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It is difficult for sulfonated poly(ether ether ketone) (SPEEK) to possess both high proton conduction and vanadium resistance owing to the degree of sulfonation. Herein, the composite membranes (S/GO-TpTG) with cationic covalent organic nanosheet (TpTG) crosslinked graphene oxide (GO-TpTG) are prepared to enhance selectivity by optimizing the ion transport channels. The GO-TpTG can efficiently transport protons utilizing its cationic porous structure and acid-base pairs' interaction with SPEEK. Meanwhile, it can block vanadium ions through the Donnan exclusion and physical blocking effects. The S/GO-TpTG membrane with 3 wt% GO-TpTG exhibits excellent proton conductivity (82.7 mS cm−1) and selectivity (77.9 × 10−7 cm2 min−1). The VRFB with this membrane exhibits excellent energy efficiency (88.6–81.0 % at 100–200 mA cm−2), cycle durability, and self-discharge time (209.8 h). This study confirms the great potential of GO-COF to balance proton conductivity and vanadium resistance, and provides an effective strategy to optimize proton channels. [Display omitted] • The TpTG crosslinked GO is introduced into SPEEK to prepare S/GO-TpTG membranes. • Continuous proton transport channels have been reconstructed in S/GO-TpTG membrane. • The composite membranes exhibit high H+/Vn + ion selectivity. • At 200 mA cm−2, the EE of cell equipped with S/GO-TpTG membrane is up to 81.%. [ABSTRACT FROM AUTHOR]

The trade-off issue between proton conduction properties and stability is a constraint on the commercial application of non-fluorinated proton exchange membranes for fuel cells. To alleviate the issue, the multi-block N-heterocycle poly(aryl ether sulfone)s with ether-free hydrophilic blocks (b-SPDPESs), which is composited by diphenyl sulfone moieties and biphthalazindione structures with dense pendant benzenesulfonic groups, are developed to prepare high-performance membranes. The self-assembly effect of block copolymers not only improves the membrane stability but also constructs regular proton conduction channels. Moreover, the conduction channel consists of hydrophilic blocks without ether bonds, which effectively improves the tolerance of the membrane to radicals. The hydrogen-bond network between sulfonic groups and N-heterocycles in the channel improves the proton conduction efficiency, inhibits the swelling of the membrane, and improves the stability of the membrane. As a result, the swelling degree of b-SPDPESs membrane is only 15.8 %, the proton conductivity is as high as 238 mS cm−1, the membrane aging broken time at 80 °C is between 4 and 6.6 h, and the fuel cells loading the membranes and feeding with hydrogen and air perform the max power density of between 0.65 and 1.25 W cm−2. Modulating the sequence structure of chains and constructing multiblock polymers containing ether-free N-heretrocyclic blocks with sulfonic groups improve the stability of membranes while ensuring their proton conductivity. [Display omitted] • Multi-block SPDPESs containing ether-free hydrophilic blocks is constructed. • b-SPDPESs membranes perform fine physicochemical stability and proton conductivity. • The hydrophilic blocks without ether bonds enhance membrane oxidation stability. • Fuel cell with b-SPDPESs membrane performs a power density of up to 1.25 W cm−2. [ABSTRACT FROM AUTHOR]

The use of proton exchange membrane water electrolysis (PEMWE) for hydrogen production is considered a promising technology due to its high theoretical current density, gas purity, and energy efficiency. In this study, a fluorinated sulfonated hydrocarbon polymer was used to prepare hydrocarbon−based membranes for PEMWE that displayed exceptional stability. Notably, the SFPAE-60 membrane has a proton conductivity of up to 293.1 mS cm−2 at 80 °C and 100%RH, but its volumetric swelling ratio is only 47 %. Its dimensional stability is significantly better than that of previously reported sulfonated poly (aryl ether)−based proton exchange membranes (>100 %). The PEMWE based on the SFPAE-60 membrane achieves a current density of over 4800 mA cm−2 at 2.0V, confirming the membrane's applicability in actual water electrolysis. The results indicate that the electrolyte membrane of fluorinated sulfonated hydrocarbon polymer performs well in the PEM electrolyzer. [Display omitted] • Synthesis of a Fluorinated Sulfonated poly (aryl ether) for the Preparation of PEMWE Based Membrane. • The SFPAE-60 membrane has a proton conductivity of up to 293.1 mS cm−2 at 80 °C and 100%RH. • At the same level of dimensional stability, proton conductivity can be increased by >60 %. • Using SFPAE-x MEA, a current density of over 4800 mA cm−2 was achieved at a voltage of 2.0 V. [ABSTRACT FROM AUTHOR]

High-temperature proton exchange membranes (HT-PEMs) were created by incorporating quaternate polymeric ionic liquids (PILs) with a triazine structure into polybenzimidazole (OPBI). The membranes that were developed demonstrate excellent proton transport and retention capabilities for phosphoric acid (PA). It was found that the best overall performance of the cross-linked membranes was achieved at the ideal ratio of 30 wt% PIL. The proton conductivity of OPBI-PIL-30 % membranes at 180 °C was 126.71 mS cm−1. The PA retention was 69.37 % after 240 h of testing at 80 °C and 40 % RH. The PA retention was 91.61 % at 160 °C, indicating its superior acid retention ability. The OPBI-PIL-30 % membrane was assembled into a single cell with a peak power density of 448.99 mW cm−2 at a current density of 1490 mA cm−2. These excellent performances suggest that cross-linked composite membranes containing bulky structures and quaternary ammonium groups are one of the potential materials for HT-PEMs. [Display omitted] • High-density quaternized polymer ionic liquids for proton exchange membranes. • The proton conductivity of OPBI-PIL-30 % membrane at 180 °C was 126.71 mS cm−1. • The PA retention of OPBI-PIL membranes reached 91.61 % at 160 °C after 240 h. • The PA retention of OPBI-PIL membrane reached 69.37 % at 80 °C/40 % humidity. • The highest peak power density of OPBI-PIL membrane at 160 °C was 448.99 mW cm−2. [ABSTRACT FROM AUTHOR]

In this paper, amino-phosphate bifunctionalized graphene oxide (PA-GO) was successfully synthesized by amination reaction of graphene oxide followed by acid modification with hypophosphorous acid. A series of composite proton exchange membranes were successfully prepared by adding modified GO to sulfonated poly (aryl ether ketone sulfone) matrices containing carboxyl groups (C-SPAEKS). The prepared composite membranes were performed by a series of tests. The C-SPAEKS@1%PA-GO had the best performance, which was able to achieve the tensile strength of 42 MPa while possessing the high proton conductivity of 128.23 mS cm−1 at 80 °C. In addition, the peak power density of C-SPAEKS@1%PA-GO reached 677.67 mW cm−2 at a current density of 2082.8 mA cm−2, which was almost four times that of the pure membrane (166 mW cm−2). And after 44 h at a constant current density of 0.1 A cm−2, the C-SPAEKS@1%PA-GO membrane could still maintain 54.1 % of the original voltage. It can be seen that our work has achieved certain results, and the functionalized modification of graphene oxide could greatly improve the comprehensive performance of proton exchange membranes (PEMs). [Display omitted] • Introduction of PA-GO increased the transfer sites of protons. • The introduction of PA-GO contributes to the enhancement of membrane conductivity. • The introduction of PA-GO improves the thermal stability of the membrane. • The highest power density of composite membrane was 677.67 mW cm−2. [ABSTRACT FROM AUTHOR]

Anion exchange membranes (AEMs) are promising for recovering acid from different engineering effluent due to their lower energy consumption, positive environmental impact, and potential for providing clean water resources. Utilizing the diffusion dialysis (DD) process, AEMs effectively retain metal ions while selectively allowing fast proton permeation. Achieving high hydrophilicity, proton conductivity, and ion exchange capacity through exact control of polymeric structure and chemical composition is crucial for enhancing the efficiency of the acid recovery process. This study presents the findings on the impact of novel Poly(ionic liquid) on cellulose acetate-based AEMs for acid recovery through DD application. In this study, interconnected nanochannel AEMs with high acid permeability are engineered using a straightforward blending technique. Poly(3-butyl-1-vinylimidazolium bromide-co-methyl methacrylate-co-styrene) (poly([BVIM]-[Br]–co–MMA-co-Styrene, PIL) is blended with cellulose acetate to achieve ionic crosslinking, resulting in a mechanically stable membrane. The dosage of PIL within the membrane matrix plays a vital role in determining the prepared membranes' physicochemical properties and ion exchange capabilities, which exhibit excellent thermal stability. Remarkably, the optimal AEM (7.5 % PILM) exhibits a high acid dialysis coefficient (U H +) of 1.05 m/h and a separation factor (S) of 802, outperforming previously reported state-of-the-art AEMs and commercial membranes. These findings indicate that the prepared AEMs are highly effective for acid recovery through DD. Notably, our work stands out by introducing new AEMs with superior acid dialysis performance and selectivity. [Display omitted] • Cellulose acetate-poly(ionic liquid) based ionic crosslinked membranes were fabricated. • A highly ion-conductive channel is obtained from a simple polymer blending method. • The optimal 7.5 % PILM membrane exhibits an excellent U H + of 1.05 m/h and a high separation factor of 802. [ABSTRACT FROM AUTHOR]

Sulfonated poly(ether ether ketone) (SPEEK) is widely explored as the proton exchange membrane (PEM). However, it is difficult for it to have both good proton conductivity and vanadium resistance. Herein, the ionic-covalent organic nanosheets (TpTG Cl) were fabricated and added to the SPEEK matrix. The nitrogen-rich and positive charge porous structure of TpTG Cl nanosheets endowed the composite membrane with the ability to transfer H+ and block Vn + effectively. When the TpTG Cl weight proportion was 3 %, the ion selectivity of the SP/TpTG-3 is as high as 103.3 × 103 S min cm−3. As expected, the SP/TpTG-3 exhibits outstanding energy efficiency (87.0%–77.4 % at 60–180 mA cm−2) and long-cycle stability. The results suggested that the ionic-covalent organic nanosheets afforded opportunities to prepare high performance PEM. [Display omitted] • TpTG Cl nanosheets are introduced into SPEEK to prepare SP/TpTG composite membranes. • Proton-selective conduction channels are formed in the SP/TpTG membrane. • TpTG Cl endows the composite membrane with the ability to transfer H+ and block Vn+. • A VRFB with SP/TpTG membrane exhibits high cell efficiencies and cyclic stability. [ABSTRACT FROM AUTHOR]

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) × 10−2 S/cm at 160 °C. Notably, the proton conductivity can retain 1.53 × 10−2 S/cm at 80 °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/cm2 at 100 °C and 0.96 V, 369.9 mW/cm2 at 120 °C. [Display omitted] • Carbon dots are assembled with metal organic framework. • Successive proton conduction channels are derived from carbon dots@metal organic framework. • Single fuel cell exhibits the maximum power density of 369.9 mW/cm2 at 120 °C. [ABSTRACT FROM AUTHOR]

Pseudo-nanophase separation, enabled by noncovalently grafted sidechains, offers a promising approach for constructing high-performance membranes, featuring rapid ion transport, robust chemical stability, and simplified manufacturing. However, striking a balance between ionic conductivity and mechanical/chemical stability proves challenging since excessive hydrophilic grafting leads to overswelling and compromised integrity of the membranes, rendering them unsuitable for demanding applications like vanadium redox flow batteries (VRFBs). In this study, we describe a new approach for achieving high-performance VRFB membranes via employing polymer as supramolecular sidechains, rather than small molecules. This strategy achieves remarkable pseudo-nanophase separation while minimizing the utilization of functional (hydrophilic) sites. As a result, the resulting membranes exhibit exceptional robustness and proton conductivity, with an extraordinarily low area resistance of merely 0.11 Ω cm2, thus circumventing the prevailing trade-off between ionic conductivity and mechanical/chemical stability. Ultimately, VRFBs integrated with these membranes achieve energy efficiencies up to 80 % even at high current densities of 240 mA cm−2, accompanied by a remarkably low capacity decay rate of 0.064 % per cycle during long-cycle tests. This work not only achieves ultra-high conductivity with minimal functional groups, but also advances pseudo-nanophase separation strategies and provides valuable insights into optimized utilization of limited functional groups in membrane design. [Display omitted] • Polymers are proposed as supramolecular sidechains. • Underlying interaction mechanism is elucidated by experimental and simulation study. • A minimal number of hydrophilic sites enable noteworthy pseudo-nanophase separation. • Prevailing conductivity-mechanical/chemical stability trade-off is circumvented. • A VRFB with high efficiencies and slow capacity decay of 0.064 %/cycle is attained. [ABSTRACT FROM AUTHOR]

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes for high-temperature proton exchange membranes (HT-PEMs) exhibit low proton conductivity under low phosphoric acid loading and poor mechanical properties under high phosphoric acid loading. In order to overcome these disadvantages, a novel kind of porous aromatic framework framed with imidazole and triazine groups (PAF-227) was designed and synthesized, phosphoric acid (PA) was incorporated into PAF-227 by utilizing vacuum-assisted infusion to yield the product PAF-227-PA. Subsequently, this dopant was combined with polybenzimidazole (OPBI) to create the PAF-227-PA/OPBI composite high-temperature proton exchange membranes (HT-PEMs). The PAF-227-PA/OPBI exhibited high proton conductivity (0.24 S cm−1) at 200 °C, as well as a favorable mechanical property (6.73 MPa) and a high PA absorption rate (250.2 %), and the peak power density of the fabricated fuel cells was significantly increased to 678.21 mW cm−2 at 200 °C with the Pt loading of 0.3 mg cm−2. The basic sites of PAF-227 framed with rigid imidazole and triazine groups can anchoring the PA to achieve a high PA retention rate through the acid-basic interaction with PA, and provide sufficient proton conduction sites by forming hydrogen bonds with PA, and synergized with OPBI membranes to form a multiple hydrogen bond and proton transfer network for enhanced mechanical properties and dimensional thermal stability. Thus, this work provided a novel approach to the preparation of HT-PEMs, which exhibited excellent overall performance for HT-PEMs fuel cells. [Display omitted] • PAF-227-PA with imidazole and triazine groups was designed and synthezed. • 10 % PAF-227-PA/OPBI exhibited a peak power density of 678.21 mW cm−2. • 10 % PAF-227-PA/OPBI showed higher proton conductivity (0.24 S cm−1) than OPBI. • A multiple hydrogen bond and proton transfer network was formed. [ABSTRACT FROM AUTHOR]

Eliminating hydrogen peroxide and free radicals from electrochemical reactions is crucial for mitigating chemical degradation and improving the durability of proton exchange membranes (PEMs). Herein, we prepare a metal–organic framework containing manganese and cerium ions that possesses oxygen vacancy defects and amino functional groups. The prepared Ce 4 MnBDC-NH 2 acts as a catalyst for H 2 O 2 decomposition and as a free radical scavenger, and it is incorporated into a perfluorosulfonic acid (PFSA) ionomer matrix. Featuring large pore volume, high porosity, and abundant amino groups, the Ce 4 MnBDC-NH 2 is locked in a PEM. The obtained Ce 4 Mn-NH 2 BDC@PFSA composite membrane exhibits high dimensional stability, excellent proton conductivity and low high-frequency impedance, yielding a proton conductivity of up to 137 mS cm–1 and superior water electrolysis performance of up to 1.83 V at 3.0 A cm–2. Moreover, the obtained Ce 4 Mn-NH 2 BDC@PFSA membrane experiences lower weight loss during the Fenton reaction, a low fluoride-ion release rate, and excellent stability in high current density durability testing: its decay rate is only 5.2 μV h–1, which is lower than that of CeO 2 @PFSA and Nafion 117 membranes. This work provides a promising method to prepare efficient free radical scavengers for steady-state PEM water electrolysis. The prepared Ce 4 MnCBD-NH 2 acts as a catalyst for hydrogen peroxide decomposition and as a free radical scavenger, and it is incorporated into a perfluorosulfonic acid (PFSA) ionomer matrix. The obtained Ce 4 Mn-NH 2 CBD@PFSA membrane experiences a lower voltage degradation rate and excellent stability in high current density durability testing. [Display omitted] • The Ce 4 Mn-NH 2 BDC acts as a catalyst for H 2 O 2 decomposition and free radical scavenger was prepared. • The Ce 4 Mn-NH 2 BDC@PFSA membrane exhibits high proton conductivity and electrolysis performance. • The MEA based on Ce 4 Mn-NH 2 BDC@PFSA exhibit superior durability and low voltage decay rate. • The H 2 crossover in Ce 4 Mn-NH 2 BDC@PFSA membrane was obviously decreased. [ABSTRACT FROM AUTHOR]

Designing high temperature proton exchange membranes (HTPEMs) with high H+ conductivity and long durability has been challenging. Here, a comb-shaped polybenzimidazoles (CbPBI) and crosslinkable polyoxy (benzenesulfonic acid) phazenes (PBSP) proton conductors are prepared, then they are used to fabricate a series of PBSP-CbPBI membranes with good comprehensive performances. CbPBI provides high flexibility and large free volume, which facilitates the construction of proton transport channels. And PBSP is the bifunctional proton conductor and crosslinker that introduces abundant sulfonic acid groups while retaining the crosslinkable property. By strongly chemical binding with CbPBI, the basicity of the imidazole ring is enhanced, avoiding the leaching of PBSP, thus enabling the overall crosslinked membrane to exhibit a durable intrinsic proton conductivity. Benefiting from the construction of the dual crosslinked network (covalent and ionic crosslinking), the oxidative stability, dimensional stability, and fuel-blocking properties of the PBSP-CbPBI membranes perform well. The proton conductivity of PBSP(50)-CbPBI membrane reaches 0.163, 0.084, 0.057, and 0.043 S/cm, respectively, at 180 °C and different relative humidity (100 % RH, 50 % RH, 30 % RH, and 0 RH). Enduring hot-washing for 96 h, the less decay of membrane in conductivity and weight demonstrates good durability. The design strategy such as the construction of monolithic crosslinked macromolecular structures in PBSP-CbPBI membranes shows wide application prospects in HTPEMs. Benefiting from the large free volume and high flexibility offered by the CbPBI, the three-dimensional macromolecular network was easily fabricated by the covalent crosslinking between CbPBI and PBSP, which ensures the high proton conductivity and long-term durability at high temperature and wide RH. [Display omitted] • Comb-shaped polybenzimidazole (CbPBI) based on polyphosphazene has large free volume. • Polyphosphazene-based PBSP is crosslinkable and rich in sulfonic acid groups. • Three-dimensional structures is fabricated by covalent and ionic crosslinking. • The good δ and durability of PBSP-CbPBI show potential applications in HTPEMs. [ABSTRACT FROM AUTHOR]

The Proton exchange membrane (PEM) is a crucial component in the membrane electrode assembly (MEA), playing a vital role in providing a channel for water transport and acting as a bridge for proton conduction. However, during the long-term operation of fuel cells, PEM is susceptible to attack from metal ions such as Cr3+ originating from the corrosion of metallic bipolar plates, leading to changes in its transport properties. Here, we report on the impact of Cr3+ on the microstructure and mechanical properties of PEM and then correlate it with changes in water uptake and proton conductivity, studying the effect of Cr3+ contamination on fuel cell performance and durability. The study reveals that Cr3+ forms a dense cross-linking structure with sulfonic acid groups inside the ionomer, resulting in an increase in storage modulus due to the larger ion radius and higher valence state, leading to a decrease in water uptake and proton conductivity. The membrane transport properties are primarily dependent on its water content. It is observed that Cr3+ contamination reduced the fuel cell voltage and maximum power density by 47.6 % and 57.1 %, respectively, with a voltage attenuation rate up to 2.9 mV/h, nearly 14 times that of the uncontaminated condition (0.21 mV/h). These findings provide valuable insights for developing high-transmission PEMs and aid in predicting the degradation and lifespan of fuel cells under actual operating conditions. [Display omitted] • The proton transport mechanism was changed. • The flexible hydrophilic network was disrupted. • The internal nanostructure of the ionomer was destroyed. • Fuel cell durability was reduced, and premature failure. [ABSTRACT FROM AUTHOR]

Ionic two-dimensional polymer (2DP) nanosheets with unique merits are attractive candidates for next-generation proton exchange membranes (PEMs), but the fabrication of large-area 2DP nanosheet-based PEMs is still awaiting success. Here, we report a flexible and intrinsically proton-conductive polyelectrolyte (Poly(sodium 4-styrenesulfonate), PSS) assisted assembling method to fabricate large-area PEMs (∼400 cm2) using sulfonated 2DP nanosheets as building blocks. Specifically, the optimized membrane achieves a superior proton conductivity of 802 mS cm−1 (70 °C, 95 % relative humidity), owing to the construction of low-energy barrier proton conduction pathways consisted of high density of sulfonic acid groups provided by PSS and sulfonated 2DP nanosheets. Moreover, PEMs with enhanced properties can also be accomplished by introducing different polyelectrolyte, indicating the good versatility of this powerful platform method. This work opens opportunities in large-scale fabrication of 2DP nanosheet membranes and paves a way for fabricating other 2D material-based membranes for diverse applications. [Display omitted] • Large-area 2DP nanosheets-based membrane was prepared assisted by polyelectrolyte. • The resulting membranes exhibit ultrafast proton conductivity. • Electrostatic interactions endowed by polyelectrolyte enhance membrane properties. [ABSTRACT FROM AUTHOR]

Amphoteric ion-exchange membrane (AIEM) offers improved overall conductivity and proton selectivity over singly charged IEMs due to the synergistic dual-ion transference and Donnan exclusion, respectively. Herein, a sulfanilic acid (SA) grafted sulfonated poly (ether ether ketone) (S-PEEK) bearing amphoteric side-chain with sulfonate (-SO 3 -) and weak ammonium (-NH 2 +-) type ion-exchangers is designed for vanadium redox flow battery applications (VRFB). A series of SPSA-x AIEMs were prepared by tuning weight the ratio of SA grafting in S-PEEK. The physicochemical and electrochemical properties of SPSA AIEMs were thoroughly analyzed using state-of-water, ion exchange capacity and impedance spectroscopy. As evidenced by vanadium permeability analysis, SPSA AIEMs exhibit ∼250 % greater proton selectivity and ∼87 % lower vanadium ion permeability over S-PEEK at 0.6 wt ratio of SA grafting. In VRFB cell, the modified membrane (SPSA-0.60) exhibits remarkable performance demonstrating high coulombic, voltage and energy efficiencies of 96 %, 87 % and 83 % at 100 mA cm−2, respectively and outstanding durability for long cycling without compromising the efficiencies. Moreover, polarization studies evidenced peak power densities in order; SPSA-0.60 (471 mW cm−2) > Nafion-117 (448 mW cm−2) > S-PEEK (348 mW cm−2). Consequently, ∼35 % performance improvements in peak power density is achieved over S-PEEK membrane. Thus, the strategic side-chain modified amphoteric PEEK with rigid aryl extenders imparts performance increments in VRFB devices. [Display omitted] • Sulfanilic acid grafted PEEK membrane demonstrates excellent durability and improved performance in VRFB. • SPSA-AIEMs show 87 % lower vanadium cross-over at 0.6 wt ratio sulfanilic acid grafting. • SPSA-0.60 shows highest peak power density of 471 mW cm⁻2, surpassing both Nafion-117 and S-PEEK. • SPSA-0.60 exhibits 2.5 times proton selectivity compared to S-PEEK. [ABSTRACT FROM AUTHOR]

The efficiency of electrochemical storage devices, such as flow batteries, depends on the rapid and selective ion-transport capability of ion-conducting membranes. However, designing membranes with high selectivity and low resistance remains challenging. In this study, we propose a strategy that utilizes graded lattice differences to selectively shear the lattice-defective inner core form a hollow MIL-101 (HMIL-101) with ultralow-resistance reservoir transport channels and lattice-perfect ion-sieving outer shell. An approximately 1/8th-volume-ratio cavity can reduce proton transfer resistance by 86 %, and the HMIL-101 proton conductivity improves by roughly an order of magnitude (2.9 × 10−3 vs. 4.0 × 10−4 S/cm). Further membrane separation tests show precise and rapid selective ion transfer. The proton conductivity increased by 100 %, and the ion conductivity-selectivity increased 5.2 times, reaching 2.6 × 107 S cm/min3. Additionally, a 7 % enhancement in voltage efficiency at a high current density (120 mA/cm2) in aqueous organic redox flow batteries further underscores the superiority of this high-selectivity and low-resistance metal-organic framework ion-conducting membrane. Our strategy offers a new direction for designing high-performance ion transport channels within membranes. The MIL-101 graded lattice difference allowed a one-step selective shearing of the lattice defective inner core, forming hollow MIL-101 (HMIL-101) with ultralow-resistance transport channels and lattice-perfect ion-sieving outer shell. [Display omitted] • MIL-101 lattice coordination number (inner: ∼5.1; outer: ∼5.9) is analyzed. • Graded lattice difference selectively shears the MOF lattice-defective inner core. • 1/8th-volume-ratio cavity reduce the proton transfer resistance by 86 %. • In AORFB, the membranes perform better efficiency and capacity after 200 cycles. [ABSTRACT FROM AUTHOR]

Sulfonated polyimide (SPI) is a potential material for proton exchange membranes (PEMs) under some harsh conditions for its good mechanical properties and excellent thermal stability. However, the complicated preparation of monomers required for SPI and limited proton conductivity restrict its practical application. In this work, we report the significant improvements on proton conductivity of SPI membrane, by directly doping nano carbon sulfonic acid (NCSA) in casting process. The SPI are synthesized using commercial monomers and the NCSA is prepared by chemically bonding benzenesulfonic acid groups to nano carbon particles (NCPs). The proton conductivity of the composite membrane reaches ∼140 mS/cm, 2.3 times higher than the base SPI membrane and ∼50 % higher than the commercial PFSA membrane at same conditions. Atomic force microscope (AFM) reveals that the "proton pool" structure around NCSA is the main reason for the improvement of proton conductivity of SPI composite membrane. A hydrogen fuel cell with the membrane electrode assembly (MEA) using the composite membrane achieves a power density of 1.58 W/cm2 at ambient pressure with platinum loading as low as 0.1 mg/cm2 at anode. We envision the facile method of doping NCSA and reinforcement to SPI composite membrane can promote its scale applications. [Display omitted] • High-performance composite sulfonated polyimide prepared by nano carbon sulfonated acid doping. • Doped composite membrane promotes proton conductivity to 2–3 times and 50 % higher than Nafion-117. • Proton pool induced by the dope is responsible for proton conductivity increase. • A hydrogen fuel cell using the composite membrane reaches 1600 mW/cm2 at 0.1 mgPt at anode. [ABSTRACT FROM AUTHOR]

It is a technical challenge to balance the proton conductivity and stability of proton exchange membranes (PEMs) due to the restriction of this trade-off relationship. To solve this issue, a novel sandwich structured PEM is fabricated, consisting of stable polybenzimidazole (PBI) layers on both sides of the highly hydrophilic sulfonated poly (aryl ether sulfone) (SPAES) layer in this work. Phosphotungstic acid (HPW) with strong intrinsic proton conductivity is chosen to add to the SPAES layer to further enhance the proton conductivity of the sandwich membranes. The introduction of high-stability PBI and the acid-base interaction between –NH–/-NH = groups present on PBI and the –SO 3 H groups on SPAES foster a crosslink-like network structure, which makes the sandwich membrane have superior thermal, size and mechanical stability, robust oxidative resistance, together with high HPW retention ability. By optimizing the doping amount of HPW and designing PBI with richer hydrogen bonding networks and stronger electron-withdrawing groups, higher through-plane proton conductivity has achieved. The SPAES+30%HPW/IPBI sandwich membrane particularly displays the through-plane proton conductivity of 162.1 mS/cm (90 °C), fuel cell output of 608.9 mW/cm2 and voltage loss of 0.30 mV/h (80 °C), both superior to single-layer SPAES membrane. This indicates that the strategy of sandwich membranes provides a new research idea for designing stable and high proton conductivity PEMs. [Display omitted] • The sandwich-structure SPAES + HPW/PBI composite membrane was proposed. • The SPAES + HPW/PBI membrane can simultaneously achieve high proton conductivity and stability. • The SPAES + HPW/PBI membrane had a high HPW retention capacity. • PBI polymers that can form richer hydrogen bonding networks had better properties. [ABSTRACT FROM AUTHOR]

Mixed matrix proton exchange membrane is promising for fuel cell application, but maximizing nanofiller loading to enhance performance is significant challenge. This study developed a one-step electrostatic spraying strategy to prepare ultra-high Prussian blue loading (up to 66.7 wt%) in sulfonated poly (ether ketone) matrix (PB@SPEEK). By coupling the electrostatic spraying and in situ solvent evaporation densification, SPEEK fills the voids between PB nanoparticles, forming a bicontinuous microstructure in the membrane. The ultra-high PB content of 66.7 wt% enable a fully utilization of its intrinsic properties, resulting in extremely low swelling ratio of 3.4 % at 80 °C, excellent flexibility of freely folding, and nearly 100 % mass retention after 12-h immersion in Fenton reagent at 60 °C. In single-cell tests, the PB@SPEEK mixed matrix membrane shows stable internal resistance due to easily water hydration, therefore achieving excellent low-temperature peak power (1973.9 mW/cm2 at 40 °C and 2078.0 mW/cm2 at 60 °C). The strategy developed in this study enables the one-step preparation of large-area, ultra-thin and ultra-high capacity of inorganic nanofiller mixed matrix proton exchange membranes for high-performance fuel cell. [Display omitted] • A large-area flexible mixed matrix proton exchange membrane with ultra-high nano-filler content was prepared in one step. • Maximizing nanofiller intrinsic properties to overcome the trade-off between proton conductivity and membrane swelling. • Excessive dependence on temperature and humidity was minimized to enable efficient operation at low temperatures. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have attracted great interest for the development of proton exchange membranes (PEMs) in the field of hydrogen fuel cells. However, the Grotthuss mechanism of proton transfer fails to discriminate the preferential pathways on the complicated hydrogen-bond network, thus limiting cell performance. Herein, a heterocharged COF lamellar membrane with cross-layer alternating paired charge distribution was fabricated by alternately assembling the positively charged TpEB and negatively charged TpPa-SO 3 H nanosheets. We demonstrated that the TpEB nanosheet drives the proton to directional transfer along the hydrogen-bond network on the sulfonic acid periphery of TpPa-SO 3 H by significantly reducing ineffective motions in branched hydrogen-bond network for both through-plane and in-plane directions. Meanwhile, it provides a low absorption energy for proton transfer from the sulfonic acid shell. This assembly effect occurs within the three nanosheet layers during each alternate film formation (A 3 B 3) and contributes to the long-term stability of the proton conductivity for TpEB@TpPa-SO 3 H. Notably, it achieves a maximum power density of 223 mW cm−2 at 60 °C and 100 % RH, which is superior to those of 83 mW cm−2 and 22 mW cm−2 for the homocharged TpPa-SO 3 H and TpEB membranes, respectively. This work provides new insights into the design of high-conductivity PEMs from engineered COF membranes. [Display omitted] • The strategy of cross-layer alternating paired charge distribution was proposed. • Oppositely charged COF nanosheets were alternately assembled to form COF membranes. • Directional proton transfer was realized by streamlining the hydrogen-bond network. • Heterocharged membrane had a low adsorption energy for proton transfer. • This strategy increased cell power density several-fold over homocharged membranes. [ABSTRACT FROM AUTHOR]

Proton exchange membranes (PEMs) are essential components in energy storage and conversion devices, such as fuel cells and electrolyzers. In this study, we developed a series of non-fluorinated PEMs from poly (terphenyl fluorenyl isatin) with fluorene-pendent disulfonate groups. These polymers feature a microblock structure composed of hydrophobic blocks, hydrophilic blocks, and alternating blocks, arising from the differences in reactivity, concentration, and solubility between the hydrophobic p-terphenyl and hydrophilic disulfonated fluorene monomers. As a result, the sulfonic acid groups are unevenly distributed along the polymer chains, forming densely charged regions (IEC = 3.52 meq/g) with large ion clusters and lightly charged regions (IEC = 2.16 meq/g) with small ion clusters. This microstructure, combined with the degree of sulfonation, significantly influences the overall properties of the membranes, including robust mechanical strength (47.1–63.2 MPa), high thermal stability (up to 270 °C), low swelling ratio (18–25 % at 80 °C), and high proton conductivity (136–169 mS/cm in deionized water at 80 °C). The PFLSH60 membrane demonstrated comparable fuel cell performance to Nafion 212. Its hydrogen crossover current density was more than two times lower (0.86 mA/cm2 for PFLSH60 compared to 1.83 mA/cm2 for Nafion 212) under testing conditions of 80 °C and 100 % RH. This significantly reduced crossover improves fuel utilization in fuel cell stacks. This work offers valuable insights into the design of robust, high-performance PEMs by systematically analyzing the relationships between membrane structure, properties, and performance. [Display omitted] • Non-PFSA PEMs and ionomers have been developed, showing performance comparable to that of Nafion 212 membranes. • These polymers feature a microblock structure, consisting of densely sulfonated, lightly sulfonated, and non-sulfonated blocks. • The densely sulfonated blocks enhance proton conductivity but reduce oxidative stability. • The distribution of sulfonic acid groups along the polymer chains is controllable by the synthesis conditions. • The amide groups offer potential for cross-linking during fabrication of membrane electrode assemblies (MEAs). [ABSTRACT FROM AUTHOR]

Achieving the right balance between electrical conductivity and long-term reliability in high-temperature proton exchange membrane (HT-PEM) technologies contributes to sustainable energy recycling. This study involves a groundbreaking effort to create amphiphilic polybenzimidazoles by incorporating 2-isocyanatopyridine into hydroxy-polybenzimidazole (OHPBI). A high hydrogen-bond density network is constructed through two-by-two interactions between the hydroxyl group, the imidazole molecule and quaternary ammonium group. Quaternary ammonium polymeric ionic liquid is introduced to maintain high phosphoric acid (PA) doping and PA retention. The PA retention of the amphiphilic polybenzimidazole membrane is 87.5 % after 240 h at 160 °C/0 % RH. Furthermore, the peak power density of the amphiphilic polybenzimidazole membrane reach 837.8 mW cm−2 at 180 °C and the voltage decay rate is 0.23 mV h−1 after long-term operation. More specifically, the amphiphilic polybenzimidazole membranes show a conductivity of 138.9 mS cm−1 at 180 °C. This indicates that the amphiphilic polybenzimidazole membrane has both high power output and long-term stability. This work introduces an innovative method to improve the efficiency of PBI-based HT-PEM. [Display omitted] • Synthesis of amphiphilic polybenzimidazole by introducing pyridine group at OHPBI. • OHPBI-PIL-P20 has a high PA retention of 87.5 %. • The proton conductivity of OHPBI-PIL-P20 membrane reaches 138.9 mS cm−1 at 180 °C. • OHPBI-PIL-P20 has a peak power density of 837.8 mW cm−2 at 180 °C. • The voltage decay rate of the OHPBI-PIL-P20 membrane electrode is 0.23 mV h−1. [ABSTRACT FROM AUTHOR]

We propose a novel strategy to develop sulfonated poly(arylene ether sulfone) (SPAES) composite membranes that can simultaneously improve the physicochemical stability and proton conductivity of hydrocarbon-based membranes for PEMFC applications. This strategy involves the use of a sulfonated poly(arylene thioether sulfone)-grafted 2D crown ether framework coordinated with cerium3+ ions (SATS–C 2 O–Ce) as a promising filler material. SATS-C 2 O, a highly sulfonated polymer-grafted 2D framework containing crown ether holes in its skeletal structure, was prepared via self-condensation using halogenated phloroglucinol as a multifunctional building unit to form C 2 O, followed by condensation using SATS to graft the sulfonated polymer onto its edge. Ce3+ ions were directly coordinated within the crown ether holes of SATS-C 2 O via a simple doping process using aqueous Ce solution. The SPAES composite membranes containing SATS–C 2 O–Ce (SPAES/SATS–C 2 O–Ce) exhibited exceptional dimensional stability and mechanical toughness. The remarkable chemical stability of SPAES/SATS–C 2 O–Ce compared to that of pristine SPAES and SPAES/Ce (containing the same amount of Ce3+ ions but without SATS-C 2 O) was attributed to the well-dispersed state of Ce3+ ions within the SPAES matrix. Furthermore, the enhanced proton conductivity of SPAES/SATS–C 2 O–Ce surpassed those of pristine SPAES, SPAES/C 2 O, and SPAES/Ce by the formation of additional proton-conducting channels provided by the sulfonic acid groups of SATS–C 2 O–Ce, along with the improved water uptake capability of SPAES. [Display omitted] • 2D crown ether framework (C 2 O) was synthesized using tri-bromophloroglucinol. • Sulfonated polymer grafted C 2 O containing Ce ions (SATS–C 2 O–Ce) was developed. • Hydrocarbon-based composite membranes with SATS–C 2 O–Ce were prepared. • Excellent physicochemical stability and proton conductivity of composite membranes. • Outstanding cell performances of MEAs prepared with composite membranes. [ABSTRACT FROM AUTHOR]

Proton exchange membranes (PEMs) with high proton conductivity, mechanical stability, and methanol barrier capability is urgently needed for direct methanol fuel cell (DMFCs). In response, a series of highly sulfonated polybenzimidazoles (SPBI) were synthesized, followed by the creation of a unique in-situ ionic self-crosslinking mechanism via acid-base pair interactions between –SO 3 - and protonated N within the imidazolium rings of SPBI in an acidic milieu. The in-situ ionic self-crosslinking not only significantly enhances the mechanical stability of the prepared membrane, but also constructs a microstructure with a free volume radius smaller than the molecular dimensions of methanol, subsequently imparting unparalleled resistance to methanol permeation. After being reduced to an ultrathin thickness of 15 μm, the optimal SPBI-SO 3 H-200 % membrane obtains remarkable high specific proton conductivity of 33.48 S cm−2. Furthermore, the assembled DMFC demonstrates an exceptionally low methanol crossover current density of 188.25 mA/cm2 alongside high power density of 109.92 mW cm−2 within 2 M methanol fuel, significantly outperforming the methanol crossover current density of 386.06 mA/cm2 and power density of 87.13 mW cm−2 achieved by a single cell assembled with Nafion 115 membrane. [Display omitted] • Methanol tolerable SPBI was synthesized via in-situ crosslinking strategy. • Optimized ultrathin PEM exhibits high specific proton conductivity of 33.48 S cm−2. • The assembled DMFC shows a low methanol crossover current density of 188.25 mA/cm2. • Achieving a maximum power density of 109.92 mW cm−2 within 2 M methanol fuel. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) have emerged as a key research area due to their ability to convert various gaseous energy sources (such as hydrogen and methanol) into electrical energy with high efficiency and zero pollution. The design of the proton exchange membrane (PEM), which is the site for proton transfer, is critical. To explore the influence of characteristic functional groups on proton transfer mechanism in biomimetic proton exchange membranes, the crown ether structure was introduced into polymer backbone chains to mimic biological ion channels. The motion behaviors of proton were qualitatively characterized through molecular dynamics simulation. It was found that protons are strongest complexed in the best matching 18CO6-PEM case based on the analysis of RDF, residence time, interaction energy, and number of hydrogen bonds. The characteristic groups of biological proton channels with smaller or larger pores can help protons detach from the complexation under the action of an electric field. The proton transfer in crown-ether biomimetic proton exchange membranes is not just a single mechanism, but a compromise between two mechanisms in parallel. This work provides a new perspective on designing proton conduction membranes by embedding large ring motifs with intrinsic cavities and the key parameters required for establishing the proton transfer model. [Display omitted] • Crown ether-based PEMs exhibit a compromise proton transfer mechanism. • The introduction of crown ether groups enhances electrostatic interactions and selective proton conductivity. • Both water channel and electrostatic interaction crucially influence proton mobility and diffusion. • Insights from crown ether biomimetic PEMs contribute to the design of advanced fuel cells. [ABSTRACT FROM AUTHOR]

Sulfonated covalent organic frameworks (SCOFs) facilitate rapid proton conduction through densely ordered sulfonic acid groups, however, the brittleness of COFs self-supporting membranes often makes potential difficulty in fuel cell assembly and limits their power density. Herein, a highly flexible SCOF proton exchange membrane is developed through in-situ growth of a continuous BD(SO 3 H) 2 –COF microphase within porous PTFE networks. The strong hydrogen bonding between PTFE and BD(SO 3 H) 2 –COF contributes to the defect-free morphology of the BD(SO 3 H) 2 /PTFE membrane. The reinforce of PTFE network makes the membrane extremely high flexibility, achieving an elongation at break of 124.4 % even with a remarkably high SCOF mass proportion of 90 wt% (BD(SO 3 H) 2 /PTFE-0.9). This allows the membrane to be folded repeatedly, even in dry state. The swelling ratio in water at 80 °C is effectively restricted to 8.6 %, even with a high ion exchange capacity of 3.6 mmol g−1 and a water uptake of 68.2 %. The densely ordered sulfonic acid groups in continuous BD(SO 3 H) 2 –COF microphase contribute to a high proton conductivity up to 249.2 mSꞏcm−1 at 80 °C, approximately 1.5 folds that of Nafion 212. As a result, the BD(SO 3 H) 2 /PTFE-0.9 membrane achieves a fuel cell power density of 1195.3 mWꞏcm−2 at 80 °C, along with a high open circuit voltage of 1.01 V, surpassing the-state-of-the-art COF-based proton exchange membranes. This work provides a novel strategy to fabricate COFs into flexible and size scalable membranes, enhancing the performance of fuel cells. [Display omitted] • SCOF continuous microphase grows in-situ in porous PTFE network as conductive highway. • PTFE reinforce makes SCOF membrane extremely flexible, folding freely in dry state. • High elongation and fuel cell power density surpass most reported COF-based membranes. [ABSTRACT FROM AUTHOR]

This study introduces an innovative approach to graft Polyvinylpyrrolidone (PVP) onto Polybenzimidazole (PBI) to synthesise Proton Exchange Membranes (PEMs) with high performance and durability. As a widely used hydrophilic polymer in industry, PVP can add numerous nitrogen-containing functional groups to the membrane to enhance its phosphoric acid (PA) binding ability. In this work, Polybenzimidazole- graft -polyvinylpyrrolidone (PVP- g -PBI) polymers with varying grafting degrees were synthesized and tested to investigate the impact of the grafting modification on the membrane's proton conductivity, thermal properties, and electrochemical performance. With the introduction of PVP side chains, the fuel cell showed enhanced PA uptake and substantial improvements in peak power density. Notably, PBI-g-PVP membranes with a grafting degree of 22.4 % achieved a peak power density enhancement up to 1312 mW cm⁻2 at 160 °C, a 59.6 % increase over pristine PBI membranes. Due to the increased PA binding sites in the membrane, the PBI-g-PVP PEMs exhibit better PA adsorption ability and long-term durability than pristine membranes. The accelerated stress test (AST) demonstrated that the PBI-g-PVP membranes maintain a peak power density of 1105 mW cm⁻2 after a 70-h test, equivalent to 183.9 % of the pristine PBI membrane. The improved fuel cell performance and durability of PBI-g-PVP PEMs underscore the potential of this grafting strategy. [Display omitted] • Amino-terminated polyvinylpyrrolidone was grafted onto the Polybenzimidazole. • The grafting provides the membrane with more phosphoric acid binding sites. • The obtained proton exchange membrane can absorb and retain more phosphoric acid. • Fuel cells with this membranes show improved performance and long time durability. [ABSTRACT FROM AUTHOR]

A series of sulfonated poly(ether ether ketone) (SPEEK) based composite membranes (SPEEK/SPVDF) has been fabricated by blending sulfonated polyvinylidene fluoride (SPVDF) with various contents from 1, 3, 5, to 10 wt% through the solution-casting technique. The incorporated SPVDF polymer contributes to the enhanced physicochemical properties of the SPEEK matrix, and the SPEEK/SPVDF-5 membrane gives maximum proton conductivity (33.7 mS cm−1) and highest ion selectivity (46.9 × 103 S min cm−3) against SPEEK and Nafion 212. Higher energy efficiency (85.2–74.6 %) and longer self-discharge time (84.5 h) at 100–200 mA cm−2 current density prove its balanced conductivity and permeability that ensures the membrane durability of SPEEK/SPVDF-5. Moreover, the charge capacity retention rate of 26.4 % at 150 mA cm−2 for 200 cycles and 81.2 % energy efficiency for 500 cycles elucidate the hydrophilic-hydrophobic microphase structure and hydrogen bond network help in enhancing the structure stability and cyclability of the SPEEK/SPVDF membrane. This provides an alternative to exploring highly conductive and selective proton exchange membranes for vanadium flow battery applications by manipulating the interconnected hydrophilic sulfonic ion clusters and hydrophilic-hydrophobic phase domains by incorporating the hydrophilic acidity groups onto hydrophobic polymers. [Display omitted] • Partially sulfonated PVDF contributes low vanadium ion permeation. • Hydrophilic-hydrophobic domains stabilize proton transportation. • Surrounded hydrophilic sulfonic ion clusters offer membrane stability. • SPPEK/SPVDF-5 gives 500-cycled durability and 81.2 % energy efficiency. [ABSTRACT FROM AUTHOR]

Traditional phosphoric acid (PA) doped polybenzimidazole (PBI) membranes encounter many issues when used in high-temperature proton exchange membrane fuel cell (HT-PEMFC), including the loss of PA within the membrane and limitations on conductivity. The mixed matrix membranes (MMMs) synergistically combine the advantages of pore fillers and polymer matrix, making them promising candidates for HT-PEMs. Interface compatibility is the main factor affecting the further development of MMMs. This research presented OPBI composite membranes filled with porous nanosheets, featuring average pore diameters of 2.83 nm, 3.38 nm, and 2.60 nm, respectively. The high aspect ratio and plentiful nitrogen components of the nanosheets increase the π-π and hydrogen bonding interactions with the polymer matrix, resulting in outstanding interface compatibility and mechanical properties of MMMs. The results of theoretical calculations indicate that there is a stronger interaction energy between the nanosheets and PA molecules, and the abundant pore structure within the nanosheets facilitates the absorption of PA molecules, leading to the formation of a continuous PA network. Consequently, MMMs exhibited enhanced proton conductivity, as well as improved PA absorption and retention. Furthermore, the effect of pore size distribution of nanofillers on the performance of MMMs were investigated. Membranes composed of nanosheets with large pore size showed a higher conductivity of 176.7 mS cm−1 at 200 °C, leading to excellent performance and stability in assembled H 2 /O 2 fuel cells. This work offers valuable insights into the design of MMMs and high-performance HT-PEMs. [Display omitted] • Porous nanosheets have high aspect ratio and rich nitrogen content. • Porous nanosheets have excellent interface compatibility with polymer matrices. • Mixed matrix membranes have higher PA absorption and retention compared to OPBI membrane. • Faster proton transport networks can be formed with the use of large pore size nanosheets. [ABSTRACT FROM AUTHOR]

Block copolymers show great promise as low-temperature proton exchange membranes (PEMs). However, their potential as high-temperature PEMs has been less explored. In this study, we synthesized a series of segmented block copolymers of polybenzimidazole (PBI), consisting of strongly acid-absorbing Py-PBI segments and fluorine-containing 6FPBI segments, which exhibited significant microphase-separated structures. To counteract the "plasticization effect" of phosphoric acid (PA) under high acid doping level (ADL), which can compromise the mechanical strength of PEMs, 3-(2,3-epoxypropyl) propyltrimethoxysilane (KH560) was introduced as a crosslinking agent to strike a balance between the ADL and the mechanical properties. The 5 % KH560–6F 0.72 Py 0.28 -PBI membrane, which features a molar ratio of 6FPBI to Py-PBI structural segments of 0.72:0.28, demonstrates the most obvious microphase separated structure, exhibiting high ADL (29.2) and proton conductivity (165.45 mS cm−1 at 180 °C). The membrane electrode assembly (MEA) employing the segmented block copolymer membrane achieved a peak power density of 936.9 mW cm−2 at 160 °C without humidification. This study highlights the significant enhancement of membrane performance achieved by constructing continuous microphase separated structures. [Display omitted] • Controllable microphase separation was achieved by using segmented block polybenzimidazole. • Segmented block cross-linked polybenzimidazole exhibits a high ADL and proton conductivity. • The membranes achieve a good balance between ADL and mechanical properties. • A remarkable power density of 936.9 mW cm−2 at 160 °C was obtained. [ABSTRACT FROM AUTHOR]

Phosphoric acid (PA) doped polybenzimidazole (PBI) high-temperature proton exchange membrane is favored because it can achieve faster proton transfer at 180 °C without additional humidification. However, the PA-PBI membrane is faced with slow PA proton conduction kinetics below 100 °C, and failing rapid start-up of fuel cells. Herein, carbon nanotubes functionalized with phosphate groups (P-CNT) and sulfonated poly [2,2'-(p -hydroxydibenzene)-5,5′-benzimidazole] (SOPBI) composite membranes are prepared as proton exchange membranes with wide temperature range (40–180 °C). Based on the regulation of monophosphate and bisphosphate groups on P-CNT, the bisphosphate group can strengthen the vehicular mechanism of proton transport by accelerating the formation and diffusion of H 3 O+ at low temperature/high humidity, and the Grotthuss mechanism of proton transport by constructing dense hydrogen bond network at high temperature/low humidity. The 2P-CNT(6 %)/SOPBI composite membrane shows excellent proton conductivity (131.8 mS cm−1 at 80 °C/90%RH, 170.5 mS cm−1 at 180 °C/0%RH) and peak power density (378 mW cm−2 at 80 °C/100 % RH, 531 mW cm−2 at 160 °C/0 % RH) under wide temperature conditions, surpassing SOPBI membrane and other composite membranes. Furthermore, the 2P-CNT(6 %)/SOPBI composite membrane exhibits high proton conduction and fuel cell stability at both 80 °C/100 % RH and 160 °C/0 % RH. [Display omitted] • 2P-CNT/SOPBI composite membranes exhibit excellent proton conductivity at 40–180 °C. • The diphosphate group on 2P-CNT promotes the formation and diffusion of H 3 O+ at 80 °C/90 % RH. • More hydrogen bonds between 2P-CNT and PA accelerate proton hopping at 160 °C/0 % RH. • Composite membranes exhibit high power density and stability as wide-temperature-range PEMs. [ABSTRACT FROM AUTHOR]

Design and fabrication of phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes with high proton conductivity, mechanical property and phosphoric acid retention stability has been a critical challenge. In this study, a sulfonated ionic covalent organic framework (SCOF) was in-situ synthesized in the polybenzimidazole matrix. The high-density sulfonic groups and ordered channel structure of SCOF rendered the as-prepared composite membrane high proton conductivity under low phosphoric acid doping level. Additionally, the introduction of SCOF helped to immobilize the phosphoric acid, thus effectively reducing its loss and improving the acid retention stability. The acid-base interaction formed between the sulfonic acid and imidazole groups act as ionic crosslinkers, which significantly enhanced the mechanical-dimensional stability of composite membranes. As a result, the PA-PBI/SCOF composite membrane exhibited a high proton conductivity up to 542.1 mS cm−1 at 80 °C, 100 % RH and 134.1 mS cm−1 at 30 °C, 50 % RH, as well as a high mechanical strength up to 64.0 MPa (PA uptake: 67.47 %). This in-situ synthesis strategy offers a promising new approach to fabricate covalent organic framework-based composite membranes for various applications. [Display omitted] • A sulfonated covalent organic framework (SCOF) was in-situ synthesized in polybenzimidazole matrix to prepare composite membranes. • The as-prepared composite membrane exhibited high mechanical strength, proton conductivity and phosphoric acid retention stability. • The composite membrane showed comparable performance in electrochemical hydrogen compression and proton exchange membrane fuel cell. [ABSTRACT FROM AUTHOR]

In this study, we pioneered the introduction of benzophenone (DPK) as a solid solvent into polyphenylene sulfide (PPS) melt-blown, which effectively reduced the PPS melt-blown processing temperature and significantly improved the coefficients of variation of PPS melt-blown nonwoven materials. X-Co-tri@SSNF proton exchange membranes with excellent performance were prepared by functionalized modification of PPS melt-blown fabric as a substrate. The structure and properties of X-Co-tri@SSNF proton exchange membranes were systematically characterized. The results demonstrate that the 1-Co-tri@SSNF PEM exhibited a high proton conductivity of 0.183 S cm−1 at 80 °C and high humidity, significantly higher than the commercial Nafion 117 (0.135 S cm−1). Due to the heat resistance of PPS itself and the continuous dense network structure substrate of PPS nonwoven fabrics as well as the high compatibility with the membrane casting liquid, the hybrid membrane interfaces were tightly connected, so it makes the hybrid membrane perform better in terms of mechanical stability (tensile strength of 36.7 MPa), methanol permeability (4.78 × 10−7 cm2 s−1), selectivity (16.32 × 104 S s cm−3), and thermal stability (thermal decomposition temperature of around 450 °C). In addition, the 1-Co-tri@SSNF membrane electrode module exhibited excellent single-cell performance with an open-circuit voltage of 629.91 V and a peak power density of 96.29 mW cm−2 (162.9 % higher than that of Nafion 117). Therefore, the composite PEM with PPS melt-blown fabric as the matrix has a more environmentally friendly process than the commercial Nafion 117 membrane, a theoretical guidance for advancing the large-scale production of low-cost PEM. [Display omitted] • A low energy consumption PPS melt-blown process was developed for the preparation of PEMs. • PEMs with PPS melt-blown fabric as substrate has excellent heat resistance and lower SR. • Composite membranes have much lower methanol permeability than Nafion 117. • The prepared membranes have excellent single-cell performance and durability. [ABSTRACT FROM AUTHOR]

The optimal operating temperature for contemporary perfluoro-sulfonic acid (PFSA)-based proton exchange membranes (PEMs) is identified to range from 60 to 80 °C. However, operating at temperatures exceeding this threshold could offer substantial advantages. Therefore, the development of PEMs that can maintain performance at elevated temperatures is imperative. This study introduces novel SUS composite proton exchange membranes with a three-layer architecture. These membranes feature a central UIO-66-NH 2 /Nafion composite layer (U), bordered by sulfonated carbon-nanotubes/Nafion composite layers (S) on both sides. The SUS PEMs demonstrate improved proton conductivity, long-term stability, fuel cell efficiency, and gas barrier properties. Notably, at the elevated temperature of 145 °C, attributable to enhanced water retention capabilities, these membranes exhibit significant proton conductivity, reaching 0.428 S cm−1. For fuel cell evaluations, the SUS PEMs exhibited optimal performance (0.940 W cm−2) at the elevated temperature of 115 °C. These improvements are attributed to the dense S layer, which regulates diffusion rates of both water and gas molecules, and the U layer, which serves as a water reservoir due to its high retention capacity. These conclusions have been validated through computational simulations and further supported by positron annihilation spectroscopy. [Display omitted] • Synthesized SUS composite PEMs with a novel three-layer architecture. • Central UIO-66-NH 2 /Nafion layer acts as a water reservoir. • Surrounding Su-CNTs/Nafion layers regulate diffusion rates of water and gas molecules. • The membranes demonstrated enhanced fuel cell performance. • Conclusions have been validated by computational simulations and PALS. [ABSTRACT FROM AUTHOR]

Polymer with fluorene-based units has garnered significant attention and has been shown an effective way to improve the performance of proton exchange membranes due to its inherent rigidity and multiple sulfonation sites. Nevertheless, fluorene-based sulfonated poly(ether ketone)s exhibited inadequate oxidative stability resulting from the heteroatoms in the main chain. Herein, a series of poly(phenyl ketone)s polymers (PPK-DSF- x) without heteroatoms in the main chain were constructed by Yamamoto coupling and hydrolysis reactions. Since robust poly(phenyl ketone) aromatic backbone ensured commendable chemical and dimensional stability, and sulfonated fluorene-based units promoted the formation of hydrophilic and hydrophobic microscopic phase separation, the PPK-DSF- x membranes exhibited superior stability and proton conductivity. Remarkably, PPK-DSF-45 showed excellent proton conductivity at 80 °C (137.5 mS cm−1). In addition, the oxidative stability of the PPK-DSF-45 membrane was also excellent, maintaining its integrity after immersion in Fenton's reagent for 270 min. Finally, we found that the PPK-DSF-45 membrane achieved a power density of 270 mW cm-2 in the fuel cell, surpassing Nafion 212 (245 mW cm⁻2). These results indicated the potential application of fluorene-based poly(phenyl ketone)s PEMs in PEMFCs. [Display omitted] • A novel synthesis strategy for high stable sulfonated aromatic polyelectrolyte. • The robust poly(phenyl ketone) backbone are formed in the main chain. • Well-defined microscopic morphology facilitates the proton transport. • PEMs exhibit superb dimensional, thermal, oxidative, and mechanical stability. [ABSTRACT FROM AUTHOR]

Amid technological advances, rising energy demand, and environmental concerns, countries endorse green energy solutions. Prominent among them is hydrogen production via clean water electrolysis, a key strategy for sustainable development. Herein, to address the limitations of expensive and potentially harmful Nafion membranes, we have developed a new graphene oxide (GO) series membranes (hydrophilic sulfonated GO (GO-SO 3 H) linked with monovalent alkali metal ions were synthesized to fabricate the membranes) to be used in water electrolysis for hydrogen production by introducing the iodide oxidation reaction (IOR) as an alternative to the traditional oxygen evolution reaction (OER). Various modifications by sulfuric acid, methanol, and different alkali metal hydroxides (LiOH, NaOH, KOH) result in membranes with distinct properties. Characterization techniques, including ATR-FTIR, SEM, AFM, XRD, water contact angle (WCA), and electrochemical impedance spectroscopy (EIS), validated the modifications, assessed membrane morphology, interlayer spacing, hydrophilicity, and electrical properties. Among the membranes, GO-SO 3 K stood out, exhibiting the highest proton conductivity (119.16 mS) and superior potassium ion permeability (20.382 cm/s). Importantly, all GO series membranes demonstrate excellent stability in the electrochemical system. The findings suggested that GO-SO 3 K holds promise as a potassium ion-conductive membrane for efficient and sustainable hydrogen production, offering a viable alternative to conventional Nafion membranes in water electrolysis applications. [Display omitted] • Hydrophilic GO-SO 3 H linked with alkali metal ions membranes were developed for proton conductivity. • GO-SO 3 K membrane stands out, exhibiting the highest proton conductivity (119.16 mS). • K+-permeability of the GO-SO 3 K membrane (20.382 cm/s) was 5 times higher than that of pure GO. • GO-SO 3 K: A promising K+-conductive membrane for electrochemical H 2 production systems. [ABSTRACT FROM AUTHOR]

Rationally constructing proton transport channel within high temperature proton exchange membranes (HT-PEMs) plays a critical role in lowering the mass transfer resistance and thus improving the performance of HT-PEM fuel cells (HT-PEMFCs). We herein designed a microphase-separated structure to promote proton transmitting by incorporating 1,4-Diazabicyclo[2.2.2]octane (DABCO) cationic polymer into tetramethyl poly(aryl ether ketone) (TMPAEK). The flexible and cationic segments afforded a polarity difference from TMPAEK, resulting in easier phosphoric acid adsorption. High proton conductivity of 135 mS cm−1 was obtained under anhydrous conditions at 150 °C. Besides, the hydrophilic domains that containing N-heterocycle could stabilize phosphoric acid through hydrogen bonding interactions, resulting in high phosphoric acid retention of ∼80 % after 288 h test. A Peak power density of 496 mW cm−2 was achieved in non-humidified H 2 /O 2 without back pressure at 140 °C, which was higher than that of m -PBI under the same conditions. This work not only paved a way to tailor the ion conductivity of membrane, but also provided a highly competitive membrane for HT-PEMFCs. [Display omitted] • A novel cationic polymer was developed to regulate microphase separation. • Conductivity of 135 mS cm−2 was recorded owing to microstructure advantages. • Hydrogen bonding interaction led to stable PA retention of ∼80 % for 288 h. [ABSTRACT FROM AUTHOR]

The well-ordered microstructure has been demonstrated to accelerate the proton conduction process through reducing proton conduction resistance. In this research, the proton exchange membranes (PEMs) with sandwich-like microstructure have been constructed based on Kevlar nanofibers and bifunctional nanofibers of chitosan (CS) with polyvinyl alcohol (PVA). The CS/PVA bifunctional nanofibers (CPNF) layer has been prepared with electrospinning process, which is stably adhered to the Kevlar nanofibers layer owing to compatible interfacial property. The fine structure stability without layer separation is achieved even with phosphoric acid (PA) molecules doping in the prepared PA doped composite membranes. The fibrous microstructure accelerats proton conduction through regulating proton conduction pathways. The objective of accelerating proton conduction at subzero temperature has been realized, reflecting in high and stable proton conductivities. For instance, the (Kevlar/CPNF/Kevlar)/PA membrane exhibits proton conductivities of 9.75 × 10−3 S/cm at −30 °C and 8.22 × 10−2 S/cm at 30 °C. Most importantly, the fine proton conductivity stability is identified by the results of the cycle test and long-term test. Specifically, the proton conductivities are respectively 8.62 × 10−3 S/cm at −30 °C and 8.07 × 10−2 S/cm at 30 °C after a five heating/cooling cycle process. The proton conductivities remain 2.97 × 10−2 S/cm at −25 °C and 7.19 × 10−2 S/cm at 30 °C after a 1032 h non-stop test. Additionally, the single proton exchange membrane fuel cell with the (Kevlar/CPNF/Kevlar)/PA membrane exhibits the peak power densities of 279.5 mW/cm2 at 100 °C and 352.7 mW/cm2 at 130 °C. [Display omitted] • Bifunctional nanofibers were used to construct proton exchange membranes. • Accelerating proton conduction at subzero temperature was achieved. • Conductivity reached 2.97 × 10−2 S/cm at −30 °C after a 1015 h non-stop test. [ABSTRACT FROM AUTHOR]

Proton conducting membranes that operate at temperatures above 100 °C are highly sought after for use in energy devices such as fuel cells owing to the high catalytic activity of electrodes induced by elevated temperature and no requirement for water management. In the present study, novel mesoporous silica membranes were prepared by a gel-casting process using commercial colloidal silica and subsequent sintering. These membranes served as the scaffold for phosphoric acid-based electrolytes. Well-interconnected mesopores with uniform pore sizes was effective for hosting phosphoric acid (PA), and the tunable pore sizes (5.9–32.0 nm) were achieved by tuning the sintering temperature from 500 to 725 °C. High porosity (about 50%) and high hydrophilicity of silica membranes are beneficial to reach high phosphoric acid loading by an impregnation process. The PA-loaded membrane sintered at 700 °C achieved a high protonic conductivity of 0.11 S cm−1 and a peak power density of 287.3 mW cm−2 in hydrogen fuel cells at 160 °C. The conductivity is 1 order of magnitude higher than that of the pressed meso-silica membranes and comparable to that of PA-mesoporous silica spheres. This study has demonstrated a new method to construct high-temperature protonic electrolyte membranes. [Display omitted] • Uniform mesoporous silica membranes were prepared by a gel-casting process. • Mesoporous silica membranes serve as scaffold for holding phosphoric acid. • Interconnected channels within electrolyte offer fast proton transport pathway. • Electrolyte membrane achieved a high proton conductivity of 0.11 S cm−1 at 160 °C. [ABSTRACT FROM AUTHOR]

We prepared sulfonated octaphenyl polyhedral silsesquioxane (SPOSS) with its structure intact by using sulfuric acid (H 2 SO 4) at 40 °C. We discussed the effects of sulfonation using either chlorosulfonic acid (ClSO 3 H) and H 2 SO 4 on SPOSS structure and its incorporation into crosslinked sulfonated polyphenylsulfone (CSPPSU) composite polymer electrolyte membranes (PEM). An in-depth structural characterization using 29Si NMR and FTIR spectroscopies, MALDI-TOF mass spectrometry, and TGA show that phenyl loss occurred in SPOSS prepared using ClSO 3 H, resulting in a low ion exchange capacity (IEC) of 1.7 meq/g and a sulfonation degree (DS) of 1.9. In contrast, the phenyl remained intact in the SPOSS prepared using H 2 SO 4. Well-dispersed 348-nm-SPOSS-H 2 SO 4 was found to have an IEC of 2.4 meq/g and DS of 3.1 The resultant hybrid PEM of CSPPSU/SPOSS using SPOSS-H 2 SO 4 had improved swelling, mechanical and chemical strength, and conductivity. 1 wt% SPOSS-H 2 SO 4 loading had the highest conductivity (13.7 mS/cm) at 120 °C with 40 % RH. This shows the importance of the SPOSS nanocomposite structure in dispersions in the SPPSU polymer matrix and its performance as PEM. We report on an improved direct sulfonation process at a milder condition but sulfonation yield was improved. [Display omitted] • Structure analysis of sulfonated OPOSS prepared by H 2 SO 4 and ClSO 3 H were performed. • OPOSS sulfonated by H 2 SO 4 had minimal structure damage compared to ClSO 3 H. • In-depth structural analyses were done using 29Si NMR, MALDI-TOF, FTIR and TGA. • The composite polymer electrolyte membrane was prepared with improved performance. • Increased proton conductivity and strength of 76 % and 24 %, reduced swelling by 11 %. [ABSTRACT FROM AUTHOR]

A comblike polymer (SPOS) with a main/side-chain bisulfonated structure has been synthesized with 1,3-propane sulfonate as the pendant chains and poly (ether ketone) (PEEK) as the reactant by the combined post-sulfonation and ring-opening grafting reaction. Taking sulfonated PEEK as a membrane matrix, the composite membranes (S/SPOS) are prepared by the solution-blending method with varied contents of bisulfonic SPOS polymer from 10 to 25 wt%. The S/SPOS composite membranes display superior conductivity owing to synergistic enhancement in the intermolecular chain interactions and the homogeneous strengthened transportation channels from main/side-chain bisulfonic acid interconnected networks. S/SPOS-15 shows better CE (96.5–98.5 %) and EE (84.7–69.9 %) than that of Nafion 212 (CE: 92.3–95.0 %, EE: 76.1–63.7 %) at 100–200 mA cm−2. Moreover, 600-cycled durability and 77.3 % EE at 150 mA cm−2, and 71.8 h self-discharge time demonstrate its improved reliable structure and cyclic stability. This provides a promising method to prepare high-performance and low-cost membranes with desirable conductivity by homogeneous structural regulation and molecular chain synergistic interactions. The S/SPOS composite membranes display superior proton conductivity owing to synergistic enhancement in the intermolecular chain interactions and the homogeneous strengthened transportation channels from main/side-chain bisulfonic acid interconnected networks. [Display omitted] • SPOS comblike polymer with main/side-chain bisulfonated structure. • Molecular structure affinity stabilizes homogeneous-strengthened channels. • Synergistic bisulfonic acid interconnected networks satisfy high conductivity. • S/SPOS-15 presents superior battery efficiency and long-term cycling stability. [ABSTRACT FROM AUTHOR]

In order to improve the proton conductivity and antioxidant stability of proton exchange membranes (PEMs) at wide relative humidity (RH), composite membranes cross-linked with tribranched polybenzimidazole (TaPBI) and poly(azido-1-propanesulfonic acid −2,2′- methylsulfonic acid −5,5′-bis-benzimidazole) polyphosphazenes (PSBI) (TaPBI-PSBI) are prepared. TaPBI, as a branched polybenzimidazole, exhibits a large free volume. The trifunctional proton conductor PSBI-Na incorporates abundant flexible acidic groups and basic sites to enhance proton conductivity, and cross-linking groups to increase its binding strength with PBI. By casting and cross-linking, the proton conductivity, mechanical properties, and oxidation resistance of the TaPBI-PSBI membranes are significantly improved. The generation of cross-linked structures in the membranes is demonstrated by FT-IR. SEM shows that the surface of composite membrane is smooth and free of through holes. The elements are uniformly distributed. The TEM shows microphase separation occurs in the TaPBI-PSBI membrane, facilitating the formation of the continuous proton channels. The proton conductivity of TaPBI-PSBI (40) composite membrane reaches 0.170, 0.081, 0.059, and 0.037 S cm−1 at 180 °C, 100%, 50%, 30%, and 0% RH, respectively. The composite membrane is demonstrated the outstanding stability with the small decrease of proton conductivity and mass after durability testing of 96 h. The composite membrane exhibits high comprehensive performances as HT-PEM. [Display omitted] • PSBI, a cross-linkable proton conductor, has basic sites and –SO 3 H groups. • Mobility of flexible chain-linked –SO 3 H groups in PSBI increases σ at low RH. • A rich network of hydrogen-bonded ionic bonds is formed in the composite membrane. • High-temperature TaPBI-PSBI PEM presents good comprehensive properties. [ABSTRACT FROM AUTHOR]

Most Troger's base (TB)-based polymers reported for high-temperature proton exchange membranes (HT-PEMs) exhibit low phosphoric acid (PA) tolerance due to excessive swelling in PA solution. In this work, a novel dicarboxylic acid monomer containing both naphthalene and TB units (TB-N-COOH) was successfully synthesized, and the corresponding TB-based PBI homopolymer (TB-N-HPBI) was prepared for HT-PEM fuel cells (HT-PEMFCs). In addition, naphthalene units were incorporated into TB-based PBI copolymers (TB-N-CoPBIs). The resulting TB-N-HPBI and TB-N-CoPBIs exhibited high molecular weight and excellent solubility in organic solvents (e.g., DMSO and NMP) because of the twisted TB units. The incorporated naphthalene units significantly improved the oxidative stability. More importantly, the existed naphthalene units in polymer backbones endowed the membranes with excellent PA tolerance capability because of the rigid structure and poor affinity to PA, which limited excessive swelling in 85 wt% PA solution and hence promoted acid uptake capability. Among of them, the TB-N-HPBI membranes showed ultrahigh PA uptake of 508.6%, and resulting in the proton conductivity of 201 mS cm−1 at 160 °C under non-humidity conditions, which are far superior to most reported TB-based polymer membranes. In addition, the maximum peak power density (H 2 /air) of 437.2 mW cm−2 was achieved. Our present work demonstrated that the incorporation of the naphthalene units into TB-based PBI significantly promoted the improvement of comprehensive performance for HT-PEMFCs. The combination the functions of TB and naphthalene units in PBI backbones providing excellent solubility, high PA tolerance and improved PA uptake. [Display omitted] • Novel dicarboxylic acid monomer (TB-N-COOH) containing naphthalene and Troger's Base (TB) was first synthesized. • The TB-N-CoPBIs and TB-N-HPBI showed good processability because of the twisted TB units. • The incorporation of naphthalene units significantly improved PA tolerance. • The TB-N-CoPBIs and TB-N-HPBI membranes showed improved oxidative stability and electrochemical performance. [ABSTRACT FROM AUTHOR]

The sulfonated poly(ether ether ketone) (SPEEK) composite membranes (S/SPANI) are prepared by blending sulfonated polyaniline (SPANI), which was synthesized through a post-sulfonation method. With the SPANI contents varying from 1 to 4 wt%, the S/SPANI membranes exhibit excellent physicochemical properties and cell performance, and at loading 3 wt% SPANI, S/SPANI-3 presents a higher proton conductivity (43.3 mS cm−1) and superior ion selectivity (49 × 103 S min cm−3) against SPEEK and Nafion 212. Moreover, its outstanding coulombic efficiency (95.9–98.4%) and energy efficiency (EE: 80.4–70.2%) at the current density of 100–200 mA cm−2 demonstrate an optimized tradeoff of proton conductivity and vanadium ion permeability. The performance optimization guarantees enhanced durability for 600 cycles and stable EE (76%) at 150 mA cm−2, which originated from the acid-base interaction, synergistic proton network, and interconnected chain structure. So, this provides a facile method to develop high-performance membranes by introducing desirable controllable topological molecular chains to construct synergistic proton transportation networks. Through manipulating interfacial acid-base interaction and interconnected topological chain, the enhanced conductivity and selectivity of the S/SPANI composite membranes demonstrate the importance of structural regulation and building synergistic proton channels. [Display omitted] • S/SPANI-3 displays ultrahigh proton conductivity and superior ion selectivity. • An optimized tradeoff effect of conductivity and permeability. • Stable membrane structure ensures 600-time charge-discharge cycles. • Interconnected chains and acid-base interaction ensure battery durability. [ABSTRACT FROM AUTHOR]

Polybenzimidazole (PBI) is considered as the one of the most promising materials for proton exchange membranes (PEMs) owing to its negligible crossover and outstanding chemical stability. However, the low proton conductivity of PBI membrane restricts its commercial application in vanadium flow battery (VFB). Herein, the PBI hybrid membranes with high proton conductivity were prepared by introducing crystalline covalent organic frameworks (TpPa and TpPa-SO 3 H (STpPa)). Owing to the highly ordered sub-nanometer pores within TpPa and STpPa, faster proton highway was constructed in the hybrid membrane. Meanwhile, the sulfonic acid groups introduced to STpPa further provided additional proton transport sites and vanadium permeation barriers to achieve high ion selectivity. Accordingly, the cell assembled with PBI hybrid membrane with 3% STpPa achieved superior voltage efficiency (95.22%–74.84%) and energy efficiency (91.38%–74.38%) at 40–240 mA cm−2, and exhibited superb electrochemical stability during 800 cycles at 160 mA cm−2. This work offers a facile and efficient strategy to construct high-performance PBI-based PEMs by incorporating functional porous materials, which has incredible prospect for use in VFBs. [Display omitted] • Hybrid membranes with polybenzimidazole as matrix and two types of covalent organic frameworks as fillers were fabricated. • The introduction of highly ordered sub-nanopore channels effectively enhanced proton transport. • The sulfonic acid groups in backbone not only promote proton transport, but also reduced the crossover of vanadium ions. • The hybrid membrane doped with STpPa exhibited impressive efficiency in vanadium redox flow battery. [ABSTRACT FROM AUTHOR]

A satisfactory trade-off between physical/chemical stability and conductivity is crucial for high-temperature proton exchange membrane (HT-PEM) applications. Herein, a series of ether-free polyfluorenes cross-linked with zwitterionic liquids possessing both quaternary ammonium (QA+) and sulfonate ion (–SO 3 −) were prepared as crosslinked cHFTP–VIPSx via UV irradiation. Compared with non-crosslinked HFTP–TMA, crosslinked cHFTP–VIPSx exhibited enhanced conductivity, dimensional stability, oxidation stability, and phosphoric acid retention, which are attributed to the well-developed crosslinked structure and incorporated –SO 3 - groups. The as-fabricated H 2 /air single cell with a cross-linked cHFTP–VIPS30 achieved a higher peak power density (728 mW cm−2) than that of uncross-linked HFTP–TMA (287 mW cm−2) at 120 °C. Considering their enhanced performance, these cHFTP–VIPSx membranes cross-linked with zwitterionic liquid are promising HT-PEM materials for fuel cells. [Display omitted] • Polyfluorene cross-linked zwitterionic liquid was prepared as HT-PEMs materials. • Compared with HFTP-TMA, cross-linked cHFTP-VIPSx exhibited enhanced performance. • A H 2 /air HT-PEMFC with cHFTP-VIPS30 reached a power density of 728 mW cm−2. [ABSTRACT FROM AUTHOR]

Designing proton exchange membranes (PEMs) with high H+ conductivity and good dimensional stability has been a challenge. The porous structure of ZIF-8 could load ionic liquids (IL) (ZIF-8@IL). The ZIF-8@IL was coated by sulfonated polydopamine (SPDA), then ZIF-8@IL-SPDA as proton conductors was fabricated. ZIF-8@IL-SPDA would not lose in water environment like small molecule proton conductors (such as sulfuric acid, phosphoric acid, imidazole, etc.). The different loadings of ZIF-8@IL-SPDA were introduced into sulfonated poly (aryl ether ketone sulfone) containing fluorene groups (F-SPAEKS). The novel composite PEMs was investigated. The prepared hybrid matrix membrane with optimum ZIF-8@IL-SPDA doping content (1.5 wt%) showed the highest H+ conductivity of 149.87 mS cm−1 at 80 °C. In addition, a maximum peak power density of 818 mW cm−2 was achieved in a single-cell performance test of this membrane. The good dispersion of ZIF-8@IL-SPDA nanoparticles in the F-SPAEKS matrix reduced the fuel cross-over flux to 2.15 mA cm−2. Therefore, the newly prepared hybrid matrix membranes were expected to be applied in proton exchange membrane fuel cells. [Display omitted] • The functionalized nano-coated MOFs was successfully prepared. • The functionalized nano-coated MOFs increased the transfer sites of protons. • The membranes exhibited good physical and chemical properties. • The highest power density of hybrid membrane was 818 mW cm−2. [ABSTRACT FROM AUTHOR]

Reducing the thickness of membrane electrolyte is one important direction to improve Ohmic polarization and the according performance of high-temperature proton exchange membrane fuel cells for its widespread applications. Herein, we report that robust thin membranes can be formed using a soluble ether-contained poly(4,4′-diphenylether-5,5′-bibenzimidazole) with an ultra-high molecular weight of 170 kDa. Due to the enhanced chain entanglement of high molecular weight polymers, the formed thin membrane exhibits promising mechanical strength, thermal and oxidation stability. The optimized membrane with thickness of 61 μm and phosphoric acid uptake of 606 wt% has the high specific proton conductivity of 25.9 S cm−2 at 160 °C under anhydrous conditions and mechanical strength of 11.2 MPa. The accordingly fabricated membrane electrode assembly delivers a peak power density of 0.544 W cm−2 with the open circuit voltage of 0.915 V at 160 °C using air as oxidant, outperforming the value of 0.522 W cm−2 for the commercial membrane electrode assembly with thickness of 250 μm and phosphoric acid uptake of 1018 wt%. [Display omitted] • High molecular weight OPBI based thin HT-PEMs are formed. • The enhanced chain entanglement led to high mechanical strength. • The optimized membrane had specific proton conductivity of 25.9 Scm−2 at 160 °C. • The decreased membrane thickness resulted in an improved Ohmic polarization. • The H 2 /air fuel cell demonstrated a peak power density of 0.544 Wcm−2. [ABSTRACT FROM AUTHOR]