A new sulfonated poly(ether sulfone) hybrid with low humidity dependence for high-temperature proton exchange membrane fuel cell applications

Sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene/sulfonated poly(ether sulfone) and hexagonal boron nitride electrolyte membrane for fuel cell applications

Novel proton exchange membranes consisting of sulfonated polystyrene ethylene butylene polystyrene (sPSEBPS), sulfonated poly ether sulfone (SPES) and hexagonal boron nitride (hBN) were fabricated using a facile solution casting technique. The PSEBPS polymer was functionalized using chlorosulfonic acid as the sulfonating agent. Polymerization was typically conducted by taking three different monomers, namely 3,6-dihydroxy naphthalene-2,7-disulfonic acid disodium salt, 4,4'-dichlorodiphenyl sulfone, and bisphenol-A, to yield sulfonated poly ether sulfone (SPES). The resultant SPES polymer was blended with sPSEBPS followed by incorporation with an appropriate quantity of hBN. The physicochemical and structural properties of the membranes were studied in order to evaluate their compatibility with fuel cell applications. X-Ray photoelectron spectroscopy data validated the successful incorporation of the filler into the polymer matrix. Water absorption of the membranes was found in the range between 19.5 and 29.8%. The membrane loaded with 4.0 wt% of hBN showed the maximum ion-exchange capacity of 1.21 meq g^-1, whereas the control sPSEBPS/SPES membrane was restricted to 0.48 meq g^-1. The composite membrane loaded with hBN displayed higher thermal stability than that of the control sample. The sPSEBPS/SPES/hBN-4 composite membrane exhibited an ionic conductivity of 0.0329 S cm^-1 at 30 °C. Overall, the experimental data of the prepared composite membranes revealed that the materials are potential candidates for fuel cells.

Impact of MPL on Temperature Distribution in Single Polymer Electrolyte Fuel Cell with Various Thicknesses of Polymer Electrolyte Membrane

The impact of micro porous layer (MPL) with various thicknesses of polymer electrolyte membrane (PEM) on heat and mass transfer characteristics, as well as power generation performance of Polymer Electrolyte Fuel Cell (PEFC), is investigated. The in-plane temperature distribution on cathode separator back is also measured by thermocamera. It has been found that the power generation performance is improved by the addition of MPL, especially at higher current density condition irrespective of initial temperature of cell (Tini) and relative humidity condition. However, the improvement is not obvious when the thin PEM (Nafion NRE-211; thickness of 25 μm) is used. The increase in temperature from inlet to outlet without MPL is large compared to that with MPL when using thick PEM, while the difference between without MPL and with MPL is small when using thin PEM. It has been confirmed that the addition of MPL is effective for the improvement of power generation performance of single PEFC operated at higher temperatures than normal. However, the in-plane temperature distribution with MPL is not even.

Synthesis and Properties of Phosphoric-Acid-Doped Polybenzimidazole with Hyperbranched Cross-Linkers Decorated with Imidazolium Groups as High-Temperature Proton Exchange Membranes

Highly phosphoric-acid (PA)-doped polybenzimidazole (PBI) membranes exhibit good proton conductivity at high temperatures; however, they suffer from reduced mechanical properties and loss of PA molecules due to the plasticity of PA and the weak interactions between PA and benzimidazoles, especially with the absorption of water. In this work, a series of PBIs with hyperbranched cross-linkers decorated with imidazolium groups (ImOPBI-x, where x is the weight ratio of the hyperbranched cross-linker) as high-temperature proton exchange membranes are designed and synthesized for the first time. We observe how the hyperbranched cross-linkers can endow the membranes with improved oxidative stability and acceptable mechanical performance, and imidazolium groups with strong basicity can stabilize the PA molecules by delocalization and hydrogen bond formation to endow the membranes with an enhanced proton conductivity and a decreased loss of PA molecules. We measured a high proton conductivity of the ImOPBI-x membranes, ranging from 0.058 to 0.089 S cm⁻¹ at 160 °C. In addition, all the ImOPBI-x membranes displayed good mechanical and oxidative properties. At 160 °C, a fuel cell based on the ImOPBI-5 membrane showed a power density of 638 mW cm⁻² and good durability under a hydrogen/oxygen atmosphere, indicating its promising use in anhydrous proton exchange membrane applications.