High-performance imidazole-containing polymers for applications in high temperature polymer electrolyte membrane fuel cells

This work focuses on the development of high temperature polymer electrolyte membranes(HT-PEMs)as key materials for HT-PEM fuel cells(HT-PEMFCs).Recognizing the challenges associated with the phosphoric acid(PA) doped polybenzimidazole(PBI) membranes,including the use of carcinogenic monomers and complex synthesis procedures,this study aims to develop more cost-effective,readily synthesized,and high-performance alternatives.A series of superacid-catalyzed polyhydroxyalkylation reactions have been carefully designed between p-terphenyl and aldehydes bearing imidazole moieties,resulting in a new class of HT-PEMs.It is found that the chemical structure of aldehyde-substituted N-heterocycles significantly impacts the polymerization reaction.Specifically,the use of 1-methyl-2-imidazole-formaldehyde and 1 H-imidazole-4-formaldehyde monomers leads to the formation of high-viscosity,rigid,and ether-free polymers,denoted as PTIm-a and PTIm-b.Membranes fabricated from these polymers,due to their pendent imidazole groups,exhibit an exceptional capacity for PA absorption.Notably,PTIm-a,carrying methylimidazole moieties,demonstrates a superior chemical stability by maintaining morphology and structural stability during 350 h of Fenton testing.After being immersed in 75 wt% PA at 40℃,the PTIm-a membrane reaches a PA content of 152%,maintains a good tensile strength of 13.6 MPa,and exhibits a moderate conductivity of 50.2 mS cm^(-1) at 180℃.Under H_(2)/O_(2) operational conditions,a single cell based on the PTIm-a membrane attains a peak power density of 732 mW cm^(-2) at 180℃ without backpressure.Furthermore,the membrane demonstrates stable cycle stability over 173 h within 18 days at a current density of 200 mA cm^(-2),indicating its potential for practical application in HT-PEMFCs.This work highlights innovative strategies for the synthesis of advanced HT-PEMs,offering significant improvements in membrane properties and fuel cell performance,thus expanding the horizons of HT-PEMFC technology.

HETEROAROMATIC POLYMERS—HIGH TEMPERATURE POLYPYRROLONES DERIVED FROM 2,6-BIS(3',4'-DIAMINOPHENYL)-4-BIPHENYLPYRIDINE AND VARIOUS AROMATIC DIANHYDRIDES

A new type of aromatic tetraarnine containing biphenyl moiety in the side chain was synthesized via a modified Chichibabin＇s reaction. 3-Nitro-4-acetamidoacetophenone was reacted with 4-phenyl benzaldehyde in the presence of ammonium acetate to obtain 2,6-bis（3＇,4＇-diaminophenyl）-4-biphenyl pyridine （DPPA）. A series of polypyrrolones （PPys） were prepared using tetraamine and various aromatic dianhydrides via a two-step cyclization procedure. All the PPys show excellent high temperature stabilities with the initial decomposition temperatures of 530-549℃ and residual weight ratio of 49%-80% at 750℃ in nitrogen. The polymers exhibit no apparent glass transition temperatures （Tgs） except PPy-1 （Tg= 327℃）, which is derived from tetraamine DPPA and 2,2-bis[4-（3＇,4＇-dicarboxyphenoxy）-phenyl]propane dianhydride （BPADA）. In addition, the polymers have acceptable mechanical properties with the tensile strength of 65-94 MPa. The PPy films show excellent hydrolysis-resistance in alkaline aqueous medium and could maintain most of the properties even after boiling in 10% aqueous sodium hydroxide solution for a week.

Water-induced electrode poisoning and the mitigation strategy for high temperature polymer electrolyte membrane fuel cells

Engineering failure of membrane electrode assembly caused by increasingly fuel poisoning in the high temperature polymer electrolyte membrane fuel cells fed with humidified reformate gases is firstly demonstrated herein this work. Based on the results of the in-situ environmental scanning electron microscope, electrochemical analyses, and limiting current method, a water-induced phosphoric acid invasion model is constructed in the porous electrode to elucidate the failure causations of the hindered hydrogen mass transport and the enhanced carbon monoxide poisoning. To optimize the phosphoric acid distribution under the inevitably humidified circumstance, a facile and effective strategy of constructing acid-proofed electrode is proposed and demonstrates outstanding stability with highly humidified reformate gases as anode fuel. This work discusses a potential defect that was rarely studied previously under practical working circumstance for high temperature polymer electrolyte membrane fuel cells, providing an alternative opinion of electrode design based on the fundamental aspects towards the engineering problems.

Solution-Processed High Mobility Top-Gate N-Channel Polymer Field-Effect Transistors

Polymer field-effect transistors operated in the n-channel model with a top-gate/bottom-contact are processed using a solution method. The transistor performance depends on the gate dielectric layer. A high performance polymer transistor is achieved, with the saturated electron mobility of about 0.46cm2/Vs, threshold voltage nearly 0 V and subthreshold sway of about 0.9 V/decade, employing a polystyrene （PS） dielectric layer. The transistor performances are further improved with increasing current and lower operation voltages by utilizing a bi-layer gate dielectric, comprising a thin PS dielectric layer adjacent to the semiconductor to minimize the density of the interface traps for obtaining a small VT, a large μ and a poly（methyl methacrylate） （PMMA） dielectric layer with a relatively high-k adjacent to the gate electrode for enlarging the capacitance, processed from the orthogonal solvents.

Study on low temperature performance of Gussasphalt on steel decks with hard bitumen

Using a Hamburg wheel-track test device, the resistance to rutting of Gussasphalt is tested and compared. Gussasphalt with hard bitumen has good resistance to rutting. The related resistance abilities to cracking at low temperature of Gussasphalt are tested and compared through flexural experiments and the composite structure fatigue test with temperature dropping. Gussasphalt with high performance polymer modified bitumen has a longer fatigue life and a lower breaking temperature; they can be used in the future surfaces for steel bridge decks in Germany.

Synthesis of a benzoxazine monomer containing maleimide and allyloxy groups

A novel benzoxazine monomer 3-（4-allyloxy）phenyl-3,4-dihydro-2H-6-（N-maleimido）-l,3-benzoxazine （AMB） was synthesized and structure was confirmed by FT-IR, 1H NMR. Thermal analysis （DSC） of AMB showed the introduction of allyloxy group melting point and exhibited a narrow and symmetric curing exothermic window.

New thermally stable polyesters based on 2,5-pyridinedicarbonyl dichloride and aromatic diols:Synthesis and characterization

Six new thermally stable polyesters （4a-f） were synthesized through the solution polycondensation reaction of 2,5-pyridine dicarbonyldichloride （2） with six aromatic diols in N,N＇-dimethyl acetamide （DMAc） solution and in the presence of pyridine as a base. The polycondensation reactions produce a series of new polyesters （4a-f） in high yields, and inherent viscosity between 0.30 and 0.55 dL/g. The resulting polyesters were characterized by elemental analysis, viscosity measurements, thermal gravimetric analysis （TGA and DTG）, solubility test, Fourier transform infrared （FT-IR） spectroscopy and gel permeation chromatography （GPC）. C 2009 Khalil Faghihi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Facile synthesis of metal-organic frameworks embedded in interconnected macroporous polymer as a dual acid-base bifunctional catalyst for efficient conversion of cellulose to 5-hydroxymethylfurfural

5-Hydroxymethylfurfural(5-HMF),as a key platform compound for the conversion of biomass to various biomass-derived chemicals and biofuels,has been attracted extensive attention.In this research,using Pickering high internal phase emulsions(Pickering HIPEs)as template and functional metal-organic frameworks(MOFs,UiO-66-SO;H and UiO-66-NH;)/Tween 85 as co-stabilizers to synthesis the dual acid-base bifunctional macroporous polymer catalyst by one-pot process,which has excellent catalytic activity in the cascade reaction of converting cellulose to 5-HMF.The effects of the emulsion parameters including the amount of surfactant(ranging from 0.5%to 2.0%(mass)),the internal phase volume fraction(ranging from 75%to 90%)and the acid/base Pickering particles mass ratio(ranging from 0:6 to 6:0)on the morphology and catalytic performance of solid catalyst were systematically researched.The results of catalytic experiments suggested that the connected large pore size of catalyst can effectively improve the cellulose conversion,and the synergistic effect of acid and base active sites can effectively improve the 5-HMF yield.The highest 5-HMF yield,about 40.5%,can be obtained by using polymer/MOFs composite as catalyst(Poly-P12,the pore size of(53.3±11.3)μm,the acid density of 1.99 mmol·g^(-1)and the base density of 1.13 mol·g^(-1))under the optimal reaction conditions(130℃,3 h).Herein,the polymer/MOFs composite with open-cell structure was prepared by the Pickering HIPEs templating method,which provided a favorable experimental basis and theoretical reference for achieving efficient production of high addedvalue product from abundant biomass.

Manipulating dielectric property of polymer coatings toward highretention-rate lithium metal full batteries under harsh critical conditions

Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·cm^(-2)).Herein,different from the artificial layer or three-dimensional(3D)matrix host constructions,various dielectric polymers are initially well-comprehensively investigated from experimental characterizations to theoretical simulation to evaluate their functions in modulating Li ion distribution.As a proof of concept,a 3D interwoven high dielectric functional polymer(HDFP)nanofiber network with polar C-F dipole moments electrospun on copper(Cu)foil is designed,realizing uniform and controllable Li deposition capacity up to 5.0 mAh·cm^(-2),thereby enabling stable Li plating/stripping cycling over 1400 h at 1.0 mA·cm^(-2).More importantly,under the highcathode loading(~3.1 mAh·cm^(-2))and only 0.6×excess Li(N/P ratio of 1.6),the full cells retain capacity retention of 97.4%after 200 cycles at 3.36 mA·cm^(-2)and achieve high energy density(297.7 Wh·kg^(-1)at cell-level)under lean electrolyte conditions(15μL),much better than ever-reported literatures.Our work provides a new direction for designing high dielectric polymer coating toward high-retention-rate practical Li full batteries.

Phosphorus induced activity-enhancement of Fe-N-C catalysts for high temperature polymer electrolyte membrane fuel cells

Fe-N-C materials with atomically dispersed Fe–N_(4) sites could tolerate the poisoning of phosphate,is regarded as the most promising alternative to costly Pt-based catalysts for the oxygen reduction in high temperature polymer electrolyte membrane fuel cells(HT-PEMFCs).However,they still face the critical issue of insufficient activity in phosphoric acid.Herein,we demonstrate a P-doping strategy to increase the activity of Fe-N-C catalyst via a feasible one-pot method.X-ray absorption spectroscopy and electron microscopy with atomic resolution indicated that the P atom is bonded with the N in Fe–N_(4) site through C atoms.The as prepared Fe-NCP catalyst shows a half-wave potential of 0.75 V(vs.reversible hydrogen electrode(RHE),0.1 M H_(3)PO_(4)),which is 60 and 40 mV higher than that of Fe-NC and commercial Pt/C catalysts,respectively.More importantly,the Fe-NCP catalyst could deliver a peak power density of 357 mW·cm^(−2)in a high temperature fuel cell(160℃),exceeding the non-noble-metal catalysts ever reported.The enhancement of activity is attributed to the increasing charge density and poisoning tolerance of Fe–N_(4) caused by neighboring P.This work not only promotes the practical application of Fe-N-C materials in HT-PEMFCs,but also provides a feasible P-doping method for regulating the structure of single atom site.

PREPARATION AND CHARACTERIZATION OF SOLUBLE SULFONATED POLYBENZIMIDAZOLE FOR PROTON EXCHANGE MEMBRANE MATERIALS

A series of sulfonated polybenzimidazoles(sPBI-SF)were prepared from 2,2-bis(4-carboxyphenyl)hexafluoro- propane(BIS-B-AF),3,3′-disulfonyl-4,4′-dicarboxyldiphenylsulfone(DSDCDPS)and 3,3′-diaminobenzidine(DAB)at various stoichiometric ratio by solution copolycondensation in poly(phosphoric acid).The chemical structure of the resulting sPBI-SF was confirmed by FTIR and ~1H-NMR.The sPBI-SFs with high molecular-weights(M_n=39400-65500)were soluble in DMF,DMSO or DMAc.Therefore,they could form some transparent a...

New optically active poly(amide-imide)s derived from N,N'-(4,4-diphthaloyl)-bis-L-leucine and hydantoin derivatives:Synthesis and properties

Six new optically active poly（amide-imide）s （5a-f） were synthesized through the direct polycondensation reaction of N,N′-（4,4′- diphthaloyl）-bis-L-leucine （3） with six hydantoin derivatives （4a-f）. Tripbenyl phosphite （TPP）/pyridine in the presence of calcium chloride （CaCl2） and N-methyl-2-pyrrolidone （NMP） were successfully applied for direct polycondensation. The polycondensation reactions produce a series of new poly（amide-imide）s （5a-f） in high yields, and inherent viscosity between 0.42 and 0,55 dL/g. The resulting poly（amide-imide）s （5a-f） were characterized by elemental analysis, viscosity measurements, thermal gravimetric analysis （TGA and DTG）, solubility test and FT-IR spectroscopy.

Progress in Recycling of Composites with Polycyanurate Matrix

Thermoset based composites are used increasingly in industry for light weight applications, mainly for aircraft, windmills and for automobiles. Fiber reinforced thermoset polymers show a number of advantages over conventional materials, like metals, especially their better performance regarding their strength-to-weight ratio. However, composite recycling is a big issue, as there are almost no established recycling methods. The authors investigate the recyclability of polycyanurate homo- and copolymers with different recycling agents under different conditions. Also the influence of the recycling process on the most important reinforcement fibers, i.e. carbon-, glass-, aramid-, and natural-fiber is investigated. The authors find that: the recycling speed is not only dependent on the temperature, but also is significantly influenced by the particular recycling agents and the polycyanurate formulation. Hence, the stability against the recycling media can be adjusted over a broad range by adjusting the polymer composition. Furthermore, the authors find that the inorganic reinforcement fibers (carbon and glass) are almost unaffected by neither recycling agent at either temperature. Aramid-fibers degrade, depending on the particular recycling agent, from slightly up to extremely strong. This leaves one with the possibility to find a combination of matrix resin and recycling agent, which does not affect the aramid-fiber significantly. In the case of natural fibers, the dependence on the particular recycling media is very strong: some media do not affect the fiber significantly;others reduce the mechanical properties (tensile strength and elongation at break) significantly, and still others even improve both mechanical properties strongly. From the Recyclate, the authors synthesize and subsequently characterize a number of new polyurethane thermosets (foamed and solid samples) with different contents of recyclate, exhibiting Tg in the range of 60°C to 128°C.

Effects of Branching Strategy on the Gene Transfection of Highly Branched Poly(β-amino ester)s

Highly branched poiy(β-amino ester)s(HPAEs)have emerged as one type of the most viable non-viral gene delivery vectors,both in vitro and in viva.However,the effects of different branching strategies on the gene transfection performance have not yet been explored.Here,using triacrylate(B3)and diamine(B4)as the branching monomers,a series of HPAEs were synthesized via the"A2+B3+C2"and"A2+B4+C2"strategies,respectively.Results show that the branching strategy plays a pivotal role in dictating the physiological properties of the HPAE/DNA polyplexes and thus leads to obviously different cell viability and transfection efficiency.Comparatively,HPAEs synthesized via the"A2+B3+C2"branching strategy are more favorable for DNA transfection than that synthesized via the"A2+B4+C2"strategy.This study may provide new insights into the development of HPAEs based non-viral DNA delivery system.

Flexible,robust and highly efficient broadband nonlinear optical materials based on graphene oxide impregnated polymer sheets

We report a simple solution-processed method for the fabrication of low-cost,flexible optical limiting materials based on graphene oxide(GO) impregnated polyvinyl alcohol(PVA) sheets.Such GO–PVA composite sheets display highly efficient broadband optical limiting activities for femtosecond laser pulses at 400,800,and 1400 nm with very low limiting thresholds.Femtosecond pump–probe measurement results revealed that nonlinear absorption played an important role for the observed optical limiting activities.High flexibility and efficient optical limiting activities of these materials allow these composite sheets to be attached to nonplanar optical sensors in order to protect them from light-induced damage.

THE PERFORMANCES OF HIGH PRESSURE JET OF PURE WATER AND POLYMER SOLUTION WITH CONICAL NOZZLE

In this paper, the effects of polymer additives and nozzle shape on the proper- ties of high pressure water jet discharging into the air are investigated by theory and experiments. Criteria of judging the jet quality are put forward. And, a method that can be used in analysing the fluid flow within the nozzle is developed. Then, the calculated results are compared with the experiments that we carried out; it is shown that the degree of agreement between the two is good. At last, the mechanism to improve on the jet quality with polymer additives is discussed.