In-plane redistribution of radical scavenger during PEMFC real-world automotive operation and impact on catalyst-layer local oxygen transport resistance

Automotive operations cause non-homogeneous performance decay through the polymer electrolyte membrane fuel cell active area. This work discusses the local ageing of the cathode catalyst layers of commercial membrane electrode assemblies after 1000 h of dynamic load cycling, as well as after hundreds of hours of single low power and high power operation. Cerium is uniformly dispersed in the membrane at the beginning of life to improve the membrane durability, acting as OH/OOH radical scavenger. Micro X-ray fluorescence technique revealed an in-plane heterogeneous cerium distribution in the aged fuel cells. Cerium is observed to deplete in the air middle/outlet region and to accumulate at the air inlet. A modelling analysis permits to link this cerium distribution pattern to the planar ionic potential profile established during the realistic operation of fuel cell. While the lack of cerium at outlet makes the membrane more susceptible to failure, its accumulation at the drier inlet is responsible for the contamination of the cathode catalyst layer, increasing the local oxygen transport resistance and reducing the performance at high current density.