Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 2-Sidechain Phosphorus-Containing Polyacids

Macromolecules containing acidic fragments in side-groups—polyacids—occupy a special place among synthetic polymers. Properties and applications of polyacids are directly related to the chemical structure of macromolecules: the nature of the acidic groups, polymer backbone, and spacers between the main chain and acidic groups. The chemical nature of the phosphorus results in the diversity of acidic >P(O)OH fragments in sidechain phosphorus-containing polyacids (PCPAs) that can be derivatives of phosphoric or phosphinic acids. Sidechain PCPAs have many similarities with other polyacids. However, due to the relatively high acidity of −P(O)(OH)2 fragment, bone and mineral affinity, and biocompatibility, sidechain PCPAs have immense potential for diverse applications. Synthetic approaches to sidechain PCPAs also have their own specifics. All these issues are discussed in the present review.

Proton Conductivity Enhancement at High Temperature on Polybenzimidazole Membrane Electrolyte with Acid-Functionalized Graphene Oxide Fillers

Graphene oxide (GO) and its acid-functionalized form are known to be effective in enhancing the proton transport properties of phosphoric-acid doped polybenzimidazole (PA-doped PBI) membranes utilized in high-temperature proton exchange membrane fuel cells (HTPEMFC) owing to the presence of proton-conducting functional groups. This work aims to provide a comparison between the different effects of GO with the sulfonated GO (SGO) and phosphonated GO (PGO) on the properties of PA-doped PBI, with emphasis given on proton conductivity to understand which functional groups are suitable for proton transfer under high temperature and anhydrous conditions. Each filler was synthesized following existing methods and introduced into PBI at loadings of 0.25, 0.5, and 1 wt.%. Characterizations were carried out on the overall thermal stability, acid doping level (ADL), dimensional swelling, and proton conductivity. SGO and PGO-containing PBI exhibit better conductivity than those with GO at 180 °C under anhydrous conditions, despite a slight reduction in ADL. PBI with 0.5 wt.% SGO exhibits the highest conductivity at 23.8 mS/cm, followed by PBI with 0.5 wt.% PGO at 19.6 mS/cm. However, the membrane with PGO required a smaller activation energy for proton conduction, thus less energy was needed to initiate fast proton transfer. Additionally, the PGO-containing membrane also displayed an advantage in its thermal stability aspect. Therefore, considering these properties, it is shown that PGO is a potential filler for improving PBI properties for HTPEMFC applications.

Performance of Quaternized Polybenzimidazole-Cross-Linked Poly(vinylbenzyl chloride) Membranes in HT-PEMFCs

High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) are mostly based on acid-doped membranes composed of polybenzimidazole (PBI). A severe drawback of acid-doped membranes is the deterioration of mechanical properties upon increasing acid-doping levels. Cross-linking of different polymers is a way to mitigate stability issues. In this study, a new ion-pair-coordinated membrane (IPM) system with quaternary ammonium groups for the application in HT-PEMFCs is introduced. PBI cross-linked with poly(vinylbenzyl chloride) and quaternized with three amines (DABCO, quinuclidine, and quinuclidinol) are manufactured and compared to the state-of-the-art commercial Dapazol PBI membrane ex situ as well as by evaluating their HT-PEMFC performance. The IPMs show reduced swelling and better mechanical properties upon doping, which enables a reduction in membrane thickness while maintaining a comparably low gas crossover and mechanical stability. The HT-PEMFC based on the best-performing IPM reaches up to 530 mW cm^-2 at 180 °C under H₂/air conditions at ambient pressure, while Dapazol is limited to less than 430 mW cm^-2 at equal parameters. This new IPM system requires less acid doping than conventional PBI membranes while outperforming conventional PBI membranes, which renders these new membranes promising candidates for application in HT-PEMFCs.

Synergistically integrated phosphonated poly(pentafluorostyrene) for fuel cells

Modern electrochemical energy conversion devices require more advanced proton conductors for their broad applications. Phosphonated polymers have been proposed as anhydrous proton conductors for fuel cells. However, the anhydride formation of phosphonic acid functional groups lowers proton conductivity and this prevents the use of phosphonated polymers in fuel cell applications. Here, we report a poly(2,3,5,6-tetrafluorostyrene-4-phosphonic acid) that does not undergo anhydride formation and thus maintains protonic conductivity above 200 °C. We use the phosphonated polymer in fuel cell electrodes with an ion-pair coordinated membrane in a membrane electrode assembly. This synergistically integrated fuel cell reached peak power densities of 1,130 mW cm^-2 at 160 °C and 1,740 mW cm^-2 at 240 °C under H₂/O₂ conditions, substantially outperforming polybenzimidazole- and metal phosphate-based fuel cells. Our result indicates a pathway towards using phosphonated polymers in high-performance fuel cells under hot and dry operating conditions.

Improved performance of poly(vinyl pyrrolidone)/phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)/graphitic carbon nitride nanocomposite membranes for high temperature proton exchange membrane fuel cells

To achieve desirable performance of a polymer electrolyte membrane with higher proton conduction and better mechanical strength is a challenging work in the development of the phosphoric acid (PA) doped solid-state membrane.