Polymer electrolyte membrane fuel cells (PEMFCs) expect a promising future in addressing the major problems associated with production and consumption of renewable energies and meeting the future societal and environmental needs. Design and fabrication of new proton exchange membranes (PEMs) with high proton conductivity and durability is crucial to overcome the drawbacks of the present PEMs. Acid-doped polybenzimidazoles (PBIs) carry high proton conductivity and long-term thermal, chemical, and structural stabilities are recognized as the suited polymeric materials for next-generation PEMs of high-temperature fuel cells in place of Nafion® membranes. This paper aims to review the recent developments in acid-doped PBI-based PEMs for use in PEMFCs. The structures and proton conductivity of a variety of acid-doped PBI-based PEMs are discussed. More recent development in PBI-based electrospun nanofiber PEMs is also considered. The electrochemical performance of PBI-based PEMs in PEMFCs and new trends in the optimization of acid-doped PBIs are explored.

As the concentration of amphiphilic invertible polymers (AIPs) in both polar and nonpolar solvents increases, the AIP macromolecules self-assemble into polymeric micelles. The resulting invertible micellar assemblies (IMAs) have a controlled size and morphology determined by macromolecular composition and hydrophilic lipophilic balance (HLB) of the AIPs. It has been demonstrated that AIPs can rapidly switch the conformation in response to changes in the environmental polarity, thus facilitating, micellar inversion. In combination with IMAs’ ability to solubilize otherwise insoluble substances, inversion can be promising for rapid and controlled cargo delivery and release in applications that require simultaneous utility in polar and nonpolar media. While IMAs have been demonstrated to interact with peptides, fundamental pictures of micellar inversion remain elusive and became the focus of this work, including the behavior of the incorporated peptide in IMAs at the molecular level at different polarities of the environment and how polymer composition impacts such behavior. To trigger conformational changes of the micelle-forming AIPs, acetone (no self-assembly occurs in acetone) was added into the peptide-loaded IMAs aqueous solutions. Electron Paramagnetic Resonance (EPR) in combination with peptide spin labeling was used to probe the local environment of an antigenic peptide at various acetone concentrations. The obtained results are consistent with the previously revealed micellar structure. Increasing acetone percentage clearly impacts the extent of IMA inversion as reported by the labeled peptide and quantified by semiquantitative spectral analysis. The conformational changes are different for the two AIPs differing in the macromolecular composition. Conformational changes clearly relate to the HLB of the AIPs macromolecules and can certainly be meaningful in controlling the IMAs-mediated peptide release.

“Host–guest” interactions between self‐assembled micellar nanostructures from amphiphilic invertible polymers (AIPs) and two peptides, swine‐origin Influenza A surface protein Hemagglutinin and research antibody peptide V5, are investigated by changing the polymer concentration and polymer/peptide ratio in the aqueous solution. Formation of mixed micellar assemblies from AIP and each peptide is revealed using detailed 1H NMR spectroscopic study. Peptide molecule localization in the micellar assemblies depends on the specific interactions between amino acid functional groups of the peptide and polymer fragments. The resulting mixed micellar structures can be considered as a promising material toward delivery and stimuli‐responsive sustained release of peptides.

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This article reports a comparative experimental study of the hygroscopic and mechanical behaviors of electrospun polybenzimidazole (PBI) nanofiber membranes and solution-cast PBI films. Aselectrospun nonwoven PBI nanofiber mats (with the nanofiber diameter of ~250 nm) were heat-pressed under controlled temperature, pressure and duration for the study; lab-made solution-cast PBI films and commercially available PBI films (the PBI Performance Product Inc., Charlotte, NC ) were used as the control samples. Thermogravimetric and micro-tensile tests were utilized to characterize the hygroscopic (moisture absorption) and mechanical properties of the PBI nanofiber membranes at varying heat-pressing conditions, which were further compared to those of solution-cast PBI films. Experimental results indicated that the PBI nanofiber membranes carried slightly higher thermal stability and less hygroscopic properties than those of solution-cast PBI films. In addition, heat-pressing conditions significantly influenced the mechanical properties of the resulting PBI nanofiber membranes. The stiffness and tensile strength increase with increasing either the heat-pressing pressure or duration, and relevant mechanisms were explored. The present study provides a rational understanding of the hygroscopic and mechanical behaviors of electrospun This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as