Carbon Monoxide Poisoning Mechanisms and Mitigation Strategies for Polymer Electrolyte Membrane Fuel Cells

Fuel cells represent a viable option for the diversification of renewable energies, necessary to meet the increasing energy demand and reduce the emissions of greenhouse gases (GHGs). Among the challenges polymer electrolyte membrane fuel cells (PEMFCs) face for their deployment, are the adverse effects that the presence of CO provokes in their performance and durability. A deeper understanding of the mechanisms occurring during the poisoning is needed in order to develop more efficient mitigation strategies that contribute to the competitiveness of PEMFCs. In this work, the spatial variations and temporal dynamics occurring in the presence of CO were studied. As a means of mitigating the effects of CO poisoning, short-circuiting strategies were evaluated. First, preliminary studies that evaluated the short-term effects of CO under different operating conditions were presented in a single cell. Next, an array of localised reference electrodes measured directly the anodic overpotential in three different locations of an MEA exposed to CO under galvanostatic control, where self-sustained potential oscillations were observed. This information was complemented by the measurement of the concentration of CO2 in the outlet that followed the evolution of the oxidation of CO. In the following study, a segmented-in-series system combined with different diagnostic techniques including thermal imaging, current interrupt and mass spectrometry was studied in the presence of two different concentrations of CO. The setups studied contributed to show the variations in the coverage of CO throughout the systems, and the effects of the local conditions in the oxidation of CO. These results highlight the importance of the distribution of the poisoning for the design and optimization of mitigation strategies against poisoning. Short-circuiting of the individual cells of a segmented-in-series stack was presented as an alternative, as the different patterns of the shorts (length and frequency) can be adjusted depending on the degree of poisoning, dependant on the location of the cells in the stack