Search

We have developed a base mediated formamidation of amines with CO under mild conditions, which allows for the synthesis of a wide range of aromatic and aliphatic formamides in high yields and gram amounts in the absence of a transition metal.

Side-chain imidazolium–phosphate ion pairs PEMs with regulated imidazolium content were constructed by copolymerization and subsequent methylation processes.

Advanced water electrolysers represent a new direction in the field of low-cost green hydrogen production. However, the high cost of precious metal-catalysts in proton-exchange-membranes electrolysers, the high gas permeation of porous diaphragms and the alkaline instability at elevated temperatures (

Great efforts have been conducted to develop high temperature proton exchange membrane fuel cell (HT-PEMFC) due to its features of enhanced electrocatalyst reactivity, simplified hydrothermal management system and high CO tolerance of catalysts, and remarkable progress has been achieved. However, the easy leaching of phosphoric acid (PA) from the membranes during operation limits its commercial scale-up in complicated environments. This concept here mainly focuses on the recent developments for mitigation of PA loss in PEMs. The probable mechanisms of PA loss are proposed. The approaches to improve PA retention for example via introduction of phosphonic acid by covalent bond, using ion-pairs interaction and siphoning effect, and blending with inorganic nanoparticles are described in detail. Among these strategies, the siphoning effect from the intrinsic microporous PEMs is the most efficient and enables the cell to operate flexibly within a broad temperature range. Therefore, this concept may provide new ideas for the scientists to retain PA, to improve the cell performance and expand the potential applications of PA doped PEMs at elevated humidity and wide temperature range.

Synthesis of hybrid architectures for sulfur host materials has been certificated as an efficient way to enhance the performances of lithium-sulfur (Li–S) batteries owing to the generated synergetic effects from each component. However, it remains challenging to construct hybrid nanostructures with reasonable structure and rational composition to achieve high-performance of Li–S batteries. Here, a coordinated nanostructure constituted of the Mo2C nanoparticles embedded in the micro-flowered high content N-doped (11.73 at.%) carbon substrate (Mo2C@NC) is synthesized via using protonated g-C3N4 as the template, which is used as the sulfur host for Li–S batteries. Owing to the physical entrapment from the porous carbon substrate with special micro-flower morphology, and the synergistic chemisorption from pyridine N sites and polar Mo2C nanoparticles, the as-prepared Mo2C@NC can afford a high content of sulfur loading and enables fast/reliable sulfur electrochemistry. Given these, the Mo2C@NC based cathode with a high sulfur content of 76% delivers a high initial discharge capacity of 1403.7 mAh g−1 at 0.1 C. Even at a high rate of 2.0 C, it still shows desirable electrochemical performances with an initial capacity of 910.6 mAh g−1 and superb cycling stability with an average capacity decay rate of only 0.001% per cycle over 500 cycles. Moreover, upon a high sulfur loading of 5.5 mg cm −2, the Mo2C@NC/S cathode can still maintain decent sulfur related electrochemistry and achieves a high areal capacity of 5.56 mAh cm−2 with excellent stability. It is expected this work provides a new perspective to the rational design of conductive and polar material that suitable for high-efficiency and long-lasting Li–S batteries.

Membrane-based separation technology holds great promise to effectively address separation needs in chemical industries due to advantages in energy efficiency, scalability, and small footprint. Mixed matrix membranes based on polymer/metal organic frameworks (MOFs), which combine the ease of processability of polymer materials with the excellent adsorption characteristics of MOFs, have been widely investigated for gas separations. The preparation of gas separation membrane materials with both high flux and gas selectivity is the key to achieving efficient gas separation. Recent research results show that the permeability coefficient and gas pair selectivity of mixed matrix membrane materials are hardly improved simultaneously by adding second phase materials such as MOFs. When the loading of MOFs increases, most membranes have common problems such as particle agglomeration and non-selective interfacial defective structures, which lead to a significant decrease in separation performance. To resolve these issues, research scientists are devoted to tailoring the interfacial microstructure of mixed matrix membranes with an aim to exceed the Robeson upper limit. Many novel characterization techniques coupled with simulation studies were carried out to probe the filler dispersion behavior and interfacial structure within membranes in order to provide rules for rationally designing mixed matrix membranes. A variety of approaches have been proposed to finely tune the interfacial interaction by constructing hydrogen bonding and covalent bonding in the membranes. For example, synthesizing functionalized MOFs via mixed-linker or ligand exchange methods provides a good option to enhance interfacial adhesion within membranes. The amino groups, hydroxyl groups and other organic functional groups in MOFs have the capability to create hydrogen bonding. Moreover, these groups can preferentially adsorb specific gas molecules (such as CO2 molecules) to improve gas selectivity. Some researchers post-functionalized MOFs to graft reactive groups on their surface, incorporating them with cross-linkable polymers. Then the light/heat induced crosslinking reaction occurred within the membrane to seal its defective structure, thereby achieving a substantial improvement in membrane separation performance. The past publications on mixed matrix membranes in the decade demonstrated that the researchers have much more in-depth understanding and insights on the fabrication process, membrane morphology, and structure-property relationship of mixed matrix membrane materials. With respect to fundamental research, research scientists are committed to investigating the MOFs properties including crystal morphology, coordinated metal ion, functional groups on membrane performance. To yield high performance mixed matrix membranes, highly permeable polymers were rationally designed as the polymer matrix. However, to complement their widespread industrial application, scale-up of hollow fiber mixed matrix membranes needs to be further investigated. The membrane stability in humid gas feeds is required to be improved. It is also of importance to develop stable, cost-effective and scalable MOFs fillers. With a specific focus on interfacial manipulation of MOFs/polymer mixed matrix membranes for gas separations, this paper mainly reviewed the research progress in the fields of MOFs/polymer-based hybrid matrix membranes for gas separations. It focuses on three aspects: (1) Research progress on optimizing and characterizing the interfacial structure; (2) fundamental understanding of the influences of MOFs and polymers properties on membrane performance; (3) research progress on scale-up of mixed matrix membranes. Finally, the future development direction of mixed matrix membrane materials is proposed in order to provide research ideas for the rational design of high-performance mixed matrix membranes.

Certain polymers with very high free volume demonstrate a continuous network of interconnected void spaces due to the shape and rigidity of its macromolecular composition; as such, it becomes an in...

To investigate the effect of perfluorinated substituent on the properties of anion exchange membranes (AEMs), cross-linked polynorbornene-based AEMs with perfluorinated branch chains were prepared via ring opening metathesis polymerization, subsequent crosslinking reaction, and quaternization. The crosslinking structure enables the resultant AEMs (CFnB) to exhibit a low swelling ratio, high toughness, and high water uptake, simultaneously. In addition, benefiting from the ion gathering and side chain microphase separation caused by their flexible backbone and perfluorinated branch chain, these AEMs had high hydroxide conductivity up to 106.9 mS cm−1 at 80 °C even at low ion content (IEC < 1.6 meq g−1). This work provides a new approach to achieve improved ion conductivity at low ion content by introducing the perfluorinated branch chains and puts forward a referable way to prepare AEMs with high performance.

High-performance membranes exceeding the conventional permeability-selectivity upper bound are attractive for advanced gas separations. In the context microporous polymers have gained increasing attention owing to their exceptional permeability, which, however, demonstrate a moderate selectivity unfavorable for separating similarly sized gas mixtures. Here we report an approach to designing polymeric molecular sieve membranes via multi-covalent-crosslinking of blended bromomethyl polymer of intrinsic microporosity and Tröger’s base, enabling simultaneously high permeability and selectivity. Ultra-selective gas separation is achieved via adjusting reaction temperature, reaction time and the oxygen concentration with occurrences of polymer chain scission, rearrangement and thermal oxidative crosslinking reaction. Upon a thermal treatment at 300 °C for 5 h, membranes exhibit an O2/N2, CO2/CH4 and H2/CH4 selectivity as high as 11.1, 154.5 and 813.6, respectively, transcending the state-of-art upper bounds. The design strategy represents a generalizable approach to creating molecular-sieving polymer membranes with enormous potentials for high-performance separation processes., Microporous polymers become increasingly attractive as materials for the fabrication of permeable and selective gas separation membranes but separation performance is often limited by broad pore size distribution. Here, the authors design a porous polymer membrane via multi-crosslinking of miscible blends of microporous polymers enabling simultaneous high permeability and selectivity.

Poly[2,2’-(1,4-naphthalene)-5,5′-bibenzimidazoles] (NPBIs) were successfully synthesized in Eaton's reagent and first investigated as dense proton exchange membranes for vanadium flow batteries. The basic properties of NPBI were characterized and compared with poly[2,2’-(4,4′-oxybis(1,4-phenylene))-5,5′-bibenzimidazoles] (OPBIs) and Nafion® 212. NPBI displayed superior solubility in common aprotic polar solvents and hence eliminated the processability issues of PBIs for large scale application. The amorphous structure of NPBI endowed the membranes with higher acid doping level (2.2) compared to OPBI membranes (2.0) in 3 M H2SO4. NPBI membranes thus exhibited lower area resistance than OPBI membranes. Both NPBI and OPBI membranes demonstrated ultra-high selectivity compared with Nafion® 212. The NPBI membrane was more stable than OPBI in oxidizing 30 wt% H2O2 solution, confirming its excellent oxidative stability. Assembled in batteries, 15 μm thickness NPBI membrane conferred an energy efficiency (EE) of 91% which is higher than Nafion® 212 (85%) and OPBI (88%) at 40 mA/cm2. In addition, during long-term cycling (around 900 cycles) in single-cells, both NPBI and OPBI membranes mainly suffered from creep deformation instead of chemical degradation. Combining the inexpensive initial materials, mild synthesis condition, excellent solubility, high chemical stability and impressive performance, the NPBI membranes hold the potential for large scale use in vanadium flow batteries or even broader fields, like fuel cells.

Practical implementation of anion exchange membranes (AEMs) having N-cyclic quaternary ammonium (QA) in alkaline fuel cells is demonstrated. Two kinds of QAs are incorporated along PPO backbone, including six-membered (DMP) and bis-six-membered N-cyclic QA (ASU). PPO-ASU membranes with bulky ring size display the highest hydroxide conductivity of 76.5 mS cm−1 at 80 °C, due to more developed microphase separation. Unfortunately, AEMs with N-cyclic QA cations undergo chemical degradation with >45% ionic conductivity loss for PPO-ASU membrane after storage in 10 M NaOH at 80 °C for 250 h. Post-analysis of these AEMs reveals that Hoffmann elimination and ring-opening by SN2 substitution are the dominant degradation mechanisms, which is in agreement with the results for model compounds. ASU-based AEMs exhibit a maximum power density of 124.7 mW cm−2 in a single H2/O2 fuel cell at 60 °C. However, durability testing of fuel cell with the AEMs shows a 90% performance loss after operating at 0.3 V for 40 h. Further NMR analysis suggests that SN2 substitution triggered ring-opening is the dominant pathway for the degradation of AEMs, leading to the unsatisfactory fuel cell durability. These findings that compare the in situ and ex situ stability of AEMs give some insights on future directions for developing advanced AEMs.

A series of polystyrene (PS)-grafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) having pendent quaternary ammonium groups were synthesized as anion exchange membranes (AEMs) by the “grafting onto” method via a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed click chemistry. The length of PS grafting chains was controlled readily during ATRP. As expected, the polystyrene grafting chains showed excellent miscibility with PPO backbone. Therefore, transparent, flexible and tough membranes were obtained by solution casting. The miscible PS grafting chains induced well-defined hydrophobic-hydrophilic separation of the as-obtained PPO AEMs as confirmed by small-angle X-ray scattering (SAXS) technology. Moreover, the hydrophobic grafting chains can effectively control the water absorption, and thus improve the dimensional stability of AEMs in water. The PS-grafted AEMs showed higher IEC-normalized hydroxide conductivity but lower water uptake than the typical AEM without PS side chains, which may be attributed to the well-defined micro-phase separation in AEMs. The highest hydroxide conductivity of 15.9 mS/cm was achieved at 20 °C in spite of its low IEC value of 1.21 meq./g. Alkaline stability testing in 1 M NaOH at 80 °C demonstrated that PS-grafted PPO AEMs with side-chain-type QA cations showed excellent alkaline stability as evidenced by the change of hydroxide conductivity and the 1H NMR analysis after 500 h testing. Further H2/O2 alkaline fuel cell using PS-grafted PPO AEMs showed the maximum power density of 64.4 mW/cm2 at a current density of 140 mA/cm2, which is much higher than that of typical AEMs with C-16 alkyl grafting chains.

The rigid Troger's base microporous polymers were utilized to fabricate mixed matrix membranes with NH2-MIL-53 (Al) nanocrystals. Such N containing polymers have the ability to interact with NH2-MIL-53 (Al), therefore yielding transparent, robust, and plasticization–resistant hybrid membranes. The resulting membranes show a remarkable increase in gas permeability up to 3 times as a result of improved gas diffusivity and solubility without the selectivity loss. Much more improvements in CO2 solubility arise from the presence of CO2-adsorbing sites in Troger's base polymers and the CO2-selective adsorption properties of NH2-MIL-53 (Al), correspondingly leading to increased CO2 solubility selectivity. The gas separation performance shifts toward Robeson upper bonds upon the addition of MOFs. Particularly, the H2/CH4 separation performance overcomes the 2008 Robeson upper bond. In mixed gas feeds, the membranes display CO2 gas permeability up to 308 Barrer and CO2/N2 and CO2/CH4 mixed gas selectivities of 25.4 and 23.6 with virtually no evidence of plasticization. Much higher mixed-gas selectivity than permselectivity in these membranes are strongly correlated with the strongly adsorbing CO2 gas molecules blocking transport of large size molecules.

A new generation of solvent processable fluoropolyolefin was prepared and explored for durable anion exchange membrane fuel cells. By one-pot Ziegler-Natta copolymerization of a fluorinated monomer (1-(but-3-en-1-yl)-4-fluorobenzene) with 11-bromo-1-undecene and subsequent quaternization with trimethylamine, a series of tetraalkylammonium-functionalized fluoropolyolefin was synthesized by varying the molar ratio between monomers. The excellent solubility of the quaternized fluoropolyolefins provided by fluorinated moieties enabled the solvent processability to afford transparent and robust AEMs (PBFB-QA). Compared to heterogeneous quaternized membranes (H-PBFB-QA) and the corresponding non-fluorinated AEMs counterparts, the homogeneous quaternized PBFB-QA membrane showed lower water uptake due to the high hydrophobicity of fluorine atoms and more compact entanglement of polymer chains during solvent casting process. It was found that PBFB-QA membrane with an IEC of 1.47 meq/g showed the highest hydroxide conductivity of 29.2 mS/cm at 20 °C in spite of its low water uptake (11.9 wt%) and hydrated number (λ = 4.4). Thus, fluoropolyolefin AEMs standed out from the other reported polyolefin-based AEMs with the highest λ-normalized hydroxide conductivity, indicating the efficient ion transport in AEMs with the aid of less water. In addition to high ionic conductivity, fluoropolyolefin AEMs also exhibited excellent alkaline stability, and the retention of the conductivity of PBFB-QA-18 membrane was 89.5% after 700 h of aging in 1 M NaOH at 80 °C. More importantly, in contrast to the non-fluorinated polyolefin-based AEMs, fluoropolyolefin AEM showed better initial fuel cell device performance with a maximum power density of 133 mW/cm2 at 60 °C, and impressive device durability of alkaline fuel cell using the fluoropolyolefin AEM was observed with no loss of performance over 80 h of operation at 60 °C at a constant cell voltage of 0.3 V.

To produce a stable anion exchange membrane (AEM) for deployable electrochemical devices with a long lifespan, we here present the synthesis and properties of a series of piperidinium-functionalized poly(2,6-dimethyl phenylene oxide)s with different locations of piperidinium groups along the polymer backbones. A distinct phase separated morphology was observed for long side-chain-type AEMs (LSCPi) as confirmed by AFM analysis, which in turn enabled its higher hydroxide conductivity over side-chain-type (SCPi) and standard benzylmethyl piperidinium AEMs (BPi). A hydroxide conductivity of 29.0 mS cm−1 at 20 °C was achieved for the LSCPi membrane with an IEC value of 1.57 meq. g−1. This level of conductivity was lower than that of the corresponding QA-based AEMs (LSCQA) (38.7 mS cm−1 at 20 °C), probably as a result of its low IEC accompanied by low water uptake. The LSCPi membrane displayed excellent alkaline stability with 98% retention in conductivity after 560 h of testing in 1 M NaOH at 80 °C, and no obvious degradation was detected by NMR analysis of the aged sample. To demonstrate the feasibility of piperidinium-functionalized AEMs, both SCPi and LSCPi membranes were fabricated into a membrane electrode assembly for the H2/O2 alkaline fuel cell and AEM water electrolyzer applications. The highly conductive LSCPi membrane showed good cell performance with a peak power density of 116 mW cm−2 at 60 °C in alkaline fuel cells and 300 mA cm−2 at 1.80 V at 50 °C in AEM water electrolysis working with pure water. Although a gradual drop in performance was observed for both the alkaline fuel cell and water electrolyser durability testing at a constant current during the test of 8.7 h and 35 h respectively, the high durability of AEMs having piperidinium cations was verified by post-mortem analysis of aged AEMs by NMR spectroscopy. The current findings provided fundamental insights into the durability of AEMs under ex situ and in situ operating conditions and demonstrated that the piperidinium-functionalized AEM appears to be a promising material for durable AEM-based devices.

Conventional proton exchange membrane fuel cells (PEMFCs) operate at a narrow temperature range, either under low temperature conditions (80‒90°C) using fully-humidified perfluorosulfonic acid (Nafion®) membranes or under non-humidified high temperature conditions (140‒180°C) using phosphoric acid (PA)-doped membranes to avoid water condensation-induced PA leaching. To allow wide operational flexibility over the full spectrum of temperature and humidity ranges, we present an innovative design strategy by using PA-doped intrinsically ultramicroporous membranes constructed from rigid and contorted high free volume polymers. The membranes with an average ultramicropore radius of 3.3 Å showed a significant siphoning effect as confirmed by the delocalization of PA in 31P NMR, thus allowing high retention of PA even under highly humidified conditions and presenting more than three orders of magnitude higher proton conductivity retention than conventional dense PA-doped polybenzimidazole membranes (PBI/PA). The resulting PEMFCs display impressive performance over a much broader temperature range from − 20 to 200°C and can accomplish over 100 start-up/shut-down cycles even at − 20°C. The broad operational flexibility rendered from the high PA-retention can ultimately simplify heat and water management and thereby reduce PEMFC costs.

Highly permeable and selective membranes that exceed the conventional permeability-selectivity upper bound are attractive for energy-efficient gas separations. In the context microporous polymers have gained increasing attention owing to their high porosity and exceptional permeability. However, the moderate selectivity of microporous polymers caused by inherent broad distribution of cavities leads to a loss of valuable gas products, making them unfavorable for separating similarly sized gas mixtures. Here we report a new approach to designing polymeric molecular sieve membranes via multi-covalent-crosslinking of miscible blends of Polymer of Intrinsic Microporosity, i.e. bromomethyl (PIM-BM) and Tröger's Base (TB), enabling simultaneously high permeability and selectivity. Selective gas permeation is achieved via adjusting reaction temperature, reaction time and the oxygen concentration with occurrences of polymer chain scissor, rearrangement and thermal oxidative crosslinking reaction simultaneously. Upon a thermal treatment at 300 oC for 5h, membranes exhibit an O2/N2, CO2/CH4 and H2/CH4 selectivity as high as 11.1, 155.7 and 814.1, respectively, with an O2, H2 and CO2 permeability of 18.2, 358.2 and 67.6 Barrer, respectively, transcending the state-of-art upper bounds. The design strategy represents a generalizable approach to creating molecular-sieving polymer membranes with enormous potentials for energy-efficient separation processes.

Ion-solvating membranes based on polybenzimidazoles (PBI) have attracted increasing attention in alkaline water electrolysers due to their robust mechanical strength and excellent gas-tightness. However, they suffer from significant chemical degradation under alkaline conditions, especially at elevated temperature. Herein, we present an alkaline-stable ion-solvating membrane based on poly (2,2’-(1,4-naphthalene)-5,5′-bibenzimidazole) (NPBI) for alkaline water electrolysis application. The chemical composition and electrochemical properties of NPBI based ion-solvating membrane with bulky naphthyl groups around benzimidazolide C2 position was investigated when doping with different concentrations of KOH. More importantly, compared to poly (2,2’-(m-phenylene) -5,5′-bibenzimidazole) (m-PBI) membrane with sole phenyl next to the benzimidazolide moieties, ex-situ alkali stability test in 6 M KOH at 80 °C for 228 days demonstrated that introducing bulky naphthyl moieties around benzimidazolide C2 position in the backbones could increase the alkaline resistance for NPBI membrane, which agree well with model compounds investigation. In alkaline water electrolysis tests circulating 6 M KOH solution at 90 °C, membrane electrode assembly (MEA) with NPBI membrane demonstrated a current density of 2.5 A/cm2 at 2.01 V. Preliminary durability study of alkaline electrolysers was undertaken at 0.5 A/cm2 and 90 °C, demonstrating the excellent durability for NPBI-based MEA that stably operated for 298 h, while gradual voltage increase was observed after 148 h for the electrolyser with m-PBI membrane attributable to the significant chemical degradation of the membrane.