Membrane processes relevant for the polymer electrolyte fuel cell
Research in the Proton Exchange Membrane Fuel Cell (PEMFC) is important to
get an efficient fuel cell that can be used as an energy carrier, for example in the
transport sector. Understanding the different phenomena and variations in temperature,
heat and other quantities is critical. Non-equilibrium thermodynamics is used
to establish a 1-dimensional model for transport processes in a Nafion membrane
system consisting of heat and mass transport, and for a PEM fuel cell with heat and
transport of mass and charge.
The Nafion membrane in part 2 is coated with a Sigracet layer of either GDL10AA
without Teflon or with GDL10BA with 5 % Teflon. Outside of these layers is liquid
water. The absorption enthalpy between liquid water and the Sigracet layer has
been found by combining experimental data with the established simulation model.
For GDL10AA without Teflon this absorption enthalpy ranges from -460 J/mol to
-3380 J/mol for mean temperatures of 30 oC and 75 oC respectively. For GDL10BA
with Teflon this absorption enthalpy ranges from 1150 J/mol to 7850 J/mol for mean
temperatures of 30 oC and 75 oC respectively. The heat capacity value of water for Sigracet GDL10AA and GDL10BA was found to be 10 J/K mol and 223 J/K
mol respectively. The effect on the absorption enthalpy and the sign and value of
the water flux by changing the temperature and material properties is studied. This
study has found that the heat conductivities play a minor role when it comes to
transport of water compared to the diffusion constant of the Nafion membrane and
the Sigracet layers.
A simulation model is established for the PEM Fuel Cell in part 3. Only variations
in quantities along one dimension is considered. Non-equilibrium thermodynamics is
used to properly describe heat and transport of mass and charge. The system has a
Nafion membrane coated with a Sigracet layer of GDL10AA without Teflon at both
ends. Outside of these layers are water vapor with hydrogen at one side and oxygen
at the other. Case studies such as the reversible limit is studied in detail to confirm
the accuracy and validity of the simulation model. Profiles of temperature, chemical
composition, water content, measurable heat flux, electrical potential and entropy
production are found by use of the simulation model for various current densities.
A polarization curve by plotting the cell potential for different current densities is
found. Additionally study and a sensitivity analysis for the PEM fuel cell are carried
out to fully understand transport processes and the effects from material properties.
Place, publisher, year, edition, pages
Institutt for kjemi , 2013. , 176 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-22427Local ID: ntnudaim:9484OAI: oai:DiVA.org:ntnu-22427DiVA: diva2:649671
Kjelstrup, Signe, Professor