Sulfonated Polyimide Membranes Constructed by Main-Chain and Molecular-Network Engineering Strategy for Direct Methanol Fuel Cell.

Excessive swelling is one important factor that leads to high fuel permeability and limited operating concentration of methanol for proton exchange membranes. Herein, a collaborative strategy of main-chain and molecular-network engineering is applied to lower swelling ratio and improve methanol resistance for highly sulfonated polyimide. Two m-phenylenediamine monomers (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine and 4,6-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine) with tetrafluorostyrol groups are designed and synthesized. Two series of cross-linked sulfonated polyimides (CSPI-Ts, CSPI-Bs) are prepared from the two diamines, 4,4'-diaminostilbene-2,2'-disulfonic acid and 1,4,5,8-naphthalenetetracarboxylicdianhydride. The rigid main-chain structure is cornerstone for wet CSPI-Ts and CSPI-Bs remaining stable at elevated temperatures. The introduction of hydrophobic cross-linked network further improves their dimensional stability and methanol resistance. CSPI-Ts and CSPI-Bs show obviously improved performances containing high proton conductivity (121 ± 0.27-158 ± 0.35 S cm-1 ), low swelling ratio (9.6 ± 0.40%-16.1 ± 0.01%) and methanol permeability (4.14-7.69 × 10-7 cm2 s-1 ) at 80 °C. The direct methanol fuel cell (DMFC) is assembled from CSPI-T-10 with balanced properties, and it exhibits high maximum power density (PDmax ) of 82.3 and 72.6 mW cm-2 in 2 and 10 m methanol solution, respectively. The ratio of PDmax in 10 m methanol solution to the value in 2 m methanol solution is as high as 88%. The CSPI-T-10 is promising proton exchange membrane candidate for DMFC application.

Stable Hexaazatrinaphthalene-Based Planar Polymer Cathode Material for Organic Lithium-Ion Batteries.

Organic materials have garnered intensive focus as a new group of electrodes for lithium-ion batteries (LIBs). However, many reported organic electrodes so far still exhibit unsatisfying cycling stability because of the dissolution in the electrolytes. Herein, a novel azo-linked hexaazatrianphthalene (HATN)-based polymer (AZO-HATN-AQ) is designed and fabricated by the polymerization of trinitrodiquinoxalino[2,3-a:2',3'-c]phenazine (HATNTN) and 2,6-diaminoanthraquinone (DAAQ). The abundant redox-active sites, extended π-conjugated planar conformation, and low energy gap endow the AZO-HATN-AQ electrode with high theoretical capacity, excellent solubility resistance, and fast Li-ion transport. In particular, the fully lithiated AZO-HATN-AQ still keeps the planar structure, contributing to the excellent cycling stability. As a result, AZO-HATN-AQ cathodes show high specific capacity (240 mAh g-1 at 0.05 A g-1), prominent rate capability (98 mAh g-1 at 8 A g-1), and outstanding cycling stability (120 mAh g-1 after 2000 cycles at 4 A g-1 with 85.7% capacity retention) simultaneously. This study demonstrates that rational structure design of the polymer electrodes is an effective approach to achieving excellent comprehensive electrochemical performance.

Molecular structure design of planar zwitterionic polymer electrode materials for all-organic symmetric batteries.

All-organic symmetric lithium-ion batteries (LIBs) show promising prospects in sustainable energy storage systems, due to their environmental friendliness, structural diversity and low cost. Nevertheless, it remains a great challenge to explore suitable electrode materials and achieve excellent battery performance for all-organic symmetric LIBs. Herein, a squaraine-anthraquinone polymer (PSQ) electrode material was designed through rational molecular engineering. The well-designed extended π-conjugated system, donor-acceptor structure, abundant redox-active sites and rational manipulation of weak inter-/intramolecular interactions endow the PSQ electrode with outstanding electrochemical performance. The capacity of the PSQ cathode can be optimized to 311.5 mA h g-1 by in situ carbon-template polymerization. Impressively, PSQ-based all-organic symmetric LIBs displayed high reversible capacity (170.8 mA h g-1 at 50 mA g-1), excellent rate performance (64.9% capacity retention at 4000 mA g-1 vs. 50 mA g-1), ultralong cycle life up to 30 000 cycles at 2000 mA g-1 and 97% capacity retention after 2500 cycles at 500 mA g-1, which is one of the best comprehensive battery performances among the all-organic LIBs reported thus far.

π-Conjugated Hexaazatrinaphthylene-Based Azo Polymer Cathode Material Synthesized by a Reductive Homocoupling Reaction for Organic Lithium-Ion Batteries.

A novel hexaazatrinaphthylene-based (HATN) azo polymer (PAH) was synthesized from a newly designed tri-nitro compound trinitrodiquinoxalino[2,3-a:2',3'-c]phenazine (HATNTN) through a Zn-induced reductive homocoupling reaction and used as a cathode material for lithium-ion batteries (LIBs). The integration of redox-active HATN units and azo linkages can improve the specific capacity, rate performance, and cycling stability of the PAH cathode. The control LIBs were assembled from HATNTN, in which HATNTN can be electrochemically reduced to an HATN-based azo polymer. Compared with the HATNTN cathode, the PAH cathode delivers higher specific capacities with much-improved cycling stability (97 mA h g-1 capacity retention after 1500 cycles at 500 mA g-1, which is around 28 times that of the HATNTN cathode) and considerably better rate performance (118 mA h g-1 at 2000 mA g-1, which is around 90 times that of the HATNTN cathode), simultaneously. This work provides a chemical polymerization strategy to construct extended π-conjugated azo polymers with multiple redox centers from nitro compounds for developing high-performance LIBs.

Microporous polyimides with high surface area and CO2 selectivity fabricated from cross-linkable linear polyimides.

Linear polyimides of intrinsic microporosity have been intensively investigated for gas separation due to their microporous structure and high surface area. The microporous structure in the linear polyimides of intrinsic microporosity comes from their contorted structure. Therefore, most linear polyimides without contorted structure do not have micropores. In this work, the microporous polyimides are constructed through the condensation of a cross-linkable dianhydride monomer with two novel nitrogen-rich diamine monomers and post crosslinking reaction. The linear polyimide precursors without contorted structure have the same main-chain structure. The introduction of crosslinked structure endow the crosslinked polyimides (PI-CLs) with microporous structure. The microporous structure in PI-CLs can be tuned by changing the substituents of the linear polyimide precursors. The PI-CLs have competitive CO2 uptake capacity (7.3-9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF3-PI-CL) shows high CO2/N2 and CO2/CH4 selectivity (72 and 22) at 273 K, which are among the best results for reported porous materials. This work reveals that the introduction of crosslinked structure and changing substituents is an efficient method for constructing microporous polyimides with abundant micropores and excellent CO2 selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure.

Effects of amphiphilic monomers and their hydrophilic spacers on polyacrylamide hydrogels.

Hydrogels based on physical interactions have been extensively studied due to their special network structure and excellent mechanical properties. In this paper, a series of hydrogels based on hydrophobic interactions were prepared via the free-radical copolymerization of acrylamide and polymerizable amphiphilic monomers dodecanol polyoxyethylene (n) acrylates (AEO-n-AC, n = 3, 7, 9, 15, 23) by a simple and facile method. The prepared single-network hydrogels cross-linked by the self-assemble AEO-n-AC micelles acting as cross-linkers exhibited great tensile strength of 0.45 MPa and excellent compression strength of 4.5 MPa. Transmission electron microscopy tests reflected that the morphologies of the self-associated micelles were determined by the hydrophilic segment of the amphiphilic monomers, which further affected the mechanical properties of the hydrogel. Amphiphilic monomer with appropriate length of hydrophilic spacers could significantly enhance the tensile strength of the hydrogel. Meanwhile, amphiphilic monomers with long hydrophilic segment were advantageous for the compression properties of the hydrogel. Furthermore, the hydrogels exhibited excellent micro self-repair ability during the cycling tensile and loading-unloading test even at the strain and compression were 400%, 0.95, respectively. This discover of hydrophilic spacer effect is of great significance for the design of physical interaction-based hydrogels with high strength and compression properties.

Fabrication of fluorescent holographic micropatterns based on azobenzene-containing host-guest complexes.

On the basis of photoinduced surface relief gratings (SRGs) with fluorophore/azo-complexes, a novel and facile method for fabricating stable and bright fluorescent two-dimensional micropatterns, whose color could be easily adjusted by changing the corresponding fluorophores, was developed for the first time.