A Study Of Mechanical Properties Of Proton Exchange Membrane

The Proton Exchange Membrane (PEM) is the crucial part of Proton Exchange Membrane Fuel Cells (PEMFCs) and its reliability has essential influence on the life of PEMFCs, so it is important to study the mechanical properties of PEMs.The Dynamic Mechanical Analyser (DMA-Q800) is used to test the basic mechanical properties in this work. The Nafion? -212 was exerted the cyclic stresses at its operating temperature(85℃), and the change of its ratcheting strain and strain rate was observed. Moreover, the effect of mean stress, stress amplitude and strain rate to the ratcheting strain were investigated. In addition, its mechanical properties in the soaking environment of high temperature(70℃) was studied too. Besides the research of the effect of soaking time, strain rate and soaking or not soaking on the tensile property, the effect of stress and soaking or not soaking on the ratcheting behavior was studied. The tests results indicated that Nafion? -212 was rate dependent material and the strain rate affected its tangent modulus, ratcheting strain and strain rate at high temperatures. Else, the mean stress, stress amplitude etc. had different influence on its cyclic loading properties. Being soaked in the deionized water had certain effect on its mechanical properties. The stress of specimen at the same strain level was increased as the increase of soaking time. But the tensile property tended to become stable after the specimen was soaked for 24 hours. The effect of soaking or not was small on the ratcheting trend, while the ratcheting strain of no soaked specimen was bigger than that of soaked specimen under the same stress level.The mechanical properties (tensile property, creep-recover property, stress relaxation) of a kind of domestic PEM were studied under different temperatures and strain rates with strain controlled methods. The relationship between elastic modulus, stress, strain and temperature, loading rate was obtained. The experimental results indicated that the glass transition temperature of GEFC?-105 based on Tan Delta was slightly higher than Nafion?-212. In the creep-recover test, the creep strain increased quickly with the increase of stress, and the increase was more significant as the temperature went higher. Additionally, the creep strain increased slightly as the increase of temperature too. In the relaxation tests, the bigger the initial strain, the bigger the initial stress. And the stress declined rapidly first, then reached equilibrium gradually. While under the same strain level, the higher the temperature, the lower the initial stress and the stress within the whole relaxation progress. Based on the research of the constitutive relation of polymer, a creep equation involving time, temperature, stress was studied. Moreover, the creep curves at various temperatures were predicted. The prediction of creep curves used with the improved Findley creep model was good.