Study of degradation of membrane-electrode assemblies of hydrogen-oxygen (air) fuel cell under the conditions of life tests and voltage cycling

Abstract

The degradation processes of HiSPEC 9100 (60% Pt/C) and 13100 (70% Pt/C) cathodic monoplatinum catalysts, which were tested under the model conditions and in the composition of membrane-electrode assemblies (MEA) of hydrogen-air and hydrogen-oxygen fuel cells, are studied. It is shown that, in all cases, the main reason for a decrease in the catalyst activity was a decrease in its surface area, which was caused by the coarsening of platinum nanoparticles, irreversible oxidation of a fraction of active centers, and the destruction of the catalyst due to the carbon support oxidation. The results of electrochemical measurements are supplemented with the structural investigations by the methods of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the degradation processes of MEA in the accelerated stress tests (AST) are similar to those in the long-term life tests. With respect to a decrease in the catalyst active surface area, the application of 2500 cycles in the voltage range of 0.6 to 1.2 V in the AST is equivalent to the life tests for 1010 h. During the fuel cell operation, the destruction of polymer electrolyte proceeds along with the catalyst degradation. This leads to a decrease in the ion-exchange capacity of the membrane and ionomer in the composition of cathode active layer.