S/cm @25°C has been measured for EO/Li ratio of about 20. The transport number measured by the Bruce and Vincent method [4] was t+=1,0 for the single ion conductor, demonstrating the effective grafting of the counter anion. This value has been validated by measuring the diffusion coefficients of 7Li and 19F in NMR. To our knowledge, this is the first time a real unity transport number is reported in the literature for a polymer electrolyte. Moreover, the electrochemical stability of this single ion system extends from 0 to 6V vs Li+/Li. These experiments suggest the interest of using the single-ion polymer in the formulation of composite positive electrode with high potential cathode materials, due to its stability in potential. Li metal is considered the ultimate anode for Li-batteries. The long-term electrochemical stability has been evaluated in symmetric Li/polymer electrolyte/Li cell. The cell is cycled at a constant current density of 0.2 mA/cm2. After 200 h of cycling the voltage reaches solely 2V. Accordingly, the grafting of the anion to the network limits an overpotential in the cell, allowing a more stable system over time.Second, the garnet Li6.4La3Zr2Al0.2O12 (LLZO) of the oxide family was associated to the previous polymer matrix. This garnet presents a high conductivity (10-4 S/cm @ 25°C), a good chemical stability not only against lithium metal but also against air and humidity, which is not the case of sulphides homologues. A 3D-fibrous network obtained by the electrospinning method was carried out with a solution containing the inorganic precursors, a polymer and an appropriate solvent [5]. Then this membrane is calcined at 850°C to obtain the 3D fibrous network of LLZO. The resulting self-standing porous inorganic material (~80% of porosity) exhibits a conductivity of the order of 10-6 S/cm @25°C. It was then impregnated with the polymer matrix precursors by capillarity and following by a polymerization. A self-standing membrane as thin as 80 µm containing 9%vol of LLZO was obtained. The conductivity of this hybrid membrane is comparable to that of the polymer (10-7S/cm @ 25°C). The resulting hybrid is mainly polymeric where the ionic conduction was realized by the polymeric matrix and the inorganic acts as a mechanical reinforcement. Preliminary results on high content of LLZO hybrid will also be presented, where a synergy of the both components is observed.[1] Janek. Nature Energy. 2016. Vol 1(9)p.16141. [2] Yue. Energy Storage Materials. 2016. Vol 5p.139-164. [3] Zheng. Chem Soc Rev. 2020. Vol 49p.8790-8839. [4] Bruce. Solid State Ion. 1988. Vol 28–30p.918–922. [5] A. La Monaca. Electrochemistry Communications. 2019. Vol 104p.106483. Figure 1

Structural Features of 4-VP-HEMA-SiO<sub>2</sub> Hybrid Membranes and Their Proton Conductivity

Hybrid organic-inorganic membranes based on tetraethoxysilane and orthophosphoric acid-doped copolymers of 4-vinylpyridine (4-VP) and 2-hydroxyethyl methacrylate (HEMA) were formed by the sol-gel synthesis method. The membranes are characterized by high values of exchange capacity and proton conductivity. An increase in the proton conductivity of hybrid organo-inorganic membranes compared to the initial copolymer can be associated with the generation of water of crystallization during the formation of a silicon dioxide fragment, which follows from quantum-chemical modeling of the local structure of the membrane, which includes an organic part from the copolymerization product of 4-VP with HEMA (44 atoms) and an inorganic part of 27 atoms, repeating the structure of the silicon dioxide block.

Biomimetic mineralization of nacre-inspired multiple crosslinked PVA/CaAlg/SiO2 membrane with simultaneously enhanced mechanical and separation properties

Inspired by the natural nacre structure, we propose a new strategy to fabricate mineralized, multiple crosslinked hydrogel membranes with the “rigid silica in soft polymer” nacre-like structure. In-situ SiO2 nanoparticles (NPs) and polyvinyl alcohol/sodium alginate (PVA/NaAlg) are used to simulate the rigid “bricks” and soft “mortar” compositions of nacre, respectively. The nacre-like mineralized (PVA/CaAlg/SiO2) membrane showed a higher tensile strength of 4.1 ± 0.08 MPa, excellent pure water flux of 170 ± 3 L/m2h, and an oil/water rejection rate of 99 %. The interwoven hierarchal structure, similar to nacre, was determined by SEM analysis. In addition, incorporating SiO2 NPs increases the anti-swelling, roughness, and hydrophilicity of the membranes. PVA/CaAlg/SiO2 membrane exhibited excellent superhydrophilicity (WCA value was 0°) and superoleophobicity underwater (OCA value was 162°). PVA/CaAlg/SiO2 membrane also showed excellent separation performance for water-soluble organic pollutants and can be used for dye separation with rejection efficiencies of 99.5 %, 99.1 %, and 98.3 % for Congo red (CR), Alizarin red (AR), and Sunset yellow (SY), respectively. Moreover, PVA/CaAlg/SiO2 membrane had outstanding long-term filtration and antifouling performance. The biomineralization-inspired structure provides a promising technique that can be used to prepare high-performance organic-inorganic membranes with great promise for wastewater separation application.

Research progress and prospects on hydrogen separation membranes

Abstract Membrane separation technologies, with a broad application prospect in the field of hydrogen separation, are characterized by the simplicity of the devices, high energy efficiency and environmental friendliness. The performance of separation membranes is the primary factor that determines the efficiency of hydrogen separation. Therefore, the development of hydrogen separation membranes is always a research focus. This paper presents and reviews the research developments and features of organic membranes, inorganic membranes and hybrid matrix membranes for hydrogen separations. First, the characterization methods of key index parameters of membrane materials are presented. Second, the performance parameters of different types of membrane are compared. Finally, the trend of technological development of different types of membrane materials is forecast.

Tailoring the Interfacial Interactions of Porous Polymer Membranes to Accelerate Atomic Layer Deposition: The Latent Path to Antifouling Membranes

Atomic layer deposition (ALD) is a powerful strategy to engineer hybrid organic-inorganic membranes with emergent functionalities. The combination of atomic-level thickness control, wide materials palette, and unprecedented conformality allow the physiochemical properties (e.g., hydrophilicity) of mesoporous polymer membranes to be precisely tuned. The nucleation of ALD materials growth on polymer surfaces relies on chemical interactions between the ALD metalorganic precursor and functional groups in the polymer structure and these interactions dictate the number of ALD cycles required to achieve a continuous coating. Strategies to enhance these interactions could enable desirable properties such as anti-fouling behavior to be imparted on inert polymer surfaces that lack the necessary functional groups for ALD nucleation. In this study, we demonstrate that the reactivity of polyacrylonitrile (PAN) membranes towards ALD metal oxide (MO) precursors with Lewis acid characteristics is enhanced by introducing Lewis base functional groups (amidoxime: Am) on the PAN backbone. The resulting Lewis acid-base interactions accelerates the MO nucleation in Am-PAN and reduce the number of deposition cycles required to achieve hydrophilicity compared to the untreated PAN membrane. Unveiling the reaction mechanism, the in-situ FTIR intensity changes established enhanced interaction dynamics between the ALD MO precursors and the Am-PAN membrane, unlike the PAN membrane. For similar MO cycles, through both spectroscopic and thermogravimetric analysis, we observe enhanced MO loading in the Am-PAN membrane compared to the PAN membrane. Here we have verified that strong Lewis acid-base interactions led to enhanced loading for a range of ALD MO materials including Al2O3, TiO2, SnO2, and ZnO. Most importantly, the Al2O3-Am-PAN hybrid membrane showed 23.3% higher antifouling capability compared to the pristine PAN membrane. Our approach expands the scope of design options for fouling-resistant porous hybrid inorganic-organic membranes and may reduce manufacturing costs of water treatment membranes.

(Energy Technology Division Research Award) Interplay between Synthesis, Mechanisms and Performance of Electrocatalysts and Ionomers for Ion-Exchange Membrane Fuel Cells

Ion-exchange membrane fuel cells (IEMFCs) are a family of electrochemical energy conversion and storage devices characterized by several attractive features, including outstanding energy conversion efficiency and a clean operation. IEMFCs are a cornerstone of the “hydrogen economy”, one of the most promising avenues to decarbonize the energy sector, with the ultimate purpose to curtail the emissions of greenhouse gases and mitigate global warming. Therefore, a goal of great practical relevance is to devise highly performing, durable and inexpensive IEMFCs .IEMFCs consist of an electrolyte membrane sandwiched between two electrodes. At the membrane-electrode interfaces are located electrocatalytic layers (EC layers) comprising suitable electrocatalysts (ECs) able to promote the redox processes exploited by the IEMFC operation. The IEMFC sub-families are distinguished by the attributes of the membrane, especially in terms of: (i) chemical features (e.g., polymeric backbone); (ii) mobile ion(s) (e.g., protons for proton-exchange membrane fuel cells, PEMFCs, OH- anions for anion-exchange membrane fuel cells, AEMFCs); and (iii) operation temperature. In the environment modulated by the ionomer, the properties of the ECs , with particular reference to the chemical composition of the active sites and support morphology, are correlated to their performance. Hence, to obtain an IEMFC exhibiting a high performance and durability is imperative to rationally design membranes and ECs that are: (i) highly compatible with one another; and (ii) able to express their best performance and durability in the same set of operating conditions.This contribution overviews our research activities aimed at the development of ECs and membranes for application in PEMFCs, high-temperature PEMFCs and AEMFCs. The topics include: (i) the innovative approaches for the synthesis of the functional components; (ii) the aspects of their physicochemical characterization, together with the unique and comprehensive frameworks contrived for the integration and interpretation of the experimental outcomes; and (iii) the steps to integrate the functional components in high-performing IEMFC prototypes.The ECs considered here are meant to promote the oxygen reduction reaction (ORR), a sluggish electrochemical process that is a major bottleneck in the operation of IEMFCs fueled with hydrogen. State-of-the-art ORR ECs are based on Pt nanoparticles supported on carbon (“Pt/C” ECs). Pt/C ECs warrant a sufficient performance, but suffer from a poor durability and require a high loading of platinum, a strategic element that is prone to trigger supply bottlenecks especially in the event of a large-scale rollout of IEMFCs. The ECs devised in our research laboratory are aimed at addressing all of these issues with materials exhibiting a number of unique features, as follows. (i) Active sites with either an intrinsic ORR kinetics much improved above the Pt baseline or completely “Pt-free”, consisting of an “active metal” (e.g., Pt, Fe) whose performance is boosted by one or more “co-catalyst” (e.g., Co, Ni, Cu, Sn). (ii) Strong, covalent interactions between the active sites and the C-/N- ligands of the “coordination nests” on the surface of the EC support, warranting a high durability. (iii) A support featuring a “core-shell” morphology, wherein a “core” consisting of suitable carbon system(s) is covered by a carbon nitride (CN) “shell”, bestowing facile charge and mass transport features (Figure 1(a)). The resulting ECs bestow the IEMFC a high performance with a minimized loading of Pt. Specifically, the PEMFC prototypes mounting the ECs here described yielded more than 20 kW∙gPt -1.The second main topic of this overview is the development and the study of the conductivity mechanism of separator membranes for IEMFCs. The latter consist mainly of ionomer matrices (e.g., perfluorinated systems such as Nafion™, SPEEK and developmental anion-exchange block copolymers), both pristine and doped with suitable nanofillers (e.g., conventional ceramic oxoclusters, “core-shell” oxocluters, among many others). The matrix-nanofiller interactions modulate the physicochemical features of the resulting hybrid inorganic-organic membrane, allowing to improve crucial features for applications in IEMFCs such as: (i) mechanical stability; and (ii) conductivity in dry conditions and high temperature. Other separator membranes are overviewed, including: (i) anion-exchange ionomers based on polyketone matrices (Figure 1(b)); (ii) hybrid inorganic-organic membranes for HT-PEMFCs based on oxocluster nanofillers and polybenzimidazole-like matrices; and (iii) membranes swollen with proton-conducting ionic liquids. These membranes underwent a thorough characterization elucidating their morphology, structure, thermal properties, thermomechanical relaxations and electric response (Figure 1(c)). The integration of all the above knowledges yielded a unique, comprehensive and general framework which proved crucial to elucidate the interplay between the physicochemical properties of the different phases within each membrane and their overall conductivity mechanism. This allowed to trigger the development of new high-performing separator membranes for application in IEMFCs. Figure 1

Fabrication of a Modified Polyethersulfone Membrane with Anti-Fouling and Self-Cleaning Properties from SiO2-g-PHEMA NPs for Application in Oil/Water Separation

To prepare anti-fouling and self-cleaning membrane material, a physical blending modification combined with surface grafting modification has been carried out; first, poly (2-hydroxyethyl methacrylate) grafted silica nanoparticles (SiO2-g-PHEMA NPs) were synthesized using surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and used as a blending modifier to fabricate a polyethersulfone (PES)/SiO2-g-PHEMA organic–inorganic membrane by the phase-inversion method. During the membrane formation process, hydrophobic PES segments coagulated immediately to form a membrane matrix, and the hydrophilic SiO2-g-PHEMA NPs migrated spontaneously to the membrane surface in order to reduce interfacial energy, which enhanced the hydrophilicity and anti-fouling properties of the PES/SiO2-g-PHEMA membrane. Importantly, the membrane surface contained abundant PHEMA segments, which provided active sites for further surface functionalization. Subsequently, the carboxyl-terminated fluorocarbon surfactant (fPEG-COOH) composed of hydrophilic polyethyleneglycol segments and low-surface-energy perfluorinated alkyl segments was synthesized via the esterification of fPEG with succinic anhydride. Lastly, the PES/SiO2-g-PHEMA/fPEG membrane was prepared by grafting fPEG-COOH onto surface of the PES/SiO2-g-PHEMA. Thus, a versatile membrane surface with both fouling-resistant and fouling-release properties was acquired. The PES/SiO2-g-PHEMA/fPEG membrane has a large oil–water flux (239.93 L·m−2·h−1), almost 21 times that of PES blank membrane and 2.8 times of the PES/SiO2-g-PHEMA membrane. Compared with the unmodified PES membrane, the flux recovery ratio increased from 45.75% to 90.52%, while the total flux decline ratio decreased drastically from 82.70% to 13.79%, exhibiting outstanding anti-fouling and self-cleaning properties. Moreover, the grafted fPEG segments on the membrane surface show excellent stability due to the presence of stable chemical bonds. The grafted segments remain at the surface of the membrane even after a long shaking treatment. This suggests that this PES/SiO2-g-PHEMA/fPEG membrane material has potential for application in oil/water separation.

Hybrid Organic–Inorganic Membranes for Photocatalytic Water Remediation

Mismanagement, pollution and excessive use have depleted the world’s water resources, producing a shortage that in some territories is extreme. In this context, the need for potable water prompts the development of new and more efficient wastewater treatment systems to overcome shortages by recovering and reusing contaminated water. Among the water treatment methods, membrane technology is considered one of the most promising. Besides, photocatalytic degradation has become an attractive and efficient technology for water and wastewater treatment. However, the use of unsupported catalysts has as its main impediment their separation from the water once treated. With this, providing the membranes with this photocatalyzed degradation capacity can improve the application of photocatalysts, since in many cases their application improves their recovery and reuse. This review describes the general photocatalytic processes of the main inorganic nanoparticles used as fillers in hybrid polymeric membranes. In addition, the most recent hybrid organic–inorganic membranes are reviewed. Finally, the membranes formed by metal–organic frameworks that can be considered one of the newest and most versatile developments are described.

Hybrid organic-inorganic membranes based on sulfonated poly (ether ether ketone) matrix and iron-encapsulated carbon nanotubes and their application in CO2 separation.

The need to reduce greenhouse gas emissions dictates the search for new methods and materials. Here, a novel type of inorganic–organic hybrid materials Fe@MWCNT-OH/SPEEK (with a new type of CNT characterized by increased iron content, 5.80 wt%) for CO2 separation is presented. The introduction of nanofillers into a polymer matrix has significantly improved hybrid membrane gas transport (D, P, S, and αCO2/N2), and magnetic, thermal, and mechanical parameters. It was found that magnetic casting has improved the alignment and dispersion of Fe@MWCNT-OH carbon nanotubes. At the same time, CNT and polymer chemical modification enhanced interphase compatibility and membrane CO2 separation efficiency. The thermooxidative stability, and mechanical and magnetic parameters of composites were improved by increasing new CNT loading. Cherazi's model turned out to be suitable for describing the CO2 transport through analyzed hybrid membranes. The comparison of the transport and separation properties of the tested membranes with the literature data indicates their potential application in the future and the direction of further research.

Membranes for separation of alkali/alkaline earth metal ions: A review

The alkali metal and alkaline-earth metal elements, located in the adjacent main-groups of the periodic table, always have similar electronic structures and chemical properties. Thus, they are usually coexisting in ores or water resources. The separation of alkali metal ions and alkaline-earth metal ions has significant application prospect in seawater desalination, resource recovery and energy storage, which are paramount for the sustainable development of the environment, resources and energy. Membrane technologies have been investigated extensively in this area and have attracted widespread attention because of their advantages of environmental friendly and energy efficient. Accordingly, this work reviews recent advances in various types of membranes focused on the separation of alkali and alkaline earth metal ions, including organic membranes, inorganic membranes and mixed matrix membranes. Moreover, this review provides insights into the design and fabrication of membranes, the separation mechanisms, and the advantages and current challenges of each membrane.

Hierarchical structure control of MgAl2O4 porous ceramics and application to organic polymer filtration membrane

AbstractAsymmetric porous ceramic membranes typically have a very thin top layer with finer pores covered on thick porous layers with micrometer‐scale pores. In this study, triple‐layer asymmetric MgAl2O4 filtration membranes composed of (i) an Al2O3 support layer (circular pellet with ~10 µm pores) prepared by dry pressing, (ii) a reactively sintered MgAl2O4 intermediate layer (~40 µm in thickness), prepared by dip‐coating with tackifier (PEG‐20000), and (iii) another reactively sintered finer MgAl2O4 membrane layer (~20 µm in thickness), prepared by dip‐coating without tackifier. Different from our previous studies for the microfiltration of submicrometer‐sized particles, in this study we have challenged the ultrafiltration of water‐soluble polymer molecules. Their filtration performance was investigated by removing 1 million molecular‐weight polyethylene oxide (PEO) from water. The rejection rate of the triple‐layer asymmetric filtration membrane to PEO was ~14%. The all‐ceramic membrane in this study showed a comparable rejection rate with the reported inorganic–organic membrane, and it must be promising for excellent chemical and thermal stabilities as well as long durability.

(Invited) Designing Ionic Scaffold for Efficient Solid Electrolyte for All Solid State Battery

All solid state battery has gained recently much attention because of their potential to store more energy while being safer to operate compared to liquid electrolyte Li-ion batteries. The development of solid electrolytes with superior electrochemical properties is highly desirable. Representatively, sulfide and oxide-based solid electrolytes have been vigorously researched and demonstrated for high-performance all-solid-state batteries. The oxide-based solid electrolytes have superior electrochemical stability compared to the sulfide one, but relatively low ionic conductivity and low processability owing to their mechanically rigid and brittle features which must be taken into consideration to achieve high-performance all-solid-state batteries. In this presentation, different synthesis and processing approaches will be presented to design efficient Li-ion conducting ceramic. Their ionic conductivity measured at room temperature will be discussed as function of their microstructure (porosity, pparticle size, chemical composition,...).First, we study the synthesis, the fabrication of dense ion-conducting ceramic such as (Li1.3Al0.3Ti1.7(PO4)3) LATP and (Li7La3Zr2O12) LLZO and their electrochemical characterization. Starting from “sol-gel” like synthesis coupled with heating at high temperature, we have succeeded to achieve dense ceramic with ionic conductivity of ~10-4 S/cm for LLZO and for LATP, attesting good quality of the purity and crystallinity. More interestingly, we have also developed an innovative synthesis and processing approach to sinter LATP with suitable properties in one single step, with the aid of microwave heating. Pure and crystalline LATP ceramics are achieved in only one single step starting from amorphous, compacted LATP’s precursors powders. Despite a relative density of 88%, the ionic conductivity is about 3.14 x 10-4 S.cm-1 at ambient temperature.With the objective of developing hybrid organic-inorganic membrane, we extend our knowledge on the synthesis of 3-D network of crystalline LATP or LLZO fibers by coupling an electrospinning process with the sol-gel synthesis followed by an optimized thermal treatment (atmosphere, temperature and dwelling time). Depending on the processing parameters of electrospinning, different fiber mats organization and density have been achieved. The Li+ ion conductivity of these fibers mats was evaluated by impedance spectroscopy at ambient temperature. As an example, the Li ion conductivity for LATP was estimated to be 3 × 10−4 mS/cm; note that this value is not affected by the water content used in the electrospinning chamber and therefore by the microstructure of the LATP mat. Of course, this value is low compared to that observed on the dense ceramic; this is linked to the porosity of the LATP fiber mat of about 60%. Taking into account the porosity of the fiber mats, the conductivity values are corrected and finally the corrected conductivity value is 1 order of magnitude higher than the one achieved on ceramic with low relative density. This result shows that good particle−particle contact is achieved along the LATP fibers and that most of the LATP fibers are connected to each other to ensure a continuous Li ion pathway throughout the porous ceramics.

High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells

Silica nanosheets (SN) derived from natural vermiculite (Verm) were successfully incorporated into polyethersulfone–polyvinylpyrrolidone (PES–PVP) polymer to fabricate high–temperature proton exchange membranes (HT–PEMs). The content of SN filler was varied (0.1–0.75 wt%) to study its influence on proton conductivity, power density and durability. Benefiting from the hydroxyl groups of SN that enable the formation of additional proton–transferring pathways, the inorganic–organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm2 at 150 °C without humidification when the content of SN is 0.25 wt%. Furthermore, exfoliated SN (E–SN) and sulfonated SN (S–SN), which were fabricated by a liquid–phase exfoliation method and silane condensation, respectively, were embedded in PES–PVP polymer matrix by a simple blending method. Due to the significant contribution from sulfonic groups in S–SN, the membrane with 0.25 wt% S–SN reached the highest proton conductivity of 51.5 mS/cm and peak power density of 546 mW/cm2 at 150 °C, 48% higher than the pristine PES–PVP membranes. Compared to unaltered PES–PVP membrane, SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150 °C. Using a facile method to prepare 2D SN from natural clay minerals, the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT–PEMs.

An efficient barrier toward vanadium crossover in redox flow batteries: The bilayer [Nafion/(WO3)x] hybrid inorganic-organic membrane

A family of hybrid inorganic-organic ion-exchange membranes (IEMs) is prepared, indicated as [Nafion/(WO3)x]. The IEMs consist of Nafion® dispersing different loadings (x) of tungsten oxide nanofiller. Morphology studies carried out by scanning electron microscopy (SEM) and micro-Raman investigations reveal that one side of each hybrid IEM exhibits a high concentration of the WO3 nanofiller. In the remaining part of each IEM the concentration of the filler is much lower and constant. The correlation between the asymmetrical nature and the performance of the hybrid IEMs is studied in a single-cell vanadium redox flow battery (VRFB). In comparison with the Nafion 212 reference, at the same current density of 50 mA∙cm−2, [Nafion/(WO3)0.587] demonstrates: (i) a higher Coulombic efficiency (93% vs. 88%), a higher energy efficiency (75% vs. 65%) and a higher capacity retention (62% vs. 42%).

(Keynote) Electrical Response and Conductivity Mechanism in Ion-Exchange Membranes

Electrochemical energy conversion and storage systems are very important in today’s worldwide efforts to decarbonize the energy sector. Indeed, these systems exhibit a very high energy conversion efficiency, are easy to scale-up and are not affected by geographical constrains [1]. Two important examples of these systems are ion-exchange membrane fuel cells (IEMFCs) and redox flow batteries (RFBs). On one hand, ion-exchange membrane fuel cells are particularly suited for light-duty vehicles and small-scale stationary systems (e.g., auxiliary power units) owing to their high energy and power densities. On the other hand, redox flow batteries are ideally suited to the large-scale storage of energy for the power grid as they are characterized by a very high turnover efficiency and an outstanding cyclability [2].Electrolyte membranes (EMs) are present at the core of both IEMFCs and RFBs. The role of such EMs is to: (i) keep separated the electroactive species involved in the redox reactions taking place at the electrodes and, at the same time, (ii) ensure a facile and selective migration of ions to prevent the polarization of the device and allow for the establishment of large current densities. As of today, the most widely adopted EMs are based on perfluorinated ionomers such as Nafion™, SPEEK and other similar macromolecules [3, 4]. These systems exhibit a high conductivity, chemical and electrochemical stability; however, they also suffer from important drawbacks such as: (i) a dramatic drop in conductivity at T > 80°C and in dry conditions; (ii) poor mechanical properties; and (iii) a high permeability to active species (e.g., vanadium) [5]. Consequently, it is often necessary to: (i) add humidification modules to ion-exchange membrane fuel cells, thus raising the bulk and cost of the device; or (ii) especially in the case of vanadium redox flow batteries (VRFBs), use thick EMs that curtail the current density.These drawbacks can be addressed by implementing several different strategies, that include: (i) the introduction of a filler in the EM, giving rise to a hybrid inorganic-organic membrane [6]; (ii) the fabrication of EMs with different macromolecules (e.g., polybenzimidazole, PBI) [6-11]. All of these strategies operate by modulating the physicochemical properties of the EMs, with a particular reference to the phase segregation at the nano/mesoscale [3]. This work overviews the study of the interplay between the physicochemical properties (i.e., the chemical composition, thermoanalytical properties, morphology and structure) and the electrical response of hybrid ion-exchange membranes by means of advanced investigation techniques such as Broadband Electrical Spectroscopy (BES).The results allow to elucidate the interplay among chemical and physical properties of the different phases within each EM and their conductivity mechanism. Indeed, the understanding of the relationship taking place between structure and ion conduction mechanisms is crucial in order to trigger the development of new high-performing proton and anion conducting membranes for applications in fuel cells and redox flow batteries.

Hybrid organic-inorganic materials on the basis of acrylic monomers and TEOS prepared by simultaneous UV-curing and sol-gel process

In this work cross-linked hybrid organic-inorganic membranes consisting of polymeric matrix functionalized with sulfonic groups and uniformly distributed silica domains have been successfully synthesized through in situ polymerization strategy via photo-initiated copolymerization of acrylic monomers (acrylonitrile AN, acrylamide AAm, 3-sulfopropyl acrylate potassium salt SPAK) and simultaneous formation of silica counterpart using TEOS-based sol-gel system. N,N′-methylenebis(acrylamide) (MBA) was used as a cross-linker. The ratio between monomers was maintained stable, whereas the amount of added sol-gel system was varied. The influence of inorganic component content on properties of hybrid polymer-inorganic membranes was investigated. Chemical composition, thermal properties, structure and morphology of the obtained hybrid membranes were investigated by ATR-FTIR, TGA, DSC, SEM and EFTEM. Proton conductivity of the synthesized membranes was high (7.6 to 13.5 mS/cm) and increases with an increase of silica content. The prepared membranes were thermally stable up to 90 °C, and exhibited proton conductivity and swelling coefficients sufficient for possible use as proton-conducting membranes.

Preparation and characterization of UV-curable cross-linked organic-inorganic membranes

Preparation and characterization of UV-curable cross-linked organic-inorganic membranes