Johannes Bender

Anion exchange membranes based on poly(pentafluorostyrene) (PPFSt) functionalized with tetramethylguanidinium are described in this study. By incorporating flexible thiohexyl groups onto PPFSt followed by functionalization with tetramethylguanidine and its quaternization with dimethylsulfate, free standing anion exchange membranes were fabricated. The resulting membranes were doped in phosphoric acid (PA) and applied for high temperature proton exchange membrane fuel cells (HT-PEMFCs). The 60% thiohexylated and 40% tetramethylguanidinium-functionalized PPFSt membrane (M-PPFSt-TH-TMG) showed higher phosphoric acid doping level (ADL) than meta-PBI (m-PBI) membrane: 13.5 PA/guanidinium to 4.9 PA/imidazole respectively. Conductivity of the M-PPFSt-TH-TMG membrane displayed 322 mS·cm-1 (ADL 13.5) and is therefore higher than the one of m-PBI membrane showing 203 mS·cm-1 (ADL 4.5) at 160 oC. The fuel cell performance was measured at 160 oC with non-humidified gases and without back pressure on both anode and cathode sides and compared with commercial MEA (Celtec-P 1100W). A PA doped M-PPFSt-TH-TMG MEA showed higher performance than the commercial one exhibiting 793 and 656 mW·cm-2 respectively measured under the same condition. The highest performance was obtained with the membrane M-PPFSt-TH-TMG: this membrane showed a peak power density of 1.31 W·cm-2 in H2/O2 FC at 160 oC with 2 bars of backpressure on both anode and cathode sides. A stability test in FC showed no significant decay running at a constant current density of 217 mA·cm-2 at 160 oC with non-humidified gases for 100 hours. An accelerated stress test (AST) carried out via thermal cycling between 80 and 160 oC with humidified gases showed rapid decay over the first 20 cycles, followed by stabilization.

As an alternative to common perfluorosulfonic acid-based polyelectrolytes, we present the synthesis and characterization of proton exchange membranes based on two different concepts: (i) Covalently bound multiblock-co-ionomers with a nanophase-separated structure exhibit tunable properties depending on hydrophilic and hydrophobic components’ ratios. Here, the blocks were synthesized individually via step-growth polycondensation from either partially fluorinated or sulfonated aromatic monomers. (ii) Ionically crosslinked blend membranes of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones combine the hydrophilic component’s high proton conductivities with high mechanical stability established by the hydrophobic components. In addition to the polymer synthesis, membrane preparation, and thorough characterization of the obtained materials, hydrogen permeability is determined using linear sweep voltammetry. Furthermore, initial in situ tests in a PEM electrolysis cell show promising cell performance, which can be increased by optimizing electrodes with regard to binders for the respective membrane material.

Bipolar interfaces located directly between a proton conducting membrane and an anion exchange ionomer based anode catalyst layer are investigated in membrane electrode assemblies for water electrolysis.

Metathesis of N‐heterocyclic chloroarsines with sulfur‐based nucleophiles furnished thio‐substituted 1,3,2‐diazarsolidines and 1,3,2‐diazarsolenes. Crystallographic and NMR spectroscopic studies revealed that a thiocyanato‐diazarsolene exhibits a salt‐like structure composed of weakly interacting thiocyanate and arsenium ions, while the remaining products formed neutral molecules. The structural data indicate that the heterocyclic framework induces an elongation of exocyclic As−S bonds that is more prominent in diazarsolenes than in diazarsolidines and parallels the bond polarisation effect established for N‐heterocyclic phosphines. The NMR data suggest that diazarsolenes undergo facile inversion of the pyramidal configuration at arsenic, which was successfully modelled by DFT studies.