The S-shaped negative differential resistance during the electrooxidation of H ₂/CO in polymer electrolyte membrane fuel cells: Modeling and experimental proof

In the present contribution, the operation of a low temperature polymer electrolyte membrane fuel cell (PEMFC) with H ₂/CO and N ₂/CO mixtures is studied. The aim of the work is to clarify a discrepancy between earlier experiments with conventional electrochemical arrangements and experiments carried out with PEMFCs: Investigations of CO oxidation with rotating disk electrode (RDE) setups in acidic electrolytes revealed a hysteresis in the polarization curve around the onset overpotential of CO oxidation, which was not found in PEMFCs so far. The proof of a hysteresis in the PEMFC polarization curve could be interesting in terms of fuel cell performance, because it was argued that its presence also influences the oxidation of H ₂/CO mixtures. Indeed, in the present work, this hysteresis during operation with a N ₂/CO mixture is found, but it is seen that it disappears once H ₂ is added. To understand the background of these studies, a spatially lumped model is derived.