Neutron imaging of operando proton exchange membrane fuel cell with novel membrane

The performance of an alternative membrane based on aromatic multiblock copolymer was compared to that of the conventional perfluorosulfonic acid (PFSA) polymer membrane during fuel cell operation. The fuel cell with the alternative membrane exhibited more severe voltage loss than the conventional at current densities above 0.6 A/cm2 with fully saturated reactants. To rationalize this difference, operando high-resolution neutron imaging was used to investigate water distribution in the fuel cells, in parallel with impedance measurements. The type of membrane strongly affected water distribution, not only from anode to cathode, but also in-plane between ribs and channels. Specifically, in the alternative membrane, ionomer in cathode catalyst layer was less hydrated and dried as current density increased. The voltage loss with the alternative membrane was ascribed to ionomer drying rather than to the accumulation of liquid water, in accordance with the evolution of ohmic resistance. Furthermore, the alternative membrane experienced swell/shrinkage resulting in material shifts during the operation. These results pinpoint that developing new ionomers for fuel cells require not only to quantify the bulk transport properties of alternative membranes compared to PFSA, but also to evaluate their interfacial properties and the impact of ionomer on water management.