Jin Ran

Alkaline polymer electrolytes containing pendant dimethylimidazolium groups for alkaline membrane fuel cells

Novel anion exchange membranes (AEMs), based on poly(phenylene oxide) (PPO) chains linked to pendant 1,2-dimethylimidazolium (DIm) functional groups, have been prepared for evaluation in alkaline polymer electrolyte membrane fuel cells (APEFCs). Successful functionalisation of the PPO chains was confirmed using 1H-NMR and FT-IR spectroscopies. The ionic conductivities of the resulting DIm–PPO AEMs at 30 °C are in the ranges of 10–40 mS cm−1 and 18–75 mS cm−1 at 60 °C. The high ionic conductivities are attributed to the highly developed microstructures of the membranes, which feature well-defined and interconnected ionic channels (confirmed by atomic force microscopy, AFM, measurements). Promisingly, the ion-exchange capacities (IECs) of the DIm–PPO AEM are maintained after immersion in an aqueous KOH solution (2 mol dm−3) for 219 h at 25 °C; a previously developed monomethyl imidazolium PPO analogue AEM (Im–PPO) showed a significant decline in IEC on similar treatment. This reduction in undesirable attack by the OH− conducting anions is ascribed to an increase in steric interference and removal of the acidic C2 proton [in the monomethyl Im-groups] by the methyl group in the DIm cationic ring. Moreover, the maximum power densities produced in simple beginning-of-life single cell H2/O2 fuel cell tests increased from 30 mW cm−2 to 56 mW cm−2 when switching from the Im–PPO AEM (fuel cell temperature = 50 °C) to the DIm–PPO-0.54 AEM (fuel cell temperature = 35 °C) respectively (even with the use of lower temperatures).

Enhancement of hydroxide conduction by self-assembly in anion conductive comb-shaped copolymers

An anion exchange membrane (AEM) was prepared from comb-shaped copolymers bearing locally and densely functionalized side chains. In this study, we synthesized the graft copolymer of bromomethylated poly(phenylene oxide)-graft-quaternary ammonium functionalized 4-vinylbenzyl chloride (BPPO-g-QVBC), using an activator regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) of QVBC from a BPPO macroinitiator. The BPPO-g-QVBC graft copolymers with a combination of a high graft density and appropriate graft length present advanced materials for AEMs. Flexible and transparent membranes were obtained by casting the polymers from NMP solutions, and displayed a microphase-separated morphology with nano-sized ionic clusters embedded in the hydrophobic BPPO matrix. Accordingly, the resultant membranes show considerably high conductivities, up to 0.1 S cm−1 at 80 °C, derived from the special polymer architecture. This study gives some pioneering insights and directions from the viewpoint of macromolecular design to prepare highly conductive AEMs.

Simultaneous Enhancements of Conductivity and Stability for Anion Exchange Membranes (AEMs) through Precise Structure Design

Polymeric materials as anion exchange membranes (AEMs) play an essential role in the field of energy and environment. The achievement of high performance AEMs by the precise manipulation of macromolecular architecture remains a daunting challenge. Herein, we firstly report a novel rod-coil graft copolymer AEM, possessing rigid hydrophobic main chains and soft hydrophilic graft chains. The low graft density, which can alleviate the adverse influences of ioinc graft chains on the main chains, was obtained by using the living polymerization technique. Consequently, the grafted ionic groups which result in the degradation of polymer backbone was decreased to a small degree. Moreover, the relatively long graft chains induced the nanophase separation between the hydrophobic polymer chains and hydrophilic graft chains, which creates a convinient pathway for high hydroxide ion mobility. Such an accurate molecular design simultaneously improves the hydroxide ion conductivity and alkaline stability as well as dimensional stability.

Anion exchange membranes (AEMs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and its derivatives

Polymeric anion exchange membranes (AEMs) attract increasing attention, because they have prominent roles in various energy and environment-related fields. The most important prerequisite toward high performance AEMs is to search for an appropriate base polymeric material, which should be chemically stable and easily handled for fabricating AEMs. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is considered to be a promising candidate since it enables versatile routes to obtain high performance AEMs. Furthermore, the properties of these AEMs can be feasibly adjusted and controlled to meet various application requirements. In this review, recent advances in PPO based AEMs are comprehensively presented. Herein, we highlight the strategies used for designing PPO based AEMs and hope to provide promising principles, concepts, and routes into the synthesis of other polymer based AEMs.

A Novel Methodology to Synthesize Highly Conductive Anion Exchange Membranes.

Alkaline polyelectrolyte fuel cell now receives growing attention as a promising candidate to serve as the next generation energy-generating device by enabling the use of non-precious metal catalysts (silver, cobalt, nickel et al.). However, the development and application of alkaline polyelectrolyte fuel cell is still blocked by the poor hydroxide conductivity of anion exchange membranes. In order to solve this problem, we demonstrate a methodology for the preparation of highly OH− conductive anion exchange polyelectrolytes with good alkaline tolerance and excellent dimensional stability. Polymer backbones were grafted with flexible aliphatic chains containing two or three quaternized ammonium groups. The highly flexible and hydrophilic multi-functionalized side chains prefer to aggregate together to facilitate the formation of well-defined hydrophilic-hydrophobic microphase separation, which is crucial for the superior OH− conductivity of 69 mS/cm at room temperature. Besides, the as-prepared AEMs also exhibit excellent alkaline tolerance as well as improved dimensional stability due to their carefully designed polymer architecture, which provide new directions to pursue high performance AEMs and are promising to serve as a candidate for fuel cell technology.

Click Chemistry Finds Its Way in Constructing an Ionic Highway in Anion-Exchange Membrane

To find the way to construct an ionic highway in anion-exchange membranes (AEMs), a series of side-chain-type alkaline polymer electrolytes (APEs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymer backbones were synthesized via Cu(I)-catalyzed click chemistry. The resulting triazole groups and quaternary ammonium (QA) groups facilitate the formation of a continuous hydrogen bond network, which will lead to high hydroxide conductivity according to Grotthuss-type mechanism. Microphase separation induced by long alkyl side chains contributes at the same time to further improving the hydroxide conductivity of the resultant AEMs. Hydroxide conductivity as high as 52.8 mS/cm is obtained for membrane TA-14C-1.21 (IEC = 1.21 mmol/g) with the longest pendant chain at 30 °C, and the conductivity can be increased to 140 mS/cm when the temperature was increased to 80 °C. Moreover, the corresponding water uptake is only 8.6 wt % at 30 °C. In the meantime, the membrane properties can be tuned by precisely regulating the hydrophilic/hydrophobic ratio in the cationic head groups. Compared with AEMs containing triazole and quaternized trimethylammonium head groups, enhanced dimensional stability and mechanical properties are obtained by tuning side-chain chemistry. However, the alkaline stability of the membrane is not as stable as anticipated, probably because of the existence of the triazole ring. Further study will be focused on increasing the alkali stability of the membrane. We envisage that the side-chain-type APEs meditated by click chemistry bearing long hydrophobic side chains pendant to the cationic head groups hold promise as a novel AEMs material.

Synthesis of soluble copolymers bearing ionic graft for alkaline anion exchange membrane

In this study, we report firstly the synthesis of a soluble quarternary ammonium salt and the corresponding graft copolymer P(VDF-g-QVBC) (poly(vinylidene fluoride-graft-quaternary ammonium-functionalized 4-vinylbenzyl chloride)), via atom transfer radical polymerization (ATRP) of QVBC from a PVDF macroinitiator. 1H NMR spectra indicate the successful synthesis of a series of copolymers with different graft ratios by varying the amount of monomers. The soluble quarternary ammonium-containing copolymers are composed of hydrophobic backbones and hydrophilic graft chains, which allow for favorable nano-scale phase separation during the solvent casting process. As a consequence, the resultant membrane exhibits excellent ionic conductivity as high as 45 mS cm−1, which suggests its potential application in alkaline anion exchange membrane fuel cells. In addition, semi-crystalline nature of PVDF macromolecules imparts the graft membrane excellent thermal and mechanical stability which are required for fuel cell application. Different from available studies of AEMs based on insoluble quarternary ammonium-containing copolymers, this study served as a model system for improving hydroxide conductivity from the viewpoint of self-generated nano-phase separation, and gives pioneering understanding of the morphology–property relationship in novel graft copolymer AEMs.

Alkaline Anion-Exchange Membranes Containing Mobile Ion Shuttles.

A new class of alkaline anion-exchange membranes containing mobile ion shuttles is developed. It is achieved by threading ionic linear guests into poly(crown ether) hosts via host-guest molecular interaction. The thermal- and pH-triggered shuttling of ionic linear guests remarkably increases the solvation-shell fluctuations in inactive hydrated hydroxide ion complexes (OH(-) (H2 O)4 ) and accelerates the OH(-) transport.

An ordered ZIF-8-derived layered double hydroxide hollow nanoparticles-nanoflake array for high efficiency energy storage

A facile room-temperature synthesis of ZIF-8 nanoflakes using insoluble inorganic crystal zinc nitrate hydroxide nanoflakes as the Zn source has been demonstrated in this study for the first time. The transformation mechanism is discussed and investigated. It is found that apart from the acid–base affinity between zinc nitrate hydroxide and 2-methylimidazole, the specific layered crystal structure of zinc nitrate hydroxide is also responsible for the transformation kinetics. As a typical proof-of-concept application, the prepared ZIF-8 nanoflake array is subsequently used as a sacrificial template for constructing layered double hydroxides with extraordinary hollow nanoparticles-nanoflake architectures, in which each nanoflake comprises numerous hollow nanoparticles. Due to its unique structure, which facilitates effective ion and charge transfer without compromising the high surface area, the NiCo layered double hydroxide nanoflake array exhibits a very high capacity of 971.4 C g−1 at a current density of 1.9 A g−1, as well as excellent rate capability and durability. Furthermore, an assembled asymmetric supercapacitor integrated with commercial active carbon shows a high specific energy density of 52.1 W h kg−1 and a power density of 16.5 kW kg−1. The strategy proposed here gives significant insight into the synthesis of metal organic frameworks and provides a very important reference for the controllable design of MOF-based structures.

Guanidylated hollow fiber membranes based on brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) for gold sorption from acid solutions.

Novel guanidylated hollow fiber membranes are prepared based on brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) under mild reaction conditions. 1H-pyrazole-1-carboxamidine hydrochloride (HPCA) is employed for the guanidylation in aqueous solution at room temperature. The obtained guanidylated PPO hollow fiber membranes (GPPO HFMs) contain 0.31-0.95 mmol/g guanidyl groups and show high affinity to tetrachloroauric anions (AuCl(4)(-)) in acid solutions. For 0.1M HCl solution containing 57.8 mg gold/L, the sorption amount can get as high as 130 mg/g. Besides, the GPPO HFMs show preferable selectivity toward gold in multicomponent solution containing Mg(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II). A system of comparison experiments involving the sorption behavior of GPPO HFMs and quaternary aminated HFMs are also performed. The results reveal that driving forces for the high adsorption of gold mainly involve complexation mechanism. Overall, the obtained GPPO HFM is a promising chelating material for the recovery of gold.