Investigation Of MEA Degradation In PEM Fuel Cell By Driving Cycle

Proton exchange membrane fuel cells (PEMFC) have attracted much attention due to their advantages, such as high power density, high energy conversion efficiency, zero or low exhaust and quick startup at low temperature et al. However, cost and durability are the major challenges in the commercialization of PEMFC. So far, there is no recognized test method to evaluate the durability of membrane electrode assembly (MEA). And the degradation mechanism of MEA is not well studied.In this paper, to evaluate the durability of MEA, simulated condition durability testing methode was formulated by considering proton exchange membrane fuel cell vehicle's actual operation conditions and effects of each condition on MEA's durability. Each simulated driving cycle consisted of ten periods (OCV, idle condition, rated condition, overload condition, idle-rated cycle condition, idle-overloading cycle condition and open circuit-idle cycle condition), and lasted for 430min. The single cell performance, electrochemical active surface area (ECSA) and hydrogen permeability were tested after each driving cycle.The durability of CS8 (platinum loading of cathode and anode were both 0.4 mg/cm2), CS4 (platinum loading of cathode and anode were 0.3 mg/cm2 and 0.1mg/cm2) and GCS8(Graphite carbon support catalyst, platinum loading of cathode and anode were both 0.4 mg/cm2) were studied by driving cycle testing methode. The study showed that the performance degradation rate of CS4 was about 5 times compared with CS8. The consumed cathode ECSA for each driving cycle of CS8 and CS4 were almost the same. Performance degradation rate of GCS8 was only half of CS8. The consumed cathode and anode ECSA for each driving cycle of CS8 were 3 and 1.3 times compared with GCS8.According to the relationship of Pt content, Pt loading and ECSA of catalysts, we could predict that the catalyst durability of CS4 could reach or exceed the durability of CS8 when platinum loading of cathode and anode were 0.26 mg/cm2 and 0.14mg/cm2 with 20wt% Pt/C catalyst.The degradation mechanism of MEA was studied by TEM, FE-SEM and XPS. The degradation of catalyst was the dominated reason for performance degradation of MEA. And the degradation of catalyst mainly expressed as the decline of ECSA. The corrosion of Carbon Support, growth of Pt particle and lossing of Pt element in catalyst layer were the three main reasons for catalyst degradation. After 23 driving cycles, the cathode and anode catalyst layer of CS8 declined 4μm and 3μm respectively. Pt particle size of cathode and anode increased from 3nm to 5.5nm and 4.5nm. Content of Pt atoms in cathode and anode catalyst layer decreased from 1.3% to 0.95% and 1.06%. And Pt element was found in membrane near the cathode and anode catalyst layer. After 13 driving cycles, the thickness of cathode and anode catalyst layer of CS4 declined 1.5μm and 2.5μm. Pt particle size of cathode and anode increased from 3nm to 5.0nm and 3.5nm.