Summary: Novel poly(aryl ether sulfone) copolymers containing 2,5‐biphenylpyridine and tetramethyl biphenyl moieties were synthesized by polycondensation of 4‐fluorophenyl sulfone with 2,5‐(4′,4″ dihydroxy biphenyl)pyridine and tetramethyl biphenyl diol. Copolymers with different molecular weights and different monomer compositions were obtained. These copolymers exhibit excellent film‐forming properties, mechanical integrity, and high modulus up to 250 °C, high glass transition temperatures (above 280 °C) as well as high thermal stability up to 400 °C. In addition to the above properties required for PEMFC application, this novel material shows high oxidative stability and acid doping ability, enabling proton conductivity in the range of 10−2 S · cm−1 above 130 °C.Synthesis of copolymers with high acid uptake and ionic conductivity.magnified imageSynthesis of copolymers with high acid uptake and ionic conductivity.
Oxides on the surface of Pt electrodes
are largely responsible
for the loss of their electrocatalytic activity in the oxygen reduction
and oxygen evolution reactions. In this work we apply near ambient
pressure X-ray photoelectron spectroscopy (NAP-XPS) to study in operando the electrooxidation of a nanoparticulated Pt
electrode integrated in a membrane-electrode assembly of a high temperature
proton-exchange membrane under water and water/oxygen ambient. Three
types of surface oxides/hydroxides gradually develop on the Pt surface
depending on the applied potential at +0.9, + 2.5, and +3.7 eV relative
to the 4f peak of metal Pt and were attributed to the formation of
adsorbed O/OH, PtO, and PtO2, respectively. The presence
of O2 in the gas-phase results in the increase of the extent
of surface oxidation, and in the growth of the contribution of the
PtO2 oxide. Depth profiling studies, in conjunction with
quantitative simulations, allowed us to propose a tentative mechanism
of the Pt oxidation at high anodic polarization, consisting of adsorption
of O/OH followed by nucleation of PtO/PtO2 oxides and their
subsequent three-dimensional growth.
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