Radicals in Fuel Cell Membranes: Mechanisms of Formation and Ionomer Attack

Radical intermediates formed during polymer electrolyte fuel cell (PEFC) operation cause degradation of the proton exchange membrane. Generation and decay of the radicals HO•, H•, and HOO• in the membrane was simulated based on a kinetic framework with H2O2 as precursor. The degradation of the PFSA membrane was assumed to proceed via end-group attack. Two chemical environments were considered, a fuel cell test and an ex situ Fenton test. It was found that the reaction pathways and corresponding radical concentrations differ considerably. In particular, no H• is formed in a Fenton test due to the absence of H2. The influence of the concentration of Fe-ion impurities and end-groups on the radical concentration and rate of ionomer attack was studied. The calculated fluoride emission rate shows fairly good agreement with experimental results reported in the literature.