To mitigate against free radical attack of the membrane in proton exchange membrane fuel cells (PEMFCs), free radical scavengers (e.g. oxides/salts of manganese or cerium) can be used [1e5]. While these additives greatly prolong the lifetime of the membrane, recent work has demonstrated that they can dissolve, with the resulting cations accumulating in the cathode catalyst layer (CCL) [6e8]. These cations bind with the ionomer's sulfonate groups in the CCL, resulting in greatly reduced proton availability and thus greatly reduced end of test (EOT) performance.