•Ti3C2Tx@NC is prepared by in-situ dopamine self-polymerization and carbonization.•NC intercalation prevents Ti3C2Tx sheet re-stacking and forms 3D composites.•NC enhances electrical conductivity and provides electroactive sites to composite.•NC significantly enhances the specific capacitance of Ti3C2Tx by 281%.•The intercalated structure offers adequate cycling stability to Ti3C2Tx@NC.Two-dimensional transition metal carbides, MXenes, with large surface area, excellent electrical conductivity and chemical stability, have proved promising for energy storage. However, the irreversible re-stacking and low capacity of MXenes restrict their development and practical applications. Here, the N-doped carbon decorated MXene (Ti3C2Tx@NC) composites were synthesized via an in-situ self-polymerization of dopamine on the surface of Ti3C2Tx followed by a carbonization process. The Ti3C2Tx and Ti3C2Tx@NC were systematically characterized, which have been manifested that NC were equably decorated on the surface and interlayer of Ti3C2Tx sheets and a unique three-dimensional composited nanostructure was fabricated. Such nanostructure can confer both high surface area of NC layer and effective avoidance of the restacking of Ti3C2Tx sheets, whilst, importantly, rendering the composites good conductivity and additional pseudocapacitance. As a result, the optimized Ti3C2Tx@NC-2 composite exhibited a high specific capacitance of 442.2 F g−1 under a current density of 1 A g−1, which is 281% higher than that of Ti3C2Tx. As a further description, Ti3C2Tx@NC achieved an excellent cycling stability with capacitance retaining 91.9% after 5000 cycles and a high rate capability of 92.5% at 10 A g−1. Besides, the Ti3C2Tx@NC-2-based symmetric supercapacitor presents a delighted energy density and power density. Therefore, the elaborately designed Ti3C2Tx@NC composites provided a pregnant exploration for energy-related applications.Download high-res image (176KB)Download full-size image

•Functionalized Ti3C2Tx sheets with sulfonated polymer brushes is prepared.•Ti3C2Tx-SO3H is embedded in SPEEK and CS respectively to obtain composite PEMs.•Ti3C2Tx-SO3H provides new hopping sites and transfer pathways to composite PEMs.•This donates remarkable promotion on both hydrated and anhydrous proton conduction.•Composite membranes display improved thermal and structural stabilities.Here, Ti3C2Tx sheets, a representative of MXenes, with lamellar structure and hydrophilic surface are prepared, and then functionalized with sulfonated polyelectrolyte brushes (Ti3C2Tx-SO3H) through a facile surface-initiated precipitation-polymerization. The Ti3C2Tx-SO3H is then utilized as a new nanofiller to fabricate hybrid proton exchange membrane, where both acidic sulfonated poly (ether ether ketone) (SPEEK) and basic chitosan (CS) are employed as polymer matrixes. The resultant hybrid membranes are systematically characterized and measured including their microstructures, water uptake and proton conduction properties. The results demonstrate that using the sulfonated polyelectrolyte brushes, Ti3C2Tx-SO3H sheets construct efficient proton transfer pathways and connect the inherent conduction channels/paths in polymer phase. This significantly enhances the proton conduction of polymer membrane including SPEEK membrane and CS membrane, under both hydrated condition and anhydrous condition. Particularly, the incorporation of 10 wt.% Ti3C2Tx-SO3H readily offers 144% and 66% increase in proton conductivity, respectively, to SPEEK membrane and CS membrane under hydrated condition. Furthermore, the hybrid membranes achieve improved thermal and mechanical stabilities. These results herald further advances to preparing functionalized MXenes and their relevant hybrid materials with enhanced performances.Download high-res image (300KB)Download full-size image

Conductive polymer electrolyte membranes are increasingly attractive for a wide range of applications in hydrogen-relevant devices, for instance hydrogen fuel cells. In this study, two-dimensional Ti3C2Tx, a typical representative of the recently developed MXene family, is synthesized and employed as a universal filler for its features of large specific surface area, high aspect ratio, and sufficient terminated −OH groups. The Ti3C2Tx is incorporated into polymer matrix to explore its function on membrane microstructure and proton conduction property. Both phase-separated (acidic Nafion and sulfonated poly(ether ether ketone)) and non-phase-separated (basic chitosan) polymers are utilized as membrane matrixes. The microstructures, physicochemical properties, and proton conduction properties of the membranes are extensively investigated. It is demonstrated that Ti3C2Tx generates significant promotion effect on proton conduction of the composite membrane by facilitating both vehicle-type and Grotthuss-type proton transfer, yielding several times increased proton conductivity for every polymer-based composite membrane under various conditions, and the composite membrane achieves elevated hydrogen fuel cell performance. The stable Ti3C2Tx also reinforces the thermal and mechanical stabilities of these composite membranes. Since the MXene family includes more than 70 members, this exploration is expected to open up new perspectives for expanding their applications, especially as membrane modifiers and proton conductors.Keywords: hydrogen fuel cell; MXene; organic−inorganic composite membrane; proton conduction property; universal active filler

Herein, nanocomposite membranes are fabricated based on functionalized graphene oxides (FGOs) and sulfonated poly(ether ether ketone) (SPEEK), followed by being impregnated with imidazole-type ionic liquid (IL). The functional groups (acidic group or basic group) on FGOs generate strong interfacial interactions with SPEEK chains and then adjust their motion and stacking. As a result, the nanocomposite membranes possess tunable interfacial domains as determined by its free volume characteristic, which provides regulated location for IL storage. The stored ILs act as hopping sites for water-free proton conduction along the FGO-constructed interfacial channels. The microstructure at SPEEK-FGO interface governs the IL uptake and distribution in nanocomposite membrane. Different from GO and vinyl imidazole functionalized GO (VGO), the presence of acidic (−SO3H) groups confers the p-styrenesulfonic acid functionalized GO (SGO) incorporated nanocomposite membrane loose interface and strong electrostatic attraction with imidazole-type IL, imparting an enhanced IL uptake and anhydrous proton conductivity. Nanocomposite membrane containing 7.5% SGO attains the maximum IL uptake of 73.7% and hence the anhydrous conductivity of 21.9 mS cm–1 at 150 °C, more than 30 times that of SPEEK control membrane (0.69 mS cm–1). In addition, SGOs generate electrostatic attractions to the ILs confined within SGO-SPEEK interface, affording the nanocomposite membrane enhanced IL retention ability.Keywords: anhydrous proton conductivitys; functionalized graphene oxide; interfacial microstructure; ionic liquid uptake and distribution; nanocomposite membrane

•A series of hybrid membranes are prepared using fillers with different structures.•The fillers (0-D, 1-D, and 2-D) are sulfonated to ensure close surface component.•The effect of filler’s structure on microstructure of hydrid membrane is explored.•For single-kind filler series, 2-D filler has the strongest conduction promotion.•The synergy effect of different kinds of fillers is systematacially investigated.For hybrid membrane, the polymer-inorganic interface along filler surface can be facilely created to be distinctive and controllable pathway for mass transfer. Herein, three kinds of fillers are used as inorganic additives including zero-dimensional silica (0-D, SiO2), one-dimensional halloysite nanotube (1-D, HNT), and two-dimensional graphene oxide (2-D, GO), which are functionalized by sulfonated polymer layer to ensure close surface component. Then the fillers are incorporated into two types of polymer matrixes (phase-separated sulfonated poly(ether ether ketone) and non-phase-separated chitosan) to prepare three series of hybrid membranes with single-kind filler, double-kinds fillers, or triple-kinds fillers, respectively. The microstructures, physicochemical properties, and proton conduction properties (under hydrated and anhydrous conditions) of the membranes are extensively investigated. It is found that (i) for the single-kind filler-filled membranes, 2-D filler has the strongest promotion ability for proton conductivity of membrane due to the constructed wide and long-range pathways for proton transfer; (ii) while for the hybrid membranes with double-kinds fillers, instead of synergistic promotion effect, the fillers cause more tortuous transfer pathways within membranes and then decrease proton conductivity; (iii) the hybrid membranes with triple-kinds fillers exhibit similar behavior but a little higher conductivity than the membranes with double-kinds fillers.

•Multi-functional SiO2 nanospheres are synthesized to prepare TFN membrane.•Interfacial interactions between polymer matrix and nanospheres are manipulated.•Different polymer–nanosphere interfacial morphologies are proposed.•The relationship between membrane microstructure and SRNF performance is explored.•Tunable organic solvent flux and enhanced solute rejection are achieved.Herein, a series of thin film nanocomposite (TFN) membranes are prepared by incorporating functionalized silica nanospheres into polyethyleneimine (PEI) matrix for solvent resistant nanofiltration (SRNF). Three functional groups are grafted onto the nanospheres in form of polymer layer via distillation–precipitation polymerization for manipulating the free volume cavities of PEI matrix by interfacial interactions along PEI-nanosphere domains. The effects of nanospheres on the microstructures, physicochemical and permeation properties of TFN membranes are investigated systematically. The tested data suggest that the nanospheres are uniformly dispersed in PEI matrix without obvious defects, offering the excellent thermal stability and appropriate solvent resistance to the membranes. The microstructures of TFN membranes are elaborately regulated by varying the fractional free volume (FFV) and surface hydrophilic/hydrophobic nature, jointly yielding the tunable permeation properties. In particular, the permeate flux of ethanol is elevated from 21.2 to 30.8 L m−1 h−1 with the increase of FFV from 0.452% to 0.473% by incorporating various hydrophilic nanospheres. Meanwhile, the addition of hydrophobic nanospheres provided much higher fluxes for n-heptane from 0.1 to 21.7 L m−1 h−1, due to the enhanced solution capability. Moreover, the presence of nanospheres donates high rejection ability and promising operation stability to the TFN membranes.

In this research, novel quaternized polymer spheres (QPSs) with a high quaternary ammonium (QA) group loading amount and a controllable structure are synthesized and incorporated into a chitosan (CS) matrix to fabricate a composite membrane. Systematic characterizations and molecular simulation are adopted to elaborate the relationship between the QA structure of QPSs and physical-chemical as well as ion conduction properties of composite membranes. The well-dispersed QPSs generate repulsive interaction to CS chains, endowing the composite membrane with promoted chain mobility and water uptake and thereby enhanced hydroxide conductivity. The QPSs work as hydroxide conductors within the membranes, affording a hydroxide conductivity increase over 80%. As the hopping sites in the membrane, the QA group with moderate OH– combination/dissociation capability exhibits higher OH– conductivity. By comparison, the QA group with the highest or lowest potential displays slightly lower OH– conductivity. Besides, extending the chain length of the QA ligand generates obvious steric hindrance and then impedes OH– combination.

Proton carriers are essential for highly conductive polymer electrolyte membranes. Herein, a series of nanofibrous composite membranes (NFCMs) are prepared by facilely incorporating a polymer matrix (sulfonated poly(ether ether ketone) (SPEEK) or chitosan (CS)) into a PVA/SiO2-based nanofiber mat. By changing the functional groups (acid, base or neutral) on the nanofiber mat, three types of composite proton carriers (I-type: acid–neutral or base–neutral, II-type: acid–acid or base–base, III-type: acid–base or base–acid) are generated at the interfacial domains of NFCMs. These carriers construct continuous conductive pathways by means of the inter-lapped nanofibers and inter-connected polymer matrix. Through the investigation of proton conductivities under both hydrated and low humidity conditions, it is found that NFCMs with I-type proton carriers show low proton conduction properties due to the deficient proton hopping sites. By comparison, II-type carriers display an increase of carrier loading amount, thus affording enhanced proton transfer abilities to NFCMs. III-type proton carriers (acid–base pairs) exhibit a distinct induction effect, by which protonation and deprotonation are promoted, resulting in superior low-energy-barrier proton hopping pathways. Thus, it is reasonable to state that the carrier loading amount and the interactions within them are both crucial to proton migration. In addition, the superior proton conduction abilities of III-type proton carriers confer favorable fuel cell performances on the NFCMs.

•Sulfonated polymer brush modified GO (SP-GO) as filler of composite membrane.•Tailored membrane structures by tuning polymer brush length and SP-GO content.•Improved interfacial compatibility between SPEEK and GO by the polymer brush.•Enhanced proton conductivities under hydrated and anhydrous conditions.•Lowered proton hopping barrier due to the formation of facile pathways.Sulfonated polymer brush modified graphene oxide (SP-GO) fillers with controllable brush length are synthesized via the facile distillation–precipitation polymerization, and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate composite membranes. The influences of SP-GO upon the microstructures, including thermal and mechanical properties, water uptake/swelling, proton conduction, H2 permeability and single PEMFC performances of composite membranes are intensively investigated. It is found that the SP-GO fillers are uniformly dispersed and tend to lie perpendicularly to the cross-section surface of the whole membrane, which allow SP-GO fillers creating inter-connected and broad ionic pathways through the sulfonic acid groups in polymer brushes. Meanwhile, the SP-GO fillers connect the ionic clusters in SPEEK matrix via interfacial interactions. In such a way, proton-transfer highways are constructed along the SPEEK/SP-GO interface, which lower the proton transfer activation energy and enhance the proton conductivities of the composite membranes under both hydrated and anhydrous conditions. Furthermore, elevating the brush length on SP-GO could further enhance the proton conductivity. Compared to SPEEK control membrane, a 95.5% increase in hydrated conductivity, an 178% increase in anhydrous conductivity and a 37% increase in maximum power density are obtained for the optimal composite membrane.

•ImIL was incorporated into SPEEK to prepare composite membrane via IL-swollen method.•ImIL loading amount was accurately controlled by the preparation conditions.•ImIL was enriched in ionic clusters to form facile and continuous transfer channels.•ImIL gave significant enhancement in anhydrous conductivity to composite membrane.•Comparison of preparation (IL-swollen or solution casting) method was conducted.Herein, a series of composite membranes based on sulfonated poly(ether ether ketone) (SPEEK) and imidazole-type ionic liquid (ImIL) are prepared through IL-swollen method as anhydrous electrolytes for fuel cell. The IL loading amount is accurately controlled by preparation conditions (e.g., ultrasonic power, treatment temperature, and treatment time). The influence of IL on physicochemical properties of composite membrane is systematically investigated. The IL is enriched into the ionic clusters of SPEEK matrix driven by electrostatic attractions, thereby broadening them to form inter-connected channels. IL provides anhydrous hoping sites and low-energy-barrier paths of imidazole-sulfonic acid pairs to composite membrane. Through the channels, these sites form facile pathways and significantly enhance the anhydrous conductivity of composite membrane. Particularly, the composite membrane containing 43% IL achieves a 52 times higher conductivity (9.3 mS cm–1) than that of the control membrane (0.179 mS cm–1) at 140 °C. Increasing IL loading amount will further elevate the anhydrous conductivity. The dynamic IL release and the concomitant conductivity of composite membrane are investigated. Moreover, another team of composite membranes are prepared by solution casting method for exploring the influence of preparation method on the microstructure, IL retention ability, and conductivity of IL-incorporated membrane.

Design and fabrication of thin film nanocomposite (TFN) membranes with tunable solvent permeation properties is highly required to meet the demands of practical applications. Herein, a series of TFN membranes are elaborately fabricated by embedding cyclodextrins (CDs) into hydrophilic polymeric membrane (e.g., polyethylenimine, PEI). Within the active layer, hydrophobic cavities of CDs serve as exquisite pathways for nonpolar solvents, whereas the free volume cavities of the PEI matrix act as efficient pathways for polar solvents, constructing a dual-pathway nanostructure. The solvent permeation properties of these two pathways can be accurately tuned by adjusting the cavity size of CD and the fractional free volume (FFV) of PEI. Increasing the cavity size of CD allows larger nonpolar solvent to permeate, meanwhile increasing solvent flux. For instance, varying the cavity size from 0.60 to 0.75 nm elevates the toluene (0.60 nm) permeance from 0.13 to 2.52 L m–2 h–1 bar –1. Similar behaviors are observed for polar solvents when increasing the FFV of PEI by adjusting the PEI–CD interfacial interactions. Particularly, the isopropyl alcohol permeance is elevated from 3.37 to 4.16 L m–2 h–1 bar –1 when increasing FFV from 0.489% to 0.502%. Moreover, the rejection ability and extended trial of TFN membranes are also explored.Keywords: Cyclodextrin; Interfacial polymerization; Organic solvent nanofiltration; Thin film nanocomposite membrane; Tunable solvent permeation properties;

Graphene oxide (GO) and functionalized GO have been widely employed to design and fabricate polymer–inorganic nanohybrid materials for electrochemical applications. In this study, a series of imidazolium-functionalized graphene oxide (ImGO) nanosheets bearing different types of ligands (namely butyl, decyl, carbethoxy, and benzyl groups) on quaternary ammonium (QA) groups are prepared via distillation–precipitation polymerization and quaternarization, and then embedded into chitosan (CS) to fabricate nanohybrid membranes. The addition of ImGO significantly enhanced the thermal, mechanical, and anti-swelling stabilities of membranes due to the strong electrostatic attractions at CS/ImGO interface. More importantly, hydroxide ion transport highways were constructed at CS/ImGO interface via interfacial interactions. Meanwhile, the influence of the ligands on QA groups on the physicochemical properties, OH− conductivity, and conduction mechanism is systematically elucidated. Due to the optimal hydrophilicity and ion exchange capacity, ImGO with carbethoxy group as the ligand confers the highest OH− conductivity on nanohybrid membrane (up to 1.02 × 10−2 S cm−1 at 90 °C and 100% RH, about four times of that of CS control membrane). Correspondingly, a fuel cell with such a membrane shows an OCV of 0.71 V and a maximum power density of 75.8 mW cm−2 at a current density of 298.8 mA cm−2.

Herein, a series of composite membranes with optimized solvent permeance and rejection are prepared by combining the advantages of hybridization and cross-linking techniques. Polyethylenimine (PEI) and hydroxyl terminated trifluoride polydimethylsiloxane (PDMS) are cross-linked with trimesoyl chloride as the skin layer, which is isotropic rather than hierarchical. The chain mobility of PEI is inhibited upon hybridization and cross-linking, affording enhanced solvent resistance and thermal/mechanical stabilities. The composite membrane achieves high rejection ability with the rejection of PEG 1000 of about 100%. Additionally, the synergy of hydrophilic PEI and hydrophobic PDMS segments gives acceptable solvent permeances for acetone (up to 2.7 L m–2 h–1 bar–1) and ethyl acetate (up to 1.4 L m–2 h–1 bar–1). The membrane microstructures are facilely tuned by regulating PDMS content and cross-linking time, allowing the efficient optimization of solvent resistant nanofiltration performances. Moreover, the operational stability and the separation of lotus seedpod proanthocyanidins–ethanol/water mixtures are investigated to evaluate the practical application of the composite membrane.

A new approach to the facile preparation of anhydrous proton exchange membrane (PEM) enabled by artificial acid–base pairs is presented herein. Inspired by the bioadhesion of mussel, polydopamine-modified graphene oxide (DGO) sheets bearing –NH2 and –NH– groups are fabricated and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare the nanocomposite membrane. The DGO sheets are interconnected and homogeneously dispersed in SPEEK matrix, which provides unique rearrangement of the nanophase-separated structure and chain packing of nanocomposite membrane through interfacial electrostatic attractions. These attractions meanwhile induce the generation of acid–base pairs along the SPEEK–DGO interface, which then serve as long-range and low-energy-barrier pathways for proton hopping, imparting an enhanced proton transfer via the Grotthuss mechanism. In particular, under both hydrated and anhydrous conditions, the nanocomposite membrane exhibits much higher proton conductivity than the polymer control membrane. The enhanced proton conductivity results in the nanocomposite membrane having elevated cell performances under 120 °C and hydrous conditions, yielding a 47% increase in maximum current density and a 38% increase in maximum power density. Together with the stable conduction property, these results guarantee the nanocomposite membrane's promising prospects in high-performance fuel cell under anhydrous and elevated temperature conditions.

•Sulfonated nanotubes (SHNTs) with tunable –SO3H group loading are synthesized.•SHNTs are embedded into SPEEK matrix to prepare nanocomposite membranes.•SHNTs enhance the thermal and mechanical stabilities of SPEEK membrane.•SHNTs interconnect the ionic channels and endow continuous proton pathways.•Nanocomposite membranes achieve high proton conductivity with low transfer barrier.Proton exchange membrane (PEM) with high proton conductivity is crucial to the commercial application of PEM fuel cell. Herein, sulfonated halloysite nanotubes (SHNTs) with tunable sulfonic acid group loading were synthesized and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare nanocomposite membranes. Physicochemical characterization suggests that the well-dispersed SHNTs enhance the thermal and mechanical stabilities of nanocomposite membranes. The results of water uptake, ionic exchange capacity, and proton conductivity corroborate that the embedded SHNTs interconnect the ionic channels in SPEEK matrix and donate more continuous ionic networks. These networks then serve as proton pathways and allow efficient proton transfer with low resistance, affording enhanced proton conductivity. Particularly, incorporating 10% SHNTs affords the membrane a 61% increase in conductivity from 0.0152 to 0.0245 S cm−1. This study may provide new insights into the structure-properties relationships of nanotube-embedded conducting membranes for PEM fuel cell.

•Composite membrane with covalently cross-linked PEI-PDMS as skin layer is prepared.•Hydrophilic–hydrophobic hybrid network is formed in the skin layer.•The membrane attains good solvent resistance in both polar and nonpolar solvents.•The membrane achieves acceptable permeate flux for both polar and nonpolar solvents.•The membrane shows promising long-term stability for SRNF application.A new approach to the facile preparation of high-performance composite membrane for solvent resistant nanofiltration is presented herein. Within the composite membrane, hydrophilic polyethyleneimine (PEI) and hydrophobic hydroxyl terminated trifluoride polydimethylsiloxane (PDMS) are cross-linked as skin layer, whereas polyacrylonitrile (PAN) ultrafilitration membrane serves as support layer. The microstructure and physicochemical properties of the membrane are extensively investigated. It is found that PEI chains and PDMS chains are covalently cross-linked via trimesoyl chloride through interfacial polymerization, generating hydrophilic–hydrophobic hybrid network. The cross-linking inhibits the chain mobility of PEI, affording the composite membrane enhanced thermal and mechanical stabilities relative to the membrane without PDMS. Combining the advantages of both hydrophilic and hydrophobic materials endows the composite membrane with excellent solvent resistance properties and nanofiltration performances in both polar solvents and nonpolar solvents, such as isopropanol, butanone, ethyl acetate, and n-heptane. Particularly, the composite membrane achieves permeate fluxes of 37.8, 3.5, 5.4, and 4.7 L m−2 h−1 for these four solvents, respectively, along with the area swellings below 3.2%. After being equilibrated in these solvents, the composite membrane exhibits good structural stability with molecular weight cut-off of 600. The operation stability of the composite membrane is also explored.Download high-res image (124KB)Download full-size image

•MASM with loose and thin electronegative surface layer onto AEM is prepared via IP.•Polymerization of benzene-rich monomer and cross-linker yields this kind of layer.•The base AEM ensures sufficient fluxes for both monovalent and bivalent anions.•Surface layer obviously inhibits SO42 − transfer but maintains Cl− and NO3− migration.•Intercept of SO42 − on MASM surface elevates Cl−/SO42 − selectivity by up to 472.2%.Herein, a novel thin electronegative layer with loosely porous structure is fabricated through interfacial polymerization of benzene-rich monomer (2,5-diaminobenzenesulfonic acid (DSA) or 3,5-diaminobenzoic acid (DMA)) and cross-linker (trimesoyl chloride), using the blend of polyvinyl alcohol and quaternized-chitosan as base membrane. The base membrane achieves adequate fluxes for both monovalent and divalent anions but limits monovalent/divalent anions permselectivity to below 2.5. By comparison, the thin and porous surface layer endows the dual-layered membrane with only slight flux reduction of below 9.0% for monovalent anions, yet a 30.6% flux reduction for SO42 − based on Donnan-effect and steric effect. The effective intercept of SO42 − on membrane surface weakens its competitive transfer with Cl−, thus the Cl−/SO42 − permselectivity is significantly elevated by 472.2% from 1.8 to 10.3, which is even 36.3% higher than that of commercial Neosepta ACS. Furthermore, the antifouling potential and thermal/mechanical stabilities of the dual-layered membrane are improved assisted by the hydrophilic and electronegative features of coated layer and its covalent bonds with base layer. DSA and DMA, two analogous monomers, are utilized and compared to verify the universality of this nanostructure, helping to explore the structure-performance relationship.Download high-res image (250KB)Download full-size image

•FGOs with acid/base polymer brushes or block copolymer brushes were designed.•FGOs were dispersed into SPEEK or CS matrix to fabricate composite membrane.•Interaction between matrix and brush governed interfacial microstructure of membrane.•Interconnected and wide proton transfer network were formed along FGOs surface.•Over six times’ increase of proton conductivity were achieved by 5 wt% FGO.For composite membrane, efficient mass transfer between polymer and filler can trigger synergic promotion effect through the tunable interfacial nanodomains. Herein, four kinds of functionalized graphene oxide nanosheets (FGOs) bearing polymer brushes (phosphoric acid brushes, imidazole brushes, acid-base or base-acid block copolymer brushes) are designed exquisitely, and then embedded into two typical polymer matrixes (acidic sulfonated poly(ether ether ketone) and basic chitosan) to prepare composite membranes. It is found that the strong electrostatic attractions drive the brushes insert into polymer matrix and form interconnected networks, affording enhanced thermal/mechanical stabilities and enlarged free volume. Especially, the attractions from outer segment even drag the inner segment to deeply insert into polymer matrix for FGOs with acid-base copolymer brushes, yielding wide and long-range interfacial networks. When employing as proton conductors, these networks can ultrafast transport protons between FGOs and polymer matrix using the functional groups (especially acid-base pairs), affording 6.7 times’ increment of proton conductivity to polymer membrane. The synergic promotion effect is governed by the width and amount of interfacial networks (pathways). The effect of these polymer brushes on acidic membrane and basic membrane are investigated and compared extensively to explore their functions on membrane microstructure and mass transfer.

Proton carriers are essential for highly conductive polymer electrolyte membranes. Herein, a series of nanofibrous composite membranes (NFCMs) are prepared by facilely incorporating a polymer matrix (sulfonated poly(ether ether ketone) (SPEEK) or chitosan (CS)) into a PVA/SiO2-based nanofiber mat. By changing the functional groups (acid, base or neutral) on the nanofiber mat, three types of composite proton carriers (I-type: acid–neutral or base–neutral, II-type: acid–acid or base–base, III-type: acid–base or base–acid) are generated at the interfacial domains of NFCMs. These carriers construct continuous conductive pathways by means of the inter-lapped nanofibers and inter-connected polymer matrix. Through the investigation of proton conductivities under both hydrated and low humidity conditions, it is found that NFCMs with I-type proton carriers show low proton conduction properties due to the deficient proton hopping sites. By comparison, II-type carriers display an increase of carrier loading amount, thus affording enhanced proton transfer abilities to NFCMs. III-type proton carriers (acid–base pairs) exhibit a distinct induction effect, by which protonation and deprotonation are promoted, resulting in superior low-energy-barrier proton hopping pathways. Thus, it is reasonable to state that the carrier loading amount and the interactions within them are both crucial to proton migration. In addition, the superior proton conduction abilities of III-type proton carriers confer favorable fuel cell performances on the NFCMs.

A new approach to the facile preparation of anhydrous proton exchange membrane (PEM) enabled by artificial acid–base pairs is presented herein. Inspired by the bioadhesion of mussel, polydopamine-modified graphene oxide (DGO) sheets bearing –NH2 and –NH– groups are fabricated and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare the nanocomposite membrane. The DGO sheets are interconnected and homogeneously dispersed in SPEEK matrix, which provides unique rearrangement of the nanophase-separated structure and chain packing of nanocomposite membrane through interfacial electrostatic attractions. These attractions meanwhile induce the generation of acid–base pairs along the SPEEK–DGO interface, which then serve as long-range and low-energy-barrier pathways for proton hopping, imparting an enhanced proton transfer via the Grotthuss mechanism. In particular, under both hydrated and anhydrous conditions, the nanocomposite membrane exhibits much higher proton conductivity than the polymer control membrane. The enhanced proton conductivity results in the nanocomposite membrane having elevated cell performances under 120 °C and hydrous conditions, yielding a 47% increase in maximum current density and a 38% increase in maximum power density. Together with the stable conduction property, these results guarantee the nanocomposite membrane's promising prospects in high-performance fuel cell under anhydrous and elevated temperature conditions.