Nanoindentation Investigation On Mechanical Properties Of Fuel Cell Membranes

As a promising energy conversion device,fuel cell has attracted wide attention due to its high efficiency and low emission.However,the mechanical properties of the fuel cell membrane could be degraded when sustained stresses act on it,which will have a considerable impact on the service life of fuel cell.It is of great significance to study the mechanical properties of acid and alkaline fuel cell membranes under different conditions.Based on nanoindentation and uniaxial tension method,the mechanical properties of acid and alkaline fuel cell membranes has been studied.Nanoindentation experiments were carried out on acid proton exchange membrane Nafion^?117 under three different loading conditions.On this basis,the mechanical response of Nafion^?117 at different temperatures was further studied.The creep behavior of a new generation of acidic proton exchange membrane Nafion^?212 under different peak loads and temperatures was studied.The creep behavior was analyzed by Findley and Burger models.The effects of peak loads and experimental temperatures on the creep behavior were compared by dimensionless analysis.A kind of alkaline QDPSU anion exchange membrane was synthesized in laboratory.The mechanical properties of the membrane in thickness and length directions were studied by nanoindentation and uniaxial tension methods.Its viscoelastic and fatigue behaviors in two directions were compared.The results show that the key point to reduce the material deformation is the fast loading/unloading rate,long holding time and low peak load.The high frequency stress process may be the main reason for accelerating strain accumulation and crack initiation.In more frequent acceleration/deceleration or startup/shutdown processes,the life of membranes may be shortened.Fuel cell membranes have a good shape memory and a temperature-dependent shape recovery rate.Their viscosity increases significantly at high temperatures,while the mechanical properties of the membrane change sharply near glass transition temperature.This study provides a basis for optimizing the working conditions of fuel cell polymer membranes and further understanding the failure mechanism.It also gives new ideas for the establishment of nanoindentation-uniaxial tension testing system.