Long-term cell degradation mechanism in high-temperature proton exchange membrane fuel cells

► In situ endurance tests were conducted on HT-PEMFC with PBI membrane. ► Post analyses were performed on the 0, 2000, 12,000, 15,000 and 17,860 h cells. ► Time changes in membrane thickness and catalyst particle size were shown. ► Its degradation was caused by the migrations of PBI from membrane to CL. ► The migration of phosphoric acid from membrane to CL followed PBI migration.