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Polymer composite membranes are fabricated using poly[2,2'-(m-phenylene)-5,5′-bibenzimidazole] (PBI) as a polymer matrix and imidazole functionalized graphene oxide (ImGO) as a filler material for high temperature proton exchange membrane fuel cell applications. ImGO is prepared by the reaction of o-phenylenediamine with graphene oxide (GO). The compatibility of ImGO with PBI matrix is found to be better than that of GO, and as a result PBI composite membrane having ImGO exhibits improved physicochemical properties and larger proton conductivity compared with pure PBI and PBI composite membrane having GO. For example, PBI composite membrane having 0.5 wt% of ImGO shows enhanced tensile strength (219.2 MPa) with minimal decrease of elongation at break value (28.8%) compared with PBI composite membrane having 0.5 wt% of GO (215.5 MPa, 15.4%) and pure PBI membrane without any filler (181.0 MPa, 34.8%). The proton conductivity of this membrane, at 150 °C under anhydrous condition, is 77.52 mS cm−1.

Comb-shaped polysulfone copolymers were synthesized by the click reaction, copper(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition, using polysulfone having azidomethyl side group (PSf-N3) and sulfonated polytriazole having one ethynyl chain-end group. PSf-N3 was prepared by the substitution reaction of polysulfone through chloromethylation followed by azidation, and sulfonated polytriazoles having one ethynyl chain-end group was synthesized via the click reaction using 1,4-diethynylbenzene and 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt tetrahydrate with CuI followed by end-capping process. Tough, flexible, and transparent membranes could be prepared by solution casting from the comb-shaped polysulfone copolymers and ion exchange capacity (IEC) of the resulting membranes could be controlled by changing the chain length of the sulfonated polytriazoles. The comb-shaped polysulfone membranes showed enhanced physicochemical stability and significantly higher proton conductivity when compared with a sulfonated poly(arylene ether sulfone) (SPAES) membrane having a similar IEC due to the distinct hydrophilic-hydrophobic phase separated morphology. The fuel cell performance of membrane electrode assembly with the comb-shaped polysulfone membrane is superior to those with the SPAES and Nafion-212 membranes at the various operating conditions.

A series of pore-filling membranes are prepared by impregnating porous cross-linked benzoxazine-benzimidazole copolymer P( p BUa- co -BI) substrates with sulfonated poly(arylene ether sulfone)s (SPAES)s having different degree of sulfonation for polymer electrolyte membrane fuel cells operating at high-temperatures (>100 °C) and low-humidity ( p BUa- co -BI) substrates are prepared by extracting dibutyl phthalate (DBP) included in P( p BUa- co -BI) films using methanol. The P( p BUa- co -BI) films are prepared by stepwise heating the casted N,N- dimethylacetamide solution containing the mixtures of poly[2,2′-( m -phenylene)-5,5′-bibenzimidazole] (PBI), 3-phenyl-3,4- dihydro-6- tert -butyl-2 H -1,3-benzoxazine ( p BUa), and DBP to 220 °C. The pore-filling membranes are found to have much improved dimensional stability and mechanical strength compared with the SPAES membranes. Although the proton conductivity values of the pore-filling membranes are slightly smaller than those of the SPAES membrane, their cell performance is superior to that of the SPAES membrane at 120 °C and 40% RH conditions because ultrathin pore-filling membranes (15–20 µm) having high mechanical strength can be prepared and they can contain a larger content of chemically-bound water.

Proton conductive porous substrates consisting of cross-linked benzoxazine-benzimidazole copolymers are developed for practical application of reinforced pore-filling membranes in polymer electrolyte membrane fuel cells operating at high-temperatures (>100 °C) and low relative humidity (

Sulfonated poly(arylene ether sulfone) (SPAES) based composite membranes were prepared with core–shell silica particles having poly(4-styrenesulfonic acid) and poly(4-vinylpyridine) in shell layers named S–Si and P–Si, respectively, to investigate the effect of acidic and basic silica fillers on membrane properties. The core–shell silica particles were obtained by hydrolysis of vinyltrimethoxysilane followed by radical polymerization of vinyl monomers (4-styrenesulfonic acid sodium salt and 4-vinylpyridine) on the silica particle with vinyl groups. Incorporation of S–Si and P–Si into SPAES increased dimensional stability, mechanical strength, and proton conductivity of the membranes. In particular, P–Si was found to be more effective filler materials to improve these properties by additional well-connected hydrophilic channels having sulfonate/pyridinium structures formed around the silica particles through the acid–base interaction between the pyridine groups of the P4VP shell and the sulfonic acid groups of SPAES.

Sulfonated poly(arylene ether sulfone) membranes with cross-linked structures (C-SPAES) were simply prepared by simultaneously casting and heating the polymer solutions composed of sulfonated poly(arylene ether sulfone) with azidomethyl side groups (SPAES-N3), cross-linkers such as 1,4-diethynylbenzene and 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt tetrahydrate, and a click reaction catalyst such as CuBr and N,N,N′,N″,N″-pentamethyldiethylenetriamine in N,N-dimethylacetamide, where SPAES-N3 were prepared by the substitution of sulfonated PAES (SPAES) through chloromethylation followed by azidation reaction. C-SPAES membranes obtained using the optimum amount of the cross-linkers showed much improved chemical and physical stabilities and mechanical strength compared with linear SPAES membrane. Since the cross-linked structures were formed by the cross-linker having sulfonic acid groups, C-SPAES membranes showed higher ion exchange capacity and proton conductivity than the linear SPAES membrane...

Sulfonated poly(arylene ether sulfone) (SPAES) composite membranes were prepared using thermally-treated graphene oxide (GO) and poly(2,5-benzimidazole)-grafted graphene oxide (ABPBI-GO) as fillers for proton exchange membrane fuel cell (PEMFC) applications. Pristine graphene oxide was obtained from graphite by chemical oxidation, and 3,4-diaminobenzoic acid was then reacted with pristine graphene oxide to obtain ABPBI-GO. When GO and ABPBI-GO were incorporated into the SPAES matrix, the dimensional stability and mechanical strength of the membrane were improved. In particular, the SPAES/ABPBI-GO composite membranes exhibited improved dimensional stability, larger Young's modulus, and larger elongation at break than the SPAES/GO composite membranes due to the acid–base interaction between the sulfonic acid group of the SPAES matrix and the basic imidazole unit of ABPBI-GO. In addition, the SPAES/ABPBI-GO composite membranes possessed higher proton conductivity than pristine SPAES and SPAES/GO composite membranes because the acid–base interaction can generate additional proton conduction pathways in the membrane structures.

Cross-linked sulfonated poly (ether ether ketone) (C-SPEEK) membranes for direct methanol fuel cell (DMFC) applications are prepared using SPEEK with chloromethyl side groups (SPEEK-Cl) and poly (2,5-benzimidazole)-grafted graphene oxide (ABPBI-GO) as a cross-linker. The C-SPEEK membranes exhibit remarkably improved physicochemical stability and decreased methanol permeability compared to a pristine SPEEK membrane and SPEEK composite membranes composed of SPEEK and GO based fillers such as GO and ABPBI-GO. Although the proton conductivities of the C-SPEEK membranes are smaller than those of the pristine SPEEK and SPEEK composite (SPEEK/GO and SPEEK/ABPBI-GO) membranes, cell performances of the membrane electrode assemblies (MEAs) using the C-SPEEK membranes with the optimized contents of ABPBI-GO (cross-linker) are better than those using the pristine SPEEK and SPEEK composite membranes due to the well dispersion of ABPBI-GO by forming an effectively covalent bonded network structure with SPEEK-Cl resulting in the decreased methanol permeability. The maximum power density of the MEA with the C-SPEEK membrane (86 mW cm−2) is larger than those with the pristine SPEEK (71 mW cm−2) and SPEEK composite (69 mW cm−2) membranes at 60 °C with 1.5 M methanol/air feed condition.

Liquid crystal (LC) alignment behaviors of poly(methyl methacrylate) derivative films containing different amounts of plant-based and renewable cardanol moieties were studied for the first time. The poly(methyl methacrylate) derivatives containing the cardanol moieties (HCP#) were prepared using 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) and methacrylate (MMA) as monomers. These polymer films exhibited good optical transparency in the visible light region. The LC cells made from the polymer having 100 mol% of 2-hydroxy-3-cardanylpropyl methacrylate (HCP100) as the alignment layer showed vertical LC alignment having a pretilt angle of about 90°, while those made from HCP# films having smaller than 69 mol% of 2-hydroxy-3-cardanylpropyl methacrylate exhibited random planar LC alignment behavior. The vertical LC alignment behavior on the HCP100 film was ascribed to the hydrophobic HCP100 surface generated by the nonpolar cardanol groups in the polymers. The thermal stability of the LC cell made from UV irradiated HCP100 film (HCP100C) was enhanced compared with HCP100 due to the formation of the cross-linked structure of the unsaturated hydrocarbon in the cardanol group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using the HCP100 as a LC alignment layer. This can give the basic idea for the design of LC alignment layers based on renewable cardanol resource containing polymer films.

Semi-interpenetrating network (semi-IPN) membranes based on sulfonated poly(arylene ether sulfone) (SPAES) were developed for application in polymer electrolyte membrane fuel cells (PEMFCs) operating at high temperature (>100 °C) and low relative humidity (

For polymer electrolyte membrane fuel cell (PEMFC) applications at elevated temperature (>100 °C), a series of cross-linked benzoxazine–benzimidazole copolymer, P(HFa- co -BI), membranes are prepared by casting a solution of poly[2,2′-( m -phenylene)-5,5′-bibenzimidazole] (PBI) and di-functional benzoxazine monomer, 6,6′-(hexafluoroisopropylidene)bis(3-phenyl-3,4-dihydro-2 H -benzoxazine) (HFa), in N , N -dimethylacetamide prior to stepwise heating to 250 °C. The films are also viable to manufacture to large quantities and area by roll-to-roll coating. The resulting cross-linked copolymer, P(HFa- co -BI), membranes are found to be thermally and mechanically stable. Although the proton conductivity values of P(HFa- co -BI) membranes are smaller than that of the PBI membrane, their cell performance (0.68 V at 0.2 A cm −2 at 150 °C) is close to that of PBI membrane and their long-term durability ( ca . 3116 cycles on in situ accelerated lifetime mode of load cycling testing) is found to be far superior to the PBI membrane.

Cross-linked copolymer membranes were prepared by casting poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) solutions containing 6-fluoro-3-(pyridin-2-yl)-3,4-dihydro-2H-benzoxazine (pF) in N,N-dimethylacetamide, with subsequent step-wise heating to 220 °C. The phosphoric acid (PA) content, proton conductivity, and cell performance were found to increase with the increase in benzoxazine content in these membranes. The proton conductivities of the cross-linked copolymer membranes reached 0.09 S cm−1 at 150 °C under anhydrous conditions. Membrane-electrode assemblies (MEAs), prepared using the cross-linked copolymer membranes, showed larger operating voltage, 0.71 V at 0.2 A cm−2, than those from commercially available PBI membranes. Additionally, the MEAs were durable until 1,077 cycles, with slow lifetime loss rate, −0.14 mV h−1 on in situ accelerated lifetime mode (load cycling test).

Here we report new H3PO4-doped cross-linked benzoxazine–benzimidazole copolymer membranes showing high proton conductivity and long-term durability for use in proton-exchange membrane fuel cells at elevated temperatures (>100 °C). The cross-linked copolymer membranes were prepared by mixing of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) with 3-phenyl-3,4-dihydro-6-tert-butyl-2H-1,3-benzoxazine (pBUa) in N,N-dimethylacetamide, with subsequent stepwise heating to 220 °C, and even large-sized films (30 cm × 140 m) could be easily prepared. The membranes showed high proton conductivities of up to 0.12 S cm–1 at 150 °C under anhydrous conditions. Membrane–electrode assemblies (MEAs) employing the membranes showed operating voltages of 0.71 V at 0.2 A cm–2. Furthermore, the MEAs displayed long-term durability up to 1999 cycles, with much slower performance decay, −0.03 mV h–1, than those prepared using the PBI membrane in in situ accelerated lifetime mode (load cycling testing).

A series of poly(thiophene) derivatives with decyl-oligo(oxyethylene) side groups, (PDnET) is synthesized via oxidative coupling polymerization. PD3ET and PD4ET with longer oligo(oxyethylene) units exhibited a liquid crystalline phase with well-ordered lamella structures, although PD3ET showed a more ordered structure than PD4ET. PD1ET and PD2ET have shorter oligo(oxyethylene) groups than PD3ET and show less-ordered structures with liquid-crystalline phase observed. The UV-vis spectra indicated that the maximum absorption wavelengths of PDnET increase when the number of oxyethylene units increases from 1 to 3; however, the maximum absorption wavelength of PD4ET is lower than that of PD3ET. Therefore, the most ordered and conjugated structures are obtained when the number of oxyethylene units is three.

Cross-linked poly(2,5-benzimidazole) (C-ABPBI) membranes consisting of wholly aromatic groups were prepared by a reaction between three-arm poly(2,5-benzimidazole)s with three carboxylic acid end groups (T-ABPBI) and 3,3′-diaminobenzidine (DABI) in poly(phosphoric acid) (PPA) during the casting process. T-ABPBI was prepared by the polymerization of 3,4-diaminobenzoic acid and 1,3,5-benzenetricarboxylic acid in PPA, and the polymerization solution was directly used for the casting process. The cross-linking process improved the chemical stability of the host polymer, poly(2,5-benzimidazole) (ABPBI). The C-ABPBI membranes could contain a larger phosphoric acid (PA) content than the membranes of linear polybezimidazoles, such as ABPBI and poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole]. Consequently, the C-ABPBI membranes showed higher proton conductivity values than the linear polymer membranes. For example, the C-ABPBI-50 membrane could contain a PA content >84 wt.% with a proton conductivity of 0.12 S cm−1 at 150 °C under anhydrous conditions.

Cross-linked benzoxazine–benzimidazole copolymer membranes with interpenetrating network structures containing a large amount of phosphoric acid (PA) were prepared by a direct casting method for polymer electrolyte membrane fuel cells at elevated temperatures. The direct casting solution was prepared by adding 6-fluoro-3-(pyridin-2-yl)-3,4-dihydro-2H-benzoxazine into the polymerization solution of 3,4-diaminobenzoic acid in poly(phosphoric acid) (PPA). Once the PPA in the membranes has been hydrolyzed to PA, the membranes can contain large amounts of PA and showed high proton conductivity, ca. 0.14 S cm−1, at 150 °C under anhydrous conditions. Membrane–electrode assemblies (MEAs) prepared using the copolymers showed high operating voltages of 0.69 V at 0.2 A cm−2, long-term durability for up to 1584 cycles, with much slower performance decay than those prepared using poly(benzimidazole) homopolymers, such as poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] and poly(2,5-benzimidazole), from the in situ accelerated lifetime test.

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