Preben J.S. Vie

Influence of Ammonium on Conductivity and Water Content of Nafion 117 Membranes

Ion-exchange equilibria of ammonium between an aqueous phase and Nafion 117 were measured at 10, 25, 40, and 60°C by equilibrating the membrane in 0. 1 M chloride electrolytes of known cation composition. The water content in the membrane phase decreased linearly with increasing cation fraction of ammonium in the membrane phase (y NH + 4 ) from λ H2O = 21.2 (moles of water per mole-sulfonic acid groups) in proton form Nafion in pure water to λ H2O = 13.2 in ammonium form Nafion in a 0.1 M chloride solution. The conductivity was measured by ac impedance in a two-electrode setup using a stack of membranes. The conductivity also decreased linearly with increasing y NH+4 from 97 to 25 mS/cm at 25.0°C. Our results indicated that the conductivity of Nafion was isotropic, however, available literature is not conclusive on this matter. The temperature dependence of the conductivity was measured, and the fitted activation energy in an Arrhenius-type equation was found to depend on membrane composition and hence water content.

Through-Plane Thermal Conductivity of PEMFC Porous Transport Layers

We report the through-plane thermal conductivities of the several widely used carbon porous transport layers (PTLs or GDLs) and their thermal contact resistance to an aluminium polarisation plate. We report these values both for wet and dry samples and at different compaction pressures. We show that depending on the type of PTL and possible residual water, the thermal conductivity of the materials varies from 0.15 to 1.6 W K−1 m−1 — one order of magnitude. This behaviour is the same for the contact resistance varying from 0.8 to 11 10−4 m2 K W−1 . For dry PTLs the thermal conductivity decreases with increasing PTFE content and increases with residual water. These effects are explained by the behaviour of air, water and PTFE in between the PTL fibres.Copyright

Fuel cell performance of proton irradiated and subsequently sulfonated poly(vinyl fluoride) membranes

Abstract Proton irradiated and sulfonated poly(vinyl fluoride) (PVF-SA) membranes have been tested with respect to fuel cell performance and swelling in water. Swelling of the PVF-SA membranes was clearly lower than that of the Nafion® 117 and 112 membranes. In fuel cell tests the performance of the low price PVF-SA was better than Nafion® 117 membranes tested under similar conditions. In contrast, the Nafion® 112 membrane performed better than the PVF-SA membrane. The low ohmic resistivity of Nafion® 112 and the compatibility between Nafion membrane and Nafion impregnated electrodes explain this. PVF-SA membranes suffered from degradation during the fuel cell testing.

In Situ Calorimetric Measurements in a Polymer Electrolyte Fuel Cell

We present calorimetric measurements on a single isothermal polymer electrolyte fuel cell, operated on dry hydrogen and oxygen at 50 °C. The measured heat production of the complete cell was decomposed into ohmic and non-ohmic heat effects. The results predicted the thermo-neutral potential of the cell within 7% error. The part of the heat production that originated mainly from the cathode overpotential, was analyzed in terms of standard overpotential theory, giving an exchange current density of the bulk cathode overpotential of 6×10−4 A/cm2 and a transfer factor of 0.27. (The cathode catalyst surface area was not determined.) This is the first time an overpotential of an electrode has been determined from its heat production.Copyright