Research on PEMFC resistance relaxation characteristics and degradation under thermal cycles with different residual water locations

The storage problem at low temperatures is one of the technical barriers to commercialization in the future for the polymer electrolyte membrane fuel cell (PEMFC). In this study, the resistance relaxation characteristic under different pretreatment methods before low-temperature storage of PEMFC is analyzed. The effect of residual water in different PEMFC locations on its storage performance after thermal cycles are investigated. The evolution curves of resistance after the purging process are different under equilibrium, cold, and hot purge and the percentage drop of cell resistance at relaxation stage under three methods are 14.5%, 66.3%, and 73.1%. It is found that the most likely reason for relaxation is membrane water structure reorganization. The voltage of the cell with no purge and purged to the end of the first stage becomes smaller at low current density after 20 freeze/thaw cycles. The charge transfer resistances of the cell with no purge, purged to the end of the first stage, and purged to the end of the second stage increase by 8.2%, 15.6%, and 7.4%, respectively. And the cell purged to the end of the first stage has the largest decay rate of electrochemical surface area. The result implies that the performance degradation after freeze/thaw cycles is associated with the water in the ionomer of catalyst layers, which freezes between ionomers and Pt particles at low temperatures.