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In this study, graphene oxide-intercalated montmorillonite (GO-MMT) layered stacks were introduced into a poly-(2,5-benzimidazole) (ABPBI) matrix via in situ synthesis to prepare composite membranes (GO-MMT/ABPBI) for wide-temperature range (0–180 °C) fuel cell applications. After the introduction of GO-MMT nanocomposites, the ABPBI membranes showed improved tensile strength, water and phosphoric acid retention ratio, and proton conductivity. The GO-MMT/ABPBI membrane was highly conductive when operated from 0 to 180 °C and attained proton conductivities of 50.3 mS/cm (0% RH/180 °C) and 38.3 mS/cm (98% RH/90 °C), respectively, which were about 1.6 and 1.7 times those of the pristine ABPBI membrane under the same conditions. This improved performance was because the nanolayered stacks of GO-MMT confined phosphoric acid and water within its interchannels via hydrogen bonds. This paper demonstrates the potential application of composite membranes in fuel cells with a wide operating temperature range. [ABSTRACT FROM AUTHOR]

Summary: Star copolymers with good film‐forming and mechanical properties were in situ synthesized for fabricating proton exchange membranes. The monomers of 3,4‐diaminobenzoic acid were first grafted onto glycidyl‐polyhedral oligomeric silsesquioxane (G‐POSS) cores and then propagated to the poly(2,5‐benzimidazole) (ABPBI) chains. The introduction of the star copolymer improves the movement of the ABPBI polymer chains, resulting in a lower internal viscosity and larger free volume that favor increased membrane flatness and absorbilities of water and phosphoric acid molecules, respectively. It was found that the star copolymers with 1.0 wt% of incorporated POSS (ABPBI‐1.0POSS) had the best balance of the acid retentivity and film‐forming property as well as mechanical properties that are desirable for proton exchange membranes without PA loss operating at high temperatures. The enhanced cell performance characteristics obtained using the ABPBI‐1.0POSS‐based membranes indicate that star copolymers are promising materials for use in high‐temperature proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • NGO nanoparticles were embedded into SPI polymers through in-situ synthesis. • In-situ synthesis was more favorable for NGO dispersion and well-constructed interface compared to physical blending. • The fracture strength of NGO-SPI composite membrane was approximately 61 MPa. To mitigate the severe degradation of mechanical properties and stability of highly sulfonated proton exchange membranes (PEMs) caused by the sulfonic acid groups, amino-functionalized graphene oxide (AGO) was embedded into sulfonated polyimide (SPI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of AGO nanoparticles facilitated the enhancement of the crystallinity of the composite membrane, with the well-constructed interface and dispersion. The resulting AGO-SPI composite membrane exhibited high mechanical strength and stability. The fracture strength of AGO-SPI composite membrane was approximately 61 MPa, which was 1.85 times higher than that of pure SPI. Meanwhile, the weight loss of AGO-SPI composite membrane in Fenton's reagent was only 2.11 %. Additionally, at 90 °C/98 % RH, the proton conductivity of AGO-SPI composite membrane reached 50.1 mS cm−1, which was 3.53 times higher than that of pristine SPI. The results suggest the promising application prospects of the proton exchange composite membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • The sHNT improved the interfacial compatibility between the inorganic particles and the polymer matrix due to the acid–base interactions. • High proton conductivity was due to the fast proton conduction paths of the sHNT and the well-constructed interface. • The peak power density of the PA-doped 3 % sHNT/ABPBI composite membrane reached 0.212 W cm−2 at 160 °C under anhydrous conditions. Phosphoric acid-doped polybenzimidazole (PA–PBI) membranes face challenges, such as the easy loss of free PA and the reduced mechanical strength caused by the "plasticization effect" of PA, limiting their application in a wide temperature range. In this study, sulfonated halloysite (sHNT) was used to modify poly(2,5-benzimidazole) (ABPBI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of halloysites in the composite membrane enabled the capturing of PA and water, while its nanoporous structure provided additional paths for proton conduction. Sulfonation modification of halloysite improved the interfacial compatibility between the inorganic particles and the polymer matrix, with the –SO 3 H groups providing extra proton hopping sites. Due to the well-constructed interface, the resulting sHNT/ABPBI composite membrane exhibited high mechanical strength and excellent proton conductivity across a wide temperature range. The 3 % sHNT/ABPBI composite membrane exhibited a breaking strength of approximately 130 MPa, which was 1.6 times that of pure ABPBI. Moreover, the proton conductivity of the composite exceeded 0.01 S cm−1 at temperatures ranging from 40 to 180 °C. At 160 °C, the peak power density of the PA-doped 3 % sHNT/ABPBI composite membrane was 0.212 W cm−2, which was 1.33 times higher than that of the pure ABPBI membrane. These results show that the composite membrane has potential applications in a wide temperature range. [ABSTRACT FROM AUTHOR]

To prevent phosphoric acid (PA) from leaching and harming traditional polybenzimidazole-based proton exchange membranes, polyethyleneimine-confined halloysite nanotubes (PEI@HNTs) were embedded in poly (2,5-benzimidazole) membranes to construct rich ion pairs that stably conducted protons. With the aid of supercritical carbon dioxide, PEI oligomers with basic groups were confined in HNTs. Then, through in-situ synthesis, highly-dispersed PEI@HNT enhanced the mechanical stability of composite membranes, whose basicity improved the absorption and retention capacity of PA. The PEI@HNTs/ABPBI composite membrane exhibited excellent mechanical strength and electrical performance over a temperature range of 40–180 °C. The through-plane proton conductivity of the 5%PEI@HNTs/ABPBI composite membrane was 0.061 S cm−1 at 98% relative humidity and 90 °C and 0.049 S cm−1 under anhydrous conditions at 180 °C. This performance was attributed to strong hydrogen bonding between PEI and PA, as well as the excellent retention of bound water within the HNTs. The peak power density of PA-doped 5%PEI@HNTs/ABPBI composite membrane reached 0.235 W cm−2 and 0.418 W cm−2 at 120 °C and 180 °C under anhydrous conditions, respectively, which were 1.68 and 1.96 times higher than those obtained with the pristine PA-ABPBI membrane. These results highlight the potential of this composite membrane for applications requiring a wide temperature range. [Display omitted] • PEI-confined halloysite nanotubes were prepared by supercritical fluid-assisted filling. • Peak power density of PA-doped 5%PEI@HNTs/ABPBI reached 0.418 W cm−2 at 180 °C/0% RH. • High proton conductivity was due to fast proton conduction paths of PEI@HNTs. [ABSTRACT FROM AUTHOR]

Abstract To broaden the operating temperature range of phosphoric acid (PA) doped polybenzimidazole membrane-based proton exchange membrane fuel cells (PEMFCs) toward low temperatures, a novel series of poly(2,5-benzimidazole) (ABPBI)/sulfonated sepiolite (S-Sep) composite membranes (ABPBI/S-Sep) with low PA doping levels (DLs) were prepared via in-situ synthesis. The desirably enhanced mechanical, thermal, and oxidative stabilities of ABPBI/S-Sep composite membranes were achieved by constructing ABPBI chains arranged along the sepiolite (Sep) fibers and acid-base crosslinks formed between S-Sep fibrous particles and ABPBI chains. Benefiting from the richness of high temperature stable bound water and the excellent water absorbability of Sep particles that enable the formation of additive proton conducting paths, the composite membranes retained bounded PA and achieved much higher proton conductivities under both anhydrous and hydrous conditions compared to PA-doped ABPBI membranes. Proton conductivity values above 0.01 S/cm at 40–90 °C/20–98% RH conditions and 90–180 °C/anhydrous conditions as well as peak power density of 0.13 and 0.23 W/cm2 at 80 and 180 °C with 0% RH, respectively from the ABPBI/2S-Sep composite membrane are more holistic compared to Nafion at low temperatures and polybenzimidazole-based membranes at high temperatures, respectively. The excellent properties of ABPBI/S-Sep composite membranes suggest them as prospective candidates for PEMFCs applications in a wide temperature range. Highlights • Sepiolite nanoparticles with high specific surface area and porosity are synthesized. • Proton conductivity of ABPBI/2S-Sep is above 0.01 S/cm at 40–180 °C with RH ≥ 20%. • High proton conductivity is due to the multi-conduction paths of composites. [ABSTRACT FROM AUTHOR]

The preparation of traditional graphene oxide (GO)-based proton exchange membrane (PEM) composites asks for multiple transfer steps due to the different solvent requirements of GO preparation and polymer synthesis. Moreover, GO is easy to agglomerate in polymer matrix, it is difficult to give full play to the excellent proton conductivity of single/few-layered nanosheets. Herein, a novel transfer-free in-situ method is developed to prepare poly(2,5-benzimidazole) (ABPBI)-grafted electrolytic graphene oxide (EGO) composites (ABPBI-EGO) for high-temperature (HT) PEM fuel cells applications. The process involves the in-situ electrochemical oxidation and exfoliation of graphite foil into single/few-layered EGO in Eaton's reagent and followed by in-situ synthesis of ABPBI-grafted-EGO composites in the same reagent. This strategy leads to a single or few-layered dispersion of EGO nanosheets in ABPBI matrix, thus significantly improving the physicochemical performance. By constructing fast proton-conducting channels through single/few-layered GO nanosheets, composite membranes without free phosphoric acid exhibit superior proton conductivities over the whole temperature range of 120–180 °C. ABPBI-0.5EGO composite membrane-based fuel cell achieves a power density of 349 mW/cm2 at 180 °C, which is nearly 2.3 times higher than the original ABPBI membrane. Thus, this transfer-free in-situ strategy shows great promise for developing high-performance HT-PEMs. [Display omitted] • A transfer-free strategy for ABPBI-EGO composites preparation in Eaton's reagent. • High-quality EGO firstly electrolyzed from graphite foil in Eaton's reagent. • ABPBI-EGO without PA loss showed 47.0 mS/cm of σ at 180 °C. • ABPBI-EGO-based single cell showed 349 mW/cm2 of power density at 180 °C. [ABSTRACT FROM AUTHOR]

Proton-exchange membrane fuel cells (PEMFCs) that operate from room temperature to high temperatures (e.g., 200 °C) are desired for fuel cells used in vehicles and combined heat and power systems. In this work, polyethyleneimine-filled sepiolite nanorods (PEI@SNR)-embedded poly(2,5-benzimidazole) composites (ABPBI/PEI@SNR) were synthesized in-situ to enhance their proton conductivity and minimize phosphoric acid (PA) leaching. They were then applied in PEMFCs between room temperature and 200 °C. The physicochemical and electrochemical properties of the composite membranes were characterized. The composite membranes showed enhanced thermal, oxidative, and dimensional stability and achieved proton conductivities above 0.01 S/cm from 40 to 200 °C at a relative humidity of 0–100%. This performance was attributed to abundant hydrogen bonds between PA, ABPBI, and PEI, and the strong retention of bound water within sepiolite nanorods (SNRs). The maximum power density of the cell based on the PA-doped ABPBI/5PEI@SNR composite membrane reached 0.16 W/cm2 at 80 °C and 0.27 W/cm2 at 180 °C and an anhydrous environment, which were respectively 2.2 and 1.5 times higher than those of the PA-doped ABPBI membrane. The cell performance was much better than previously reported zeolite-embedded polybenzimidazole membrane-based PEMFCs, indicating that the composite membranes have good application prospects in PEMFCs operating over a wide temperature range. [Display omitted] [ABSTRACT FROM AUTHOR]