Investigation of Catalyst Degradation After Single Cell Life Tests

Abstract

To investigate the effect of fuel cell operating conditions on catalyst agglomeration of a platinum catalyst, several single cell life tests were carried out under different conditions. It was found that catalyst agglomeration was accelerated by higher temperature operation, while it was not accelerated by higher current density (∼1.5 A/cm²) nor by higher potential (∼0.85 V) when the operating temperature was 100°C. Catalyst agglomeration was much more severe in the cathode, and the surface area of the platinum catalyst was decreased from 58.9 m²/g to 30.6 m²/g after a life test for 4000 hours. Because there was no sign of platinum dissolution/precipitation in the ionomer phase and there was a peak tail in the direction of larger particles in the particle distribution after 4000 hours, this catalyst agglomeration may be caused by a crystallite migration mechanism and a coalescence growth mechanism. In addition, to investigate the degradation of the CO-tolerance performance of a platinum-ruthenium catalyst, 5000-hour life tests and several life tests for shorter periods were carried out. It was found that the CO-tolerance performance was gradually decreased with time and that one of the reasons for the degradation was considered to be decomposition of the platinum-ruthenium alloy. It was also found that an air-bleeding technique could reduce the loss of cell performance due to the degradation of the CO-tolerance performance but may slightly accelerate the catalyst material degradation.