Osmotic Pressure of Water in Nafion^®

Mechanical failure modes leading to cracks or breeches in proton exchange membrane fuel cells are driven by mechanical forces associated with swelling from water uptake and shrinkage from dehumidification. To determine the magnitude of compressive mechanical stress imposed by water swelling in a proton exchange fuel-cell membrane, the osmotic pressure of water in a perfluorosulfonic acid ionomer (Nafion^® N 117) membrane was measured using a hydrostatic piston-cylinder device with an in-situ hydrophilic frit. Experiments indicate that hydrostatic stresses greater than 103.5 MPa are created in a membrane when swollen with water at 23℃ suggesting that pressure from water swelling can distort Nafion N 117-based structures as the osmotic pressure is of the same order of magnitude as the flow stress of Nafion N 117.