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The design of ion conductive functional side chains is critical to tune the selectivity of protons to vanadium ions in ion conductive membranes for vanadium redox flow batteries (VRFBs); however, it is far from satisfactory. Herein, the concept of a quinone convertible sulfated ion conductive side chain is proposed with tunable Donnan effect and strong proton conducting ability. The electrically neutral phenol group in the side chain will be chemically converted to quinone of lower electronegativity in situ in the highly acidic VRFB operating environment, which leads to about a 5 fold increase in zeta potential to repel vanadium ions. Meanwhile the sulfate ester cationic exchange group in the side chain dominates the well-formed ion clusters (7.85 nm) and hydrogen bonding for fast proton conduction. With a quinone group capacity (IECQ) of 2.43 mmol g−1 in the polybenzimidazole (PBIPhOSO3-q-2.43), the low area resistance (0.23 Ω cm2) and vanadium permeability (3.2 × 10−9 s cm−2) contribute to about a 16.5 fold increase in H+/Vn+ selectivity as compared with the Nafion 212 membrane. The corresponding VRFB shows a low discharge capacity decay rate (0.31% per cycle) and high energy efficiency (87.7%) at 100 mA cm−2 and remains stable during the 500 cycle test. The performance is superior to that of the most recently reported amphiprotic ion conductive membranes. [ABSTRACT FROM AUTHOR]

Anion exchange membrane fuel cells (AEMFCs) are a new generation of energy conversion technology that excels proton exchange membrane fuel cells in terms of oxygen reduction kinetics. The development of high-performance and durable anion exchange membranes (AEMs) has been a top priority for AEMFCs. In this work, we design and fabricate a novel series of AEMs by co-polymerizing tetraphenylmethane with 1-methyl-4-piperidone and p-terphenyl and subsequent quaternization of the resulting polymer. This strategy creates four-arm star shaped polymer components in the fabricated AEMs so that the polymer chain packing density is lowered, creating a high fraction of free volume in the membrane, which can help build ion channels with lower OH− transport resistance. The resulting qPTTP-7 AEM shows a markedly improved ion conductivity (142.71 mS cm−1 at 80 °C). After 1000, 2000 and 3000 h treatments in 1 M NaOH at 80 °C, the membrane showed an ion conductivity retention rate of 98%, 93% and 86%, respectively. With such an AEM, the H2–O2 single cell yields a peak power density of 1.37 W cm−2 at 80 °C, and the fuel cell can operate at a constant current over 150 h without much voltage decay. [ABSTRACT FROM AUTHOR]

Interconnective sieving pores are fabricated by the hydrolysis of ionic clusters in precursor ion-conductive membranes to provide a versatile strategy for the proton transport-ion selectivity trade-off in vanadium flow batteries. The sulfate ester group has higher acidity than the well-formed hydrophilic ionic clusters in the precursor dense membrane and converts into smaller hydroxyl groups by subsequent hydrolysis, producing numerous angstrom-scale pores (4–8 Å) as independent H+/Vn+ ion sieving units. Meanwhile, the collapse of electrostatic interactions between the precursor sulfate ester groups and the membrane swelling during hydrolysis induced interconnection of the hydrated ionic clusters; therefore, the converted hydroxyl groups tend to disperse in the hydrophilic domains to form the interconnected collection of numerous sieving pores as broad proton conductive channels. By tuning the porous morphology by ion exchange capacity, excellent cell performance is achieved (high energy efficiency of 85.8%, low discharge capacity decay of 0.22% per cycle, and stable operation of 1000 charge–discharge cycles at 100 mA cm−2), which is better than that of Nafion 212 and most contemporary porous membranes. [ABSTRACT FROM AUTHOR]

Designing membranes with highly ion-selective conductivity is one of the key questions for the large-scale application of redox flow batteries, which can unlock the potential of the renewable energy industry. The selectivity of ion exchange membranes is usually limited by the larger size of the nanochannels than that of redox-active ions. Herein, sub-1-nanometer channels of membranes were constructed through covalently bonding the polysilsesquioxane nanocages with multiple branched amino groups onto a polymer material. The synergistic effect of super hydrophilicity, extra functional amino groups and matched sub-1-nanometer sieve structure accomplished the sieving of proton to redox-active ions and ensured fast proton conduction. The ultrahigh proton-selective conductivity of 1.18 × 1011 mS s cm−3 enabled high electrochemical performance and surprisingly excellent durability over 7000 cycles (>4000 deep cycles for energy applications) even in the harsh environment of a vanadium flow battery. These results indicated that the new membrane design with multi-scale ion-sieving nanochannels is promising for high-efficiency and durable redox flow batteries. [ABSTRACT FROM AUTHOR]

A hydrophilic–hydrophobic microphase separation structure is essential for anion exchange membranes (AEMs) to balance ion conduction and mechanical strength. However, continuous hydrophobic microphase will inevitably become a barrier for ion conduction between dispersed hydrophilic ionic clusters. In this study, throughout ion conductive highway networks are constructed in quaternized polybenzimidazole (PBI) AEMs, in which OH− could break through the hydrophobic polymer backbone by forming dense hydrogen bond networks with pyridine nitrogen (–N＝) in PBI repeating units, and a tri-cationic/non-cationic ether pendant side chain is proposed to greatly improve ionic aggregation that was still difficult to achieve in reported quaternized PBI membranes. The molecular dynamics simulation indicates comparable OH− coordination through ionic bonds in hydrophilic microphase and hydrogen bonds in the hydrophobic microphase. The as-prepared membranes exhibit excellent toughness to fabricate ultrathin self-supporting AEMs (10 μm) with low ohmic resistance. H2/O2 fuel cells achieves a high peak power density of about 1162.3 mW cm−2 at a large current density of 2749.5 mA cm−2, which is the highest value among recently reported PBI-based AEMs and multi-cation side-chain type AEMs. The design of throughout conductive highway network makes the highly stable commercial PBI material one of the best candidates for AEMFCs. [ABSTRACT FROM AUTHOR]

"Fishnet-like" ion-selective nanochannels for advanced membranes are designed for the first time to enhance the efficiency and durability of flow batteries. A fishnet-like structure with 10 nm ion-transport channels is achieved by tuning the hydrophobic/hydrophilic nanophase separation structure of the membrane, in which absorbed water molecules are restricted around hydrophilic polyethylenimine (PEI) chains by hydrophobic polybenzimidazole (PBI). Owing to the size-exclusion and high-density protonated amine groups of PEI fishnets, the membrane exhibits ultralow VO2+ permeability without sacrificing its ion conductivity, ensuring high energy efficiency of vanadium flow batteries. Furthermore, the demonstrated vanadium flow battery with the fishnet-based membrane steadily run at 120 mA cm−2 over 2000 cycles (about 120 days). These findings provide a new strategy for the design of high-performance and cost-effective membranes for vanadium flow battery applications. [ABSTRACT FROM AUTHOR]

An advanced ion-selective membrane containing a dynamic hydroxyl-based 3D H-bond network is first proposed for improved efficiencies and stability in flow battery applications. The 3D H-bond network structure is constructed by the nanoscale aggregation of hydrophilic dense-hydroxyl side chains anchored to hydrophobic polybenzimidazole. This unique dynamic H-bond network creates proton transport highways as well as vanadium permeation barriers across the membrane, leading to an ultralow vanadium ion permeability (＜10−9 cm2 s−1) and remarkably low area resistance (0.32 Ω cm−2). This membrane exhibits high coulombic efficiencies (CE: 98.0–99.2%) and energy efficiencies (EE: 88.9–77.9%) at high current densities (80–200 mA cm−2), together with a long lifetime of over 800 cycles (about 42 days) at 120 mA cm−2 in vanadium flow batteries. The design of dynamic 3D H-bond networks provides a promising strategy for the development of highly ion-selective and stable membranes for flow battery application. [ABSTRACT FROM AUTHOR]

Bis(oxazoline)-derived N-heterocyclic carbene (IBiox) supported rare-earth (Sc, Y, Lu) trialkyl complexes have been synthesized and structurally characterized, and their catalytic activity in the (co)polymerization of α-olefins has been studied. The treatment of Ln(CH2SiMe3)3(THF)2 with one equivalent of freshly prepared IBiox afforded the rare-earth metal complexes (IBiox)Ln(CH2SiMe3)3THFn (Ln = Sc (1), n = 0; Y (2), n = 1; and Lu (3), n = 1) in good yields. Single crystal X-ray diffraction study showed that 1 is pseudo tetrahedral, while 2 and 3 are distorted trigonal bipyramidal with coordinated THF. The Ln–C(carbene) bond distances in 1, 2, and 3 are 2.352, 2.550, and 2.479 Å, respectively. DFT calculations were performed to study the bonding scheme and the structural stability. Complex 1 showed a high activity for 1-hexene polymerization by activation with 2 equivalents of [Ph3C][B(C6F5)4], and the resultant polymers are predominantly vinylene end groups (ca. 95%). Moreover, the catalyst system based on 1 proved to be effective for the copolymerization of 1-hexene with 1,7-octadiene, affording the copolymers with about 20% pendant vinyl groups. The hydrophilicity of the copolymers was improved by modifying the vinyl groups with carboxyls via a thiol–ene reaction. [ABSTRACT FROM AUTHOR]

Polybenzimidazole (PBI) membranes with nanophase-separated structure induced by non-ionic hydrophilic side chain are designed and fabricated for vanadium flow batteries (VFBs). The designed PBI membranes are prepared by grafting non-ionic hydrophilic side chains via an N-substitution reaction. This molecular modification induces nanophase separation and formation of hydrophilic clusters, which act as effective proton transfer pathways, hence dramatically improving the proton conductivity. Meanwhile, the vanadium permeability is inappreciable due to the appropriate size of hydrophilic clusters and Donnan exclusion of protonated grafted-PBI membranes (GPBI). Free from ion exchange groups, GPBI membranes maintain the good chemical stability of the pristine PBI membrane. As a result, the designed membrane exhibits an impressive performance, combining ultrahigh proton conductivity, ion selectivity and chemical stability. The GPBI-based VFB exhibits a coulombic efficiency of over 99% and an energy efficiency of 84% at 120 mA cm−2, the highest reported for dense PBI membranes for VFB applications. The decent stability of GPBI membranes is demonstrated by the stable performance over 200 charge–discharge cycles and the ex situ immersion test. This work provides a new insight into the design of high-performance PBI membranes for VFB applications. [ABSTRACT FROM AUTHOR]

A novel alkaline group, hexamethylenetetramine (HMTA) with four tertiary amine groups and β-hydrogen-absent structure, has been employed as mono-quaternization reagent to prepare HMTA mono-quaternized polysulfone anion exchange membranes (PSF-QuOH AEMs). Analyzed by molecular dynamics simulations, mono-quaternized HMTA shows a superior aggregating ability by strong electrostatic interaction with hydroxide to suppress water swelling even at high IECs. In particular, the PSF-QuOH membrane with a high IEC of 2.23 mmol g−1 exhibits a low swelling ratio of 21% even at 60 °C. The resulting high concentration of cationic groups and the interactions between multiple hydrogen atoms in HMTA and hydroxide/water are helpful to induce the formation of the continuous and efficient hydrogen-bond networks, promoting ionic transport. High hydroxide conductivity of 35 mS cm−1 is achieved at 20 °C. Excellent swelling resistance also benefits the mechanical and chemical stabilities of the PSF-QuOH membranes. A considerable mechanical strength of 17.7 MPa is observed in the fully hydrated membrane. The hydroxide conductivity is stable at around 86% of the initial value after 1 M KOH immersion at 60 °C for 168 h. [ABSTRACT FROM AUTHOR]

The relationship between the proton conductive channel and the hydrated proton structure is of significant importance for understanding the deformed hydrogen bonding network of the confined protons which matches the nanochannel. In general, the structure of hydrated protons in the nanochannel of the proton exchange membrane is affected by several factors. To investigate the independent effect of each factor, it is necessary to eliminate the interference of other factors. In this paper, a one-dimensional carbon nanotube decorated with fluorine was built to investigate the independent effects of nanoscale confinement and fluorination on the structural properties of hydrated protons in the nanochannel using classical molecular dynamics simulation. In order to characterize the structure of hydrated protons confined in the channel, the hydrogen bonding interaction between water and the hydrated protons has been studied according to suitable hydrogen bond criteria. The hydrogen bond criteria were proposed based on the radial distribution function, angle distribution and pair-potential energy distribution. It was found that fluorination leads to an ordered hydrogen bonding structure of the hydrated protons near the channel surface, and confinement weakens the formation of the bifurcated hydrogen bonds in the radial direction. Besides, fluorination lowers the free energy barrier of hydronium along the nanochannel, but slightly increases the barrier for water. This leads to disintegration of the sequential hydrogen bond network in the fluorinated CNTs with small size. In the fluorinated CNTs with large diameter, the lower degree of confinement produces a spiral-like sequential hydrogen bond network with few bifurcated hydrogen bonds in the central region. This structure might promote unidirectional proton transfer along the channel without random movement. This study provides the cooperative effect of confinement dimension and fluorination on the structure and hydrogen bonding of the slightly acidic water in the nanoscale channel. [ABSTRACT FROM AUTHOR]

A novel integrally thin skinned asymmetric anion exchange membrane (ISAAEM) with sufficiently low ion exchange capacity (IEC) was proposed to improve the chemical stability of AEMs for vanadium flow batteries (VFBs). The ISAAEM with an IEC of 0.72 meq. g−1 showed low area resistance, slight VO2+ crossover and good electrochemical performance in VFBs. [ABSTRACT FROM AUTHOR]

Poly(ether ether ketone) (PEEK) with multiple quaternary ammonium groups on pendent side chains is synthesized through the chloromethylation di-quaternization route, using bi-functional 1,4-diazabicyclo [2,2,2]octane (DABCO) as quaternization reagent. The materials are made into tough and transparent anion exchange membranes (AEMs) by solvent casting. The purpose is to promote efficient hydroxide ion conductive channels, which are particularly important and challenging to improve hydroxide conductivity of AEMs due to the inherently low mobility of hydroxide ions. Transmission electron microscopy (TEM) images show ionic clusters of bigger size scattering in the di-quaternized membranes compared with the mono-quaternized membranes. Given similar ion exchange capacities (IECs), the di- quaternized membranes exhibit much higher values of effective hydroxide ion mobility (~3.5 × 10-4 cm2 s-1 V-1) than the mono-quaternized membranes (~1.7 × 10-4 cm2 s-1 V-1). The structure of multiple quaternary ammonium groups on the pendent side chain promotes hydrophilic-hydrophobic micro-phase separation and efficient hydroxide ion conductive channels in the membranes. As a result, hydroxide conductivity of the di-quaternized membranes is about 2 to 3 fold higher than that of the mono-quaternized membranes with similar IEC, exhibiting a high value of about 35.3 mS cm-1 at 25 °C. At a certain IEC, the di-quaternized membranes have fewer pendent side chains on the polymer backbone, which also benefits the mechanical and chemical stabilities of the AEMs. [ABSTRACT FROM AUTHOR]

Bis(oxazoline)-derived N-heterocyclic carbene (IBiox) supported rare-earth (Sc, Y, Lu) trialkyl complexes have been synthesized and structurally characterized, and their catalytic activity in the (co)polymerization of α-olefins has been studied. The treatment of Ln(CH2SiMe3)3(THF)2 with one equivalent of freshly prepared IBiox afforded the rare-earth metal complexes (IBiox)Ln(CH2SiMe3)3THFn (Ln = Sc (1), n = 0; Y (2), n = 1; and Lu (3), n = 1) in good yields. Single crystal X-ray diffraction study showed that 1 is pseudo tetrahedral, while 2 and 3 are distorted trigonal bipyramidal with coordinated THF. The Ln-C(carbene) bond distances in 1, 2, and 3 are 2.352, 2.550, and 2.479 Å, respectively. DFT calculations were performed to study the bonding scheme and the structural stability. Complex 1 showed a high activity for 1-hexene polymerization by activation with 2 equivalents of [Ph3C][B(C6F5)4], and the resultant polymers are predominantly vinylene end groups (ca. 95%). Moreover, the catalyst system based on 1 proved to be effective for the copolymerization of 1-hexene with 1,7-octadiene, affording the copolymers with about 20% pendant vinyl groups. The hydrophilicity of the copolymers was improved by modifying the vinyl groups with carboxyls via a thiol-ene reaction.

A binary noble-metal-free cocatalyst consisting of ZnIn 2 S 4 and In(OH) 3 was developed via a facile one-step hydrothermal method. The ZnIn 2 S 4 /In(OH) 3 modified ZnWO 4 nanocomposite exhibited enhanced photocatalytic H 2 evolution activity compared to all the related pure samples and binary composite photocatalysts under visible light irradiation. The enhanced photocatalytic hydrogen production activities can be attributed to the synergistic effects of the favorable light trapping ability and efficient spatial charge separation. The photocatalytic hydrogen evolution activity over other semiconductors, such as Zn 2 SnO 4 and TiO 2 , can also be significantly increased by loading ZnIn 2 S 4 /In(OH) 3 as a cocatalyst. The results clearly demonstrated that ZnIn 2 S 4 /In(OH) 3 is discovered as a new class of earth-abundant cocatalyst for water-splitting under visible light irradiation. It is expected that our work could provide a new strategy to improve the visible light response of semiconductors and facilitate their application in water splitting., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)