Inorganic Membranes for Hydrogen Separation

Hydrogen, one of the most promising energy carriers for the future, is currently produced mainly by natural gas reforming or coal gasification, where mixtures containing H₂, CO₂ and contaminants like CO, H₂S and CH₄ are obtained. Among other methods, membrane technology has received special attention due to its potential efficiency for hydrogen separation, simplicity of operation, low energy consumption, and because it is environmentally friendly. For this application, the inorganic membranes can be essentially divided into five main families: metallic and proton conducting (dense phases), and silica, zeolite and carbon molecular sieve (porous solids). Over the past 20 years, palladium-based membranes have been the most studied and implemented at industrial level; however, recent advances in other membrane types have received a great deal of attention. This article critically reviews more than 520 publications, highlighting the latest research developments on inorganic membranes for the recovery and purification of hydrogen, with emphasis on their structural characteristics, synthesis, commercial application, drawbacks and challenges. Furthermore, a large compilation of data is provided in Supplementary Material divided according to membrane type.     

Hybrid Organic–Inorganic Silica Gel Carriers with Controlled Drug‐Delivery Properties

Pure and modified silica materials were synthesised by a sol–gel process and used as carrier for the controlled release of ibuprofen, selected as model drug. A one‐step synthesis was optimised for the preparation of various silica–drug composites by using tetraethoxysilane and 3‐aminopropyltriethoxysilane as precursors at different molar ratios. The presence of aminopropyl groups on the silica surface influences the drug‐delivery rate leading to a high degree the desorption process controlled.     

An In Situ Carbonization–Replication Method to Synthesize Mesostructured WO3/C Composite as Nonprecious‐Metal Anode Catalyst in PEMFC

A meostructured WO₃/C composite with crystalline framework and high electric conductivity has been synthesized by a new in situ carbonization–replication route using the block copolymer (poly(ethylene glycol)‐block‐poly(propylene glycol)‐block‐poly(ethylene glycol)) present in situ in the pore channels of mesoporous silica template as carbon source. X‐ray diffraction, X‐ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetry differential thermal analysis, and N₂ adsorption techniques were adopted for the structural characterization. Cyclic voltammetry, chronoamperometry, and single‐cell test for hydrogen electrochemical oxidation were adopted to characterize the electrochemical activities of the mesoporous WO₃/C composite. The carbon content and consequent electric conductivity of these high‐surface‐area (108–130 m² g^?1) mesostructured WO₃/C composite materials can be tuned by variation of the duration of heat treatment, and the composites exhibited high and stable electrochemical catalytic activity. The single‐cell test results indicated that the mesostructured WO₃/C composites showed clear electrochemical catalytic activity toward hydrogen oxidation at 25 °C, which makes them potential non‐precious‐metal anode catalysts in proton exchange membrane fuel cell.     

A Novel Route to Organic–Inorganic Hybrid Nanomaterials

The in situ formation of functionalized silica nanoparticles is reported. The reactive stabilizers used in the study, [3‐(2‐bromoisobutyryl)propyl]triethoxysilane and [3‐(2‐bromoisobutyryl)propyl]ethoxydimethylsilane, have an atom transfer radical polymerization (ATRP) initiator at the noncondensable end. Condensation with tetraethoxysilane yields silica nanoparticles with a surface‐immobilized initiator. The size of these functionalized silica nanoparticles can be controlled by varying the time of initiator addition and initiator concentration. The silica particle sizes ranged from 10 to 300 nm. With the initiator functionalized silica nanoparticles, ATRP synthesis was performed with styrene, tert‐butyl acrylate, and methyl acrylate to produce organic–inorganic nanomaterials.

     

Combining Light Harvesting and Electron Transfer in Silica–Titania‐Based Organic–Inorganic Hybrid Materials

A convenient protocol to fabricate an organic–inorganic hybrid system with covalently bound light‐harvesting chromophores (stilbene and terphenylene–divinylene) and an electron acceptor (titanium oxide) is described. Efficient energy‐ and electron‐transfer processes may take place in these systems. Covalent bonding between the acceptor chromophores and the titania/silica matrix would be important for electron transfer, whereas fluorescence resonant energy transfer (FRET) would strongly depend on the ratio of donor to acceptor chromophores. Time‐resolved spectroscopy was employed to elucidate the detailed photophysical processes. The coupling of FRET and electron transfer was shown to work coherently to lead to photocurrent enhancement. The photocurrent responses reached a maximum when the hybrid‐material thin film contained 60 % acceptor and 40 % donor.     

Two‐in‐One: Inherent Anhydrous and Water‐Assisted High Proton Conduction in a 3D Metal–Organic Framework

The development of solid‐state proton‐conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel‐cell technology. A 3D metal–organic framework (MOF) with acid–base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water‐assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid‐state proton‐conducting materials that work under both anhydrous and humid conditions.     

Hybrid Organic–Inorganic Antiperovskites

Substitution of A‐site and/or X‐site ions of ABX₃‐type perovskites with organic groups can give rise to hybrid perovskites, many of which display intriguing properties beyond their parent compounds. However, this method cannot be extended effectively to hybrid antiperovskites. Now, the design of hybrid antiperovskites under the guidance of the concept of Goldschmidt's tolerance factor is presented. Spherical anions were chosen for the A and B sites and spherical organic cations for the X site, and seven hybrid antiperovskites were obtained, including (F₃(H₂O)_x)(AlF₆)(H₂dabco)₃, ((Co(CN)₆)(H₂O)₅)(MF₆)(H₂dabco)₃ (M=Al³⁺, Cr³⁺, or In³⁺), (Co(CN)₆)(MF₆)(H₂pip)₃ (M=Al³⁺ or Cr³⁺), and (SbI₆)(AlF₆)(H₂dabco)₃. These new structures reveal that all ions at A, B, and X sites of inorganic antiperovskites can be replaced by molecular ions to form hybrid antiperovskites. This work will lead to the synthesis of a large family of hybrid antiperovskites.     

Triazole Functionalized Sol-Gel Membranes,Effect of Crosslink Density and Heterocycle Content on Water Free Proton Conduction and Membrane Mechanical Properties

Freestanding, ion conducting, membranes were synthesized by incorporating triazole-containing tetracyclosiloxanes into a polyethylene glycol-tetraethyl orthosilicate (PEG-TEOS) based sol-gel matrix. These membranes show comparable or higher proton conductivities than their linear, liquid, polysiloxane analogs and fall within an order of magnitude of the target ion mobilities for use in proton exchange membrane fuel cells (PEMFC's). The absence of any unbound PEG or cyclic siloxane was confirmed by proton nuclear magnetic resonance (¹H-NMR), while the chemical structure and composition of the membranes was corroborated by Fourier transform infrared (FTIR) spectroscopy. Thermogravimetric analysis (TGA) indicated that the membranes are stable up to 180°C and differential scanning calorimetry (DSC) analysis showed complete suppression of PEG crystallization after incorporation of the triazole-functionalized cyclosiloxanes. An increase in the molecular weight of the PEG chains used to create the sol-gel matrix produced membranes with increased flexibility and higher proton conductivities at temperatures below 100 °C. Pulse field gradient echo (PFG) NMR studies showed an increase in the apparent diffusion coefficient of the sol-gel threaded cyclosiloxane motifs compared to the linear polysiloxanes, indicating a significant reduction on the coupling between mechanical strength and ion transport capability.     

An Organic–Inorganic Hybrid Exhibiting Electrical Conduction and Single‐Ion Magnetism

The first three‐dimensional (3D) conductive single‐ion magnet (SIM), (TTF)₂[Co(pdms)₂] (TTF=tetrathiafulvalene and H₂pdms=1,2‐bis(methanesulfonamido)benzene), was electrochemically synthesised and investigated structurally, physically, and theoretically. The similar oxidation potentials of neutral TTF and the molecular precursor [HNEt₃]₂[M(pdms)₂] (M=Co, Zn) allow for multiple charge transfers (CTs) between the SIM donor [M(pdms)₂]^n? and the TTF^.+ acceptor, as well as an intradonor CT from the pdms ligand to Co ion upon electrocrystallisation. Usually TTF functions as a donor, whereas in our system TTF is both a donor and an accepter because of the similar oxidation potentials. Furthermore, the [M(pdms)₂]^n? donor and TTF^.+ acceptor are not segregated but strongly interact with each other, contrary to reported layered donor–acceptor electrical conductors. The strong intermolecular and intramolecular interactions, combined with CT, allow for relatively high electrical conductivity even down to very low temperatures. Furthermore, SIM behaviour with slow magnetic relaxation and opening of hysteresis loops was observed. (TTF)₂[Co(pdms)₂] ( 2‐Co ) is an excellent building block for preparing new conductive SIMs.     

Highly‐Ordered Hybrid Organic‐Inorganic Isoporous Membranes from Polymer Modified Nanoparticles

Summary: Organic‐inorganic hybrid materials consisting of nanosized silica particles with surface grafted PS or PS‐b‐PMMA were synthesized using ATRP. These hybrid materials were used in the fabrication of highly‐ordered isoporous membranes. Optical characterization revealed that the membranes consisted of hexagonally ordered pores of uniform size. The combination of an open pore structure and high surface area makes isoporous membranes into materials of high interest in fields as biotechnology and photonics.

Image from optical microscope of hybrid nanoparticle membrane of SiO₂‐g‐PS with hexagonally‐ordered pores.     

The Effect of Humidity upon the Crystallization Process of Two‐Step Spin‐Coated Organic–Inorganic Perovskites

Moisture is shown to activate the reaction between PbI₂ and methylammonium halides. In addition, two activating mechanisms are proposed for the formation of CH₃NH₃PbI₃ and CH₃NH₃PbI_3?xCl_x films from a series of carefully controlled experiments. When these rapidly formed perovskite films are directly fabricated into the devices, poor photovoltaic properties are found, due to heavy surface charge recombination. However, the cell performance can be significantly enhanced to 13.63 % and to over 12 % in the steady state for CH₃NH₃PbI₃ and to 15.50 % and over 14 % in the steady state for CH₃NH₃PbI_3?xCl_x, if the rapidly formed perovskite film is annealed. Thus, it is believed that moisture (below 60 % RH) is not a problem for the fabrication of highly efficient perovskite solar cells.     

The Significance of Ion Conduction in a Hybrid Organic–Inorganic Lead‐Iodide‐Based Perovskite Photosensitizer

The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid‐state properties, these materials surprised by anomalies such as a huge apparent low‐frequency dielectric constant and pronounced hysteretic current–voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build‐up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic–inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.     

Synthesis and Evaluation of Novel Proton Exchange Membranes Containing the Semisquaric Acid Group

We focus our attention here on semisquaric acid, which is known to show high acidity, as a new proton dissociating group for proton exchange membranes (PEMs). The introduction of a squaric acid group into aromatic polymers was conducted by the reaction of lithiated aromatic polymers and diisopropoxy squarate, followed by treatment with hydrochloric acid. A resulting polyphenylsulfone membrane with the squaric acid group introduced (PPSf‐SQ, IEC = 4.1 meq·g⁻¹) showed proton conductivity of 1.0 × 10⁻¹ S·cm⁻¹ at 80 °C under 95% relative humidity, which indicates that the semisquaric acid has the potential to become an alternative proton‐conducting group for PEMs.

     

Proton Conduction in Metal–Organic Frameworks and Related Modularly Built Porous Solids

Proton‐conducting materials are an important component of fuel cells. Development of new types of proton‐conducting materials is one of the most important issues in fuel‐cell technology. Herein, we present newly developed proton‐conducting materials, modularly built porous solids, including coordination polymers (CPs) or metal–organic frameworks (MOFs). The designable and tunable nature of the porous materials allows for fast development in this research field. Design and synthesis of the new types of proton‐conducting materials and their unique proton‐conduction properties are discussed.     

Hybrid Organic–Inorganic Thermoelectric Materials and Devices

Hybrid organic–inorganic materials have been considered as a new candidate in the field of thermoelectric materials since the last decade owing to their great potential to enhance the thermoelectric performance by utilizing the low thermal conductivity of organic materials and the high Seebeck coefficient, and high electrical conductivity of inorganic materials. Herein, we provide an overview of interfacial engineering in the synthesis of various organic–inorganic thermoelectric hybrid materials, along with the dimensional design for tuning their thermoelectric properties. Interfacial effects are examined in terms of nanostructures, physical properties, and chemical doping between the inorganic and organic components. Several key factors which dictate the thermoelectric efficiency and performance of various electronic devices are also discussed, such as the thermal conductivity, electric transportation, electronic band structures, and band convergence of the hybrid materials.     

微孔聚四氟乙烯增强复合质子交换膜研究

质子交换膜燃料电池(PEMFC)由于具有能量转化率高、环保等特点而受到广泛关注。作为质子交换膜燃料电池核心组件之一的关键材料质子交换膜(PEM)成为燃料电池研究的热点。聚四氟乙烯(PTFE)微孔膜由于具有高的化学和尺寸稳定性,被用来作为复合质子交换膜的增强基底。本文对当前微孔PTFE增强复合质子交换膜的研究进展进行了综述,介绍了微孔PTFE与全氟类离子树脂、部分含氟类离子树脂和非氟类离子树脂等的复合情况,着重说明各种复合增强的类型和方式,并比较了复合改性前后各种膜的物性特点,最后展望了微孔PTFE复合增强膜的未来研究趋势。     

Molecular Relaxations in Hybrid Organic–Inorganic Materials Prepared by a Sol–Gel Process

Organic–inorganic hybrid materials based on alkoxy-silane-terminated macromonomers synthesised from a hydroxy-terminated hydrogenated polybutadiene, H-PBD, have been investigated. Different morphologies of the hybrid materials are obtained according to the conditions of the synthesis and to the non compatibility between the organic and the inorganic components. In order to establish the relationships between the structure and the properties of the organic–inorganic (O/I) materials, infrared, small-angle X ray scattering, transmission electron microscopy, dynamical mechanical spectroscopy and dielectric measurements have been performed. This paper focuses especially on the analysis of the dielectrical relaxations in a large range of frequencies and temperatures compared with the dynamic mechanical one to propose a model of morphology of the final O/I materials. It is found in particular that a distinct interfacial region between the organic-rich phase and the silicate clusters is developed in the case of the low acid-to-alkoxide ratio for hybrids (based on γ-amino propyl triethoxysilane) (i.e. for the long periods of gelation). © 1997 John Wiley & Sons, Ltd.     

燃料电池用高温质子交换膜

与传统质子交换膜燃料电池相比,高温质子交换膜燃料电池(HT-PEMFCs)不仅可以提高催化剂对CO 的耐受能力,还能简化水热管理,提高能量转化效率.高温质子交换膜是实现高温操作的关键部件之一.掺杂无机磷酸的高温质子交换膜因为在高温度(100～200℃)和低相对湿度下具有较高的质子传导率,以及较长使用寿命而成为研究的热点...