The thermal-mechanical properties of functionally graded membrane electrode assembly of PEMFC.

Proton exchange membrane fuel cell (PEMFC) is one of the most promising clean energy technologies in the future because of its advantages of having zero pollution and high-power generation efficiency. However, the commercialization of PEMFC is difficult because of the constraints of operational lifetime and cost. Membrane electrode assembly (MEA) is the core component, and its durability determines the performance and life of PEMFC. Owing to the different expansion properties of each layer in MEA, stress concentration and uneven distribution are easily occurred in the process of dynamic cycling of PEMFC, causing the electrode crack and delamination and highly dropping the cell performance. We established the sandwich molecular model of functionally graded membrane electrode assembly (FG-MEA) and investigated the coefficient of thermal expansion and elastic modulus by molecular dynamics simulation. The relationship between gradient structure of FG-MEA and thermomechanical properties was discussed. Three FG-MEA models were established by adding different volume fraction of platinum (Pt) particles along the thickness direction of the membrane. It was found that with the decrease of gradient value, the coefficient of volumetric thermal expansion decreases and elastic modulus along gradient direction slightly increases. The results were in agreement with the estimation of empirical formula of exponential function. The research provides an idea and theoretical reference for the design of FG-MEA materials.