The mutual restriction between conductivity and alkaline stability is an obstacle for the widespread application of anion exchange membranes (AEMs). In this study, the quaternized cellulose (QC) has been synthesized and introduced into the prepared quaternized poly(4-vinylpyridine) grafted polyvinylidene fluoride (PVDF-g-QP4VP). Quaternized cellulose effectively promotes hydroxide ions conduction through forming uninterrupted channels based on quaternary ammonium groups. Additionally, the quaternized poly(4-vinylpyridine) grafted polyvinylidene fluoride can further accelerate the hydroxide ions conduction process. Quaternized cellulose is stably combined with quaternized poly(4-vinylpyridine) grafted polyvinylidene fluoride even if the PVDF-g-QP4VP/ 10%QC membrane has been immersed in 2 M KOH solution at 80 degrees C for 960 h. As a result, the hydroxide ions conductivity reaches 197.5 mS/cm at 80 degrees C and maintains 177.2 mS/cm for 960 h. The promoted hydroxide ions conduction is also realized even at subzero temperature, such as the hydroxide conductivity of 7.18 mS/cm at-25 degrees C and 45.9 mS/cm at 30 degrees C in a ten-cycle test of-25 degrees C-30 degrees C. A single fuel cell equipped with PVDF-g-QP4VP/10%QC displayed the maximum power density of 585.9 mW/cm2 at 60 degrees C.

The accelerated hydroxide ions conduction and the enhanced alkaline stability are extremely desired to promote high level of the commercialization of anion exchange membranes (AEMs). Learning from the trees to transport water molecules by capillary action, we construct the electrospining membranes with biomimetic fibrous structures based on polyacrylonitrile (PAN) and imidazolium ionic liquid of 1-butyl-3-methylimidazolium hydroxide (BmimOH) to boost the hydroxide ions conduction at subzero temperature. The composite membranes efficiently reject the permeation of most cations or other anions but only permit the conduction of hydroxide ions. The composite nanofibers of PAN-BmimOH have the uniform dimension of (245 ± 12) nm in dimension, reminiscing of the tubes in stalks of plants. The hydroxide conductivities reach (2.90 ± 0.70) mS/cm at −25 °C and (40.7 ± 3.4) mS/cm at 60 °C. Mechanism research reveals that the directional arrangement of PAN nanofibers with imidazolium ionic liquid promotes the hydroxide ions conduction process. The single fuel cell is composed of the PAN-BmimOH membrane with a peak power density of 712.2 mW/cm2 at 60 °C. This research not only shows the composite nanofibers with efficient hydroxide ions conduction, but unveils an unexplored pathway for the potential application of ionic liquids in accelerating hydroxide ions conduction at subzero temperature.

The restriction on synchronous improvement of hydroxide ions conductivity and alkaline stability of anion exchange membranes (AEMs) causes the tortuous road to the deep commercialization of anion exchange membrane fuel cells. Herein the AEMs with the multilayered structure deriving from the biomaterial of sesbania gum (SG) and functionalized sesbania gum are constructed through the spinning coating process and the electrospinning process. The multilayered distribution of quaternized SG (QSG) and carboxymethylated SG (CSG) constitutes successive hydrophilic channels in microstructures. A couple of the electrospinning polyvinylidene difluoride (PVDF) nanofibers (PN) layers are closely adhered to the inner (QSG/CSG)3 layer through the cold-pressing process. The outer PN layers resist continuous attracts from hydroxyl radicals under strong alkaline conditions. As a result, the PN/(QSG/CSG)3/PN membrane exhibits the hydroxide ions conductivities of (2.37 f 0.982) mS/cm at -25 degrees C, (71.0 f 4.84) mS/cm at 30 degrees C and (243 f 6.13) mS/cm at 80 degrees C. Notably, the hydroxide ions conductivity reaches 1.53 mS/cm at -25 degrees C and 18.1 mS/cm at 30 degrees C in a ten-cycle of heating/ cooling process. A fabricated single fuel cell with the PN/(QSG/CSG)3/PN membrane presents the maximum power density of 634.5 mW/cm2 at 60 degrees C. From our perspective, the accelerated hydroxide ions conduction process and the acceptable hydroxide ions conductivity stability are achieved since the chemically inert PVDF nanofibers as protective layers confine the hydroxide ions conduction pathways.

The portability is one kind of the most concerned development trends in the commercial application of proton exchange membrane fuel cells (PEMFCs). The proton exchange membranes (PEMs) are thus required with high flexibility besides the qualified fuel cell performance. In this study, flexible PEMs were prepared through carbon black (CB) doped phenolic formaldehyde (PF) resin crosslinked functionalized polystyrene-block-poly(ethyleneran-butylene)-block-polystyrene (SEBS). Specifically, SEBS has been sequentially functionalized with dimethylmaleic anhydride and crosslinked with PF to form the PF resin crosslinked functionalized SEBS (DSEBS-PF). In the prepared DSEBS-PF/CB composite membranes, DSEBS-PF containing the rigid benzene ring in DSEBS and the hydrophilic hydroxyl in PF guarantee enough stiffness and flexibility. Additionally, the oxygen-containing functional groups on the surrounding of CB and carbonyl groups in DSEBS synergistically constitute continuous protons conduction channels. Consequently, phosphoric acid molecules doped composite membrane of DSEBS-PF/0.5%CB/PA presents the proton conductivity of (1.58 +/- 0.006)x10(-1) S/cm at 160 degrees C. Correspondingly, the stretched composite membrane maintains complete microstructure after the biaxial stretching thirty times with the proton conductivity of 5.39 x 10(-2) S/cm. Additionally, the stable proton conductivity is achieved in the cooling/heating cycles process and the long-term period measurements. The proton conductivities are respectively 6.84 x 10(-2) S/cm at 80 degrees C after 360 h and 7.92 x 10(-2) S/cm at 120 degrees C after 210 h, 3.20 x 10(-2) S/ cm at 30 degrees C and 1.24 x 10(-2) S/cm at -30 degrees C in the five cycles process. Therefore, the single fuel cell displays the peak power density of 703.3 mW/cm(2) at 130 degrees C.

For anion exchange membranes (AEMs), the alkaline stability is expected to be enhanced on the premise of high hydroxide ions conductivity. In this study, the AEMs with multilayered microstructures are fabricated through spin coating Kevlar nanofibers and quaternized dual-polymers of quaternized polyvinyl pyrrolidone (QPVP) with quaternized polyepichlorohydrin (QPECH). Kevlar nanofibers as skeleton regulate hydroxide ions conduction along nanofibers. QPVP-QPECH containing a large amount of quaternary ammonium groups function as hydroxide ions conduction carriers. The synergistic effect of QPVP with QPECH in hydroxide ions conduction process has been demonstrated while the (Kevlar/QPVP-QPECH)10(1-1) membrane possesses the improved hydroxide ions conductivity. Specifically, the membrane displays the hydroxide ions conductivity of (70.2 ± 3.11) mS/cm at 80 °C and the power density of 609.5 mW/cm2 at 60 °C. Furthermore, the satisfactory alkaline stability is determined by the long-term hydroxide ions conductivities and retention ratios, such as 61.1 mS/cm and 87.9% at 80 °C, 18.8 mS/cm and 88.7% at 30 °C for 840 h. Additionally, the hydroxide ions conductivities in the ten-cycle heating/cooling process reach 2.26 × 10−3 mS/cm at −25 °C and 1.55 × 10−2 mS/cm at 30 °C.

The high flexibility is the future development trend of anion exchange membranes (AEMs) to meet the requirement of portability for anion exchange membrane fuel cell (AEMFC). This research focuses on constructing flexible AEMs with the accelerated hydroxide ions conduction even at subzero temperature. The flexible AEMs composing with quaternized poly (2,6-dimethyl-1,4-phenylene oxide) (QPPO) and polystyrene-block-poly (ethylene-ran-butylene)-block-polystyrene bromide (SEBSBr) can withstand external mechanical force owing to the highly flexible SEBSBr moieties. The prepared QPPO/N-SEBSBr membrane possesses stable microstructures even if it is folded and biaxially stretched. The rectangular membrane is folded in the width direction for 3 times and the square membrane is biaxially stretched by sequentially stretching 10 % strain in the X and Y direction for repeating thirty times. The accelerated hydroxide ions conduction behaviors are achieved in the range of-25 degrees C-25 degrees C and 30 degrees C-80 degrees C. Specifically, the QPPO/N-SEBSBr membrane exhibits the hydroxide conductivity of 2.31 mS/cm at-25 degrees C and 80.6 mS/cm at 80 degrees C. The fine alkaline stability is confirmed by the slight decrease on hydroxide conductivities during the ten-cycle of-25 degrees C-30 degrees C measurement. A single fuel cell equipped with the (Q/N-SBr)-bs membrane shows the maximum power density of 321 mW/cm2.

Nanofibers are believed to effectively conduct protons by regulating proton conduction pathways in proton exchange membranes.

High flexibility is one of future developing trends for proton exchange membranes (PEMs). Herein, our group designs the PEMs with fibrous microstructures. Specifically, carbon black (CB) with citric acid (ca) as the stabilizer doped polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) constitutes successive protons conduction channels. SEBS with the rigid benzene ring and the hydrophilic ca-CB impart enough stiffness and flexibility of the SEBS/ca-CB nanofibers membranes. The constructed fibrous microstructure guides the protons conduction through confining protons conduction channels. Phosphoric acid (PA) molecules are combined with citric acid in ca-CB through intermolecular hydrogen bonds. Consequently, the SEBS/0.1 %ca-CB/PA membrane exhibits the proton conductivity of 1.38 x 10-1 S/cm at 140 degrees C. The preferred membrane maintained complete morphology without cracks on the surface after the uniaxial and biaxial stretching thirty times. Correspondingly, the uniaxially and biaxially stretched SEBS/0.1 %ca-CB/PA membranes exhibit the proton conductivities of 8.41 x 10-2 S/cm and 9.04 x 10-2 S/cm. Notably, high proton conductivities in cooling-heating cycles and long-term period are reflected in 2.11 x 10-2 S/cm at-30 degrees C and 5.54 x 10-2 S/cm at 30 degrees C after 168 h, 4.32 x 10-2 S/cm at-30 degrees C and 1.64 x 10-1 S/cm at 30 degrees C in the five cycles cooling-heating process. Additionally, a single fuel cell exhibits the peak power density of 494.4 mW cm-2 at 130 degrees C.

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Covalent organic framework (COF) exhibits the great potential to promote proton conduction under low relative humidity for proton exchange membranes (PEMs). In this research, quick and stable proton conduction has been achieved since the prepared COF and polyvinylidene fluoride (PVDF) nanofibers are believed to constitute successive proton conduction channels. The PVDF-COF nanofibers membrane is prepared through the in-situ growth of COF along PVDF nanofibers. The fine compatibility can drive the stable combination of COF with the PVDF nanofibers in PVDF-COF nanofibers. Most importantly, the fibrous PVDF nanofibers accelerate proton conduction through confining the proton conduction pathways. Additionally, ionic liquids of 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazole hexafluorophosphate (BmimPF6) as proton conduction carriers have been introduced to accelerate proton conduction in the prepared PVDF-COF/BmimCl/ PA and PVDF-COF/BmimPF6/PA membranes. Phosphoric acid (PA) molecules are combined by COF and ionic liquid cations with the formation of intermolecular hydrogen bonds. As a result, the PVDF-COF/BmimPF6/PA membrane exhibits the proton conductivity of (1.81 +/- 0.07) x 10(-1) S/cm at 160 degrees C. The long-term proton conductivity stability is determined, deriving from the proton conductivities of 1.77x10(-2) S/cm at 80 degrees C and 1.42x10(-2) S/cm at 110 degrees C in the 400 h non-stop measurement. The single fuel cell equipped with the PVDFCOF/BmimPF6/PA membrane represents the open circuit voltage of 0.927 V and the peak power density of 178.8 mW/cm2 at 100 degrees C, 0.907 V and 326.5 mW/cm2 at 120 degrees C.

Multilayered microstructures can accelerate the proton conduction process in proton exchange membranes (PEMs). Herein, we design and construct PEMs with microstructures based on bifunctional nanofibers and sulfonated poly(ether ether ketone) (SPEEK) nanofibers. Specifically, the bifunctional nanofibers composed of poly(vinyl alcohol) and chitosan are prepared and then combined with the electrospun SPEEK nanofibers. The stable microstructure is derived from the compatible interfacial property of nanofibers and the formed hydrogen bonds. The multilayered microstructure consisting of nanofibers accelerates the proton conduction even at subzero temperature because of regulating the proton conduction pathways. Specifically, the (SKNF/CPNF/SKNF)/PA membrane exhibits the proton conductivities of (0.951 +/- 0.138) x 10-2 S/cm at -30 degrees C and (7.32 +/- 0.37) x 10-2 S/cm at 160 degrees C. Additionally, the fine proton conductivity stability is demonstrated by the proton conductivity in the long-term test and the cooling/heating cycle test, such as 1.67 x 10-2 S/cm at -30 degrees C (after 1000 h), 4.52 x 10-2 S/cm at 30 degrees C (after 810 h), 1.12 x 10-2 S/cm at -30 degrees C, and 1.01 x 10-1 S/cm at 30 degrees C in the cooling/heating process (5 cycles). The single fuel cell possesses an open-circuit voltage of 0.886 V and a peak power density of 0.508 W/cm2 at 130 degrees C.

During the development of anion exchange membranes (AEMs), there is a dilemma of mutual restriction relationship between quick hydroxide ions conduction and reinforced alkaline stability. In this research, the necklace shaped metal-organic framework (MOF) crystals decorating carbon nanotube oxide (OCNT) is prepared through the self-assembly process owing to the interfacial tension force and intermolecular hydrogen bonds. The necklace shaped MOF@OCNT is introduced into quaternized poly(phenylene) oxide (QPPO) to synergistically improve hydroxide ions conduction and alkaline stability of the QPPO/MOF@OCNT membrane. The hydroxide ions conduction process is accelerated even at subzero temperature owing to the formation of oriented hydroxide ions conduction channels. Additionally, MOF@OCNT can resist hydroxide radical (OH-) continuous attacks to functional groups in the polymer molecular chains of QPPO. As a result, QPPO/MOF@OCNT exhibits the hydroxide conductivities of 3.20 mS/cm at -25 degrees C and 44.8 mS/cm at 80 degrees C. Most importantly, the enhanced alkaline stability is revealed from the ten-cycle hydroxide conductivity and the long-term hydroxide conductivity. After immersing in 2 M potassium hydroxide (KOH) solution for 48 h, the tensile stress of QPPO/ MOF@OCNT reaches 24.1 MPa. A single fuel cell with QPPO/MOF@OCNT as the electrolyte exhibits the peak power densities of 0.133 W/cm2 at 30 degrees C and 0.610 W/cm2 at 60 degrees C.

Successive proton conduction channels are constructed with the spin coating method in flexible proton exchange membranes (PEMs). In this research, phosphoric acid (PA) molecules are immobilized in the multilayered microstructure of Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) polymer molecular chains. As a result, successive proton conduction channels can accelerate the proton conduction process in the prepared membrane with the multilayered microstructure. Additionally, the microstructure fractures of the composite membranes from the external force of folding and stretching operations are modified by the inner PA molecules. Notably, numerous PA molecules are further combined through formed intermolecular hydrogen bonding. The stretched membrane absorbs more PA molecules owing to the arrangement of PA molecules, Kevlar nanofibers, and SEBS molecular chains. The stretched membrane thus exhibits the enhanced proton conduction ability, such as the through-plane proton conductivity of 1.81 x 10-1 S cm-1 at 160 degrees C and that of 4.53 x 10-2 S cm-1 at 120 degrees C lasting for 600 h. Furthermore, the tensile stress of PA-doped stretched membranes reaches (3.91 +/- 0.40)-(6.15 +/- 0.43) MPa. A single proton exchange membrane fuel cell exhibits a peak power density of 483.3 mW cm-2 at 120 degrees C.

The realization of high hydroxide ion conductivity on the premise of enough alkaline stability is basic of the practical application of anion exchange membranes (AEMs). In this research, we propose a facile way to enhance the hydroxide ion conductivity at subzero temperature through constructing multilayered microstructures of AEMs. Graphene oxide (GO) nanosheets and 3,6-diazaspiro[5.5]undecane bromide (DSUBr) are alternately deposited on the surface of a quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) membrane with the layer by layer self-assembly process. Multilayered and compact microstructures are retained even if the prepared QPPO/(GO/DSUOH)5 5 membranes are immersed in 2 M KOH solution for 300 h. The hydroxide ions conduction resistance is reduced, deriving from the well-ordered dispersion of components. For example, the QPPO/2-(GO/ DSUOH)5 5 membrane exhibits the hydroxide ion conductivities of 0.922 mS/cm at-25 degrees C and 58.5 mS/cm at 80 degrees C. Furthermore, the prepared AEMs possess the enhanced hydroxide ion conductivity owing to the fine dimension and component stabilities. After the ten-cycle hydroxide ion conductivity stability test, the retention rates of hydroxide ion conductivity are 99.4 % at-25 degrees C and 105 % at 30 degrees C. Additionally, the residual hydroxide ion conductivity reaches 61.6 mS/cm at 80 degrees C in 2 M KOH solution for 624 h. A single fuel cell equipped with the QPPO/2-(GO/DSUOH)5 5 membrane exhibits the maximum power densities of 80.8 mW/cm2 2 at 30 degrees C and 351.6 mW/cm2 2 at 60 degrees C.

The mutual restriction between hydroxide ions' conductivity and alkaline stability is the main obstacle for the practical application of anion-exchange membranes (AEMs) in anion-exchange membrane fuel cells. In this research, we designed a binary polymer nanofiber of polyvinylidene fluoride (PVDF) and polystyrene-block-poly (ethylene-ran-butylene)-block-polystyrene (SEBS) through an electrospinning technique. A quaternized covalent organic framework (QACOF) was then synthesized to accelerate the conduction of hydroxide ions consisting of successive and hydrophilic hydroxide ion conduction channels based on the quaternary ammonium groups. Additionally, the ordered microchannel structures of QACOF could further accelerate the hydroxide ion conduction process. The novel AEMs were thus constructed via the re-stacking of PVDF-SEBS binary polymer nanofibers with the designed QACOF. The QACOF could closely adhere to the PVDF-SEBS binary polymer nanofibers even when the PVDF-SEBS/1% QACOF membrane was immersed in 2 M KOH solution for 480 h. As a result, a fabricated single fuel cell equipped with the PVDF-SEBS/1% QACOF membrane exhibited the maximum power densities of 89.8 mW cm-2 at 30 degrees C and 264.2 mW cm-2 at 60 degrees C. In particular, reinforced hydroxide ion conduction and remarkable conductivity stability at subzero temperature were realized owing to the confinement of hydroxide ion conduction by the chemically inert PVDF-SEBS binary polymer nanofibers. For instance, the hydroxide conductivity of the PVDF-SEBS/1% QACOF membrane was 2.58 mS cm-1 at -25 degrees C and 32.4 mS cm-1 at 80 degrees C in a 480 h test. The mutual restriction between hydroxide ions' conductivity and alkaline stability is the main obstacle for the practical application of anion-exchange membranes (AEMs) in anion-exchange membrane fuel cells.

High temperature proton exchange membranes (HTPEMs) with multilayered structures based on carbon dots@metal organic framework (CDs@MOF) and Sulfonated Poly(Ether Ketone) (SPEEK) have been prepared with the spin coating technique. In this research, carbon dots (CDs) are self-assembled with metal organic framework (MOF) to form the composite of CDs@MOF. Successive proton conduction channels consisting of CDs@MOF and sulfonated groups in SPEEK facilitate to conduct protons in multilayered structures of the prepared composite membranes. Additionally, CDs@MOF can combine phosphoric acid (PA) molecules deriving from the formed intermolecular hydrogen bonding. The proton conductivity is further improved because of the multilayered structures reducing the proton conduction resistance. Specifically, the (SPEEK/40%CDs@MOF)3/ PA membrane exhibits the maximum proton conductivity of (5.02 +/- 0.64) x 10(-2) S/cm at 160 degrees C. Notably, the proton conductivity can retain 1.53 x 10(-2) S/cm at 80 degrees C after a 200 h non-stop test. The open circuit voltage peak and power density of a single fuel cell based on the (SPEEK/40%CDs@MOF)(3)/PA membrane respectively reach 0.95 V, 258.2 mW/cm(2) at 100 degrees C and 0.96 V, 369.9 mW/cm2 at 120 degrees C.

Graphene oxide (GO) nanosheets were believed to possess the merits of extraordinary mechanical property, wide surface area and low price, etc. Polyvinyl chloride (PVC) nanofibers were prepared through the electrospinning technique and combined with GO nanosheets to construct the (PNs/GO/PNs) es membrane with sandwich structure. Furthermore, imidazolium-GO (ImGO) nanosheets were synthesized through the cations of imidazolim-based ionic liquids grafting GO nanosheets. In the prepared membranes, GO and ImGO nanosheets functioned as proton conduction carriers and combined phosphoric acid (PA) molecules with intermolecular hydrogen bonds. The outer PVC nanofibers mats protected the inner GO nanosheets layer and served as an efficient proton conduction media. On the basis of it, the prepared PA doped membranes possessed the improved proton conductivity and enhanced mechanical property, deriving from fast proton conduction and compact structure. Specifically, (PNs/GO/PNs)(es)/PA and PVC/ ImGO/PA membranes exhibited the maximum proton conductivities of 9.26 x 10(-2) S/cm and 2.63 x 10(-2) S/cm at 150 degrees C. The residual values were respectively 9.02 x 10(-2) S/cm and 3.41 x 10(-2) S/cm after a 384 h non-stop at 120 degrees C. Notably, the tensile stress of the (PNs/GO/PNs)es/PA membrane reached 11.6 MPa, higher than 7.11 MPa of the (PNs/GO/PNs) es membrane. The research revealed that GO and ImGO nanosheets promoted proton conduction through combining PA molecules with the reduction of proton conduction resistance in high temperature proton exchange membranes (HTPEMs). (c) 2023 Elsevier B.V. All rights reserved.

The imidazolium ionic liquid of (Kevlar/bmimCl/SEBS)5 membrane was immobilized in flexible proton exchange membranes (PEMs) with the spin coating technology. In the prepared (Kevlar/bmimCl/SEBS)5 membrane, the imidazolium ionic liquid of 1-butyl-3-methylimidazolium chloride (bmimCl) functioned as glue to modify the microstructure fracture from the stretching operation through occupying the cracks. The proton con-duction resistance was reduced with the well-ordered distribution of components in the multilayered microstructure. Although the doped phosphoric acid (PA) molecules charged the proton conductivity, the imidazolium cations of bmim+ could participate in the proton conduction through the formation of continuous proton conduction channels. In this research, the folding and stretching operations exerted the negligible effect on micro-structure and property of the prepared PEMs. Besides the modification of bmimCl, the deformation of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SBES) molecular chains and Kevlar nanofibers in the stretching operation contributed to main-tain the stable microstructure. The stretching and folding operations led to slight variation on the membrane property. Specifically, the proton conductivities were respectively 3.21 x 10-2 S/cm and 4.16 x 10-2 S/cm at 160 degrees C, which were even superior to 2.77 x 10-2 S/ cm of the pristine membranes. Furthermore, the tensile stress values of the folding and stretching membranes can reach (18.9 +/- 1.19) MPa and (32.6 +/- 2.63) MPa.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Carbon nanotubes (CNTs) with a high aspect ratio can theoretically realize the concept of channel-like proton transport clusters. In this research, carbon nanotubes oxide (OCNTs) with large amounts of oxygen-containing groups constituted successive proton conduction channels, deriving from the surface oxidation of CNTs. Pro-ton exchange membranes (PEMs) with sandwich structure were constructed through a couple of polyvinyl chloride nanofbers (PNs) mats wrapping a thin OCNTs layer. In the prepared (PNs/OCNTs/PNs)es membrane, the outer polyvinyl chloride (PVC) nanofibers delayed the leakage of the inner OCNTs and enveloped phosphoric acid (PA) molecules. Furthermore, more PA molecules were combined by the oxygen-containing groups of hy-droxyl, epoxy and carboxyl on the surface of OCNTs with intermolecular hydrogen bonds. For the (PNs/OCNTs/ PNs)es/PA membrane, the good structure stability, high proton conductivity and reinforced mechanical property were derived from the compact structure, fast proton conduction and the formation of inorganic-organic com-posites. Specifically, the maximum proton conductivity was 4.46 x 10-2 S/cm at 160 degrees C, higher than 2.75 x 10-3 S/cm of the PVC/OCNTs/PA membrane. Notably, the tensile stress values reached 5.42 MPa of the (PNs/ OCNTs/PNs)es membrane and 7.32 MPa of the (PNs/OCNTs/PNs)es/PA membrane. Even after a 350 h non-stop measurement at 120 degrees C, the (PNs/OCNTs/PNs)es/PA membrane could have the complete surface, albeit with tiny cracks on cross section. The proton conductivity could maintain the proton conductivity of 3.17 x 10-2 S/cm at 160 degrees C. The research revealed that OCNTs provided the channel-like ionic clusters for proton conduction and sandwich structure accelerated proton conduction in the OCNTs-based membranes.

The flexible proton exchange membrane (PEM) was constructed through alternate deposition of Kevlar nanofibers and polydopamine (PDA)-coating polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) with spin coating technology. In the prepared (Kevlar/PDA@SEBS)5 membrane, the Kevlar nanofibers could withstand the external mechanical force owing to the fiber structure, while the flexible PEM was folded or stretched. The adhesive PDA coating was formed with the self-polymerization of dopamine protected the molecular chains of SEBS and further supported the flexible PEM. The structure of PDA coating SEBS could avoid the microstructure fracture of the flexible PEM during the folding and stretching operations. Notably, the multilayered structure promoted the phosphoric acid (PA) molecules motion through reducing the ion conduction resistance. For instance, the pristine (Kevlar/PDA@SEBS)5/PA membrane exhibited the proton conductivity of 4.11 × 10–2 S/cm at 160 °C, which was comparable to 4.13 × 10–2 S/cm of the folded membrane and (4.07–4.78) × 10–2 S/cm of the stretched membranes. The stable microstructure guaranteed the stiffness, such as 4.15 MPa of the (Kevlar/PDA@SEBS)5-fold/PA membrane and (3.50–6.34) MPa of (Kevlar/PDA@SEBS)5-stretched/PA membranes. Furthermore, the stretched membrane possessed the long-term proton conductivity stability, which was indicative of the microstructure and component stabilities.